A doubt on using Beseler PM1A color analyzer to determine exposure of B&W print

[Xícara]

Hello,

I've recently started doing B&W enlargements. My enlarger came with a Beseler PM1A color analyzer and I've been using it to analyse the contrast of negatives in order to select the appropriate filter for multi-grade paper. On pages 13-14 of the PM1A manual (http://looscanons.com/php/download.php?f=beseler/pm1A.pdf), there are instructions on how to use the device to determine the exposure of an unknown negative. I have a doubt about the procedure, which I'll get to below - sorry if this is a bit long-winded!

The prior step in determining the exposure for an unknown negative is to make a control or "good print" as a reference for a given paper and magnification. Once a good print has been made the user takes note of the aperture and exposure time. Leaving the magnification and aperture of the enlarger lens untouched and using the white light sensor of the PM1A, the user positions the "reading aperture" of the PM1A sensor directly under the darkest region of the projected image still with evident detail. The user then adjusts the white knob of the PM1A until the meter reads null. The white control knob setting is then noted.

To determine the exposure for an unknown negative and for the same magnification/paper used in the control, the user returns the white control knob setting where it read null with the control and the aperture of the lens to the prior setting. A diffuser is then placed in the light beam of the the projection and the aperture of the lens adjusted until the meter reads null. This aperture may then be used to make the new exposure with the exposure time used for the control or, presumably, the exposure time may be adjusted using the original aperture, to compensate for the number of adjusted stops.

Finally, my question is, why is the control reading for white light set using a non-diffused reading for the darkest region of the control projection with detail and not simply by using a diffused reading? ie. Why isn't the diffuser used to record the control null reading?

Another thing to mention is that I do not have the original PM1A diffuser. I'm using a piece of frosted plastic from a fruit juice bottle, as suggested to me on a different forum.

I'd be grateful for any comments.

Thanks!

 

[tezzasmall]

Hi,

having just read your post, I immediately went and browsed 'Using a Paterson exposure meter' on this site and then read a number of posts. I did this as having had one of the Paterson meter's in the past, it sounds like it may work in a similar way to what you have, what with the frosted diffuser. Doing so might help you understand things a little.

Oh, and just looking at your Flickr page, you have some good images on there.

In the mean time I hope that some one else comes along to answer you main question.

Terry S

PS And a quick browse of RH design's product instructions might help a little as well, as the Analyser has a measuring probe and it may (but not sure) help explain your question as well:

http://www.rhdesigns.co.uk/darkroom/index.html

 

[Xícara]

having just read your post, I immediately went and browsed 'Using a Paterson exposure meter' on this site and then read a number of posts. I did this as having had one of the Paterson meter's in the past, it sounds like it may work in a similar way to what you have, what with the frosted diffuser. Doing so might help you understand things a little.

Thanks Terry. Found some interesting things with your search string, such as using common "reference tones" in the good print and in the unknown (eg. skin tones, grass, clouds). Will keep looking and also check out the RH designs link.

 

[ic-racer]

When you calibrate the baseboard meter, you can base your exposure on a highlight, a shadow, a gray card incorporated into a similar negative, or you can place a diffusor over the enlarging lens, or even use a reading taken with no film in the carrier! I have used all the methods and each has its advantages and disadvantages. For example, a reading taken with no film in the enlarger is(was) best for printing color transparency to Cibachrome, etc.

 

[Xícara]

When you calibrate the baseboard meter, you can base your exposure on a highlight, a shadow, a gray card incorporated into a similar negative, or you can place a diffusor over the enlarging lens, or even use a reading taken with no film in the carrier! I have used all the methods and each has its advantages and disadvantages. For example, a reading taken with no film in the enlarger is(was) best for printing color transparency to Cibachrome, etc.

Thanks, I see. A lot clearer now. All the best!