Densitometer reading fluctuation

[bong]

I bought a used Macbeth TD-504 from eBay and, as expected, it came with no manual. It seem pretty straightforward to use. What bothers me is that I can't get repeatable readings off of my negatives. For example, after I zero the densitometer on a blank frame and read a film test sequence, I will often get readings that vary by .03 units when I do a second pass.

<p>

Is this variance normal or do I have a dying beastie in my hands? I found someone who may be able to send me a copy of the manual but in the meantime, how long should I hold the turret down on the negative for a reading? If I hold it long enough (>5 seconds?) the reading will sometimes fluctuate. Is there a specific technique for lowering the turret onto the negative?

[eric_blevins1]

I've found when doing readings from control strips with our

densitometer,(an ESECO) a lamp, placed close by, actually was

affecting the readings. When it was on, the reading would be one thing

and when it was off, it read something else. We've started doing our

readings in subdued lighting now. Maybe you're having a similar

problem?

I have seen the flucuateing readings that you speak of also (usually

it flashes back and forth between 2 #'s). I'm not 100% sure about

this, but I think it may be normal.

The type of densitometer we use is set up for transparencies (Status A

filter) as opposed to one that reads negatives (status M filter). Do

you know for sure which one you are set up with? If you are reading

negs. through a staus A filter, your readings will not be correct. We

had trouble with this when we bought our densitometer, because they

sent us one that read negs. and we wanted it to monitor our E6 line,

but we finally got it worked out.

Hope this helps.

[jorge_gasteazoro]

Well, it all depends wether the fluctuation is in the high end or the

low end, for example: If you are reading a density of 1.80 and it

varies +/- .03 then you are within the 1% variation densitometers

usually have, but if you are reading a density of 0.15 and it varies

by .03 then you are screwed!

I also had the same problem, an ebay guy sold me an ESECO speedmaster

supposedly in excellent condition, and the piece of ^%$^ would not

zero and/or hold calibration, so now I know why he sold this unit.

[Bill C]

Hi Bong; in it's day (early '70s ?) that densitometer would have been

second to none. Readings should (assuming the instrument is in good

condition) only vary by about 0.01; that is, if you read a density of

0.50 one time, it would not be unususal to get a second reading of

0.49 or 0.51. If the second reading were 0.51, all subsequent

readings should continue to be either 0.50 or 0.51.

 

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Here are a couple of things you should be aware of: 1) these

instruments needed a good warm up to get stable; say 30 minutes. 2)

Like Eric Blevins pointed out, you MIGHT be influenced by outside

light. There should be a black (rubbery material) ring around the

probe to seal out extraneous light; if this is missing, room light

might be affecting you.

 

<p>

 

Another obvious (?) thing is the lamp alignment. The filament should

be projected squarely into the measuring aperture. If it's

off-center, jiggling, etc. might make your readings vary. To check

this, lay a small piece of tracing paper (a post-it note or cigarette

paper, etc will do fine) over the measuring aperture. You should see

an image of the lamp filament here; fuzzy is ok, but it should be

close to centered.

 

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Anything else, I probably can't help much, but feel free to email with

questions. PS; in taking readings, just push down the handle that

lowers the probe; as soon as the reading comes on, it should be

stable.

[bong]

After using the densitometer again last night, I was relieved to find

that it was behaving as Bill C. described. Then again, I get the same

amount of fluctuation (+/- .03) whether I'm reading high of low values

so Jorge may be right and I just threw away good money. Nevertheless,

I get what information I need and I have to content myself with that

for now. My thanks to all :)