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Old December 22nd, 2003, 03:09 PM   #1
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Static 35mm Adapter Solution

For those of you interested in a static 35mm adapter that produce upright image, see the following design (not meant to be pretty other than functional).

http://f2.pg.photos.yahoo.com/ph/lou...=/35mm+Adapter

You can see full size image (look for the button above/blow the image).

You are authorized to use this design for personal use.
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Old December 22nd, 2003, 03:29 PM   #2
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Hi Vendible.
Shouldn't that be a roof pentaprism? I think that if you use a plain pentaprism (as you appear to show) the image will be laterally inverted.
Best,
Helen
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Old December 22nd, 2003, 03:46 PM   #3
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"Shouldn't that be a roof pentaprism? I think that if you use a plain pentaprism (as you appear to show) the image will be laterally inverted."

I have carefully check and rechecked (see the ray trace). The design is very similar to the viewfinder on a SLR camera, except the order is reversed.

The penta prism does not invert the image, it only redirects the image 90 degree. Then the mirror does the inversion. A roof prism by itself will invert the image, but you will have to shoot at a right angle.

I'll just mention the dove prism. To get a 24x36 or 36x36mm dove prism will require a length of at least 150mm, just by itself. Mirror and penta prism is still the best combination.
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Old December 22nd, 2003, 05:02 PM   #4
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Vendible,

I am referring to a roof pentaprism, not a roof prism. Nearly all SLR cameras use a roof pentaprism - a plain pentaprism (as you have shown, which is not like the ones in most SLR cameras) leaves the image laterally inverted. That's why SLRs use roof pentaprisms. If you don't believe me, look at the shape of the top of an SLR.


Best,
Helen
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Old December 22nd, 2003, 05:21 PM   #5
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Helen,

http://f2.pg.photos.yahoo.com/ph/lou...m=DSC00140.jpg

Thanks for pointing that out. I'll recheck and make sure what exactly it is.

If you could draw or refer me to a picture, that would help.
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Old December 22nd, 2003, 06:34 PM   #6
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Helen,
After some reading I think you are right, roof pentaprism. Thanks again.
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Old December 22nd, 2003, 06:40 PM   #7
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Yes, Helen is correct.

Thank you Helen!

- don
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Old December 22nd, 2003, 06:44 PM   #8
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roof pentaprism

i have two roof pentaprism, one from SLR 35mm camera and one from 6x6 camera. i'm not expert on physics, but i think that ROOF makes the difference here. in BOTH cases (35 and 6x6) the ROOF exist, not just ordinary penta prism.
if you look closer inside the prism - you will see almost invisible thin line which is the uppermost part of that roof, but when you look through eyepiece it looks flat. no splited image, no visible left and right half, but whole image.

in my opinion, just in that ROOF part the image changes the position - left goes to right, right to left, and then after that transition goes to your eyepiece.

and before that (in SLR cameras - or - in your project) finally the miror makes it upside down, so we see it normally.

again - i'm not physics guru, but in my opinion WITHOUT that ROOF image will be still wrong.

i can send to certain e-mail my photos of this roof pentaprism, to show in more visible way what i'm talking about. so anyone can see it. (or if someone has possibility to put it on his server... and make a link in this thread?)

filip

p.s.
i know that this sounds like almost a coinsidence, but i bought the pentaprism (roofprism) just because of that - to use it in agus35 modyfied project and have proper position of the image.
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Old December 22nd, 2003, 06:49 PM   #9
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Hi Filip,

Send the file to me taylor@moorefilms and I will post for you.

Taylor
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Old December 22nd, 2003, 06:54 PM   #10
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Clarification:

Pentaprism will deflect image 90 degrees without any inverting(up/down) or reverting (left/right) to the image.

Roof Pentaprism will deflect image 90 degrees and revert (left/right) the image, but does not invert (up/down) the image.

Using a pentaprism with a mirror will invert the image but not revert.

Using a roof pentaprism with a mirror will invert and revert the image.

Problem solved.

http://f2.pg.photos.yahoo.com/ph/lou....dnm=img13.jpg
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Old December 22nd, 2003, 07:35 PM   #11
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problem solved

yes, that's it!

penta roof+mirror=success!
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Old December 22nd, 2003, 07:49 PM   #12
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to taylor

taylor,

i just sent the pictures of my pentaprism to you.

thanks
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Old December 22nd, 2003, 08:32 PM   #13
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This roof pentaprism introduces some more design problems because the outgoing surface is smaller than the incoming surface. That's OK for a camera view finder, but in this case, the bigger projected area, the better (more detail is preserved).

Dove doesn't work because it only inverts the image, doesn't revert it.

I'm looking for another solution.
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Old December 22nd, 2003, 09:48 PM   #14
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For what it is worth, you may find the following Optics FAQ handy:
http://www.edmundoptics.com/TechSupport/optics.cfm

Optics:
http://www.edmundoptics.com/IOD/Browse.cfm?catid=10

Fresnel Lenses:
http://www.edmundoptics.com/IOD/Disp...Productid=2039

Ohhhhh! (this looks very familiar)
http://www.edmundoptics.com/IOD/Disp...productid=1966

T-Mount Adaptors (hmmmm...):
http://www.edmundoptics.com/IOD/Disp...productid=1460

More Lens Adaptors:
http://www.edmundoptics.com/IOD/Disp...productid=1459

Video Lenses?:
http://www.edmundoptics.com/Catalog/Custom/218.cfm

Cool!!!:
http://www.nightowloptics.com/addfra...product=NOCA42

- don
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Old December 22nd, 2003, 11:28 PM   #15
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Ok, I have verified that with a normal penta prism and a roof prism, you can create a correct inverted and reverted image.
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