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Old February 13th, 2006, 03:26 PM   #16
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Join Date: Feb 2004
Location: switzerland
Posts: 2,133
how to tell if your GG is ok :

the first test you can do is to check for the lens, if there is any distorsion.
draw a line on a paper.
slide the gg-lens on the paper and look a the line.
It should stay straight as much as possible when it reach the edge of the lens.
if not, you will need to add a lens to correct that later.

check transparency:
You should not be able to see anything trough the gg, except a diffuse white light . apply the gg to a newspaper. you should see the text as sharp and clear as if the gg would be transparent.
lift up a bit the gg from the paper. the text should disappear almost immediately and should not be visible with about half an inch (12 mm) of distance.
if you get this, you will probably not have to worry about hotspot.
most people have problems with gg because they are too transparent (you can see the back of the lens trough the gg).
This could happen if you insist too much on last polishing with 1550 Alu. oxide. So if you get a perfect surface (no scratch) after a while. stop and make a test, insisting to much just create new scratches and does not improve really.

how to prevent scratches:
use a piece of glass as support (20x20cm is ok).
put you aluminum oxid into a small recipient with cover (i use baby food pot).
put 2 or 3 coffee spoon into the pot, fill with mineral water up to half. I cannot recommend regular water, since it can contain sand.
shake a bit (about 30 sec). open the pot, use a syringe to get some. just take from about 10mm deep from the surface (some impurities are floating, other goes to the bottom of the pot).
for the begining, you can use it just after shaing the mix, for the end of the work, you can wait between 10 sec to 1 min to make sure you got only the finest aluminium oxide.
the mix looks like milk ot white water.
work with it with a mix of small circular and linear motion. rotate the lens under your finger, so pressure does not apply alway the same place.
The water will evaporate and the mix will dry while you work. add more from the syringe to keep it wet, but not too much liquid.
if you feel/hear some scratch (like sand rolling under the teeth), stop, wash everything with mineral water and start again. You probable have a grain in the mix and scratched your lens.
If you get a can of compressed air (the one used to clean lens), use it to dry the lens sometime and check how it goes.
Giroud Francois is offline   Reply With Quote
Old February 14th, 2006, 03:16 AM   #17
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Join Date: Feb 2006
Location: St. Petersburg, Russia
Posts: 46
> Ivan, I'll sell you mine for $25, shipping included. I used it for my adapter and it worked great. It's an Optosigma FL70mm plano-convex lens, then same used in Richard Mellor's design. The size is 52mm.

Ben: what are you going to sell exactly? the PCX lens? is it ground already? will it fit my design?
the bad thing is, my marumi macro +10 doesn't have threads on the outside, does it mean i will have to use glue?

Thanks Giroud
Ivan Egorov is offline   Reply With Quote
Old February 14th, 2006, 08:07 AM   #18
Join Date: Jun 2005
Location: Hollywood, CA
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Ivan, I'm selling 50mm 70fl:part number 011-2870 from Optosigma: http://www.optosigma.com/miva/mercha...herical+Lenses

Unground, unthreaded. A cool tip I learned: Buy a cheap UV filter, unscrew the unside to take out the filter, and what you're left with is a filter casing that you can insert any optical element into with the same diameter to make threaded. For instance, if you wanted to turn this PCX that I'm selling into a mountable 52mm optical element, just replace a 52mm UV filter glass with the PCX lens. I could do it for you before I shipped it to you if you wanted me to.
You can do the same with your macro +10.

I don't know if it will fit your design or not yet--give me some more details. Are you using a threaded design, or are you gluing everything together? What size are your empty filter rings? What size is your macro? The best bet, I believe, would be to buy a project box to house the spinning CD in, and then glue a filter ring to one side so you can attach your macro, condenser, camera, etc. And then attach an SLR mount to the other side.
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