Maximum density

[swmcl]

Hi,

Can someone tell me whether it is the type of film or the developer that generates the maximum density on the film ? I am looking at film spec sheets and most don't advertise the 'max density' but I see that the FP4+ sheet does have a curve that peters out at less than 2 (see page 4 of the pdf). Doesn't this mean that it cannot display more than say 6 or 7 stops ? (Each stop being 0.3 on the density scale).

Can one get greater density out of a film depending on developer or is it fixed in the design of the film ?

Densitometers go to a density of 4 which would again be say 13 or 14 stops yes ? Are there films or combinations that go to beyond 3 ?

The reason I ask these questions is because I picked up a photography book the other day that said B&W film could record beyond 14 stops. I can't see how unless one were to interpret a 'stop' as being say a 0.2 step on the curve rather than a 0.3.

Cheers,

Steve

[Rafal Lukawiecki]

Steve, to answer the question if a film can or cannot record X number of stops you need to look not just at the film density range, but at the relationship between the light being recorded, on the horizontal scale of the curve, and the film's response as density, on the vertical. You count the stops being recorded, just as you wrote, as 0.3 logE, but on the horizontal, the X axis. What you want to see is that for a range of stops there is a meaningful change is density on the vertical, Y axis. Where the curve is flat, you get no separation, therefore you are not registering any "stops" of light additional to those already recorded.

For example, to record 14 stops, which you mentioned, you would like to see a curve that is not flat (or nearly so) over an exposure range of 14 * 0.3, that is over some 4.2 units of exposure (logE). With a typical film contrast, eg. about 0.6, this would produce a density range of as much as 2.4 logD on the negative. Some film/developer combinations can get you such a response, as indeed, it is not the film alone that matters, though it is the key to it.

The rest of the story is how this recorded data, on the density, vertical axis, gets to represent something on paper. This is all a matter of the selected paper's contrast, or if you think of the paper's very own curve, its own useful exposure range.

[N Dhananjay]

The subject luminance range that can be recorded is not a function of the Dmax of the film (unless you were trying to get close to a 1:1 relationship, which you usually do not). Rather, it is a function f the entire chain. Usually, the subject luminance range is compressed in the film density range and then expanded out in the paper density range. In other words, the longer the subject luminance range, the lower the contrast to which you would develop the negative.

Usually, in the chain, the limiting factor is the paper. Paper typically has a Dmax of about 2.1 or thereabouts, which means it can record about 6-7 stops. If you tried to record 14 stops on the negative and then translate that to paper, you are eventually compressing the 14 stops in the subject onto the available 7 - each 'zone' will be poorly separated and the local contrast will be terrible. Now, if there are unused bits in that range, you may be able to make a good print by trying to use various techniques to steal contrast from the unused area and redistribute it in the useful area but it is all usually more trouble than it s worth. So, in general, making photographs with 14 stops is a bit pie in the sky and if one is interested in that, becoming a lighting artist on the stage will be more satisfying.

What you are trying to do in the negative making stage of the chain is to get a negative that matches the scale of your paper. Different grades of paper accommodate different negative density ranges. So, what you are trying is - compress the subject luminance in the negative to the appropriate amount so that when it is matched up with the appropriate paper, it will yield an appropriate print. In reality, a 1:1 relationship is not obtainable because of toes and shoulders on the characteristic curves, flare in lenses etc. There is also a question of aesthetic preference which seems to lean towards somewhat heightened midtone contrast.

Cheers, DJ

[Bruce Watson]

...I picked up a photography book the other day that said B&W film could record beyond 14 stops.

Way back when the first Tmax film was introduced (1980s?) I remember reading an article that said that Tmax was linear for more than 20 stops. Linear to well beyond a density of 4. Basically completely opaque outside of Kodak R&D labs.

But just because it can, doesn't mean you should. What would you hope to accomplish by generating that kind of density? Just the Callier Effect would be killer.

Indeed, if you're going to print on silver gelatin paper or scan, you're much better off with a Dmax less than 1.3. Some of the alt processes want more density, but nothing approaching 4.0 IIRC.

[swmcl]

Guys,

I should mention that I have no darkroom and do not intend to. I'm going digital for the printing. Therefore, my intention is to use the film as a recording device getting a full data-capture as it were. I just need to get things right in my head.

Cheers,

[Lenny Eiger]

Guys,

I should mention that I have no darkroom and do not intend to. I'm going digital for the printing. Therefore, my intention is to use the film as a recording device getting a full data-capture as it were. I just need to get things right in my head.

Cheers,

It doesn't actually work that way. When you "overdevelop" to spread the tones out farther you add a lot of contrast to the image. If you scan this film you will have a print that is too contrasty for most people.

