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Old February 24th, 2004, 05:39 PM   #331
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Hi Jim

1-Shure you have to remove the glass from the ring.

2-That's why you have to start whit bigger grain , to make the surface of the glass even .Sometime you could put a bit of pressure in the center but not much.

That's the reason why you need two pieces of glass plus your filter, you grind on one for a time and then you change for the other one .Otherwise the surface of the glass you'r using for grinding start to become uneven .(concave)

Hope you understand, I am missing some english word to explain it more clearly.

By the way I whil send you some new image in 1 hrs.

Alain
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Old February 24th, 2004, 05:46 PM   #332
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Jim I was thinking of using the same thing - uv filter on a ring.

Here is what I was thinking of doing:
Get a small round mirror from a craft store, a small suction cup like one from a childís toy dart, attach a shaft to the suction cup, the cup to the backside of the mirror and the shaft to a dremel, then buff away.

I have not done this yet, but that is my plan. Although I may have a hard time keeping it even.
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Old February 24th, 2004, 05:54 PM   #333
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Move the filter, not the tool

Hmmmm - I've always understood the grinding process as this (and I think this is what Alain is describing).

Take a large piece of glass - say 8x10. Put it down flat on a clean work area. Put your grit mixture onto this and smooth it out a bit. Then you take the glass from the UV filter (or whatever your real ground glass is going to be) and put it down on this 8x10. Space your fingers out evenly across the back of the filter and work it in circular motions on the much larger piece of glass. So you're moving the UV filter across some larger piece of glass... not putting some tool to the stationary uv filter.

This is what Alain means... after a while, the area of the 8x10 will get ground in under the pressure from your filter, and you either have to move to a different spot or get a different piece of glass
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Old February 24th, 2004, 06:00 PM   #334
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Alain: how did you remove the filter from the ring?

In your original image of the ground glass -- the close-up -- it's still in the ring after being ground. I'm confused :/

- jim
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Old February 24th, 2004, 06:08 PM   #335
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In order to remove it, you must have one of the filters that has a 'retaining ring' (not all do... my Hoya is completely unopenable). If it has a retaining ring, you'll usually see two slots across from one another on one side of the filter. You use something called a 'span wrench' which is like a double-headed screwdriver which stretches across the filter and when its in the slots, you turn it, lifting out the retaining ring.
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Old February 24th, 2004, 06:12 PM   #336
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Jim

Yes ,because I put it back on the ring so I can use it to screw on my other parts.
My adapter is made from aluminium tubing that screw on each other

Normaly the tiffen filter have a ring that you unscrew to remove the glass, but take care they are somtime hard to remove.Take care to not scracth you glass and not to scrap the screw or (filets in french)


Jonathon
That's it . But I normaly change from one glass to the other every
5 to 10 min.

Alain
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Old February 24th, 2004, 06:12 PM   #337
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Filter Removal

Jim, most of the filters I've seen have an inner ring that needs to be unscrewed from the outer ring, thus releasing the filter. Professionals use a spanner wrench to do it:

http://www.edmundoptics.com/IOD/DisplayProduct.cfm?productid=1457

Expensive stuff... Look at their Instruction Sheet )PDF file), you may want to make one...

P.S. You guys type too fast, I'm always late with my replies :).
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Old February 24th, 2004, 06:17 PM   #338
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Alain, what kind (size, source?) of tubing are you using? I'm still playing with PVC...
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Old February 24th, 2004, 06:21 PM   #339
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I have remove it whit a small screwdriver but whit precaution.
hold your filter whit something realy steady ,like a vice ,and that's it

Alain
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Old February 24th, 2004, 06:24 PM   #340
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Damn, this is an annoying detail I wish was included earlier.

My filter has these two notches seated opposite of eachother, so I'm assuming this is a retainer ring filter. The thing doesn't want to budge, though :/

edit: nevermind

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Old February 24th, 2004, 06:27 PM   #341
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---Alain, what kind (size, source?) of tubing are you using? I'm still playing with PVC...


