Crop Sensor Enhances Zoom? [closed]

Question

Possible Duplicate:
What is the difference between focal length and crop factor?
Does my crop sensor camera actually turn my lenses into a longer focal length?

I keep reading about how crop-sensors enhance the zoom of an image.

Example: A 50mm lens is effectively a 70mm lens.

What causes this to happen and how do you get the ratio to know what your lens is? In other words, How do you get 50mm=70mm?

Asked by Lynda

Answer

Crop sensors are smaller than full frame sensor. The full frame sensor size came from the old days and has been used as a standard for digital sensors size.

From Wikipedia

Crop factor is related to the ratio of the dimensions of a camera's imaging area compared to a reference format; most often, this term is applied to digital cameras, relative to 35 mm film format as a reference. In the case of digital cameras, the imaging device would be a digital sensor. The most commonly used definition of crop factor is the ratio of a 35 mm frame's diagonal (43.3 mm) to the diagonal of the image sensor in question; that is, CF=diag35mm / diagsensor. Given the same 3:2 aspect ratio as 35mm's 36mm x 24mm area, this is equivalent to the ratio of heights or ratio of widths; the ratio of sensor areas is the square of the crop factor.

So to determine your crop factor, you need to know your DSLR sensor size. It's 1.5 for Nikon, 1.6 for Canon, 2.0 for Olympus, 1.5 for Pentax and 1.5 for Sony.

To calculate the effective focal length or the focal length multiplier, use this formula:

focal length multiplier = focal length x crop factor.

For example, let's say that your crop factor is 1.5 and your lens's focal length is 50mm, then the focal length multiplier = 1.5 x 50 = 75mm.

Now you have to bare this in your mind, the physical focal length of your lens didn't change at all. What you see in your photo is the effect of your crop sensor, let me explain more:

Look at the image below, the red rectangle is for the full frame sensors, now if you are using a lens on a full frame camera and used 50mm lens to get this picture below, the photo will be everything inside the red rectangle. If you replaced your lens with a 75mm lens you will get a photo with everything inside the blue rectangle. Which is the same if you mount your 50mm lens on a cropped sensor camera with crop factor = 1.5

Crop Factor doesn't enhance the zoom, it just gives you the field of view that you would see if you zoomed more.

The image below is from this Wikipedia article.

Answered by Akram Mellice

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Do full frame camera require more power than a crop sensor camera?

Question

I had a Canon 60D and used to get around 800 to 1000 shots on full battery charge. I've now traded my 60D to a 5D Mark II and it looks like it requires a lot more power.
Is this normal for a full frame camera? The 5DMII and 60D use the same battery.

Asked by Vivek

Answer

All else being equal, yes.

A bigger sensor requires more power. Advancement in power-saving technologies can sometimes improve that but with higher pixel counts being the norm, we do not see much of that. Each pixel requires circuitry so higher megapixels require more power than making the sensor bigger.

Luckily bigger cameras have room for bigger batteries which compensates nicely until you get to the huge DSLRs with integrated grips which are rated upwards of 4000 shots per charge! Otherwise, most DSLRs are given batteries to last them between 500 and 1000 shots per charge.

Keep in mind the shots you get are highly dependent on usable. Using the flash is the most power hungry thing to do, followed by using the LCD, including Live-View and Video capture.

The stats for the 60D vs 5D are misleading because the CIPA standard requires 50% flash use if there is one, which the 5D does not have.

Answered by Itai

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Do any Nikon FX cameras allow square-format shooting with DX lenses?

Question

When one uses a Nikon DX (APS-C) camera on an FX camera body, the camera automatically enters a "DX crop mode", using only the center portion of the sensor to match the DX format, as explained on Nikon's web site.

The FX format is roughly 36×24mm, while DX is 24×16mm, and it's this smaller size that DX crop mode uses. Notice that the short edge of the FX format is equal to the long edge of DX — and of course the image circle is perfectly round, not oblong. Do any Nikon full-frame cameras allow a "square DX" format, either 24×24mm (with some possible vignetting in the extreme corners) or slightly reduced?

Asked by mattdm

Answer

Square format is not supported, but 5:4 aspect ratio offered by D3, D3s, D800 and D800E is only slightly wider, 30mm. The nice thing is that the viewfinder is electronically masked, so you can compose with good precision. This aspect ratio is not provided on a D700 or D3x.

Alternatively, you could always crop in post.

Of course, you'll also need to disable Auto DX Crop.

Answered by Imre

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Does a 35mm prime lens show the same bokeh as a 50mm prime lens on a cropped sensor?

Question

I came to know that a 50mm prime lens on a cropped sensor behaves like an 75mm prime lens.

So, does the 35mm prime lens behave like a 50mm prime lens on a cropped sensor?
If yes, then will it show the same bokeh as the 50mm lens on a cropped sensor?

Asked by Anisha Kaul

Answer

The only different between full frame and crop sensors is that the crop sensor is smaller - so the smaller sensor only sees only the center of the full frame image.

Or, another way to put it is that the picture you get from a crop sensor is the same picture you get from a full frame if you crop it and only leave the middle part.

So, does cropping effect bokeh? obviously not, but...

Cropping does have the same effect as zooming in, that's why the field of view of a Nikon APS-C at 35mm (or Canon APC-C at ~30mm) is similar to the field of view of a full frame with a 50mm lens.

