I'm learning photography and all its elements. Probably this question is really stupid, but I have to ask.

I'm not dealing well when the question is equipment and one of the reasons I know this is because of the negative comments in my answer:

How do I choose a telephoto zoom lens?

When I asked that question, I didn't know these lenses are for different purposes. In fact, I still don't know. To me, they all look like telephoto and I can take the same kind of pictures with them: birds, surfing, etc.

All I know about lens categories I learned here: http://www.usa.canon.com/cusa/consumer/products/cameras/ef_lens_lineup

But I don't understand several things, like:

How can a EF 17-40mm f/4L USM be an "Ultra-Wide Zoom" and the EF-S 18-55mm f/3.5-5.6 IS be a "Standard Zoom"? One starts with 17mm and the other one with 18mm, they look the same! In my mind, a wide angle lens should start, at least, with 10mm.

How can a EF 50mm f/1.8 II be "Standard & Medium Telephoto" and EF 50mm f/2.5 Compact Macro be "Macro"? They have the same focal length!

Here's what I think is true at the moment: A lens has two important aspects: focal length and aperture. That's all I have to care about. Of course it's not correct, that's why I want some advice to get in the right way of thinking when I buy my next lens. So, what can I read to make the right differentiation between them? How can I know which lens is better for my purposes?

OBS: I'm a fan of the chosen answer in this question: How to choose a lens for my first DSLR? I love to keep things simple and I don't care too much about technical details. It can seem like paradoxical stuff because of this question, but it's not. I'm asking this because I want to buy the right lenses without wasting money, but in the simplest way.

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    \$\begingroup\$ Its not that this isn't a great question or that people don't all ask this when new to photography - it is that a question that is TOO BROAD can fill a book with answers, and is not suited for the format here at stack exchange. Simple questions are great, but a simple question just may not work here! Try asking a specific question you have, "would the 17-40mm f/4L USM be good for birds, surfing, and baby portraits?" That will typically give great results! \$\endgroup\$
    – dpollitt
    Commented Sep 11, 2011 at 15:37
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    \$\begingroup\$ Your other question was closed because we had no knowledge of what the lens was going to be used for. It would be like asking on a cooking forum what ingredients to use, but not telling us what you wanted to cook! We all love chocolate, but it might not taste good in your steak! Try providing an example of what your current equipment can't do well, and why you want to buy a new lens, that would help in addition to what type of photography you do and would like to do. \$\endgroup\$
    – dpollitt
    Commented Sep 11, 2011 at 15:40
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    \$\begingroup\$ The question about categorization of wide angle lenses is asked and answered here: photo.stackexchange.com/questions/15370/… \$\endgroup\$
    – mattdm
    Commented Sep 11, 2011 at 16:19
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    \$\begingroup\$ This question has some others embedded in it, but it seems to mostly be frustration with response to an earlier question combined with constructively wanting to know how to get the most out of the site. That's not bad/wrong, but I'm nominating it to be moved to meta.photo.stackexchange.com. \$\endgroup\$
    – mattdm
    Commented Sep 11, 2011 at 16:28
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    \$\begingroup\$ @Luiz, you mention "negative comments" to your other question. While sometimes that does happen, I just went back and reread that, and I'm not seeing negativity, just requests for clarification, which were never followed up on. \$\endgroup\$
    – mattdm
    Commented Sep 12, 2011 at 3:22

4 Answers 4


How can (EF 17-40mm f/4L USM) be "Ultra-Wide Zoom" and (EF-S 18-55mm f/3.5-5.6 IS) be "Standard Zoom" ?

The EF 17-40mm lens fits a full-frame (35mm size sensors) camera. The EF-S 18-55mm fits only a cropped-sensor camera (APS-C size, like any Canon DSLR other than 5D and 1D). On a crop sensor camera, your lens' Field of View (FoV) at the 18mm end is similar to a (18 x 1.6 =) 28.8mm lens on a full-frame camera (which is considered the "standard" sensor size for lens classification).

This is why the 17-40 is "wide" and the 18-55 is "standard".

How can a (EF 50mm f/1.8 II) be "Standard & Medium Telephoto" and (EF 50mm f/2.5 Compact Macro) be "Macro"? They have the same focal length!

