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Wednesday, 16 January 2013


Every tool has a quirk or two--no matter how well designed. Embrace the oof and work with it. Oh, how Zen--an easy state to reach in the Bay area.

Not sure whether this has already been mentioned, but could it be a temperature-related problem? Is it possible for example that it was a cold night, and this caused contraction of the base to which the sensor was attached at a different rate than the sensor, introducing curvature in the sensor? Or just the two sides of the sensor being made of different materials, again introducing curvature. I would guess even a tiny amount of curvature might be enough to throw part of the focal plane out. I have no idea whether or not this is an issue with sensors (and whether for example it depends on how the sensor is attached to the camera or the materials that go into making the sensor), but it's worth a thought, especially if it was a cold night.

Doing definitive bronzing/silvering studies on different papers probably will require access to spectrographic and/or chromatographic equipment and the money and time to do a full experimental design. Resources I am sure you don't have (me ether!). Once, Kodak might have been a resource, but now, outside a few government or university labs, or some otherwise oriented industrial labs, I have no idea where it could be done. Maybe Wilhelm labs could do this. If there was sufficient interest in the question. Given the great reduction in the use of silver based prints, I don't think the interest is there. Maybe a Phd thesis topic for some student looking for an 'arcane' topic?

I am glad at least someone was working on this B+W paper problem. I remember having so many fights with our lab on this and the only solution that was presented to us was the "Kodak promise of excellence" program. Basically Kodak would reprint your photo for free, however only if you also used Kodak film, which we hadn't done in the past. I believe they didn't cover the retouching either (understandable quite difficult to do) so the photographer was still out of pocket. It really was a frustrating time for B+W and all though we had a few prints returned to us I am sure there were quite a few clients who just scrapped the prints and thought less of us. We even had a print returned to us last month, but guess where Kodaks lifetime guarantee is now. We did have a printer we occasionally used for special prints who worked by hand and used Fuji paper, of which we never had a problem with.

Such cases are quite common in complex computer systems also. There are bugs which are not really repeatable or even worse, they happen quite often, but are not traceable because of heisenberg's rule - universe is quite a nasty place to live :-)
Sometimes however, such problems can be detected by source code analysis (when you have one, that's why opensource is not that bad).
So, just get me the source code for the universe and I shall solve your problem in a finite time :-)

Experiments don't have to be hard if you do proper Design of Experiments (DOE).

I'm constantly surprised at the number of scientists and engineers that have never heard of, let alone were trained in, DOE.

Heisenberg's Oscilloscope

There once was a certain high end piece of broadcast video equipment that has some permanently attached test leads. The manufacturer could never reproduce a particular intermittent problem when the board was hooked up to the scope but when they returned that model to customers the problems would recur. They never found the problem on the scope , but leaving a pair of test leads clipped in kept it from ever recurring so in they stayed.

Any problems we had in science labs was usually down to the water.

I can make RC spots appear when I wash prints in tap water, which contains minerals. When I use MilliQ water for all processing steps, including the wash, I cannot make them appear. I suspect that the reaction may require a catalyst or initiator, and that UV alone can be insufficient to make the reaction occur.


Dear Ctein,

I just want to thank you belatedly for Post Exposure which you referred to me for further reading awhile back (in answer to a comment in your exposure range series). I didn't realize beforehand that you were giving away a book!

Although I'll probably never be shooting film, I find Post Exposure eminently useful when "developing" my digital photos in Lightroom. Being acquainted with the science behind post-processing is empowering, and encourages one to "experiment" while shooting and in post. To a layman, it's a very good read for its inclusive and "deathless" prose ;)

Thank you.

BTW, your web site is looking great with the new template.

Re: bronzing/silvering -

So that's what that is! I have quite a few RC prints that are bronzing. (Including one that I can't print digitally to save my life... go figure...) The bronzing is a very different effect from those that were improperly washed. I have been wondering what was going on, and now, after at least 10yr, finally know.

Thank You Ctein!!!


This is also a big problem in software engineering. Many a vague bug report is rejected as "could not reproduce", for similar reasons. There are just too many variables. If QA or engineering can't see the problem, then they can't fix it.


Btw, for those of us still making silver gelatin prints, Sistan is still available, now under the Adox label as Adolux Adostab. Freestyle carries it in the US.

This is probably already mentioned, but to me the most logical explanation seems a problem with image stabilization. When it is parked in a wrong position, or started up in a wrong position, I can imagine the problem you found.

