Film of "grain" with HC1

Bob Hart · October 22nd, 2006, 07:41 PM

Something else I put in the unauthorised manual, which I have not yet bothered to progress furthur is this :-

""""""""""""""""""""""""""""""""
LONG TERM STORAGE:

Remove batteries.

Avoid where possible storing the appliance in hot environments to prevent deterioration of rubber components and bonded joints.

Put a spare lens cap or gaffer tape on the SLR mount to keep dust out.

Store the Letus35 with the groundglass oriented in a horizontal position, that is with the lens mount directly facing up or down. -

This will minimise any tendency for the flexing joints which support the mechanism to deform under constant weight.

""""""""""""""""""""""""""""""""

I had speculated privately, that over time, in upright storage, the rubber grommets would deform under the constant load of gravity and cause a narrower elliptoid excursion of the groundglass.

A similar method of mounting older turntable AC motors for acoustic dampening had the same problem. In practical terms it was a life of appliance issue unlikely to emerge before the appliance wore out from normal everyday use.

I never seriously thought it could become an issue with the Letus so soon if at all and there well could be another cause.

As Michael has discovered, rotating the grommets in the groundglass carrier is pretty much the cure.

A better implementation would be to leave one pair of grommets on one pillar alone, rotate another pair on another pillar 120 degrees, then the third pair on another pillar 240 degrees.

This would then ensure symmetric redistribution of the distortion to cancel the effect. I don't think this is an option on the Letus as the grommet on the base of each pillar is bedded into the front support with a permanent adhesive bond.

In this instance, rotating each of the grommets on the groundglass carrier 90 degrees might have the best effect to start off with, then as Michael has discovered, experiment with rotating each until the best effect is achieved.

Mike Kim · October 23rd, 2006, 06:50 PM

I think I fixed the motion problem. Thanks for the help everyone.

Now I only have to get rid of that white spot:

Quote:

Originally Posted by Bob Hart

There is a small spot, chip or blemish on the GG which appears near the left number on your paper. This is seen as a very narrow pale coloured elliptoid ring with a spot at either end.

It's a spot in the GG that looks whiter than the rest of the glass, but it seems permanent.

Bob Hart · October 23rd, 2006, 10:04 PM

The white spot is something that probably can't be fixed except by replacement of the groundglass or removing it and re-dressing the finish - that is not something I would recommend to the novice.

Probably best contact Quyen or maybe check with Jim Lafferty to see if he will be releasing his polymer based GG panels in Letus versions. This is a development of his wax experiments.

Wax diffusers hail back to the "Boss" screen for still-imaging and the Movietube for motion imaging if you go back far enough.

Wax GGs were pursued to enable in association with larger groundglass image sizes, the use of a fixed groundglass. He has developed a polymer version. How it stacks up when used for a smaller GG area like 24mm in moving systems I don't know.

Wax didn't work for me as I found it impossible to control the wax layer thickness over CD sized disks but the image from wax was otherwise absolutely the best for sharpness and grain artifacts.

If the grains in the polymer are no more evident than on an AO5 dressed groundglass, then it could be a viable replacement for the Letus screen if this cannot be had as a separate part.

Henry Clayton · December 4th, 2006, 02:17 AM

Quote:

Originally Posted by Bob Hart

Something else I put in the unauthorised manual, which I have not yet bothered to progress furthur is this

Bob, is the unauthorised manual, in whatever state of completion, available to the general public? I've been hoping such a thing would come along.

H.

Bob Hart · December 4th, 2006, 10:02 AM

Henry.

Anything in my comments which might be of any use has been posted here in the Letus threads. The remainder of my stuff is basically a product description and my understanding of the theory involved. P+S Techniks own website has useful info for managing the Mini35 and Pro35.

Much info in those manuals is helpful in a general sense for understanding the Letus35 models.

October 22nd, 2006, 07:41 PM	#16
Bob Hart Inner Circle Join Date: Dec 2003 Location: PERTH. W.A. AUSTRALIA. Posts: 4,476	Something else I put in the unauthorised manual, which I have not yet bothered to progress furthur is this :- """""""""""""""""""""""""""""""" LONG TERM STORAGE: Remove batteries. Avoid where possible storing the appliance in hot environments to prevent deterioration of rubber components and bonded joints. Put a spare lens cap or gaffer tape on the SLR mount to keep dust out. Store the Letus35 with the groundglass oriented in a horizontal position, that is with the lens mount directly facing up or down. - This will minimise any tendency for the flexing joints which support the mechanism to deform under constant weight. """""""""""""""""""""""""""""""" I had speculated privately, that over time, in upright storage, the rubber grommets would deform under the constant load of gravity and cause a narrower elliptoid excursion of the groundglass. A similar method of mounting older turntable AC motors for acoustic dampening had the same problem. In practical terms it was a life of appliance issue unlikely to emerge before the appliance wore out from normal everyday use. I never seriously thought it could become an issue with the Letus so soon if at all and there well could be another cause. As Michael has discovered, rotating the grommets in the groundglass carrier is pretty much the cure. A better implementation would be to leave one pair of grommets on one pillar alone, rotate another pair on another pillar 120 degrees, then the third pair on another pillar 240 degrees. This would then ensure symmetric redistribution of the distortion to cancel the effect. I don't think this is an option on the Letus as the grommet on the base of each pillar is bedded into the front support with a permanent adhesive bond. In this instance, rotating each of the grommets on the groundglass carrier 90 degrees might have the best effect to start off with, then as Michael has discovered, experiment with rotating each until the best effect is achieved.

October 23rd, 2006, 10:04 PM	#18
Bob Hart Inner Circle Join Date: Dec 2003 Location: PERTH. W.A. AUSTRALIA. Posts: 4,476	The white spot is something that probably can't be fixed except by replacement of the groundglass or removing it and re-dressing the finish - that is not something I would recommend to the novice. Probably best contact Quyen or maybe check with Jim Lafferty to see if he will be releasing his polymer based GG panels in Letus versions. This is a development of his wax experiments. Wax diffusers hail back to the "Boss" screen for still-imaging and the Movietube for motion imaging if you go back far enough. Wax GGs were pursued to enable in association with larger groundglass image sizes, the use of a fixed groundglass. He has developed a polymer version. How it stacks up when used for a smaller GG area like 24mm in moving systems I don't know. Wax didn't work for me as I found it impossible to control the wax layer thickness over CD sized disks but the image from wax was otherwise absolutely the best for sharpness and grain artifacts. If the grains in the polymer are no more evident than on an AO5 dressed groundglass, then it could be a viable replacement for the Letus screen if this cannot be had as a separate part.

December 4th, 2006, 10:02 AM	#20
Bob Hart Inner Circle Join Date: Dec 2003 Location: PERTH. W.A. AUSTRALIA. Posts: 4,476	Henry. Anything in my comments which might be of any use has been posted here in the Letus threads. The remainder of my stuff is basically a product description and my understanding of the theory involved. P+S Techniks own website has useful info for managing the Mini35 and Pro35. Much info in those manuals is helpful in a general sense for understanding the Letus35 models.