Just what I got. But as I said the value displayed for the F70-210
doesn't make sense. As far as I can tell the predicted aperture is
based on only the maximum aperture possible with the lens. It cannot
get data from the lenses chip, and just like an "A" lens you get no
change in reported aperture when you zoom, the F70-210 while it's mated
with the F 1.7x adapter, it works just like an A lens...
I assume the difference between the FA43 and the FA77 is caused by the
the 43 reporting it's maximum aperture as 2.0 in "A" lens speak, and the
77 reporting it's maximum aperture as 1.7. Which would magnify the
actual speed difference.
Now I've been looking at the contact diagrams and the contacts on the
back of the F70 to 210. It seems that the contact labeled m1 in the A
lens chart must always be 1 since it's simply bare metal on the lens
mount and the contact the is labeled m2 must always be 0 since it's a
plastic plug. The only thing that makes sense is that the other
electrical contacts change value depending if the digital data pin is
live or shorted.
For the lens to report itself as an "A lens" f4 maximum aperture the
three pins closest the digital data pin labeled r1, r2 and m1 must have
the value of 010, and the minimum aperture of 32 it must show m2 and r3
with a value of 10, (at 70mm). However it can't do that since the m2
position is a plastic plug! What it seems the lens must be doing is
changing the electrical properties of the r1 and r2 pins to report
itself as an 4.5 maximum aperture lens to the F 1.7 adapter, and since
it can't report itself as anything else, (based on the chart on the Ka
mount page), as having a minimum aperture of f45. The adapter then adds
it's factor bringing the aperture to 8.0 with a minimum aperture of f81,
which is the observed behavior.
Conclusions:
1.) The F 70-210 f4.0~5.6, reports itself to "Ka" class devices as an
f4.5 max aperture lens with a minimum aperture of f64 if the data
contact is shorted and not passing data.
2.) I have way too much time on my hands right now...
So that seems reasonable to me, of course I could be wildly wrong but it
fits the observed behavior. It's probably described in the repair
manual for the lens, too bad I don't have one.
Bob Sullivan wrote:
PJ,
Here's what I get for minimum apertures in the K20D viewfinder...
F70-210 f4-5.6 reports f8 with AF1.7 converter.
F28/2.8 reports f4.5 with converter.
FA43/1.9 reports f3.5 with converter.
FA77/1.8 reports f2.8 with converter.
Regards, Bob S.
On Thu, Dec 4, 2008 at 1:13 AM, P. J. Alling <[EMAIL PROTECTED]> wrote:
All right, I don't know what to make of this. My F 70-210 4.0~5.6 works
fine on the *ist-D and *ist-Ds and everything seems to be reported
correctly.
When I mount it on the 1.7x AF adapter the maximum aperture is reported as
f8, now I don't quite understand, because that just looks wrong I was
expecting it to report f 6.7. So I figure I'll calculate the approximate f
stop of that combination with fCalc. So naively I just punch in the
numbers. f4.0 returns 7.21. Hum That's only 1/3 stop off of f8.0 so maybe
that's right, but that's less than 2/10 from 6.7...
So I decide to test using another lens. I'd never use this combination but
it was available, so I put the FA 20-35 and FA 1.7x maximum aperture is
reported as f6.7 what? Well that's less than 2/10s stop off the actual
value in the other direction. Now I'm really curious so I try the FA 28-70.
That too reports f6.7. Next I try an A lens, lets see, I have the A*300
f4.0 so I try that. Lo it too reports f6.7. Consistency at least.,
reporting the nearest standard 1/2 stop to the actual value.
Maybe it's variable aperture lenses that give strange results so I figure
I'll try the F 35-70 3.5-4.5, now that reports 6.7??? That's just about
2/10s of a stop off, and it's the next normal click stop...
<Aside> Now lets say right here that according to the information on Boz's
page there is no way for the camera to know that it's a variable aperture
lens mounted on the camera, that information is carried by the digital data
pin and there's no pass through for that on the AF 1.7x converter, the
converter substitutes it's own digital data. So it's working from the
maximum and minimum aperture data on the original A specification.</aside>
But now I'm really curious. What about the A28 f2.8. Once again a
combination I'm unlikely to ever use. fCalc thinks it should be f5.05 the
camera reports it as f4.5. Once again under 2/10 of a stop variance and the
next closest normal click stop once again consistency.
All right what about a 1/3rd party lens? The only one I've presently got
that will fill the bill is the Vivitar S1 70-210 f2.8~4.0. The aperture at
70mm is the same as the A 28mm but it's a variable aperture lens. Result is
the same as the A 28mm, which is what I would have expected if it weren't
for the behavior of the F 70-210 with the 1.7x converter.
So I decide to try the FA 43mm limited. I expect the combination to show a
maximum aperture of f3.5, and yes I'm not disappointed, once again the
nearest standard click stop to the actual, (well starting from a base of
f2.0 since there's no pin combination in the A specification for a max
aperture of f1.9), value.
So lets recap. The only lens that gives a result at variance with what I
would expect is the F 70-210. All the maximum apertures are a bit off of
actual, but all the lenses and the F 1.7x report consistently to the
nearest standard click stop, all on the high side except the F 70-210mm
f4.0~5.6. Which reports to the low side and a bit more than 1/3 of a stop
off.
This is actually bugging me, I know it shouldn't but it is. The next
nearest value should be f 6.7 for the 70-210. All the other f4.0 maximum
aperture lenses and the F 1.7x adapter report a maximum aperture of 6.7.
All the other lenses report within 2/10 of a stop of their actual maximum
apertures. All the other lenses I tested reported values constant with the
f4.0 maximum aperture lenses, all quite predictable.
None of this seems to effect actual exposure either, just the reported
aperture. The only place this would be a problem would be with off camera
flash, and variable aperture lenses make hash of that anyway, so it
shouldn't bug me yet it does.
I'm wondering if anyone has an explanation, I certainly can't come up with
one that makes any sense. (Except that I'm obsessive compulsive and I
already knew I had those tendencies).
--
You get further with a kind word and a gun, than with a kind word alone.
--Al Capone.
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