Crop factor and perspective

[amitkhanna84]

Hey,

Short version: I know crop factor affects FOV but does it also affect perspective?

Long version:
I know that you need to multiply the focal length by the crop factor to obtain equivalent focal length on a full-frame camera and it makes sense to me as far as Field of View is concerned (meaning what portion of the subject is visible in the photo). So if 10 people are standing in a straight line in front of me... with the crop camera, maybe I can get person 4, 5 and 6 in the frame... and if I use the same lens in a full frame from the same distance, maybe I can get everyone from position 3 to 7 etc.

... but I have seen people use the same multiplication logic while talking about perspective related stuff... e.g. "To get that wide angle distorted look, you should use a focal length of, lets say, 16mm ... but since you are on a crop camera you should use 10mm"

OR "50mm is a great focal length for portraits since faces look very pleasing ... but on your crop factor the equivalent would be 30mm"

I can't seen why a cropped sensor would produce a different perspective, the lens is creating the same image in both the cases. Do you agree? Are the above two statements wrong?

Amit

[OsmosisStudios]

Perspective DOES NOT change. DOES NOT.

Heres a trick: throw a 50mm lens onto your camera. Now shoot with both eyes open. The image you see in the viewfinder should be the same as what your naked eye sees, regardless of camera. However, on a crop-body camera, your photos will show the same scene with that 50mm lens than would have a full-frame camera with a 75mm lens.

The same applies to the wide angle: The reason I LOVE my 10-24 is because, at 10mm, the perspective is SO exaggerated that it makes me laugh. I liked the fisheye, but I couldnt live with the distortion, so instead I get the awesome perspective.

[sk66]

Originally Posted by OsmosisStudios

Perspective DOES NOT change. DOES NOT.

Heres a trick: throw a 50mm lens onto your camera. Now shoot with both eyes open. The image you see in the viewfinder should be the same as what your naked eye sees, regardless of camera. However, on a crop-body camera, your photos will show the same scene with that 50mm lens than would have a full-frame camera with a 75mm lens.

The same applies to the wide angle: The reason I LOVE my 10-24 is because, at 10mm, the perspective is SO exaggerated that it makes me laugh. I liked the fisheye, but I couldnt live with the distortion, so instead I get the awesome perspective.

+10
IMO, a 50mm (actually closer to 55mm) is "normal" regardless of camera, wide angle "distortion" will be the same (you'll just capture less of it with a crop body), and portrait compression with something around 80mm is still ideal for most subjects, you'll just need to be further away.
That said, I'm really enjoying taking people pics with my 12-24....and not for funny distortion, for drama.

[OsmosisStudios]

Originally Posted by sk66

+10
IMO, a 50mm (actually closer to 55mm) is "normal" regardless of camera,

Not to be picking infinitesimally small nits: 45mm is closer to "normal", where "normal" is defined as the diagonal of the capture plane area.

normal = sqrt (36^2+24^2)
normal = 43.267mm

On Medium format (120): 79.54 (which is why 80mm is considered a normal lens on MF).

[Henry Wilt]

Not to drag this away from the original OP's question but, I read that "normal" perspective differs from one person to another depending on their eyes. Is that not correct?

[jdepould]

Originally Posted by Henry Wilt

Not to drag this away from the original OP's question but, I read that "normal" perspective differs from one person to another depending on their eyes. Is that not correct?

It depends on how you define normal. If you define it as it relates to sensor size, like Os, then no, it doesn't change. If you define it as it relates to natural eye characteristics, then yes, it might.

[i speak in math]

Originally Posted by OsmosisStudios

Not to be picking infinitesimally small nits: 45mm is closer to "normal", where "normal" is defined as the diagonal of the capture plane area.

normal = sqrt (36^2+24^2)
normal = 43.267mm

On Medium format (120): 79.54 (which is why 80mm is considered a normal lens on MF).

And now you know why Pentax chose 43mm for their FA 43mm limited

[OsmosisStudios]

Originally Posted by i speak in math

And now you know why Pentax chose 43mm for their FA 43mm limited

And why Pentax is both weird and aimed squarely at engineers

[Henry Wilt]

Originally Posted by jdepould

It depends on how you define normal. If you define it as it relates to sensor size, like Os, then no, it doesn't change. If you define it as it relates to natural eye characteristics, then yes, it might.

But surely the size of the sensor has nothing to do with what equates to "normal". A smaller sensor just crops the image so there is less angle of view, it doesn't magnify the image at all. The jist of the article I read was that "normal" equated to what is seen through the view finder would be the same as seen without the camera and lens, i.e. no magnification. That said, it is always possible that I have completely misunderstood it.

[OsmosisStudios]

Originally Posted by Henry Wilt

The jist of the article I read was that "normal" equated to what is seen through the view finder would be the same as seen without the camera and lens, i.e. no magnification. That said, it is always possible that I have completely misunderstood it.

50mm is 50mm, whether it's cropped or not. It's still normal.

Like I said earlier, put a 50mm lens on your camera and look through the viewfinder, but keep your other eye open: they should still show the same magnification (ie none)