Homemade 35mm Adapter

[Brett Erskine]

Rai-
Buddy you are DEAD on! Thats a perfect example of how to make a smooth, professional oscillator. Our designs are so similar its scary right down the where and how its counter weighted. I looked everywhere for off set shafts that are ready made but couldnt find them (at least not that small). You have to make me some of those. If anyone else has a idea of where you can get some let me know. I may have to have them computer lathed. My set up makes it oscillate alittle too wide.

Im on the hunt for a ultra quiet motor. What do you plan on using? Im hoping to find a tiny 7.2v DC motor so that I can just use another camera battery to run it. It would be nice to know what the RPMs of the P+S Technik motor but my guess is at around 1000rpm we shouldnt have any problem. Early on in this project people were using motors out of CD players but reported that they didnt spin quite as fast as they needed to. Then again back then people werent using quality GG or focusing screens so maybe it will be fast enough now. A CD player motor runs at 500rpm. Going alot faster will insure that you wont see the grain but you have to remember the faster the motor the noiser it generally is and you dont want to pic up the sound of the motor in your on camera mics. 1000rpms sounds like a good ball park because we are oscillating the GG instead of spining it. But the best solution would be to have a variable speed controler on a motor that can go alot faster than that. Why? Sometimes we shoot at 1/500sec shutter speeds instead of 1/48th. This quick shutter speed is sure to catch the imperfections on the glass if it isnt oscillating fast enough.

I wouldnt change anything on your design ;-) Everything looks good. I could only recomend that you add a few things that you havent shown yet. Make the mount the motor and the oscillating mechanism on the same plate and when it comes time to house everything in a project box have the everything inside attach to the project box by mounts that have rubber bushings. This is the best place for them. I noticed that you are using rubber bushings where the bearings sit. This is a good idea because you made your own off set shafts but if you switch to some that are precision made (all exactly the same) I would loose the rubber bushings because they cause a little slack in a system that doesnt need it at that point. It some speeds it might actually create strange vibrations if you have the bushings there. You want thoughs three points to be solid.

Lastly if you havent already made it you might find it alittle easier to build if you have 4 off set shafts instead of three. Its easier to find something ready made with 4 holes pre drilled equally apart than 3 holes in a triangle. But more importantly you can make your over all design smaller then. The reason is the off set shafts dont have to be set so far out from the ground glass in order for the O ring to clear it. This is even more aparent if you plan on using a rectangle shaped focusing screen instead of round GG. Personally Im going to go with a Beattie Intenscreen or a Minolta Acute Matte focusing screen. These screens are anywhere from 1 to 4 stops brighter than anything else out there and our adapters need all the light they can get. They do however use fresnels to focus the light instead of a optical lens but Im starting to get real tired of buying a bunch of different plano convex lenses trying to do the same job. As many of us know the optical quality of fresnels arent as good as a plain lens BUT these Minolta and Beattie screens use a much finer etched fresnel lens then others out there. You cant see it. They are perfectly calibrated to give you a even field without any hot spots as well. They are extremely light weight which is a must if you plan on oscillating it. Lastly the microscopic fresnel rings act to contain light that would otherwise diffuse alot more with traditional GG. The result is a sharper image with more contrast. On top of that you can increase most of these advantages if you use a medium format focusing screen instead of a 35mm screen. Grain gets smaller and image gets sharper and has more contrast by at least a factor of 4X. Now this is all true if you plan on using medium format lenses but you can also use 35mm lenses with at least some of the benifits mentioned. You cant use a 35mm sized focusing screen anyways on a oscillating style adapter because the focusing screen needs to be a bit larger than the target area of the lens because its oscillating. You can also get alot of them pre mounted in a frame. Perfect for attaching to your off set shaft.

Alright I better stop there and save the rest for later otherwise people wont want to read all of this info because the post is too long. Anyways Rai since we are working in the exact same direction we really have to work together on this. Email me and/or post info on parts and I'll do the same.

Brett Erskine
BErskine@mail.com

P.S. What camera are you using? I've got a source for cheap DVX100 battery docking mounts to power the motor.

[Bob Hart]

Brett.

Have you examined making your eccentric shafts in the manner small-scale aero engine cranks are made.

