What is the camera's influence on lenses' optical properties?

Question

I installed my 50mm f/1.4 Nikon lens on my Olympus E-P1. I notice some properties of the lens changed — namely, magnification and DoF both increased.

I understand magnification increases because of the smaller sensor (which results in crop). Is it only that, or is magnification also influenced by the adapter (because the lens is further away from the sensor)? Also, why is DoF larger?

Are there any other lens properties that change when changing the camera?

I'm talking about optical properties, not certain features (such as autofocus) not being supported with different lenses.

Asked by ibz

Answer

The lens properties stay exactly the same. However, you might record the image differently.

Sensor size is going to be the biggest factor, as you noticed, as it affects both field of view and depth of field.

And since you're recording a smaller area in the center of the image circle, you're (probably — individual results may vary) getting the best part of the lens, and corner softness and possibly vignetting won't be as significant.

The smaller sensor doesn't inherently increase magnification. If you're printing the resulting image at the same size, that'll require you to magnify it more, but the size of the image projected by the lens remains the same.

The distance to the sensor is the focal length of the lens, and this doesn't change. Or it shouldn't — some combinations of camera mounts and lenses make adapters which put the lens in exactly the right place impossible, so focal length will change slightly and you'll probably lose the ability to focus at infinity (and possibly be able to focus a bit closer, which will increase magnification). This shouldn't be the case with Nikon lenses adapted to micro four thirds, though — the flange distance is so small that there's plenty of room for an adapter.

Other things, of course, will depend simply on the different properties of the sensor — depending on the camera, the photosites might be closer together, for example, and Nikon and Olympus are going to render colors somewhat differently. None of that is the lens itself, though.

Answered by mattdm

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Why do two cameras with different resolution but both with 2/3″ sensors, and same mount and lens, give a different view?

Question

In testing, I have a circle on a piece of paper. I need to mount a camera at a fixed distance so that the circle just captures the top and bottom of that circle.

Im testing this because I need to make a case for a camera that I do not have. But I do have 2 other cameras with the same 2/3in sensor size. So I figured I would test with them to take the measurements for the case.

When setting this up, one camera ends up being .5in closer than the other camera. I tested it with both a 12mm and a 16mm lens.

Both cameras are 2/3in sensors with a c-mount. I am literally using the same lenses for the measurements, just moving it to the other camera.

One camera is a 5mp sensor, the other is a 3.5Mp sensor. But I figured the sensor size being the same this wouldn't be an issue. Also the Flange focal distance of a c-mount lens is fixed too.

Any ideas on what could be causing this?

Extra Information

• The cameras are industrial video cameras made by allied vision. The prosillica GX 1920 and the manta 504
• I do not think this can be a viewfinder issue because I am reading the raw sensor output for the testing

Asked by Adam Meyer

Answer

The two sensors are slightly different sizes. It is possible that sensor position varies but that is likely to create focussing problems, a sensor plane shift of half an inch would probably lose you infinity focus.

But by far the most probable explanation is differing sensor sizes which give you a different field of view, which you have to compensate by moving one of the cameras.

Lots of camera specifications, such as sensor size, focal length, even the number of megapixels are rounded for convenience and are hence not accurate enough to base other measurements on.

Answered by Matt Grum

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Do compact and DSLR cameras have the same sensor size if they have the same number of megapixels?

Question

In the analog camera, I understood the impact of using a 35mm film vs using a 70 mm film.

However in digital world, I dont know if the sensor size is the same for compact and DSLRs. In other words, if I use a compact and DSLR both of 12 megapixels and, say, with a lens of 35mm, will there be any difference in terms of resolution of the image?

Asked by Dheer

Answer

Sensor area doesn't determine resolution in the same way as the film era. Back then simply increasing the area of film would yield a similar increase in the size you could print, and therefore the detail you captured. In the digital world sensors can have different numbers of pixels per cm

Both 12MP compact and DSLR will resolve similar levels of detail but the DSLR sensor will be about 5-6 times bigger in each dimension. The extra size tends to provide better low light abilities as well as shallower depth of field at the same f-stop. This is because at the same f-stop a small and large sensors receive the same light per unit area, however a larger sensor receives more light in total leading to a reduction in photon noise. The difference in depth of field is due to the need to use a longer focal length for the same field of view, giving a larger apparent aperture.

