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

[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

[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.in...-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...

[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...84.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