Densitomer Help

[padraigm]

HI All,

Just purchased a Macbeth T500 Densitometer from the bay... Light come on and it makes reading . I have a stouffer 4X5 21 step tablet. As a quick test I zeroed the instrument on #1 the clearest and then read number two. It's a non calibrated step wedge but it is assumed to in .15 increments. It turns out it reads more like .2... So what to do no instructions.. I plan on using for some film speed tests and alternative contact printing. Should I be calibrating just on the light source, do I need other something else? Any help would be greatly appreciated.


Thanks in advance

Patrick

 

[henry finley]

Oddly, a google search of this model does not show up. As a printer I'm fairly familiar with densitometers, enough to tell you that there are enough different types withing the MacBeth line alone, that I would not expect much of anybody who can help you without seeing some material about it. WITH some manual material, I can probably answer your questions OK, if you can link up some to me or something. A Stoufer 21 step is (was) a step wedge for offset camera use, not home darkroom. I feel certain it is worthless for your purpose.

 

[padraigm]

Thanks Henry. I believe you are right about the 21 step wedge. I have looked at stouffer and they sell a calibrated transmission step wedge for ~$17 so I will probably go with that. There is a zero knob on the front and calibration knob on the back. I would imagine with known values it will not be too hard to figure out how to calibrate. I guess this is a pretty old unit. Hoping I did not buy another another piece of junk

 

[henry finley]

Wait a minute--slow down. Get me a photo of it. Is it one with a sensing unit on a heavy round cord, that closes on a hinge? And there's a little circle it closes down to? Iim guessing a reflection densitometer. Probably from the 80's? Is it LED or analog meter? Doin't just be squandering money on step wedges, yet. You might have something, or it could be junk.

 

[henry finley]

Thanks Henry. I believe you are right about the 21 step wedge. I have looked at stouffer and they sell a calibrated transmission step wedge for ~$17 so I will probably go with that. There is a zero knob on the front and calibration knob on the back. I would imagine with known values it will not be too hard to figure out how to calibrate. I guess this is a pretty old unit. Hoping I did not buy another another piece of junk

When I say that Stauffer wedge is useless, that is only partly true. Lacking the original Mac Beth or MacBeth-recommended Kodak wedge,whichever it called for; At least a Stouffer will get you by on 1 and 21 just to see if the old densitometer has any kind of linearity still in it. Remember, densitometers are very much like radios, to the extent they have filrter capacitors (wjich get leaky) and resistors (which drift). Translated, that means not to expect labaratory-accurate readings. Not 30 years later, and not with yellowed 30-year-old step wedges. But in practical darkroom terms, if the unit has a fair amount of it's original linearity left it it, You can proceed to ballpark your 1 and 21 readings to get to know the unit a little. By that time, you might finding yourself in the darkroom fabricating your own step wedges. Do that, and then proceed to try to fabricate an 18% wedge that reasonably matches an 18% card. If black, white, and middle gray all turn out somewhear near, that is your cue that the machine is not junk yet. From there, for photographic purposes, is all the accuracy you need, nothwithstanding perfect labatraoty readings. I typed faster than my ability. PS--remember--Ansel Adams and Kodak did not see eye to eye on what middle gray was. But it's YOUR darkroom--middle gray is YOUR call.

 

[gordrob]

If your densitometer is a TD500 rather than a T500 check out this link for instructions on how to use it. Normally Macbeth identified their units at TD for a transmission unit, RD for a reflection unit and TR for a unit that combined both reflection and transmission.

http://www.largeformatphotography.i...6136-calibration-procedures-for-Macbeth-TD500

Gord

 

[Bill Burk]

Stouffer 21 step grayscales are far from worthless. I'd say they're the most valuable thing in a home darkroom.

Coupled with a Macbeth densitometer you should be good to go. Sure there are zero and calibration adjustments. I'd stay off them unless you have the instruction manual and a calibrated patch.

But just because the first step of 21 steps measures .20 instead of .15 isn't going to end its value. Check what difference reads between each step. That's where you should "average" .15 between each step. If you are even close to that +/- 0.02 is real close.

