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Old October 6th, 2004, 03:05 PM   #1
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Question on lenses...

This must have been discussed before, but I can't find it. Plus it doesn't really have to do with the Mini35, but along the same vein...

Does it make sense to adapt 16mm lenses for an XL1s instead of 35mm lenses? I figure since the 16mm lenses are designed for a smaller target frame, that it would be closer to the size of the CCDs and wouldn't exhibit as much of a focal length increase as you get when you slap a 35mm lens on there.

Plus there's some pretty good 16mm lenses out there...

Just a thought.

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Old October 6th, 2004, 04:19 PM   #2
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You placed your thread in the mini35 P+S technik area. If you
are using such an adapter the focal length doesn't increase
at all. That only happens with the Canon EF adapter for example.

Which are you talking about? The mini35 adapter mounts 35mm
lenses, not 16mm. Neither will any other adapter I'm aware off.
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Old October 6th, 2004, 04:36 PM   #3
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i suppose he means if it is possible to use 16mm lenses on the mini35 at all.
i think when you use 16mm lenses (pl mount f example) on the mini35 the focal length is doubled. a 10mm focal length 16mm lense will be 20mm focal length on a mini35.
correct me if im wrong
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Old October 6th, 2004, 04:40 PM   #4
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I believe that is wrong Elmar. It would be true if you mounted
a 16mm lens directly to it. DON'T FORGET that the 35mm adapter
has a 35mm surface! NOT a 1/3" CCD surface. So the image will
be smaller in the center of the screen instead of bigger and
"zoomed in". That would happen if you where to mount an
imax lens on the adapter or something.
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Old October 6th, 2004, 04:50 PM   #5
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hmmmmm... you could be right. but what would happen when you connect a 10mm focal length 16mm lense pl mount to the mini35 ?
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Old October 6th, 2004, 04:52 PM   #6
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Actually, I did post it in the wrong area.

I'm talking about mechanically adapting a lens to the XL1s, as in the EF adapter, not using the Mini35.

Which forum should I post the question in?
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Old October 7th, 2004, 03:21 AM   #7
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I've moved it to the aproriate forum, please continue with this
thread.

So your question is what would happend if you where able to
mount a 16mm lens to the XL1S? Or are you seeking for an
adapter that could do it?

Elmar: I'm not sure if it will get to be a wider lens, but it will only
use a small portion of the CCD's. So it will be like a small image
frame surrounded by black (when using the mini35)
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Old October 7th, 2004, 10:04 AM   #8
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Well, both questions, actually.

There's been a lot of discussion about how a 35mm film lens gets a 7.2x focal length increase when you mechanically adapt it to an XL1s. The main reason being (from what i understand, anyway) that the lens is designed to project an image on a target much larger than the CCD (namely the 35mm film). So the CCD only "sees" the small center section of the lens image.

I was thinking, though, that maybe if you used a 16mm lens instead of a 35mm lens. Wouldn't the 16mm lens be designed to project onto a smaller target (the 16mm film), which is closer to the size of the CCD? Wouldn't that result in less magnification of the image on the CCD and a closer approximation of the true focal length of the lens?

The reason I'm asking is that there's a LOT of really good 16mm lenses out there -- Cooke, Angeneiux, Zeiss, etc. -- most likely much better than the Canon stock lenses. So wouldn't it make sense to use the better lens if it was closer to the real focal length?
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Old October 7th, 2004, 11:15 AM   #9
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Whether or not those lenses would be better for *this* digital
camera, I don't know. Canon makes some high quality glass
themselves as well.

But yes, your theory is sound. A 35mm lens mounted directly to
the XL1S will have a 7.2x magnification factor since it only sees
the small middle portion (lens throws a much larger picture, ie
the 35mm negative is larger than the CCD's).

Your also correct in that a 16mm lens will have a much smaller
magnification (somewhere around 3.3x would be my "guess"?).

However from what I've heard from other people you will not
gain much in the often sought out depth-of-field reduction and
to my knowledge there is no 16mm adapter.

Probably there just isn't enough demand (Canon doesn't make
16mm lenses?) and increase in quality or shortened depth-of-
field to warrant it?

Or I might be totally wrong...
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Old October 7th, 2004, 12:18 PM   #10
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<<<-- Originally posted by Rob Lohman :
However from what I've heard from other people you will not
gain much in the often sought out depth-of-field reduction and
to my knowledge there is no 16mm adapter.
-->>>

Your points make sense. The part about the depth of field isn't gelling in my mind, though.

