[tripodquest]

so the middle format to FF crop factor is about 1.95:1. if a lens is 35mm and made for middle format, it means that it's still 35mm and will look like a 35mm correctly on FF but be a 18mm wide angle on middle-format, and something longer on aps? right? and the "for middle format" simply means it also covers the 60x60 film area as well as anything below it?

[boriscleto]

A 35mm lens is a 35 mm lens. A Medium Format 35mm lens simply has a larger image circle than a 135FF 35mm or APS-C 35mm. If you mount a MF 35mm on an APS-C camera it is still a 35mm lens with the equivalent FoV of 53mm on 135FF.

[PJ1]

"Crop factor" is not a useful way to describe what is going on. Angle of view (or field of view) is what it is all about. Most of us (I think) find it easy to work down from FF to APS-C because that is what we are most familiar with. But it is harder to go up from FF to MF.

Here is the simple explanation (I hope).

A 50 mm lens designed for MF will give an image circle covering roughly a 6cm x 6cm sensor (or film) and an angle of view of about 78 degrees. This is a comparatively wide angle.

Put that same 50 mm lens on a FF camera with a 36mm x 24 mm sensor (or film) and a lot of that image circle is not used (it is "cropped out' if you like). The angle of view drops to about 46 degrees and the lens is no longer wide angle but is like any "normal" 50mm FF lens on that body.

Now put that 50mm lens on a camera with an APS-C sensor of about 22.6mm x 15.7 mm and even more of the image circle it produces is "cropped out". It is now a short telephoto with an angle of view of about 30 degrees.

So the lens is a 50mm lens, no matter what body it is fitted to and behaves just like a 50mm lens made for that body. The only thing that is changing is the amount of the image circle produced by the lens that is being used. The less of the image circle that is used, the tighter the angle of view becomes.

To use another example, 80 mm is about "normal" focal length for MF. It becomes an 80 mm "portrait length" lens on FF. and an 80 mm "short telephoto" on APS-C (where you might say "it gives roughly the same angle of view as a 120 mm lens on FF". But it is still an 80 mm lens, no matter what body it is used on).

Hope this helps.

[stevebrot]

Crop factor is a meaningless term. Truly. And it is even more meaningless when applied to formats where the frame ratio is other than 3:2 or where the format is larger that 35mm film (crop factor < 1). I mean, isn't it sort of silly to reference FOV for all formats to 35mm film?


Steve

[tripodquest]

&quot;Crop factor&quot; is not a useful way to describe what is going on. Angle of view (or field of view) is what it is all about. Most of us (I think) find it easy to work down from FF to APS-C because that is what we are most familiar with. But it is harder to go up from FF to MF.

Here is the simple explanation (I hope).

A 50 mm lens designed for MF will give an image circle covering roughly a 6cm x 6cm sensor (or film) and an angle of view of about 78 degrees. This is a comparatively wide angle.

Put that same 50 mm lens on a FF camera with a 36mm x 24 mm sensor (or film) and a lot of that image circle is not used (it is &quot;cropped out' if you like). The angle of view drops to about 46 degrees and the lens is no longer wide angle but is like any &quot;normal&quot; 50mm FF lens on that body.

Now put that 50mm lens on a camera with an APS-C sensor of about 22.6mm x 15.7 mm and even more of the image circle it produces is &quot;cropped out&quot;. It is now a short telephoto with an angle of view of about 30 degrees.

So the lens is a 50mm lens, no matter what body it is fitted to and behaves just like a 50mm lens made for that body. The only thing that is changing is the amount of the image circle produced by the lens that is being used. The less of the image circle that is used, the tighter the angle of view becomes.

To use another example, 80 mm is about &quot;normal&quot; focal length for MF. It becomes an 80 mm &quot;portrait length&quot; lens on FF. and an 80 mm &quot;short telephoto&quot; on APS-C (where you might say &quot;it gives roughly the same angle of view as a 120 mm lens on FF&quot;. But it is still an 80 mm lens, no matter what body it is used on).

Hope this helps.

thank you, that makes a lot of sense and I thought as much, I just wanted to make sure. I got confused ever since I heard the term "crop factor"...