Important note:

Differences in light gathering ability, DOF are not absolute and depend on the actual lenses that are available. For example it is true that for a small sensor compact and DSLR with f/2.0 lenses the DSLR will gather more light and have shallower DOF, however if you compare a 35mm DSLR to a medium format camera (with larger sensor) you might find that f/2.0 lenses aren't available for the medium format, so the smaller sensor 35mm DSLR can gather more light and attain shallower depth of field due to the availability of fast lenses.

Second note:

Not all compacts have small sensors, some now have sensors the same size as most DSLRs, such as the Fuji x100, Sigma DP1, the new Canon G1X and the Sony NEX range, and some are in between - e.g. the micro 43rds and the Nikon 1 series.

Answered by Matt Grum

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What are the cheap alternatives to DSLRs to get “large sensor image quality”?

Question

In a review of an entry level DSLR, I found this:

[this] is an excellent DSLR but make clear that a DSLR is no longer the only way to gain large sensor image quality at this price [around $500]

What are the alternatives the reviewer is alluding to? Would they still have interchangeable lens?

To be clear, I'm not after specific models, I'm just interested in understanding the kind of camera the reviewer had in mind.

Asked by UncleZeiv

Answer

Apart from DSLRs which have normally the largest sensors (full frame or APS-sized) there are some other types of cameras that have at least larger sensors than the typical compact.

For example there is the Micro-Four-Thirds-Standard (see http://en.wikipedia.org/wiki/Micro_Four_Thirds_system), which has a relative large sensor (18 mm × 13.5 mm), but I don't think there are cameras in the price range about $500. If I recall correctly these cameras are rather in the $1k-area.

The best compromise between sensor size and price below $500 would be a compact with a larger-than typical sensor like a Canon s95 or Olympus XZ-1.

Answered by sarnu

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Why do the 600D/7D sensors have more noise at high ISO than 5Dmk2 or 1Dmk4?

Question

Hi I'm wondering why the high ISO performance in a 5Dmk2 or 1Dmk4 is so much better than a 600D or 7d? I've been trying to photograph the milky way galaxy and when I use an ISO of 6400 I have an incredible amount of noise on the 600D, but I've seen the same ISO used with the 1Dmk4 and 5dmk2 to achieve wonderful photos without any apparent noise. I'd have to say the same for ISO 3200 which I can't get picturea without bad noise, ISO 1600 works but that causes noticeable star trails as the exposure becomes longer than the calculations I make using the declinations. Is this because of more pixels in the sensor size? Or do different cameras just have different ISO performance? Thanks for any insight.

Answer

The bigger the pixels, the less noise there is. This is a matter of physics. More light gets accumulated in each pixel and so it take more noise to appear significant.

The 600D and 7D have APS-C sensors which are small and have a high megapixels count. This makes their pixels comparatively smaller than the 5D Mark II which has a larger sensor and hence larger pixels since the resolution is not much higher than that of the 7D.

You can see the same thing in the Nikon range by comparing the D3X and D3S which are both full-frame cameras but one has twice the number of megapixels. The one with fewer megapixels shows less noise because each pixel is larger.

The extreme example of this is the poor performance of compact cameras which have tiny sensors. The last factor is technology because newer sensors show improvement over previous generation but physics cannot be beaten.

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Why do small sensor cameras use proportionally larger mounts?

Question

After seeing the Pentax Q which uses a sensor with 5.6X crop factor that is miniature compared to its mount and now the Nikon 1 system with its 2.7X crop factor also looks like its sensor is small compared to the mount, I am curious to know why these mounts are not much smaller?

