Is brightness a function of exposure time ?

[thycore]

Hello Everyone, I wish you all happy Christmas & New eve 2018 !

I am still making Denisyuk holograms, and trying to master this step before going any further with a more expensive set involving mirrors or lenses.

At the moment my setup is :

Laser source : 100mw laser diode with collimating lens removed.
Shutter : arduino micro controller which controls a servo-motor which rotates a shutter ON or OFF.
Holofilm sandwiched between 2 glass panes & secured properly.
I use exposure time of 0.5 second and after processing I got a very sharp image of my test subject (a magnetic harddrive without top cover)

The image is sharp, but somehow "dark", if I use the "sun" as light, the image is very bright and satisfying but, with an inside lamp it's kinda too dark to be great.

I made an other hologram using "Ultimate plates" and these looks just wonderful bright & sharp including with my poor inside lamp.

Question : is this related to the "film grain size" or something ?
Or is it a question of sensitivity & therefore a question of exposure time to have some "ligther" hologram with my holofilm ?

Thanks !

[pluto]

I think the ultimate plates just have a better diffraction efficiency, not sure what the 'holofilm' you mentioned is though. Can you post a link to where you bought it?

[lobaz]

Hi,
there are too many variables.
The simple answer to your question is: yes, image brightness is a function of exposure time. If you expose for too short time, you will have problems to develop the plate, i.e. recorded fringes are too weak. Thus, low brightness. You can develop the plate longer, of course, but the developer attacks unexposed emulsion as well, which means that noise increases.
If you expose for too long time, parts of emulsion that should not be exposed due to interference get some light energy as well. The plate is then overexposed. Again, contrast between "exposed" and "unexposed" parts of the emulsion is low, which leads to low brightness. You can definitely develop for shorter period of time or use weaker developer.
Anyway, for a specific development conditions and a specific recording setup, there is just one exposure time that gives the brightest image. If you are over or under, you get dimmer result.

Image brightness then depends on material + developer + bleach combination, grain size, wavelength of the laser and many other factors.

Best,
Petr

[thycore]

Thank you very much for such detailed info

I made 10 tests on same material, same subject, with 10 different exposure time and.. yes

I clearly have a "best" result in the middle, not enough is dark, too much is blurry, the best for me being around 1,5 secs exposure.

I also found that my D-19 developer needed to be refreshened, it was too old.

I'm using this formula : http://holowiki.org/wiki/Ewesly_/_Holog ... Kodak_D-19

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By any chance, any idea how I could prepare my D-19 in 2 solutions A and B stored separately to longer the shelf duration ?

[Ed Wesly]

"By any chance, any idea how I could prepare my D-19 in 2 solutions A and B stored separately to longer the shelf duration ?"

The trick is to keep the developing agents separate from the alkali, which is also known as the activator. See page 6 in http://edweslystudio.com/Formulae/Developers/CWC2g.pdf to see how it was done for CWC2. I leave it as an exercise for the student to do the same for D-19.

Here are some D-19 variations: http://edweslystudio.com/Formulae/Developers/D19.html

Have fun!

After posting, checked the link above, it's the same as mine!

[thycore]

Hey,

Thank you so much for your explanations & links, I read it through and it was really a good learning for me

I prepared some splitted D-19 yesterday night, I now have part A and part B like this :

D-19 Part A :
2 g Metol
90 g Sodium Sulfite
8 g Hydroquinone
5 g Potassium Bromide
0.5 litre water

D-19 Part B :
52.5 g Sodium Carbonate (monohydrated)
0.5 litre water

I suspect I may have an incomplete solution due to the lower water volume in the both parts, especially the Potassium Bromide salt did not solve completely and I had some remaining cristals in the erlenmeyer despite heating at 50°C. I also had some unsoluted Sodium Carbonate on my Part B, but I suspect this is due to a too quick immersion, it formed some sort of calcite nuggets which won't solve anymore.

It seems to behave like expected for now when mixing back in equal quantity just before developing

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Regarding my dichomate based bleach, and due to the extreme toxicity of the material, I tend to re-use the bleach bath several times (like for 10-15 holograms over 2-3 months) to avoid the "breaking-bad-like cooking phasis", is there any chance my bleach bath would be the gulty one for salty deposits on my holograms ? Of course an old chemistry would bleach wayyyy slower, but would this also carry some bleached silver which would stick back to the film ? I wish I could replace this Potassium Dichromate by something better for the environnement !

[Ed Wesly]

Surprised that the potassium bromide didn't dissolve, even with heating. Try grinding the crystals into smaller chunks and see if they dissolve.

Sodium carbonate definitely does dissolve more readily in warm water, like 38 - 40C. That is why it fell out of favor as a laundry washing detergent, as colored clothes needing cold water cleaning. I use the "Arm & Hammer" brand of "All Natural Super Washing Soda" when I am out of the laboratory grade carbonate.

The dichromate based bleach goes bad with use, and that depends on how much silver gets dissolved in it. When it starts taking longer than 2 minutes is when I stop using it.

And it is responsible for the fine powdery deposits on your holos! I mix most of my chemistry with tap water, except for this one, as the minerals in the water will precipitate out due to the dichromate doing its job. Jeff Blyth recommends immersing the holo in a tray of distilled water before and after the bleach to prevent this from happening. Immerse the holo in a 1% solution of sodium sulfite after the bleach works to clear it out.

For some fun precipitation, put some ordinary table salt into some used bleach, and silver chloride crystals will form! And you can play with them to see their light-sensitivity and how they don't dissolve in water but do dissolve in thiosulfate, or fixer solutions!

Potassium permanganate can also be used as a reversal bleach, good luck getting your hands on that stuff! (Somehow used in the drug trade, need to sign a form when buying it from Photographers' Formulary!) Here's a recipe: http://edweslystudio.com/Formulae/Bleaches/S13.html. This bleach is temperamental, as Kodak found out, when switching to that formula in the B&W reversal film developing kit in the '90's.

I seem to recall that Jeff B. also had a recipe for disposing of dichromate solutions, but I don't remember where it was.

[pluto]

Potassium permanganate can also be used as a reversal bleach, good luck getting your hands on that stuff!

Quite easily and cheaply available on eBay It's not a particularly hard to get or watched chemical, although some states go overboard with this kind of stuff (you need a permit to buy an erlenmeyer flask in Texas!)

[jrburns47]

It's been literally 40 years since I used potassium permanganate so I may remember incorrectly- is it an oxidizer that can be used to make explosives? I vaguely remember that it's highly staining...

[Din]

It's been literally 40 years since I used potassium permanganate so I may remember incorrectly- is it an oxidizer that can be used to make explosives? I vaguely remember that it's highly staining...

KMnO(4), so yes, strong oxidiser. It used to be a component of photographer's flash powder. It was also used to cure (or relieve, anyway) various foot problems; you soaked your feet in a solution of pot permanganate (I can attest this actually works!). It stains everything brown. Dilute sulphuric acid will get rid of the stain.