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Old June 28th, 2005, 11:28 PM   #1
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Fresnel to get rid of hotspot?

I've tried a Beattie screen and I've tried an Optosigma GG, I like the grain on the Optosigma, but I don't like the grain on the Beattie. The other major drawbacks on the Beattie are the price and availability....

So I've been trying to get rid of the hotspot on the Optosigma with condensers (still working on that), and wondered if something like this would work attached to the back in the same manner as with the Beattie:

http://www.physlink.com/estore/cart/...eet.cfm?SID=37

Or one of these:

http://www.edmundoptics.com/onlineca...1AA6897F1CEAC4

Has anyone tried this?

Cheers
Andy

Last edited by Andy Gordon; June 29th, 2005 at 12:00 AM.
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Old June 29th, 2005, 02:19 AM   #2
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Woah weird I have one of those screens from the first link...and eventually (once my garage is evacuted of all the useless junk that parts me and my tools) I'm going to try and use that for my single element adaptor. I haven't actually tried it as a fresnel, but it is huge. Also it has these long ruts in it that I think will show up in your image (kinda like those ridges on holographic materials)
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Old June 29th, 2005, 03:36 AM   #3
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Quote:
Originally Posted by Andy Gordon
Has anyone tried this?
Yes, it works. But you have to hold Fresnel close to GG (if wants to rotate, its almost imposible). And get fresnel with very good resolution, or you will endup with image similar to digital zoom used :)
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Old June 29th, 2005, 05:45 AM   #4
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But the ones Andy posted do nothing at the size of a GG. I just tested it. You see very big lines and it does nothing to the hotspot. If you are going to make a static adapter, the best option would probably be a condenser lens.
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Old June 29th, 2005, 05:49 AM   #5
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If you choose good one, you can get what you want...

http://web.datriware.com/gfx_photos/articles/p849.jpg
http://web.datriware.com/gfx_photos/articles/p850.jpg
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Old June 29th, 2005, 09:57 AM   #6
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Fresnel

I have the edmunds optics fresnel lens #NT32-589.

it does a nice job of elimintating the hot spot, but the grooves (prisms) are large and show up as concentric rings on the image. I was doing some reading about fresnels, and the size of the prism grooves are a balance between efficiency and image quality. Smaller grooves = higher resolution, bigger grooves = brighter image, loss in resolution.

The edmund screen could be sanded or blasted to make the flat side a matte finish and used as a bright screen if it were oscillated to eliminate the groove pattern. Could be the best of both worlds, high efficiency and high resolution.

Maybe?
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Old June 29th, 2005, 11:09 AM   #7
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Quote:
Originally Posted by Donnie Wagner
The edmund screen could be sanded or blasted to make the flat side a matte finish and used as a bright screen
Only to end up with a "home made" version of the real thing. Right? Arenít you guys lucky to find some answers without spending a dime?:
http://dandiaconu.com/gallery/album20
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Old June 29th, 2005, 12:16 PM   #8
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Quote:
Originally Posted by Dan Diaconu
Only to end up with a "home made" version of the real thing.
rotf... I just saw the shots :)))))) I have tried this also :) Looks similar, maybe little bit better... But... what can we want from 20 cirles :)

Hey, Dan... I cant see any grain there, are you oscilating it ? Can you take it with Z1 in HDV, so we can see the resolution... What about the light loss ? Are you going to sell it ? lol
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Old June 29th, 2005, 02:03 PM   #9
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hmmmmmrrrrrr..... that is the way to end a thread. Some of us had more fun with these toys than others. Previous solution is a good and inexpensive way to "practice" with a Fresnel type screen but unsuitable (imo) for revenue (sale, rental, production) Movement is unsuitable due to COARSE Fresnel. Even if it would work (somehow), why go all that trouble to shake a lesser quality screen? Do the best, use the best, get the best! Cut corners and corners will hunt you down. Quality of work and choices we make is what sets some apart from others (same goes for shooting, directing, editing, driving, etc) Do you think I "enjoy" spending close to $US 200 on a screen? and then $%#^@& my pants while I handle it so the money don't go down the drain? (as they did while learning...) My 2c.
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Old June 29th, 2005, 02:48 PM   #10
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Dan, but I have tried this four months ago... Not making fun on this. And I posted pictures with much better fresnel, that works ! Important is to have fresnel side to lens and then GG. Of course there is much better and more expensive way without stress...

What just makes me laught is your shot. I know its better to show it, than talking thousands words, but its too funny. In the other hand, it costs 70 cents here :) But If you take better fresnel lens (where you cant count circles by eye like on this one), you will end up with much better result. What I tried, is spinning matte glass with static fresnel facing SLR.
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Old June 29th, 2005, 03:37 PM   #11
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good. all clear.
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Old June 30th, 2005, 10:58 AM   #12
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I thought I was the only one that %$^@@ my pants!
Dan out of all the images so far, you seem to have the most success with a focusing screen as far as image brightness. Now that all the camera manufacturers are going that route, shouldn't they be coming down in price?
I agree with you Dan, spending $200.00 is alot for anyone, but I guess you had the guts to go for it, for that, I salute you.
Now, if I could only find a Focusing screen at a charity shop...
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Old June 30th, 2005, 11:04 AM   #13
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Quote:
Originally Posted by Mandy Leo
Now, if I could only find a Focusing screen at a charity shop...
Hey... visit eBay... Where do you think I bought Maxwell ? I am from Europe, we do not have Intersceen or Maxwell here. And on eBay there is a lots of Beatties... I bet you can get it for $40, or get any for $20 (with scratch or so) for testing.
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Old June 30th, 2005, 12:48 PM   #14
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Quote:
Originally Posted by Mandy Leo
Now that all the camera manufacturers are going that route, shouldn't they be coming down in price?
They should, shouldn't they go dam nit! But they're stubborn, ainít they?
Quote:
Originally Posted by Mandy
you had the guts to go for it, for that, I salute you
Yeahh.... such guts! Doing NOTHING takes a lot more guts! I was a coward! (;-0)< But I salute you back, you're not a veggie either.
Quote:
Originally Posted by Daves
or get any for $20 (with scratch or so)
hmmmmm..... why bother scratching them myself when I can get them scratched already...(save some laundry money as well)...damí...why didn't I think of that? Thanks Daves!
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Old June 30th, 2005, 04:03 PM   #15
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OK, back to the subject of this thread, I am still in the experiemental stage of my adapter. I have been changing my mind of which path to go down, spinning or static. I think im going static. Anyhow...

I took my old 35mm cam apart to get at its ground glass and fresnel lens. this fresnel CERTAINLY has a possitive effect at both brightening the image and getting rid of the hotspot. Only thing is, this fresnel is too small for an adapter and has a centre hole.

So, since that 'test' was successfully, i was looking here at fresnel lenses:
http://www.knightoptical.co.uk/acata...ndardrange.htm

but im not sure what to pick. they state a focal length for each, but what would i choose? same as the 35mm lens im using?

Anyhelp here would be great.
Cheers,
Wayne.
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