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Old May 16th, 2007, 04:43 AM   #16
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Noah Yuan-Vogel,

I have yet to try the Snod35 on an HD cam. My guess is that it would perform as well as the other pre-made adapters though. I'm basing this on the fact that I have shot in very low light and at high f/stops with little to no sign of grain.

As for the spacer rings. I bought them from an ebay seller. I haven't seen them listed lately though.

Here is on old listing just for reference:
http://cgi.ebay.com/72mm-Spacer-Ring...QQcmdZViewItem

..and here is the sellers ebay store:
http://stores.ebay.com/ASIAN-CAMERA-LLC

A note about the 72mm spacers... they work great and are a decent price, but I have come across a few that did not thread into each other well. I don't think they are cut and threaded to precision, but again I have only come across a few that were duds.

I'm not sure how well the 62mm spacer would work. The ground glass holder only needs about 2-3mm of room around the edges to vibrate, so I would imagine that you could slim things down enough to fit.

FD mounts (and most mounts) are around 45mm inside diameter and 55mm outside diameter.

I'm not sure what you are asking as far as the "filter" goes.

Rich Hibner,

I would use step up/down rings as Cole mentioned.
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Old May 16th, 2007, 09:01 AM   #17
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Thanks for your answers. I'm just waiting for some parts and then we will see how it goes. i'm planning on trying a different focusing screen option though since I'm not yet sure I like the idea of grinding my condenser lens. the results I have seen from CD groundglasses have looked pleasing, so I intend to test CDs as well as some other polycarbonate and acrylic samples with varying grit sandpapers I've ordered. If anyone has any suggestions regarding what yields best results, I'd love to hear it. polycarbonate? acrylic? effect of grinding at varying coarsenesses? My understanding is that less grit allows more light transmission, so imagine with a oscillating solution it will be best to find the coarsest grain that also works in terms of resolution, grain, diffusion.
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Old May 16th, 2007, 12:25 PM   #18
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Grinding is very slow and I never had good results. There are always scratches that is very hard to remove. Aluminum oxide dont leave scratches, so try to find sand dust of this kind. gg has to be rough and shiny at the same time, but then you got vigneting problem that you have to solve with aditional condenser lens. Daniels wax tutorial is great and wax grain is perfect but you loose to much of light. I think that best is to leave all this and yust buy Canon focusing screen.
It is very good, no vigneting and very fine grain.
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Old May 16th, 2007, 12:37 PM   #19
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When i said grinding I meant with aluminum oxide powder. I used to use an optosigma 1500grit groundglass which had some issues with transmitting some aerial image. With the results ive seen other people getting from spinning sanded CDs, i figure it will be much easier to cut and sand a bunch of polycarbonate squares and have easily exchangable and replaceable focusing screens. from the samples ive seen with such focusing screen materials, the transmission characteristics seem quite favorable. working with plastics could just make things a lot easier as opposed to glass. I'll let you know how it goes. In my experience, pre-made canon/nikon focusing screens are great in terms of low-grain and certainly of better quality than i'd likely be able to create on my own, but i think they lose a lot of light. Plus, plain matte focusing screens arent as easy to come by as I'd like. I guess if things dont work out, i could always buy a used beattie intenscreen focusing screen at b&h for $65
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Old May 16th, 2007, 01:25 PM   #20
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Huan, this is my test with ee-s focusing screen. Left side is clean screen, right side is pasted (just for testing;so its very clumsy looking) with microcrystaline wax (nivea baby cream...). This is 4 stops gain and very slight vigneting.
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Old May 23rd, 2007, 11:13 PM   #21
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I have had great results with grinding my own glass. I did several tests with various grits of aluminum oxide and silicon carbide. In the tests I critiqued the images for hot spot/vignetting and for grain. The best overall image was from the glass ground with the 12 micron aluminum oxide.

For the best results, fully rinse the glass every 5 minutes or so (Your gg and the glass that you are using as the base surface). I found that with 12 micron aluminum oxide I can get a nice ground surface by grinding for a total of 20 minutes. So, that would be four, 5 minute grinding times... stopping between each to fully rinse both pieces of glass.

Using 25 micron aluminum oxide or 500 grit silicon carbide will slightly improve the glass's ability to diffuse the light. In my tests however, the difference was only slightly noticeable with very wide lenses (28mm and shorter). I can use my 35mm with the 12 micron grit aluminum oxide glass with no signs of vignetting. My 28mm does fine most of the time depending on the setting. The 25 micron aluminum oxide and the 500 grit silicon carbide are much more difficult to grind and often leave several noticeable pits in the glass surface. Also, with these two grits of lapping powder, the grain becomes an issue.