I have use part's of len's that I have unmount to make my adapter.

I keep everything,and turn it to something else. :-)

Alain
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Old February 25th, 2004, 12:17 AM   #342
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theory to thoughts...

i'm just amazed at how addictive this project is for everyone. we are discussing lot's of different issues at once, it's crazy and great at the same time...

so here is what i've figured out so far... ideally you WILL affect the image quality using a FRESNEL lens, so optimally you want to go with a cheap and better CONDENSOR LENS like here, http://www.edmundoptics.com//IOD/DisplayProduct.cfm?productid=2032

secondly, you can use a GROUND GLASS or as a better quality alternative a HOLOGRAPHIC DIFFUSER-but they are expensive, unless your on the Euro...

so far the K.I.S.S. (keep it simple stupid) seems to be the ideal configuration, which goes as such for a standard DV cam:

PRIMARY LENS+spacer+GROUND GLASS or HOLOGRAPHIC DIFFUSER + CONDENSOR LENS+spacer+[if you need a +7 or greater macro]=mounted to the DV lens

at this moment i'm crawling up the walls trying to figure out a better method for xl1/xl1s version as it seems a bit tricker-you can almost put a lens right up to the CCDs themselves-so this creates much more complex optical arrangement that needs to be optimized.

comments, thoughts, quips?

back to work...
-D
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Old February 25th, 2004, 07:48 AM   #343
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Condenser Lens Specs?

Hey All,
This thread is amazing! I stumbled onto it accidentally and havenít been able to leave it alone. I started building my Agus 35 when I found the separate Alain 35 thread and so Iím building both simultaneously. Iím at the point where I now need to install a condenser lens to help with the hot spot in the middle of the image. My first question is, what are the condenser lens specs others have used? Does it depend on my choice of SLR lens or are all of you using the same condenser lens? I followed the link to the Edmunds optics condensers but I have no idea which lens is right. I read in a thread earlier that a condenser from an old slide projector might work. Has anyone tried that?
Second, does the condenser lens really go between the GG and the camcorderís lens? You are still focusing on the GG with the camcorder lens, right? So you focus through the condenser lens? This doesnít make sense to me as I guessed that the condenser would spread the light more evenly across the GG as it does with a slide projector. Can anyone set me straight on this? You all are amazing. Thanks for a totally entertaining project.
Oh, BTW, can anyone provide a link on more info about the Hollographic Diffuser mentioned by Dino in the previous post?
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Old February 25th, 2004, 08:12 AM   #344
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http://www.edmundoptics.com/IOD/Disp...productid=1363

That's Edmund's holographic diffusers - pretty expensive. In general, I've found most things available at Edmunds for up to 75% less in other places. Holographic diffusers, unfortunately, are not one of those items I've found anywhere else :-(

I've learned some interesting things messing around with the optics removed from my 35mm SLR.

All of the optics involved (other than the objective lens) are rectangular and exactly 36mm x 24mm -- the size of a 35mm film negative.

However, the round objective lens definitely 'sees' a circle - which is significantly larger than the 36mmx24mm footprint.

One thing I've noticed about my rectangular optics is that they seem to be completely covered, evenly, with image. I can't help but wonder if some of the corner distortion others have seen comes from not zooming in quite enough. With a circular image on a ground glass, I would think it would be hard to gauge where the 'true' 36x24 frame lies...

An Agus builder could theoretically draw a 36mmx24mm rectangle right onto the ground glass - and focus their camcorder on this rectangle. I'd bet they would find significantly less distortion within the boundaries of this frame (especially with a condensor or two). Alternatively (if you didn't want to mark up your hard-earned ground glass), you could insert another piece of glass with the marked frame.
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Old February 25th, 2004, 08:14 AM   #345
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Here's an (unfinished) article on the cropping I'm talking about... be sure to read pages one and two - the cropping is shown on the second page...

http://www.digitaldingus.com/articles/fov/fov.html
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