Considerations when purchasing a prime lens?

Question

What should I be aware of when buying a prime lens (other than that it will fit my camera)? What specs should I pay close attention to?

Asked by Dan Seaver

Answer

Aside from focal length, the most important thing to consider is the maximum aperture of the lens. That's what people are often looking for when they buy primes. The max aperture is usually part of the lens description such as: 50mm f/1.8 where 50mm is the focal length and f/1.8 is the maximum aperture. The lower that "f/" number is, the better low-light performance the lens will have and the more shallow the depth of field you can get out of the lens.

Other considerations are the same as any other lens: autofocus quality, whether it has IS or can do macro (if you want/need it), if it has a rotating front element (if you plan to use a circular polarizer with it), etc.

Besides those things, there's not much else to look into regarding specs. You can get sharpness test results along with data on distortion, CA, etc on http://photozone.de and search for other reviews on Google. Flickr and it's groups can also help, people often have test data or sample photos you can view large to get an idea of the image quality you can expect -just make sure you get a large sampling of data since poor test conditions or methods can make a lens look worse than it really is.

Answered by Erica Marshall

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How does one track action with a fast telephoto prime lens?

Question

With my normal-range prime lenses, I tend to shoot with both eyes open — what I see in the viewfinder has a high correspondence to what I see with my other eye. With my 70mm (105mm in 35mm-equivalent terms), it's a little trickier, but not so much that I really ever have to think about it.

With the Pentax DA★ 200mm f/2.8, though, it's a different story, for two reasons. First, at 300mm-equivalent, the field of view is so radically smaller than my unaided vision that it's just confusing to operate with two eyes. And second, the depth of field is so small that if I move away from my target, there's good odds I'm just looking at blur.

If this were a zoom lens, I might consider tracking the scene at a wider focal length and then zooming in. But that's not an option.

Clearly, people use these lenses for sports and wildlife photography all the time. What's the trick? I was at a not-so-fast-moving kung fu demonstration, and kept losing people. I can't imagine catching a bird in flight; do people just point at a flock and hope something is in the field of view? Is this just a matter of really learning to know the lens, or is there something I can do?

Asked by mattdm

Answer

Based on the last two answers I may be missing the point of the question here, but instead of worrying about aperture, your question more directly relates to how do I track action.

Tracking abilities I would split into 3 categories.

1. The Camera
2. The Lens
3. You

Part 1: The Camera

Some cameras just wont do tracking particularly well. You really need one that can do continuous auto-focus (not all do). This is the AI Servo mode if you're in Canon land, or on Nikon there is a C/S/M setting that does this (you want C for Continuous). I'm afraid I can't comment on Pentax, but refer to your manual. So set your camera to continuously focus.

The next thing to check is to ensure it is using all available AF points. Again, this varies by camera, but you may have a diamond of 7 or 9, or be lucky enough to have more - 19, 51, 61.....depending on make and model of camera. Just make sure all of them are enabled.

Also, think about the metering mode you choose. for things against the ground, or landscapes, you may want evaluative or full metering, but for a bird or aircraft in the sky, choose centre-weighted or spot metering.

Finally, choose your shooting mode appropriately. For action shots you will want shutter priority mode. I think Pentax use the mnemonic "Tv", as do Canon. Nikon and others just use "S". Then set a shutter speed appropriate to your action. Fast moving = 1/1000th or more. Slow subjects = 1/250th maybe? The benefit of your fast lens will be felt as you can keep the ISO low whilst still getting correctly exposed shots.

Part 2: The Lens

I'm not sure this pertains to you as its about image stabilisation, and I think the Pentax uses in body stabilisation. But in the Canon/Nikon world long lenses with IS/VR modes also have a stabiliser "mode". If you have this, ensure the mode is set correctly for your shooting type. Mode 1 is generally for overall use, handholding, normal shooting. Mode 2 usually only tries to correct vertically, so is useful for panning. Perhaps in the body of the Pentax you can select the mode too??

Also, the AF of the lens must be sufficiently fast to keep up with the constant refocussing by the camera body. But the lens you suggest has an SDM motor which seems to be well liked and fast.

Part 3: You

Practice your panning. Practice following targets across the ground and sky. It doesn't have to be in the dead centre of the frame but there's nothing worse than a raft of photos of your favourite car, plane, bird, etc with it's back end cut off! You may find a change of stance helps, or to hold the lens differently, or use a Monopod. Also, I would not tend to keep both eyes open as when you are tracking action, it only serves to distract you. Concentrate on whats in the viewfinder as thats what the camera sees.

I hope that helps?

Answered by Mike

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Do I need a filter for my prime lens in order to protect it from dust, splashes, etc?

