@aparat. Kudos for performing these sytematic tests. However, I have a question re: your determination of film speed from the logE-D curves as shown on your post #53 above
Here's the set. Three stops either side of the "0", or 320 ISO on my Sekonic meter. Somewhere between 320 and 640 for these would be pretty nice. 200/160 is a little crispy.
View attachment 319027
Here's the set. Three stops either side of the "0", or 320 ISO on my Sekonic meter. Somewhere between 320 and 640 for these would be pretty nice. 200/160 is a little crispy.
View attachment 319027
OT: I "tested" a bunch of Ferrania P30 when they (like Catlabs) had no data aside from some suggested best practices. It was contrasty like Catlabs unless I exposed it at iso50 or below, and at those speeds it worked in a way that could be scanned or wet printed without too much difficulty. But for me it was an expensive time waster only to learn that the film was too slow for my intended use. That's when I got out of the business of testing undocumented films.To me, those look over-developed. Which isn't particularly surprising, given that I expect that was what was being targeted when CatLabs arrived at with its recommendations. Negatives that I find to be under-exposed and over-developed. Those sort of negatives appear to be quite popular now.
Yes, I happen to agree with you. I've seen it done both ways in the literature. Please, see below for a more detailed explanation.I find Ilford "Relative log exposure" more intuitive as more exposure results in higher negative density. Kodak, Foma and many other film manufacturers use this convention.
Could you post your software to a new thread? Some of us would appreciate being able to compute ISO, CI, etc., from densitometer measurements. I hope the software is written in a popular language with free compilers/interpreters such as Python, C, C++, or even Fortran.
@aparat. Kudos for performing these sytematic tests. However, I have a question re: your determination of film speed from the logE-D curves as shown on your post #53 above
Skipping other "details", the speed is based upon the point on the curve at Base+Fog+0.1. But your measured exposures do not reach low enough values to measure Base+Fog.
Perhaps it is the graphing software, not showing the whole dataset. Which brings up the point, is the software available? I have constructed my own EXCEL spreadsheet to automatically find the parameters, but it is very much like a house of cards. One click in the wrong spot could destroy its function and take weeks to figure out. Not a fan of any Microsoft product.
I haven't tried 1+50 yet. It would be my preferred dilution for this speed film, but 19 min seemed like a very long time, and the 9 min for 1+25 seemed more reasonable, so I started there. Once I zero in on what the film can do, I will try 1+50 next.This is a very interesting progression. Thank you for including it! It seems Rodinal 1+25 time, temperature, and agitation provided by the manufacturer work out perfectly for you. I wonder whether the 1+50 of 19 minutes gives the same contrast. Have you tried 1+50, by any chance? Also, I cannot tell from this picture, but is this a scan or a photo on a light table?
To me, those look over-developed. Which isn't particularly surprising, given that I expect that was what was being targeted when CatLabs arrived at with its recommendations. Negatives that I find to be under-exposed and over-developed. Those sort of negatives appear to be quite popular now.
Ha Ha Ha! That's exactly my experience with P30. I gave my rolls away, too.OT: I "tested" a bunch of Ferrania P30 when they (like Catlabs) had no data aside from some suggested best practices. It was contrasty like Catlabs unless I exposed it at iso50 or below, and at those speeds it worked in a way that could be scanned or wet printed without too much difficulty. But for me it was an expensive time waster only to learn that the film was too slow for my intended use. That's when I got out of the business of testing undocumented films.
I offered to give the rest of my P30 to a friend that tried one of my rolls and he declined saying he was already dealing with PTSD from the first roll. ;-)
Edit: I added the quote marks around the word tested to make sure people don't think I was doing what @aparat is doing, which is on another level entirely. I don't have those skills!
But, I am also thinking that this is a losing battle - I think the film is just plain high contrast. There are better films if you want a wider tonal range.
I'd still like to see more results with a meaningful amount of more exposure, plus less development.
After posting my comment #76, I thought maybe you had measured B+F outside the step wedge, in an area totally not exposed (which is the correct way). Or, as suggested by ic-racer in post #78, "Perhaps it is the graphing software, not showing the whole dataset."Am I correct in understanding what you said about the measured exposures do not reach low enough values to measure B+F that there was too much exposure? You have a very good eye. Yes, ideally, the toes would be longer, but this was just a test run to establish how much exposure the Catlabs film needs to produce well-formed curves. There will be more analysis coming after I buy more film. The Catlabs B+F is 0.1and the exposure does produce this density on the first step of the step tablet, which is then plotted. The Arista film's B+F is 0.3, which is high. I am not sure why it's so high. I just bought this film fresh and ran the test twice to be sure. My old Arista negatives are around 0.28. The first step of the step tablet reaches the density of 0.31, so it is 0.01 higher than B+F, which is within the margin of error for my densitometer, so I just let it go. Is that what you mean?
So, the the Catlabs film, B+F is 0.1, the speed point density is 0.2, and for Arista it is 0.41. The relative log exposures for the speed points are 2.79 and 2.62, respectively. This setup is not professionally calibrated, so the results are probably only within 1/3 stop, as @Romanko pointed out. Also, please note that these numbers come from measuring the "ISO" predicted curves (curves that have the G of 0.62), not the actual curves. Hope that answers the question.
@aparat. But your measured exposures do not reach low enough values to measure Base+Fog.
