Help me calibrate my homemade densitometer!

[Anupam Basu]

Ok! So it's not a densitometer but I think it might be an usable substitute. I modified an idea I found on the internet to produce what seems to be quite a decent setup.

I start with a cheap photocell from radioshack and mount it inside an empty reloadable 35mm canister that lets light in from the top. All that's left to do is hook the ends to a $15 digital multimeter, put it under a table lamp or an enlarger and you have a densitometer ... Er, well, at least you have something that converts different film densities to a series of numbers that are reproducible.

Now what I need to do is to verify whether this is accurate enough for home-brew film testing purposes - for that it would be great to have a strip of film with known densities. So I am wondering if any of the folks here with a densitometer would be willing to send me such a strip.

Thanks,
Anupam
I am attaching my results from a test run on Fomapan 400. I created a quick spreadsheet to make things easier.

 

[Kino]

Stouffer Graphics Arts has a very reasonably priced Transmission Density Wedges http://www.stouffer.net/TransPage.htm. MUCH cheaper than calibrated Kodak Wedges. I prefer the Kodak calibrated wedges for my workplace, but these work just fine for home use.

You need a densitometer? I have an old Macbeth Quantalog vacuum tube-based, analog needle densitometer in my basement that needs work; you can have it for the cost of shipping.

There used to be a man in Columbus, Ohio who would work on the older Macbeth's when I briefly maintained Ohio State University's Dept of Photo and Cinema still photo labs, but last time I used him, it was over 15 years ago and I don't even know if he's still around.

Heck, with this link, http://www.pauck.de/marco/photo/stuff/manuals/manuals.html you will find the operation and service manual for it and you can probably either fix it yourself or have it repaired by someone who is good with electronics.

I hate to see it lay around and gather dust when you might be able to use it. I just use the XRite 310s or Macbeth 924s at work if I need to measure density.

Sorry folks, I only have one! ;-)

Send me a APUG message to set up shipment if you are interested.

 

[Dan Henderson]

I second the opinion of using a Stouffer step tablet. The one I have is graduated in steps of .10, or 1/3 stop.

If you have a good film scanner or flatbed scanner with transparency adapter, you can use it along with the step tablet as a densitometer. There was a very good article describing this process in the last issue of Photo Techniques. I am now using it and finding it working very well.

 

[ChuckP]

I've used small pieces of neutral density filters to calibrate a system. Maybe not 100% correct to do it that way but close enough for checking film curves.