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Old April 24th, 2008, 12:47 PM   #1
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35mm DoF questions

I opened a thread in the HV-20 section but I should have really put it here.

Anyway, I'm building a static 35mm DoF adapter using the "Asian" extension tubes and http://www.jetsetmodels.info/pics/konzept1.jpg as a guide. I've been experimenting with different configurations and "gg" materials and have gotten differing results, none of which are really great.

Initial test:
http://i120.photobucket.com/albums/o.../35mmtest1.jpg
http://i120.photobucket.com/albums/o.../35mmtest3.jpg

Second test using wax gg:
http://i120.photobucket.com/albums/o...test2_wax1.jpg
http://i120.photobucket.com/albums/o...test2_wax2.jpg

I added an "achromat" - an objective lens from an old pair of binoculars - I saw someone else had done that with very good results. However, my achromat is in the wrong place according to Daniel's diagram - instead of being really close to the camcorder, it's actually about 2" in front of it. When I moved it close to the camcorder, it did not change the focus ability of the camcorder, but it did produce a softer, less detailed image.

Q: Why is my achromat in a completely different location (that seems to work better in this particular case)?

Q: The wax gg - basically I took a 55mm UV lens, shaved some white wax onto it, baked it in the oven until the wax melted, let it cool, then added a second UV filter as a "protector". I think the wax is too thick and is softening the image:

http://i120.photobucket.com/albums/o...test3_wax1.jpg

Q: Should I be thinking of replacing my current bino achromat with a proper macro that attaches to the front of the camcorder? Would that help? Or am I really seeing issues with the gg? Both?

Thanks.
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Old April 24th, 2008, 01:17 PM   #2
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Paul.


Wax is a pretty hard beast to tune up to perfection but it can be done as the Movietube products demonstrate.

Some time way back there was published here a brew made up of bleached beeswax and parrafin wax or microcrystalline wax. I think the percentage of beeswax was 15%.

Getting the wax to be a consistent thickness between two pieces of glass was a challenge. Some achieved it by making shims or spacers of cooking foil to separate the glass panels an even distance and used capilliary action of the close fitting surfaces to draw the wax up.

The names Frank Ladner and Oscar Spier come to mind when wax is mentioned so a search for their past posts might be helpful.

Your wax layer may be a bit thick which will soften the image as well as losing a lot of light.

My own opinion is that for the home-builder using a HDV camera, a fixed wax groundglass might be a bit of a dead-end unless the environment provides lots of light. Others may differ with me on this subject and have a perfectly valid alternative suggestion to make.

I had a play with wax between two glasses on a spinning disk and it was by far the absolute best groundglass for resolution, however on a 125mm diameter disk, control of thickness around the entire disk I found impossible.

This introduced an unacceptable flickering effect so I went back to glass disks.

For a much smaller diameter disk in an oscillating or orbital setup, wax should be a viable method.


One jpg from my tests is here :-

http://www.dvinfo.net/media/hart/waxds002.JPG


There are others on the bottom of the list you will find at :-

http://www.dvinfo.net/media/hart


Your binocular lens may be less powerful than desirable. You may also need to turn the lens around back-to-front before you can use it close to your camcorder lens successfully. An achromat in the ballpark of 7+ to 10+ as jetset suggests is about right for non-flip adaptors.

Front of 7+ achromat to groundglass will be about 125mm or about 5". Zoom may need to be about 50mm for framing the motion picture frame of 24mm width, can be less for the 36mm wide still image frame but you then risk edge or corner brightness falloff.

Last edited by Bob Hart; April 24th, 2008 at 01:31 PM. Reason: error
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Old April 24th, 2008, 01:55 PM   #3
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By the way... It's totally off topic, but I think you should keep that second wax adapter. It gives the image a very organic old 16mm look without post work that could be interesting for some projects.

Just trying to look at the bright side of life...
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Old April 24th, 2008, 05:29 PM   #4
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Thanks for the replies.

