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Old May 11th, 2012, 11:26 AM   #31
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Re: 35mm adaptors dead?

That is fantastic information. Thank you!
So: Those images above were both taken with the 20-35 f/2.8
Is it a characteristic of f/2.8 that creates the vignette, or a characteristic of it being a zoom lens? Because f/2.8 is pretty fast.

Below is an image taken with the 50mm. The vignette is not as extreme, but it's still there.

Regarding the diopter, I read somewhere that on a fixed-lens camera, vignetting could be worsened by omitting the diopter. I do have one, BUT: the relay lens is built so that it protrudes into the body of the Letus, into the space that the diopter occupies. So the two seem to be mutually exclusive.


I just spoke with Letus, and they told me that there's no getting around vignette with wide-angle lenses without using an academy frame relay or zooming in (which is sort of ironic, since the wide-angles are why we NEED adapters in the first place, but never mind). I'm sending it in for service to see if they can iron it out a little.

In the meantime, the few of you who are still using adapters instead of DSLRs can watch a very short documentary we shot with both a Letus on the JVC GY-HD200u and Canon Mark II here: http://earthhouseproductions.com/fil..._of_the_stove/
I recommend blowing it up to fill the screen (but then, I would).

See if you can tell which is which!

And, to bring the topic back from my personal problems to the question "are 35mm adapters dead," that video won a cash prize at a small film festival recently. While I can't exactly say that the Letus was responsible for the win, it didn't hurt. I took the Mark II to a sawmill last week and came back with almost nothing useable because of the vibration on the cutting platform combined with the rolling shutter. And I thought I was saving time by NOT packing my JVC/Letus rig. So--personally, I don't think it's "dead," maybe just "overpriced."
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Last edited by Finn Yarbrough; May 11th, 2012 at 08:36 PM. Reason: New Information
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Old May 11th, 2012, 08:34 PM   #32
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Re: 35mm adaptors dead?

It would seem that the relay lens itself has the ability for close focus. I had imagined that somehow you might have been using both the relay and the achromatic dioptre in series but you are not, so that is that out of the way.

The issue is not so much with the fastness of the lens but that in combination with the exit pupil diameter as far as I can work out. The f2.8 zooms mostly have a smaller exit pupil. It is also the tendency of wide angle lenses more so to vignette.

So at the wide end, your zooms are most likely to vignette even with iris opened up. When zoomed in, the vignette may be less apparent but a broader less dense corner brightness falloff may replace it.

So it is a general rule to use f1.4 lenses when you can get them, f1.8 lenses if you can't. The f2.8 prime lenses are starting to become a bit iffy, the longer lenses less so, the wider lenses below about 40mm are not really going to cut it.

The Letus adaptor design seeks to use as much of the groundglass area as practicable to proportionally reduce in relative scale to the image frame, the size of each groundglass "grain" pattern, which is in the ball-park of a five micron texture. It is possible for the Letus adaptors when carefully set up, to resolve sharper than the practical resolution of your camera.

I observe that your 50mm f1.4 lens image is slightly dark on one corner. If you can make sure the relay lens is dead square mounted into the rear of the Ultimate and not slightly skewed, this may go away. The Ultimate I understand has an x-y-z opitcal axis adjustment. I don't know where this is or how it works. If you can find it, trimming adjustments with this may also move the dark corner.

The lens set I settled on in the end was :-

Sigma-for-Nikon 20mm f1.8 ( adequate but a bit soft and flary wide-open ).
Nikon 28mm f1.4 ( expensive ) 28mm f2 shoud be fine, may darken in corners.
Nikon 35mm f1.4
Voigtlander-for-Nikon 40mm f2
Nikon 45mm f2.8
Nikon 50mm f1.4
Nikon 85mm f1.4
Nikon 105mm f1.8
Sigmatel-for-Nikon 135mm f1.8
Nikon 200mm f2.

