please help me with condenser lens Im really stuck

A

Albert

New member
Hi all,

first I have to thank all of you guys that made this forum.
This is a great information source with great people.

Can someone help me with my problem?
Ive build a spinning 35mm dof adapter that works good but I have a hotspot that I cant eliminate completely. Its visible at f5.6 and upper. Ive spent much money on different lenses and parts and now im really really stuck :cry:.

Ive used several condenser lenses:
DCX (doubleconvex) d50mm / FL 100mm
bi-aspheric d55mm / FL 50mm
PCX (planoconvex) d50mm / FL 100mm
PCX d50mm / FL 77mm

The bi-aspheric is good but I get barrel distortion and soft edges.
By using the DCX the distortion is gone but I have a slight hotspot.
The PCX has color abberration.
The lenses were mount between gg and camcorder. Approx. 15mm from gg.

I read hundreds of these old posts but Im totally confused now what I should use finally for the condenser lens and at which distance from gg to eliminate the hotspot completely. Ive tried pretty much and its definitely the condenser lens. My SLR Lens is a Pentax 55mm / f1:1.2 and my camcorder is a small sony trv 120.

Thanks
Albert
 
Hi Wayne thanks for taking your time to help me.
Its a little sony trv 120 with 37mm threads. The distance from gg to my camcorder lens is 70mm. Its already a very long adapter I think.
May it be possible that one DCX +10 is not powerful enough?
The +20 bi-aspheric lens would work fine but it has this distortion and soft edges. What lens would you recommend me?

PS. I dont use an achromat because I can focus on the gg by zooming in.

Albert
 
I tried to incresease the distance but the hotspot remains :-( .

Someone a solution for this problem?
What condenser lenses do you use in your diy adapters?

Albert
 
Albert, i built my own spinner too, it would be best to post a thumbnail from your tests so we can see if your problem is a condenser. It could be your GG. What type are you using by the way?

Ted
 
Hi Ted,

I made my disc out of a acrylic plate 2mm thick I didnt used a cd. I made the same spinner like Ettore Giraldi and sanded it with 320 sandpaper.

Heres a test picture.
SLR lens was at 5.6 and the +13 PCX was used as condenser. Is +13 enough? What condenser lens do you use because I dont know how strong it should be.

http://www.mypicshare.com/7a8dzeb8pic.html

thank you
Albert
 
Its you GG Albert. Its not diffused enough and is letting a lot of aerial image through. Once you get that GG figured out then we'll figure out your PCX issues, before i got an achromat, I used a stack of closeups equivalent to +11. It was already sufficient, even the achromat from Dennis wood, for his brevis, is around +10 is what i'm using right now.

For now, your GG needs work.
I use a frosted CD and the image is acceptably smooth and sharp for me.

I tried the sanding a clear CD method, but I didnt get it even and frosted enough thus getting similar results you got.

I'll post my test shots below so you can guage what a frosted cd can do.

The set up is frosted CD from (maxell? not sure though) and achromat from Brevis.
I'm using a 80mm mamiya lens at f1.9. the close up is 150mm at f3.5

1181966474.jpg


1181966619.jpg
 
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Hi albert,

can you do a light-bulb test with your diffuser?
Put your diffuser in front of a light bulb and check it out. If you can see the coil filament of the lightbulb through your gg than its not diffuse enough like ted said. If you see a blur spot of the lightbulb then its ok and you have a condenser problem.

Daniel
 
Hi Daniel,

Ive made the tests with my actual sanded disc and an old one.
On my actual diffuser disc the filament coil is not visible and the diffusion is good. On the old diffuser disc the filament coil is visible because I used finer sandpaper. So it has to be the condenser lens but nobody tells me what lens they used for their adapter to get an idea what to try.

http://www.mypicshare.com/j5suwjubpic.html
http://www.mypicshare.com/o2z1z0d9pic.html

thank you
Albert
 
I had the same problem with my vibration setup +selfmade gg's but I found a solution to eliminate that hotspot and still using an image path of 36x24mm.
I also used the same method in my i-35HD. I think it will work for your spinning setup also. You will need three additional parts that are very easy to get.

PM me and I will send you a drawing + instructions.

cheers
Daniel
 
Hey Daniel,

thank you very much. It worked!
The hotspot is gone thats really amazing.

All the best
Albert
 
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