Dale Backus: Oh Frank, thanks for pointing me to your old tests - i checked out as much as i could and i was very impressed at the lack of grain, how was your system set up? I noticed a little vignetting and hotspotting, were you using a condenser?

Actually, I don't think any of those had a condenser except the one that mentions it in the file name. ("MicrowaxAdapter_Test_Condenser.mpg") So they could have actually been better as far as not having the vignetting if I had a condenser on them.

Later on I built one (held together with tape) that used a condenser from some magnifying glasses (the kind you would use in fly-tying or jewelry making). It worked well. http://70.147.193.182:81/mwtest/adapter_pic_05.jpg

Dale.
The 35mm motion picture image frame is 24mm wide. If you want to be faithful to the motion picture film look, then this is as big an area off the groundglass as you need.

A simple test is to cut a 24mm x 18mm rectangle out of a piece of paper, place this in the path on your groundglass and see if you camera is picking up all of the image area. You may find you are shooting inside of it by about 2mm.

Hey Bob
Great information.


Just to expand a little on this, let's not forget that the 35mm frame you mention is a movie frame, or what we know in stills photography as a half frame.

The 135 stills format is 24x36mm, since film passes though a 35mm stills (135) camera (and certain movie cameras) horizontally, not vertically, as in a regular 35mm movie camera.

So, if you're going to use 35mm movie lenses (in PL, Arri, BNCR or OCT-19 mounts or similar), you're going to want the movie 24x18 frame, but if you're going to use 35mm stills lenses (in Nikon, Canon, Pentax etc mounts) then you're going to want the 18x36 sized gate/frame.

If you use a stills lens in a movie gate (which you can, a lot of cinematographers do), then your lenses are going to turn out twice as narrow in angle of coverage and you'll be looking at twice the magnification on your focussing screen. Every stills lens turns out twice as tele when mounted on a movie gate or half frame camera. Which also means the potential for twice as much grain on the screen if you're using a fixed screen converter, etc..

Your typical movie lenses are very expensive, because to take a half frame 35mm gate and blow it up to the size of a cinema screen demands a lot higher optical engineering standards and build quality than a full frame stills lens does, just blowing up to a 16x20 print.

Here are a few more differences: movie lenses usually come with gears built in for follow focus, no click stops on their apertures (i.e. smooth aperture pulling), and a focussing helix designed for movies (focus pulling) and not for stills.

This means that one would typically have to rotate the focus ring on a stills lens some 270 degrees or more to get from infinity to nearest focus, whereas a typical movie lens would half that rotation amount.


HTH
Cheers
Chris

Thanks a lot for your awesome replies, guys. One question though, for Bob.

After reading your post several times i was tryin to figure something out... a relay lens (macro?) is necessary to potentially sharpen the image? Using my proposed lens layout: Lens < Condensor < GG < Achromat, would you still agree with this? OR do i need to put a Macro between the achromat and the GG? Does the achromat not act as a macro as well?

As for the Back Focus, the Letus35 HD100 comes with a backfocus lens that mounts directly to the HD100 body... is that completely necessary? My tiny little brain tells me if we just got everything at the perfect distance away to match the focal length of the JVC's imager, than we wouldn't need it? Thanks guys... really appreciate it

Guys you gotta help me!

I'm really getting down the the point where i'm starting to order stuff, and (due to my very limited cashflow right now) don't have a lot of room for screwing up. I read another post saying that with a 50mm 100FL Condensor, that would yield good results. Is there something wrong with using a condensor of shorter FL?

I really would like to know whether or not the Backfocus lens that comes with the Letus for the JVC HD100 is necessary or not.

Also, if i put a condensor in front of the GG, does the achromat need to placed at the FL of the condenser? It seems like something does, just not sure what.

Any help would be greatly appreciated. Thanks guys...

Dale

Chris Leong here
I'm building a DOF adaptor as well.

So what I figure is this:

Firstly, if your camera can focus down to within a couple of inches from its front element, then you can get started without anything.

