Film base density check

[Captain_joe6]

I developed a test roll of Plus-X today, exposed with a gray card per Ansel Adams' instructions in The Negative, and developed it in a somewhat-expiration batch of D-76. The developer hasn't given me any problems in the past, but for some reason, I couldn't achieve a Zone I density of .1 above fb+f measuring with my Kodak Model 1 Color Densitometer. So I shot another test roll. Same results.

So the question is, what sort of film base + fog density should I expect with this film-developer combination? If I develop for the recommended time, should I increase or decrease development to increase the density, or is that even possible? I just want to eliminate the possibility of my densitometer being wildly out of adjustment. I zeroed it out, but maybe the whole thing is off?

Thanks!

 

[Tom Hoskinson]

Calibrate your densitometer (your densitometer instruction manual should provide the procedure).

 

[Captain_joe6]

Well, I've done that. Its that old Kodak Model 1, the analog, look down the tube kind, and its pretty basic, just turn the knob until the small circle is as bright as the big circle, but no brighter. Voila! Calibrated.

What I'd like to know, though, is if my measurement of 0.3 for fb+f is reasonable or not. That'll at least tell me if my densitometer is worth the 99 cents I paid for it plus the hour of cleaning it got.

 

[Tom Hoskinson]

Assuming your densitometer is a transmission densitometer, check it against a transmission density step wedge - like a Stouffer.

 

[Ray Heath]

g'day Captain

so, why bother with all this?

just go out and capture images of real subjects that interest you, process the film and assess the results of real images taken in real conditions and get a real feeling for what you are trying to achieve

 

[Captain_joe6]

Oh rest assured, I do that too, I'm just a little on the obsessive-compulsive side, I had the day off work, and it was pouring rain outside. So I thought to myself, 'I've got this densitometer here and I don't want to go outside, what better to do than a film test!'

And thats how I spent my day. That and trying to get a few things printed that I'd been meaning to print for a while now.

 

[Roger Hicks]

What I'd like to know, though, is if my measurement of 0.3 for fb+f is reasonable or not. That'll at least tell me if my densitometer is worth the 99 cents I paid for it plus the hour of cleaning it got.

Yes, 0.3 for fb+f is reasonable for 35mm but far too high for 120.

A useful trick is to scrape off some of the emulsion with your thumbnail while it is wet, and measure fb alone. Then you can measure fog levels separately.

Cheers,

R.

 

[jstraw]

g'day Captain

so, why bother with all this?

just go out and capture images of real subjects that interest you, process the film and assess the results of real images taken in real conditions and get a real feeling for what you are trying to achieve

I see this sort of post around here with some sort of regularity and they get on my wick.

When I read a post with a question I can't answer, I move on. I don't stop to evaluate the merits of the question, the endeavor it applies to or worse yet, suggest other priorities. The guy wants to know how to use his densitometer, not your opinion on whether or not he should do.

I don't mean to pick on you, Ray. And I apologize for the rant.

 

[radiantdarkroom]

I don't know much about the technicalities of your situation but would you not find out the effects of the developer if you took a piece of the unexposed film and just fixed and washed that peice and then measured it against the developed film?

 

[Captain_joe6]

jstraw has really hit this one on the head, with the slight exception that I already know how to use my densitometer. I just need to find out if the reading I took was unreasonable or not, which would in turn tell me if my densitometer was anywhere near accurate or not. I got a fb+f reading of 0.3, which I, having no prior experience with this sort of thing, had nothing to compare to. If somebody had piped in saying that I should be getting 0.1 or 0.5 or something considerably different like that, then I would at least know that my equipment and possibly my methods were faulty.

Now, considering that 0.3 is in the ballpark, I have narrowed down my possible causes of error. What was happening is that I would shoot the roll as directed, develop, stop (acid), fix (kodak rapid fix w/hardener), and dry as normal. That all went fine, except that the highest zone I density I was achieving was only .05 above fb+f, and all the other zones were off as well, by large degrees (more than .2 usually) from their target densities. I now believe that this has been caused by a combination of my developer being somewhat exhausted, and over-agitation with the Rapid Fix, causing bleaching of the shadows.

And I do value Ray's comment, things like that help to keep us tied to what is really important to our craft. If I spent all my time in the darkroom, sure, I'd have a number of really great prints, but never anything new.

Thanks all for your help, and continue to pipe in responses if you like!

 

[gainer]

A hypochlorite bleach such as Clorox will remove the emulsion. If there is a base density you will be able to measure it. An unexposed piece of film developed normally will allow you to measure B+F. IIRC, Plus-X in D-76 has little dye in the base. That dye is to prevent light piping and is more valuable in high speed film. HP5+ has a fairly dense base. Pipiing could also be prevented by a layer of dark dye between base and emulsion which also serves for antihalation. These dyes will be removed in processing, even in sulfite-free developers, sometimes leading to consternation of first time users of a phenidone-ascorbic acid-alkali developer due to the dark color of the used developer, sometimes green, sometimes blue.

