Originally posted by Astro-Baby but ONLY when that lens is on the Chinon body
Yep...That body does not like those lenses.
Originally posted by Astro-Baby if I put the camera on brief and keep it there with a cable release I can look inside and although once a lens is mounted I can't physically see the tab I can see the ring that the tabs mounted on moving as the aperture shifts and the meter in the Chinon is completely consistent - i.e. it will suggest f5.6 at 500th but if I drop the speed down a notch to 250th the meter will centre up on f8 of thereabouts - so its consistent but madly wrong.
You may be able to see the body-side tab from inside the mirror box, but what you don't see is how well it is engaged. With no lens on the bodies, compare the appearance of the Chinon's tab with that on either of your Pentax bodies. Now compare the lens-side tab on the zooms to that on the M 50/1.7. Is the body-side tab on the Chinon crooked, scratched, or bent? How about the tabs on the lenses. You may need a magnifying glass.
Now, put all three lenses at maximum aperture with none mounted to the Chinon body. Starting with the M 50/1.7, mount the lenses to the Chinon body, taking care to leave the aperture ring at the maximum aperture position and put the zooms at the their
minimum zoom setting with all three lenses focused to infinity. Record the suggested shutter speed and whether the aperture number in the viewfinder agrees with the lens setting. At that position, the body-side follower should be at the same position (close to maximum deflection) for all three lenses regardless of which are mounted and should result in the very similar metered EV* for all three lenses. For convenience, you might want to put the shutter dial in the Auto position. Meter against an evenly-lit blank wall or something similar. Don't be concerned about compliance to expected Sunny-16 values.
Repeat for the two zooms at their maximum focal length. I would expect the Chinon zoom to require 2/3 stop slower shutter speed assuming it is a 28-50/3.5-4.5. This last was sort of a "dumb-Steve" moment as I realized that both were probably variable aperture zooms and as such should be evaluated at their shortest focal length. This may well be the smoking gun.
If the tab on the body is other than properly aligned, the tab in the lens may slip fully or partially past it.
Steve
* EV is simply a numeric representation of the exposure provided for particular combination of shutter time and lens aperture. The Wikipedia entry on Exposure Value has an equivalence table (
LINK). Also helpful is Ken Storch's table of equivalent exposure stops (shutter, aperture, and ISO), (
LINK)