My GG isn't really a sandwich. It's two 55mm UV filters stacked together with the wax layer (whatever thickness - probably 1/16" or more) simply cooled to one of the UV filters. Thus there was nothing done to smooth it or make it uniform other than gravity. While the images are definitely soft (and Jose, you are dead on - it does have an old-time organic look to it), it is/was educational to me because I had tried a piece of CD case (almost transparent but not quite) and got a definite hot spot in the center of the image. You can see it to some degree with the first images. The wax eliminated this particular issue.

The light loss is big, but looking at some footage I shot this morning I think if I get the "gg" right the light issue will at least be less of an issue.

Now, the achromat. My optics knowledge are definitely not up to scratch as I paid no attention to which way around it went in - I did not think it would matter. I will check this. I presume the flat side should point towards the camcorder while the convex side should point toward the focus "screen"?

Thanks again.
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Old April 24th, 2008, 05:37 PM   #5
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Quote:
Originally Posted by Bob Hart View Post
Paul.
Front of 7+ achromat to groundglass will be about 125mm or about 5". Zoom may need to be about 50mm for framing the motion picture frame of 24mm width, can be less for the 36mm wide still image frame but you then risk edge or corner brightness falloff.
Currently my "achromat" is about 2 inches in front of the camcorder lens, and about an inch from the "gg". My configuration is different to what you describe, what Daniel describes, and what I've read on the net. Is it possible my results are skewed because of the placement of my achromat? Does it have to be right up against the camcorder, or is it okay to be, say, 1cm in front of it?
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Old April 24th, 2008, 06:12 PM   #6
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Don't know much about adapters but I've seen a few pro units and achromats look like they're very close to the camera lens. Take a look at this:

http://www.sgpro.co.uk/products/sgpr...unit/box03.jpg

Or here: http://cinevate.com/website/brevisdemo/ (Launch 3d demo and turn it to see the achromat).
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Old April 24th, 2008, 10:16 PM   #7
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Thanks for the links.

I took my adapter apart and discovered I was mistaken about the placement of the achromat - it actually is close to the camcorder (not right up against the lens as there are a couple of adapters in the way). It was yesterday that the achromat was further away.

I also noted that the achromat was the wrong way around - I've reversed it but it's too dark to really test it out. I'll know more tomorrow.
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Old April 25th, 2008, 02:17 AM   #8
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As a rule of thumb it seems the achromat has to be as close as possible to the front element of the camcorder lens.

The clips below are my contribution to the debate. The EX1 exercise shown in the first clip uses the achromat from my AGUS35 arrangement via a home-made bridgepiece to the Mini35-400.

With the EX1 and its wider field-of-view 1/2" imager, this arrangement exhibits a little edge softness which other adaptor builders have had to engineer around.

(The actual Mini35 Z1 relay lens is quite different to the traditional achromatic dioptre home-builders and the alternative manufacturers are using in that the front optic of the group is a concave face not convex as the normal achromatic dioptre is found to be.

P+S Technik's EX1 relay is still under development.)

http://www.youtube.com/watch?v=kpm72LpoV0k

http://www.youtube.com/watch?v=CnweOEEqlRY


1/16" wax layer thickness is a little too thick. Beyond a certrain thickness the light loss suffered does not seem to increase as much but resolution falls off. The thickness of a strip of cooking foil is about what you need.

Last edited by Bob Hart; April 25th, 2008 at 02:20 AM. Reason: added text.
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Old May 6th, 2008, 10:15 AM   #9
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I've been experimenting with different materials/configurations - I've now ordered an Ee-A screen based on the results I got with a salvaged 35mm focus screen.

With salvaged focus screen and binocular lenses used as achromat:
http://i120.photobucket.com/albums/o...bar/fubar1.jpg
http://i120.photobucket.com/albums/o...bar/towel1.jpg

With salvaged focus screen and .6x WA lens
http://i120.photobucket.com/albums/o...mdoftest13.jpg
http://i120.photobucket.com/albums/o...mdoftest14.jpg
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