Calibrate a transmission densitometer

[wskmosaic]

I have just purchased and am awaiting delivery of my first transmission densitometer--a Tobias TBX. All I know about it is that it comes with a power cord and will light up. I didn't pay a lot for it, but probably too much.

I own a 31-step Stouffer wedge. Where do I go from there?

I don't have a manual; I haven't the foggiest notion of what else I need to calibrate the thing or how to go about it.

I photograph with black and white film.

Any guidance or information will be appreciated.

Please don't transmit guffaws!
tnx
Warren

[Bill Burk]

There is a chance you will not need to "calibrate" it. Just use it. If your work doesn't need to be scientifically relied upon then a few points of error will not hurt much. Certainly would not hurt as much as trying to calibrate and messing it up.

Most densitometers have a button to press to zero them. Just press the head down on nothing and zero it. Then check the steps of your 31-step scale. Do not expect the steps to be exactly what the chart says. If the numbers make sense then you can just use it as-is.

Sometimes you'll get a calibrating film (or plaque) with a densitometer. If so, then you can look for steps to calibrate using the reference density.

[Leigh]

Do you expect to get different answers here than at photo.net and APUG?

- Leigh

[Sal Santamaura]

Do you expect to get different answers here than at photo.net and APUG?...

Do you expect readers will respect you for behaving that way? The LFPF has no rule prohibiting someone from duplicating their own posts elsewhere. Despite significant membership overlap, there are people who don't participate at all three forums. Asking a snide question which puts down the OP for inquiring in more than one venue doesn't diminish him; it makes you appear petty.

[Ken Lee]

I just had mine calibrated by the manufacturer (X-Rite). It wasn't cheap, but it's certified accurate and they give you a calibration step-wedge with the actual numbers on it, so that you can check against a known reference in the future.

You can purchase a Stouffer step wedge - for more money - that has been checked by Stouffer, and the actual numbers are written alongside. This will help, but it won't actually calibrate your machine, and will only cover the visible portion of the spectrum. (Some densitometers measure UV)

[Leigh]

I did provide a lengthy response to his query on photo.net, including how to tell the
difference between calibrated and uncalibrated Stouffer step wedges.

While writing that response I googled the product and found that the manual was available online.
How many other people wasted their time doing the same thing, when the OP could have done it
himself and not inconvenienced others?

In the time it took him to post the same question on (at least) three different fora, he
could have downloaded the PDF manual, and had complete and accurate information.

Teaching people how to do proper research benefits everyone.

- Leigh

[Sal Santamaura]

Do you expect to get different answers here than at photo.net and APUG?...

...Teaching people how to do proper research benefits everyone...

Asking a snide question is not teaching someone how to do research, proper or otherwise.

After many years here, I've concluded that actual attempts at teaching people how to do proper research is futile. With the hope of encouraging newcomers to large format photography, I sometimes spoon feed or reply to previously answered questions, but mostly remain silent. There doesn't seem to be a shortage of others who will post the same information over and over and over again. It's evident by comparing post counts to Join Dates.

[wskmosaic]

First, thanks to Bill Bork. That was helpful.

And otherwise, I do apologize for the trouble I mighrt have caused; I was not aware of the size of the overlap. And indeed I did get different answers on each, some more helpful than others.

I invariably do my best to help myself. It's only when I run into blocks that I ask other photographers.

Thanks, and, again, apologies.

Warren

[Sal Santamaura]

...I do apologize for the trouble I mighrt have caused...

Don't apologize for causing trouble -- you didn't!

In addition to learning about densitometer calibration, I hope you also pick up some insight about searching. Google can be your friend. At the end of whatever words or phrases you need information on, simply add "site:url" to perform an advanced search. For example, to see what was previously discussed on the LFPF forum concerning the topic of this thread, you'd enter:

calibrate transmission densitometer site:largeformatphotography.info

[JBAphoto]

In practice (with an Eseco TRC-60D) I have found that a cheap uncertified Kodak nr2 step wedge works very well for neg' highlight density calibration to achieve results that print well with my enlarger in my darkroom

I suggest that this crude way of finding a starting point will work if you use the results in your own practice

For the real deal try the Wise and Wonderful Web for a pdf of the book of destructions for your own densitometer

Important - don't let your digital friends jibe you about using it to measure the density of film photographers

John