And that "extra zoom" means that to fill the frame with the same subject on a crop sensor you will be at a greater distance than with a full frame - and distance to subject does effect DOF.

So, the quality and shape of the bokeh doesn't change in any way but the amount of bokeh does change (simply because distance to subject changes).

Answered by Nir

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When do the differences between APS-C and full frame sensors matter, and why?

Question

I'm trying to decide on a higher-end digital SLR, and I'm down to choosing between an APS-C model and a full-frame model.

I understand that the sensors are of different sizes, and as such have an effect on the perceived magnification of the lens, with the smaller APS-C sensor having an effective focal length greater than what it otherwise would be with a full frame sensor. But why does this matter?

• What things should drive my choice between one or the other?
• In which situations is one better than the other, and why?

Asked by Winston Smith

Answer

• One major difference is that a FF camera produces a depth of field that's around 1.3 stops shallower than an APS-C camera for the same subject & framing. This is most important when you have the aperture as wide as possible, e.g. for portraiture. To replicate the look of a 50 f/1.4 lens you'd have to use something like a 31 f/0.9 lens, which doesn't as far as I know exist!

Quick and dirty comparison image, APS-C Canon 30D left, FF Canon 5D right, same lens (FF image was zoomed in, however to give the same field of view), same composition, both f/2.8

• Another difference is that if you're using a lens designed for a full frame camera (like all Canon EF lenses) you are making full use of the image circle, which is less demanding of the optics and so you can expect a sharper image for the same number of megapixels. It's true that some lenses get softer toward the edge of the image, but you will still get higher average sharpness with most lenses, and telephotos will be sharper right across the frame. The crop factor of APS-C cameras takes the middle out of the lens and blows it up, losing sharpness in the process in a similar manner to a teleconverter.

• Larger formats allow for sharper optics. One of the driving forces for larger formats (other than the relatively constant resolving power per unit area of film) has been that it allows lenses to be produced which resolve a greater number of line pairs per picture height. Going full frame on a DSLR benefits from this to an extend - see: With all other things equal, in a DSLR, will a larger sensor produce a sharper image?

• A bigger sensor means bigger pixels, which in turn means you capture more light usually achieving lower noise levels in the process. Greater dynamic range goes hand in hand with this.

• You get a larger, brighter viewfinder on a full frame camera, which can be helpful composing shots. Having said that, I personally find the 5D viewfinder too large, I've not used a 7D but it has a very high spec 'finder.

• You have more mirror to move on a full frame camera. The larger mirror used to mean shooting speed is limited (the mirror on my 5D moves so slowly I can actually see the world slide sideways/up for an instant) however high speed full frame models are now available.

• Likewise the mirror box, focussing screen and pentaprism are larger, meaning the camera is larger and heavier.

• Lens hoods are designed for FF image circle and are therefore slightly more effective on FF cameras. This mostly applies to prime lenses, as zoom lens hoods are designed cut to accommodate the widest zoom setting, so everything else is already non optimal. If you're using an EF lens on a crop camera you ideally want the hood tighter (since the extra shading will lie outside the smaller sensor a tighter hood wont vignette.

I have nothing against APS-C cameras but for any format it makes sense to use lenses designed for your sensor size. The range of EF-S lenses is smaller than the range of EF lenses. However for some uses (sports etc.) the smaller sensor size is helpful for the extra reach and speed it allows. Also the better noise characteristics of a FF sensor don't quite make up for the higher ISO you need to use get the same exposure when stopping down to match the DOF as a crop. So if you have to maximise DOF crop has a slight edge.

If there are EF-S lenses available for what you want to shoot then it wont be noticeably worse choosing this camera. However I feel full frame gives you more flexibility (speed aside) - as you can get the same deep DOF as a crop, but go narrower if you need to.

Answered by Matt Grum

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Fancy technology cropped vs old technology full frame - Which will give better images?

Question

After selling my 1Dmk2 last year the time has come to get myself a new body, all along I'd decided that I wanted to do more "wow" pictures, big landscapes and do some more portait photography (up until now I had been doing mainly motorsport photography).

My budget is such that I can't afford a 5Dmk2, so the obvious candidate would be a 5Dmk1, its been around for a while and is famous for producing stunning images.

However, the thought has crept into my head that a 7D might be a better option, it's had the benefit of 3 or 4 years extra development and the Dual Digic4 processors, but has this allowed the image quality to catch up with the 5D?

(I'm trying to keep the question generic, but if you want to tailor your answer I use 17-40L, 50mm and 70-200f2.8L and I'm not bothered about shooting video)

Asked by LC1983

Answer

As a former 5D owner I can tell you that using full frame, even on a camera as 'old' as that one, is a joy. The colours and image quality on that 12MP sensor are amazing. You will notice the benefits particularly with your 17-40mm lens.

If I were in your position, I wouldn't hesitate to pick up a second hand 5D.

Answered by Nick Miners

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What are the advantages to using EF-S lenses on Canon APS-C cameras?

Question

I know EF-S lenses are "optimized" for crop sensors but what are the exact advantages to using an EF-S lens? Does it give better color, sharpness, depth of field, etc...?

In addition, do EF-S lenses still have the crop factor magnification as regular EF lenses do?

Answer

The advantages of EF-S lenses:

• Having the rear element sit closer to the film allowed Canon to use scaled down versions of existing lens designs as a starting point, cutting development costs.