I thought the primary purpose of the mini35 and its various relatives is to provide the elusive film MOTION effect, which is nearly impossible to reproduce accurately in DV. It does so by allowing the DV camera to rephotograph a projected image from the lens, instead of taking an image directly through the lens. I didn't think its purpose was primarily to adapt a 35mm lens to DV. There's plenty of mechanical adapters for that.

But as for DOF: Isn't depth of field solely a property of the lens itself, irrespective of the target surface (film, ccd, mini35 ground glass, etc?) Or am I wrong, and the target surface DOES contribute to the DOF effect in some way?

Doesn't it follow that if a lens can produce a very shallow depth of field, that it can do so no matter what surface it's projecting onto?

... or have I taken too many drugs again... :)

--R
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Old October 9th, 2004, 11:29 AM   #11
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Hi,

There two things (no three) I think I can offer to this discussion.

One; you have to take into consideration that there are issues of depth of focus (something different than Depth of field), when dealing with 16mm and 35mm film lenses (not to be confused with 35mm photo lenses - there is a focal length/magnification difference because of the image size differences), you want, to project an image directly on to your cameras chips. That is to say that there is a very specific distance from the back element of the lens to the plane where it projects a sharp image. This distance is different for different lens mounts. A 16mm C mount for a Bolex has a pretty shallow depth of focus and a 16mm bayonet has a deeper depth of focus (basically what back focus is), but I don't think that it is deep enough to reach the chips on the XL1s. You would have to remove that thick bit of glass protecting the CCD you see in there, I think it's called the prism. But I think doing that, would void the warranty.

As far as depth of field is concerned, I think that there are some misconceptions about what the mini 35 is supposed to do. I'm kind of assuming, because I'm new to this thread. But from what I have heard around town, and what Rob (kind of) said - people think that the mini 35 has some magic effect on the depth of field that is not achievable with "normal" video lenses. I don't think that this is true. I used the mini 35 last week for the first time, and my impression is, that the device forces you to shoot video more like film (for a number of reasons), and that that causes a lot of the film look. But what makes the image look filmy, is the moving grain caused by the oscillating ground glass.

Depth of field is effected by the image size. A smaller image size will have more depth of field than a bigger one with the same focal length. (That's what I just read in Lenny Lipton's guide) That may sound like an argument for the effects of the mini 35, but I think that there are a lot of ways you can get very shallow depth of field without the mini 35, or drugs.

I hope that this is not too confusing.
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Old October 10th, 2004, 10:23 AM   #12
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Target size does effect depth of field, that's why our smaller
sensors in combination with the lenses create a deep depth of
field. 35mm is a much larger area which in turn creates a much
shallower depth of field, see our DoF skinny:

http://www.dvinfo.net/articles/optics/dofskinny.php

The mini35 was made to get more filmic images, use better glass
and let professional operators use equipment they are familiair
with including follow focus systems and such.
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Old October 10th, 2004, 07:19 PM   #13
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I may be repeating some things.

A 16mm cine lense will cause vignetting. You can't use a 16mm lens on the Mini35, because you are projecting a smaller image onto the groundglass. The camera is seeing the groundglass, not the image projected on to 1/3" CCD's. The Mini35 groundglass is approximately as big as an Academy 35mm motion picture frame 22mm x16mm. Full Aperture 16mm is 10.3mm x 7.5mm. You are projecting a smaller image into a larger frame. It could actually be an interesting "look", but I'm talking in terms of the "right" way to do it.

I forget the physics (and to again, oversimplify), the smaller the format the greater your depth of focus. I won't explain it because I'll mess it up :~). I think someone else did a good job in an earlier post, above.

Go here for the Mini35 series 400 user manual. This should be helpful.

Also go to ZGC's site and the P+S Technik websites.
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Old October 11th, 2004, 03:05 AM   #14
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I don't mean to be a smarty-pants, but "depth of focus" is not the same as "depth of field", just to confuse everything a bit.

Depth of field is the area which is in front of the lens (where the object you are filming is), and depth of focus is the same thing, but behind the lens (where you are trying to get the image focused onto something that will record it, like a ccd or film).

Otherwise, I think you got the rest right.
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