DIY Ground Glass??
 

Im using Daniel Schweinerts tutorial on DIY ground glass but now Im trying to use frosted Plexi Glass. My question is, how can I "mimic" the ultra fine fresnel pattern on Canon Ee-A Focusing Screens that allows the light to spread evenly and not create the annoying "hotspot??" when I use the frosted plexi glass alone, I get GREAT DOF, but the only light comes from the hotspot and that sucks because its like MAJOR vignetting, but not really because its just a matter of having light spread around. Some other questions. Diffuser vs Condenser? I heard that in order to get rid of the hotspot, I needed a condenser or a biconvex lens of 100mm focal length. Im seriously lost. HELP!!!

Hi Gary,

I've been experimenting with this exact question - trying to find a "GG" that I can use. The hot spot is dependent on the translucency of the material - an almost transparent CD case yielded a major hot spot. A somewhat thick plexiglass screen salvaged from a slide/photo/film-to-video converter yielded no hot spot, but because the material was somewhat thick, the focus was mushy.

Wax also reduced the hot spot to almost nothing, but it had other issues. Of course a lot depends on how much you can zoom in - this is why you need the achromat.

I've tried various materials with various results and, thus far, by far the best is a focus screen - I'm currently using one I salvaged from an old Canon AE1 just to see what kind of results it would produce. Take a look:

CD case, slightly translucent: hotspot
http://i120.photobucket.com/albums/o.../35mmtest3.jpg

Thick wax between two UV filters (for dust): softness, light loss
http://i120.photobucket.com/albums/o...test3_wax1.jpg

Thin wax on UV filter, hard pressed sandwich w/tinfoil spacer: grain
http://i120.photobucket.com/albums/o...test2_wax2.jpg

Salvaged Canon focus screen w/dual binocular lenses as achromat:
http://i120.photobucket.com/albums/o...bar/fubar1.jpg

Salvaged Canon focus screen w/ 0.6x WA used as achromat:
http://i120.photobucket.com/albums/o.../fubar3_sm.jpg

All of these tests were done using a static gg/setup based on Daniel's overall design. I used materials I had on hand and none have worked as well as the focus screen (even with the focus aid in the center). I plan on adding the vibrating part soon, but I have more experimenting to do - I have ordered a +4 and +10 diopter to replace the 0.6x WA hoping to get rid of the color fringing.

HTH

I had great succsess using a laminating pouch like this: http://svp.co.uk/product/peach_lamin...ches_6068_x100

I used it in a rotating design, but the screen is so fine-grained that i think it could work in a vibrating design as well. Here is a small test I shot with it: http://pettersen-prod.com/laminating...12K_Stream.mov

The camera was a dvx100 and the lenses I used were Canon FD 50mm f1.8, FD 35mm f2.8 and FD 24mm f2.8. Here is a pic of the setup: http://www.isarapix.com/pix36/1203178497.jpg

Good luck!

Hey Jon,

Your DOF adapter making very good picture !

use achromat or macro lens ?
I not see chromatic aberration... is very good :)

thanks for sharing this laminating thing ...I try it !

I used two binocular front elements, inspired by Daniel Schweinert's tutorial. Im not sure what binocular I used, but I'm pretty sure the elements are coated. The only problem with the adapter is that it makes a lot of noice. I'm not sure why, but I think it has to do with the crappy motor I'm using.

Image-wise, I was baffled of how much the footage from my DIY adapter compared to the footage from my newly aquired SGpro.

Jon, laminating pouch film have both sides the same. Both sides are smooth and glossy. Did you just choose any side to face the camcorder lens?

i've seen your setup over a dvxuser. i did notice on this video there was something weird at the beginning...like you could see movement in the GG when you moved. I remember you saying that it was just the laminating pouch and the G force keeps it from moving back and forth. maybe that's what happens when you pan and move it fast GG becomes slightly visible. i think there is a way to mount it better. i'll do some tests with the pouches when i get all my parts in.

i ordered a GG substitute from a company today. i should get that in bit and my box i had to oder as well off line. i have a motor i'm going to try out as well. i've had good success in the past with 35mm adapters and the spinner i'm building i think will be my best so far. a lot of time and development went into it.

Rich, you are right.

I did however shoot a short with it only a few days later and didn't experience the problem then. Some of the scenes had a lot of running, but the GG obviously kept in place. Im suspecting that the weird thing in the start of the other test film was because of low battery.

You can see the short here: http://pettersen-prod.com/Skromt.mov (p.s. It's in norwegian)

Here are some BTS pics as well: http://jpettersen.blogspot.com/2008/...men-skrmt.html

what are you using to spin the GG? a broken cd player?
i'm gonna use a DC motor and see what i can get. i was thinking that if you use a dc motor you can take two pieces of circle plastic and mount the laminating pouch right in between the two. no worries of it moving back and forth.

Im using a CD player motor, yes.

That could work, the only thing I'm worried about is that the plastic will probably increase light loss and degrade the general optical quality.

how much light loss are you receiving now?
it would probably be .2 stops for each piece of plastic so maybe .5 all together?

http://www.tapplastics.com/shop/prod...34023510884759

This is regular acrylic plastics. Very to no little light loss and distortion. Optically when spinning it's just like the rest. You can take a hole saw and drill just about any size up to 5inches. This would even be good if you wanted to sand blast or sand down period.

You could order a sample for $2.00's.
Like I said, once I get my project box, which is just around the corner, I'll be able to test the lamination pouches. The pouches seem to a do a good job like he light shaping diffusers.

I not completely sure of how much light I lose, but I think it's about 1-2 stops. Just a bit more than my SGpro.

If the two plastic discs only lose .5 stops, I think it could work. Maybe you can even try to cut one plastic disc to an oversized CD and glue the pouch to the plastic where the image isn't projected.

Good luck! Looking forward to seing how this works out.

you have any shots of bokeh?

that would probably work. just finding a more stable way to keep the pouch from moving back and forth is the objective.

if there was some kind of glue spray to where you can spray the acrylic and put the pouch on it would stick. that would be perfect.

Check out the short I posted earlier. That's the only bokeh shots I have.l

As long as the glue doesn't degrade the image quality it would be good. Still, I would try to put as little as possible between the slr lens and camera lens.

Have you recieved your project box yet?