Kirk, the concept of slope in a point is as difficult to understand for some people today as it was for the philosopher Zeno. The concept is still fundamental, so Achilles will still outrun the tortoise - regardless of what some people insist on believing.
-- Ole Tjugen, Luddite Elitist
You know Jay, I dont know if everything is a contest, but I least I am not afraid of showing the product of my expertise......something you clearly are. As to being named along Kirk and Stephen, dont flatter yourself too much, I will admit they know what they are talking about....that is not the case with you...
Originally Posted by jdef
My one thought. SBR as defined by Davis is a measurement of shadowed and lit areas of the scene. To this difference is added 5...so that a difference of 1 stop would yield an SBR of 5+1 or 6. I can also see that a planar surface that is evenly lit would be 0+5 =5. So, If one is using SBR as defined by Davis how do you mange to get an SBR <5? other than extreme flare.
I have no problem with the idea that reflected readings will produce differences of less than 5 stops.
David Kachel in writing in Photo Techniques magazine recommended the use of Koadak Professional Copy Film for large expansions. It is a double coated emulsion. Exploiting these differences allows substantial expansion to take place.
Adam's conjectured that Technical Pan film, now discontinued, might be of some usage since one can produce extreme contrast with the film.
I am nowheres near up-to-date on Ortho sheet films but I would imagine that there are several which are slow, fine grained and quite capable of pluss development....the problem may well be to have little enough contrast so that you have no created far more expansion than is desired.
Originally Posted by Claire Senft
Jay has started a new thread that takes this subject in a slightly different direction. It promises to be very interesting. You should check it out and maybe even repost this message there.
Claire - That was one of the questions I had when I started this thread. Determining development times for situations that would be associated with SBRs less than 5 is easy. Just do the testing and you will probably find a point that lies in that range, if you use short enough development times.
Originally Posted by Claire Senft
So the big question I had was how could you actually measure the lighting conditions if they did fall in that range. By my understanding of Davis's definition, you should not have these situations as you pointed out; 5-0=5.
But if you check on pages 3, 4, and 5 of this thread, Sandy King did address metering techniques that could be employed for scenes that may need this level of expansion. He says it works.
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One of course may use terminolgy as they wish. I am very much under the impression that Mr. Phillip Davis id the originator of this term Obviously. I may be incorrect as i so often am. However, If I am not than I do NOT believe an SBR of <5 exists as staed above.
I am not that most percetive reader but I saw nothing written by Mr. King that changes my opinion...and I am a photographer who highly values and greatly appreciates Mr. King's opinion.
I value Sandy's opinions too.
Originally Posted by Claire Senft
But I agree with you about the less than 5 SBR idea. The solutions offered do seem kind of kludgy, as I said earlier. I need to play with it and see what happens in the real world.
I too was confused by this and asked Phil about two years ago. Here is his response:
Originally Posted by Kirk Keyes
You obviously can't measure a 4-stop SBR directly but it's certainly possible to assign a range of less than 5 to your subject if you want to treat it to much higher than normal development. The "5 stop minimum" is based on the incident meter dome's 18% transmittance which is equivalent to 2-1/2 stops less than 100%, and (when doubled), perhaps coincidentally, closely matches the typical reflectance range of flat copy, such as a magazine page with "black" ink on "white" paper. In other words, reflectance readings of those extremes of tone are usually in the vicinity of 1.5 which is equivalent to 5 stops.
It's reasonable, therefore, to assume that any 2-dimensional, uniformly illuminated subject — (and this is important) that you wish to reproduce with realistic contrast — can be considered to be a 5-subject, regardless of its apparent tonal range. If its a normal full-scale subject, it'll be reproduced that way in the print; if it's a low-contrast subject (gray on gray) that's how the print image will also look.
But that may not be how you'd like to interpret it. For example, you might want to photograph a petroglyph of brown pigment on gray rock of similar value. Using a 5-stop (or greater) range will produce a very low contrast image so you might arbitrarily treat it as a 4-stop subject which will greatly increase development time and therefore increase image contrast significantly.
The ExpoDev Palm program is set up to make this possible with the Incident metering method (not the ZS). You can take a single "low" reading to establish the exposure then arbitrarily enter a "high" reading that's as much as 2 stops less (corresponding to an SBR of 3 stops). This is very strong medicine and it's very likely that common materials won't be able to produce that degree of contrast, but if you have a film/dev combination that will permit it, you can enhance image contrast dramatically.
Incidentally, you can check your materials to see if they're capable of working in that contrast range by dividing your paper ES by the SBR. For example, if your ES is 1.0 and the SBR is 5 stops (1.5) the appropriate average gradient is 0.67, which most popular materials will handle easily. But if you decide on a 4-stop SBR the result (1/1.2=0.83) may not be within range, and a 3-stop SBR (1/0.9=1.1) is more than most common materials can handle, although there are a few exceptions. If you're using the ExpoDev program it'll warn you if your chosen input values exceed the materials' capabilities.
No need to send crow feathers; I'm just delighted to hear that you've given BTZS a chance!
Jorge - thanks for posting that. It's exactly what I was looking for.
Originally Posted by Jorge
Interesting work-around he suggested for the software. And that he mentioned rock art - as that seems to be a favorite subject for many of us out in the western US.
Jdef you are correct that Davis has covered the usage of both the spotmeter as well as the incident meter and recommends both his zone system as well as the incident system. That being said the terminology SBR is a term for the incident system not for the zone system.