 

[sanking]

If the issue is, does your densitometer read accurately, I would suggest investing in a Stouffer 21 step transmission step wedge, at less than $10. These step wedges begin at Step 1 with B+F, and every step goes up by about log 0.15. Although not calibrated, actual values of Stouffer step wedges are rarely off by more than about log 0.02 in the low and mid densitiy steps so they can certainly serve as a good guide as to whether or not your densitometer is working.

Sandy King

 

[gainer]

Also a graph of density measured by your meter against nominal density of the Stouffer wedge will give a better idea of your meter's accuracy than the measurement of any one step. You could get a calibrated step wedge, but the expense is not worth it for most purposes.

 

[Ray Heath]

I see this sort of post around here with some sort of regularity and they get on my wick.

When I read a post with a question I can't answer, I move on. I don't stop to evaluate the merits of the question, the endeavor it applies to or worse yet, suggest other priorities. The guy wants to know how to use his densitometer, not your opinion on whether or not he should do.

I don't mean to pick on you, Ray. And I apologize for the rant.

you make a good point j, but i feel there is always room for another opinion even if that opinion does not address the original question

often when reading technical questions such as this i wonder if the poster is not being mislead, it seems to me that some things don't need to be high tech, why not just use materials as intended by the manufacturer, they know more about this stuff than we as users ever need to, we should just get out there and create

 

[percepts]

if your zone 1 neg is only very slightly more dense than any part of the film which was not exposed then you should be able to see that and know that the zone 1 neg is approx 0.1. i.e. its in the right area.

i.e. you can check for approx zone 1 density value just by looking at the neg. No need of densitometer for that. It becomes more difficult/impossible to do it that way the higher the zone.

so if your zone 1 neg is as clear as unexposed area of film then you probably need more exposure and not more dev. Infact using more exposure may require less dev but you will have to test for that.

On the other hand, if your zone 1 neg is denser than unexposed area and your densitometer says its same as unexposed area, then you need to sort your densitometer.

 

[Daniel_OB]

Never used not D-76 nor plus-x, but they are all somehow similar. Density of fog+Base for that film should be around 0.15-0.2,as I can reacall for my ilford films (for plus-X should not be far away form say Delta100 or Agfa APX100). 0.05 for zone I is about the right, zone II around 0.15 should be fine, zone V around 0.55-0.65. Zone V density is depend of curve (exposure-density) and is different for different films and developer combinations, for the same developing time. Possition of zone I and II is difficult to change by developing time or developer kind. I do not measure fog any more just it is not so important for you actually measure density above the fog. I just visually check is the density of fog similar to zone II above fog (skretch clear part to compare). What actually you should be, I think might be you alrady know it, the zone VIII should be around 1.15-1.25 (normal negative) depend of enlarger, and it is measure for deveping time.
Could you please also describe how your curve deviates from straighr line.

www.Leica-R.com

 

[Captain_joe6]

Well, I haven't had time to plot out the curv, but I'm going to get to it ASAP now.

The thing that I'm finding is that none of my negatives are where they need to be, not even when I expose the supposedly ISO 125 film at ISO 64, or even at 32. It would seem to me that a correct zone I would be encompassed in that range somewhere. I'm measuring with a spot meter and checking for even luminance across my gray card (which there is), and even at ISO 64 the image of the card is *just barely* visible above the film base, and only when I hold it at just the right angle. Things aren't much better for ISO 32, where there is just a faint hint of density when I hold it over a white piece of paper, but still not where it should be in terms of net density. I wonder if anybody else has encountered this large difference between stated and actual speed when using Plus-X with D-76.

I'm going to mix up a new batch of developer and some regular (non-rapid) fix this week some time and repeat the test a third time.

Does anybody know if uneven development could be caused by there being only one roll of film in the tank, but enough chemical to fill the tank (16oz in a 2-roll SS tank)? I'm just trying to rule out any possibilities as far as chemical use is concerned.

Thanks for all your help, all. I think its great that I can get all these viewpoints in one easy place. Maybe we should do a sensitometry 101 sort of thing for all to read and absorb.

 

[percepts]

could be a host of reasons but sounds like you have wrong exposure.

I assume you have switched your camera to "manual" mode and then closed down four stops from your metered reading to get to zone 1 cos if you didn't set it on manual then you will have problems. (assuming it has non manual modes)

Could be your developer as you suggest.
Could be a problem with your camera.
Could be a problem with your light meter and did you set it to correct iso.

you will just have to eliminate all possibilities through testing but as I said, zone 1 neg should just be faintly visible difference from fb+fog.

If the developer is not working then higher zones will also be thin. What density do you get for say a zone VIII?