RH Designs Analyzer Pro - Altering Contrast Adjusts Exposure time?

[logan2z]

I've had an RH Designs Analyzer Pro for a long while and think its a great piece of darkroom gear. But there is one behavior of the device that I don't completely understand and the manual hasn't been much help in clarifying it:

Sometimes when I adjust the contrast controls on the Analyzer to see the effects of a contrast change the device also automatically bumps up/down the exposure time. I'm not quite sure what it's trying to do by making an exposure time change when the contrast grade is altered. At first I thought it was trying to maintain the highlight values from the previous contrast grade but that doesn't seem to be it as it is often the case that the exposure change shifts the highlights relative to their value at the previous contrast grade.

I'm probably missing something obvious but I thought another Analyzer Pro user here might be able to tell me what that something is.

 

[MattKing]

If it is programmed for Ilford MGIV papers, it may be taking into account the behavior of those papers when the filtration moves to the higher contrast grades.

 

[Nicholas Lindan]

Have a look at the HD curves for MGIV contrast grades.

Fiber base: http://www.darkroomautomation.com/support/mgivfbhd.jpg

Note that fiberbase has the lower grades cross over at a reflection density of 0.4

RC: http://www.darkroomautomation.com/support/mgivrchd.jpg

While the RC variant of the paper has this 'constant density/exposure' point at a density of 0.55

So things can get pretty messy (er, complicated) pretty quickly, even for two papers that are, ostensibly, the same emulsion.

My understanding is that the Stopclock products use an idealized HD curve, which may or may not fit the actual HD curve of the paper. You might try recovering the calibration data from your timer and plotting it. If you bought the unit used the previous owner may have entered his own idea of calibration constants, and that may explain any odd behaviour.

For anything more than this you should contact RH Designs https://rhdesigns.co.uk/

 

[mmerig]

Have a look at the HD curves for MGIV contrast grades.

Fiber base: http://www.darkroomautomation.com/support/mgivfbhd.jpg

Note that fiberbase has the lower grades cross over at a reflection density of 0.4

RC: http://www.darkroomautomation.com/support/mgivrchd.jpg

While the RC variant of the paper has this 'constant density/exposure' point at a density of 0.55

So things can get pretty messy (er, complicated) pretty quickly, even for two papers that are, ostensibly, the same emulsion.

My understanding is that the Stopclock products use an idealized HD curve, which may or may not fit the actual HD curve of the paper. You might try recovering the calibration data from your timer and plotting it. If you bought the unit used the previous owner may have entered his own idea of calibration constants, and that may explain any odd behaviour.

For anything more than this you should contact RH Designs https://rhdesigns.co.uk/

Papers besides Ilford MGIV have the changes in exposure as a different contrast is selected. Some of it is the one-stop change when going over filter grade 3.5 (or there about). But there are usually small changes in exposure when shifting to a different contrast grade above or below this threshold.

I calibrated the RH Designs AP for the four papers I use, and they all have these shifts in exposure. The shift happens when the AP is used normally. That is, at least one exposure reading is made, and then contrast is changed. If the user just enters an exposure manually without taking a reading, the exposure time will not change if the contrast value is changed. The AP also has reciprocity failure built-in, so the step increases are a little different than expected. There is another thread about this somewhere.

 

[logan2z]

If it is programmed for Ilford MGIV papers, it may be taking into account the behavior of those papers when the filtration moves to the higher contrast grades.

This is using my own custom calibration for Ilford MG FB paper.

I'm sure the Analyzer is taking into account the behavior of the paper as the filtration changes and I expect that, but I would expect it to only reflect those changes on the grey scale without any modification of the exposure time.

 

[logan2z]

If you bought the unit used the previous owner may have entered his own idea of calibration constants, and that may explain any odd behaviour.

I bought the unit new and calibrated it myself for Ilford MG FB paper.

For anything more than this you should contact RH Designs https://rhdesigns.co.uk/

My last inquiry to them went unanswered so I thought I'd try here first this time.

 

[logan2z]

The shift happens when the AP is used normally. That is, at least one exposure reading is made, and then contrast is changed. If the user just enters an exposure manually without taking a reading, the exposure time will not change if the contrast value is changed.

Right, trying to understand why that is the case.

 

[pentaxuser]

Just a curious bystander here but it seems from what mmerig has said that the Analyser "overrides Ilford's MG filters through the range of contrasts provided by the filters which retain the same exposure from 00 to 3.5 and then double exposure for grades 4-5

If that's the case then does the user ignore what Ilford has said( same exposure 00 -3.5 and double for 4-5) and sticks with what the Analyser tells them is the correct exposure for each grade or half grade change as the Analyser gauges the correct exposure more accurately

So in effect the user of the Analyser changes the filters to the grade closest to what the Analyser has said the grade should be and then uses that exposure with combined with the nearest grade filter?