Now I know you're buying commercial and I'm building, but the principles are the same, so check this out, please. I promise to be brief, but thorough.

Just in the design phase, I got a Nikon extension tube set, an old portable CD player that didn't work any more, a project box from Radio Shack, some of those milky CDs from the ends of those bulk CD packets, a battery holder, switch and potentiometer.

I think the most expensive things for me were the tube set (with Nikon mounts) and the potentiometer. Everything else was next to zero. (i.e. I had lying around the house anyway).

Okay, so then there follows a period of fooling around with actual construction vs what looks good on paper.

Mainly it was, for me, getting the motor that spins the CD mounted solidly enough not to lose focus, yet also isolated from the rest of the system so it would not vibrate/shake the rest of the system and not be too noisy. I ended up with a double mount design, one sturdy one with rubber shock mounts to isolate the entire motor/CD assembly, and one fine adjustment mount, also shock mounted but less so, since this stage is where I'm carrying the fine back focus settings, and has to stay where it's put.

At this stage, if your camera can focus on a 24x36mm rectangle at around 2" away or less, you can simply set the box with the mount and the Nikon lens up, spin the GG, and shoot the GG image as is.

Eventually you're going to have to find some way to fix the assembly to the front of the lens. I just ordered a Cavision 15mm rod system, but you can do what you want, as long as it's steady and won't fall apart before you're done shooting.

Now comes the fun part.

When the image is projected by the stills camera lens onto the spinning GG,
there's no frame, or gate on it. It's just a circular image on the GG.

You can frame as much of it as you want to, even have the corners fall off (vignette) by zooming out. Or you can zoon in and get just the center part of the GG image.

Now most zoom lenses will focus closer the wider they're zoomed out.
A lot of camera lenses won't actually focus down to 2" in front of the lens unless they're zoomed out.

So you're stuck with using the wider part of your lens.

Which is where CA (chromatic abberation) typically lives, at the edges of the lens.

So, in order to get rid of that part, and also to enable a more macro setting altogether, you add a glass/glass (achromat) lens doublet in between your camera and the GG so you can a) focus closer and b) reduce or eliminate the CA at the fringes of your image.

Also, if you find that your image isn't uniformly bright across your screen (i.e. is fading or falling off at the edges, then that's a sign that some kind of condensor may be required.

Now, what strengths to use? What diameter glass?

Well, that depends. What you really have to do is to learn your camera's lens.
By this, I mean that each lens has its own design compromises, construction cost being one of them.

A certain lens will not be super sharp at certain distances and at certain focal lengths (zoom settings).
At others, however, it kicks optical butt.

What you have to do is to get your camera working in those optical sweet spots, , where everything's at its sharpest and least distorted, and bring that sweet spot down to focus on your GG.

The catch-all setting for that seems to be a 10x macro achromat doublet, which is what most of the commercial DOF vendors are supplying.

If you'll notice, most high end 10x macro filters for stills cameras are, in fact, two element achromats, BTW.

What diameter? Well, that depends on your camera's front lens size and the size of the part of the GG you're shooting.

If you have a smaller video camera with only a 48mm front end, like an HC1 of the new Canon, then you'll not need to go much wider than a 52mm macro. And there are plenty of 48mm achromats available to you as well.

If your lens is wider, then probably a 72mm achromat would be useful.
Step up or step down rings (from 82mm to 72mm, for instance) can be used to adapt your particular camera lens to the 52mm or 72mm achromat sizes.
They're very inexpensive too, and not completely necessary, per se, for setting up purposes.

I'll say this again, so you're clear - the rings aren't necessary, you can just hold the macro filter up on front of the camera, or tape it there. You'll still get an image. Then you can refine it, fool with, set it to your own camera's sweet spot.

If you can get focus, an achromat isn't necessary either, . Just get one of those cheapo sets of +1 +2 +3 +10 closeup sets for your camera, available from eBay all day long, then fool with them and find the sweet spot on your camera's lens.

