Green Button Stop-Down Metering Acting Differently

MSM · 08-10-2010, 06:42 PM

Originally posted by dlacouture

Problem is that it will work for wide open apertures only (as it won't stop the lens down anymore), so you would better use Av mode in this case anyway...

I guess there is no easy solution to this "mirror up" problem...

Perhaps I am mistaken with what you are saying. With the M42's in M mode and the lever switched to manual on the lens barrel, the aperture is 'stopped down' when you change the aperture setting on the aperture ring. The viewfinder gets darker. In my case, hitting the green button updates the shutter speed to any corresponding aperture change I make with the aperture ring. With the tape in place, I can adjust from 2.8 to 4 on the aperture ring, hit the green button and the shutter speed automatically doubles. This all occurs without any mirror flip if I use the tape. Otherwise, it sounds like I am taking a picture prior to taking the picture.

As mentioned, I don't have any M series lenses. I know in the case with these lenses, when you adjust the aperture ring, you can still view wide open. Then when hitting the green button, the camera stops the aperture down and meters and opens back up. The tape trick may not work in this case. But for the M42's that are bigger and as such cover the contacts, it seems to work.

I know that I can use the Av mode with the M42's but I had found the the metering seemed to be better and more consistent with my K10d if I used the M mode. I have not compared Av v. M mode with the Kx. Also, I enjoy using the M mode with my AF lens and I use it also with off camera flash. So it makes sense to me to learn one mode well.

dlacouture · 08-11-2010, 01:52 AM

I was indeed talking about M lenses, not m42!

With M lenses, if the camera does not close the aperture, then the metering will be off.
So, if you isolate a M lens, it will be accurate only wide open...

MSM · 08-11-2010, 12:12 PM

Originally posted by dlacouture

I was indeed talking about M lenses, not m42!

With M lenses, if the camera does not close the aperture, then the metering will be off.
So, if you isolate a M lens, it will be accurate only wide open...

I see what you mean. Thanks.

pimpim · 09-01-2010, 02:37 AM

I have a similar problem, but more awkward:

I just tried an old Porst Color Reflex pancake on my K-X.

Differently from using the green button with my other manual aperture lenses, for the Porst there is no movement of the shutter and/or mirror when I use the green optical preview button. It does adapt the shutter speed if I am at darker/lighter places, and the Av button shows me a metering value, but it appears to be only for full open.

When taking a picture, the aperture ring does seem to work, so I can extrapolate the desired shutter time / ISO for my other aperture values based on the full open value. Anyone has similar experiences?

Cideway · 09-01-2010, 02:52 AM

Originally posted by Marc Sabatella

Even in optical preview, the Kx does that. No one seems to know why. I'm guessing it is somehow connected to the fact that the K-m on which the K-x was based lacked optical preview at all, and the only way they could figure out to implement it without a redesign of the body was to couple it to the regular shutter firing sequence.

Likely what is happeneing is that the aperture mechanism is linked into the mirror operation, with that high speed video of the K10D shutter cycle, you can see that the aperture closes down and then the mirror flicks the mirror comes down and the aperture starts to open. With all the other pentax cameras except for the K7 and Km/x there is is a seperate mechanism for the aperture control, with the K7 the aperture control is motorised and my guess would be that with the Km/x it would be the same mechanism that flicks the mirror. The aperture closing charges the mirror and the mirror returning charges the aperture return, so to reset the process after stoppping down the mirror has to go to release the aperture back to wide open.

This is just a guess but i think it does explain the behaviour based on what i know and can infer about the mechanics of the cameras.

MoiVous · 09-01-2010, 03:46 AM

Originally posted by Cideway

Likely what is happeneing is that the aperture mechanism is linked into the mirror operation, with that high speed video of the K10D shutter cycle, you can see that the aperture closes down and then the mirror flicks the mirror comes down and the aperture starts to open. With all the other pentax cameras except for the K7 and Km/x there is is a seperate mechanism for the aperture control, with the K7 the aperture control is motorised and my guess would be that with the Km/x it would be the same mechanism that flicks the mirror. The aperture closing charges the mirror and the mirror returning charges the aperture return, so to reset the process after stoppping down the mirror has to go to release the aperture back to wide open.

This is just a guess but i think it does explain the behaviour based on what i know and can infer about the mechanics of the cameras.

Interesting idea Chris.

Although not discussed here (or anywhere else I can find), could that be an explanation of my K200D and FA50 f1.4 when I mount it on some Pentax Auto K extension tubes? Doesn't happen with any other lens in combination with the tubes, but it happens with FA50 f1.4......hmmmm

Cheers

pimpim · 10-22-2010, 10:59 PM

Ok, I have two Porst lenses now, the 40mm f/2.5 and the 50mm f/1.7 (good one, that one), and both do not work with the green button. Is it Pentax-lenses only? I thought it was not doing TTL, just actually doing a preview shot and adjusting the light, so maybe I'm wrong?

Brydzo · 03-29-2011, 09:56 PM

There's is a way to make M lens work in AV mode perfectly:

All you have to do is press the lens lock button and rotate your lens CCW about 10 degrees. Then you can use it in Av mode. Just be careful not to twist the lens focus adjustment so far as to make the lens drop off (mine is hanging on very firm and confident). I also heard you can drill extra lens lock but I didn't try that yet.

