Good day,
I really appreciate you guys for having this forum.I bought a holokit from integraf and just beginnng to shoot holograms. I just follow the insruction from integraf's website and i read it takes approximately 5 to 7 seconds to record a hologram using 5 mw laser. I have a 1 mW HeNe laser on standby and I want to atleast use it. Can anyone inform me how to determine the exposure time in recording holograms? I want to calculate it on my own so if ever I can have different laser and plates, I can easily figure out how many seconds I would expose it.
Im using PFG-01 plates 63mm x 63 mm with JD-2 developer.
Thanks everyone,
Donald
how to determine exposure time?
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Colin Kaminski
how to determine exposure time?
If you are happy with the exposures at 5 to 7 seconds you can use 10 to 15 for you HeNe as a starting place and adjust from there. Your diode is about 4mw and you probably are throwing away about half of the light because the beam is very elliptical.
Another way is to make a test plate. Make a 1/2" wide slot in 2 black cards and advance them across the plate as you increase the exposure time. You can start with 5 seconds and double the exposure each time.
Another method is to buy an exposure meter and measure the exposure of a set up that is producing good results. If a new set up has half of the light then you double the time. You can make an exposure meter by hooking up a solar cell to a ohm meter and measuring the current (not the voltage).
If you want a starting place the slavich's web site lists the exposure energies of all of their films and you can calculate the energy hitting the plate. I have found this the least reliable method because so much depends on processing. For instance I have to increase exposure time when my JD-2 is cold. A hologram I was particularly happy with was 2.5" plates exposed with an Integraf laser for 30 seconds! But I had spread the beam greatly to get the reference power more even at the edges and the developer was about 50 F. I now heat my developer to 70 F in the winter.
Another way is to make a test plate. Make a 1/2" wide slot in 2 black cards and advance them across the plate as you increase the exposure time. You can start with 5 seconds and double the exposure each time.
Another method is to buy an exposure meter and measure the exposure of a set up that is producing good results. If a new set up has half of the light then you double the time. You can make an exposure meter by hooking up a solar cell to a ohm meter and measuring the current (not the voltage).
If you want a starting place the slavich's web site lists the exposure energies of all of their films and you can calculate the energy hitting the plate. I have found this the least reliable method because so much depends on processing. For instance I have to increase exposure time when my JD-2 is cold. A hologram I was particularly happy with was 2.5" plates exposed with an Integraf laser for 30 seconds! But I had spread the beam greatly to get the reference power more even at the edges and the developer was about 50 F. I now heat my developer to 70 F in the winter.
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JohnFP
how to determine exposure time?
If the plate requires 100uJ/cm^2
And your laser is 1 mW
Remember that 1 watt for 1 second = 1 Joule
1 mw for 1 second = 1mJ
1 mW = 1000uW
So a 1 mw laser has the expanded beam such that only 2/3 of the beam is being used.
.666mW = 666uW = 666uJ/second
Now a 4" by 5" plate = 10.16cm x 12.7cm = 129cm^2 or ~130cm^2
So using "If the plate requires 100uJ/cm^2" and we have 130cm^2 then 100x130 =
13000uJ required.
If energy reaching the plate is 666uJ/second and we need 13000uJ then how many seconds are required?
13000/666 = 19.5 seconds.
So for using a plate that requires 100uJ of energy and the plate is 4" by 5" with a 1mW laser expanded to using only 2/3 of the energy ... about 20 seconds would be required.
I double checked it and believe this to be correct but if anyone has corrections feel free to interject.
And your laser is 1 mW
Remember that 1 watt for 1 second = 1 Joule
1 mw for 1 second = 1mJ
1 mW = 1000uW
So a 1 mw laser has the expanded beam such that only 2/3 of the beam is being used.
.666mW = 666uW = 666uJ/second
Now a 4" by 5" plate = 10.16cm x 12.7cm = 129cm^2 or ~130cm^2
So using "If the plate requires 100uJ/cm^2" and we have 130cm^2 then 100x130 =
13000uJ required.
If energy reaching the plate is 666uJ/second and we need 13000uJ then how many seconds are required?
13000/666 = 19.5 seconds.
So for using a plate that requires 100uJ of energy and the plate is 4" by 5" with a 1mW laser expanded to using only 2/3 of the energy ... about 20 seconds would be required.
I double checked it and believe this to be correct but if anyone has corrections feel free to interject.
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Roli
how to determine exposure time?
I have a 8MW Laser = 8000uW
If I only use 2/3 of the beam for a 4" by 5" plate (130cm²)
= 13000uJ required
= 13000/5333 (2/3 of 8000) = 2,43 seconds
This seems to be very short!
I´ve tried it with PFG01 (80uJ/cm²) with my 8MW Laser on a 6.3 x 6.3 plate.
Calculation:
2/3 of beam used
6.3 x 6.3 =approx 40cm²
80uJ/cm² required for PFG01
80 x 40 =3200uj required
2/3 of 8000uW = 5333
3200/5333 = 0,6 seconds
Result: no results after 3 tests
Thank´s in advance for any further ideas!
Roland
If I only use 2/3 of the beam for a 4" by 5" plate (130cm²)
= 13000uJ required
= 13000/5333 (2/3 of 8000) = 2,43 seconds
This seems to be very short!
I´ve tried it with PFG01 (80uJ/cm²) with my 8MW Laser on a 6.3 x 6.3 plate.
Calculation:
2/3 of beam used
6.3 x 6.3 =approx 40cm²
80uJ/cm² required for PFG01
80 x 40 =3200uj required
2/3 of 8000uW = 5333
3200/5333 = 0,6 seconds
Result: no results after 3 tests
Thank´s in advance for any further ideas!