Dear semilog,

Well, don't know if it's ozone being photo-generated by the titanium dioxide in the paper, might just be triplet state oxygen. But, yeah, that's the prevailing wisdom, that oxygen is the intermediary and it's not a direct reaction between the titanium dioxide and the silver. It doesn't require UV, by the way. Visible light will do just fine… dammit.

It's also clearly extremely sensitive to processing conditions; prints usually do not silver out uniformly; there will be areas that do that are intermixed with areas that don't.

I was half tempted to subject some test prints to scanning electron microscopy and an electron microprobe (I've got a friend with that gear), but I didn't get around to it. My interest was of a practical bent–– could I nail down the proximate cause and could I find a solution to it. The answer seemed to be yes and yes, and after that it became more of abstract interest. Which pushed it way down the to-do queue, I'm afraid. One of those “in my copious spare time” things.

pax \ Ctein
[ Please excuse any word-salad. MacSpeech in training! ]
-- Ctein's Online Gallery http://ctein.com 
-- Digital Restorations http://photo-repair.com 

Dear J and John,

This was covered in the previous column, but since you posted the comments here…

Atmospheric distortion does not jump around in such a way that when you're doing a panoramic sequence it ONLY shows up in the right 25% of each frame and does so in each and every frame consistently.

Well, not unless the gods are really out to get you!

If it's a divine malevolence, not much I'm going to be able to do about it.

pax / cursed Ctein

Maybe it was an earthquake.

BTW Re: Bronzing...

The photographic department I was running back in the 90's was chugging along perfectly, everything copecetic, until the company replaced our carpeting with a nice, trendy colored, industrial carpeting. Within three months, everybody's RC prints they had thumbtacked to bulletin boards started bronzing! I had never seen anything like it, and always worked in commercial studios that had been using RC paper since it's introduction! I had RC stuff since the dawn of time just thumbtacked to stuff and never had a problem, even the older prints didn't bronze like the new stuff. They must have changed the formula in the paper...

My own, previously unstated, opinion was that the blur might have been caused by a heat plume from an unseen roof vent between the lens and subject.

I occasionally get such blur patches photographing wide urban scenes from high vantages. Consider this wide scene from August. Now look at a detail of the men. Beam me up, Scotty!

Winds will make such plume blurs seem unreproducible.

Diurnal Wander

Six Stages of Debugging should always be kept in mind.

1. That can’t happen.
2. That doesn’t happen on my machine.
3. That shouldn’t happen.
4. Why does that happen?
5. Oh, I see.
6. How did that ever work?

The problem is business marketing folks see "issues" as stage 1 or 2 problems to be denied.

The engineers or scientists or software developers at least get to stage 3 and then work hard on stage 4 (the topic of this post) to get to stage 5.

Re the defunct Agfa's Sistan: other than the above-mentioned Adolux-marketed Adostab, Ag Stab is commonly available over here in Europe. Same formulation as Sistan. Even the spec sheets linked in photochemical webshops are often old Agfa Sistan PDF docs.

Searching the ever-resourceful APUG forums for "homemade Sistan equivalents" (essentially K thiocyanate plus wetting agent), one can find a revealing post from 2005 by a contributor signed as "Photo Engineer", ominously located in Rochester, NY. It ends on the immortal line:

There is an article published by Ctein on this subject. I recommend it to you all.


These mighty words should be inscribed in bronze, silver, and titanium.

Dear Tom,

Fresh carpeting has all sorts of nasties outgassing from it. Classic case. Not a change in paper formulation, a change in the environment.


Dear Ken,

Same problem with your hypothesis as with the rain/mist/turbulence theories. It has to magically appear in the right 25% of each frame, no matter what direction the camera's pointed in -- remember, I was photographing a pano sequence.

pax / Ctein

Software design, which I also really enjoy, is more like Mathematics....you have to envision what you have, see what you want, and imagine what the space in between looks like.....

But that's a whole other set of skills.....both activities are fun.....but in different ways.

For a long time, when I would hear people say that mathematics was like software development, I would argue against that with them....then one day I had a long chat with my brother, who was pursuing a PhD in mathematics, about exactly how one did pure research in math, and what thought processes were involved.....not too humble to say I was mistaken......

Designing software and finding new math is the same mental process.....

And it is mathematics.....not science....

The difference between software and math is that software has to run on the machine in front of people and math doesn't. There are certainly similarities in the thought processes and in the nature of combining abstract ideas in the ether ... but actually shipping software is more of an engineering activity than anything else. Although a lot of actual engineers would also object to that statement given how fragile the stuff seems to be.

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