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Thread: APS-C Question. EF AND EF-S

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    APS-C Question. EF AND EF-S

    Dumb question time,

    Just thinking, If you use any EF lens on a APS-C body, do you times focal - zoom length by 1.6?
    I.E 70 - 200 = 112 - 320, and then with EF-S (Say 17-85 as is) it is as stated, designed for the APS-C processor ??

    Trying to work out what lenses will give me the coverage I want. 17 EF-S = 17, and then if correct 17 EF = 27.2 approx.

    Help please...

    I think i'm confusing myself.

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    Can of worms ??

    The Focal Length does not change.
    It is the field of view that changes, and it changes on all lenses

    So a 70-200mm lens is still a 70-200 lens but has the field of view of a 112-320mm lens.

    The narrower field of view gives the perception that you are using a longer lens
    Last edited by MarkChap; 05-10-2010 at 4:16pm.
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    Geez, Roosta. I think it dozen matter (and 12 of the other) whether it's EF or EF-S. You just multiply/divide by the given crop factor. It's just the back of the lens that differs between the two types. Am.
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    You are confusing yourself (I've been there!). 50mm is 50mm end of story whether it is a EF or EF-S lens. ie put a EF 50mm lens on your 50D, and then a EF-S 50mm (if they made one) on your 50D and the result will be exactly the same.

    But take a EF 50mm and put it on your 50D and then take it off and put it on your 5D (if you had one) and there would be a difference in field of view. The lens is still sending the same image circle to the sensor, but a 50D with it's smaller sensor only uses the centre bit of it (hence the term crop) and therefore looks like you have more zoom.

    So - The only time you might want to start thinking about crop factors etc is if you want to compare what the same lens will be like on a full frame vs crop sensor camera.

    I'm a little reluctant to post this link because I want to try and keep it simple, but it might help you with comparing lenses.
    http://www.tamron-usa.com/lenses/lea...comparison.php
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    So if I was to get say the Full Frame Canon 24-105mm F4L it is only going to see an narrower picture not increse minimum focal distance.

    I'm trying to work out what lens to buy, 10-20odd or 17-70 or 24-70/105 for a general purpose lens, but would like to cover long exp and landscape shooting.. ??????

    Any ideas.?

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    Makes sense now. Thanks for putting it in those terms, killing me with lenses decessions, still like the 24-70/105L's but wasn't sure. So that clears it up alot.

    Thanks again.

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    Probably a question best answered in your other thread, but anyway...

    The first question is, what camera will you be using? Your 50D or do you plan to upgrade? Answer that and we're half way there.

    If you are not going to upgrade to full frame, then it is simple. You want one or two lenses as we discussed in the other thread to cover ideally from around 10mm to 50-80-100 whatever. You can also look at just about any lens as they will all almost certainly be suitable. ie all the EF and EF-S lenses and just about anything from the other brands.

    If you are going to upgrade, then you want to cover a range of around 16mm to whatever. This will limit your choices though, as they must be EF or suitable for full frame.

    Notice I said 10mm on Crop, 16mm on full frame. A 10mm on a 50D will give the same result as a 16mm on 5D.

    Now remember that a EF-S lens is only suitable for crop sensors, Sigma, Tamron etc will have the same set up, many of their lenses will only be suitable for crop sensor camera. I'm not familiar with Tamron, but it appears at this link that the 17-50 is only for crop sensors.

    Have a look at this link particularly page 6 about the crop sensor and why a lens designed for crop sensors won't work on full frame (or as they refer to it here '35mm film' - essentially the same thing)

    I know all this sounds way to complicated, but once you decide if you are going to shell out the $3k to go full frame it will be simpler.

    Re your other question about long exposure shooting, any lens can do that, what you need there is a decent tripod and maybe a remote shutter release for the camera.

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    Quote Originally Posted by Roosta View Post
    Dumb question time,

    Just thinking, If you use any EF lens on a APS-C body, do you times focal - zoom length by 1.6?
    I.E 70 - 200 = 112 - 320, and then with EF-S (Say 17-85 as is) it is as stated, designed for the APS-C processor ??

    Trying to work out what lenses will give me the coverage I want. 17 EF-S = 17, and then if correct 17 EF = 27.2 approx.

    Help please...

    I think i'm confusing myself.

    ANY lens, EF or EF-S, when you are using an APS sized sensor (other than the 1D series) you will have to multiply the focal number of that lens by 1.6X to get the field of view focal length equivalent.

    Imagine your CF Memory Card as the size of a Full Frame sensor.
    A lens like say, 50mm will project an image on that CF card and we see it as 50mm equivalent.
    Imagine, now, that you place a small postage stamp over the CF Card.
    This is like the APS cropped sensor.
    The 50mm lens still projects the SAME field of view, but the postage stamp can only capture THAT much. That's why they call it cropped.
    That cropped image looks like it was projected by an 80mm lens, but it is only apparent, because a lot of the image got lost on all sides.
    The multiplier factor for the difference is 1.6 (for Canon)
    So: 50mm X 1.6 = 80mm
    Your 50mm lens mounted on an APS camera will behave like it was an 80mm.

    Note: The CF Card and postage stamp are for illustration purposes only and are not the actual real sizes of the sensors.
    Last edited by RaoulIsidro; 05-10-2010 at 6:08pm.
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    Mate, thanks again, the Tamron link is very simple at getting the message across. I wasn't understanding the "CROP" factor. But since you put it across that way above it all make sense.