Obviously if you're starting with a larger achromat, you won't be using the edges of the achromat, so CA will be reduced compared to if you were zoomed full out and using the edges of the achromat.

Once you're clearer (after taping and screening several times) which settings are best for your camera, then you can sell the lower cost stuff back on eBay and substitute the higher priced elements.

It may be that you only need a +3 your lens to get its sweetest zoom setting to frame nicely on the image in the GG. Maybe with that +3, you're zoomed, maybye a third of the way wide, close enough to get by most all of the CA in your camera lens and in the +3 adaptor.

Maybe it's a +5. Whatever.

Point is, every lens design is different and so you've got to do a little hunting and pecking to get the best combination for your own camera combination.

To sum up - start off with the stuff you know you're going to need that's common to all DOF boxes - a box, a stills lens, a stills mount for that lens, some kind of GG.

If you need a macro set to help focus your camera on the GG image, then get one of those cheapo everything-in-it sets, and start experimenting with all of the various diopter strengths (maybe it will end up by being a +5, then a +1, for instance, that seems sharpest to you).

Get everything working, tape stuff, watch it. Change one thing at a time and shoot some more stuff. Better? Worse? Check the colors at the edges, the brightness at the corners. Any distortion at the edges? Keystoning? Barrel distortion? CA?

Settle down on the best combination of video lens focus, video focal length / macro lens length / GG to camera distance (the GG to stills lens distance will, of course, be fixed). Then upgrade your components and build it out nice.

Quite Easily Done.

HTH, YMMV, etc.

Cheers
Chris

Ha, thanks a lot Chris.

That was a big help. It made me realize that it's a process. My JVC HD100 has interchangeable lenses, i'm going to see tomorrow if i can get away with adapting straight the the body of the camera, without having to use a backfocus lens. Someone once told me it needs the backfocus lens, but i want to be sure, because that's another 1 or 2 stops i can have back if i don't need it.

I will definitely give your process a try. Also, those Nikon lens tubes seem like the way to go, can you point me to a good place to find those?

Let me know how yours goes... i'd love to see some test footage sometime. What camera are you using?

Thanks again, really.

Chris.

Well written.


Dale.

You are stuck with using some kind of lens on the JVC HD 100 for relay, whether it is the original which came with the camera plus a close-up attachment on front, or a smaller substitute prime lens.

Relay using the original camcorder lens and a +7 Century Optics 58mm in 72mm sleeve mounted onto the focusing barrel of the JVC lens is quite effective, certainly to the 720P limit of the camera. The whole thing is awkwardly long however.

The dioptre has to mount to the front of lens and not to the 82mm fixed filter mount because the lens barrel comes forward or backward as you rotate it.

The adaptor, I mounted to the 82mm filter mount which is part of a fixed shroud around the lens barrel the light shade fits onto. Watch for crossing the threads. This shroud looks like metal but is actually plastic which is why you cant clamp around it as the pressure deforms it onto the lens barrel and jams it.

The downside is that for this method you have to cut an 82mm filter thread into a custom adaptor mount which is not an option for many people.

The front of the JVC lens has anti-reflective flutes cast into it. This portion of the lens is also plastic.

While there is no thread there, one of the flutes is of almost the same diameter as a 72m filter mount so it is possible for testing purposes to carefully screw the 72mm achromat's72mm filter thread into this small ledge and have it bind in place.

Easiest is to hold the achromat square-on and rotate the lens barrel as the thread binds into place.

Optically, there is only a short range available in adjustable distance from groundglass to front of achromat. You can use the backfocus on the JVC lens to help find the groundglass if it is just outside the lens focus adjustment but if you use the backfocus to fix your final setup, your zoom movement will no longer hold focus.

Thanks a lot for the help, Bob.