They make the shaft and crank wheel as one piece but press a hardened pin into an offset hole.

The optical application would not impose anywhere near the loadings that an internal combustion engine does so it would be feasable to press a simple plain shaft into a crank wheel as well.

I imagine your machinery could stack drill three crank wheels to sufficient accuracy. It is a whole lot easier than setting up a fourjaw chuck to these accuracies.

You could then use needle rollers as used in automotive universal joints for the crank pins. These have a fine hardened finish to a standard none of us could hope to match. You might even find larger rollers for the crank shafts themselves.

Getting the holes to size and finding a strong enough press in a home workshop environment would be an issue but this is the way I would go about it.

It might be worth a search on the Sarich Orbital engine. It was an innovative design but was a commercial dead-end because automotive piston engine production lines would have had to have been heavily redesigned. Instead, Sarich moved to licence the supporting techologies such as fuel injection.

One of their early difficulties was with the idler cranks. These were not driven but were free locators for the orbital piston which ran on a centre crank. The problem was to be resolved with "diaphragm bearings". I don't know how far they took this but I think it was an innovation to permit larger tolerances in mass production machining and misalignment in fit-up.

I think these operated in a similar manner to self-aligning roller bearings.

[Bob Hart]

Since last test on the 5 micron oharadisk I have tried two clear disks with a layer of 90%/10% paraffin wax and beeswax blend. The two disks were separated by pieces of alfoil arranged around the outer edge and are permanently embedded in the composite disk.

I found difficulty in getting a consistent grading of crystallisation across the entire disk. The grading appears to be no smaller than 5 micron aluminium oxide which has been allowed to wear to exhaustion and backpolish has commenced.

Early tests indicate the resolution does not appear to have improved.

Variable density flicker is apparent in high contrast lighting conditions.

Subjectively the colours seem to be richer.

The glass disks used were rejects due to cracks. These were not in the image area but I was not keen to use them and risk scratching up my lenses if they flew apart. With two disks bonded together with a wax layer that is no longer an issue.

The glass-wax composite disk is much heavier - (2 x 0.9mm plus thin wax layer). I expected severe run-out and vibration across the focal plane however the wax disk runs perfectly true. Run-up and run-down of the motor takes much longer.

It is also much quieter as the wax dampens the ringing of the glass disk. The single glass disk was transmitting more motor bearing noise than the plastic CD-Rs.

When I capture some frames I'll ask Chris Hurd to post them. So far the rotating "boss screen" looks promising and capable of furthur improvement.

ADDENDUM: The images from the composite disk are named "waxds002.jpg" or similar.

[Bob Hart]

Furthur to above, Chris Hurd has kindly posted the .pdf files, the filmlooked Agus35 frame and the wax composite disk tests as www.dvinfo.net/media/hart.

The wax disk seems to require more diligence on white balance than the other versions or direct into camcorder. There is a 1.5 f-stop density variation around the disk which is where the flicker is coming from, so more work to do yet.

The matching faces of the two glass disks may have to be finished to plano specs which is beyond the capability of my home made finisher.

Due to the low melting point of the wax blend, it should be feasable to make composite disks out of dressed CD-R disks or CD-R spacer blanks. They may have to be temporarily stabilised by glueing to a firm face. - So maybe the wheel travels full circle, back to plastic.

[Bob Hart]

Furthur to above, I have requeseted Chris to post another .jpg of a wax composite disk image which was shot in overcast conditions against the light also a proposed layout for an erecting version of the plumber's AGUS35 as a .pdf file. This file should not be used as a builder's diagram as it is yet incomplete. It looks bulky but is so due to need to use available low cost components. It should not be overly heavy.

[Chris Hurd]

Those have been uploaded... see http://www.dvinfo.net/media/hart.

[Bob Hart]

SOME NOTES ON THE AGUS35 ERECTOR PD150P VERSION.

If anyone is developing along the lines of the erecting Australian plumber's version using PVC sewer pipe, some issues have emerged.

The use of pipe caps for the lens and camera mounts. - There are a few suppliers of plastic end caps. Whilst they all comply with the dimensions of the pipe they are meant to cap, some are thicker and more robust than others. I suggest staying with the Iplex cap which is thicker, provides material to machine down and seems to have a slightly higher melting point.

