On ebay all I have seen are the real big counter top densitometers. ON the BTZS video I bought davis uses a small one. When reading what people write here they talk about different channels but when I look at the descriptions of densitometers I don't see specific mention of different channels of light being measured or of included filters.
I am so confused!
Does anyone know who makes the little densitometer that davis uses in the BTZS video?
DO all densitometers measure the different channels, and how important are they? I develope in pyrocat but will also be developing in non-staining developers in the near future.
Typically a color transmission densitometer will read in three color channels and a visual channel (B&W density). The blue channel read out is more accurate then the visual channel when one is using a staining developer such as Pyrocat since it indicate the additional density imparted by the proportional stain. Additionally other densitometers such as the Xrite 361T will read UV which is even more accurate when one is printing alt process with a film that has been developed in a staining developer like Pyrocat. I imagine that Phil Davis uses a black and white densitometer of some type (I have not seen the video that you mention). The reason that I think that is most likely is that Davis at latest report did not support staining developers in his research.
The Heiland TRD2 is pretty small. X Rite used to make (not sure if they still do) portable densitometers both for reflection and transmission that were pretty small, you were able to put them on your pocket.
If you do an X Rite search on e bay on the home page you will get results for the best ones available. The ones you are looking for are, X Rite 361T, 369T, 310T (these are only transmission B&W) or the 810 or 811 which are both transmission and reflection color densitometers. If you plan to do alt printing, then the ones you need are the 361 or 369 as they both have an UV channel. If all you plan to do is silver then the color densitometer with both transmission and reflection capablities are the best.
A quick explanation of colour densitometer 'channels':
For comparative purposes (comparing the readings from one densitometer with another) 'Status' colour filters are used. The common ones for colour photographic materials are 'Status M' and 'Status A' and there will be three filters - red, green and blue.
Status M is used for materials that are intended as an intermediate part of the process - eg camera negative film that will be printed. Therefore the M filters are intended to represent the response of colour print materials. They don't do that particularly well, but that's a longer story. I'll explain later if you wish.
Status A is used for the final image, whether it is a transparency or a print.
A transmission densitometer can, therefore, have both M and A, while a reflection densitometer may only have A. The Status filters will be in addition to a 'visual' channel as well which covers all visible wavelengths. This is typically done with a Wratten 106 filter.
Typically, dichroic (spectral interference) filters are used for the Status filters. They are very stable through the years. You can swap out the Status M filters for dye based filters to improve the match with the response of your paper, for example, but those filters won't remain as stable as dichroics.
Other filter types include:
Status T - wide band RGB filters for graphic arts prepress etc use, typically gelatin filters.
Status I - narrow band, graphic arts, typically dichroic.
UV - typically Wratten 18A, for alternative processes.
Ortho - for ortho processes (had you guessed?)