Macro is not about focal length, but rather maximum magnification - which is proportional to the minimum focusing distance (MFD). Just how close can you be to your subject and still focus.

A lens has two important aspects: focal length and aperture

These are usually the most important features, but certainly not the only ones. The focal length will determine your FoV (and thus affect your perspective). The max Aperture will determine your minimum Depth of Field (DoF) and your ability to take photos in low light. Other than that, you should consider lens quality - optics, but also construction. Image Stabilization may be important to you. More specific needs will determine whether you need a Macro lens, weather resistant lens (like Canon L series), Diffractive Optics (DO) lens (for compactness) or catadioptric lens (relatively low weight for big apertures and long FL, with extremely low chromatic aberrations.

For starters, though, you should really concentrate in the first couple of items. You should know from previous experience what range of parameters you need for your photography style.


Hopefully you will find my answer helpful in a general sense. I think the best way to learn is to do so here is an exercise that helped me when I started out. I got it from one of the Time books on photography.

The different focal lengths affect your perspective (as mentioned by ysap). The best way to see this for yourself is to place a (patient) subject in an open area like in a park with receding lines like a path. Using the shortest focal length you have, position yourself so that the subject takes up a large part of the frame. maybe shoot a park bench and have the width of the bench take up the width of the frame. Note this size and take a picture. Now select a focal length mid way between your shortest and longest. Move back until the bench takes up the width of the frame again. Take a picture. Then select the longest focal length and repeat the process. You can take as many steps as you like.

When you are done, take one more picture with your shortest focal length again, but from the distance you used for the longest focal length. If you compare all but the last photo, you should see that while the main subject has stayed about the same size, the foreground and background have shifted. If the main subject was rather flat, it may not have changed at all. Objects (especially lines) closer and further will have changed angles. The long lens gives a 'flatter' look.

Now take that last picture and crop it until the subject fills the frame again. The perspective will be the same as the longest lens. So if the camera's sensor had infinite resolution, you would only need the widest lens to take all your pictures (I'm ignoring depth of field, etc.) You would only need to change your position to get the perspective you wanted. Alas, cameras aren't perfect so we have to make lots of choices.


EF 17-40mm f/4L USM and EF-S 18-55mm f/3.5-5.6 IS are two very different lenses the clue is in the EF vs EF-S designation. EF-S means it is for crop sensor cameras only where the sensor is smaller and therefore gives a smaller field of view for the same focal length. Now if you mount both the EF 17-40mm and a EF-S 18-55mm on a crop sensor camera body they will give almost the same result at 17mm or 18mm however the EF lens is designed for full frame camera bodies which give a much larger field of view. What does this mean? Well on a crop sensor you have to multiply the focal length by a scaling factor representing the size difference of the cropped sensor with respect to a full frame sensor. In Canon cameras this factor is 1.6 so the EF-S is designed for crop sensors and should have the multiplier applied to the focal lengths to give an equivalent field of view to a full frame camera 18 x 1.6 = 28.8 which is suddenly not so wide.

As you suggest focal length and aperture are the two things that are important with lens choice and I think the reason you were getting confused is because some lenses are made to only work on cameras with crop sensors, designated EF-S in Canons case. If you take this into account and remember that for such a lens you have to multiply the focal lengths by a crop factor then things should start to make a lot more sense.

The difference between a macro lens and a telephoto is that the macro lens is designed to work with short distances between the lens and the subject typically about 9" in the case of the EF 50mm f/2.5 Compact Macro as a posed to around 18" for the EF 50mm f/1.8 II. The focal lengths being the same they will give the same field of view. Macro lenses can be used the same as a standard telephoto lens but generally won't give the same image quality for longer range shots. The term telephoto just means that it is a long focus lens where the physical length of the lens is shorter than the focal length.

When you go for your next lens my advice would be to decide what you want to shoot and then go to a good specialist camera store where you will be able to get some advice on what meets your needs.


More applicable in 2019 than at time of asking:

Get any mirrorless camera. Gather a handful or two of "junk" lenses (off brand M42 lenses are cheap and great for that), and appropriate adapters. Do comparison shots of the same scene with a couple of these - especially wide open. Analyze the results under magnification (trivial on a computer), practice recognizing the various possible imperfections, and research their causes. Warning: You sometimes actually find very viable lenses by accident that way.


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