Odd metering with Ricoh XR-1s
I have two SLR bodies, Ricoh XR-1s and Carena CX-300, and I've noticed Ricoh's strange behavior. While Carena measures more or less OK and simply loses the plot in low light (1EV error at most under normal conditions, completely unreliable below EV5 @ 50 asa, something to be expected), Ricoh does something odd: with Pentax-M 50/1.7 it constantly underexposes by 1 EV, and with other lenses it's accurate. This behavior is repeatable - every time my 50/1.7 goes on, the meter would underexpose an image by~1EV.
I've tested it as well, as possible: flat surfaces, evenly lit. I've compared it with an exposure meter that always worked well - not that it does matter... I've changed ISO and lighting conditions, the lenses was changed many times per body during these tests. Same lens works OK with the other body.
Any thoughts? Or is it me being wrong somehow?
That is odd, I dont have a 1s but I have 2 XR2 bodies, one with a Pentax 50/1.4 and the other with a Vivitar 50/1.7 and they always agree. With a fully manual camera like yours I cain't think of anything to cause it, but We have some really serious lens people on here that can probably figure it out
The lens needs to tell the body both the maximum aperture and the current aperture
Try with the lens set at /1.7 is there still an error?
Try setting the ISO offset for correct exposure indication while you investigate.
oops the lens only needs to indicate how much it is stopped down from its maximum.
I've decided to go with the two instruments offering 1/3 fstop measurement accuracy: the suspected body and my light meter - the meter is not important, it's just a mean of helping myself or memorize stuff and relate to and it just happens to work correctly. What is odd, is lens X giving different reading, than lens Y by as much as 1 fstop. I use evenly back lit surfaces, like lamp shade or LCD screen, so focal length is not a factor to consider.
Lenses: Pentax-M 50/1.7 and Auto Revuenon zoom 80-200 1:4.5 were somewhere around -2/3 fstop off wide open (meaning an underexposure), Miranda 28/2.8 and Pentax F was within 1/3 fstop from what the light meter said.
Rotating iso dial works as expected from 14 din up, changing aperture also - all changes are accurately shown by the meter. Iso dial set at 13 works as if I'd set it to 12 though.
One more thought crossed my mind. I've changed the batteries quite recently... But maybe it's the batteries, that make the problem here? Other button cells I have are half-depleted, these two are the best freshiest newest couple, two months old or so. But, assuming that all the couplers/mechanics and sensors are OK, and the internal meter is calibrated properly, maybe 1.7 is simply bright enough to make the batteries act as if they were depleted, and the cheap Revuenon is imprecise to a similar degree, even if it feels heavy and solidly built?
It's not the camera being off by a minor degree that gives me the headache, but not knowing the reason.
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The camera requires silver oxide cells not alkaline and there is a battery check mechanism...
Yups there is a battery check, and it would be my first camera actually requiring silver oxide and refusing alkaline, but I know that's possible, batteries are the first factor I'll try to rule out in a couple of days, most shops supply only alkaline, maybe watchmakers will have silver ones.
So, after visiting a shop nearby... Xmas, this is not a battery issue.
Back to square one, I'm gazing at aperture tabs in my lenses, there's something odd with how they're placed. I assume wide open position of a "leading edge" of a tab should be consistent, but it's not. Lenses giving consistent results have this tab set perfectly in the right spot. Pentax M has the tab set 0,6mm more "away", Revuenon - 2mm, hitting the spot closed to first full aperture (so from 4.5 to 5.6). The movement of the tabs seems to be far greater than possible error resulting from 0.6 offset, it would result in ~0.25 fstop error only.
Edit: this still ay be an issue with how the rest of the bayonet was machined...
Last edited by q_x; 12-19-2013 at 10:26 AM. Click to view previous post history.
Use the Force, Luke!
Ok I checked several Pentax k lenses to hand
wide open each index ring had an identical offset with my venier calliper within less than 0.1mm or so to nearest lug tip
but a 3rd party 2.8 zoom was way off
I'll try more lenses and meter each with my K1000 and silver cells - soon gotta eat.
Note the K1000 does not need silver cells...
Sorry bad measurements when I do it proper I.e. from correct edge of aperture index follower they are all identical within 0.2 of mm - under 1/3 of stop
I'll try the meter this evening as well.
Can you check you are measuring from correct datum