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-   -   Prism for use with the 35mm adaptors (https://www.dvinfo.net/forum/alternative-imaging-methods/33498-prism-use-35mm-adaptors.html)

Anders Floe October 15th, 2004 12:15 PM

Prism for use with the 35mm adaptors
Have anyone found a prism which is both big enough and is colorcorrected so it could work with the homemade 35mm adaptors(to flip the image)???

Bob Hart October 16th, 2004 08:30 PM

For PD150/VX2000,PD170/VX2180, with +7 achomatic diopter, two 40mm x 40mm x 56mm prisms of 40mm thickness across all faces seem to be large enough to relay a 24mm x 18mm standard 4:3 motion picture academy frame. These seem to be fairly commonly available.

When you search, use the search term "rightangle prism" or "right angle" or "right angled" prism. "90 degree prism" should also find it for you.

Anders Floe October 17th, 2004 02:39 PM

Will any of these prism work? :


Bob Hart October 17th, 2004 07:58 PM

The coated prisms on that web page will not work. They are a special product intended to be very stable, optically precise mirrors.

Also, all the prisms I saw on the list were too small but they may have other prisms listed.

The coating is on the hypotenuse face and is totally reflective.

The hypotenuse face is the one you want to be clear as the image passes in through one half-face and out again through the other half-face.

Reflective surfaces on the small sides would be great.

I did not search the website for other prism products as I am on a very slow landline here. (720 bytes per second on bad days).

Anders Floe October 18th, 2004 04:11 AM

Thanks for the quick explanation.

I found another prism which is up to 60mm and with no coating.


Will it work??? If the prism is 6 cm then it will allow for the filmsize to be 8,5cm * 6cm = 36mm - or what?

I just realized how long it has been since I've used math for anything.

Anders Floe October 20th, 2004 08:57 AM

Sorry for my absurd math above (I was really tired ;-) ).

The 40mm prism on the page below should work just fine right??? It has a 40mm * 40mm surface which should work perfectly with the 36mm * 24mm frame, right?


I really need help on this. Thanks

Anders Floe October 20th, 2004 02:19 PM

I e-mailed the company and will post whatever response they give. I have also asked them what the price will be with the coating on the small sides.

Bob Hart October 21st, 2004 08:41 AM

I am sorry I cannot be much help on the above prism mentioned. 40mm? on which face. You really need to ask Thorlabs the dimensions on all faces and the common thickness across all.

As a really rough guide, the longest face on the prism has to be at least 56mm for the 24mm x 18mm frame because the lower half of the upright prism is almost hard against the groundglass if you use a +7 power close up lens.

I am not an optical engineer and I can only vouch for what has worked for me when I have put things together.

The two prisms each overlap each other by only half on the longest face. You also have to give up a bit of area to support the prism face by its edges.

Anders Floe October 21st, 2004 08:46 AM

So I would be home-free if I bought the 60mm *60 mm (square part of the prism)???

Valeriu Campan October 21st, 2004 06:23 PM

I have dismantled the "pentaprism" of the Mamya C (medium format twin reflex) stills camera. It is called PORROFLEX and inside there are only 3 mirrors!!! A similar setup with 4 mirrors would inverse the image properly for the video camera.
Isn't there a significant loss of light with the prisms combo?

Bob Hart October 21st, 2004 11:44 PM

There is, which is probably why P+S Technik seem to use a combination prism-mirror path.

With mirrors the mounting has to be precise for so many more components, a build quality probably outside of the realm of many here.

Prisms are fixed on two surfaces each in this application which means less complication for mountings to be made, even less if the two prisms are glued together at the common half-face.

Anders Floe October 22nd, 2004 05:05 AM

So it is just a question of allignment??? If so couldn't you just mount the mirrors individually on some kind of mount so you could adjust them and with a laserpen point to see if the allignment is correct?????

By the way would the light travel as far with four mirrors as with 2 mirrors and a prism????

Richard Mellor October 22nd, 2004 12:26 PM

hi everyone I am sure you could align prism correctly on this system .




this is a german site with an exploded view of the $10,000
35mm adapter. I am sure ..... the thorlabs cage and tube system could do this to the same tolerences


Anders Floe October 22nd, 2004 12:57 PM

I have a hard time getting an overlook of the different parts - could you perhaps make a quick drawing or explanation which explains exactly how you would put the parts together??

Richard Mellor October 22nd, 2004 01:12 PM

hi everyone :I have a number of these parts on order .
the first stage is to build a static adapter.

these are the componets I plan to use.




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