Minimum Aperture on 240mm Schneider Symmer-S

[tgtaylor]

The Schneider catalog says f64 but the aperature scale only reads to f45. However the aperature level continues past f45 and the blades close correspondingly. Am I correct in assuming that when the aperature lever is fully closed past the f45 marking it is at the f64 aperature? If so, then why didn't Schneider notate the f64 aperature on the scale?

Thomas

[Preston]

Thomas,

I have a Schneider Symmar-S 210 that does the same thing: The aperture closes down beyond the marked f45. Whether it's actually f64, I don't know. I suppose one could run a test of some kind to see.

If it does truly close down to f64, I also wonder why Schneider didn't mark it as such? Good question, sir.

--P

[polyglot]

Mine ("Symmar-S 5.6/240 Multicoating", #14290xxx) is marked all the way out to f/64.

[IanG]

I think Schneider changed the scales at some point. The f64 is probably compromised by diffraction, like Preston my 210mm Symmar S stops down past f45 possibly nearly to f90.

The late production 150mm f5.6 Xenar (Copal #0) has a scale that goes to a marked f64 it'll stop down about half a stop more.

Ian

[E. von Hoegh]

F:64 will be 1/2 the diameter of the aperture when it is set at f:32. Why not measure yours, instead?

[wallrat]

There is an easy way to measure it too. You remove the cells and place the shutter on a flatbed scanner with the shutter open on T. Scan at a known resolution them blow up the aperture iris to a size large enough to easily see. You can then either count the pixels or draw a line across it in an image editor. The resolution (pixels per inch or mm) divided by the length of the line in pixels is the diameter. It's surprisingly accurate and imho, much easier than using a caliper on such a small opening near such fragile blades.

[E. von Hoegh]

There is an easy way to measure it too. You remove the cells and place the shutter on a flatbed scanner with the shutter open on T. Scan at a known resolution them blow up the aperture iris to a size large enough to easily see. You can then either count the pixels or draw a line across it in an image editor. The resolution (pixels per inch or mm) divided by the length of the line in pixels is the diameter. It's surprisingly accurate and imho, much easier than using a caliper on such a small opening near such fragile blades.

I use drills as gauges.

[Lachlan 717]

Can't you simply extrapolate the divisions already on the aperture scale for the additional range of movement and mark them for the supplementary stops?

[E. von Hoegh]

Can't you simply extrapolate the divisions already on the aperture scale for the additional range of movement and mark them for the supplementary stops?

No.

[Lachlan 717]

No.

Why is it, then, that all of my shutters have the same distance between the f stop markings? Your response is rendered incorrect based on this literal observation. Why should the common distance between stops suddenly change just because the markings stop?

As long as the aperture control goes to the next [predicted] f stop location or beyond, it should follow the preceding distance ratio.

[E. von Hoegh]

Why is it, then, that all of my shutters have the same distance between the f stop markings? Your response is rendered incorrect based on this literal observation. Why should the common distance between stops suddenly change just because the markings stop?

As long as the aperture control goes to the next [predicted] f stop location or beyond, it should follow the preceding distance ratio.

Because not all shutters have linear F-stop scales. In fact, most do not.

[Lachlan 717]

Are they a logarithmic scale, rather than linear? If so, it shouldn't be difficult to work that out.

(And the degree of error in marking the f stop location, the error in aligning the ring AND possibly reciprocity failure enduced by these apertures will surely render the tiny difference in location rather moot?)

[ic-racer]

It is likely not very accurate at that small setting because of the slop in the aperture mechanism. You can put a dot there if you want. On my Angulon 210 (with big numbers on the scale) f64 would be between the 4 and the 5 of "45" Some Copal 3 aperture scales that I have seen have two additional dots, indicating both f65 and f90.

[E. von Hoegh]

Are they a logarithmic scale, rather than linear? If so, it shouldn't be difficult to work that out.

(And the degree of error in marking the f stop location, the error in aligning the ring AND possibly reciprocity failure enduced by these apertures will surely render the tiny difference in location rather moot?)

I'll stick to measuring, thanks.

[Lachlan 717]

I'll stick to measuring, thanks.

No need to thank me; it's your time to waste.

[E. von Hoegh]

No need to thank me; it's your time to waste.

Waste time? You have to be joking. I would measure the diameter at f;32, select a drill half that diameter, close the aperture (gently) on it and mark the scale.

You're suggesting that it would take less time - and be more precise - to calculate from the spaces between apertures on a possibly non linear scale??