View Full Version : Film of "grain" with HC1
October 21st, 2006, 11:42 PM
I'm using the first and regular Letus35 model with a Sony HC1. I'm getting good results but whenever I close the aperture of the Canon FD lenses to 2.8 or higher, I get a film of something I don't know how to describe. They're like diagoanl lines. Better if you see it for yourself, check out the white surface of the paper I'm holding. It appears with both 50mm and 28mm Canon FD lenses. I know the Letus35 is not too clean but what I'm getting is not dirt (I checked and tried cleaning some weeks ago). Also, this is more noticeable with more light.
Shutter speed was set to 60.
Got any clue of what it could be? I'm shooting next weekend and I don't want to use only 1.4...
October 22nd, 2006, 01:40 AM
It looks like the GG isn't moving. Or it's perfectly in sync with the shutter.
October 22nd, 2006, 05:07 AM
I don't know the HC1.
That said, what you describe may not be the Letus if it is a fixed artifact AND is a visible diagonal pattern. A groundglass is a random finish or should be unless it has been aggressively cleaned or polished with a woven cloth containing hard fibre in the blend.
If you haven't touched, cleaned with cloth or tried to modify the groundglass with Nivea on a cloth, the camcorder itself may be creating the diagonal pattern.
I think the imaging chip in the HC1 is a CMOS device. If it is a single CMOS and not three, it might produce a moire pattern if it gets too much light or if the iris has closed to almost a pinhole.
Pixel shift technologies may be creating something but I know too little about it to do anything but simply dream or nightmare the possibilty.
This is a situation where my little bit of knowledge makes me a danger unto myself and thus anyone else who heeds what I say. So please, do not make any judgements on any product on my say so.
Try a piece or several of ND filter gel in between the macro lens and the camcorder lens to force the camcorder aperture to open up a little more. For experiment, if you cannot get ND gel, try pale red, blue and green (if you can get it), cellophane wrap from your local florist or stationer.
Lay these three together and you'll get something which might be seen by the camera as ND although the colours are still likely to be weird. At least this will tell you if too much light is the problem.
Other than that, I am at a loss to assist.
October 22nd, 2006, 06:16 AM
Furthur to above.
I managed to get the clip to download and work.
There seems to be three things at play against you.
Firstly, your piece of paper carries the numbers 5.6. Was this your SLR lens aperture? Aperture of f5.6 may bring groundglass artifacts into the picture in the lighting conditions you are in.
Secondly, there seems to be a problem with the groundglass motion. 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. This hints that the excursion of the GG is not circular (orbital) but almost linear which is why you are seeing a diagonal pattern.
Under adverse SLR aperture and lightng conditions, an artifact which might be described as soft edged faint freckles may become evident in the image of a groundglass working a circular motion. In your instance, these are manifest as lines.
When the Letus motor is operating, is there a sharp buzzing sound which suggests there may be contact between two parts inside? The normal sound of the Letus is a very soft dull hum. During your use of the Letus, has the battery pack at any time come off and pulled up tight on the wires?
Any contact between moving parts in the Letus will block the circular (orbital) excursion from being truly circular. If the battery pack has pulled up tight on the wires and pulled them tight inside the Letus, then the groundglass may be tethered by the motor wires and prevented from moving in a true circular (orbiting) excusion. I doubt this has happened as Quyen pegs the wires down firmly with clear adhesive.
Your lens seems to provide very good wide-angle coverage. This and a brightness falloff to the corners suggests you may not be zoomed in far enough on the groundglass. This is not relevent to the linear movement of the groundglass but will aggravate a tendency for groundglass artifacts in adverse lighting conditions
I understand there was a special model of the Letus made by Quyen for the HC1.
You probably should contact him regarding the apparently almost linear excursion of the groundglass and definitely contact him regarding the appropriate model for the HC1 or mods you may need to do to yours to bring it to the same design.
Ignore my prevous post.
October 22nd, 2006, 06:49 AM
1. Yes, 5.6 was the lens aperture. But the lighting conditions and the aperture selection were made so to accentuate the "grain" (still don't know how to call it). I've tried 2.8 aperture with the 50mm lens under intense sunlight and you can see the diagonal lines as well.
2. No, the sound of my letus is the same I've heard in every sample here and the same it was since I got it from Quyen. But yes, the battery pack has been pulled out once on the tires accidentally. The pack fell and ended hanging on the wires but the wires are pegged down very firmly indeed.... since I hadn't noticed any difference in the motor's performance (at least sound-wise).
3. Yes, I forgot to zoom in enough.
So you say the motor's not moving the GG as it should? How can I fix that?
I'll contact Quyen and redirect him to this thread, and I will comment any news.
October 22nd, 2006, 08:02 AM
I'm really only guessing, but the wire conductor may have pulled through its insulation which may have become stretched on the outside and may be tethering the groundglass by a shortened and possibly gathered (crinkled) insulation on the inside. The glue bond to the wire insulation would still be intact.
Alternatively, the wiring may have rippled or coiled under tension of gathered insulation and may be directly contacting the side of the groundglass carrier. this would not make any added noise.
The orientation of the linear movement of the groundglass is consistent with the motor wiring pulling sideways left and slightly down on the left side. My recollection is the motor is high on that side of the groundglass carrier as viewed from the camcorder end.
Only a pull-down and inspection will tell the truth there. I didn't see any sign of a soft side to the image which would indicate displacement of the GG on its rubber mounts.
The Letus excursion tends to be a little more elliptoid than circular but yours is the most extreme I have seen, so I suspect there is a fault there somewhere.
