maximizing viewing angle on reflection holo

rzeheb · Post by **rzeheb** » Tue Oct 27, 2009 2:09 pm

Can anyone offer recommendations for maximizing the side to side viewing angle on reflection image plane holos? My most recent H2s are bright, sharp and with lots of depth, but the viewing angle seems very narrow. I was wondering, can the angle be expanded by doing mutliple exposures with the reference beam coming in from different directions for each exposure (like what you would do if you were creating a multiplex holo)? Is there a simpler way to do this that does not involve mutiple exposures? What factors impact on viewing angle? Sorry to be asking all these rapid-fire questions.

I guess I'm a bit charged up with my recent success :dance: but definitely ready to move forward and all help is much appreciated.

BobH · Post by **BobH** » Tue Oct 27, 2009 2:46 pm

rzeheb wrote:Can anyone offer recommendations for maximizing the side to side viewing angle on reflection image plane holos? My most recent H2s are bright, sharp and with lots of depth, but the viewing angle seems very narrow. I was wondering, can the angle be expanded by doing mutliple exposures with the reference beam coming in from different directions for each exposure (like what you would do if you were creating a multiplex holo)? Is there a simpler way to do this that does not involve mutiple exposures? What factors impact on viewing angle? Sorry to be asking all these rapid-fire questions. I guess I'm a bit charged up with my recent success :dance: but definitely ready to move forward and all help is much appreciated.

Jeff Murray proposed a great method for doing what you ask. You put a mirror on each side of the master plate, at 90 degrees to it (like the sides of a box) with the mirrored surfaces pointing inward toward each oher. When you make the transmission master recording, the mirrors reflect the side information from the object (that normally would've missed the plate) onto the master plate.

In the reflection H2 system, the master sends the side information back out off the mirrors and toward the H2 plate. It's like having a larger master. The problems with the method are:
1) you'll see lines floating out in the space of the master where the mirrors and master intersect. This can be minimized by getting the mirror edges right in contact with the master's emulsion,
2) it's difficult to light the object around the mirrors. This is obviously image dependant.
Otherwise, it's a good method for those who want to make it work. Jeff published the method in one of the ISDH conferences, possibly '91.

JohnFP · Post by **JohnFP** » Tue Oct 27, 2009 4:48 pm

The larger your H1 is and the closer to your H2 in the copy the larger the viewing angle will be.

Another simple trick, if you can't do larger H1''s, is to turn the H1 plate sideways to lose a little veritical paralax to gain a little horizontal. In other words, if you do and 8x10 with a tranfer to 4x5 and the 4x5 is diplayed with the long side vertically, then create the master such that the 10" is the side to side creating the 4" on the final hologram. That way you have 10" of master making the 4" horizontal paralax while giving up to the 8" making the 5" of the vertical paralax (which we don't need much of anyway).

This is why I simple love a reflection H1 to reflection H2. Even with the same size plates (H1 and H2) with a 4 inch deep object, image planed 2" you will get a very large viewing angle.

rzeheb · Post by **rzeheb** » Tue Oct 27, 2009 6:17 pm

Bob, John, thank you both! After reading Bob's post I walked away and thought about it a bit then drafted a reply which is pasted, below. As you can see, John's comments exactly confirm what I was wondering. I pasted my coments in anyway (hate to waste good typing) but thanks for answering my questions in advance!!

O.K. So if I may be permitted to "read between the lines" what this tells me, Bob, is that the viewing angle is a function (at least in part) of the size of the master plate compared with the copy plate and the distance between them. I can envision the viewable angle of the copy being defined by an angle between a point on the copy plate (say in its center) and two lines drawn from that point; one going to the extreme right edge of the master plate and the other going to the extreme left edge of the master plate. If my assumption is true then one could increase the viewing angle by increasing the size of the H1, decreasing the size of the H2 or bringing the H2 closer to the H1 (all constrained by beam angles and spread). In my particular case I was using a 6.3 by 6.3 cm master plate that was 22 cm away from a 6.3 by 6.3 cm copy plate. The calculated viewing angle (based on these assumptions) turns out to be about 20 degrees which is pretty damn close to what I seem to be getting!! Is any of this remotely close to reality or did I just waste a lot of electrons in this message??

JohnFP · Post by **JohnFP** » Wed Oct 28, 2009 11:26 am

Yup, sounds pretty close to me (16.3 degrees). Pretty narrow. No electrons or neurons wasted.

Now decrease that distance by half and you get 32 degrees.
or
Doulble the size of the H1 (12.6 x 12.6cm) you get 32 degrees
do both
so the distance is 11 and the H1 (12.6 x 12.6) and you get about 60 degrees...

rzeheb · Post by **rzeheb** » Wed Oct 28, 2009 11:37 am

I love it when the fog clears. Nice to have a plan forward. Thanks again for the very helpful info.

John Klayer · Post by **John Klayer** » Fri Oct 30, 2009 4:05 am

Jefferey Murray explains his side mirrors H1 some more on Frank's "ning" site.

I'd like to try it once I understand it.

JohnFP · Post by **JohnFP** » Fri Oct 30, 2009 10:08 am

Hey Bob, I never mentioned TY. That is a very neat technique I have not heard of before.

John Klayer · Post by **John Klayer** » Sat Nov 14, 2009 4:48 am

I figured out Jefferey Murray's genius idea. Wow! This is something I just have to try.