I like to top out at about 1.4-1.6 for scanning film, more than many here like. That's quite a bit less than 4.0. If you want to make contrasty images, however, there's nothing saying you shouldn't.

I still use the zone system, even with the ability to correct things somewhat in the scanner and in PhotoShop, it is still better to get a perfect negative than not. There isn't that much leeway.

Lenny

[Jim Noel]

A simple test for DR and d-max.
Tape a step wedge to the film.
Expose on an evenly lit area like a north facing wall.
Calculate the exposure for Zone X.
Develop as you normally do.
A second sheet developed 40% longer will give you a higher d-Max, and with some film/developer combos, a longer scale.

[Jim Fitzgerald]

Steve, I will tell you my experience and I am by no means one of the scientific types. I just know what I see and have in my hands right now. I shot a scene last year in the Redwoods with 8x10 Efke 25 Developed in Pyrocat-HD 2:2:100 for 12:00 minutes.The readings are: 3.53-.50 for a net of 3.03DR. It makes an amazing carbon transfer print and the highlights are hot but have plenty of detail and carbon transfer can tame it in the print. I have several others and this neg runs the gamut of range from zone I to Zone XI possibly higher. To bad Efke is gone.

[swmcl]

So much for me to think about here. Jim, I assume your densest part is 3.53 and the least dense is 0.50 making a range of 3.03 ? I'm just sticking to normal processes but it does sound good I must admit. That to me is a piece of film able to record 10 stops or thereabouts (10 x 0.3 = 3.0). I'm primarily using FP4 in Pyro Glycol 1.5:1.5:100 (4.57ml per square inch of film) for 11 mins @ 20C rated at 64 and shadows on Zone 3.5 to 4 - which gives me something like a density of 1.6 at Zone 11 (?)

Is the scanner a linear device or a logarthmic one ? Surely it is linear ?

Lenny, in my ignorance I have assumed that a 12 or 14 stop image in front of me can be put on film. If it can be put on film then I can choose how to print it later. The important part is to get a useable negative - be it slightly over or under exposed for the main subject. If I can get every image to say from a 5 stop to 10 or 11 stops on film then I have freedom to change later. Its just that the datasheet says a Dmax of less than 2 ! Lenny I trust your judgements and take your advice seriously - thanks.

What is it when a digital photo is 'expanded' ? Is it a quantisation error - or approximation ? So you shoot a scene with an 8-bit sensor and then stretch the data to fit a 16-bit range you get the comb yes ? I feel it is like that when you shoot onto a film with a range of say 2.0 and then try to get 14 stops (@ 0.3) out of it ... It just feels wrong in a way but then again, it is an analogue medium not a digital one. My tests didn't get beyond 1.7 for FP4 and that was with 2:2:100 and 10 mins at zone 11. The film seems to show a linear response but at around 0.15 per zone (not 0.3).

What I take from this discussion is that I should shoot more and worry less !

I hope to get out this weekend.

Cheers all !

[Emmanuel BIGLER]

I have placed here a copy of the official specs fot the discontinued Kodak technical Pan film
http://cjoint.com/?CDDsfBXWDZK

As you can see on page 10/12 of the pdf document, when processed with either Dektol or D-19 developer, you can reach a D-max equal to 4. But the gamma is extremely steep, above 3. On page 11, you can see the density when processed in technidol; with this very special chemistry you can get a value of .65 for the gamma, but the plotted diagram does not show any density values above 2.

Now that Kodak technical pan is discontinued, you can still find microfilms on the market as well as special chemistry to process microfilm as a continuous-tone negative with a low gamma value.
Among pupular European microfilm supplies for the hobbyist, you'll find Agfa Copex Pan Rapid, a classical microfilm; and packaged in rolls and 4x5" sheets, ADOX CMS-20. if you process Copex or ADOX CMS-20 in Dektol or D-19, sure that you'll get a D-max around 4. Low contrast developers for microfilms are available from SPUR or ADOX.

The Kodak T-max data sheet is here
http://www.kodak.com/global/en/profe...4016/f4016.pdf
curves shown do not climb above D=2.5 when you keep the gamma around 0.65. Do not forget that if you want to print the negative directly on silver-halide paper, you'll have hard times to compress all this dynamic range on any available printing paper. And scanners capable of a D-max=4 are not that easy to find.

Hence only Kodak people might have seen with technical pan or T-max a useable density range of 3 with a gamma of .65, yielding, in theory, an exposure range of 1 to 10^{3/.65} = 10^{4.6} ~= 40,000 i.e. about 15 f-stops.
20 f-stops = 1 to 1 million = 10^{6} hence the corresponding density range @gamma=0;65 = 6x0.65 ~= 4. A challenge to actually see this, but if Kodak people have achieved it with T-max, we can believe them.