Using a 660nm laser to expose legacy AgX Agfa, Ilford, HRT (BB) plates
Posted: Mon Mar 14, 2022 2:33 pm
Project Description:
Twenty four 4x5 inch, red sensitive glass plates exposed to test new Cobolt Flamenco 660nm 500mw laser.
Plate types tested: Agfa 10E75 NAH, Agfa 8E75 (NAH), Agfa 8E75HD (NAH), Ilford SP696T (NAH), HRT BB640 (NAH).
All plates ranging in age from about 20 to 45 years old.
Hologram test setup: H2 transfer camera, H1 was 15 year old 12x16, 8E75HD NAH ruby pulsed portrait master exposed at 694nm transferred to 4x5" H2 image area, 1:1, both H1RC & H2RB collimated.
The purpose of these hologram tests was to ascertain whether or not the 660nm laser wavelength, and, more specifically, the Cobolt Flamenco laser, is suitable for exposing legacy Agfa, Ilford, and HRT red sensitive silver halide hologram plates and film. The plates and film tested were all originally designed for use with 632.8nm, 640nm, and/or 694nm laser light. In summary, the answer is yes, 660nm works well for successful exposures of these legacy materials.
The surprise finding (to me) is that these very old materials have lost two to three orders of magnitude of sensitivity as they’ve aged. Although not included in this series of test exposures, similar legacy green sensitive materials from the same manufacturers have not lost much sensitivity. Since it’s possible to make good exposures on all the red sensitive materials tested, regardless of this loss of sensitivity, it seems possible that it’s the red sensitizing dye(s) used that have lost sensitivity.
Some holographers making optical display holograms and using red sensitive legacy materials, particularly the Agfa 8E75HD and Ilford SP696T & SP673, use 632.8nm HeNe lasers with a maximum output power of about 50mw.
Newer SLM DPSS lasers at 640nm are now available at output powers up to 500mw as well as the 500mw 660nm laser used for these tests. Manufacturer's spec sheets for their legacy red sensitive materials show that their materials are very sensitive at 660nm as well as the more typically used 632.8nm and 640nm.
A major difference in these two new lasers is that the 660nm units are about 60% of the cost of the 640nm units and the 660nm units have double the warranty.
Anecdotally, holographers have found these legacy red sensitive materials to be significantly less sensitive than when new. The reasons have been variously ascribed to fogging and dark reaction, etc. while stored. It is this holographer's opinion that the poor results obtained by others, with these much lower power lasers, may have simply been the result of insufficient exposure due to a large loss of red light sensitivity in the legacy materials. The possible proof of this is demonstrated by the good results obtained when these same materials were exposed to two to three orders of magnitude more exposure than was required when new.
I welcome constructive comments and criticisms.
Below is a link to an Excel spreadsheet with data on each of the 24 test exposures. I tried to upload it here directly but it's too large (all the photos) for the forum to accept. Please let me know if you have trouble accessing the link.
Please note that the numerous Excel spreadsheet explanatory cell notes and photos will not be visible unless you download the XLSX spreadsheet to a computer (not iPhone or iPad).
https://www.dropbox.com/scl/fi/thlco6vy ... 75fwd0i3gq
Twenty four 4x5 inch, red sensitive glass plates exposed to test new Cobolt Flamenco 660nm 500mw laser.
Plate types tested: Agfa 10E75 NAH, Agfa 8E75 (NAH), Agfa 8E75HD (NAH), Ilford SP696T (NAH), HRT BB640 (NAH).
All plates ranging in age from about 20 to 45 years old.
Hologram test setup: H2 transfer camera, H1 was 15 year old 12x16, 8E75HD NAH ruby pulsed portrait master exposed at 694nm transferred to 4x5" H2 image area, 1:1, both H1RC & H2RB collimated.
The purpose of these hologram tests was to ascertain whether or not the 660nm laser wavelength, and, more specifically, the Cobolt Flamenco laser, is suitable for exposing legacy Agfa, Ilford, and HRT red sensitive silver halide hologram plates and film. The plates and film tested were all originally designed for use with 632.8nm, 640nm, and/or 694nm laser light. In summary, the answer is yes, 660nm works well for successful exposures of these legacy materials.
The surprise finding (to me) is that these very old materials have lost two to three orders of magnitude of sensitivity as they’ve aged. Although not included in this series of test exposures, similar legacy green sensitive materials from the same manufacturers have not lost much sensitivity. Since it’s possible to make good exposures on all the red sensitive materials tested, regardless of this loss of sensitivity, it seems possible that it’s the red sensitizing dye(s) used that have lost sensitivity.
Some holographers making optical display holograms and using red sensitive legacy materials, particularly the Agfa 8E75HD and Ilford SP696T & SP673, use 632.8nm HeNe lasers with a maximum output power of about 50mw.
Newer SLM DPSS lasers at 640nm are now available at output powers up to 500mw as well as the 500mw 660nm laser used for these tests. Manufacturer's spec sheets for their legacy red sensitive materials show that their materials are very sensitive at 660nm as well as the more typically used 632.8nm and 640nm.
A major difference in these two new lasers is that the 660nm units are about 60% of the cost of the 640nm units and the 660nm units have double the warranty.
Anecdotally, holographers have found these legacy red sensitive materials to be significantly less sensitive than when new. The reasons have been variously ascribed to fogging and dark reaction, etc. while stored. It is this holographer's opinion that the poor results obtained by others, with these much lower power lasers, may have simply been the result of insufficient exposure due to a large loss of red light sensitivity in the legacy materials. The possible proof of this is demonstrated by the good results obtained when these same materials were exposed to two to three orders of magnitude more exposure than was required when new.
I welcome constructive comments and criticisms.
Below is a link to an Excel spreadsheet with data on each of the 24 test exposures. I tried to upload it here directly but it's too large (all the photos) for the forum to accept. Please let me know if you have trouble accessing the link.
Please note that the numerous Excel spreadsheet explanatory cell notes and photos will not be visible unless you download the XLSX spreadsheet to a computer (not iPhone or iPad).
https://www.dropbox.com/scl/fi/thlco6vy ... 75fwd0i3gq