Question

From here: http://photo.stackexchange.com/a/569/5205

UV Filters:
Many photographers feel that it is worthwhile to put a UV filter on the front of every lens, on the basis that this will protect the front lens element - from dust, scratches and catastrophic damage if the lens is dropped. In other words, it is a kind of insurance policy against lens damage. I understand that Scott Kelby takes this position.

Since prime lenses are not supposed to zoom can dust, water, etc still get inside it if I don't use a filter?

Asked by Anisha Kaul

Answer

The filter doesn't protect against dust getting "into" the lens, it just protects the front element. So the arguments for a filter are equally valid for zooms and primes.

Personally I don't use them, as they have a negative impact on image quality. Always keeping you lens hood on is another way to protect the front element.

Also, I recently damaged my lens (a prime), as I dropped it while changing lenses. Two elements fell out the back, and the focusing system got ruined, but the front element is intact. So the filter is no magical protection for your lens.

Answered by Pete

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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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How to compare the focal length of a 50mm prime lens with the default lens of a point and shoot camera?

Question

To imagine the 50mm focal length of a prime lens 1.4F, can I simply zoom the lens of my point and shoot camera up to 50mm?

Will both the focal lengths be same?

Any other way to imagine the focal length 50mm of prime lens 1.4F when what you only have is a point and shoot camera with 70mm max zoom?

Asked by Anisha Kaul

Answer

If your point-and-shoot has the typical 1/2.3" format sensor and you are trying to compare it to a 50mm lens on a cropped-sensor DSLR (in your case, a Nikon, if I recall correctly), then there's a little bit of math involved.

The compact's sensor has a 3:4 aspect ratio. It measures 6.16mm by 4.62mm, with a diagonal of 7.70mm.

The Nikon DX sensor has an aspect ratio of 2:3 and measures 23.6mm by 15.8mm. That would give a diagonal of 28.4mm.

It's normal to compare lenses based on the diagonal of the negative/sensor. I don't like that approach, though, since the aspect ratio is different. It's best to compare images with the same aspect ratio, and in the case of both of these sensor formats, the full length of the short side of the sensor will be used when an image is printed in a 4:5 aspect ratio. That is, an 8x10 picture made with either camera would involve cropping the longer dimension. So it's safe to compare just the shorter dimension of each camera/lens combination.

The 50mm lens on the Nikon is about 3.165 times the length of the shorter side (the height when the camera is held horizontally). That means that in order to get the "same" 8X10 from your compact camera, the lens would have to be set to 3.165 times the shorter side of its sensor, or about 14.6mm.

If your compact has a different-sized sensor, the math will still hold. Find out what format of sensor it uses, then multiply the shorter side of the sensor by 3.165 to find out how far out the lens needs to be zoomed to approximate the 50mm lens. Do note, though, that the field of view for our hypothetical 8X10 print is the only thing the two cameras will have in common.

Or, if you want to do it without the math, my rather standard 8-1/2" (about 21.5cm) tall head will completely, but just, fill the frame of a Nikon DX in "landscape" orientation from the top of my bald pate to the bottom of my chin using a 50mm lens from almost exactly three feet away. So a volunteer or a ruler three feet (90cm) away or a mirror 18 inches (45cm) away will be enough to show you how far to zoom.

Answered by Stan Rogers

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How can one use a reversing ring with Nikon G lenses?

Question

So, this blog (credit to mattdm for pointing it out) says:

Firstly, when you turn the lens around you obviously lose the CPU connection between the lens and the camera, so say goodbye to autofocus, metering (in most cases) and aperture control (though I’ll come back to that)

Then:

The advantage of this old lens is that it has a manual aperture ring, which neatly neutralises the loss of automatic control mentioned above.

So, since G lenses don't have an aperture ring, aperture can't be controlled anyhow if we reverse the lens?

Secondly, is it practical that we set the metering and the aperture (manually) before taking the lens out and reversing it?

Is there any other way to get around this problem in G lenses (assuming that the camera bodies have the manual focus, aperture, metering controls)?

Asked by Anisha Kaul

Answer

With some non-G lenses, there is a switch on the lens that will release the aperture ring so that you can manually control it, even off camera or reversed, to set the aperture to whatever value you want (but as you close down the aperture, the viewfinder will get dimmer).

With G lenses, there is no aperture ring. There is a mechanical lever though, which closes down the aperture. You can slide that lever and the aperture will close. As the blog points out, you can fix that lever in place with tape or poster tack.

When you reverse the lens, the aperture will close to its smallest opening (f/22 or whatever). Moving that lever can open it back up to the widest aperture, or somewhere inbetween (although very hard to control exactly)

The camera body will not know what aperture is set since it will not have any electrical contact (and will wonder where that lever went!). So best to set exposure to manual and set an appropriate shutter speed. You won't need to set an aperture since the camera can't control it anyway.