• The need to project a smaller image circle allows wide angle designs to be lighter by having smaller glass elements as vignetting is not as severe.

• Having the correct size image circle helps with flare, as does having a lens hood designed for the camera sensor size. Projecting a larger than necessary image circle basically means letting extra light into the camera that doesn't contribute to the image, which is a recipe for flare as this light can bounce back off the rear element and onto the sensor.

• Projecting a smaller image circle allows sharper designs to be produced, the lenses used in compact cameras have tiny image circles but are able to resolve many more line pairs per mm than SLR lenses. So all being equal (which it never is!) an EF-S lens on APS-C camera would be slightly sharper than an EF lens on APS-C. It wouldn't be shaper (in terms of line pairs per picture height) than an EF lens on FF, but that's another question - for more information see:

With all other things equal, in a DSLR, will a larger sensor produce a sharper image?

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What is the DT series of Sony lenses?

Question

Among the Sony lenses there are some types with a DT abbreviation and some are without it. Those having DT called DT-series.

What does DT mean? What is the difference between DT-series lenses and the rest of Sony?

Answer

DT (Digital Technology - source) means that the lens is designed to work with a cropped sensor camera. It should not be used with a full frame sensor or 35mm film. If you use it with a full frame sensor then some of the image would be black, particularly towards the corners, as the light projected by the lens would not cover the sensor.

Having a smaller area to project light on to means that lenses can be smaller, lighter and are generally cheaper. However if you later upgraded your DSLR body to one with a full frame sensor you would have to replace the lens.

Similar questions:

• What is the difference between EF and EF-S lenses? (Canon)
• DX or FX lenses ? (Nikon)

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What is DT series of Sony lenses?

Question

Among the Sony lenses there are some types with a DT abbreviation and some are without it. Those having DT called DT-series.

I didn't manage to find out what does DT mean. Could you help me? What is the difference between DT-series lenses and the rest of Sony?

Answer

DT (Digital Technology - source) means that the lens is designed to work with a cropped sensor camera. It should not be used with a full frame sensor or 35mm film. If you use it with a full frame sensor then some of the image would be black, particularly towards the corners, as the light projected by the lens would not cover the sensor.

Having a smaller area to project light on to means that lenses can be smaller, lighter and are generally cheaper. However if you later upgraded your DSLR body to one with a full frame sensor you would have to replace the lens.

Similar questions:

• What is the difference between EF and EF-S lenses? (Canon)
• DX or FX lenses ? (Nikon)

Check more discussion of this question.

Does a crop sensor affect closest focusing distance? Why does it not affect focal length in EXIF data?

Question

Since I am considering to buy the Nikkor 105mm micro VR, I wondered if the cropped sensor does affect the closest focusing distance of 0.31m?

Thinking about this, the following additional (and theoretical) question came up: I have a Nikon D7000 which has a 1.5 crop factor, so for my understanding the focal length multiplies with 1.5. Lets say a lens at 100mm results in 150mm focal length. In the EXIF data of the picture however the value of 100 is saved. Shooting the same lens with a film or full-frame camera, the focal length is 100mm and also saved as such. I was wondering why crop-sensor cameras do not use and save the "real" focal length to the EXIF data, so the picture data is comparable without taking camera and lens into account?

Answer

Focal length is a measure of the lens's ability to bend light. As such this figure doesn't change when you use a smaller sensor. What actually happens when you use a smaller sensor is that your field of view narrows. Field of view is dependant both on the focal length and the format (the size of your film or sensor). The ubiquity of 35mm film among amateur photographers in the last half of the 20th century effectively took format out of the equation and lead to focal length being used to categorize the field of view.

When digital arrived and suddenly all sorts of different sensor sizes were being used the idea of a crop factor was introduced to people relate to the field of view they expected from a certain focal length on 35mm. This is not a problem so long as you realise the focal length doesn't really change, the crop factor operates only on the field of view (a crop factor of 2 halves the field of view). I agree that it would be nice to have the field if view stored in the EXIF data, seeing as the camera knows both the focal length and sensor size!

The concept of crop factors (and the term "full frame" which I avoid using at all costs) is only really used by small format photographers - no-one using medium format refers to their camera as having a 0.7 crop factor! Likewise if you were to mount a 50mm medium format lens on a 35mm sensor DSLR, it will act just like any other 50mm lens.

Similarly the minimum focus distance is a property of the lens (and distance to the sensor) and thus doesn't change when you use a different size sensor.

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Why did camera manufacturers create crop sensor cameras?

Question

Why did camera manufacturers create crop sensor cameras? Was there a business reason? Did they figure that crop sensor cameras are cheaper to manufacturer, which would in turn lower prices and make it easier to penetrate the amateur photography market?

I'm under the assumption that full frame cameras were created first and crop sensor cameras have come along only recently (relative the entire life of cameras).

Answer

There were economic reasons, but they were not about getting to amateur market; it was more like getting any market. The main merit seen in early digital photography was speed of delivery (no need to develop films), so news agencies were the first targets.

During the dawn of digital photography, a full frame sensor would have been enormously expensive to produce. The technology was just not ready to produce perfect silicon wafers of that size; even the smaller ones were the price of a really nice car (or a top-notch medium / large format system). The first commercially available dSLR, Kodak DCS (1991, a.k.a. DCS100), managed to sell 987 units (with 1.3MP 1.8 crop factor sensors, some of them monochrome) priced at $20k...$25k (almost a median US household income). Provided that most professional photographers were convinced (and correct) that digital image quality was significantly worse than film, the market would have been too small for full frame cameras at their enormous price.

