Focal Length & Crop Sensor…
I am trying very hard not to get obsessed with this topic. But to be fair, this is an issue that directly impacts my work, rather than being merely of academic interest. So it’s not so much that I am obsessing, as that I genuinely need to figure out what’s happening in order to choose a suitable lens for my photoshoots.
A hypothetical question, for anyone reading this: What focal length would you say is the lens used to take the first photo, above? What about the second photo, immediately below this text? I deliberately did not label the photos to make an unbiased guess possible. {And I should add that neither of the photos is strategically cropped to simulate a different focal length, so this not a trick question.}
To my eye it looks like the first photo was taken with a 35mm lens. And the second photo with either a 24mm or maybe a 28mm.
This is technically correct. The first photo was taken with the 35mm Voigtlander Colour Skopar. And the second photo with the 24mm Zeiss Jena. However… Since I am using a crop-sensor, their equivalent focal lengths should be something like 50mm and 35mm, respectively. Which to me simply does not look to be the case. In the first photo the proportions look fairly true-to-life, but there is more background showing than would a 50mm taken from the same vantage point. In the second photo the model looks unnaturally long and narrow, with exaggerated limbs. That degree of wide angle distortion is not characteristic of a 35mm, according to my experience.
Here is another one with the 24mm Zeiss Jena. You can see that I am positioned slightly above the model when taking the photo, and as a result there is quite a bit of foreshortening (the shoulders look exaggerated, the legs compressed). Again, this is more in line with how a true 24mm behaves, or maybe a 28mm, rather than a 35mm equivalent.
What’s even more strange though… is that the lenses only sometimes behave like their true focal lengths. At other times they act like the equivalents they are supposed to be according to the crop factor. Perhaps it has to do with how closely I stand to the subject, or other factors I am not taking into consideration. I am still figuring it out.
And I suppose I do not need to understand the technical reasons why I am seeing what I am seeing. I just need to choose lenses according to what my eyes are telling me, rather than according to the conversion charts. When I used my former full-frame DSLR setup, I alternated between a 50mm lens and a 35mm lens, and would like to get the equivalent of these two focal lengths with my current setup - which is what I thought I would get with a 35mm and a 24mm on the crop sensor. But the images I am seeing make me question that. The 24mm in particular, cannot reliably be used as a 35mm equivalent. Perhaps an actual 35mm and an actual 50mm might be my best options if I need natural perspective. I will continue to experiment.
