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-   -   I can't detach the Nikon lens!!! help! (https://www.dvinfo.net/forum/alternative-imaging-methods/90552-i-cant-detach-nikon-lens-help.html)

Giovanni Speranza April 3rd, 2007 11:11 AM

I can't detach the Nikon lens!!! help!
I attached my Nikon lens to the Letus and suddently i noticed that the lens has not the old little lever that let's you detach it. Maybe that lens can only be detached with some "release button" on the camera...
So my question:
Now how do i detach the Nikon lens from the Letus35??? HEEEEEEELLLP

btw: the image quality is wonderful, very sharp and no vignetting.

Bob Hart April 4th, 2007 05:38 AM


Step 1.

Remove the lens mount and lens from the LETUS35 by by loosening off the thumbscrew and sliding the mount forward. You do not want to be wrestking the lens whilst the mount is still on the Letus otherwise you may wreck something.

Step 2.

Now that you have the lens mount off with the lens still attached on front, have a look in from behind. You'll need strong light and maybe close-up glasses or magnifier if you are like me.

A likely cause of the jam is at the tiny end-stop screw on the lens in the bayonet channel may have gone under one of the bayonet lugs, caught on the undersurface and begun to screw itself out and come up tight.

Check to see if there is a sign that this screw has gone under, you might need to put some lube in there and patiently work at it until it comes loose. If it has turned, it should initially resist then screw itself back up and become looser on the undoing journey.

Remember the ikon unscrews clockwise as facing from the front.

If the bayonet has simply tightened on the lugs temselves, you may need to think about going right on through but ore better, again put some lube in and patiently work at looosening it.

Giovanni Speranza April 4th, 2007 08:05 AM

Thank you Bob, will this mean that this kind of lens doesn't work with Letus?
In other words, i don't understand if this is a jam, or if this is normal with such lenses; maybe instead i simply don't know how to remove a Nikkor lens.....

Bob Hart April 4th, 2007 10:37 AM

(Thank you Bob, will this mean that this kind of lens doesn't work with Letus?)

To the contrary. As you have discovered, the Nikon lenses work fine optically when backfocus is correctly set up. The issue is with the non-genuine Nikon mount on the reversable version.

The mount and the bayonet lugs are turned and milled from one piece of aluminium stock. There is no issue with the precision of the work. The lenses fit but it is not a Nikon mount.

Two desirable features have been deleted in the Letus version; a conforming pressure on back of the lugs to maintain the flange face contact of the lens and mount and a locking function.

The Nikon mount has five components of function (not including electrical connections). My description of them is generic and may not be correct.

The camera body, which includes a clearance channel for the flat spring and llugs on the lens.

The flange ring and face, which incorporates bayonet lugs.

The flat spring with a detent bulge for each bayonet lug on the lens.

Releasable locking pin which locates in a radial channel on the lens.

A limit stop in the form of a tiny screw in the bayonet channel in the lens.

The flange face shares responsibility with the flat spring for maintaining the lens flange in positive face contact, retains and supports the flat spring's detent bulges which are loaded compressively to hold the lens tightly.

Each of the bulges and its partner lug on the ring combine as a conforming wedge to provide positive contact pressure of the flange faces, eliminate slackness due to off-spec machining or wear, provide some initial locking function and maintain accurate focal distance from the image plane.

The materials which comprise the spring and ring are a harder and disimilar metal to that of the matching lens fittings and of a polished finish to eliminate pressure galling and minimise wear.

Each of the components including the camera body is an expensively machined precision part.

Set radially in the channel machined into each lens barrel for the lugs on the mount is a tiny screw which limits how far the lens will turn in the mount.

The lens is positively locked by a pin which springs out from a hole in the flange ring into a matching radial channel in the lens flange face and can be retracted to release the lens.

Quyen's reversable mount is one single part. It seems apparent that design compromises intended to keep costs affordable for the moviemaker with a limited budget have been made.

The mount's front face is the flange face.

Locking of the lens in the mount and positive maintainance of lens and mount flange face contact relies entirely on tightness of the face fit of the lugs on the lens on the inner rear faces of the lugs in the mount.

This is created by the friction of a wedging function effected by the machining of the lugs on the mount and the lens.

Variations in the fit of the lens due to wear or machining variations between each example can defeat this friction component which is also the only locking function available on the reversable mount.

The mount material is soft aluminium. The lugs can wear down.

If the stop screw in the lens has been worn or damaged, it is possible for this screw to injure the lug it is intended to butt against, bypass it and jam if the lens is also a worn loose fitting example.

This misadventure can be caused by a user familiar with the feel of the genuine Nikon, seeking that feel of a friction building and turning the lens a little tighter to lock it.

The combination of damaged screw and loose fit is highly likely in heavily worked used lenses many adaptor owners are likely to have purchased.

In the event of a permanent looseness developing, the only options for restoring a tight fit are to add a packing material like thin adhesive tape, or a paint-on metal adhesive to the flange face or to mechanically deform the soft material of the flanges inside the reversable Letus mount to take up the excessive clearance.