There isn't really any point in setting the metering before reversing for a number of reasons:

• metering will assume an aperture, but once reversed you will be setting (potentially) a different aperture using that lever

• you are unlikely to get the same amount of light through the lens when reversed, depending on the size of the two ends of the lens - most surely there will be less light transmitted when reversed.

Answered by MikeW

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Is it difficult to focus on 1.4F prime lens, and if it is how to counter that?

Question

Does difficulty in focusing have anything to do with 1.4F (Nikon G)?

Will it be still difficult if I use manual focus?
Is auto focus too slow?

Is there a way to counter it?

This example photo (from a photozone review) was taken taken at f/1.4. Isn't the whole trunk in focus here? If it's so hard to get everything in focus at f/1.4, why aren't some parts of trunk out of focus?

Asked by Anisha Kaul

Answer

No matter what the maximum aperture of the lens, the plane of absolute focus is the same. That is, if you shoot with a 50mm f1.4 or a 50mm f2.8 at, say, 10 feet out, it is focused on the exact same specific point of your subject. The difference is that at f1.4 a thin slice appears to be in focus and at f2.8 a thicker slice appears to be in focus.

So, let's say you are using the 50mm f1.4 lens set to f8. The resultant picture shows a thick slice of area in focus, just as a normal zoom lens set to f8 would. When you are focusing to take that photo, regardless of which lens and what focusing mode you use, you aim to focus on the exact same plane. In that regard, focusing with either lens is neither more or less difficult.

Of course, experience says that's not quite true: most will agree that focusing an f1.4 lens is more difficult than focusing an f5.6 zoom lens. The reason it's considered more difficult is because of that narrower plane of focus which shows less in focus and therefore makes it a little difficult to tell what precisely has been focused on. That's sort of a misnomer, however, because if your lens is set to f8 placing the plane of focus in exactly the correct location is irrelevant: the resulting photo will have a larger depth of field and hide any inaccuracy you had when focusing.

But, people don't buy an f1.4 lens to shoot at f8; they buy them to shoot at f1.4! If you misfocus slightly when shooting at f1.4, it won't be hidden like when shooting at f8. You do need to worry about being more precise in placing focus where you want it when shooting with such a large aperture. Is it more difficult? I think that depends upon your perspective and understanding:

• Perspective: a thin plane of focus means it's easy to see exactly what is in focus. You can tell precisely where you have focused and it's no surprise what the resulting photo looks like.
• Understanding: using a wide-area AF mode is almost asking for trouble, for example, because it's trying to focus on much of your scene, which can't be rendered entirely in-focus at f1.4. Use a single-point AF mode to place focus precisely. If using manual focus you need to have a feel for how much throw the focus ring has to recognize how much to turn it to pull your subject into focus -- just racking back and forth trying to find it will get you nowhere.

Working with an f1.4 lens isn't anything to be concerned with, IMO, because after using it for a while you'll have a good feel for it and know best how to use it.

Regarding your example photo:

Isn't the whole trunk in focus here? Why aren't some parts of trunk out of focus then?

Look close -- the whole trunk is not in focus. near the edges of it you can see it's a little soft. I bet that they could have stopped down to f1.6 or 1.8 and the edges would be a little more in focus, and the rest of the scene would basically be unchanged.

Answered by Dan Wolfgang

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Nikkor f/1.8G 35mm or 50mm?

Question

I'm new to photography. I got Nikon D3100 with 18-55 KIT.

I was looking to buy 1.8f prime lens.

I found two options.

AF-S DX NIKKOR 35mm f/1.8G and AF-S DX NIKKOR 55mm f/1.8G

Which one you guys prefer ?

Asked by ChamingaD

Answer

The question here doesn't — or shouldn't — come down to what we prefer, but rather what you want to use it for. These lenses (because of their different focal length) have a significantly different angle of view, which means that they serve different purposes. Eventually, you may find that you want both.

On your APS-C Nikon, the 50mm lens acts as a short portrait lens. It's kind of awkward for most anything else, but is just about perfect for taking head-and-shoulders portraits. I say awkward because it's not enough "reach" to pick out details like a longer telephoto lens, but is narrow enough that it's difficult to frame indoor scenes. That doesn't mean you can't use it more generally, of course.

The wider 35mm acts as a normal lens — it gives a comfortable and versatile field of view that doesn't feel either wide-angle or telephoto. For that reason, if you're just going to pick one of the two, this is probably going to be your best bet. But it depends on what you're looking for — a portrait lens may be just what you need.

Answered by mattdm

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How can I accurately focus manually on an APS-C DSLR?

