how to determine exposure time?

JohnFP · Post by **JohnFP** » Thu Apr 29, 2004 10:52 am

A third of the energy is what I usually throw away by expanding the beam to get a uniform illumination. Physically it looks like about half the beam but power wise it is about a 1/3 because of the gaussian profile.

Peace!

Roli · Post by **Roli** » Thu Apr 29, 2004 10:57 am

The result is a dim image from the edges to the center - but only sometimes.

Developer is made fresh each time and I have no temperature variations in my room.

Maybe it´s overexposed - because the plate goes dark within 30 seconds (approx 60%).

I will make another session this evening to check it again.

Thank you all for support!!!

Cheers

Roli

Michael Harrison · Post by **Michael Harrison** » Thu Apr 29, 2004 10:10 pm

30 seconds is pretty fast. I would try cutting the exposure time in half.

How are you testing the stability of your table and environment? What kind of shutter are you using? Are you doing a single-beam Denisyuk?

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If someone says it can't be done but they haven't tried it, don't believe them.
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Roli · Post by **Roli** » Fri Apr 30, 2004 2:42 am

Good morning everybody!

I´ve tried to expose half time and I´ve also tried to exposte one plate step by step starting with 1 sec. up to 10 sec.

I got a image at 2 sec. up to 6 sec. but all of them where very dim.

I also performed some stability test with interferometry with good results.
I have a magnetic shutter which has no connection to the table (mounted on the wall.

Current setup is single-beam Denisyuk.

The plates are very "milky" after drying and I have small parts on the plate (some mm²) with a very clear and bright image but 99% are very dim - even with slow air-drying. The plates are not fogged because I have an uneven darkening during development. I also can see the image on the plate before drying.

Thank´s!

Roli

JohnFP · Post by **JohnFP** » Fri Apr 30, 2004 7:23 am

Milky? You mean milky white? That is strange for silver halide. Almost like the developer is not right.

Try to dilute the devoloper with double the water it calls for. So if it calls for a 1:4 developer to water try 1:8 developer to water. Then you may have to adjust your exposure. I would try around 4 seconds with the diluted developer.

Also for a reflection, which will make it much brigher, you need to bleach it. I have not heard any mention from you on bleaching the reflection hologram.

Dinesh · Post by **Dinesh** » Fri Apr 30, 2004 11:07 am

I don't know the dolumol developer, but are you making it up yourself? The milkiness sounds like contaminated chemistry or a fixer that's too concentrated. However, you did not mention fixing or bleaching, so I suspect contamination or too strong a developer.

Roli · Post by **Roli** » Fri Apr 30, 2004 12:16 pm

It´s not milky white, it´s like a milky shine when you look through the plate.

I use dichromate for bleaching - it works fine in combination with "Dokumol" which is a developer from Tetenal.

I will check this - recommended is 1:4 - I will try 1:8!

Thank´s
Roli

Tony · Post by **Tony** » Fri Apr 30, 2004 12:21 pm

The milkiness might be caused by using chlorinated tapwater for rinsing before or after bleaching. As I learned from this excellent forum, the combination produces an insoluble white precipitate. Use distilled, DI, or at least bottled water for mixing chemicals and rinses...

Colin Kaminski · Post by **Colin Kaminski** » Fri Apr 30, 2004 1:32 pm

"I use dichromate for bleaching - it works fine in combination with "Dokumol" which is a developer from Tetenal.

I will check this - recommended is 1:4 - I will try 1:8!"

1 to 9 is the most common dilution used for this developer.

It is very high contrast, I believe that means it has a high gamma, which would make exposure and developer times critical. Are these conclusions correct? Dinesh?

Bob · Post by **Bob** » Fri Apr 30, 2004 2:05 pm

It sounds to me like you may be using a developer that is unsuitable for holography. What's wrong with D-19? By the way, when using pre-packaged D-19, prepare the entire amount. Otherwise, you'll never know what the composition of your developer is.