When you use any lens on "A" setting, and set aperture with the body, there shouldnt be any variation with fstop related to metering sensitivity range as you chose smaller fstops, i.e. metering is done wide open regardless of selected f stop for the exposure. If you are getting exposure variation vs fstop with the lens on "A" then you are not getting accurate fstops with that lens when controlled by body or the corresponding shutter speed for the smaller stops is inaccurate or BOTH combined is giving you noticable variation. jco
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Godfrey DiGiorgi Sent: Wednesday, January 24, 2007 7:36 PM To: PDML List Subject: A test of meter/exposure calibration between *ist DS and K10D A test of meter/exposure calibration between *ist DS and K10D Text at http://homepage.mac.com/godders/mCAL/calibration-K10-DS.txt I've read on DPReview.com many people saying that metering with pre-A series lenses was off in the K10D. I only have one such lens and don't use it often, but I decided to give a try to see if I could find a big calibration difference by using one repeatable lighting setup and comparing results between the *ist DS and K10D bodies. This is far from an exhaustive test but was interesting ... I used an FA35/2 AL and a Zenitar 16/2.8 FE. The FA lens will act exactly like a pre-A series lens if I unlock the aperture ring from the A position and set it manually to a specific f/opening, so the metering should be the same as it would be for the Zenitar. There is a difference in the way pre-A and A-later series lenses iris mechanisms are calibrated, however, so I wanted to explore that a little bit too. I chose a simple target .. the white wall in my office .. and set up the tripod and remote release. For each body, I set the exposure to Manual mode, set the focus to Manual mode, and the ISO to 200. I did one body at a time, running through the whole sequence of exposures. The sequence went like this for each body: For a baseline check, I used a Sekonic L328 incident light meter to obtain a reference exposure. I started with the FA35 on "A" aperture ring setting and made the exposures at f/[EMAIL PROTECTED] sec and f/[EMAIL PROTECTED] sec. I then switched to f/4 and f/16 with the aperture ring and repeated the same sequence, to test the alternative way the iris mechanisms are regulated in the lens' two modes of operation. Next I allowed the camera body to meter the exposure with the lens set at A for f/4 and again for f/16. Next again with the same lens, f/4 and f/16 setting on the lens. And then finally I switched to the Zenitar and did the same two exposures at f/4 and f/16, allowing the body to do the metering. The capture was all in RAW mode and I didn't want RAW processing to influence exposure results. Files were downloaded to my computer and opened with Camera Raw 3.6. The same specific point in the image was set for each frame and the white balance adjusted with the eyedropper tool to ensure even color rendering. (The ACR defaults render K10D RAW exposures in this light with a lot more yellow than DS RAW exposures, but all adjust beautifully to a neutral tone.) I then captured the histogram readings with all other settings at the defaults. The results are the histograms shown in this chart: http://homepage.mac.com/godders/mCAL/calibration-K10-DS.jpg The left column is the DS, the right is the K10D. The first four rows show the FA35, first with aperture controlled by the body setting at f/4 and f/16, and then with the lens' aperture ring setting f/4 and f/16. These are the manually set exposures from the external incident light meter. As you can see, they are pretty regular and even. The remaining four rows show what the in-camera reflective meter nets at the same aperture settings ... first two using the body controlled aperture, the next two using the lens' aperture ring. Note that there is more variation here between f/4 and f/16, even with the body set aperture setting, because you're hitting the bottom of the meter's sensitivity range. Then, in the next two rows, you see that at f/16 the Manual-semi automatic stop down setting really does bottom out and the f/16 exposure is well underexposed. The last two rows show the Zenitar 16. Note that the same characteristic between f/4 and f/16 holds, the latter being well beyond the Manual-semiautomatic stopdown range, and that the shape of the spikes is a little different (due to the lens' much wider field of view). Looking at the full range of tests and comparing the DS vs K10D metering with both lenses, I'd have to say that the two bodies are pretty consistent in how they respond and they're all certainly within a reasonable range of correct, on target exposure relative to the reference incident exposures on top. The four f/16 exposures that are well underexposed are simply beyond the metering range, the other drop from the reference shows the difference between an incident light reading and a reflected light reading. Proper exposure with a reflected light meter on this target would require approximately a +0.7 to 1.0 EV exposure compensation setting. There is some variation, but I feel it's all well within reasonable calibration accuracy. Godfrey -- 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