Roland
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JohnFP
how to determine exposure time?
Thanks in advance. His match mine. I just want to make sure I am not missing something.
Peace!
Peace!
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JohnFP
how to determine exposure time?
Even without calculating, 1/2 second for a 2.5 x 2.5 plate seems pretty close with a 8mw laser.
First- are you attempting a transmisson or reflection and what is your table geometry?
How dark does it turn in the developer after how long?
What kind of developer are you using.
Michael recently stated that he overexposes but underdevelope.
Have you tried to make a test strip plate. Basically card off all light except a strip of plate, expose for specific time. Then card off all but another strip, expose with different time, etc. What you will have is 3 or 4 strips of exposures on the same plate what will be developed exactly the same. See which one comes out better.
First- are you attempting a transmisson or reflection and what is your table geometry?
How dark does it turn in the developer after how long?
What kind of developer are you using.
Michael recently stated that he overexposes but underdevelope.
Have you tried to make a test strip plate. Basically card off all light except a strip of plate, expose for specific time. Then card off all but another strip, expose with different time, etc. What you will have is 3 or 4 strips of exposures on the same plate what will be developed exactly the same. See which one comes out better.
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Roli
how to determine exposure time?
Yes, I´ve tried two strip plates too.
With 5 sec I had the best result (bright green)with the first test.
But it´s very strange - I´ve made this test twice and I got very poor results with the second plate - even with 5 seconds?
I made a refection - single beam.
Developer: Dokumol
Developing time: 1 min.
Roli
With 5 sec I had the best result (bright green)with the first test.
But it´s very strange - I´ve made this test twice and I got very poor results with the second plate - even with 5 seconds?
I made a refection - single beam.
Developer: Dokumol
Developing time: 1 min.
Roli
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JohnFP
how to determine exposure time?
How dark did it go in the one minute?
You may have stability problems if you cannot repeat getting a hologram and exposure and processing were same.
WHat kind of laser are you using?
Lastly, take an object that is bright white and has a flat back and a flat front. Lay it on its back. Lay the plate directly on the front. Let settle for 5 minutes at least. Try your test plates this way. If the plat is laying directly on the object you will illiminate the possiblilty of movement of the object to plate. A large white button would be great for a 2.5 x 2.5 plate. Don't forget to block the leading edge of the plate with black tape or something so the light does not enter into the edge of the plate.
You may have stability problems if you cannot repeat getting a hologram and exposure and processing were same.
WHat kind of laser are you using?
Lastly, take an object that is bright white and has a flat back and a flat front. Lay it on its back. Lay the plate directly on the front. Let settle for 5 minutes at least. Try your test plates this way. If the plat is laying directly on the object you will illiminate the possiblilty of movement of the object to plate. A large white button would be great for a 2.5 x 2.5 plate. Don't forget to block the leading edge of the plate with black tape or something so the light does not enter into the edge of the plate.
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Roli
how to determine exposure time?
Thank you!
I don´t think that stability is the problem - I´ve tried a white flat object (ceramic) and I´ve also tested the stability.
Sometimes I get a very good result (very bright yellow or green)
Sometimes I have a very poor image with the same setup and chemistry.
Maybe the plates are too old (4 years) or the humidity is too high (75-80%)
But I will check it again!
Cheers
Roli
I don´t think that stability is the problem - I´ve tried a white flat object (ceramic) and I´ve also tested the stability.
Sometimes I get a very good result (very bright yellow or green)
Sometimes I have a very poor image with the same setup and chemistry.
Maybe the plates are too old (4 years) or the humidity is too high (75-80%)
But I will check it again!
Cheers
Roli
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Dinesh
how to determine exposure time?
The exposure calculations depend on how much you're expanding the beam, remembering the Gaussian fall-off. Is the beam uniformly bright across the 4x5 and falling off outside the edges of the film? In other words, if you substituted an 8x10 would you see a bright, uniform center of diameter 5 in with decreasing brightness? Where is the missing 1/3? Also, you say the plate is 4 years old. In that case the sensitivity of the film is probably no longer 80 uJ/cm^2, it decreases with age. However, if you got good results with 5 secs, it seems that at least you have a working exposure.
What kind of bad results? Is there no image, is it dim, is it bright at the edges but dim in thecenter? Do you develop to the same darkness? Is the developer made fresh each time, or do you re-use it? Is there any temperature variation in your darkroom? High humidity should not affect Silver Halide. The grains of Silver halide may get a little further seperated by humidity if the gelatin swells, but not so much that it'll affect recording. The age may be an affect. If you suspect age, expose for longer. Ideally, it should go about 50 to 60% dark in about 2 minutes. If it takes much longer, you've underexposed, if it goes dark too quickly (under a few seconds) you've overexposed. Assuming some part of the film is obstructed by the filmholder, if the entire film goes dark, it's fogged (it's been exposed to white light).
What kind of bad results? Is there no image, is it dim, is it bright at the edges but dim in thecenter? Do you develop to the same darkness? Is the developer made fresh each time, or do you re-use it? Is there any temperature variation in your darkroom? High humidity should not affect Silver Halide. The grains of Silver halide may get a little further seperated by humidity if the gelatin swells, but not so much that it'll affect recording. The age may be an affect. If you suspect age, expose for longer. Ideally, it should go about 50 to 60% dark in about 2 minutes. If it takes much longer, you've underexposed, if it goes dark too quickly (under a few seconds) you've overexposed. Assuming some part of the film is obstructed by the filmholder, if the entire film goes dark, it's fogged (it's been exposed to white light).