I have also used a Sigma-for-Nikon 14mm f2.8 on an unmodifed Letus Extreme. On the modified Letus Extreme which conveys as much groundglass area as I can get in chasing 2K image groundglass resolution, the 14mm vignettes. However with the wider image, the field-of-view of the 20mm comes closer to the 14mm. On your Ultimate, a 14mm f2.8 may vignette, maybe not. The Sigma lens is a bit soft wide-open.

The most practical everyday core set of lenses would be :-

35mm f1.4, 50mm f1.4, 85mm f1,4. maybe the 105mm, which is the definite portrait lens.

In an ideal world you will not be choosing these lenses just to conveniently frame the subject from a comfortable fixed point but to use their perspective characteristics as well as their depths-of-field for creative reasons.

Take heed of people like Chris Barcellos and Charles Papert when it comes to reasons for lens choice. I am far less accomplished than they in this business.

Last edited by Bob Hart; May 11th, 2012 at 08:37 PM. Reason: error
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Old May 12th, 2012, 11:29 AM   #33
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Re: 35mm adaptors dead?

Thanks for the link to your short film. Straightforward and unadorned, a delight. I like what you did with the decending tilt reveal with the window by turning a glare problem into a creative move with the aperture pull.

As for wide shots with 35mm adaptors, it was established fairly early in the piece that groundglass adaptors were sought more for their ability to render 35mm film-style shallower depths of field for a given field of view than the bare camera lens. Early adoptors went overboard on that for a while, then began to play with the options some 35mm wide lenses conferred.

It was theorised in discussions here that it might be better to use the bare camera for the widest shots when resolution really counts to reproduce textures such as stony distant ground or foliage. From recall, I think the jury remained out on the topic and it became a matter of personal preference and style.

It is possible to achieve slightly wider fields-of-view with 35mm adaptors on some video cameras, versus the bare camera and its standard lens.

There is a it of a trade-off with all groundlgass adaptors, finer texture means more light transmission, better resolution at expense of hotspotting, vignetting and "oily" bokeh. The coarser texture yields a more filmic result but loses a lot of light and sharpness.

You can take a wider view off the coarser groundglass for less vignetting to significantly restore sharpness but lose light performance or go in closer on a finer textured groundglass to get inside the vignette and chase better light performance. The sharpness yield seems to be slightly better for the finer texture but there is not a lot in it. You lose some, you gain some. It all comes down to a balance of factors.

P+S Technik went for a 22mm wide image frame for their Mini35-400 which was the benchmark everyone was chasing. They made a very good groundglass, a reliable motion system and a very precise instrument to filmcamera technical standards.

Those of us who home-built and most of the alternative builders who went commercial with their designs opted for a groundglass that was larger than the Mini35-400 which from the outset was intended to comply closely with the 35mm motion picture film "academy" frame size and reliably yield images with no vignetting.

Those of us who went with wider adaptors accepted the trade-offs that came with chasing a wider image off the groundglass for the sharper results which could be had, even if that meant a smaller choice of lenses we could achieve consistent results with. My recall is that the commercial builder-vendors went with that choice in that it also assisted meet the higher sharpness requirements of the then upcoming 1920 x 1080 cameras like the Sony PMW-EX1 and EX3 which advanced from the 1440 x 1080 HDV standard.

The Letus Ultimate is the final developement and most mature of the Letus line of 35mm adaptors. I don't think there is much more if anything you can do to enhance it.

The fastest wide-view "affordable" used 35mm format lens I could find was the Kinoptik 9.8mm f1.8. If used on adaptors which relay a wider than academy frame off the groundglass, this lens vignettes, so yielded for me no more practically useful a field of view than the 14mm f2.8 which vignettes at a wider groundglass frame but yields a similar field of view with a softer vignette.

That is the wall groundglass adaptors seem to hit and in practical terms, 35mm motion picture film cameras as well when it comes down to lenses affordable to the likes of us.

Last edited by Bob Hart; May 12th, 2012 at 11:59 AM. Reason: error
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