Question

My favorite portrait lens is the Nikon 50mm 1.4G. I love the light and what it is capable of. My problem with it is that on my D90 the AF is sometimes horribly slow, and in many cases (mainly low light) I can't auto focus at all. I use AF lock as much as possible, but for many shots I really wish I could just use manual focus. The problem is that I'm usually wrong about whether my subject is in focus or at least completely in focus. So my question is...

Are there any recommendations you can make for training my eye to be sure my manual focus is accurate? Any diopter adjustments or calibrating tools? Any eye exercises to train myself to recognize a true focus?

I know that I would probably have better AF performance on a more expensive body, but for now I think it's good practice to train myself in manual focus anyway. Thanks for any assistance.

Answer

One of your problems is that the matte screen in your camera (this is what you are actually looking at through the viewfinder, it's a semi-transparent plastic screen that sits at the top of the mirror-house, below the prism housing) is designed to give a nice bright useable image through a slow autofocus lens such as your average f/3.5-5.6 consumer zoom. This is good if you are using a consumer zoom, but very bad if you are trying to focus a fast prime lens. The reason is that the extra screen brightness is bought at the expense of focus accuracy - is unable to show you the small depth of field at larger apertures than about f/2.8-ish. In other words, if you look at the image from an f/1.4 lens through this matte screen, the depth of field you see will be that of f/2.8 and not f/1.4. Again, for a consumer zoom this is entirely irrelevant but for a fast prime it is highly misleading. You physically cannot focus a fast prime accurately through such a matte screen; you are just not getting the information needed.

A solution for manual focusing is to replace the default "fast" matte screen with an old-school, coarse-grained one which will show you accurate depth of field for a faster lens, and more "pop" when things come into focus. You may also get a screen with a split-prism center, or one with a prism-ring round the center.

I'm not sure if Nikon offers such alternative mattes for the D90 but third parties might although installation is likey to be a bit more fiddly in that case. The downsides to a coarse-grained matte screen is that it affects light-metering, and that the view from lenses slower than about f/2.8 will be darker (much darker, in the case of an f/5.6 lens) in the viewfinder. The matte does not affect autofocus performance in any way though.

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Will a prime lens help me get better portraits at a wedding?

Question

I have a Canon 600D with the EF-S 18-55mm f/3.5-5.6 IS lens. I have a friend's wedding coming soon, and I'm not sure if my zoom lens will do a good job or not. I was thinking of buying a prime lens so I can get better portraits, but I'm not sure if this is true.

The wedding will be in a hall with different light situations (sometimes it's bright, sometimes it's dark, and they'll use laser lighting a lot), there is a garden associated with the hall, and the wedding will be at night. I'm not the official photographer for the event.

Answer

Prime lenses are excellent options for portrait work, especially at wedding venues. Prime lenses are less forgiving when it comes to varied situations and framing. Instead of moving the zoom ring, you have to move your feet. If you are the main photographer for an event, no one is going to mind you moving around to get the shot. If you are an audience member attending the wedding as a guest, it may be considered rude to get move around so much for a shot.

Typically indoor weddings have poor lighting, at both the ceremony and reception events. Because of that, fast lenses of at least f/2.8 are usually the standard. You could fill your gear bag with zoom lenses at f/2.8, and shoot weddings very well, but it would likely be less expensive to purchase a few f/1.4, f/1.8 or f/2.0 lenses that are wider yet.

Another benefit of prime lenses is that typically they are smaller and lighter then a professional grade zoom lens.

For portraits specifically, a wider aperture will provide you with a more blurred background, referred to as bokeh. It also will let you stop action such as a moving bride or groom, and allow you to use a lower ISO setting if you are worried about noise.

Overall, prime lenses are a great option for wedding photography, because they are particularly good at portrait work, especially in low light.

To get started these questions may help you with your first purchase:

• Is it worth it to have the 50mm f/1.8 Canon lens?
• Is a 50mm f/1.8 or 50mm f/1.4 a good lens for portraits in low light?

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What is a 200mm lens good for?

Question

I just found that there is a 200mm lens at my school. It is a Canon with Image Stabiliser (with red detail). It is old, at least 10 years. It has been great playing around with it, but I really don't know what it is good for. What type of photos is it built for. I recall vaguely a friend telling me that a lens with no room to change the zoom will give you better focus... but apart from that I am not sure what type of photos it is good for. I want to take it to the sports field and capture some sports in action.

Update: The lens is a "Canon EF 200mm 1:2.8 L II Ultrasonic". It does not say anything about image stabaliser :(

Answer

A 200mm lens is in the category of lenses called "fixed focal length" or "prime", which cannot zoom in and out. The more common lens type is the zoom, which does allow you to zoom in and out.