The vertical position of the image tube may have to be amended in the side view published in www.dvinfo.net/media/hart. To provide clearance for the camcorder mount, the tube centreline has to be offset to the right relative to the SLR lens centreline which introduces a close fit to the left lower diameter of the front cap for the lens mount. If machining it directly into the cap as I do, this may not matter but if metal mounts are used, there may not be sufficient material for them to be screwed onto unless the image tube centreline is lowered about 12mm (1/2").

If the appliance is to be entirely supported by baseplate and rods and the end cap needs only to block light and carry a hole to pass the image to the camcorder, this offset may not be required.

Due to the wider diameter there is now a greater span between the upper edge of the lens mount and upper edge of the front SLR lens mount cap. Use of heavy or long SLR lenses may require a metal plate to be added inside the cap for support or for a metal mount to span the full internal diameter of the cap to prevent trembling of the image. The use of a baseplate and rod mounting system is recommended for the appliance in this circumstance as the camcorder itself will likely fall apart.

The original idea of using ply or craftwood caps to hold the prisms down onto the prism parterplate will not work for two reasons :-

The timber will bend because large holes have to be made to pass the image.

To be strong enough, they have to be too thick. This adds too much distance to the optical path for a 4+ dioptre to frame the 4:3 academy frame without zooming in all the way which then introduces too much light loss.

The traditional method of retaining the prisms with small bars is recommended. Do not use rubber as an anti-chip cushion. It will comply or cut through and the prism may drop out. (Did in my case onto cement = lamentations.) Hard woollen felt has been a good substitute so far.

For the parterplate, craftwood has turned out to be a scizoid beast. It is fine grained, routs and carves nicely but has poor strength in the horizontal direction. It delaminates randomly with drilling and fitting of screws. Compession between two pieces of hardwood is recommended for this task.

[James Hurd]

Does anyone know a way of getting rid of the *pattern* created by the spinning CD grain? I've got some 1000 AO arriving monday. Has anyone used this on a plastic cd?

Here are a couple of pics of my rig so far. I'll be working on the rods in the morning. The video is of my wifey. She was on a computer so don't let the blue glow fool you. (The matte blox was just for fun...)

http://www.sunrushmusic.com/agus35/1.jpg
http://www.sunrushmusic.com/agus35/2.jpg
http://www.sunrushmusic.com/agus35/Test1.wmv


Thanks for any comments!

[Bob Hart]

I am unsure of the "pattern" you describe. I am assuming that it is a scintillation or moving film grain style effect.

If this is what you are getting, it is I think caused by pinpoint highlights occurring in the disk image sharply and intensively enough to register is a motionless object in a single frame even though the disk is spinning fast enough past the camera view to eliminate texture from the image.

It should by and large go away when you achieve a finer groundglass texture on your disk.

When you dress your next disk, get hold of a sharp scalpel or fine trimmmer blade and remove the raised ring in centre of the data area of the disk and the raised rim. You can dress these off with a coarser grade of abrasive but at the inconvenience of having to dress out larger scratches in the image area.

These larger scratches are a real pest with plastic. The only solution is absolute cleanliness and very little pressure.

I achieved a good finish by rolling one in a tumbler I made for dressing glass disks, in about 15 minutes. You need to mount the disk to an accurately flat circular object slightly larger and firm, not flexible. Keeping the dressed surface of your disk flat is essential otherwise you are going to make yourself a lens or two or three or more around the disk and you will get movement of the image however slight which will degrade it.

Beeswax, candlewax or paraffin wax is good for mounting for our purposes. It melts below boiling point of water and seems not to injure the disks so far. I do it by placing the disk (in my case glass oharadisks on my flat pieces of metal), putting this on top of a ceramic topped electric cooker then turning on the element below to a slow setting, waiting for the wax to melt and spread beneath the disk, then sliding the whole thing off the hotspot to a cool place on the stovetop for the wax to set. With a flastic disk you may need to keep it pressed flat with another perfectly flat object on top of it through the whole mounting process of melt to cool down.

Dont dismount it on the stovetop but cook it off in a pot of water. You don't need to boil it. When the wax floats off pick up as much as you can off the water surface with tissues befroe hauling the disk out.