I tested the Canon Ee-a and Ee-s screens and noted an equal amount of vignetting/ hot spot (compared to the 12 micron aluminum oxide glass). I have also made a variety of wax screens (as per Daniel's tutorial). They seem to perform well aside from the light loss. The one issue with using the microscope slide glass is that they can create strange linear-shaped lens flare. Otherwise, I think they are great as well. My experience is that making the wax screens is much more challenging than grinding. Much of the success of the wax focusing elements depends on the thickness of the wax (distance between two glass slides) and the mixture of wax that you are using. I have looked for coated slides in hopes of eliminating the strange lens flare, but haven't found any yet. I know Edmond Optics sells very thin optical glass sheets that are coated. This would most likely solve the lens flare problem with the slide glass.

Finding/making a good GG is a challenge. I have been very happy with the 12 micron grit aluminum oxide glass, but I'm sure there are other good solutions out there as well.
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Old May 24th, 2007, 05:13 AM   #22
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A long while back reference was made to there being different microstructures to the pits created by sililcon carbine and those by aluminium oxide. The carbide pits are more like long chips out of the glass rather than near-round pits.

These can apparently be of such magnitiude as to require much dressing with the finer aluminium oxide to diminish them.

20 minutes by hand? I have been using a tumbler which cycles at about 95 per minute and for each stage I give them about 3 hours before I am satisfied the grade is even across the entire surface. This is however for full CD-R sized disks, not smaller focus screens.
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Old May 24th, 2007, 02:36 PM   #23
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Hi Justin,

Thanks for posting your tutorial online, very well done. I have a question as I await 1 pound of 9micron Alum. Oxide that is in transit. I will be using your method to grind the Nikon F3 focus screen. I believe you mentioned somewhere that you had been using your screen with only SD cameras ( not HD ) ( is that accurate ? ) and because I will be using it on an HD camera I thought I would try 9 micron ( also finding 12 micron aluminum oxide proves to be a bit more difficult in small quantities so I justified the purchase of 9 micron believing the higher resolution of HD would show the 12 micron grain too much ). I know you prefer 12 micron but I would like your opinion on what results I should expect with 9 micron. Is it a total waste of time ?
( I am using Daniels vibrating holder and have been testing with the Nikon D element and see quite a bit of a "hot spot". Also, I am curious how much pressure you use when grinding , would you call it firm, or light pressure ?
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Old May 27th, 2007, 04:29 AM   #24
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Bob,
That could very well be true, but I'm honestly not sure. From my tests, 500 grit silicon carbide came in at a close second to the 12 micron aluminum oxide. In my brief experience with grinding, I found that aluminum oxide of 25 micron and up caused too many chips in on the surface. The 500 grit silicon carbide will make a nice surface that is slightly rougher than a surface ground with the 12 micron aluminum oxide. The only issue with the 500 s.c. is that it is just rough enough that the grain becomes a slight problems in low light (and there is slightly more light loss). The advantage of using 500 s.c. over the 12 micron a.o. is that it does a slightly better job at diffusing the light. It is a very slight difference though, and frankly may just be due to the way I did the tests.

Jake,
You are right I have only ever used the Snod35 (and ground F3 plano-convex) with my DVX. Grain has never been an issue with the 12 micron and the DVX, so I would guess that it would do fine with HD as well. This would not be the case if the GG was stationary however. I would hesitate using the 9 micron aluminum oxide. The grain will be much finer, but the surface will most likely not be rough enough to hold the image on the surface, which will result in a hot spot. You might be fine in most situations, but as you use a smaller aperture or when the scene has a good deal of contrast, the hot spot will become evident. You may also notice that the image becomes progressively more yellow/brown as you close the aperture. It is worth a shot, but you might want to give it a good test run before fully trusting it to important footage. I have got great images with 3 and 5 micron grit aluminum oxide, but only with good light and a large aperture. Have you tried http://willbell.com for the 12 micron? You will have to call them; you can't order the lapping powders from their site. They have mailed small quantities of 3,5, 12, and 25 micron aluminum oxide in the past.

I used a Nikon D screen for a while as well. I would say that as far a grain goes the D screen is comparable to glass ground with 500 grit silicon carbide. The D screen is slightly brighter than the 12 micron aluminum oxide glass, which may be related to the hot spot that you mentioned. Keep in mind that vignetting and hot/spot may decrease as the the GG is moved further from the camera's lens. How far you can move it all depends on the camera and achromat you are using. I have tested various distances between the GG and the camera and honestly have not see much, if any, difference. Just FYI.