    I've only just got the 50D, was toying with the 7D and or waiting for the 60D, but wanted a DSLR not a DSLR/VIDEO, and the 7D was out of my price range. so.

    Yes I got the info from my other thread, good stuff there, so its whether I go for the 24-70-105 or the Tamron/Sigma 17-70 F2.8's which will cover the same as designed for the 1.6 crop factor.

    Will go and try them on my 50D when I get back into town(Work Away).

    What where you shooting with, posts on the train station and police car, because thats what I want to try to achieve, longer exp and low light, Top shot, the inside of the train station by the way.

    Thank again for your patience.

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    and this one time, at band camp! I used an Olympus 4/3 DSLR and got 2x the amount of zoom! WOW!

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    [QUOTE=RaoulIsidro;694836]ANY lens, EF or EF-S, when you are using an APS sized sensor (other than the 1D series) you will have to multiply the focal number of that lens by 1.6X to get the field of view focal length equivalent.

    Got now, easy when people put it that way. Etherial got to me before with the plan english version, so thanks Raoul....

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    If you like shooting landscapes why look at a 24 - 70/105? On a crop sensor that's 38mm (approx), I would be looking at the 17 - 70 (well actually I'm looking at the Sigma 10-20, but that's another story). Or for a truly versatile lens at a resonable price why not the Tamron 18-270?

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    Quote Originally Posted by Roosta View Post
    Mate, thanks again, the Tamron link is very simple at getting the message across. I wasn't understanding the "CROP" factor. But since you put it across that way above it all make sense.

    I've only just got the 50D, was toying with the 7D and or waiting for the 60D, but wanted a DSLR not a DSLR/VIDEO, and the 7D was out of my price range. so.

    Yes I got the info from my other thread, good stuff there, so its whether I go for the 24-70-105 or the Tamron/Sigma 17-70 F2.8's which will cover the same as designed for the 1.6 crop factor.

    Will go and try them on my 50D when I get back into town(Work Away).

    What where you shooting with, posts on the train station and police car, because thats what I want to try to achieve, longer exp and low light, Top shot, the inside of the train station by the way.

    Thank again for your patience.
    No probs mate, it is one of the hardest things to get your head around, but once you do you'll be right. The 60D or 7D are great choices, the 7D is great value for money. They are both crops and I think would suit you fine, but I wouldn't be upgrading from the 50D anytime soon, it is a great camera.

    Don't be put off by video, just because it is there doesn't mean you have to use it. And it doesn't affect anything else about the camera. It will be in every camera soon enough. I didn't want it either, but I was surprised I have used it a bit.

    I answered the questions re my night photos in that thread, they were all the 7D with 24-105/4 IS, they ranged from around 5 to 25 seconds exposure.

    Thanks for the comments. Feel free to ask any more questions, PM if you wish, but try and keep things on the forums to help others out too.


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    Quote Originally Posted by JM Tran View Post
    and this one time, at band camp! I used an Olympus 4/3 DSLR and got 2x the amount of zoom! WOW!
    Don't go there!

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    Quote Originally Posted by RaoulIsidro View Post
    ANY lens, EF or EF-S, when you are using an APS sized sensor (other than the 1D series) you will have to multiply the focal number of that lens by 1.6X to get the field of view focal length equivalent.


    The multiplier factor for the difference is 1.6 (for Canon)
    So: 50mm X 1.6 = 80mm
    Your 50mm lens mounted on an APS camera will behave like it was an 80mm.
    Yes and no
    Yes multiply x 1.6 for the equivalent field of view

    But a 50mm lens still behaves like a 50mm lens, only with a cropped field of view.
    The perspective is still that of a 50mm lens.

    I am not trying to confuse anyone, or make life difficult, but we have to stop the perpetuation of the myth that lenses "behave" differently on an APS sensor, they do not.
    The sensor crops the image circle produced by the lens, plain and simple.

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    Quote Originally Posted by RaoulIsidro View Post
    ANY lens, EF or EF-S, when you are using an APS sized sensor (other than the 1D series) you will have to multiply the focal number of that lens by 1.6X to get the field of view focal length equivalent.
    Just to be pedantic, there are a few different crop factors out there. The 1D series has a couple, to summarise:

    1Ds Full Frame
    1D 1.3x crop factor
    5D Full Frame
    7D, 60D, 550D, 1000D 1.6x crop factor

    You get the idea, and other brands have their nuances too, they aren't all 1.6x.

    Here is another good resource (wikipedia - crop factors) I think the picture they use has been posted here on the site somewhere too, maybe in the new to photography section.
    Last edited by etherial; 05-10-2010 at 6:56pm. Reason: Engrish

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    Dont need the lenght of the 18-270, and if I up-grade down the line, it will be to a full frame body Canon.

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    Quote Originally Posted by MarkChap View Post
    I am not trying to confuse anyone, or make life difficult, but we have to stop the perpetuation of the myth that lenses "behave" differently on an APS sensor, they do not.
    The sensor crops the image circle produced by the lens, plain and simple.
    Yeap, The old saying, "Once you say it out loud"

    Got through to me alot easier when Etherial explained it in laymans term, as did yourself in first post.

    Thanks for your input.

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