If it is a glass disk you have to let it cool down in the water after it has been separated from the baseplate. A plastic disk can probably survive the sudden cooling in air without warping.

Cleaning off the wax is hard. With glass you can peel it off with a fine razor blade. With plastic that is not an option as you will scratch it. A trigger spray laundry stain remover (Preen) seems to do it followed up with a water and detergent wash, then metholated spirit or blue window cleaner.

If you dress a CD-R, then use this method to polish off the metallic layer.

If the finish is a little too opaque, you can back-polish with a soft dry flannel cloth or felt to restore a little transparency. This is best done by putting the disk back onto the waxed baseplate and dressing lightly against a flannel stretched over a flat surface. A table or benchtop corner would be adequate. If you polish by handholding the disk, there is too much chance of variable density around the disk and undesirable flicker in the image. With 1000 grade AO, I don't think you will need to back-polish.

No guarantees.

[Bob Hart]

Initial tests with the erecting path through 40mm right-angle prisms are encouraging. These have been done with the prism assembly unenclosed so there is some whiteout. There is light loss via the prism path and this seems to aggravate any tendency towards hot-spotting.

Provision for fine parallel adjustment and right angle adjustment of the prisms relative to each other appears to be essential as the image skews noticeably even with only a minute defect in cutting the mount channels in the parterplate. A metal plate may be the only realistic option as the timber is too compliant when the mount screws are tightened up.

[James Hurd]

Thanks for the response Bob. The pattern that I'm seeing is the grain of the CD spinning. I'll try a couple of your ideas and see what happens!

Thanks again!

[Bob Hart]

*pattern*

I forgot to ask if you are keeping the camcorder shutter speed at 1/100th of a second or slower. 1/50th is better but not always an option. A fast shutter speed is going to cause the motion of the disk to be frozen in each frame which will cause a random grain pattern.

If your camera is auto and won't allow you to control the shutter speed, then you may find you have to reduce the amount of light into the camcorder with neutral density filters to force the camcorder into longer periods of exposure per frame. Unfortunately, having learned on film cameras, I don't know the equivalent electronic terms for shutter speed or exposure time.

[James Hurd]

Thanks Bob!
I remember reading that from one of your posts. I'll try it (my camera supports many shutter speeds)! I played around with some wax last night. It looked pretty good at first, but when comparing it to the frosted CD, it looked like I was going to be losing quite a bit of light.

Did you say using 1000 AO would work on a plastic CD?

Thanks!

[Bob Hart]

Wax.

It needs to be a thin layer. Thats when the variable density problems occur. I tried a thicker layer but found the severe light loss you described.

From my informal tests so far, it seems the losses through a thicker wax layer plus an erecting prism array may bring the "film speed" of a PD150 camcorder from around ASA320 down to about ASA50 or slower which for my purposes will defeat any creative advantages the system provides..

So I am staying with the glass disk for the time being as the resolution on the spinning disk does not seem different, only the grain in still frames is less evident on the wax image.

The AO should work. If you hand dress your disk on a piece of glass, make sure everything is absolutely obsessively clean. A scritch on glass becomes a great gouge on plastic. Also don't use too much pressure but let the slurry do its work unhurried.

If you use a razor to trim the raised areas on you plastic disks, wear gloves and bend the blade into a slight curve and use a slicing action. With practice this works fine. A Stanley knife blade or snap-off blade is better. Use a lateral rocking motion to ease the blade along at about 25 degrees inclination if you have not enough fine control over it. It is less likely to skid off across the disk into the image area.

[James Hurd]

At least for moving glass.

I have a vinal plotter/cutter machine to make stickers, signs, etc. Well several years ago I made a sign out of a thin vinal material to was supposed to mimic etched glass. So today, I took a clear cd, stuck the vinal on the cd and trimmed the excess sticker off. It's amazing. Absolutely no grain or spinning pattern like I got with the pre-frosted cd from maxell. I also compared it to the cd I used AO100 on and it's clearly a better picture with no hotspot. To be honest, I think I'm through looking for ground glass! And, I've got a 100' X 1' of this stuff!

Now for the erecting! (and maybe oscillation...)