The first FF dSLR, 6MP Contax N Digital, came 11 years later at $7000, a sixth of average US household income. 11MP Canon 1Ds was announced at $8k the same year.

Smaller sensors were (and still are) several times cheaper, and with the 1.5 or 1.6 crop factor, the quality difference was (and still is) not that big to justify the cost difference for most people. At the same time with 1Ds, APS-C Canon 10D was announced at only $2k.

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Does shooting at lower RAW resolution using crop sensor camera mimics qualities of full frame cameras?

Question

I'm not talking about changes to the focal length.

I've read many post that say in full frame camera the pixel density is lower compared to crop sensor camera's and so it captures more light and has thus has better ISO performance and greater dynamic range. So if I change by crop sensor camera to shoot at a lower resolution, will that equate to a better pixel density and mimic the performance of a full frame (or medium format) or will it always shoot at maximum resolution and the reduce the size?

--EDIT: 1--
I've a Canon 60D and I've 3 options for RAW image sizes (RAW, M-RAW amd S-RAW). If RAW is just a dump from the Camera sensors, How can their be 3 different sizes? Does the camera also scale down RAW images as well?

Answer

Given that you have a Canon, the lower RAW modes, mRAW and sRAW, DO INDEED UTILIZE ALL of the available sensor pixels to produce a richer result without the need for bayer interpolation. The actual output format, while it is still contained within a .cr2 Canon RAW image file, is encoded in a Y'CbCr format, similar to many video pulldown formats. It stores luminance information for each FULL pixel (2x2 quad of 1 red, 1 blue, and 2 green pixels), and each chrominance channel is derived from half pixel data (1x2 pair of 1 red+1 green or 1 blue+1 green).

I am not exactly certain what the specific low-level hardware read and encoding differences between mRAW and sRAW are, however generally speaking the smaller the output format, the more sensor pixel input information you can use for each output pixel. The small amount of interpolation present in m/sRAW is moot, as both formats interpolate far less than native RAW. It should also be noted that neither mRAW nor sRAW are actual "RAW" formats in the normal sense...sensor data IS processed and converted into something else before it is saved to a .cr2 file.

For more details about YUV derived formats and Canon sRAW, see my answer here: Why isn't the xvYCC color space seeing uptake for still photography?

From "Understanding What is stored in a Canon RAW .CR2 file":

The sRaw format (for "small RAW") was introduced with the 1D Mark III in 2007. It is a smaller version of the RAW picture.

For the 1D Mark III, then the 1Ds Mark III and the 40D (all with the Digic III), the sRaw size is exactly 1/4 (one fourth) of the RAW size. We can thus suppose than each group of 4 "sensor pixels" is summarized into 1 "pixel" for the sRaw.

With the 50D and the 5D Mark II (with the Digic IV chip), the 1/4th size RAW is still there (sRaw2), and a half size RAW is also appearing : sRaw1. With the 7D, the half size raw is called mraw (same encoding as sraw1), 1/4th raw is called sraw (like the sraw2).

the sRaw lossless Jpeg is always encoded with 3 colors component (nb_comp) and 15 bits.

Jpeg code of Dcraw was first modified (8.79) to handle sRaw because of the h=2 value of the first component (grey background in the table). Normal RAW have always h=1. Starting with the 50D, we have v=2 instead of v=1 (orange in the table). Dcraw 8.89 is the first version to handle this and the sraw1 from 50d and 5D Mark II.

"h" is the horizontal sampling factor and "v" the vertical sampling factor. It specifies how many horizontal/vertical data unit are encoded in each MCU (minimum coded unit). See T-81, page 36.

3.2.1 sRaw and sRaw2 format

h=2 means that the decompressed data will contain 2 values for the first component, 1 for column n and 1 for column n+1. With the 2 other components, decompressed sraw and sraw2 (which all have h=2 & v=1), always have 4 elementary values

[ y1 y2 x z ] [ y1 y2 x z ] [ y1 y2 x z ] ...
(y1 and y2 for first component)

Every "pixel" in sRAW and mRAW images contain four components...a split Y' component (y1 and y2), as well as an x (Chrominance Blue) and z (Chrominance Red). All four components (from a 1/2 image perspective, sRAW1/mRAW) have a column height of 2 (h) and a width of 1 (v). This indicates that the Luminance value (Y') is comprised of a FULL 2x2 pixel quad...or two 2x1 pixel columns stored in y1 and y2.

The references below do not seem to specifically state this, so I am speculating a bit here, however with the sRAW2 (1/4 raw) I believe Luminance information would be derived from a 4x4 pixel block where h=4 and v=2. Encoding chrominance would get more complex at a 1/4 size image, as the bayer color filter array on the sensor is not arranged in neat red and blue columns. I am unsure whether alternating 2x1 height columns are processed for each Cr and Cb component, or if some other form of interpolation is performed. One thing is certain...the interpolation of source data is always larger than the output data, and no overlapping (as in normal bayer interpolation) occurs as far as I can tell.

