True 35mm field of view?
 

I saw this posted on the form sometime ago but I can't remember where.

I've got a Letus Elite and with my EX1 I find that I need to zoom in to about 77 in order to get rid of all the vignetting. Now if I put a 35mm lens on the front of my camera, what is the true field of view that I'm looking at when I'm zoomed in at 77? (Ex: is it 38mm because I'm zoomed in so much or could it be 32mm because the GG is so large?)

Thanks,

Good question. I don't have an exact answer but I suspect it's less than 35mm. I too zoom in between Z75-77 depending on what lens I have on. I would be curious to know the answer too.

The way I've tested this in the past is to take my SLR with a zoom lens on it - say a 24-70 if I'm using my 24mm or 50mm lens, and make a target for the camera - say, a focus chart. Now granted, the 35mm frame is more of a square aspect ratio than HD cameras, but I place my SLR as close to my rig as possible, and zoom in on the target so the top and bottom spacing matches what I see on the camera. Hope that makes sense.

I can't remember my exact results - I tested my redrock M2 before with the XH-A1, but have recently upgraded to the Encore and a Sony EX1 and I am curious about the same thing. I'll try and provide some (very un-scientific) results when I get around to doing this test :)

That would be great if you could do the tests. I've been interested in this for quite some time.

I have an Extreme, and it's just about the same as my SLR. That is, I get the same field of view on my EX1 zoomed to 77 or so as I do on my SLR with the same focal length lens. If anything, the Letus is a bit wider.

I'm zoomed to about 77 as well on my encore. I'll be interested to do these tests asap!

Do you letus users 'see' the ground glass ever?

I've seen examples of letus and at times saw the ground glass.

a bit wider??? that kinda seems impossible unless your SLR viewfinder is cropped to less than 100% of your 35mm film plane. some SLR camera's viewfinders only allow you to view 90%-95% of the image. Pro SLRs allow you to see 100% if not very, very close to 100% of the image.

I'm zoomed in to Z69 on our Ultimate. No I've never seen the ground glass.....well, except when I forget to turn it on. hehehe

I'd be curious to know if there's an focal length multiplication going on, but in my non-technical experience, there doesn't seem to be. When I use our Nikon 17-35mm lens, it is VERY wide. If there is any multiplication, it can't be much.

The Letus GG is very much larger than the 24x36mm full frame (135) 35mm 8 perf horizontal stills camera gate, almost 1.5x as large.

This means there's quite a bit of leeway when you zoom into the center of the projected circle of light for your final image.

I tested this by cutting out a 135 paper mask and physically inserting it into the Letus and was surprised by how much extra GG there is (this is an Extreme I'm talking about, don't have an Ultimate).

The zoom setting was around 80? for the same size as the mask. I didn't take exact note of it (I will next time) but it was higher than I'd thought.

The Nikon lenses are engineered to cover the 135 frame, with just a little left over in the corners to stop vignetting. So if you zoom in to chop off, say 5% at the corners, that would be about the same as your 135 frame, and at that setting a 35mm stills lens will cover 54.25 degrees horizontal or 63.25 degrees diagonal, which is what a 35mm stills camera lens is designed to do.

Any wider than this will result in using the Nikon lens outside its design limits, and may lead to vignetting, edge and corner distortion, etc., especially at wider focal lengths.


Don't forget that "full frame 35mm movie" is in fact the same as a half frame (4 perf vertical) stills format.

i.e. a "standard" 50mm lens in 135 (stills camera) works out to a medium tele in a 35mm movie camera. The angle of view is the thing, and this is dependent on the diagonal dimension of the final frame/gate.

Put more simply, a Nikon 50mm (standard) lens put onto an Arri 35mm movie camera will yield a medium telephoto shot.

Or, a standard lens has around a 40 degree horizontal acceptance angle, whereas a medium tele (say a 105mm Nikon lens on a 135 camera) accepts only around 19 degrees horizontally.

Just by the bye and FWIW, this is one benefit of a director's viewfinder, and, with cameras themselves being so much smaller and lighter than they once were, probably the major benefit these days:

if you find yourself working with various different formats of cameras (you know, one day/job shooting 35mm film, then 16mm film, then HD), then you can sight your shot angle with the viewfinder and then call out the correct focal length for the shot you're seeing for the format you're shooting in that day/job/whatever, rather than having to do all that calculation in your head.

Thanks for all the work you did Chris. That's very helpful to know!