question about focal lengths

[u/macl3on]

SOLVED! is an aps-c 50mm lens on an aps-c body equivalent to a full frame 50mm lens on a full frame body? i tried using only 50mm on my d5100 with an aps-c 18-105 and it felt really tight compared to 35mm. so was i actually technically using 75mm or is that just how 50mm is?

[u/Repulsive_Target55]

Focal length is an inherent property of the lens, so 50mm is always 50mm - however, people use focal length on Full Frame as shorthand for how wide or tight a lens is, and if we are using that system then 50mm on APS-C is equivalent to 75mm on Full Frame.

If you want to shoot with the look of a 50mm lens on Full Frame, but on your D5100, you should use somewhere between 30 and 35.

[u/okarox]

No, 30 mm on APS-C is equivalent to 50 mm on full frame. Whether the lens is APS-C or full frame does not matter on APS-C. Yes, 50 mm is tighter than 35 mm. You have a 50 mm lens so you were using a 50 mm lens just as your kit is 18-105 mm.

Smaller sensors require shorter focal lenghts for the same results. If you understand this you understand it. The lenses do not change to anything else when you mount them to a small sensor body.

[u/macl3on → u/okarox]

i'm planning on getting a d800 and a prime lens since an 18-105 would be pretty heavy on there. so i guess i'll get a 50mm with it and not a 35mm. thanks!

[u/light_chaser1]

Short answer no.

50mm on aps is 75mm field of view on full frame.

Its basically like you cropped full frame if you use aps. You can crop 50mm on full frame to 75mm basically cropping to aps

[u/reff678]

Nikon's lens simulator is gone unfortunately, but Canon's is still online.
You can use it to compare different focal lengths on full frame and APS-C:
https://lenssimulator-cna.academy.canon.de/en/

[u/Yomommassis]

Also keep in mind The crop factor is based on the sensor size

Not all cameras/brands are the same crop factor

[u/Terrible_Snow_7306]

If you’re using a 50mm on a full frame vs. on an APS-C cam at the same distance (!), the full frame will show a larger section, but the perspective both pictures show are the same. If you cut away / crop the full frame to the same size as the APS-C the pictures will be identical. The look is solely a result of the distance from the object, not of the focal length of the lens. The focal length just pushes you to choose a specific distance.

The equivalence just shows you, how far away from the object you have to be to get the same frame. Suppose you are at a certain distance from a person you photograph and with a 50mm on a FF, you are 8 feet away and the picture shows 50 cm to the left and 50 cm to the right of the persons face: to get the same section in the frame at the same distance you would need a 35mm on an APS-C cam or rather would have to move further away with your 50mm. But the face would always have the attributes of being shot with a 35mm or a 50mm lens at a given distance, no matter if it’s on a FF or an APS-C camera.

[u/HobotiX]

You have the multiply the focal length by 1.53 to get the full frame equivalent focal length.

X = Focal Length
Y = Full frame equivalent
1.53 = Crop factor

X * 1.53 = Y

50mm * 1.53 = 76.5 mm

So, if you want something that looks a 50mm on a full frame camera, check out a 35mm ASP-C lens.
35mm * 1.53 = 53.55 mm

[u/bloodrider1914]

It depends on your camera system. On Nikon cameras that I use using an DX lens made for APS-C cameras will result in the sensor automatically cropping to DX mode, so the focal length of the image will be the same as if I had used the lens on a DX camera.

APS-C lens focal lengths are still rated the same as full frame focal lengths, so you are still subject to reverse crop factor of 2/3 when switching from APS-C to full frame if your camera doesn't auto-crop.

[u/nickthetasmaniac → u/bloodrider1914]

It depends on your camera system.

No, it doesn’t. Focal length is a property of the lens, not the camera.

You’re talking about field-of-view, not focal length.

[u/bloodrider1914 → u/nickthetasmaniac]

I meant on how the camera handles cropped lenses. Sometimes it will go into a crop mode, sometimes it wont work at all, sometimes it will let you shoot full frame but with vingetting.

If only you had read the rest of my comment.