Macbeth densitometer help for dummy?

[Usagi]

Hi,

I got Macbeth TR-944 densitometer. It is old (dated at 1984) but readings are very accurate.

But...

Although I got all stuff, including calibration strips and macbeths calibration "patchs". I am really helpless with this equipment. The manual (Operator's Manual) does not help much. It only tells how to use different modes like Density, Memory Bank, HD-LD, Offset Null Density...

So far I have only used it as Density mode and for transmission measurements.

And yes, I got good readings with it but there are something weird. When I take measurement, the displayed value is always relative change to previous value!

So if I want to get absolute density, I have to remove negative (or any other target) from the measurement area and take plain null reading. Then take the measurement.

This is frustrating, and as far as I understand from the Operators Manual, this really is not the proper way to use densitometer.

I am guessing that I have some button at wrong position or I have densitometer at wrong mode...

I will be very pleased of any help.

I put picture of densitometer and it's panel section as attachment.

 

[analogsnob]

I used a tr924 for years. It was similar but not as fancy.

Start by reading with nothing in the beam and push "zero" once on each filter position. The transmission filters "M" is for color negative readings, "A" is for readings from transparencies, the yellow is "visual" density. Used the calibration film to read through the visual filter and using the calibrate pot on the back make the reading match the stated value.

All of this should be in density mode. Make sure you are not using the offset controls or the hd-ld modes. hd-ld is a shortcut for plotting process control and not needed otherwise.

The refelection probe is used by positioning the circle over the area to be read (start with the check plaque white) push the head down to read, there is a small button on the probe push it once for each color and the reading should match the stated value. If the reading does not match use the visual filter and while holding the button in adjust the reflection zero pot on the back of the machine. The black patch should be read on visual and the value adjusted to match the aime using the reflection range pot on the back of the machine.

With no memory or offset the density read should be the correct value.

Hope this helps

 

[Usagi]

Thank You

When I put power on and do zeroing procedure, it does not help. Even though the density button's led is on, I guess that there might be something wrong. I don't know if offset values are set to something or not.
But for some reason, the displayed density is always relative to previous, with + or - mark

 

[analogsnob]

Macbeth is now owned by Xrite I don't know where in your country to get it serviced but try the Xrite website for info. Before you give up try exercizing the buttons sometimes the mechanizm can gum up and get stuck. It certainly seems that the hd-ld is stuck on because the offsets produce a reading that would be wrong by the same amount all the time. The offsets are designed to make accounting for things like film base fog more convenient so when working correctly one makes the first reading of blank film with the offset button pushed and then all density readings will then be read as if the first value was zero.

 

[Usagi]

Hi, I will do that. Actually it seems that the densitometer's cover is easy to open. And it is really robust, not like nowaday's plastic digital toys
So I will soon be wiser.

 

[brian_mk]

This is an old thread but I still own a TR-924 densitometer...

It's not been used for a few years.
I used to use it to calibrate the colour filtration settings for my Durst Modular 70 Enlarger.
I would try and shoot a Kodak grey card along with each batch of films.
I would then make a small test print from the grey card frame, measure the RGB density values and use them to adjust the enlarger filtration.
I knew things were ok when the test print density values matched the kodak grey card.
The grey card density readings should be R=0.74, G=0.74, B=0.74.

I powered it up the other day just to see if it still works.
I had the idea of maybe using it to check the calibration of an inkjet printer.

I tested it using a couple of different Kodak gray cards.
I measured R=0.75, G=0.75, B=0.71.
That's not bad for a vintage piece of kit from the 1980s.

I was wondering why the B reading is a bit low and if it can be corrected?
Could it be the reflection lamp has aged?
Has the blue filter in the measuring head aged differently to the R & G filters?
Could it be the photo detector? Does anyone know if it uses a photo diode or photo transistor? Would the colour sensitivity change over time?

The calibration procedure apparently does not allow you to adjust the calibration separately for each colour channel.
There are only two adjustment pots on the rear panel for reflective measurements. They apply to all 3 colour channels (and white).
One adjusts the white or minimum density reading, the other adjusts the black or maximum density reading to match reference patches.