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11-03-2010, 06:36 PM   #1
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Sigma 105mm Macro questions

Couple of questions regarding this lens.

1. It's got a manual / automatic focus ring to switch between modes. I've noticed that even if it's in manual mode, if the camera is still in auto focus, the camera still focuses the lens. I assume it's more just for disabling the motor so you won't burn it out trying to reef on it?

2. I'm sure this is more camera related, not lens, but if I'm using the lens NOT in A mode (for the aperture), how do I get the camera to meter? (AV mode) On my *istD, I was sure I would use the green button, but doesn't seem to do this on my K7. Or does it only do it in manual mode, and I'm mistaken how it worked on my *istD?

11-03-2010, 06:48 PM   #2
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QuoteOriginally posted by eccs19 Quote
1. It's got a manual / automatic focus ring to switch between modes. I've noticed that even if it's in manual mode, if the camera is still in auto focus, the camera still focuses the lens. I assume it's more just for disabling the motor so you won't burn it out trying to reef on it?
Don't have the particular lens, these is only my guess:

The manual/automatic focus ring doesn't really turn the lens into "manual" focus mode. Rather, when at "auto" setting, it disengages the focus ring from the focusing mechanism inside the lens so when the body focuses the lens, the ring does not rotate. At "manual" setting, the ring rotates when the body focuses the lens.

Of course if you really want to focus manually, you have to (1) set to MF on the body and (2) switch the lens to "manual" so you can focus the lens using the focus ring.

I don't think there is a motor inside the lens.

QuoteOriginally posted by eccs19 Quote
2. I'm sure this is more camera related, not lens, but if I'm using the lens NOT in A mode (for the aperture), how do I get the camera to meter? (AV mode) On my *istD, I was sure I would use the green button, but doesn't seem to do this on my K7. Or does it only do it in manual mode, and I'm mistaken how it worked on my *istD?
In Av mode and with the lens not at A aperture setting, the K7 takes the photo at full aperture. If you want to meter using the green button, you have to switch the K7 body to M. This is the same with K10D, K20D (and probably all current Pentax bodies).
11-04-2010, 05:34 AM   #3
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Thanks for the info. Sounds like you confirmed what I was thinking.
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