An update for those who are interested:

I've been experimenting heavily with methods of microcrystalline wax as my ground glass. I'm using microscope slides for the glass, and microwax for the GROUND :). At first i tried a mixture of beeswax and microwax. It applied nicely, and i was surprised with the results, but i decided to give 100% microwax a try. The microwax is far more sensitive to the imperfections in the glass, so the main obstacle is coming up with a way to clean the glass PERFECTLY. I've been experimenting with methods, but haven't had a lot of time this week to tinker with that specifically.

I tried the microwax with two layers of double-sided tape, and that yielded a very nice finish. It was almost perfect and with much less noticeable grain the the beeswax and microwax mixture (about 5-95 mixing ratio) So even a small amount of the beeswax added quite a bit of grain. I'm not having trouble at all getting the capillary action to work with the microwax alone, but the evenness varies every time. I still strongly believe it has to do entirely with the cleaning of the glass. I then tried using one piece of double-sided tape between the glass, and it still worked, but with more noticeable "cleaning" marks. It wasn't bad at all, but it looked good because there was a substantial amount of difference in the translucency between the two. It seems you could almost get another half or full stop by cutting the thickness in half.

I'll be working on a test rig soon, so hopefully i can post some pictures and footage in the near future.

one question though... I chose microwax because that's apparantely (or atleast in some form) what MovieTube is using. I heard they use a mixture however - any idea how his system can result in such a grainless static solution, especially if he's not using pure microwax for GG?

Thanks guys...

Look for waxrex 2405. it's next to impossible to get, but it's a big rumor that is what g35 used and it's slightly yellow in color, another rumor that is what the color of the g35 had.

Way way back in Noah's time or so it seems, when the earlier experiments were going on, I vaguely and probably incorrectly recall there was reference to the Movietube and boss screens. Apparently the magic potion was 15% beeswax in paraffin wax I think??????

Microscope slides look smooth and even but I think you will find that they are not dead flat, therefore between two, you will get variations in wax layer thickness. I found when grinding them for fixed groundglasses that there were high spots on them.

There is a correction to make on my previous post. I referred to a 72mm 7+ achromatic dioptre. What I neglected to mention was the the dioptre I used was a Century Optics 58mm filter mount 7+ in a 57mm to 72mm ring.

The diameter as applied to the front of the JVC standard lens was still 72mm as mentioned but so far as I know, it may not be possible to get a 72mm 7+ dioptre.

There's a few .jpgs of some old wax experiments of my own at

www.dvinfo.net/media/hart

right at the bottom of the list you will find at this address.

They were large CD-R sized spinning disks. Wax rules but I found it impossible to control the thickness evenly which resulted in unacceptable flicker of the image.

Very interesting - i heard in passing that Movietube used paraffin and beeswax, but then heard they used microwas. I looked around and learned that microwax was characterized by extremely fine crystals, which seemed ideal for a static GG, especially for HD. The paraffin and beeswax mixture seems like it would be terrible for a static solution.

Overall, what did you find worked best for you? You seem to have been around this topic for quite some time, i'd be interested to know what you think is ideal.

It would be VERY nice to figure out a static solution, but i wouldnt' sacrifice that for an inferior image. I went through the Agus thread a bit, and he had some amazing looking stuff. Can you buy Agus35's anywhere, or is there a tutorial on how to make them?

Thanks Bob

Half a day with my greasy fingers on P+S Technik's latest groundglass making machine to make a larger than standard groundglass would do me fine.

However, dreams aside, for home-building, real glass remains my preference, dressed with five micron aluminium oxide and a very slight backpolish with cerium oxide to pick up a little more brightness.

Wax is better. Jim Lafferty has been doing some interesting stuff with an alternative.

Most recently, I have seen some interesting fogging on lenses from bad UV cure cementing of elements. This is caused by contamination of the bond by unclean glass, stuff like oil or moisture. This fogging is transparent but experimentally might be provoked to groundglass opaqueness.

I'll leave that to others to play with as I am not too keen on toxic chemical exposure.

AGUS35 is more or less a generic expression of many of the designs. The original form is CD-R retail case, opaque CD-R disk, CD player motor and hub, switch and battery power, close-up lens if needed.

