Density Opinion

[Richard Ryerson]

Hello all!

Thank you all for welcoming a new comer to your forums. It was very nice to have a question answered without digs, insults and hostilities. The answers were great!

Have another for you guru's.

A little background.

I just recently purchase an old Macbeth TD-502 densitometer. The seller said that it wasnt able to calibrate but it returned consistent results. The price was right and I thought that I could take readings from a "known" Stouffer T3110 step wedge, use that as a base and read negative densities.

When I got the machine, I decided to see if I could calibrate it, despite the seller's oppinion. Low and behold, it calibrates! Every step reading of the T3110 is what it's supposed to be. Wow, got a break!

Now, off to the races. Let's take some gray card exposures, FB+F, Zone I, Zone V and Zone VIII at varying speeds. 28, TMAX 100 35mm, exposures in all; Whoops can't find either one of my gray cards, use a piece black construction paper instead. (This should be cool right? Its all about what the equipment 'thinks' it's looking at)

Equipment/Chemicals/Process:
Canon F1 original w/ 50mm f/1.4 lens
Pentax 1/21 analog spot meter
TMAX 100 35mm bulk
D-76 1:1 developer
Temp/Time: 68/8.5 min

develop as per my normal development procedures which is the Kodak recommendations for TMAX 100 and D-76 1:1. Agitation is consistent at 5 inversions every minute.

After letting the film dry over night I get everything together to read the densities. I am as giddy as a kid in a candy store! Make sure the densitometer is calibrated, yup step 1 reads .05; step 31 reads 3.05, steps in the middle are what you'd expect. Great!!!

Lets read the FB+F and Zone I exposures from the 100 speed test to gauge the film speed.

FB+F = .21
Zone I = .22

Huh? thats odd, I can see the density in the neg for Zone I, but I am shooting for .1 + (FB+F) right? Well I should see something close to .31, right?

On to the next group of exposures (125) these are the same. ??? Lets just clear to the end for the 50 ASA test. It reads

FB+F .21
Zone I .23

What is going on here? only .02 over FB+F? Am I missing something?

What are your opinions about whats wrong? I have my own opinions, but I will keep them to myself for now. Don't want to boot strap idea's about whats wrong.

Thanks again for all your help.

Best regards,

Rick

[Nick_3536]

Does the 502 have a zero button? If it does could you have zeroed after taking the first reading?

[Richard Ryerson]

Nick,

It has a zero knob on the front and the calibrate screw on the back.

I have checked and double checked and triple checked the numbers. So the possibilities of advertently hitting the knob is slim to none.

Also, the zero knob requires many revolutions to show an affect. I bet it's on the order of .01 per revolution. Quite interesting.

Thanks and Best regards,

Rick

[Kirk Keyes]

If every step of your T3110 reads correctly, then you can eliminate the densitometer from the equation. How about metering - did you meter off the black card with the spot meter? Did you account for lens extension in the exposure. If you are metering with a spot meter, and then focussing the lens for a short distance, you need to add some time to the exposure. Perhaps your meter reads high? How did it compare to the meter in the Canon? (The Canon built in meter would have corrected for the lens extension.) Maybe your effective film speed is less than 50? Try doing a series of exposures for all the zones and plot the data out.

[jose angel]

Considering that all the process is correct with a densitometer made for B/W films, and the densitometer is reset to zero onto the blank area of the film, a difference in 0.01dLog from B+F to zone I shows an underexposed or underdeveloped film.

If reseting is not possible, and your reading is based on that blank (unexposed) area of the film, results are the same subtracting 0.21 to your readings.

I develop films with a Jobo processor. In my experience, the damn TMX is a very low speed film. I must expose it from 32 to 64 ASA to obtain a bit of shadow detail in "normal" situations. I haven´t here my data charts, but I try to remember that my "N" developing time is around 8-10 minutes at 21ºC -in the Jobo-. It makes me think that you are underexposing at least 2/3 stop and probably underdeveloping your film.

[jose angel]

What about your readings of zone VIII?

[John Cook]

Lots to cover here. But just a few thoughts:

The zero adjustment on most densitometers I have used usually has much more of a hair trigger than that. Just touching the knob will cause the needle to jump.

Second, you didn't mention warm-up time. May not be the prime issue in this case, but just so you know. Densitometers drift like crazy. Very unstable when cold. Nearly impossible to get the same series of readings twice in a row. Before using, turn the unit on and allow it to warm internally for a prolonged period. At least five or ten minutes, maybe more.