Just out of interest, logan2z, does your analyser tell you to increase at each grade by the same percentage and what is the Analyser's exposure in relation to what Ilford tells.? Is it always more than the filter's exposure

From an "end result" aspect does the Analyser's exposure give you a better print? .

It all sounds very complicated.

Thanks

pentaxuser

 

[mmerig]

Calibration involves a range of exposures and contrast grades for a given paper type, enlarger set-up, and developer. The unit comes with some calibration (like Ilford MG IV with a diffusion head), but RH Designs recommends a user doing their own calibration. If you use a color head, you would calibrate to that instead of a set of filters, etc.

Changing the exposure does not change the contrast, so you can stay with that filter if the contrast looks good but you need to go darker or lighter in the highlights. But changing the contrast changes the exposure to keep the same shade of white -- with all of the papers I am familiar with at least. It's not an RH Designs thing, it's inherent to the paper.

Chris Woodhouse of RH Designs helped write "Way Beyond Monochrome", and that book has a section on the interaction between contrast and exposure. The book has tables showing the changes in exposure (in f-stops or exposure factor). I used a table to make time corrections when changing contrast before I started using an RH Designs AP.

The end result is no better than a test-strip, but it takes me a lot less time and paper to get a decent print than with a test strip. I still use a small sheet of paper (say 4 by 5) for a test when printing large prints, to make sure I don't waste a big sheet of paper. I am a Luddite by nature, but the RHD AP has saved me tons of time and paper compared to test-strips.

It's not that complicated once you get used to it. I have all of my calibration curves written down, and can post them if anyone is interested. I use an Omega DII, with separate condensers (depending on the lens focal length), Ilford filters, and Dektol/Bromophen 1:3 at 2 minutes. The papers are: Ilford MG IV Resin Coated(RC) glossy, MG RC Glossy, Warm tone RC Pearl, and Ilford MG fiber-based.

Making an exposure reading gives the unit a reference so it knows where it is on the curve, and it adjusts exposure accordingly as contrast is changed.

 

[logan2z]

But changing the contrast changes the exposure to keep the same shade of white -- with all of the papers I am familiar with at least. It's not an RH Designs thing, it's inherent to the paper.

I assumed that's what the AP was compensating for and I mentioned it in my first post.. The thing that threw me, though, was that changing the contrast setting by only 1/2 grade on the AP shifted some of the highlight tones to the right of the greyscale. But the initial highlight reading I took using the probe was off the scale (represented by a blinking LED) so I couldn't tell if its value was maintained after the contrast change. Perhaps it was and the AP was behaving as designed by increasing the exposure to maintain the highlight value in the face of a contrast grade increase.

Thanks for confirming my initial thought and clearing up my confusion.

 

[RalphLambrecht]

I've had an RH Designs Analyzer Pro for a long while and think its a great piece of darkroom gear. But there is one behavior of the device that I don't completely understand and the manual hasn't been much help in clarifying it:

Sometimes when I adjust the contrast controls on the Analyzer to see the effects of a contrast change the device also automatically bumps up/down the exposure time. I'm not quite sure what it's trying to do by making an exposure time change when the contrast grade is altered. At first I thought it was trying to maintain the highlight values from the previous contrast grade but that doesn't seem to be it as it is often the case that the exposure change shifts the highlights relative to their value at the previous contrast grade.

I'm probably missing something obvious but I thought another Analyzer Pro user here might be able to tell me what that something is.

trust your first thought and the analyzer. That's how it's supposed to be!

 

[albada]

I have all of my calibration curves written down, and can post them if anyone is interested. I use an Omega DII, with separate condensers (depending on the lens focal length), Ilford filters, and Dektol/Bromophen 1:3 at 2 minutes. The papers are: Ilford MG IV Resin Coated(RC) glossy, MG RC Glossy, Warm tone RC Pearl, and Ilford MG fiber-based.

Yes; please post your calibration data. TIA!
Mark

 

[logan2z]

trust your first thought and the analyzer. That's how it's supposed to be!

 

[mmerig]

Yes; please post your calibration data. TIA!
Mark

Will do. I'll start a new thread on it, so that others can add to it, and the data won't be buried within other threads on the RH Designs AP. The format will be in table form, so that eventually someone could convert the text into a spreadsheet. Something like this:

Enlarger setup, Paper type, Developer, offsets and contrast (the curve data), Remarks

I'll have a short explanation and an example on how I do it.