If you feel confident to inspect it and can work very precisely, extracting the groundglass mechanism for inspection is a simple as undoing and completely removing the thumbscrew which holds the lens mount in place.
Once this is out, the front section which carries the mount will pull out of the tube and you can then study the motor, wiring and groundglass assemblywhich is attached to it.
You best have a vice with padded jaws with a light grip to hold the tube body as you draw the mechanism forward. It is a precisely machined part and is a snug fit in the tube and may resist being drawn forward.
There is about 18mm of shoulder contacting inside the tube or about as much as you can see when you look inside the hole after taking the lens mount out.
You need to take extremely good care to make sure it doesn't pull out suddenly, lurch sideways and the groundglass carrier accidentally touch the side of the tube, otherwise damage will be done. You also need to be holding the battery pack while you are doing this as the wires will pull up tight if you leave the pack on its velcro mount.
Wrap a piece of clingwrap over the end of the tube so nothing can get inside.
If Quyen is willing to undertake a check and repair for you, best let him do it as he knows his device best.
October 22nd, 2006, 08:02 AM
A member PMed me suggesting I should check the Letus without the SLR lens. So I did. The grain on the GG seemed normal, but when I turned the motor on, I could see the diagonal pattern when zooming in.
So, you're definately right Bob.
October 22nd, 2006, 08:19 AM
ahhhh, I get the same thing on my letus 35a and DVC30 camera once in awhile. It's not dirt, I think it's has something to do with lens's. This sometimes happens with my slower lens's in darker than ideal settings. The way I minimize it is open the lens all the way and stop down the camcorder iris a little. Or I put on a better, faster lens. Or I use more light. I have a vivitar zoom lens and unless i'm shootiing in bright daylight, I get those streaky lines. I can put on my canon 50mm 1.4 SSC lens and they are gone.
What gets me is that your lines are going the same direction as mine.
I've also noticed (may have to do with the speed of the lens) that lens's that have a smaller back piece of glass are more prone to this on my setup. don't know if it's just coincidence or if this has something to do with it.
my canon 50mm1.4 ssc and my canon 100mm 2.0 never get those streaks, my vivitar lens's sometimes do.
October 22nd, 2006, 08:26 AM
Okay I just checked the cables. They seem fine.
Oh well. I can just wait for Quyens reply.
Thank you very much for your help Bob, I really appreciate it.
Michael, I'm using a Canon 50 1.4 SSC and a 28 2.8 SSC and I get the lines with both if I close the aperture more than the lower setting (1.4 and 2.8 respectively). And I get it in bright daylight too. I think, after inspecting the device and reading Bob's posts, that it's the motor's fault, failing to make the GG's circular movement instead of linear/diagonal. So the lines would be the diagonal movement of the GG's grain.
By the way, I uploaded two pics of the cables, but I don't think they will help too much. Everything is well connected (or at least it seems). Oh, and the device (when not inside the tube) makes a buzzing sound only when upside down (if that means anything at all).
October 22nd, 2006, 08:32 AM
It is the GG. I can get the lines by stopping down my 50mm 1.4 all the way, then I rotated the whole letus and the lines rotate. hmmmm. Let me know what Quyen says.
October 22nd, 2006, 08:43 AM
What i'm confused about is, I stop down the canon lens to f16 and camcorder iris open, I get the lines. I open the the canon lens and stop down the camcorder to f16, I don't get the lines. almost like the GG has a light quota. As you can tell I know just about nothing of optics. hahaha
October 22nd, 2006, 08:43 AM
When looking at the GG without moving, the grain looks regular and normal. No diagonal lines. The diagonal lines only appear, at least in my case, when i turn the motor on. My conclusion is that the lines are the movement of the GG. If the movement was circular, the grain wouldn't be seen as lines.
I, too, get the lines in 1.4 but they are barely noticeabl; I had never noticed until I compared it with other apertures. The lines get more noticeable as you close the iris.
I sent a link to this thread to Quyen.
October 22nd, 2006, 09:14 AM
Ok, fixed it. I took the GG out and started up the motor. when looking at the pegs, you can see them, in my case, going diagonally, After inspecting a little, I thought the wires were a tad tight and the peg on that side was a tad tighter than the other two. I gave a little more play to the wires. Then I noticed that if I rotate the pegs that there was a spot where it felt a little looser or tighter. I Just rotated the pegs randomly at first, until I could see the blur of the pegs going in a circle instead of diagnal. Bingo Bango, now no more streaks. it's now just a more uniform grain. Bob is like a Genius or something.
October 22nd, 2006, 09:33 AM
What wires are you talking about? How did you give more play to them?
The pegs on my letus don't rotate, they're fixed. Could you explain further how you fixed it? I'd be greatly thankful, heh.
October 22nd, 2006, 10:08 AM
The wires that connect to the motor, they are glued to the plastic housing and to the GG. I took a razor blade (careful not to slice the wire) I cut away a bit of the glue to give them a little more play, just a little. They are kind of stiff too, so I moved them around a bit too. The pegs do rotate, they may not look like it, but they will spin (at least I can get mine to). basically it's a rod that has two rubber bushings that attach to the gg and then there is a rubber bushing that pushes into the plastic housing. you can loosen them up a hair around the GG to give it more play. Just make sure the rods are all fit in the same amount into the plastic housing. I noticed that one rod had worked itself out a hair more and had more play in it. I just played around with each rod (careful not to break the GG) until I got a more circular blur of the pegs when you are looking at the backs of them. Once I got them to blur in more of a circle and everything seemed to be good, I put it back together again and the grain was like grain instead of streaks.
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:
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, 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:
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.
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.
December 4th, 2006, 02:17 AM
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.
December 4th, 2006, 10:02 AM
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.