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05-19-2019, 07:46 PM   #1
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645Z, bulb mode, 55-100 MM 6x7 lens

Let me begin by saying that, prior to moving to the 645Z, I was a long time Canon 1Ds series user. On my 1Ds Mark III, I never had an issue using blub mode. Press the shutter. Hold it for the desired time, then release. Or, use a release. Been there. Done it. No issues.

So, today I went to a waterfall with the 645Z, a 6x7 55-100 MM lens. I took my exposure out to 30 seconds by using an aperture of 14, an ISO of 100. Then I decided I'd push past 30 seconds by increasing my aperture to 22. I set my mode to Bulb, pressed the shutter and started to count. I stopped at roughly 5 seconds. The whole image was over exposure. Next, I took out my cell phone, and as close to 5 seconds as I could, I pressed the shutter and watched the counter on the phone. 5 seconds later, same result. Long story short, I discovered that anything past roughly 1.5 seconds resulted in overexposure. Just to make sure, I changed my aperture from 22 back to 14. Switched to manual, took the same photo, no exposure problems.

I thought perhaps that there was an option I didn't know about that switched to Auto ISO. I put the camera back in Bulb, checked the ISO, it was still at 100.

Anyone having any idea what's going on?

05-20-2019, 12:32 AM   #2
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QuoteOriginally posted by nyghtfalcon Quote
I took my exposure out to 30 seconds by using an aperture of 14, an ISO of 100. Then I decided I'd push past 30 seconds by increasing my aperture to 22. I set my mode to Bulb, pressed the shutter and started to count. I stopped at roughly 5 seconds
Sorry , not understanding this. If 30 seconds is correct with f14. Then at f22 would require over 60 seconds exposure ?
05-20-2019, 12:43 AM   #3
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QuoteOriginally posted by nyghtfalcon Quote
Let me begin by saying that, prior to moving to the 645Z, I was a long time Canon 1Ds series user. On my 1Ds Mark III, I never had an issue using blub mode. Press the shutter. Hold it for the desired time, then release. Or, use a release. Been there. Done it. No issues.

So, today I went to a waterfall with the 645Z, a 6x7 55-100 MM lens. I took my exposure out to 30 seconds by using an aperture of 14, an ISO of 100. Then I decided I'd push past 30 seconds by increasing my aperture to 22. I set my mode to Bulb, pressed the shutter and started to count. I stopped at roughly 5 seconds. The whole image was over exposure. Next, I took out my cell phone, and as close to 5 seconds as I could, I pressed the shutter and watched the counter on the phone. 5 seconds later, same result. Long story short, I discovered that anything past roughly 1.5 seconds resulted in overexposure. Just to make sure, I changed my aperture from 22 back to 14. Switched to manual, took the same photo, no exposure problems.

I thought perhaps that there was an option I didn't know about that switched to Auto ISO. I put the camera back in Bulb, checked the ISO, it was still at 100.

Anyone having any idea what's going on?
My time with this camera and this lens is still slight, but you likely know that that lens stays in auto (max aperture when not exposing) unless the aperture control is set on manual. Auto means that via the 67-645 adapter the camera must control the aperture during the exposure. I think your question can be restated as: Can the 645Z using a lens that doesn't communicate with the camera other than via the iris control lever and the iris status lever operate correctly in bulb mode? I can try to repeat your experiment when I get a chance -- probably without a waterfall involved. It is possible that Pentax software didn't account for 67 lens use in bulb mode, or perhaps bulb mode requires the aperture be set manually. It's too late here for me to research the operating manual until tomorrow.

Also, related to another thread here, which adapter are you using?
05-20-2019, 04:59 AM   #4
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I've used a 6x7 pinhole body cap on my 645D using the Pentax 6x7 adapter in bulb without problems up to 2 minute exposures. I doubt there's much difference between the D and Z in this respect.

05-20-2019, 06:45 AM   #5
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I think the manuals' descriptions of what the limitations are in bulb mode are a little terse for me. On page R39 of the Menu Reference manual, with respect to the Custom setting menu C1, one can set how the shutter release button acts. {Type 1: Continuous exposure while the shutter release button is pressed; Type 2: Press the shutter release button to start exposure, and press it again to end exposure. Memo: The camera operates in the same manner when shooting with a remote control unit.} I probably should check that setting so I know what to expect.

The Operating manual's description of limitations on page 48 is compact, and not in danger of being too expository. The image below is from the adapter directions. The 67 55-100mm is an inner bayonet lens.
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05-20-2019, 04:38 PM   #6
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With the Pentax 6x7 adapter, leaving the lens switch on 'Auto' provides open aperture metering and automatic stopping down of the aperture during exposure for an inner bayonet lens (except the 75mm shift lens).

Having the lens switch on 'Man' will meter incorrectly as the camera doesn't know the lens is already stopped down leading to over exposure (the Pentax 6x7 body does know the lens is stopped down and uses a different meter circuit). With f22 set on the lens aperture ring, over exposure will exceed 4 stops with the 55-100 if the lens is set to Man when metering.
05-20-2019, 06:42 PM   #7
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QuoteOriginally posted by pschlute Quote
Sorry , not understanding this. If 30 seconds is correct with f14. Then at f22 would require over 60 seconds exposure ?
Yes, 60 seconds at F22 should have worked. It didn't - the image was over exposed at 5 seconds. So, something is very wrong

---------- Post added 05-20-19 at 06:44 PM ----------

QuoteOriginally posted by kaseki Quote
My time with this camera and this lens is still slight, but you likely know that that lens stays in auto (max aperture when not exposing) unless the aperture control is set on manual. Auto means that via the 67-645 adapter the camera must control the aperture during the exposure. I think your question can be restated as: Can the 645Z using a lens that doesn't communicate with the camera other than via the iris control lever and the iris status lever operate correctly in bulb mode? I can try to repeat your experiment when I get a chance -- probably without a waterfall involved. It is possible that Pentax software didn't account for 67 lens use in bulb mode, or perhaps bulb mode requires the aperture be set manually. It's too late here for me to research the operating manual until tomorrow.

Also, related to another thread here, which adapter are you using?
Yes, that reformulation of the question works. I am using the Pentax adapter.

---------- Post added 05-20-19 at 07:13 PM ----------

QuoteOriginally posted by johnha Quote
With the Pentax 6x7 adapter, leaving the lens switch on 'Auto' provides open aperture metering and automatic stopping down of the aperture during exposure for an inner bayonet lens (except the 75mm shift lens).

Having the lens switch on 'Man' will meter incorrectly as the camera doesn't know the lens is already stopped down leading to over exposure (the Pentax 6x7 body does know the lens is stopped down and uses a different meter circuit). With f22 set on the lens aperture ring, over exposure will exceed 4 stops with the 55-100 if the lens is set to Man when metering.
So, I just took the lens and camera out. The word "Auto" is showing on the barrel of the lens, so, I assume this means the lens is set correctly.
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