Quick clarification pls: 35mm lenses FOV and perspective

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Panamaniac
Since the D90 doesn't have a full frame still 35mm sensor, and as far as I have been able to find out it has a/or about a 16:9 motion picture 35mm sensor... does this mean that 35mm still lenses will be longer when used on the D90?

I didn't think about this but it would make sense... I am a bit confused now and since my head is spinning again I thought I'd just ask and have it clarified quickly.

Thank you!
 
And I guess the confusion might be in that I talk in motion picture terms... so for me it wouldn't be different but perhaps the confusion comes in when I read from still photography websites where 35mm means the bigger 35mm size and they would consider a 50mm more of a longer lens for portraits like we would use an 85mm... is that where my confusion stems from? But for "them" the D90 makes every lens longer... for "us" it works just like our 35mm adapters on our video cameras.

Is that it?
 
Yeah the d90 is part of the DX sensor range rather than full frame. So there's a crop factor of 1.5x

Therefore a stills 50mm lens is approximately 75mm lens on the d90, because it's cropped and zoomed in by 1.5x but it still has the characteristics of a 50mm lens I think.
 
Wait, this is getting confusing very quickly... When we use still glass on 35mm adapters, how big do we frame on the GG? I always assumed we'd set it to a frame the size of motion S35... then we'd have the DoF, perspective and FOV of motion S35. Right?

Then... would a still 50mm --which I now understand that it is a "full frame" still lens-- give us only narrower FOV and Perspective than a motion S35 lens, only or will it also give us the DoF of a ~75mm motion S35 lens?

I need to make sure I understand this once and for all...
 
It has got to be tons of explanations about this written on every other cinema related internet page. You will probably find excellent explanations through google. Despite that I have now done my own.

It doesn't matter if the 50mm lens is designed to be used on a 35 mm still camera, a super35 movie camera or if it's a magnifying glass with focal length 50 mm. The field of view will be the same when used on all cameras with equal frame size.

The smaller the sensor the smaller the field of view. Look at this picture:
1226483030.gif


Source of confusion is probably the custom of stating the equivalent focal length when used on a 35mm still camera. The reason for that is to make it easier to compare field of view of cameras with different sensor sizes. A 50 mm lens on a s35 size camera will have the same field of view as a 35 mm still camera with a 75 mm lens.
1226484024.gif
 
I understand FOV easily, but thanks for your explanation. I guess I am not making myself very clear...

Let me ask this then: In your last explanation, will the 50mm on the S35 sensor have the same DoF as the 70mm on the full frame 35mm sensor? What about perspective?
 
Very important. A 50mm lens is always a 50mm lens no matter with what camera you use it. What changes is the field of view. Since the d90's sensor is approximately the same size as Super35mm cropped, a 50mm lens will give you the same FOV and DOF on a super35mm camera and on the d90. The confusion often starts when people don't distinguish the still image 35mm format and the motion picture 35mm format. The still image 35mm format uses a much larger negative than the motion picture 35mm format (and d90). Therefore a 50mm lens on a still image camera gives you a wider FOV than on a motion picture 35mm camera or on a d90. If you wanted to get the same FOV with the still image camera as you get with a 50mm lens on a 35mm motion picture camera / d90, you would have to use a 75mm lens (crop factor 1.5). The 75mm lens would produce a little bit shallower DOF than the 50mm lens on the motion picture camera / d90.
I hope this makes sense....
 
Thanks Michael! Excellent explanation! I see where I started to be lead astray before... it is quite simple, but after hearing the stuff a thousand times I start to wonder if I really do understand the stuff and get all confused again.

Thanks Bearing for the pictures.

I am back on track now.

I guess what's important to remember here is that for the D90 you will need much wider lenses than for something like a D5 in order to get the same FOV. However, on the D90 they will behave just like (or practically like) they will on S35 cameras or adapters set up properly. This will get you used to working with S35 as a format, and you will start building up a lens bag suited for S35.

So if I could afford a still camera it should be the D90. Too bad that's not the case. :)
 
One can purchase wide angle filters to put over their lenses though to shorten the fov by 0.50x or .70x

I'm thinking of buying a few off ebay, any good?
 
cordvision said:
Same camera position and same FOV = same perspective
Click to expand...

hmmm, I just thought about it and figured out that it is not 100 % right. Only the camera position matters in terms of perspective. You can have a wide angle lens or a telephoto lens attached to your camera, as long as you don't change the position of the camera, the perspective stays the same. If the position and the FOV is the same you will get an identical image (excluding DOF).
 
cordvision said:
If the position and the FOV is the same you will get an identical image (excluding DOF).
Click to expand...
Yes, and if the aperture stays the same the change in DOF is the same as the change in frame size. 1.5 x smaller frame will give a 1.5 x longer DOF. To keep the DOF the aperture has to be 1.5 x bigger.
 
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