Candid wrote in post #4296947
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.