Next, I can't seem to figure out your ISO rating from your comments. Should be 2/3 to a full stop more exposure than manufacturer's rating. At least that's where ALL of my tests have wound up over the years.

Some day, you will make a perfect negative of a perfect exposure. You can then reverse-engineer that film to determine your ideal H&D curve for your equipment and materials. If it will help, I find that a Zone I density of 0.1 over bd+f and a Zone VII density of 0.8 over bd+f to work well for sunlit scenes printed on my Omega D5 with condenser head on Ilford VC paper with no printing filter. You may start there, if you like. Or not...

[Richard Ryerson]

Kirk:

Yeah, I don't think the densitometer is a player in the problem. As far as lens extension factor, I racked the focus out to infinity to have no extension. Granted there may be something there, due to the inaccuracies in manufacture, but this was used in all tests.

Given that I would expect some definitely notable differences in the seperate E.I. tests.

I can't compare the spot to the F1 meter considering that the F1 meter is b-roke. Hasn't worked since I got it. A primary reason for purchasing the F1 to force me to think about what I am doing.

Jose:

I did record the Zone V and Zone VIII densities in my log, but I was more focused on the Zone I considering that comes first. Find the right EI and then work on the dev time densities. I put them all on the same roll to see what the results were. Maybe I would get lucky and the Zone VIII density would show 1.2 over Zone I for the proper Zone I of .1 over FB+F. Or maybe I would be lucky enough to see the required dev time change by looking at the differences in the I, V and VIII data.

I am at work now and drudging up the numbers from memory. So please bear with me.

100 EI Test
FB+F .21

Zone I .22 / .01 over FB+F

Zone V .53 / .32 over FB+F

Zone VIII .90 / .69 over FB+F

50 EI Test
FB+F .21

Zone I .23 / .02 over FB+F

Zone V .73 / .52 over FB+F

Zone VIII 1.3 / 1.1 over FB+F

I "think" these are the numbers. I could be wrong however, but not by much.

John:

Warm up time - Sorry I failed to mention it, it slipped my mind. Being a new piece of equipment I decided to check this variable out too. And I noticed only a slight change in reading, .01 over a couple of minutes. And then it remains stable for the duration.

I did constantly retest the step wedge to see if it was changing. After the warm up adjustment, it remained constant.

The ISO rating of the film is 100. I agree that the EI will probably be 2/3 to 1 stop less exposure. This will put the rating at 64 or 50. But the issue with my tests is the Zone I densities aren't anywhere near anything tested. Im not looking for dead nuts on, just ballpark.

All:

I wanted to throw this problem out to everyone to see what jumps to mind first or foremost, before I use my spot meter as a paper weight.

While the spot meter is new to me also, the readings I get from it are very reasonable. Meaning that if it's off, it's not much. Sunny 16 medium subject shows about 14 2/3 EV. Which is a little more exposure than f/16 @ 1/125 with 100 ISO.

Since there are a few opinions now, here is what I think could be the problem.

1. The meter - The meter is reading the low light black paper incorrectly thinking it's a brighter subject than it is. 20% probability

2. The camera - The shutter speed I was could be defunct. 25% probability.

3. The camera - The lens mount or lens itself is so far off that that amount of light passing through doesnt comply (at all) with the focal ratio/aperture scale. 1% probablility

4. I/O error - Idiot Operator - The Zone I numbers sure look like Zone 0 numbers, don't they? I guess it's possible I closed down 5 stops instead of 4 when setting up for Zone I. 50% probability (yes I am giving myself some credit, the other 4% is unknown lol )

Thanks,

Rick

[Richard Ryerson]

Another thread raises another possibility here too.

Do you think that I may have the wrong sized cloggs? what size did AA wear?

[jose angel]

Richard, I asked you about the zone VIII to knows about developing time... that I think is in the reasonable way. When exposed to 50ASA, zone VIII is 1.1 over B+F, which is credible (a bit overdeveloped to my liking). It would mean that film is underexposed, but hard to think... I couldn´t ensure it without a new test. Next time, I would expose the film to 25-32 ASA and develop for a 5-10% less. I suppose that developer is fresh.

The next thing that came to my mind is the black card. Theoretically it must work, but is probably that you are squeezing the conditions to the extreme. I would repeat the test with a near 18% reflectance subject.

In my case, I´m sure the reason would be the last one! In the XXL version!