Originally posted by Dartmoor Dave Just a slightly finicky point for the sake of clarity: different focal lengths don't cause facial distortions. Different focal lengths force shooting at different distances to get the framing you want, and it's the different distances that cause the distortions. I know you knew that already, but I just wanted it to be made clear in the thread.
Shoot from too close with too wide a lens and people will look like their heads have been inflated with air hoses.
Shoot from too far away with too long a lens and people will look like their faces have been ironed flat.
So if your subject has got a big round head and a long nose and bulgy-out eyes (like me), shooting from further away with a longer lens will be more flattering. If your subject has got flat features and a button nose, going in closer and a bit wider might suit them better. Choose a shooting distance by eye, without even looking through your viewfinder, that makes your subject's particular individual features look good, then use a focal length that lets you shoot from that distance.
Originally posted by Fogel70 One of the most important aspect of photography is perspective, and perspective change with distance to subject.
A lens with tighter FOV need longer distance to subject to capture the same frame. So using the same lens on different sized sensors gives different images, either a different framing or a different perspective (or a combination of both)
To give the same framing and perspective as a 50mm lens on APS-C, you need a 75mm lens on FF. Which is why we say a 50mm lens on APS-C is like a 75mm lens on FF.
So, I think this is what I was thinking originally but I want to make sure I understand. It seems like the conversion from FF to APSC has to do with multiple things. The main difference is image size on the sensor for the same picture. Meaning, the smaller APSC will capture a smaller portion of what comes through the lens. In order to stand in the same spot and achieve the same sized image on the sensor, you would need a lens with a wider field of view. 1.5 times wider to be exact. If you wanted to use the same lens on APSC as on FF for it's distortion properties, you would have to move further away from the subject. The only problem with that is, moving away from the subject creates additional distortion in the image that may or may not be desired. Is that all correct?
Basically, what I'm getting from this is; stop trying to figure out which lens is "best" and figure out what I want to accomplish within the photo. Then use the lens and distance that best captures what I'm looking for. Is that right? Like I said earlier, right now, I've got an A 50mm 2.0 and a 100mm 2.8 Macro. It seems like these may be fine for certain portraits I'm looking for but not for others. Would you all say adding a DA 70 (because there's no way I can afford the FA 77) would kind of round things out for me? It will certainly be some time before I can pick it up (months to years) but I like knowing where I'm going so I can plan for it. In the mean time, I can also use my 18-135mm for anything needed between the two primes. The DA 50 1.8 might be in the future as well but it will depend on how the manual focus of the 50 2.0 goes. I know it's not a highly regarded lens but, for me, I think it will do fine.
Thanks for all the feedback. I love nerding out on a lot of this stuff. It definitely helps me to understand how it all works.