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Old June 25th, 2004, 10:55 AM   #931
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Rai, have you considered microlens array focus screen as GG?

It is totally grainless even to my hi-res HDV camera.

Please see here for the detailed discussion and pitfalls:

microlens focus screen discussion
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Old June 25th, 2004, 01:03 PM   #932
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agus35

Hi everyone I would like to ask for some help

I am looking for a part for my agus 35. I would like to find a way
to adjust the distance between the slr lens and the ground glass the agus 35 is made with 52mm filter rings. I found some things on a telescope site that almost work this would also help with my anamorphic lens ------- thanks in advance
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Old June 26th, 2004, 06:31 AM   #933
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Alex,
>...have you considered microlens array focus screen as GG?
>It is totally grainless even to my hi-res HDV camera.

You say it is totally grainless. Did you really test that? That can not be. It does not exist any grainless GG. A GG must even have grain, but it is just a way you look at them. A GG for a still camera is make for human eyes, and not for HDTV. You cant see any grain, but the cam see it. And microlenses are a bad way, because they have a repetition stuktur, as a lattice, and with a videocam it will produce moree´. Test it out, you will see, but if you find it work nevertheless, let me know details...
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Old June 26th, 2004, 07:09 AM   #934
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Richard.

Your enquiry says Agus35 so I presume your device is a spinner. I used a plate in the enclosure with three holes arranged in a triangle layout. Three threaded pillars face backwards and fit these holes. On those pillars are small hard coil springs. On top of each is a washer. (I used brass because it is easier to turn the adjustment by hand.) The plate goes on top of the washers. More washers go on top of the plate. A nut pulls down onto each washer. This gives adjustment in two axes relative to the lens centerline and distance adjustment from the lens. The pillar layout looks thus ---

----O-----Disc Centre-----O----




---------------O---------------

If your device is the Aldu version made of stacks of adaptor rings leading to a fixed groundglass, then I don't have an answer except perhaps to keep taking rings out or adding them until your backfocus is close, then taking one out, then cheating a half turn on each segment to lengthen until backfocus is correct, measuring the total of the added length, then dressing the contact face of each ring including the ring you took out, shorter so they all together make that length.

The other option is to make thin shims out of food foil which fit the screw hole pattern of your SLR lens mount and spacing the mount away from the focal plane with them until the backfocus is correct. You may be able to get some adjustment of your fixed groundglass inside its holder by the same means.
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Old June 26th, 2004, 08:05 AM   #935
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aldu 35

thanks bob your right .I was talking about aldu 35 . the problem is the filter spacer won,t get me to the adjustment I need. close but not a sharp focus


something like this http://www.harlequinastronomics.com/otheradapters.html
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Old June 26th, 2004, 03:19 PM   #936
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Rai, regarding microlens GG you wrote:

> You say it is totally grainless. Did you really test that?

Tested and re-tested.

Seems that because there's about 2 million micro lenses in the 24x36mm field, each lens element is therefore too small for even HD cam to resolve - but yet they do the job as a great ground glass with very little loss of light, too.

See here:

http://www.dvinfo.net/conf/showthread.php?s=&threadid=22456&perpage=15&pagenumber=4
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Old June 26th, 2004, 04:14 PM   #937
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Alex,
>Seems that because there's about 2 million micro lenses in the 24x36mm field, each lens element is therefore too small for even HD cam to resolve...

This does not convince me yet, because 2 million micro lenses on 24x36mm. That´s 2315 lenses each mm˛, but only 48/mm (on a string).
24x36 is a 3:2 format. A camcorder works with 4:3 or 16:9. Therefore a 16:9 picture is max. 24x13,5mm. If your HD cam works with 720 lines, the cam "see" 53 lines/mm, but there only 48 mirco lenses/mm. That cannot be invisible.
In order to make it invisible, it would have 2 ore more lenses each line. With a 720 line HD cam your GG would have 106 or more lenses on a 1 mm string. That means 11236 each mm˛ or approx.. 10 million for the GG. With a 1080 line HD cam your GG would have 160 lenses on 1 mm = 25600 each mm˛ or approx.. 22 million for the GG.
I had tested many GG, also Minolta, also with micro lenses, but i never found a grainless one.
Tell me the part no and i will test your GG on a optical bank and with a HD Cam, because i am open for all working 35mm parts
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Old June 26th, 2004, 04:37 PM   #938
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Rai, part number and a link to the store that sells it is in the thread I referred you too. See my previous post.

Regarding your doubts: I see what I see. Every other GG produces grain. Minolta does not. Period.
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Old June 26th, 2004, 04:55 PM   #939
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Alex, I believe you, but i would also like to see it. In the thread, they talk about minolt GG Type G and Type C. Which exact you mean?
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Old June 26th, 2004, 06:45 PM   #940
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Could anyone post a sample pic of this ground glass from Minolta?
How do you manage the problem with the markings?
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Old June 26th, 2004, 09:06 PM   #941
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minolta screen

hi everyone this is a link from the other thread

http://www.bhphotovideo.com/bnh/con...=minolta+screen
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Old June 26th, 2004, 09:30 PM   #942
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Posting a still image from a GG setup proves little. A slow image pan with parts of the image out of focus is the test I'd want to see. You see, the grain will only show up as being static if there is motion.
A media9 video of 8mbps would let you see it.
-Les
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Old June 26th, 2004, 10:41 PM   #943
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Les is right.
Also the link is useless.
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Old June 26th, 2004, 11:04 PM   #944
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Richard.

Sorry I cannot be of any help. In setting up are you attempting to work both the camcorder to groundglass focus and groundglass to SLR lens backfocus at the same time.

The only other suggestion I can make is that you make up a target, whiteboard marker lines on the groundglass to intially get that focus at optimum, then direct your SLR lens to a cardboard target, (beer carton or whatever with sharp printing on it) at a measured distance from the groundglass, set your SLR lens by the focus numbers on the lens barrel to the same, then adjust the space between the SLR lens and the groundglass until you get your sharpest image. If you measure from your groundglass to the lens mount face, it should now be in the ballpark of 46.7mm for Nikon. What the others are I don't know.

You've probably done all this stuff already but there it is anyway. Good luck.
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Old June 27th, 2004, 11:22 AM   #945
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Rai, here's the link to the GG. It's Maxxum type G.

http://www.bhphotovideo.com/bnh/cont...=173377&is=REG

The picture does not show any markings but unfortunately they are there. Plus, there's a very faint but still visible small circle right in the middle. Markings appear carved on the flat side while, while circle is on the curved side. Makes this lens unusable.
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