Finally, sRAW1/mRAW and sRAW/sRAW2 are compressed using a lossless compression algorithm. This is a critical distinction between these formats and JPEG, which also uses a ycc type encoding. JPEG performs lossy compression, making it impossible to restore pixels back to their exact original representation. Canon's s/mRAW formats are indeed able to be restored back to original full precision 15-bit image data.

References:

• Understanding What is stored in a Canon RAW .CR2 file, How and Why
  • For pulldown details, see text just before section 3.2.1
• DIGITAL COMPRESSION AND CODING OF CONTINUOUS-TONE STILL IMAGES – REQUIREMENTS AND GUIDELINES

Check more discussion of this question.

Does shooting at lower RAW resolution using crop sensor camera mimics qualities of full frame cameras?

Question

I'm not talking about changes to the focal length.

I've read many post that say in full frame camera the pixel density is lower compared to crop sensor camera's and so it captures more light and has thus has better ISO performance and greater dynamic range. So if I change by crop sensor camera to shoot at a lower resolution, will that equate to a better pixel density and mimic the performance of a full frame (or medium format) or will it always shoot at maximum resolution and the reduce the size?

--EDIT: 1--
I've a Canon 60D and I've 3 options for RAW image sizes (RAW, M-RAW amd S-RAW). If RAW is just a dump from the Camera sensors, How can their be 3 different sizes? Does the camera also scale down RAW images as well?

Answer

Given that you have a Canon, the lower RAW modes, mRAW and sRAW, DO INDEED UTILIZE ALL of the available sensor pixels to produce a richer result without the need for bayer interpolation. The actual output format, while it is still contained within a .cr2 Canon RAW image file, is encoded in a Y'CbCr format, similar to many video pulldown formats. It stores luminance information for each FULL pixel (2x2 quad of 1 red, 1 blue, and 2 green pixels), and each chrominance channel is derived from half pixel data (1x2 pair of 1 red+1 green or 1 blue+1 green).

I am not exactly certain what the specific low-level hardware read and encoding differences between mRAW and sRAW are, however generally speaking the smaller the output format, the more sensor pixel input information you can use for each output pixel. The small amount of interpolation present in m/sRAW is moot, as both formats interpolate far less than native RAW. It should also be noted that neither mRAW nor sRAW are actual "RAW" formats in the normal sense...sensor data IS processed and converted into something else before it is saved to a .cr2 file.

For more details about YUV derived formats and Canon sRAW, see my answer here: Why isn't the xvYCC color space seeing uptake for still photography?

From "Understanding What is stored in a Canon RAW .CR2 file":

The sRaw format (for "small RAW") was introduced with the 1D Mark III in 2007. It is a smaller version of the RAW picture.

For the 1D Mark III, then the 1Ds Mark III and the 40D (all with the Digic III), the sRaw size is exactly 1/4 (one fourth) of the RAW size. We can thus suppose than each group of 4 "sensor pixels" is summarized into 1 "pixel" for the sRaw.

With the 50D and the 5D Mark II (with the Digic IV chip), the 1/4th size RAW is still there (sRaw2), and a half size RAW is also appearing : sRaw1. With the 7D, the half size raw is called mraw (same encoding as sraw1), 1/4th raw is called sraw (like the sraw2).

the sRaw lossless Jpeg is always encoded with 3 colors component (nb_comp) and 15 bits.

Jpeg code of Dcraw was first modified (8.79) to handle sRaw because of the h=2 value of the first component (grey background in the table). Normal RAW have always h=1. Starting with the 50D, we have v=2 instead of v=1 (orange in the table). Dcraw 8.89 is the first version to handle this and the sraw1 from 50d and 5D Mark II.

"h" is the horizontal sampling factor and "v" the vertical sampling factor. It specifies how many horizontal/vertical data unit are encoded in each MCU (minimum coded unit). See T-81, page 36.

3.2.1 sRaw and sRaw2 format

h=2 means that the decompressed data will contain 2 values for the first component, 1 for column n and 1 for column n+1. With the 2 other components, decompressed sraw and sraw2 (which all have h=2 & v=1), always have 4 elementary values

[ y1 y2 x z ] [ y1 y2 x z ] [ y1 y2 x z ] ...
(y1 and y2 for first component)

Every "pixel" in sRAW and mRAW images contain four components...a split Y' component (y1 and y2), as well as an x (Chrominance Blue) and z (Chrominance Red). All four components (from a 1/2 image perspective, sRAW1/mRAW) have a column height of 2 (h) and a width of 1 (v). This indicates that the Luminance value (Y') is comprised of a FULL 2x2 pixel quad...or two 2x1 pixel columns stored in y1 and y2.

The references below do not seem to specifically state this, so I am speculating a bit here, however with the sRAW2 (1/4 raw) I believe Luminance information would be derived from a 4x4 pixel block where h=4 and v=2. Encoding chrominance would get more complex at a 1/4 size image, as the bayer color filter array on the sensor is not arranged in neat red and blue columns. I am unsure whether alternating 2x1 height columns are processed for each Cr and Cb component, or if some other form of interpolation is performed. One thing is certain...the interpolation of source data is always larger than the output data, and no overlapping (as in normal bayer interpolation) occurs as far as I can tell.

Finally, sRAW1/mRAW and sRAW/sRAW2 are compressed using a lossless compression algorithm. This is a critical distinction between these formats and JPEG, which also uses a ycc type encoding. JPEG performs lossy compression, making it impossible to restore pixels back to their exact original representation. Canon's s/mRAW formats are indeed able to be restored back to original full precision 15-bit image data.