For example (zero'ed on air) my 21 step Stouffer wedge reads: .04, .18, .34, .50, .67, .81...

 

[henry finley]

Stouffer 21 step grayscales are far from worthless. I'd say they're the most valuable thing in a home darkroom.

Coupled with a Macbeth densitometer you should be good to go. Sure there are zero and calibration adjustments. I'd stay off them unless you have the instruction manual and a calibrated patch.

But just because the first step of 21 steps measures .20 instead of .15 isn't going to end its value. Check what difference reads between each step. That's where you should "average" .15 between each step. If you are even close to that +/- 0.02 is real close.

For example (zero'ed on air) my 21 step Stouffer wedge reads: .04, .18, .34, .50, .67, .81...

That's why I partly recanted my position on the Stouffer. I just didn't know what actually came with the machine when it was new. I also don't know the machine exactly because a google search didn't return me any MacBeth results. I'm guessing the guy has one out of the early '80's, because I have one from then (liberated from a print shop).
My position is that given the possible age of it, I'd want to go through it from an electronic standpoint--seeing to it voltages were right, the power supply doesn't have leaky filters, and the other caps and resistors haven't changed. THEN I'd proceed to deal with it from a photographic standpoint. Having done that, and feeling I could trust it to have some decent linearity, THEN I'd go ahead with a Stouffers, unless I could get my hands on a Kodak step wedge, or whatever MacBeth packed with the machine when it was new. Come to think of it, I'll bet the sensor probably uses a CdS cell. The chances of that having the original linearity specs are highly suspect.
This is why I think an ordinary darkroom guy would do well to use it taking his readings in an arbitrary manner, and not expecting laboratory accuracy. (which isn't necessary to the purpose anyway). Sometimes I'm sickened at how fast 30 years passed, and so much from then needs overhauling now.

 

[Bill Burk]

...My position is that given the possible age of it, I'd want to go through it from an electronic standpoint... Come to think of it, I'll bet the sensor probably uses a CdS cell...

Ah, I didn't catch where you recanted, fair enough.

If a calibrated strip could be had for $17 it is a good value. At least you would know if you need to calibrate.

I think I found the picture of your auction. You may have spent a little more than I would have paid, but the difference wouldn't buy the family a dinner at McDonalds so don't sweat it. You can get your money's worth from it. If the bulb burns out, go to the hardware store and get a 12v 50w halogen. It's good enough.

In some ways your unit is different than my Macbeth TR-524, where you have an analog meter needle and I have a digital LED readout. My unit has a color turret and a tethered reflective meter on the side, while yours is designed for only black and white transmission. Otherwise they are similar "age".

Despite its age, my unit operates reasonably well and gives me useful readings. I think they used high quality parts. But, as henry finley says I do not expect "laboratory grade" readings.

The photoreceptor is trustworthy. I think it's a "photo-emission" tube type like used in early drum scanners. Cost a fortune new but way better than a CdS cell.

Look under the aperture insert, is there just a mirror there, or does it have a "turret" with two window screens above the mirror? If so, make sure the screen number (2 or 3) matches the aperture plate (looks like 2mm)...

It takes a little practice to read the needle (line up your eye so the needle reflection is behind the needle)... And maybe the gradation makes it hard to get resolution closer than 0.02 density... But really, if you get to work with it, it doesn't really matter if your readings are off a lot. Even if they are off by 0.05, you can still tell how contrasty your negatives are.

 

[padraigm]

Thanks guys. It is indeed the TD-500 the link to the auction is here http://www.ebay.com/itm/380503581136?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

I will mess with it later. There def is not .15 steps between strips. The back knob deals with gain I think.

 

[Mike Wilde]

I have a td504 I think. Yes, the gain knob on the back if step 2 is reading .2.

Check the aperture plate is not larger than the strip you are trying to read first.

Go from zero to 20 steps and set your gain, then work your way back to check linearity. They may interact, and tuning is somewhat iterative.

Verify many things before touching any settings.

 

[padraigm]

Again tanks everyone. I have ordered the calibrated stouffer and see what happens from there. Hopefully it will all align as it should. I will certainly be referring back to this thread. Thanks so much