At the other extreme, compare this to a full-frame model (technically we see the mirror but the sensor is almost the same size) whose mount is not much bigger than the circle it takes to fit the rectangular sensor.

So:

• Why the mounts were not shrunk in proportion to sensor size?
• Is there an advantage in having a bigger mount-to-sensor ratio?

Answer

I'm going to go out on a speculative limb here and suggest a few possible answers:

1. Ergonomics for ILC. If the lens is too small, it's probably not as easy to handle or may be perceived that way.

2. Optics. For handling wider apertures at longer focal lengths, you probably can only make the lens diameter so small and still make it practical for production costs and retail price.

3. Adaptations. So, if there is an adapter (in the case of the Q, from K to Q), then the larger opening may reduce or eliminate the need for optical correction in the adapter or even make it possible.

It may be some combination of all those as well, or none at all. I'm speculating. :)

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Why do some DSLRs have fewer megapixels than some pocket cameras?

Question

Some point and shoot cameras like the Olympus mju range have more megapixel capabilities than many DSLRs. Why is this? Is this because they have larger sensors or more dense ones? What are the trade-offs that are made to deliver such high density?

Answer

Pocket cameras have significantly smaller sensors than DSLRs, usually in the range of 5mm across as opposed to 22mm across. I'm not familiar with the Olympus mu range however I've seen 12 and 14 megapixel compacts.

These have more megapixels than DSLRs produced a few years ago, however it is mostly done for marketing purposes. The lenses in pocket cameras often wont have the resolving power to justify 14 megapixels, and if they did the limited light gathering ability of small pixels means aggressive noise reduction is used, smearing out any fine details.

There are reasons to produce DSLRs with lower megapixel counts, usually for speed of shooting for example the 10 megapixel Canon 1D mkIII or the 12 megapixel Nikon D3s. In any case these cameras will consistently beat a 14 megapixel compact in terms of resolution / noise, so there is no advantage to compacts when it comes to megapixels.

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How do Micro 4/3s cameras compare with DSLR cameras?

Question

What are the major (and perhaps more subtle) differences between the newer Micro 4/3s format in comparison to the well-established DSLR cameras? What are the pros and cons of the Micro 4/3s format, the camera body and lens capabilities and offerings, size/weight, etc.

Answer

The first technical difference is the fact that the sensor is smaller to the most common DSLR sensor sizes (APS-C and larger), whilst it's going to be less optimal than an APS-C, full frame or medium format (very expensive) sensor, it's still going to be far better than compact sensors. Noise will be comparable to APS-C (1.6x), though probably not quite as good, but this is also dependent on the sensor technology.

The second technical difference is that almost all Micro 4/3rds cameras currently use an electronic viewfinder, not SLR viewfinder. This means there is no phase detect auto-focus which is much quicker than contrast based auto focus. Phase detect AF can take less than a second in good light, whereas contrast AF can typically take 3-4 seconds and most often takes this long in any conditions.

Another difference is that on a lot of Micro 4/3rds cameras, the manual controls for aperture, shutter speed and ISO aren't as accessible as an SLR camera. If you plan on shooting manual with a Micro 4/3rds camera you may have to look around for the one that won't hinder you. For example, Sony's NEX-5 (not Micro 4/3rds but similar) apparently are very fiddly and it's better to just use them in an automated mode like Program mode.

A major physical difference is the size. The camera body itself is typically no larger than a large compact. The problem with this though is that the lenses are still fairly large when it comes to portability. You probably wouldn't try putting one in your pocket unless you have both a large pocket and a very short lens attached.

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How do Micro 4/3s cameras compare with DSLR cameras? Pros/Cons?

Question

What are the major (and perhaps more subtle) differences between the newer Micro 4/3s format in comparison to the well-established DSLR cameras? What are the pros and cons of the Micro 4/3s format, the camera body and lens capabilities and offerings, size/weight, etc.