References:

• Understanding What is stored in a Canon RAW .CR2 file, How and Why
  • For pulldown details, see text just before section 3.2.1
• DIGITAL COMPRESSION AND CODING OF CONTINUOUS-TONE STILL IMAGES – REQUIREMENTS AND GUIDELINES

Check more discussion of this question.

Is crop-factor a bad thing?

Question

It seems to me that there is a preference for full-frame sensors rather than cropped sensors, and I'm curious as to why. It seems to me, that the cropped sensor means that I get more bang for my buck with zoom lenses. True, I suppose it means I would need to a shorter lens to get the same wide-angle effect on the short end, but it seems like wide-angle lenses are (generally) cheaper than telephoto lenses. Am I missing something?

Answer

No, it is not a bad thing. It is not really "good" or "bad" in any sense. Its simply a different format than full-frame, which is different than medium format, etc. There are pros and cons to each. The smaller APS-C style "cropped" sensors do have some effects on lens focal length due to their field of view, and that can be beneficial or detrimental, depending on how you choose to see it. Here are some facts about sensors:

1. Cropped Sensor Formats (APS-C)
   • These are smaller sensors
     • They have higher manufacturing "yield" than larger sensors
     • As such, they are generally much cheaper
   • Photosites are generally smaller and more densely packed
     • This generally results in lower signal-to-noise ratio, more noisy pictures
     • This also means the maximum dynamic range (contrast ratio) of cropped senors is lower (less light gathering power per photosite)
   • They have a narrower field of view compared to larger sensors
   • Their narrower FOV has the effect of multiplying the focal length of any lens
     • This may be beneficial if you need super telephoto lengths (i.e. 400mm on FF ~= 640mm on APS-C, effectively)
     • This may be detrimental if you need ultra wide angle lengths (i.e. 16mm on FF ~= 26mm on APS-C, effectively)
   • The additional "effective magnification" offered by a cropped sensor is only illusory, and is not actual magnification
     • Given a large enough sensor with enough megapixels, and the same exact "crop" provided by a cropped senor can be achieved with a full-frame or medium format (however, the larger sensor would need some SERIOUS megapixels to achieve this.)
       • The 1.6x crop sensor of a Canon 450D would require a full-Frame sensor with 31mp to achieve the same crop
       • The 1.6x crop sensor of a Canon 550D would require a full-frame sensor with 46mp to achieve the same crop
2. Full-Frame Sensor Formats
   • These sensors provide the same "usable" pixel area as 35mm film
   • These sensors are larger, and have lower manufacturing yield
     • This generally means they are more expensive
   • The photosites are larger and often less densely packed
     • This results in better signal-to-noise ratio, less noisy pictures
     • Dynamic range is generally higher with larger photosites.
       • (The new Canon 1Ds IV with a 30mp+ sensor is touted as having full 16bit RAW capability, which offers much greater dynamic range than the general 12bit RAW of cropped sensors)
   • Their field of view is "normal" from the perspective of the bulk of the photography community and equipment
   • A lenses focal length is as stated when used on a full frame
3. Medium Format Sensors
   • These sensors are often much larger than full-frame (up to 57mm or larger)
     • They have extremely low yield, and thus their cost is extremely high
   • They have high density, but large photosites
     • This results in some of the best dynamic range possible in a digital sensor
     • Leica and Hasselblad's latest medium-format sensors tout 24bit RAW
   • They may have a much wider field of view than normal 35mm for a given focal length
     • A lens of a normal 35mm focal length would be shorter on medium format, providing even greater field of view
     • As with cropped sensors, the effect is illusory, and only useful when describing things at a technical level

(Note that the effect of sensor size on focal length or the apparent magnification assumes a common lens system. Medium format cameras tend to be rather specialized, so a direct comparison here is likely impossible. For the sake of discussion, the effect given similar lens system and focal lengths would thread throughout the range of sensor sizes.)

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What are the different sensor sizes used in DSLRs?

Question

What do the different sensor size names used by Canon mean? There's APS-C, APS-H and full format? What are the standards used by Nikon, Pentax, Sony, Olympus, Panasonic, and others?

What are the effects of these different sensor sizes (and the corresponding "crop factor") on lenses?

Answer

These are the different sensor sizes:

• Full frame sensor (Nikon's FX, Canon does not use special term): 36 x 24mm, no crop (actual size might differ slightly between brands and cameras)
• Canon's APS-H: 27.9 x 18.6mm, crop factor 1.3
• Canon's APS-C: 22.3 x 14.9mm, crop factor 1.6
• Nikon's DX: 23.6 x 15.8mm, crop factor 1.5 (23.1 x 15.4mm, crop factor 1.55 for Nikon 3100)

The effects of crop factor to the lenses is that the smaller sizes lessen the angle of view, but as the focal length is universally adapted to represent the field of view, you can multiply the focal lengths by the crop factor to get the indication for angle of view.

In example if you take 18-55mm zoom, it's effective angle of view on APS-C is equivalent to 18x1.6-55x1.6 ~ 28-90mm lens on a fullframe camera.

You might find this discussion about focal lengths and their equivalents useful.