Did you read the whole of my post?They do not need to be, if for instance one has established already the B+F-density in a seperate test, outside a sensitometer. It then would be sufficient to have graded exposures above that level and below the qualification level.
maybe you had measured B+F outside the step wedge, in an area totally not exposed (which is the correct way)
Implying (pending confirmation by aparat himself) that he derived the B+F from the curve(s) as displayed, at the leftmost point.Am I correct in understanding what you said about the measured exposures do not reach low enough values to measure B+F that there was too much exposure? You have a very good eye. Yes, ideally, the toes would be longer
After posting my comment #76, I thought maybe you had measured B+F outside the step wedge, in an area totally not exposed (which is the correct way). Or, as suggested by ic-racer in post #78, "Perhaps it is the graphing software, not showing the whole dataset."
But the numbers that you state above (blue text) show that you just take as B+F the lowest exposure point in the step wedge. Most obvious is "The Arista film's B+F is 0.3" (blue curve). I find it hard to believe that the blue curve, if measured further to the left, would not reach a density level of 0.2. Can you please, if you have not already done so, measure B+F in a film area that was totally un-exposed?
If true, that would mean that the Arista film's speed point is further to the left, i.e. its speed is higher; and, even if the absolute photometric calibration is not correct, that would also mean that the Catlab film is even slower relative to a "ISO100" film.
This said:
View attachment 319213
- Leave aside 1/3 stop quibbles; in b/w that is completely insignificant; in actual use much below the inevitable differences between pointing your meter a little more to the right or to the left.
- The test by oldwino https://www.photrio.com/forum/threa...film-320-pro-2022-version.194630/post-2599132 tends to show rather convincingly that 320 is not an unreasonable speed for that film. Could the long toe explain this apparent contradiction?
All good questions and observations. I would only suggest that the production of “fine photography prints” and the quest for perfection and the desire for scientific detailed data never was a quest by “everyone” on APUG. I, for instance, respect all of that but just want to make decent images of interesting subject matter that are well composed, and if they are technically flawed… so be it. I know that I’m not alone in preference for an artistic approach to photography than to quest for perfection, sometimes it seems at the expense of doing photography at all.
I’m thrilled that you are doing what you are doing. I’m equally thrilled by the work done by folks who have put the film in their cameras and taken pictures using the vendor-provided information and guidance. It all really is value added for both kinds of photography.
Thanks so much for keeping me on my toes, and for the book recommendation! I don't have it, so I'll try to find it as soon as I can. As to the effort, once I started, I'd like to finish@aparat. Thank you for your patience with my questions. My apologies for incorrectly assuming that you had taken a shortcut to the determination of B+F.
Again congratulations for your systematic measurements. If you are interested in similar topics, you might like this book:
(see buyers comments)
although at the current price I cannot recommend to buy it (I got mine 5 years ago for 10€+shipping!!) Maybe borrow from a public library.
Final note. Is that film, most probably a rebranding of a known film from a major brand, worth your efforts?
I think a lot of the new films we are seeing, whether actual new emulsions or simply rediscovered old ones, come about because of the shift in how people work with images, and expect images to look. The decline of the darkroom and the ascendence of digital photo manipulation, plus the general look of digital photography (higher native contrast, sharpness and acuity), mean that there is more room now for what many would deem "experimental" films. The overall look of CatLabs 320 is one example - it has an inherent graphic, high contrast look. It is not meant to faithfully record a scene (that requirement is met by a phone camera nowadays), but rather to convey an emotion.I hope this is not off topic. If it is, perhaps the moderator can move it to another thread or delete it. I've been away from Photrio for a few years. Before I left, I thought, perhaps erroneously, that, in the Photrio community, the "gold standard" for evaluating film performance was in terms of producing an excellent silver gelatin (or alternative process) print of an average scene, in a straightforward manner (i.e., without film masking, etc.). So, film speed, for example, would have to be considered within that context, i.e., to obtain minimum exposure required for a beautiful print. Sensitometric testing is meant to give us an generalizable, empirical account of film performance with regard to that goal. After all, we cannot test each film by doing a proper psychometric study of print quality judgments across a sizable, randomly sampled population. Is that still the broadly held belief around here? I learned a lot from Photrio members over the years!
Why do I ask? Well, I guess a lot has changed over the past few years. There are a lot of new films available, some with unconventional performance characteristics, some many years expired, some meant for aerial surveillance. There's a new generation of film photographers who aren't interested in data sheets, who don't print in the darkroom at all. They shoot, process, and digitize the film, most commonly, it seems, with a modern DSLR, and share their images online. What I gathered from the original Catlabs thread was that the company is marketing the film to that kind of customer base. There's absolutely nothing wrong with that, as far as I am concerned. To be honest, I wish I had the equipment and skills to do that myself.
However, that kind of film use might require a different set of diagnostic criteria. Film holds a lot of data. A modern digital camera can extract a lot of that data, and RAW processing software, such as Negative Lab Pro, Adobe Lightroom, Photoshop, etc., can make impressive use of all that information and produce beautiful images with ease, even from negatives that would be otherwise considered imperfect. So how do we test film in this new reality? Should we still care about sensitometry at all? How do we reconcile sensitometric results with on-screen evaluations of digital images?
However, that kind of film use might require a different set of diagnostic criteria.
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