The primary tradeoffs between prime and zoom lenses are:

• Aperture - Typically, prime lenses tend to operate at wider maximum aperture than zooms. For instance, Nikon makes 50mm, 85mm, and 105mm prime lenses that can expose down to an aperture of 1.4, whereas the best zoom lenses that cover that range can only focus down to 2.8. In terms of the photo, that can be a noticeable difference in the Depth of Field, which controls how much of the image is in focus and how much is in blurred out.
• Optical quality - Prime lenses are almost universally better optically than equivalent zooms. They achieve better sharpness by usign fewer optical elements. You can think of this as fewer pieces of glass between you and your subject, thereby reducing the amount of distortion, letting more light through, and having more fine-tuned control of the final image.
• weight - Prime lenses are always much lighter in weight than their zoom counterparts

You asked specifically about the 200mm lens. This lens is often used for:

• Wildlife - When you are on safari, or birding, your subject can be as far as 50 to a few hundred yards away, and if you still want to fill the frame of your image with that subject you need a hefty zoom. The 200mm helps accomplish that.
• Sports - Same as in wildlife, if you are standing on the sidelines of a sports game, you need to zoom in to capture the action up close in your frame.
• Portraiture - This lens is also useful for portraiture, but it requires standing very far from your subject. Some professionals will do this to achieve a very dramatic effect and a maximal blurring of the background.

This lens is best used with a tripod or monopod because when you are zoomed out that far, even the slightest bit of camera shake will significantly impact your image.

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Which prime lens to get after the 18-55mm & 55-250mm?

Question

I started out with the 18-55mm IS kit lens on my Canon EOS 550D over a year ago, and added the 55-250mm IS a couple of months back to augment my telephoto reach (based on the recommendations in one of my earlier questions). After shooting almost 5000 photos with the former and 1000+ with the latter, the biggest limitation I find is their low light shooting ability and I've ended up shooting a lot of images at ISO 3200 and\or slow shutter speeds resulting in subject blur. AF performance has also been a bit iffy in these situations. On the subjective front, I've generally preferred to shoot portraits.

To this end I did some analysis on a selected subset of my photos using Exposureplot and exiftool+Excel to quantify my results (also below), and found that 55mm is the most shot focal length followed by 18mm, both of which correspond to the lens range limits (so likely to be skewed). The usual portrait ranges (80-110) also feature reasonably given that the range was added only recently.

I also checked out the Canon lens lineup and have settled on the following shortlist based on my above analysis (given my budget of around $500):

Lens(length+Av) Macro   USM     IS      L-series
50 mm   f/1.8   No      No      No      No
35 mm   f/2     No      No      No      No
50 mm   f/2.5   Yes     No      No      No
28 mm   f/2.8   No      No      No      No
24 mm   f/2.8   No      No      No      No
50 mm   f/1.4   No      Yes     No      No
100 mm  f/2.8   Yes     No      No      No
135 mm  f/2.8   No      No      No      No
60 mm   f/2.8   Yes     Yes     No      No
85 mm   f/1.8   No      Yes     No      No
100 mm  f/2     No      Yes     No      No
28 mm   f/1.8   No      Yes     No      No
100 mm  f/2.8   Yes     Yes     No      No

The EFS 17-55mm f2.8 would serve my requirements, but is beyond my budget at present. I do plan to get it eventually. I also doubt that I'll be upgrading to a full frame DSLR, so EF-S lenses are also good for me.

To summarize, I need the following from the next lens:

1. Good low light performance
2. Suitable for portrait (haven't tried playing around with depth of field much so far, as I end up shooting wide open most of the time anyway)
3. Macro ability would be a plus (does it make sense to get a non-macro & a macro for similar focal length?)
4. Better AF performance (should be a given for the lenses as they are f2.8 or wider, and many are USM)
5. Canon lenses preferred as I'm not sure of the reliability & service\warranty options of 3rd party lenses in India

So, given this scenario, which would be the recommended lens to get?

Answer

Canon EF-S 60mm f/2.8 Macro USM

Suits (1) (2) ad (3) perfectly, and it is not expensive.

While it makes sense to get a non-macro and a macro lens for a similar focal length, I see that you are on a budget, so that wouldn't be your best choice.

I did not suggest the 50mm f/1.4 because 50mm is very slightly short for portrait, and you cannot do macro at all, even the kit lens offers a better magnifying ratio.

Lastly, allow me to point out that you can learn very little from shooting 6000 photos. You will, however, learn a lot if you try to delete 5900 photos from the 6000 you shot.

If you constantly find yourself shooting in low light condition, getting a flash may not be a bad idea at all, provided you know how to use it right.

I thought my photography would improve if I have bought a better lens. So I did, and I see less noise but no improvement. So I experiment with different ways of shooting, I shoot EVERYTHING in all kinds of situation. I no longer limit myself to shooting indoor. I try everything I can.

