RH Designs Analyser Plus - Am I using it correctly? - [Solved - Photoresistor]

Hi all,

I've just bought a used RH Designs Analyser Plus. (I've enjoyed their stopclock pro and thought I'd give it a go).

It was off ebay and sold as untested but having been working in a darkroom a couple of years ago.

I've reset all the paper channels, but my problem is in the measuring so I'm not sure if the light sensor is faulty or if I'm overthinking the process:

The instructions are to take a measurement from a shadow area first (a 'thin' part of the negative) and then from a highlight area (a 'dense' part). I do this with the two extremes of a regular negative and most of the time it fails: The first reading is ok - it sets its densitometry setting at 0.0 or null and usually shows 1 second, but then in the dense reading it almost always shows LO so I'm not sure if I'm exceeding the range or if the sensor is faulty and just cannot pick up that low level of light from the enlarger.

If I take measurements from a more conservative range it seems to work better - say 4 or 5 steps on a stouffler step-wegde, but still it will often either complain about LO for the second reading or think for ages and return an insane time of 249 seconds.

Anyone got any experience with these and have any ideas? I'm hoping it's user error rather than a dodgy second-hand unit, but I'm not averse to fixing things if a component needs swapping out etc.

Thanks. Sam

Hmmm, that is not good. My guess would be a calibration issue. How did you reset your paper channels? Did you put in zeros ('0') all over the place, or did you default to the factory defaults? The factory defaults are targeted towards Ilford MGIV papers.

Thanks for the reply. I have to say - I haven't actually tested the print times by printing yet!. I can understand that paper has a smaller dynamic range than film, but I would have thought that a tool like this would 'read' a full range negative and then suggest a correct output, rather than needed me to compress the range measured.

It's definitely been reset to standard calibration settings. I've wiped and re-entered them.

I see.

What do you see when you bring the meter in densitometer mode by keeping the probe button pressed? To test your probe and/or meter I would expose the probe to one single step-wedge value. Enter densitometer mode (you should see 0), move the step-wedge one or two steps and meter again. The meter should now tell you the difference in density.

I have the Analyser 500, so it's slightly different, but my guess is the sensor is the same. It should definitely be able to read a full range negative that needs 00 (or -1) grades. That could be a negative with a dynamic range of 1.8, or 6 stops. That should correspond to about 12 steps on a 4x5 stouffer step wedge.

If you open up the lens and/or reduce the print size so the image is brighter can it read more stops?

Hi both,

I've done some test with it as a densitometer and it seems it can see a fuller range with the lens wide open.

Using the stouffer wedge, with the enlarger about 29cm from the board (of course who knows how many lumens my bulb is kicking out) - see the table below. It will only work properly with the lens wide open which is not how I would usually print. It's a Durst L138S condenser which I would not think of as a dim enlarger. Perhaps the sensor has lost a bit of sensitivity.

[/TD][/TD]

Aperture	Stouffer Wedge 2	3	4	5	6	7	8	9	10
f4 (wide open)	0.09	0.25	0.36	0.51	0.65	0.86	0.98	1.18	1.97
f5.6	0.13	0.32	0.56	0.87	1.95	LO
f8	0.05	0.32	0.88	LO

The jump from 1.18 to 1.97 and similar one at f5.6 also seems suspect. If those are not typos something with the sensor seems off. I’d contact rhdesigns and see what they have to say. I bet a replacement sensor is reasonable, but if you’re lucky it just a setting.

The Durst 138s isn’t a dim enlarger unless you have a very low wattage bulb installed. There is no way the analyzer is working correctly.

Your densitometer readings do look a bit dodgy. I have an RH Designs Analyzer Pro, and a Stouffer Wedge T2115, and can I try and reproduce your densitometer readings as a check. What set-up are you using (film format, lens focal length)?

The 29 cm height you have is quite close (assuming that is the distance from the board to the negative), so unless the bulb is dim, it could be a bad sensor as others have mentioned. You can try doing a test strip to see if you get a reasonable print. Use f-stop increments (4,8,16,32 seconds etc.) rather than linear steps (4,6,8,12) and start with f8.

Hi all,

Thanks very much for your input thus far.

Some success! I dug around in a Arduino box of electrical components and sure enough there was one fresh photosresistor. No indication of the specs of it, but what the heck - I can always put the old one back and in any case it's definietly suspect. Sure enough with the new photoresistor soldered in it is now much more sensitive to light and is giving HI errors more readily than the repeated LOs I was getting with the old PR - this is to be expected as I'm quite close to the board.

With some stopping down the analyser seems to be working as intended and I'm able to meter both thin and dense parts of the negative, rather than just a narrow band, with the grade shift and time shift buttons working on the display as you'd expect.

I haven't tried printing yet - but that would be the next stage followed by personal calibration.

Does anyone know the actual spec of the original photoresistor? I'd like to buy an exact match. (Maybe my replacement is perfect but it's hard to tell - no markings)

A quick densitometry set of values accross the S wedge:

0.11 0.28 0.38 0.49 0.60 0.69 0.78 0.89 - looking more regular

Flapper said:

0.11 0.28 0.38 0.49 0.60 0.69 0.78 0.89 - looking more regular

Click to expand...

Yes, that is more like it. Your step wedge has 31 steps, I presume? If so, the step delta is supposed to be 0.1 and that results confirm a working LDR.

That's great that you found the problem. Sorry I don't know the correct replacement part. It still might be worth contacting RH Designs to see if they would share the part number.

Ok, another update.

I emailed the RH Designs shop, but they couldn't help with the precise photoresistor value and also speculated that their new sensors would be too sensitive as they're a different design (Photo diode as confirmed below)

I then emailed original designer Chris Woodhouse:

Sorry to bother you. I wonder if you are able to tell me the specs of the photo resistor in the Analyser Plus box's sensor? I bought an Analyser Plus second hand which - on testing - seemed to have had a faulty sensor. (see the forum post below if interested). I soldered in a new photo resistor and it seems to be working, but I would like to make sure I get the correct one.

Click to expand...

who very kindly replied within an hour or two:

If it’s a cadmium sulphide cell, it should be ok. Later models have a photo diode. You will need to calibrate though and I cannot offer any clever suggestion. Just calibrate your paper and let the offsets fall where they do.

Click to expand...

So, the machine it seems will have some tolerance for each of the photoresistors, because of the calibration range I presume.

For the record - and in case anyone searches for this in future. I bought a £10 box of photoresistors from Amazon - BGTXINGI which had a range of PR values all based on the GL55 Photoresistor model.

I ended up using a GL5516 which seems to be a little more sensistive than the original PR as I've had to offset my grade 2 (and it seems roughly all the other MGIV grades, although further testing needed) to an offset of +33. (I may swap it again for a slightly less sensitive GL5526, but I don't want to stress the circuit board with too much messing around)

The machine will now read a full negative range and also allows me to stop down sensibly and not stay wide open.

The actual fix is really easy. Open up the sensor and desolder the two legs of the old PR. Use a solder sucker to remove the old solder. Remove the old PR. Put the new PR in the board at the correct height and solder in place. Er, that's it. A cheap and easy fix if your PR sensor goes bad.

Welcome to Photrio @Flapper and many thanks for not only systematically investigating an issue, but also posting a workable solution to it! Stick around, please!