If light oil on the contact faces of the mount after you have taken the mount and lens out of the Letus35 does not help, you may have to use brute force to start the lens on the mount and then work it back and forth until it wears the mount enough to come free.

It may be risky for plastic bodied lenses which may break. Older metal bodied Nikon lenses will probably survive but if the little screw has jammed, it may break off.

I have an old Adaptamatic Auto-Tamron for Nikon which has this problem,

Make sure you hold the lens by the body and not the focus and aperture rings when you do this. Remember the lens when viewed front-on, must be twisted clockwise relative to the mount.

Best of luck with it.

Giovanni Speranza April 4th, 2007 11:52 AM

Wow, very comprehensive. As i'm not of english mother language, i understood the principle, but maybe i missed a point:
Assumed that the lens is ok, and the Letus too, to remove the lens i just have to rotate it (clockwise)?

Bob Hart April 4th, 2007 12:28 PM

Sorry I used too much words.

Unscrew the thumbscrew until mount can pull out to front.

Remove mount from Letus35.

Look inside the Letus mount from back end.

Get wooden satay stick or toothpick. Use it to put drops of oil on jammed mount where back of lens touches it.

Twist lens clockwise only until it begins to move.

Twist back a little.

Twist clockwise again.

Move it in small twists until it loosens. Then try to force it again.

(Langsam arbeit???? - Please forgive. Ich habe sehr kleine deutsch von schuljunge tagen und "Inspector Rex" und neine Franzosisch.).

Giovanni Speranza April 4th, 2007 03:14 PM

I'm too ignorant.
What i don't understand is: is this the normal procedure to detach a Nikon lens from Letus??
Or what is the normal procedure?

Bob Hart April 4th, 2007 10:04 PM

("is this the normal procedure to detach a Nikon lens from Letus?? ')

Yes. Normal procedure is to turn lens clockwise and pull out.

There is something wrong with yours. It should not be so tight.

Please make a close-up (macro) .jpg image of the mount and post it here so we can look at your problem.

Giovanni Speranza April 5th, 2007 09:39 AM

Thank you very much

Giovanni Speranza April 5th, 2007 02:46 PM


Bob Hart April 5th, 2007 07:38 PM

Did you get the lens off?

Please post a close-up .jpg here or small movie on YouTube.

Make to show the mount.

Quyen makes two types for Nikon. My help words may be wrong.

Giovanni Speranza April 6th, 2007 01:40 AM

I understood now that Letus35 Flip Enhanced has a nice button (a special screw), which is a lever.
To remove a lens just move that lever in the direction of the Letus then just rotate easily the lens. Easy as a camera.
But i risked to destroy the Letus because, following the directions from many forums members, i just had to rotate the lens... and i made some force. Fortunately, i never forced it too much. then i unscrewed the button and with a small screwer i moved the hole just to understand that it released the lens.

Bob Hart April 6th, 2007 03:32 AM

This has been a little lesson to be learned by me.

I have assumed all along that the troublesome lens mount has been the reversable mount and that the problem was similar to one I experienced.

Nowhere, I now realise, did I enquire what mount version was fitted to Giovanni's Letus35.

The advice I was giving was both badly wrong and potentially disastrous in outcome, so I offer my apologies to you Giovanni for the wrong advice I gave you.

Giovanni Speranza April 6th, 2007 03:42 AM

A little piece of paper with a drawing included with the Letus would have be helpful. This is a new feature and it could have been announced... ;)
Anyway it's allright and i'm really excited.
Next week i will probably film a little ad with it and i will post it.
I'm very impressed by Letus quality. The only fact that the ground glass is a true 35mm 4:3 screen and not a piece of rotating CD makes me happy.
I tried the M2 and i was totally disappointed by the form of the visible image. And i don't like that huge box in front of the camera. I think that letus can be comparable to a Pro35 or even better.
Bob, i have a question: Do you think that i can apply the Letus35 FE to a broadcast camera? (1/2" CCD, no lens)

Bob Hart April 6th, 2007 10:33 AM

Everything is possible with the will to make it happen.

The Letus35 XL and HD100 flip models do it direct to 1/3" CCD.

Quyen's method uses a Minolta 50mm SLR lens for a relay lens. Fixed on front of the Minolta lens is an unmounted doublet for a close-up lens to focus on the groundglass. On the back of the Minolta lens, Quyen has replace the Minolta mount with an XL or HD100 mount.

If your 1/2" CCD camera uses a B3 mount, I guess Quyen's existing arrangement with a B3 replacement mount on back of the Minolta lens might work.

His arrangement for direct relay to 1/3" CCDs seems to take an image about 22 - 24mm wide. The 1/2" CCD represents a 30% larger field-of-view for the same optics. I think his groundglass screen should be large enough.

Don't believe my words here. They are only a guess. I have been wrong lately.

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