Then, my photography improved, and I am now able to create much much better photos, using the exact same lenses that I once said is limiting.

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Why do wide angle prime lenses have relatively small apertures?

Question

I've noticed that many of the wide angle prime lenses (at least for Canon) have somewhat smaller apertures than their normal or telephoto counterparts. E.g. the regular Canon 24mm prime is f/2.8 while the 50mm prime is f/1.8.

Theoretically, it should be possible to make large aperture wide angle lenses, as their opening will be much smaller than primes with longer focal lengths. So, why are there no wide angle lenses with larger apertures? Does a larger aperture place limits on the smallest aperture a lens can have, as this could have an impact on the depth of field for landscape photography.

Answer

Broadly speaking wide aperture lenses are easier to design the longer the focal length. The reason that you don't see any 400mm f/1.4 lenses is due to manufacturing difficulties, e.g. keeping dispersion low while producing elements of the size required for such apertures. It's worth restating that the designation f/1.4 means that the size of the aperture stop is the focal length divided by 1.4, which for a 400 f/1.4 is a whopping 285mm. Technically it's the image of the aperture stop that must be that size, which means the front element has to be at least that big.

If you look at the widest of Canon's superteles you see a pattern that 150mm seems to be about the limit of what is economical:

• 400/2.8 = 142mm

• 600/4.0 = 150mm

• 800/5.6 = 142mm

Lenses with focal length less that the registration distance (about 46mm for most DSLRs) have to incorporate what's known as a retrofocal design, which is essentially a reverse telephoto group (or "wide converter") at the back of the lens. The wider the lens the more corrections have to be performed due to the retrofocal design, and these corrections are more difficult for wide apertures lenses.

You can see this if you look at the design of the Canon 24mm f/2.8 and 50mm f/1.8:

Canon 24mm f/2.8

50mm f/1.8

The reason 50mm offer such good price/performance ratio when it comes to aperture is that for 35mm cameras that 50mm sits at the sweet spot where the focal length is long enough to allow a simpler non retrofocal design, but not too long that large pieces of glass have to be used to give a good f/number.

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Does it make sense to get a non-macro and a macro of similar focal lengths?

Question

I recently asked a question on which prime lens to get after the kit lenses, and in my shortlist of lenses there was quite a lot of overlap of focal lengths along with macro & non-macro versions of a lens. From what I've read so far, macro lenses have a smaller maximum aperture than their non-macro counterparts (usually around a stop faster), and the AF performance may be poorer (some like the EF-S 60mm macro are said to have fast AF). However, in terms of optical performance, they seem to be just as good as any prime.

So, as per a comment to the earlier question, I'm asking this specifically - does it make sense to get a non-macro and macro lens of similar focal lengths? Ex. (Canon specific), the EF 50mm f/1.8 and 60mm f/2.8 macro have pretty similar focal lengths (vastly different prices though), or the 85mm f/1.8 and the 100mm f/2.8 macro.

Answer

Buy lenses based on your needs. If you do need a macro lens and a super-fast lens of the same focal length to get your photos, then yes, it makes sense to buy both lenses. If you can do with the maximum aperture of macro lens or with the minimum focusing distance of the non-macro prime, then you don't need the other.

Also, collecting lenses can be a hobby by itself. For example, there are people out there with vast collections of 50mm or 135mm lenses.

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Is it true that there are no stabilized prime lenses (and if so, why)?

Question

Fast prime lenses like the Canon 50mm f/1.4 lens work nicely in low-light situations. But I'm quite sure they would work even more nicely if they had optical image stabilizers. It seems to me that no such lenses are available in the Canon system. Is this true? Maybe even for prime lenses in general? If yes, is there a reason for this?

Answer

As of today there are 28 prime lenses with image stabilization. Almost half (13) of them are from Canon and 1 is a Canon-mount Sigma, so I would say your assumption is wrong. This is an easy lens search.

What you will notice is this is less common in the wide focal-length, with the widest stabilized lens being a 45mm Panasonic. This is because longer lenses benefit more from stabilization because they require higher shutter-speeds to give a sharp image.

Take for example a 500mm which would require 1/500s. This stabilization you can take it down to 1/125 or 1/60 even which is still a general purpose shutter-speed. Now take a 50mm which already gives a sharp image at 1/50s, you can bring that down with stabilization to 1/15 or 1/8 even. Those shutter-speeds are not suitable for moving subjects and even grass and leaves will blur. Now, of course, all shutter-speeds are useful, just that you gain more by stabilizing a long lens than a short lens. As a matter of fact, some people ask why certain wide zooms are stabilized, saying it's a waste of money!

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Why there is no Canon 50mm *IS* lens?