When shopping for lenses, one should keep in mind that when you have camera with cropped sensor, both fullframe (Canon's EF, Nikon's lenses without DX marking) and cropped sensor (Canon's EF-S, Nikon's DX) lenses are usable on your camera, but lenses made for cameras with cropped sensor are not usable on fullframe cameras.

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Does lens speed still increase meaningfully when the physical aperture is larger than the sensor size?

Question

This question came to me this morning, thinking about 50mm lenses. I have the Pentax 50mm f/1.7 (manual) and it's a very nice lens, but would be considered (relatively) slow on 35mm film, and many recommendations would be for a 50mm f/1.4.

However, doing the math, the diameter of the f/1.7 aperture wide open is 29.4mm, which is greater than the diagonal size of an APS-C sensor — effectively meaning that no part of the sensor is "hidden" by the aperture. So, the questions is, does this actually have any meaning, or is the f/1.4 lens still going to be distinctly faster for APS-C?

Answer

f1.4 will always be 2/3rds stops faster than f1.8.

The diameter has nothing to do with whether or not part of the sensor is hidden. That is a separate measurement referred to as vignetting, and not the image circle's light level. The image circle's light level/brightness is directly affected by the aperture of the lens design.

FF lens simply means the image circle is designed to cover a full frame sensor (which can be film). Using it on a APS-C will be using the inner part of the image circlce.

An APS-C lens of the same focal length and speed could have been created at a smaller size the image circle does not need to be as large, but the lens would need to be redesigned.

Also, note that the Pentax 50mm f1.7 (if this is what you have) is generally regarded as sharper and/or more contrasty than the Pentax 50mm f1.4 at common apertures up until f2.8 or so.

Pentax 50mm f1.4 advantages include one third f-stop faster, rounder aperture blades for rounder highlight bokeh only when stopped down. It may or may not have "better" and smoother bokeh as that is not simply a function of aperture blades and I have not seen any other comparisons.

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Does the Nikkor 50mm f/1.4g perform better than the f/1.8d?

Question

Looking into these two lenses, I'm getting the impression that for my Nikon D-90 with DX camera sensor that the f/1.8d would waste light that is cropped by the sensor whereas the f/1.4g would not as it is designed for the DX style. Further, the f/1.8d is not available as AF-S whereas the f/1.4g is AF-S.

Is my analysis correct and thus the f/1.4g will perform better with the DX style camera?

Answer

The Nikon AF-S 50mm f1.4 G is not designed for the smaller DX sensor and has the same image circle as the 1.8

Are you thinking of the AF-S 35mm f/1.8 G DX which is designed for a smaller sensor compared to the AF-S 35mm f/1.4G?

In any case the size of the image circle is of minor importance to the light gathering ability - only the aperture matters, as Evan states.

Despite a lens designed for a smaller image circle letting in less light total, it lets in the same light per unit area, so if you swap one lens for another designed for a larger image circle, but the same f-stop then your exposure would be the same.

The previous paragraph ignores vignetting, or the tendency for brightness to fall off across the frame. This usually gives lenses designed for a larger image circle a brightness advantage. There are other advantages to using lenses designed for the sensor you are using, such as sharpness, weight and better resistance to flare.

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Does the Nikkor 50mm f/1.8d perform better than the f/1.4g?

Question

Looking into these two lenses, I'm getting the impression that for my Nikon D-90 with DX camera sensor that the f/1.8d would waste light that is cropped by the sensor whereas the f/1.4g would not as it is designed for the DX style. Further, the f/1.8d is not available as AF-S whereas the f/1.4g is AF-S.

Is my analysis correct and thus the f/1.4g will perform better with the DX style camera?

Answer

The Nikon AF-S 50mm f1.4 G is not designed for the smaller DX sensor and has the same image circle as the 1.8

Are you thinking of the AF-S 35mm f/1.8 G DX which is designed for a smaller sensor compared to the AF-S 35mm f/1.4G?

In any case the size of the image circle is of minor importance to the light gathering ability - only the aperture matters, as Evan states.

Despite a lens designed for a smaller image circle letting in less light total, it lets in the same light per unit area, so if you swap one lens for another designed for a larger image circle, but the same f-stop then your exposure would be the same.

The previous paragraph ignores vignetting, or the tendency for brightness to fall off across the frame. This usually gives lenses designed for a larger image circle a brightness advantage. There are other advantages to using lenses designed for the sensor you are using, such as sharpness, weight and better resistance to flare.

Check more discussion of this question.

Why do the differences between APS-C and full frame sensors matter?

Question

I'm trying to decide on a model in the Canon DSLR range, and I guess it's a choice between the 7D and the 5D MkII.

I understand that the sensors are of different sizes, and as such have an effect on the perceived magnification of the lens, with the smaller APS-C sensor having an effective focal length greater than what it otherwise would be with a full frame sensor. But why does this matter?

• What things should drive my choice between one or the other?
• In which situations is one better than the other, and why?

Answer

• One major difference is that a FF camera produces a depth of field that's around 1.3 stops shallower than an APS-C camera for the same subject & framing. This is most important when you have the aperture as wide as possible, e.g. for portraiture. To replicate the look of a 50 f/1.4 lens you'd have to use something like a 31 f/0.9 lens, which doesn't as far as I know exist!

