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Standard f-number values and their "labeling" is covered by standard ISO 517. I have only the first several pages (a "free sample"). In that is this list of "standard series of f-number marking": 05.-0.7-1-1.4-2-2.8-4-5.6-8-11-15-22-32-45-64-90-128 These are of course 1n 1-stop steps. There may be standard "rounded" values for 1/3- and 1/2-step series elsewhere in the standard, but not in the part I have. Or it my be that such lists have only been concocted by camera manufacturers. (There... Read more

In several threads here over the past couple of weeks, I have been fairly emphatic that there could be sequences of numbers that would obey both of these "rules" for a substantial number of values: • If we go from one value to one 3 values further in the list, the value would change by exactly 2. • If we go from one value to one 10 values further in the list, the value would change by exactly 10. Fellow member Ted Cousins has challenged the validity of this. Upon further study of this... Read more

I have been brooding here lately over the matter of exposure meters that, for the incident light exposure metering mode, offer two confirmations, one with a hemispherical (dome) light collector (which we expect would give the meter a cardiod directivity pattern) and one with a flat (disk) collector, which we would expect to give the meter a cosine directive pattern. Almost invariably, the manufacturers of those meters state quite different values of C, the incident light metering calibration... Read more

Hey hey OPFers! I might be back! Sorry for the long (very) absence but the covid time has brung me so much more work as before… I'll try to post here at least one photo each week as "My photo of the week". Pardon me if Ido not lurk around and post elsewhere, but I'm still overwhelmed… I just arrived in Venice (Italy) for a week as it's time for a "self" residence, to decompress and prepare the images for our future exhibition (with Romain Claris for the films) at the Fonds Culturel de... Read more

I have discussed many times in recent threads that there can be a series of numbers that obeys both these rules: • If we start with any value and go forward in the list by 3 values, the 2nd value is exactly 2 times the first. • If we start with any value and go forward in the list by 10 values, the 2nd value is exactly 10 times the first. I had said that the longest list following those rules would be 30 values in length. That was in error. We can have a list following those rules... Read more

The table below gives three lists of values of the ISO speed that may be of interest: The values in the first columns ("Base list") we so chosen that they all absolutely and precisest follow these two "rules" • If we start with any value, and then go down in the list by 3 values, the second value is exactly 2 times the first value. • If we start with any value, and then go down in the list by 10 values, the second value is exactly 10 times the first value. There could be many... Read more

[This has been edited to correct an error in the "purple boxes" portion of the table.] The following table shows the assignment of film speed values to the "clicks" of the film scale dial, based on data in the manual for the L-398. I presume it also applies to the L-398A, whose manual does not have that information. There are 34 "clicks" in the scale range, only every third one labeled on the dial. The table is set up to reveal the interplay of the two schemes of values... Read more

Today shots of a beautiful flower, originating from the USA Prairie, here today a commercially sold hybrid of a Black-eyed Susan - Rudbeckia hirta (possibly R. hirta x R. fulgida) in 3D STEREO (crosseye) in reflected ultraviolet photography using different filters aside from the Baader-U filter, but different ones today for simulated bee and butterfly vision also part of my XBV filter set. All shots were done at f8-f11 on my balcony. Lens was a UV transmitting 35mm wide angle lens with... Read more

The exposure time (shutter speed) scale of the Sekonic L-398 exposure meter is marked with radial lines (the "major divisions") at what is almost certainly intended to be 1/2 stop intervals (ration of 3 between adjacent lines. In between each pair of lines are two dots (the "minor divisions"). One cannot directly align the dots with the markings on the adjacent aperture scale, but is is almost certain that they are intended to represent intervals of 1/3 stop (in the working of the "slide... Read more

The Sekonic L-398A exposure meter offers two incident light metering configurations. In one, the light collector is a flat disk. In the other the light collector is a generally-hemispherical dome. In the "disk" configuration, the directivity pattern oi the meter is probably nearly a cosine function,. Thus its meter movement would respond proportionally to the illuminance of the light it observes (with respect to the plane of the collector). In the "dome" configuration, the... Read more