Question

Canon's 50mm prime lenses are all non-IS (Image Stabilization) for some reason. Considering the popularity of these range primes, shouldn't Canon be interested in shipping a new, optically improved IS version?

Answer

There are two main reason why there's little chance we're going to see 50mm IS lens in the near future:

• 50mm lenses tend to be very simple and therefore cheap. Complicating its design with an image stabilizer group would push the price significantly higher, while the added benefit of IS wouldn't be that high at 50mm focal length.

• If you want an expensive and light-hungry 50mm, there's already the huge lump of glass that is EF 50mm f/1.2L. There's not much point in having IS in such fast (and relatively wide) lenses.

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Would a fixed or zoom telephoto lens be better for learning?

Question

My daughter has a Nikon D-90 camera body and two prime f1.4 lenses 50mm and 35mm. She is interested in learning more, and I am curious which of a zoom or fixed telephoto lens would help her best? Is getting a low f-stop lens important in a telephoto lens?

Answer

It depends on where she's feeling the limitations. I have a kit made up of 15mm, 40mm, and 70mm prime lenses (on a dSLR with the same 1.5× format as the Nikon D90), and for me, that's just about right. (I'd probably trade the 40mm for a 35mm were I starting over — tough call.) For my style, I don't miss having a zoom at all.

Since she has (and is presumably comfortable with) two prime lenses, she may feel the same way, and would just like to increase the range of focal lengths she has available. For that, another prime covering either wider-angle or more telephoto would fit nicely.

On the other hand, she might want to explore the convenience of a zoom. Having flexibility of framing can remove one-more-thing-to-worry-about from the learning process, and remove the potential need to switch lenses in the middle of the action.

Back on the first hand, though, there is a school of thought which argues that prime lenses have inherent advantages for learning composition. Mike Johnston's Case Against Zooms articulates this view well. The idea is that by learning to know a particular prime lens's inherent viewpoint, that limitation actually becomes a freedom.

Since I use my 40mm most often, I can attest to this: having used it to take thousands of photographs over the course of several years, I can know what photo my camera will make without having to actually put it to my eye. That's very useful, and helps me concentrate on taking the photographs I want to take with the view I want to have.

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Why do people recommend 50mm or other prime lenses as starting lenses for learning photography?

Question

I've seen quite a few people recommend the 50mm prime lenses, in particular the sub-$100 50mm/f1.8, as a starting lens for photographers (especially because they're likely to be using cameras with cropped sensors). From my experiences with the 18-55 mm kit lens (on a Canon EOS 550D), it seems that 50mm is not really very suited for indoor flashless group photographs where the wide aperture would be helpful. It is probably a good lens for portraits of one or two persons, and some low light photographs.

So, what are the advantages it offers over the kit zoom lenses (apart from the wider aperture), under what scenarios is it more useful, and why would you recommend it as a starting lens?

Answer

What people have generally suggested is to start with a normal lens. On a full-frame 35mm camera, that role was generally filled by the 50mm lens. On a modern crop-frame DSLR, it would be closer to 30mm (for Canon APS-C 1.6x sensors) or 35mm (Nikon, Pentax, Sony) or 25mm (Olympus and Panasonic).

The 50mm is usually suggested these days as the first good supplement to the kit lens. It doesn't really matter whose 50mm lens you're looking at, the design for the f/1.8 (or f/1.7) version has been around forever. They're all sharp to very sharp, lightweight and (most of all) cheap. And as you pointed out, they'll function well as a shortish version of the traditional medium telephoto portrait lens. But as nice as the "nifty fifty" is, it's not a normal lens on a crop-sensor camera.

A normal prime lens is very versatile. You can step back a couple of feet and get a fairly wide image field. Step forward and you can fill the frame with a single subject of interest. Neither picture will be quite what you'd get using a wide angle lens or a short telephoto, but you can get a reasonably good picture either way. The field of view subjectively matches what you tend to think you're seeing in real life, so there are no major surprises or unintentional special effects.

Working with a prime lens, though, helps you to become a better photographer. It forces you to change your point of view to find the best image rather than just standing in the easiest spot and turning a ring. You might get acceptable results using a zoom exclusively, but it's unlikely you'll get a spectacular result until you've forced yourself to take the rocky road for a while. You may decide to stick with primes (I have always had zooms, and shot an average of ten rolls of film a day -- or the equivalent -- for a couple of decades, and I bet I took fewer than two hundred shots with a zoom lens in all that time) but even if you use a zoom lens most of the time, you'll never use it in quite the same way after working exclusively with prime lenses long enough to change your habits.

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Can I use my APS-C kit lens as a reference for choosing between 50mm or 35mm prime lenses?

Question

I'm looking at getting a second lens in addition to my Nikon D7000's kit lens.

