auto focus not all its cracked up to be?

carpents · 06-19-2007, 06:54 AM

Originally posted by ChrisA

Use A-series lenses (set to A) or later, MF or AF, and no such errors arise.

It's been suggested in various quarters that with a focusing screen from a DS, the errors go away; if anyone has a K10D with such a screen, and either M/K series lenses, or A lenses that they can switch to non-A mode, it would be interesting to see the line included on Jonas B's graph.

Correct - it is the metering at smaller apertures that causes the discontinuity.

The red line on Jonas' graph is just what you are asking for. I too have swapped my focus screens and the K10 now behaves as the DS did, and vice-versa.

Jonas B · 06-19-2007, 07:43 AM

Originally posted by ChrisA

It's been suggested in various quarters that with a focusing screen from a DS, the errors go away; if anyone has a K10D with such a screen, and either M/K series lenses, or A lenses that they can switch to non-A mode, it would be interesting to see the line included on Jonas B's graph.

There is a line included in the graph for the Takumar 50/1.4, the k10D and the DS screen. As you can see it gets much better compared to the values from the same setup but with the original K10D screen.

Another interesting thing is that Sean [carpents] has showed a similar graph for several lenses. His curve is pretty much the same but the opposite... I think you can search for it. I haven't seen any explanation to this.

ChrisA · 06-19-2007, 10:36 AM

Originally posted by Jonas B

There is a line included in the graph for the Takumar 50/1.4, the k10D and the DS screen. As you can see it gets much better compared to the values from the same setup but with the original K10D screen.

Originally posted by carpents

The red line on Jonas' graph is just what you are asking for.

I do beg your pardon, I obviously didn't look closely enough. Thanks for pointing it out.

borno · 06-19-2007, 11:49 AM

Pardon my rant, but I am psyched- just got my LL60 screen and did a quick test with my old vivitar (tokina) tx 400mm f5.6 in the back yard at f8 spot meter on the bird---right on. Exposure still good with my 70-210 a also- and the grid lines are great too (I tend to tilt the camera if I'm not thinking too good). I'm a happy camper

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Entropy · 06-21-2007, 05:37 PM

Originally posted by Mike Cash

You mean the K10D won't set shutter speed in Av mode for M42 lenses, adjusting automatically as the aperture is closed down? Or does the K10D not have an Av mode?

I don't know about M42 lenses, but for K-mount M-series lenses, the K10 engages that little clutch that forces the lens wide open when mounted on a camera.

As a result, in Av mode, the camera meters as if the lens were wide open at all times, regardless of aperture ring setting. It also doesn't allow exposure compensation to be set in Av mode.

So with the K10D and K-mount manual aperture lenses, manual mode + the green button is the way to go. It would be nice if it were possible to set exposure compensation in this situation in order to avoid the need to adjust the shutter speed after every press of the green button.

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06-19-2007, 06:54 AM	#16
carpents Veteran Member Join Date: Sep 2006 Location: West Chester, PA Photos: Gallery \| Albums Posts: 1,420	Originally posted by ChrisA Use A-series lenses (set to A) or later, MF or AF, and no such errors arise. It's been suggested in various quarters that with a focusing screen from a DS, the errors go away; if anyone has a K10D with such a screen, and either M/K series lenses, or A lenses that they can switch to non-A mode, it would be interesting to see the line included on Jonas B's graph. Correct - it is the metering at smaller apertures that causes the discontinuity. The red line on Jonas' graph is just what you are asking for. I too have swapped my focus screens and the K10 now behaves as the DS did, and vice-versa.

06-19-2007, 07:43 AM	#17
Jonas B Inactive Account Join Date: Sep 2006 Location: Göteborg, Sweden Posts: 810	Originally posted by ChrisA It's been suggested in various quarters that with a focusing screen from a DS, the errors go away; if anyone has a K10D with such a screen, and either M/K series lenses, or A lenses that they can switch to non-A mode, it would be interesting to see the line included on Jonas B's graph. There is a line included in the graph for the Takumar 50/1.4, the k10D and the DS screen. As you can see it gets much better compared to the values from the same setup but with the original K10D screen. Another interesting thing is that Sean [carpents] has showed a similar graph for several lenses. His curve is pretty much the same but the opposite... I think you can search for it. I haven't seen any explanation to this.

06-19-2007, 10:36 AM	#18
ChrisA Veteran Member Join Date: Feb 2007 Location: London Posts: 393	Originally posted by Jonas B There is a line included in the graph for the Takumar 50/1.4, the k10D and the DS screen. As you can see it gets much better compared to the values from the same setup but with the original K10D screen. Originally posted by carpents The red line on Jonas' graph is just what you are asking for. I do beg your pardon, I obviously didn't look closely enough. Thanks for pointing it out.

06-21-2007, 05:37 PM	#20
Entropy Veteran Member Join Date: Jun 2007 Location: Owego, NY Posts: 976	Originally posted by Mike Cash You mean the K10D won't set shutter speed in Av mode for M42 lenses, adjusting automatically as the aperture is closed down? Or does the K10D not have an Av mode? I don't know about M42 lenses, but for K-mount M-series lenses, the K10 engages that little clutch that forces the lens wide open when mounted on a camera. As a result, in Av mode, the camera meters as if the lens were wide open at all times, regardless of aperture ring setting. It also doesn't allow exposure compensation to be set in Av mode. So with the K10D and K-mount manual aperture lenses, manual mode + the green button is the way to go. It would be nice if it were possible to set exposure compensation in this situation in order to avoid the need to adjust the shutter speed after every press of the green button.