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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 11 Nov 2007 (Sunday) 17:04
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Crop factor and portraiture

 
Candid
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Nov 11, 2007 17:04 |  #1

Hi,

Sorry to sound like an amateur, but one thing I was curious about when considering a new lens was the crop factor. I have a Canon EOS 30D, a few lenses in my arsenal and looking to add a portraiture lense since I am considering purchasing some studio flash. Now 135mm is generally one of the preferred focal lengths coupled with 105mm for nice flattering portraits. Baring in mind the 1.6X crop factor giving me 216mm and 168mm respectively. Should I still use these lenses to give the perspective flattening or should I be purchasing a lens that gives 105 or 135mm when the multiplier is taken into account. I'm thinking with the multiplier taken into account this lens will flatten perspective even more and possibly not be what I'm looking for. I was just looking to get some feedback to see if my thinking is correct and I should use the 105 or 135mm lens not accounting for the multiplier to give the flattenned perspective they offer that is desirable for portraiture.

I hope I haven't confused as I have tried to explain as best I could. Any advice will be greatly received




  
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hennie
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Nov 11, 2007 17:20 |  #2

look at this overview for an idea of different perspectives:
http://www.wlcastleman​.com …5_100_135/persp​ectest.htm (external link)
As you see the differences are very subtle.
I suggest you define the desired focal length by the type of portrait you want to shoot and your favourite working distance.




  
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SkipD
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Nov 11, 2007 17:38 |  #3

Candid wrote in post #4296947 (external link)
Hi,

Sorry to sound like an amateur, but one thing I was curious about when considering a new lens was the crop factor. I have a Canon EOS 30D, a few lenses in my arsenal and looking to add a portraiture lense since I am considering purchasing some studio flash. Now 135mm is generally one of the preferred focal lengths coupled with 105mm for nice flattering portraits. Baring in mind the 1.6X crop factor giving me 216mm and 168mm respectively. Should I still use these lenses to give the perspective flattening or should I be purchasing a lens that gives 105 or 135mm when the multiplier is taken into account. I'm thinking with the multiplier taken into account this lens will flatten perspective even more and possibly not be what I'm looking for. I was just looking to get some feedback to see if my thinking is correct and I should use the 105 or 135mm lens not accounting for the multiplier to give the flattenned perspective they offer that is desirable for portraiture.

I hope I haven't confused as I have tried to explain as best I could. Any advice will be greatly received

First of all, focal lengths in themselves don't "flatten perspective". ONLY distances to the subject and background do that. To prove this, you could shoot a series of shots of the same subject from the same place using a variety of lenses. Then, crop all but the one with the longest lens so that all of the images have the same amount of the subject shown. You will find that every one of the images is identical relative to the foreground/background relationships - the "perspective" you speak of.

If you are using known reference focal lengths for a 35mm film camera to choose lenses for an APS-C camera such as your 30D, you should divide the 35mm film camera's focal lengths by 1.6 to arrive at the equivalent focal length for the 30D.

The standard focal length recommendations for 35mm film camera portraiture for decades has ranged from about 80mm to 105mm for everyday work and occasional use of 135mm for tight head-n-shoulders shots. For the APS-C cameras like your 30D, these recommendations translate to 50mm to 65mm for everyday work and 85mm for the tight work. These are the standard recommendations and there are many people who choose to use other focal lengths for their own reasons.

What you actually want to do is to choose the distance from the subject that you want to work at, and then choose a focal length that will let you fill the frame with the subject. If you experiment with 50mm, you will find that for ordinary waist-up portraits it will work quite well and the perspective of the images (relationships of noses to ears, for example) will be flattering.


Skip Douglas
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..... but still learning all the time.

  
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Candid
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Nov 11, 2007 17:47 |  #4

Thanks for that link. The differences are very subtle indeed. I agree that perhaps working distance is perhaps a driver for my final decision as opposed entirely focal length




  
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kitacanon
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Nov 11, 2007 20:07 |  #5

Another issue is depth of focus/field (DoF)...using the 1.6x formfactor (ff) you will get more DoF on the same lens you'd use on the full frame ff, meaning that you'd need a wider aperture on the 30D to get the same DoF as on the 5D...


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Candid
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Nov 12, 2007 17:23 |  #6

Thanks all for your invaluable advice. Depth of field I wasn't aware of with the 1.6 ff, but in pointing this out I can say that I have inadvertently been aware of the results having found a few of my f5.6 portraits displaying what I felt was a large DOF based on my film days experiences and basically yielding different results. Good shout,
Thanks kitacanon




  
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penagate
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Nov 12, 2007 20:36 |  #7

kitacanon wrote in post #4297896 (external link)
Another issue is depth of focus/field (DoF)...using the 1.6x formfactor (ff) you will get more DoF on the same lens you'd use on the full frame ff, meaning that you'd need a wider aperture on the 30D to get the same DoF as on the 5D...

Please explain to me how sensor size has anything to do with depth of field.


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jra
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Nov 12, 2007 20:50 |  #8

penagate wrote in post #4304648 (external link)
Please explain to me how sensor size has anything to do with depth of field.

Quite simply because you need to work at a longer distance with a crop camera or use a wider angle lens. For example, if you take a pic with a full frame camera from 10 ft away with an 85mm lens and then wanted to get the same pic with a crop camera using an 85mm lens, you'd need to step back to 16 ft from your subject. Moving back would increase your DOF. Your other option would be to use a wider lens and shoot from the same distance with the crop camera...this would also increase your DOF.
A small sensor is the reason that P&S cameras have such a huge DOF. Hope that makes sense :)




  
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Wilt
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Nov 12, 2007 20:54 |  #9

penagate wrote in post #4304648 (external link)
Please explain to me how sensor size has anything to do with depth of field.

Smaller image (sensor or film) means that greater magnification has to be used to render the same final image size. So the COC has to be altered in size in the original image, to result in similar final size COC. Also, the shorter FL lens for the smaller format has less DOF than the equivalent AOV lens in the larger format.


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Crop factor and portraiture
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