I want to know if it's possible to use my 18m-105mm kit lens to get an idea of the focal length for a 35mm lens vs. a 50 mm lens. If I set the kit lens at 35 and 50, will that give me an accurate idea of the magnification and field of view I would get with these two lenses?

I wanted to make sure this was correct, because I know there is a crop factor with a DX camera and I’m not sure if that is taken into effect with the kit lens or not.

So will the 50mm lens, when on my D7000, produce images like when I have my kit lens on the body set to 50mm? And, the same for the 35mm?

Answer

Focal length is focal length, regardless of sensor size or whether the lens is a zoom lens. If you have tried your kit lens at 35mm and 50mm, then the framing will pretty much be the same with prime lenses of those focal lengths. Prime lenses will offer a couple things your zoom lens does not, however.

For one, they should offer better quality, as prime lenses can be constructed to perfectly project the clearest image possible for the given focal length. There are degrees of optical quality within a given prime focal length, as a higher end lens will usually use better materials and lens elements. Generally speaking, though, primes offer better quality.

Second, prime lenses usually provide much wider maximum apertures. A 50mm prime can come in anywhere from f/1.8 through f/1.2, and older manual focus lenses may even be found with maximum apertures as wide as f/0.95. Wider apertures can be more difficult to use at times (due to extremely thin DOF), but they can provide some truly fantastic bokeh.

Regarding focal lengths on a cropped sensor, there is a fairly nice correlation between the 35mm and 50mm lenses and ideal portrait focal lengths on full-frame sensors. Nikon cameras have a 1.5x sensor crop factor. That means that a 35mm lens "behaves as" a 52mm lens on full frame, due to the difference in the field of view captured by the APS-C sensor. The 50mm lens behaves as a 75mm lens on full frame. As an additional lens, 85mm lenses behave like a 134mm lens on full frame. These focal lengths fit pretty well with the ideal portrait focal lengths on full frame cameras, which include 50mm, 85mm, and 135mm.

It should be noted that 50mm lenses on 35mm film/full frame sensor produces a field of view that is very similar to the field of view of the human eye. The actual focal range for that falls between 45mm and 55mm.

So, given all of that...you can make the proper decision based on what you really want to capture. If you want to capture shots that have a relatively "normal" perspective similar to how the human eye sees, you might want to grab the 35mm lens. On a cropped sensor, it would behave like a 52mm lens. If you want a narrower field of view with smoother background blur, a 50mm or 85mm lens would give you that deeper DOF and narrower field, similar to 85mm and 135mm lenses on full frame, respectively. Finally, if you want to capture a wider field of view than the human eye, or want to get really close and capture a lot of perspective, you could get a 24mm lens, which, intriguingly, behaves like a 36mm lens on full frame.

The beauty of primes is their field of view, or effective focal lengths, are easy to translate between APS-C and Full Frame. If you take the common prime focal lengths of 14mm, 24mm, 35mm, 50mm, 85mm, and 135mm as used on full frame, you can pretty much simply "shift" them up by one place to arrive at the effective focal length ranges on APS-C. The exact focal lengths on APS-C, for reference, are: 21mm, 36mm, 52mm, 75mm, 134mm, 202mm. So long as you understand that about 50mm is the same field of view as "normal" perspective, it is fairly easy to determine which focal length to use to get the field of view/perspective you want in your photographs.

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What's the advantage of buying a fixed 50mm f/1.8 lens when my camera has an 18-55mm zoom lens?

Question

I've got a Nikon D3100 with an 18-55mm zoom lens. I'm keen to experiment with some other lenses and a friend of mine recently reccommended I purchase a fixed 50mm f/1.8 lens as he said it's good for portrait photography and capturing really sharp images. He also said that as it isn't a zoom lens it will sharpen my composition skills.

My question is - I currently have an 18-55mm zoom lens, so by purchasing a 50mm fixed lens, won't I be purchasing a spec of lens already covered by my 18-55mm lens? What are the main differences between these two lenses?

Finally - can anybody vouch for the Nikon fixed 50mm f/1.8 lens as being a good lens to go for?

Answer

At 50mm on your 18-55, the max aperture is f/5.6. On the 50mm f/1.8, the max aperture is - obviously - f/1.8. It is perhaps not immediately obvious, but f/1.8 lets in 10-12 times more light than f/5.6. That is the difference between shooting at 1/10 second shutter speed (which is absolutely a no-go for moving subjects) and shooting at 1/100 (which is a usable shutter speed for moving subjects). Big difference indoors at night, for example. It lets you shoot without flash, or with the flash used as mere fill flash instead of it being the main light-source.

Note that Nikon has two variants of the 50/1.8, one with a built-in autofocus motor and an older one without. Do get the new one.

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