As for the grinding... I was thinking of putting together a quick video tutorial of how I grind the glass. Easy to say of course, but hard to find the time to actually do it. For now, to answer you question about pressure when grinding: You don't need to apply very much pressure at all. In fact, it is more like you are dragging the glass across the surface while applying very slight pressure. Using less pressure will not hurt anything; it will just take longer to grind. Too much pressure though can cause large pits (large in comparison to the microscopic pits that you are trying to get). Hope that helps for now.
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Old May 27th, 2007, 10:21 AM   #25
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I'm having some hotspot problems. So far I've only tested 150 grit sandpaper and 800 grit wetordry sandpaper. Both have so far resulted in too many surface scratches and a significant hotspot. I'm grinding an acrylic square that is placed behind a nikon condenser like the one ground for the snod35. Looks like way too much aerial image is getting through. Any recommendations? I thought the 800 grit would be better but if anything it showed an even more distinct hotspot. I'll have to test my 1500 and 2000 grit soon. Seems like it's just not diffusing enough... anyone know if maybe it's the way i'm grinding? Maybe I just need to grind longer? I mean it looks fairly well ground to me after 5 min or so of grinding since it's plastic which grinds pretty quickly.
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Old May 27th, 2007, 12:26 PM   #26
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Sand papar is not going to give you good results (in my opinion). The silicon carbibe and aluminum oxide are lapping powders used refine the surfaces of lenses. The grit of these powders is totally different than sandpaper (ie: micron grit). Also, I would suggest using good quality glass instead of acrylic. Acrylic is probably just too soft compared to glass to get and nice even surface.
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Old May 27th, 2007, 02:09 PM   #27
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Hmm... But I like the qualities of some of the spinning CD adapters ive seen and CDs are polycarbonate. Those are usually accomplished by sanding, right? Also, from what I understand, 800grit aluminum oxide sandpaper should be about equivalent to 12micron grinding aluminum oxide grinding compound in terms of particle size and grinding qualities. Youre saying its better as a free moving powder as opposed to a powder thats been glued to paper? Is there a significant difference? Maybe i just need to use glass instead of polycarbonate/acrylic. I wonder if its alright if i still use the same sandpaper. Maybe I can try grinding the focusing screen that i got the condenser with. I wonder if the split prism in the center can be sanded off or if it goes all the way through....
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Old May 29th, 2007, 02:17 PM   #28
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Thanks for the advice Justin, I have on order the 12 micron Aluminum Oxide from WillBell ( via phone ~ it was $15 for 8 ounces ). In the mean time I shot a bit with the 9 micron nikon f3 screen. Here is a little clip ( compressed to appletv format ). 35mm f2.0 nikkor lens.

http://idisk.mac.com/jaked/Public/35mm_9micron_test.m4v

Once I test the 12 micron maybe I can determine what is causing the vignetting, the nikon lens or the ground glass....

I am happy with the results so far ... thanks to you,Daniel Schweinert, and the many that contribute here.
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Old May 29th, 2007, 08:00 PM   #29
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Jake,
I couldn't get the clip to play well on my PC. I will take a look at it again on my Mac later. From what I could tell though (played choppy), It looked pretty good. Were you using the ND filters on the camera? Just FYI, you have to use actual ND filters in front of the 35mm lens and not the ones on the camera. The true test for the 9 micron is to close down the aperture. If all is well, the color should look the same and there shouldn't be any hotspot. If the focusing element is not diffusing enough light, then the images will turn a yellowish brown and a hot spot will start to show up (as the aperture is closed down).

Was the lens 35mm as in focal length? Keep in mind that many wide lenses will cause vignetting depending on the brand and quality. So you are smart to test other lenses as well. It was hard to tell the way it played on my PC, but it didn't look like there was any vignetting.

Keep pressing on.

Noah,
I know that the M2 uses a plastic focusing element. The focusing element of the M2 that I opened up did not appear to be ground. It was about 3mm thick and was a milky-white translucent plastic. Maybe some have got it to work, but it would seem that attempting to grind plastic would just cause too many large scratches.
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Old May 29th, 2007, 10:20 PM   #30
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That makes sense since I have noticed the softness of plastic results in very fast grinding so it is very sensitive to unevenness and more prone to scratches. A harder material would grind slowly and would even out more easily. I will try grinding my focusing screen, and if that doesnt work well, my condenser lens. Anyone see any potential problems with me using this on my canon HV20 with no achromatic diopter? At the moment it is configured so the focusing plane just fits in the frame when the hv20 is full wide and it focuses on the plane with no problems whatsoever. Could be the most compact vibrating 35mm adapter ever at a length of less than 2" and a maximum diameter of 62mm. Just have to get it to work right...
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