Jim Lafferty published a project box version a while back and the makers of the Redrock M2 publish a home-build project box design and support it with a supplied groundglass disk and dioptre.

For the home enthusiast with adequate manual skills, the project box versions are the most predictable in terms of acceptable results as the cases are flat sided and the right-angles and parallel faces are already accurately established.

This link is to a look around inside my own device.

http://www.youtube.com/watch?v=CnweOEEqlRY

There are other better and more thorough designs. The only thing that this one has going for it is capability to accommodate case build errors of up to 5mm.

Ah, thank you for clearing that up for me.

Very interesting, i'm glad you got something that works for you. Any test footage taken with your preferred adapter that you could point me to?

We did run into something yesterday with our own stuff. We've been poking around our Letus35 HD100 ever since we've been flirting with the idea of making our own adapter. We took the GG out yesterday and compared it up to the light beside the wax GG i made a couple days ago.

The grain is UNBELIEVABLY more noticeable in the Letus GG. It could be somethin like 5 - 10 times more grain than the Microwax GG i made. The Letus is a vibrating method, as you probably know, so the fact that it vibrates lends itself to more grain as it is because no matter how fast it happens, it has to stop to change direction at some point, and it doesn't vibrate that quickly at all.

We're thinking we can replace the ground glass of the Letus with our Microwax GG, and get much better results. The Letus is a great adapter and provides excellent results, the abundance of grain at HD is really it's limiting factor, (besides the 1.9x zoom, which we'd REALLY like to not have...).

I'll let you know how it goes - we're excited though.

You may be pleasantly surprised at what a wax groundglass will do for you in the Letus35. There will be no variable density flicker problem like you get with a spinning disk.

There are practical reasons for the smaller GG area scanned by the JVC HD100 and Canon XL versions.

The area is faithful to the motion picture film image size. The groundglass texture Quyen uses becomes a bit coarse at that higher magnification but there was never any cause for concern over ghosting from aerial image penetration.

He uses a reversed biconvex element between the GG and his relay lens, I presume as a condensor, so I would not expect edge or corner brightness falloff to become an issue at that magnification.

Depending on the thickness of your wax layer, you may get some ghosting from aerial image coming through.

The added mass of your wax GG may be a problem for the small motor Quyen uses unless you can find thinner glass or can devise an even wax layer on a single layer of glass.

The CD sized wax disks I made up were totally scitzo, either smooth or severely out of balance to the point of breaking the wires off the motor. They were less noisy than the single glass disk which is acoustically live. They were heavier and it took longer for the motor to spin them up to speed.

If there are any stray larger grains in the wax mix, these will show as soft-edged freckles when the groundglass is vibrating.

The microwax you use. Is there a product brand or description. The nearest thing I can find here is a water emulsion used for waxing apples and it does not work.

Thanks, Bob.

http://www.spwax.com/spparaff.htm

That's where i ordered my wax. I told them i needed a sample for experimentation purposes and they had the wax to me in a few days it was very impressive. I'm pretty sure i got wax number 19. It has the highest melting point of the 3 softer microwaxes, and i thought even though it was probably harder to work with, it would be safer to use outdoors inside a black metal tube. I haven't found i too troublesome to work with though. So far the only method of applying the wax i've used is for getting a thin layer between to layers of glass by using the capillary action method. I'm sure you know what that is. It works brilliantly, even with microwax alone (or, without paraffin or beeswax). The results are a wonderfully low-noise GG. The problem is though, the thinner the layer you go, the less room for error there is, or so it seems. At first i tried using two layers of DOUBLE-SIDED scotch (duct brand, actually) tape (mainly because it was nice to have the glass stay held together during prep). I had very good results with that, even with the microwax. It seems the quality of the application depends pretty much entirely on how well the glass is cleaned. I found (especially in the thinner applications) that there would be visible streak marks and such in the wax when it dried. These were streak marks that obviously weren't visible the naked eye though, so there's no way to tell before you do it. (i'm not really a scientist, so to me anyway)

Then i tried one layer of double-sided tape, and the the streaks were a little more apparent. I want to be able to perfect this amount of thickness, because i want as little light loss as possible. The double layer thickness of microwax compared to Quyens GG, has a more opaque value that i'm trying to get away from.

