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Old July 13th, 2008, 12:34 AM   #1
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Letus/Nikon adapter Backfocus help

Does anyone understand how the back focus adjustment is supposed to work on the newer Nikon adapter for the Letus Extreme?

I recently discovered my back focus was not as good as i thought it was, and I don't really want to open my unit up again and futs around with those adjustments.

I saw 3 screws inside of the nikon adapter but loosening them didn't seem to loosen anything else. Any help would be appreciated.

Lenny Levy
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Old July 13th, 2008, 01:27 AM   #2
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Leonard.


You have drawn my attention to something I had not observed. The Letus Extreme specimen I received was near enough to spot-on out of the box, so I did not go looking for trouble.

My interpretation is that those three screws hold nothing together but are intended to take the place of fixed shims as adjustable spacers and enable the adding of length to the back of the Nikon mount whilst enabling the ability to adjust on three axes relative to the groundglass image plane which fully circular fixed shims cannot.

The mount, when inserted into the front housing would bottom out with those three screwheads butting against the contact surface of the front shoulder face if distance has to be added. That is the way I see it, however the Le brothers or Aaron may be able to elaborate on this.

The new user manual will likely also cover this.

Providing the groundglass itself is not so far rearward of the lens focal plane as to make infinity focus impossible, the screws as adjustable spacers should enable as much precision as there needs to be.

There may be a tendency for the mount to walk forward as the clamping screws are tightened, unless the mount is held firmly back against the spacer screwheads as the clamping screws are tightened.

It is a more fiddly method than the instantaneous user-adjustable backfocus/macrofocus we are familiar with on ENG lenses but easier and faster than cutting shims or quarter-circle wedges.

I think instantanous backfocus/macro ability may be found on the Ultimate, but I may be wrong. It may be a user adjustment but not usable on the fly like the ENG lenses. Philip Bloom or the Le Brothers may be able to expand on this question also.

Last edited by Bob Hart; July 13th, 2008 at 01:32 AM. Reason: wrongun
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Old July 13th, 2008, 03:02 AM   #3
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Bob, I just got an email from Hien at Letus with a PDF of the new Extreme user manual and I believe you "hit the nail on the head" as to how this works.

Lenny
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Old July 13th, 2008, 03:39 AM   #4
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Leonard:

Have you asked if they will allow it to be posted ?
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Old July 13th, 2008, 04:13 AM   #5
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Chris.


The version I have seen was a proof version not the final which might be still in the works. It is very comprehensive and provides much more owner service information than P+S Technik do for the Mini35.

I regret I did not recall the info on the backfocus screws earlier. Such is the blight of incipient Alzheimers or ADHD, whichever is applicable in my instance, probably both plus a trace of EMS (evaporative memory syndrome) as well.

The brothers give you an insight into the deeper guts of the Extreme but beyond a certain number of described dismantlement steps towards the inside, they set a limit beyond which no one should go lest they void their warranty.
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Old July 13th, 2008, 01:01 PM   #6
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I'm sure if its not posted already it will be soon.

If you send me a private email at
NSLL@pacbell.net
I'll email you my pdf.

Lenny
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Old July 13th, 2008, 01:08 PM   #7
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I've actually ordered the flip module to try to apply to various self made adapters, experimentally, as well as to my old 35A . It will be interesting to see how it will go.
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Old August 18th, 2008, 08:42 PM   #8
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is there a way to get this pdf file somewhere. I am having a heck of a time trying to adjust the backfocus...I know the concept...I would just love to read about it
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Old August 22nd, 2008, 02:22 AM   #9
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Originally Posted by Charles Barreto View Post
is there a way to get this pdf file somewhere. I am having a heck of a time trying to adjust the backfocus...I know the concept...I would just love to read about it
According to Aaron you will soon be able to buy the Ultimate backfocus as an add on for the Extreme. Zacuto is already taking orders for the modded Extreme. They call it the "Elite".
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Old August 22nd, 2008, 10:38 AM   #10
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Hi

I have adjusted back focus for the nikon mount by first setting the Gglass to about 7.2mm from the letus and being sure it has the best focus on the camera side to side top to bottom. Then put on a wide lens a 24mm in this case set to infinity and find the best focus moving the mount. The screws help if you take a screw driver and put a marking on it (screw driver), that way you can back out the screws equally.

So far all the other lenses have been in focus at infinity as well.

Hope this helps.

Chuck
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