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08-10-2010, 06:42 PM	#16
MSM Veteran Member Join Date: Dec 2007 Location: Alabama Photos: Gallery Posts: 994	Originally posted by dlacouture Problem is that it will work for wide open apertures only (as it won't stop the lens down anymore), so you would better use Av mode in this case anyway... I guess there is no easy solution to this "mirror up" problem... Perhaps I am mistaken with what you are saying. With the M42's in M mode and the lever switched to manual on the lens barrel, the aperture is 'stopped down' when you change the aperture setting on the aperture ring. The viewfinder gets darker. In my case, hitting the green button updates the shutter speed to any corresponding aperture change I make with the aperture ring. With the tape in place, I can adjust from 2.8 to 4 on the aperture ring, hit the green button and the shutter speed automatically doubles. This all occurs without any mirror flip if I use the tape. Otherwise, it sounds like I am taking a picture prior to taking the picture. As mentioned, I don't have any M series lenses. I know in the case with these lenses, when you adjust the aperture ring, you can still view wide open. Then when hitting the green button, the camera stops the aperture down and meters and opens back up. The tape trick may not work in this case. But for the M42's that are bigger and as such cover the contacts, it seems to work. I know that I can use the Av mode with the M42's but I had found the the metering seemed to be better and more consistent with my K10d if I used the M mode. I have not compared Av v. M mode with the Kx. Also, I enjoy using the M mode with my AF lens and I use it also with off camera flash. So it makes sense to me to learn one mode well.

08-11-2010, 01:52 AM	#17
dlacouture Veteran Member Join Date: Jul 2008 Location: Var, South of France Photos: Albums Posts: 1,074	I was indeed talking about M lenses, not m42! With M lenses, if the camera does not close the aperture, then the metering will be off. So, if you isolate a M lens, it will be accurate only wide open...

08-11-2010, 12:12 PM	#18
MSM Veteran Member Join Date: Dec 2007 Location: Alabama Photos: Gallery Posts: 994	Originally posted by dlacouture I was indeed talking about M lenses, not m42! With M lenses, if the camera does not close the aperture, then the metering will be off. So, if you isolate a M lens, it will be accurate only wide open... I see what you mean. Thanks.

09-01-2010, 02:37 AM	#19
pimpim Senior Member Join Date: Sep 2010 Location: Mainz Photos: Albums Posts: 253	I have a similar problem, but more awkward: I just tried an old Porst Color Reflex pancake on my K-X. Differently from using the green button with my other manual aperture lenses, for the Porst there is no movement of the shutter and/or mirror when I use the green optical preview button. It does adapt the shutter speed if I am at darker/lighter places, and the Av button shows me a metering value, but it appears to be only for full open. When taking a picture, the aperture ring does seem to work, so I can extrapolate the desired shutter time / ISO for my other aperture values based on the full open value. Anyone has similar experiences?

09-01-2010, 02:52 AM	#20
Cideway Inactive Account Join Date: Feb 2007 Location: Adelaide, South Australia, Australia Photos: Gallery Posts: 364	Originally posted by Marc Sabatella Even in optical preview, the Kx does that. No one seems to know why. I'm guessing it is somehow connected to the fact that the K-m on which the K-x was based lacked optical preview at all, and the only way they could figure out to implement it without a redesign of the body was to couple it to the regular shutter firing sequence. Likely what is happeneing is that the aperture mechanism is linked into the mirror operation, with that high speed video of the K10D shutter cycle, you can see that the aperture closes down and then the mirror flicks the mirror comes down and the aperture starts to open. With all the other pentax cameras except for the K7 and Km/x there is is a seperate mechanism for the aperture control, with the K7 the aperture control is motorised and my guess would be that with the Km/x it would be the same mechanism that flicks the mirror. The aperture closing charges the mirror and the mirror returning charges the aperture return, so to reset the process after stoppping down the mirror has to go to release the aperture back to wide open. This is just a guess but i think it does explain the behaviour based on what i know and can infer about the mechanics of the cameras.

09-01-2010, 03:46 AM	#21
MoiVous Veteran Member Join Date: Sep 2008 Location: Adelaide, South Australia Photos: Gallery Posts: 677	Originally posted by Cideway Likely what is happeneing is that the aperture mechanism is linked into the mirror operation, with that high speed video of the K10D shutter cycle, you can see that the aperture closes down and then the mirror flicks the mirror comes down and the aperture starts to open. With all the other pentax cameras except for the K7 and Km/x there is is a seperate mechanism for the aperture control, with the K7 the aperture control is motorised and my guess would be that with the Km/x it would be the same mechanism that flicks the mirror. The aperture closing charges the mirror and the mirror returning charges the aperture return, so to reset the process after stoppping down the mirror has to go to release the aperture back to wide open. This is just a guess but i think it does explain the behaviour based on what i know and can infer about the mechanics of the cameras. Interesting idea Chris. Although not discussed here (or anywhere else I can find), could that be an explanation of my K200D and FA50 f1.4 when I mount it on some Pentax Auto K extension tubes? Doesn't happen with any other lens in combination with the tubes, but it happens with FA50 f1.4......hmmmm Cheers

10-22-2010, 10:59 PM	#22
pimpim Senior Member Join Date: Sep 2010 Location: Mainz Photos: Albums Posts: 253	Ok, I have two Porst lenses now, the 40mm f/2.5 and the 50mm f/1.7 (good one, that one), and both do not work with the green button. Is it Pentax-lenses only? I thought it was not doing TTL, just actually doing a preview shot and adjusting the light, so maybe I'm wrong?

03-29-2011, 09:56 PM	#23
Brydzo Forum Member Join Date: Jan 2011 Posts: 56	There's is a way to make M lens work in AV mode perfectly: All you have to do is press the lens lock button and rotate your lens CCW about 10 degrees. Then you can use it in Av mode. Just be careful not to twist the lens focus adjustment so far as to make the lens drop off (mine is hanging on very firm and confident). I also heard you can drill extra lens lock but I didn't try that yet.