What did you mean when you said, "The area is faithful to the motion picture film image size." Are you talking about the area of his GG, or the area the actual imager picks up?

Also, what is aerial image penetration?

And lastly, since you seem to know your Letus... when you open the iris of the backfocus all the way up, you get some serious image distortion. Any idea why that is? I don't know what to call the image distortion right away, it's been a while since i've seen it, but it would be nice to use the top speed of the lens, if you know what i mean. Thanks a lot

Dale.

Thanks for the wax info. I noticed on the website there is reference to the wax being compatable with synthetic and non-synthetic resins. I wonder if it can be blended wth UV cure optical cement used for bonding doublets. If so that might be a partial means of stablising it against heat effects.

By aerial image penetration I mean if the groundglass is not opaque eough and you can see through it, therefore a little of the sharper aerial image gets through and can be seen by the camcorder as well as the soft focused groundglass image. - ghosting, a soft area around a more sharply defined object.

The image area or field-of-view aquired off the groundglass itself is dictated by the use of the 50mm focal length Minolta still-camera lens and the unmounted achromat Quyen uses on front of it and the imaging area of the 1/3" CCDs.

I stuck a 2/3" cam on back of the same Letus35 and did not pick up the GG frame edges. The result surprised me as I thought I would have picked up the edges of the mirror path as well.

I think it comes down to about 22mm to 24mm wide seen by the 1/3" CCD when a 50mm lens is used for relay.

With my own gadget on a iSony FX1, when I use a close couple and +7 achromat, it picks up the edges of the prism path if I zoom back furthur than about 40mm and this limits me to about 22mm - 24mm width off the groundglass.

The image area from the LETUS35 for Canon XL I have here was comparable.

The P+S Technik Mini35-400 I had a play with gains a bit more image width off its groundglass. Literature on the Mini35 a while back referred to an image area off the groundglass of 21mm but I think that might be an older version.

As for the distortion of the image on wide-open relay aperturethere are so many variables it would be difficult to pin it down without optical knowledge and some serious equipment. The Minolta lens is a still-camera lens designed for a 36mm image width at the focal plane.

In Quyen's arrangement only an 8mm (1/3") centre of the available image width is used, therefore the sharpest zone of many such lenses, the centre of its image is used.

There is an achromat on front which might introduce distortions at wide apertures, a reversed biconvex element about 15mm behind the groundglass which also might introduce distortions and how centred the biconvex element and the achromat are relative to the Minolta optical centre axis and to the 3CCD's on-chip optical centre axes is anyone's guess.

Then there is the CCD wedge itself which requires special optical design in the lenses feeding it because of its prism.

Still-camera lenses apparently are less likely to perform sharply at wide-open apertures than cine lenses. It is apparently an issue of design and cost.

Because the 1/3" CCD is using an 8mm centre out of this lens's available image arrea at the focal plane, any softness introduced by wide-open apertures is going to be proportionately magnified compared to what is apparent on a 36mm image from the same lens. I think this is something users will have to live with.

P+S Technik's own relay lens (apparently by Schneider-Kreuznach accordingto past readings here at dvinfo) is a very serious piece of optical quality by comparison to the Minolta consumer level lens on the Letus35. It is also very seriously priced. My guess is you could buy one and a half Letus35es for just the cost of the P+S relay lens alone.

This is where the cost-benefit debate begins and that is another story.

Also.. what is that thing the GG is mounted in, in the Letus. If i were to replace it, i might want to leave his GG fixture intact and make my own from scratch. Thanks...

The groundglass mounting panel itself which also carries the motor is something you would have to ask Quyen about. It could be a trade part from somewhere or custom made by Quyen or by a third party for him.