Quick and dirty comparison image, APS-C Canon 30D left, FF Canon 5D right, same lens, same composition, both f/2.8

• Another difference is that if you're using a lens designed for a full frame camera (like all Canon EF lenses) you are making full use of the image circle, which is less demanding of the optics and so you can expect a sharper image for the same number of megapixels. It's true that some lenses get softer toward the edge of the image, but you will still get higher average sharpness with most lenses, and telephotos will be sharper right across the frame. The crop factor of APS-C cameras takes the middle out of the lens and blows it up, losing sharpness in the process in a similar manner to a teleconverter. See this related question:

• With all other things equal, in a DSLR, will a larger sensor produce a sharper image?

• A bigger sensor means bigger pixels, which in turn means you capture more light usually achieving lower noise levels in the process. Greater dynamic range goes hand in hand with this.

• You get a larger, brighter viewfinder on a full frame camera, which can be helpful composing shots. Having said that, I personally find the 5D viewfinder too large, I've not used a 7D but it has a very high spec 'finder.

• You have more mirror to move on a full frame camera. The larger heavier mirror usually means shooting speed is limited. The mirror on my 5D moves so slowly I can actually see the world slide sideways/up for an instant!

• Likewise the mirror box, focussing screen and pentaprism are larger, meaning the camera is larger and heavier.

• Lens hoods are designed for FF image circle and are therefore slightly more effective on FF cameras. This mostly applies to prime lenses, as zoom lens hoods are designed cut to accommodate the widest zoom setting, so everything else is already non optimal. If you're using an EF lens on a crop camera you ideally want the hood tighter (since the extra shading will lie outside the smaller sensor a tighter hood wont vignette.

I have nothing against APS-C cameras but for any format it makes sense to use lenses designed for your sensor size. The range of EF-s lenses is smaller than the range of EF lenses. However for some uses (sports etc.) the smaller sensor size is helpful for the extra reach and speed it allows. Also the better noise characteristics of a FF sensor don't quite make up for the higher ISO you need to use get the same exposure when stopping down to match the DOF as a crop. So if you have to maximise DOF crop has a slight edge.

If there are EF-s lenses available for what you want to shoot then it wont be noticeably worse choosing this camera. However I feel full frame gives you more flexibility (speed aside) - as you can get the same deep DOF as a crop, but go narrower if you need to.

Check more discussion of this question.

APS-C vs Full Frame - why should I care?

Question

I'm trying to decide on a model in the Canon DSLR range, and I guess it's a choice between the 7D and the 5D MkII.

I understand that the sensors are of different sizes, and as such have an effect on the perceived magnification of the lens, with the smaller APS-C sensor having an effective focal length greater than what it otherwise would be with a full frame sensor. But why does this matter?

• What things should drive my choice between one or the other?
• In which situations is one better than the other, and why?

Answer

• One major difference is that a FF camera produces a depth of field that's around 1.3 stops shallower than an APS-C camera for the same subject & framing. This is most important when you have the aperture as wide as possible, e.g. for portraiture. To replicate the look of a 50 f/1.4 lens you'd have to use something like a 31 f/0.9 lens, which doesn't as far as I know exist!

Quick and dirty comparison image, APS-C Canon 30D left, FF Canon 5D right, same lens, same composition, both f/2.8

• Another difference is that if you're using a lens designed for a full frame camera (like all Canon EF lenses) you are making full use of the image circle, which is less demanding of the optics and so you can expect a sharper image for the same number of megapixels. It's true that some lenses get softer toward the edge of the image, but you will still get higher average sharpness with most lenses, and telephotos will be sharper right across the frame. The crop factor of APS-C cameras takes the middle out of the lens and blows it up, losing sharpness in the process in a similar manner to a teleconverter. See this related question:

• With all other things equal, in a DSLR, will a larger sensor produce a sharper image?

• A bigger sensor means bigger pixels, which in turn means you capture more light usually achieving lower noise levels in the process. Greater dynamic range goes hand in hand with this.

• You get a larger, brighter viewfinder on a full frame camera, which can be helpful composing shots. Having said that, I personally find the 5D viewfinder too large, I've not used a 7D but it has a very high spec 'finder.

• You have more mirror to move on a full frame camera. The larger heavier mirror usually means shooting speed is limited. The mirror on my 5D moves so slowly I can actually see the world slide sideways/up for an instant!

• Likewise the mirror box, focussing screen and pentaprism are larger, meaning the camera is larger and heavier.

• Lens hoods are designed for FF image circle and are therefore slightly more effective on FF cameras. This mostly applies to prime lenses, as zoom lens hoods are designed cut to accommodate the widest zoom setting, so everything else is already non optimal. If you're using an EF lens on a crop camera you ideally want the hood tighter (since the extra shading will lie outside the smaller sensor a tighter hood wont vignette.

I have nothing against APS-C cameras but for any format it makes sense to use lenses designed for your sensor size. The range of EF-s lenses is smaller than the range of EF lenses. However for some uses (sports etc.) the smaller sensor size is helpful for the extra reach and speed it allows. Also the better noise characteristics of a FF sensor don't quite make up for the higher ISO you need to use get the same exposure when stopping down to match the DOF as a crop. So if you have to maximise DOF crop has a slight edge.

If there are EF-s lenses available for what you want to shoot then it wont be noticeably worse choosing this camera. However I feel full frame gives you more flexibility (speed aside) - as you can get the same deep DOF as a crop, but go narrower if you need to.

Check more discussion of this question.