See now we are back to what I was talking about before - the apparent fact that SLR's use BOTH a condenser AND a fresnel. We need to confirm the proper order of them including the GG. Once we have that its a matter of replacing the fresnel with the same power condenser. From what I've seen SLR viewfinders have a single piece of plastic (or glass) that has a very fine fresnel pattern pointing towards the 35mm lens and the ground glass texture on the otherside. Following that is a condenser lens.

A field lens with sufficient power to bend the edge rays into the DV cam lens results in a lens with great curvature.

Not only will a lens with such a short radius of curvature produce:
- a viewed image with unacceptable pincushion distortion
- a large amount of chromic aberrations.

Two thin lenses in series will give the same power as the thick lens with great curvature.
But each of the two lenses have less curvature, thereby greatly reducing the pincushion distortion and chromic aberrations.
But for a camera it has the disadvantage of taking up space, making the camera larger.
Camera designers realized that what they needed was a very thin lens with reasonable power.
Fortunately, such a device was available: The Fresnel Lens.


But are we really concerned by space problems here with this adapor...i don't think so...



http://topcontechnotes.home.att.net/viewingsystem/page5.html

http://www-optics.unine.ch/education/optics_tutorials/field_lens.html

What about using white frost lamp effect filter material. The stuff they hang in front of film lights to defuse it? This material is cheap in small amounts, durable and grainless.

Just an idea.

Great ideas here.

DK

a freasnel would be fine to use in the adapter, there are fresnels available that have rings fine enough that there's no way the dv's ccd would pick them up, but you need to combine a condenser WITH a fresnel, like this http://topcontechnotes.home.att.net/...tem/page6.html

<<<-- Originally posted by Daniel Kohl : What about using white frost lamp effect filter material. -->>>

I tryed with that. when you zoom in to find appropriate picture - the grain is visible. i checked different types, but the grain is always visible. the good side is that is very equally placed. so, maybe someone will like it.

filip

Tavis Shaver,

What a great link. For anyone interested in this subject the whole site should be required reading.

Starting at: http://topcontechnotes.home.att.net/viewingsystem/page3.html

all the way to page 16.

Paul
dvdof.com

<<<-- A fresnel would be fine to use in the adapter, there are fresnels available that have rings fine enough that there's no way the dv's ccd would pick them up, but you need to combine a condenser WITH a fresnel, ... -->>>

This solution was chosen only for a matter of size...
2 low power condensers are better then one of high power to avoid spherical distortion.
And when u REALLY need space u can replace one condenser by a fresnel...but optically the fresnel MUST not be used in a system dedicated to record a sharp image...

is space really a limiting parameter in our equation?

what about coating some stuf on a regular glass.
For example if you already have used cyanoacrylate (instant glue) on glass, there is always a white haze around the glued parts.
You can try to heat some of this glue under a glass.
They do this for looking at fingerprint on glass.
<b>Caution: cyanoacrylate contains cyanure (lethal gaz), so it is good to take care of doing this outside and not let the gaz reach your skin, eyes or lungs.</b>

Alternatives to GG
 

Giroud-
Your talking about a similar technique as a product called a "Bosscreen". They are 4X5 and 8X10 focusing screens that are grainless. They achieve this buy melting and then hardening a very thin layer of wax sandwiched between to flat clear pieces of glass. The results are amazing!

Heres the bad news. Its going to be nearly impossible to not only find the ideal thickness of the layer of wax to use but having it lay down completely flat and even is a real feat that may only be possible by a commercially machined process. The other thing that there is a chance that Bosscreens will melt and be destroyed on a hot day. And dont even think about cutting down a commercially made one to size for the same reason. They are expensive too.

One interesting note though. Bosscreens advertise their product as having a microcrystaline layer (the wax). I know another company that says the same about their product...Movietube.

Good luck.

Just got off the phone with a highly recomended camera repair man. He confirmed that there is both a fresnel AND a condenser lens in a SLR as shown before here:

http://topcontechnotes.home.att.net/viewingsystem/page6.html

He also confirmed that without one of the two you will have chromatic abberation problems.

Bottom line is we are back to my idea of finding a replacement condenser lens for the fresnel and having two condensers working together to make a achromat field lens. This way we wont have any "pincushion" (barrel) distortion or chromatic abberation. Damn I wish we could of K.I.S.S. but that would be S.

-B

Thoughts on 'correct' grit size
 

Hey you glass grinders!

Those of you that chose to go with the 1000 grit - did you like the results? I've heard of people using 320, 600 and 1000. There was some speculation at some point that there was a point where you've gone 'too' fine and would start to lose the diffusive properties... You can go finer that 1000 grit Aluminum Oxide as well, wondering what the pros and cons of finer and finer grit are...

Any comments from the polishing among you?

Jonathon
 

I have mine done whit 9Y (9 micro bryte capsule) that is a bit smaller than 1000 and it's ok ,but after that ,there is something call Red pollishing that I have try ,but then I start losing the diffuse properties and I start to see thrue it , so ,no good.In fact it can reduce the grain more but I was not able to control the grinding enought so I start having some tranparent spot and this apend just in couple of second.

Alain

I did mine w/ 1000 alum ox, I just did a quick 1hr grind which I should do another 1hr final grind.

here is a pic, look at the top pic- notice a very small amount of grain in the edges where the light is less strong. I will do a final grind shortly to clean it up but overall I am pleased with the results of 1000.

http://aequantum.com/fresnel.jpg

Alright, here's a dumb question for Alain (or anyone with the answer):

I've got a Tiffen UV filter here and it has on both sides a raised ridge at the edge. How, if I'm supposed to have a piece of glass as my grinding implement, do I make contact with the UV filter's surface with the grit and the grinding tool?

My piece of grinding glass exceeds the diameter of the filter, and so the ridge prevents the two pieces of glass from touching. Did you use a smaller piece of glass to do your grinding? Or, did you remove the filter from its mounting ring? (and if so, how?)

Thanks...

- jim

yet another question about ground glass...

Is there anybody who really tried an holographic diffuser....
Theoretically they make the post condenser useless...

anybody with real tests?

thanks