If I was substituting, I might be tempted to make one out of a thin clear heat resisting plastic and stick a second thin plastic or glass transparent panel onto it with the wax layer.

If you are going to take his motor out and change it into your replacement panel, the chances of you buggering up the little motor are pretty good. He has encapsulated it, an added tiny dropping resistor and the fine soldering connections with adhesive.

It is a tiny can motor and the little end panel which carries the feed-through solder tags/commutator brushes is only retained by two bent tags which are part of the metal case of the motor. These are not very robust and wll not tolerate much wrestling while you cut adhesive away.

Best to buy in another motor for your own customised groundglass carrier.

Hi Dale,

if you need a carrier for your groundglass. Just gimme a drawing.
I have a little cnc-machine that makes pretty cool stuff :-)

best regards
Daniel

http://www.jetsetmodels.info/news.htm

Yeah, we'll probably build one and use a new motor.

http://www.hobbyengineering.com/H3425.html

Will that motor do the trick you think? I have no idea how powerful Quyens is, so i have no idea if this one is strong enough. Thaaanks.

Thanks Dan, i'll definitely keep you in mind!

If you are, interested we are working on a solid aluminium box with brushless micromotor (silent, fast and durable), polycarbonate treated GG and a really good self designed Barlow lens, apochromatic (apo) it produces high-contrast edges and brilliant colors, correcting even better light different wavelengths.

The release will take a bit of time anyway, got to be optimal. You will be able to put it in front of every type camera, HD or SD, theoretically this is not a problem to me, i produce one single image, don't matter what electronic eyes you have.
Thank you all!

Ettore!
What happened to you? Isn't this your thread?? LOL!!!

I've built my first adaptor (I call it a DOF Box) according to your and other's incredible posts on this thread, and while I'm happy with the results, they're not as good as yours, so I have many more questions!

Firstly, has anybody been able to confirm or deny that Ettore's 320 grit paper is a universal size? Or is 320 grit in Italy the same as 1200 grit in the USA?

I have been polishing my blessed GG for hours now and have not been able to get entirely rid of the scratch marks on the GG left by the polishing/sanding with 320. It seems better with 1200 but Ettore specifically mentioned not to go finer, hence my question.

I've also found that if you sand in a radial manner (i.e. at 90 degrees to what would be the grooves on a record) then when the glass spins the lines go away easier.


Secondly, a 6v source for a micromotor or a motor out of a 3v CD player works much better than a 3v source. Confirmed that myself so far, but maybe someone has gone further down this road already?


and thirdly, a single achromat, while okay, seems to me to fall off more than a system with a PCx as well. I posted a question on a separate thread about the Redrock M2's internal rear of stills lens PCx design. Is that to combat this problem?

Or is the falloff mainly just a function of the GG's grind?

Comments, Ettore? Anybody?

Thanks!

Okay, more results for people who are thinking of sanding their own revolving CD GGs.

I've found that the clear CDs in those CD stacks come in many different flavors.

While I was looking through Ettore's site on the smaller adaptor he's built, I realized that his (smaller) GG was cut from the clear portion of a CD case.

This is made of much thicker plastic than the clear CDs I've been choosing to start sanding on thus far.

So last night I went through my batch of clear CDs and picked out a thicker one, and...

well, you can guess the rest.

Much, much smoother. No overtly visible scratches. Relatively little sanding required (as compared to the hours of patient sanding I've been putting in so far).

I thought the thinner, almost flexible ones would be better since they had less mass and would spin flatter.
They possibly do, but also require a far finer grinding technique than I've been able to come up with by hand.

Last night I also tried a little Nivea just to honor this thread, and finally was able to see for myself what you guys have been talking about all along.

Liked it. But it's not necessary, just have the GG spinning very fast and grind it out very smooth., like you've all been saying.

Just waiting for a condenser lens to add behind the GG and I'll be ready to send some decent footage in. It's already pretty good now, just not as outstanding as it could be.

High standards, around here...