Reference Beams used in H1 to H2 transfer

[John Sonley]

Colin, I am opening this as a new thread, as it was becoming 'diluted' on the previous thread - and I'm still looking for a definitive answer.

From what I read previously, I suspect that I may be 'doing-it-wrong-way-round'.
Let me try to describe with precision my H1 to H2 transfer when making a reflection hologram:
I view the H1 with the collimated reconstruction beam impinging at the correct angle for brightest reconstruction - (30 deg. in my case) - I use a collimated beam as one was used in the making of the H1 - I view it as a normal image and I then flip it around so that I view the pseudoscopic image and mount the temporarily laminated film-on-glass into the H1 plateholder, the way I do it, the H1 emulsion faces the H2 plateholder.

I position the H2 plateholder with a white card in it to meet two requirements:
1. Centrally position the image projected from the Hi into the centre of where the 5" X 4" H2 film will be placed
2. Move the whole H2 plateholder framework closer or further away from the H1 plateholder to set the required image plane and thereby have my chosen real : virtual image setting

I then under safelight, temporarily laminate the plastic side of my 5" X 4" unexposed H2 copy film on to a glass plate and after stabilising, mount it in the correctly positioned H2 plateholder with the emulsion facing directly towards the H2 reference beam and therefore away from the H1 - that way you will eventually view the white light reconstructed hologram through the plastic backing of the H2 copy (keeps sticky fingers away from the emulsion side)

I then set up the reference beam and after about 15 minutes settling time expose and develop

At the present moment I am converging this H2 reference beam slightly - is this correct? - This is the answer I seek as the converging reference beam is the conjugate of the diverging reconstruction beam that will be used to eventually view the hologram

The holograms I make look fine and bright - I'm using the ZIP-1 formulation and an acid dichromate bleach but as I try to improve my really deep image holograms, I would like to get the techniques correct and I was concerned by what I read in my 'bible' - Graham Saxby's latest book

Please turn to Pages 185 and 186 of Graham Saxby's 3rd Edition of Practical Hotography:
On page 185 he seems to say that you need a converging reference beam, but on the picture - Fig 12.17 on Page 186 it shows a converging H1 reconstruction beam, which seems all wrong to me, as the H1 was made with a collimated reference beam and a converging reconstruction beam would distort the image from which the H2 is made

Can somebody sort me out please, with both an answer and an explanation of why - - -and what about the Saxby reference!

BRgds

John

[Kaveh]

Hi John. You have explained clearly what you are doing. I don't have a copy of Saxby to hand so can't comment on the pictures. But I can make some comments.

In general, you want recording and corresponding reconstructing beams to be conjugates of one another, i.e. each reconstruction ray is the reverse of the recording one. This is so that you do not get distortion or aberration in the image. Now the distortions and aberrations get bigger the further an image point is from the hologram plane. During recording of H1, let's say the average distance of the object from the H1 might be 20cm. This is a substantial distance, so you should take care to have conjugate beams. So when reconstructing the H1, the image must also be 20cm away.

During the recording of H2, you are projecting the image of H1 to be focused near the surface of H2. So the typical distance will be say 2cm. So the aberrations and distortions are much smaller and much less noticeable. So you need not be so careful at this stage. In the limit that the image is right on the surface of H2, it doesn't matter what the beams are like. The image will be undistorted and always at the same position.

So I would say that using a converging beam is an overkill, as a converging beam is so hard to create. If you just use a collimated beam, then diverging, you will get some distortion, but probably it will not be noticeable.

[John Sonley]

Kaveh - thank you so much and I think you are saying that if it is easy to create a converging H2 reference beam, then that will be better for a deep image reflection hologram with much of the image very 'real'.

I can easily get a converging reference beam striking my H2 as I use large plano convex lenses to create my reference beams for both H1 and H2 and simply by adjusting the distance between my spatial filter pinhole amd the lens, so the beam cam be made to diverge, collimate or converge

I'm hoping that someone can give me their view of the Saxby observations

BRgds

John

[Colin Kaminski]

Graham is talking about an H2 transfer from a transmission H1 that was made from a pulsed laser and was not collimated. Since the H1 reference beam was diverging the H1 replay beam needs to be converging at the precise angle in order to be it's conjugate. He is also showing a collimated H2 reference beam which would not have been my choice unless my replay beam was very far away.

In order for the least amount of distortion, let say we were looking to make measurments from the hologram, one would have the H2 reference beam diverging at from a point that matches the distance from the display illumination distance. Also, you would use a process that did not shrink or expand the fringes and leaves the color the exact same as the laser.

