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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 21 Jul 2009 (Tuesday) 07:37
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Once more: 17-40L vs. 17-55 2.8IS on crop camera

 
Citizensmith
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Jul 23, 2009 11:17 |  #31

wimg wrote in post #8330379 (external link)
It is true for longer lenses, too. It is caused by the different FoV, which again is caused by the cropfactor difference. Don't forget that the cropfactor also applies to long lenses.

If you'd like, I'd look up the mathematics for you. Don't know the exact formulas by heart :D.

However, you can try this by using a good DoF calculator. Keep the focusing distance the same, change FL to get the same FoV, use the appropriate CoCs, set aperture to F/4 for FF, and F/2.5 for APS-C, and you'll find you have a little less DoF on FF at F/4 than at F/2.5 on APS-C.

Kind regards, Wim

Oh no problem, and thanks for offering. It's not something I'd consider myself an expert on, and you seem to have the facts in line.


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Wilt
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Jul 23, 2009 12:50 |  #32

wimg wrote in post #8326294 (external link)
Actually, F/4 on FF has less DoF than F/2.8 on crop for the same AoV, so the 24-105L IS would be similar, be it with a longer zoom range, on FF to the 17-55 F/2.8 IS on crop.

Truth.

Example:
a. 50mm on APS-C f/2.8, DOF zone at 10' distance to subject is 1.06' deep
b. 80mm on FF f/4, DOF zone at 10' distance to subject is 0.93' deep

c. 500mm on APS-C f/2.8, DOF zone at 100' distance to subject is 1.06' deep
d. 800mm on FF f/4, DOF zone at 100' distance to subject is 0.93' deep

Note that when the shooting distance is changed, to stay proportional to the FL of the lens change, for any given format the DOF is identical!!!! So the DOF in A is the same as the DOF in C. And DOF in B is the same as DOF in D.
This is because DOF is entirely related to the apparent size of the Circles of Confusion as viewed, and this is entirely related to the size of the print and the viewing distance to the print!


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wimg
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Jul 23, 2009 12:52 |  #33

Wilt wrote in post #8331049 (external link)
Truth.

Example:
a. 50mm on APS-C f/2.8, DOF zone at 10' distance to subject is 1.06' deep
b. 80mm on FF f/4, DOF zone at 10' distance to subject is 0.93' deep

c. 500mm on APS-C f/2.8, DOF zone at 100' distance to subject is 1.06' deep
d. 800mm on FF f/4, DOF zone at 100' distance to subject is 0.93' deep

Note that when the shooting distance is changed, to stay proportional to the FL of the lens change, for any given format the DOF is identical!!!! So the DOF in A is the same as the DOF in C. And DOF in B is the same as DOF in D.
This is because DOF is entirely related to the apparent size of the Circles of Confusion as viewed, and this is entirely related to the size of the print and the viewing distance to the print!

Thanks, Wilt!

I really like the way you selected the examples, at 10X the FL and 10X the focusing distance! This should make things clear to everybody, I would think! :D

Kind regards, Wim


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Gnhntn
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Jul 23, 2009 15:15 |  #34

The Ef-S 17-55 is faster and had the advantage of IS in low light. But if there is ever the chance of upgrading to full frame go with the EF 17-40 L.


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DeMar
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Jul 27, 2009 04:50 |  #35

Thanks again for all the comments!

So now I made the move and whent to buy my gear to start with, 40D it is. About the lense I think the decission was quite typical for me... After trying to choose between those two options I then bought neither of them but something else.. :) And that was 24-105 4L IS. Many might say it doesent make any sense on a crop, but there was couple of reasons for changing my mind on last minute.

First, I was trying to find out what I really need on with this multipurpose lense, and was using my dad´s 17-85. Found the WA very nice, but even more would have liked bit more reach for travelling & hiking. Also like to shoot portraits and people in general from as far as possible to get "natural" situations and expressions etc.

Secondly, the 24-105 was in nice sale right now (-30%), and think I can get it sold pretty easily if I really will regret the decission.

I know I will miss the WA a bit, for sure. Also the speed yes, but then again I´ll use flash inside anyway etc, and will expand my bag with some primes one day. The build quality, colours / contrast, reach and the current price just changed my mind. I will also upgrade to FF when the budget allows, so I´ll guess it would be usefull then too, and will get enough WA then at least.

So difficult this is, but now the decission is made and it is time for some heavy training! Happy so far, let´s see for how long.. ;) Thanks again, time to go for some shooting now!

// Sami


40D / 50 1.8II / 10-22 / 24-105L / 70-200 F4 IS L / EX430

  
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wimg
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Jul 27, 2009 06:12 |  #36

Hi Sami,

DeMar wrote in post #8349675 (external link)
Thanks again for all the comments!

So now I made the move and whent to buy my gear to start with, 40D it is. About the lense I think the decission was quite typical for me... After trying to choose between those two options I then bought neither of them but something else.. :) And that was 24-105 4L IS. Many might say it doesent make any sense on a crop, but there was couple of reasons for changing my mind on last minute.

First, I was trying to find out what I really need on with this multipurpose lense, and was using my dad´s 17-85. Found the WA very nice, but even more would have liked bit more reach for travelling & hiking. Also like to shoot portraits and people in general from as far as possible to get "natural" situations and expressions etc.

Secondly, the 24-105 was in nice sale right now (-30%), and think I can get it sold pretty easily if I really will regret the decission.

I know I will miss the WA a bit, for sure. Also the speed yes, but then again I´ll use flash inside anyway etc, and will expand my bag with some primes one day. The build quality, colours / contrast, reach and the current price just changed my mind. I will also upgrade to FF when the budget allows, so I´ll guess it would be usefull then too, and will get enough WA then at least.

So difficult this is, but now the decission is made and it is time for some heavy training! Happy so far, let´s see for how long.. ;) Thanks again, time to go for some shooting now!

// Sami

That's a very good reason to get a 24-105. The 24-105 is a true 50 mm standard zoom, i.e., centered around 50 mm, its geometrical FL (same zoom factor from 24 to 50, as well as from 50 to 105), and therefore ideal as a portrait zoom on an APS-C camera liek the 40D. F/4 you'll need to get head and shoulder shots to eb sharp from the nose to the cheeks anyway, and bokeh is quite good, so a godo choice IMO. I used the 24-105 on my 40D for exact the same purpose, just that I found I didn't use it anymore after I sold the 40D :D.

Congratulations on your new gear!

Kind regards, Wim


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Chez ­ Wimpy
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Jul 27, 2009 07:33 |  #37

Gnhntn wrote in post #8331844 (external link)
The Ef-S 17-55 is faster and had the advantage of IS in low light. But if there is ever the chance of upgrading to full frame go with the EF 17-40 L.

I got the 17-40L in 2004 when it was still the only game in town for those looking to upgrade from the kit lens (the first five years of crop DSLRs optics were a mess, even with regards to zoom lens ranges). It worked pretty well, certainly the color and contrast were top notch, but it had issues with a soft left side 17-28 (result of Canon "servicing" it for BF). Indeed, the "keep it for FF" idea kept me using it even in the face of the newer f2.8 zooms covering the range... but when I did finally go FF, I used it once or twice to test it out, and then sold it. The lens is completely different on FF... enjoying the range on a crop camera has absolutely no bearing on its usefulness as an UWA lens. Buy for the body you have now, and sell later (even if for a small loss) instead of compromising your style. :cool:


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Once more: 17-40L vs. 17-55 2.8IS on crop camera
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