Vic, The A mode on the lens makes an electrical contact for the body. When A mode is set, the lens will stop down to f22 - unless the camera tells it to stop at f4 or f8 or f16 or f2. If your camera is stopping down a bit early, check the mechanical parts as they could be a bit bent. Otherwise, run the aperture control lever (resistor) on the camera body back and forth a number of times to improve the contact. Regards, Bob S.
On 6/16/07, Vic Mortelmans <[EMAIL PROTECTED]> wrote: > OK, so I fixed the major problem, but it seems that I still have the > other problem that I detected when examining the first. In A-mode, the > lens diaphragma is a bit smaller (about one stop, I guess) then what the > camera says. > > No big deal, but I'd like to understand what's going on. This looks more > like a mechanical problem that won't be solved by CLA? Any ideas? > > How does the A-mode work? I imagine it's like this: > > - inside the camera body, I see a litter lever that engages the > diaphragma control lever on the lens. > > - when in M-mode, the lever in the camera body just moves all the way up > (releases the diaphragma to close, but the lens mechanics will stop it > at the f-stop selected on the lens); after exposure, the lever in the > camera body moves down again, and pulls the lens diaphgragma open > > - when in A-mode, the lens allows the diapragma to be operated > completely by the lever, so it's the camera that controls how far the > lever is moved upwards, and thus how much the diaphragma is allowed to > close. > > Reasoning like this, I'd rather expect the cause of the problem to lie > within the camera... Can anyone second that? > > Groeten, > Vic > > Vic Mortelmans schreef: > > Hi, > > > > this was easy!! > > > > I went to a shop that does camera maintenance, and they estimated 75 > > euro for the job --- more than the lens is worth. So I was lucky: a good > > reason to take a look at the inside of the lens without the risk of > > destroying value. > > > > There was nothing wrong with the blades (as I expected, because oil on > > the blades should be visible, shouldn't it?), but there was oil in the > > mechanism. See the picture here: > > > > http://picasaweb.google.be/vicmortelmans/Tech/photo#5076727091233563442 > > > > It shows the back of the lens with the mount removed (only five screws > > and one loose ring, no tiny bits jumping allover the room). The red line > > indicates the two sliding parts that had oil inbetween them. Applied > > some aceton and now the diaphragma closes as snappy as it can get. > > > > Groeten, > > > > Vic > > > > > > Vic Mortelmans schreef: > >> Hi Mat, > >> > >> You're right. The blades are not 'snapping' together when releasing > >> the switch. I compared to my SMC M 28 f:2.8, which behaves a lot more > >> 'snappy'. > >> > >> I never sent a lens out for CLA... what would be a reasonable price > >> for this job? Any chance of trying this myself? > >> > >> Groeten, > >> > >> Vic > >> > >> > >> Mat Maessen schreef: > >>> On 6/15/07, Vic Mortelmans <[EMAIL PROTECTED]> wrote: > >>>> The shots on part 2 are all overexposed... > >>>> > >>>> I don't use program mode that often (mostly aperture priority), so > >>>> could > >>>> it be that this mode is malfunctioning? The diaphragma control by the > >>>> camera is certainly doing something; I did a quick test in shutter > >>>> priority mode and saw the diaphragma change when selecting different > >>>> shutter speeds. > >>> > >>> Most probably, your A50/2 need a CLA. The diaphragm blades are most > >>> likely not closing down quickly enough. You can test this manually, > >>> by looking through the back of the lens, and toggling the aperture > >>> lever manually with your finger. The aperture blades should snap > >>> closed when you release the lever, and you shouldn't feel any > >>> stiffness or resistance in the lever motion (set the lens to f22 or A > >>> for this test). > >>> > >>> -Mat > >>> > >> > > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net > -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
