Hope you can help.
A while back you mentioned that you used a spectrosensitometer to test sensitivity of emulsions to various wavelengths of light.
Can you recommend a "low budget" spectrosensitometer? Can you point me towards a typical setup or photos of a film spectrosensitometer?
1 constant voltage power supply
1 light source with a repeatable daylight type output
1 Bausch and Lomb monocrhomator
1 step wedge as wide as the output of the monochromator
1 solid mounting plate
That is the high end.
The low end is a strip of Wr 99, 98 and 70 filter mounted over a step wedge. Exposures will show relative R/G/B speeds. This is not quantitative.
Interesting ... that would be a fantastic piece of equipment for emulsion making.
How are those parts put together to be functional?
The above should include a shutter mechanism and timer for achieving different exposures.
It is linear as follows:
Light > Shutter > Monochromator > Step Wedge / object being tested.
The optical items are all mounted on a flat plate of metal for a sturdy makeup and to give optical alignment. The monochromator has a range from about 300 nm - 900 nm with an adjustment for which range - ie UV, visible or IR. It also has a filter drawer next to the shutter for any desired filter combination.
I have posted examples here of exposures. I have no good photos of the device itself.
Thanks for your reply. Your answer inspired me and I found that I already had the answer in no less than three photography books (I should have looked before I posted!). One being the 1958 edition of the Ilford Manual of Photography. Attached is a scan from this excellent book showing a spectrograph. Baker also has construction details for one.
Diffraction gratings and lenses can be purchased very inexpensively from "The surplus shed". http://www.surplusshed.com/
These companies sell step wedges.
http://www.stouffer.net/TransPage.htm also http://www.tiffen.com/Kodak%20Profes...%20catalog.pdf
Any recommendations on the part number of the step wedge that would be most suitable?
You have seen examples of wedge spectrograms that I posted here. There are many in the book by Mees and James, done by Paul Gilman.
You must calibrate it somehow.
Wow, that looks fantastically simple ... it's one of those "Why didn't I think of that?" kind of things.
I think I might build one.
What is involved in the calibration? I'm assuming you'd need to somehow correct for the spectrum of the light source? I know that you'd also probably have to mark off the wavelength scale, but that'd be easy with, say, a fluorescent lamp.
Yes they do look straightforward to construct. Everything is more difficult in the doing though....at least for me :-)
PE raises a good point regarding calibration.
I understand that a fluorescent light source would have many spectrum lines in it. See the picture of a fluroscent light spectrum at:
Baker has some paragraphs on calibration in Photographic Emulsion Technique, 1948 edition. He mentions using an arc lamp (not something widely used today). I was thinking that Light Emitting Diodes (LEDs) might be a more modern alternative.
If I ever get around to making one I would use it for relative differences. For example seeing if the emulsion was now sensitised to green light. Exposing some panchromatic emulsion such as Plus-x etc would give a "reference" spectrograph. This avoids the need to calibrate.
Yes, you need to know where UV, visible and IR are positioned and the actual wavelengths. Look at some published spectra in Mees and James or here, that I have posted to see how they look. That is about the best I can say.
Mine is calibrated, and has 2 settings. One is visible and one is IR. If I don't use a UV filter, I get a UV harmonic at 700 nm. This harmonic vanishes with a UV filter and is one of the faults of these particular instruments.
There exist three other forms:
1.sometimes you can find the Lagorio-tableau – 16 colorstripes are combined with 13-part grayscales. The tableau is around 24x30cm and was made in ?Czecheslowakia?Poland?. Named VUZORT. The U has a accent. I have heard, that other forms had exist.
2.The Schott variable Interferenzfilter from around 360 to 800nm. It is ca 27 mm x 190 mm, my is combined with a parallel graystep made by grainless bw film. Ideal for 35mm films to control.
3.In older times scientist had have a pocket-spectrometer. This is today in the program of scientific tools, but you will find often on auctions for history of technology and science. A Zeiss Jena with scale 400-700nm is combined with a simple only mechanical construction from ICA, Dresden (famous camera-company) for 6.5 x 9 cm plates, where a 8mm slit will exposed in 7 following positions. In the plate-cassettes it is simple to mount 2 parallel 35mm stripes.