[Colin Kaminski]

Just to be sure... I am talking about an H2 reflection hologram. Are you making H2 transmission holograms?

[BobH]

So I would say that using a converging beam is an overkill, as a converging beam is so hard to create. If you just use a collimated beam, then diverging, you will get some distortion, but probably it will not be noticeable.

You state the general wisdom of Holotown here, Keveh, but I think the "slight" distortion you mentioned is quite noticeable. Reconstruction sources are usually very close. Nowhere near infinity. The vast majority of image-planed reflection holograms I've seen, including mine, all show image stretch and swing, making the images look unreal. Which is generally accepted for holography in the absence of any expectation of a need for the images to be accurate.

I believe that's the reason why Denisyuk holograms can have an almost hyperrealistic look to them compared to image-planed reflection holograms. A long time ago, I made two holograms of a coyote skull. One was a typical IPR hologram using a collimated reference beam. The other was made with a reference beam converging from a large HOE I made. Hugh difference!

This is one of the big problems with the IPR technique that's been swept under the rug since the beginning, and I think is partly responsible for pictorial holography's non-acceptance. :wall: :wall: :wall: :wall: :wall: :wall: :wall: :wall: :wall:

[BobH]

At the present moment I am converging this H2 reference beam slightly - is this correct? - This is the answer I seek as the converging reference beam is the conjugate of the diverging reconstruction beam that will be used to eventually view the hologram

The holograms I make look fine and bright - I'm using the ZIP-1 formulation and an acid dichromate bleach but as I try to improve my really deep image holograms, I would like to get the techniques correct and I was concerned by what I read in my 'bible' - Graham Saxby's latest book

Please turn to Pages 185 and 186 of Graham Saxby's 3rd Edition of Practical Hotography:
On page 185 he seems to say that you need a converging reference beam, but on the picture - Fig 12.17 on Page 186 it shows a converging H1 reconstruction beam, which seems all wrong to me, as the H1 was made with a collimated reference beam and a converging reconstruction beam would distort the image from which the H2 is made

Can somebody sort me out please, with both an answer and an explanation of why - - -and what about the Saxby reference!

BRgds

John

Everything you're doing sounds right to me. The picture must be wrong. Collimated reference and reconstruction beams for the H1, converging reference to match the intended diverging reconstruction beam for the H2. Using a plano-convex lens with a conjugate ratio near 1 (instead of infinity) gives spherical aberration you might see in the image if it's too far from the plate.

[Kaveh]

You state the general wisdom of Holotown here, Keveh, but I think the "slight" distortion you mentioned is quite noticeable. Reconstruction sources are usually very close. Nowhere near infinity. The vast majority of image-planed reflection holograms I've seen, including mine, all show image stretch and swing, making the images look unreal. Which is generally accepted for holography in the absence of any expectation of a need for the images to be accurate.

I believe that's the reason why Denisyuk holograms can have an almost hyperrealistic look to them compared to image-planed reflection holograms. A long time ago, I made two holograms of a coyote skull. One was a typical IPR hologram using a collimated reference beam. The other was made with a reference beam converging from a large HOE I made. Hugh difference!

This is one of the big problems with the IPR technique that's been swept under the rug since the beginning, and I think is partly responsible for pictorial holography's non-acceptance. :wall: :wall: :wall: :wall: :wall: :wall: :wall: :wall: :wall:

I take your point, Bob. I have not been in the lab for a couple of decades, so not had to hit my head against the brick wall.

But it's all relative, so if you have a deep image and a very short reconstruction beam on the H2, you will be more distortion. I was thinking of transmission, and very shallow images.

In any case, it is then absolutely essential to get the H1 right. Make sure it focuses without any swing on a card you place where H2 goes. Highlights should be clean spots when in focus.

I very much agree that any swing will detract from the realism of the image. The brain is very clever at spotting these.

[John Sonley]

BobH - thanks for your observation which I believe matches my own and which I will try to crystallise into one sentence:

"When making an Image Plane Reflection hologram, where the H1 was originally made and is now reconstructed with a collimated beam and where the desired H2 copy hologram will be displaying deep real images (1 - 2" in my case), the least distortion of the final real image will be observed when the H2 reference beam is a converging beam, the conjugate of the eventual white light reconstruction beam"

Pheww!

And now can someone give me an answer to the Saxby reference, which to me, in the Figue, looks wrong

Brgds

John

[Jem]

When the final conclusion is reached on this subject it would be great if someone could add it to the wiki

It'll save me (and others) having to search for the thread when I need to do this

Cheers

Jem