Answer

The first technical difference is the fact that the sensor is smaller to the most common DSLR sensor sizes (APS-C and larger), whilst it's going to be less optimal than an APS-C, full frame or medium format (very expensive) sensor, it's still going to be far better than compact sensors. Noise will be comparable to APS-C (1.6x), though probably not quite as good, but this is also dependent on the sensor technology.

The second technical difference is that almost all Micro 4/3rds cameras currently use an electronic viewfinder, not SLR viewfinder. This means there is no phase detect auto-focus which is much quicker than contrast based auto focus. Phase detect AF can take less than a second in good light, whereas contrast AF can typically take 3-4 seconds and most often takes this long in any conditions.

Another difference is that on a lot of Micro 4/3rds cameras, the manual controls for aperture, shutter speed and ISO aren't as accessible as an SLR camera. If you plan on shooting manual with a Micro 4/3rds camera you may have to look around for the one that won't hinder you. For example, Sony's NEX-5 (not Micro 4/3rds but similar) apparently are very fiddly and it's better to just use them in an automated mode like Program mode.

A major physical difference is the size. The camera body itself is typically no larger than a large compact. The problem with this though is that the lenses are still fairly large when it comes to portability. You probably wouldn't try putting one in your pocket unless you have both a large pocket and a very short lens attached.

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Are full-frame cameras bad for sports photography?

Question

I was reading about crop factor from various places on the internet, and the general idea that kept building in my mind was that full-frame cameras are good for wide-angle shots but not that good for tele-photo. In Wikipedia it's written:

[...] a 200 mm lens on a camera with a crop factor of 1.5 has the same angle of view as a 300 mm lens on a full-frame camera. The extra "reach", for a given number of pixels, can be helpful in specific areas of photography such as wildlife or sports.⁶

It makes sense, but how high would the level of detail be on a full-frame with 300mm compared to the other example?

Answer

One aspect of this comparison that has not been mentioned is the fact that crop-sensor cameras are generally faster for a given price point.

• The 7D shoots at up to 8 Frames/Sec, the 5D manages 3.9 Frames/Sec
• The 1Ds III manages 5 Frames/Sec, while the 1D III/IV manages 10 Frames/Sec

In sports photography, where continuous drive is often used, those extra frames could mean the difference between capturing a player right before hie hits/kicks a ball, and actually at the moment of contact.

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Regarding using telephoto lenses on a crop-sensor body, the critical measurement here is the pixel pitch, which is the thing that actually determines how much detail you will get from a lens.

Basically, if you have two different sensors with the same pixel pitch, the larger one effectively takes the exact same image, with some cropping.

As an example, I have a 30D and a 5D2. Both have 6.4µm pixels. Therefore, every exposure on the 5D2 effectively includes the entire area that a 30D exposure would capture, with the same resolution.

However, the 7D has 4.3µm pixels, so for a given focal length, the 7D will resolve 1.5X (1.488 to be exact) the detail.

This is all assuming an ideal lens. If your lens cannot resolve fine details, either camera will produce a blurry result. Also, small pixel sizes will be less forgiving of lens defects than larger pixels, since the smaller pixels require a larger lpm from the lens. A lens that is at the edge of it's resolving capabilities on a 5D2 may not see any improvement on a 7D, since the extra pixel resolution has no effect on the lens sharpness.

There is a nice breakdown of the Canon series camera pixel pitches on the-digital-picture.com. It's about 2/3 of the way down the page.

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There are other considerations - larger pixels generally give less ISO noise, though modern image processing is advancing faster then sensors are shrinking, so it is not as much of an issue as it could be.

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Note: I am writing about canon bodies because I am a canon user, and know them far better. However, most of the arguments are much more broadly applicable, basically to anything that uses a CCD/CMOS image sensor:

• The two critical factors in a camera's FPS are Number of pixels, and ADC speed.
• The critical factor in how much detail you get from a lens is pixel pitch (Smaller pixels gets more detail, until you reach the limitations of the lens).
• The largest influence in ISO performance is pixel size (larger pixels are less noisy). The readout electronics have much more influence here, though, so it is not an absolute determining factor as the two above are.

This is true across all brands.

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