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09-10-2008, 08:44 AM   #1
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Zenitar 16mm f2.8 - exposure problem

i use a K10d + Zenitar 16mm f2.8 (fisheye): it is a M42 lens and so i must use an adapter ring (i have an original pentax ring).


i use "M" modality, i choose the diaphragm (for example f4), i push the "green button" and so i know the shutter speed (for example 1/125).

but i find problems for exposure: because i change aperture (before f4 and then f8 or another aperture) but the shutter speed is always the same!

where is my error?

09-10-2008, 08:48 AM   #2
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QuoteOriginally posted by platinum Quote
i use a K10d + Zenitar 16mm f2.8 (fisheye): it is a M42 lens and so i must use an adapter ring (i have an original pentax ring).


i use "M" modality, i choose the diaphragm (for example f4), i push the "green button" and so i know the shutter speed (for example 1/125).

but i find problems for exposure: because i change aperture (before f4 and then f8 or another aperture) but the shutter speed is always the same!

where is my error?
you are in M mode, nothing changes automaticaly

you have to keep pressing the green button every time you:

a) change aperture

b) change scene (or the scene changes)


however, this is pointless if you are using an M42 lens! simply put the camera in AV mode, it will meter on its own without a need to press anything.
09-10-2008, 08:54 AM   #3
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Unless your using a K20D, and possibly the K200D the cameras have problems metering screwmount lenses, Unless you short out the bodies electrical contacts with some tinfoil.
Then they seem to expose perfectly 95% of the time.
09-10-2008, 09:02 AM   #4
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QuoteOriginally posted by Gooshin Quote
you are in M mode, nothing changes automaticaly

you have to keep pressing the green button every time you:

a) change aperture
yes! i push the green button every time when i change aperture, but i think that the shutter speed is always for 2.8.

never change!

09-10-2008, 09:06 AM   #5
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QuoteOriginally posted by little laker Quote
Unless your using a K20D, and possibly the K200D the cameras have problems metering screwmount lenses, Unless you short out the bodies electrical contacts with some tinfoil.
Then they seem to expose perfectly 95% of the time.
can you tell me more info in easy english?

step by step, please :-)
09-10-2008, 09:12 AM   #6
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QuoteOriginally posted by platinum Quote
i use a K10d + Zenitar 16mm f2.8 (fisheye): it is a M42 lens and so i must use an adapter ring (i have an original pentax ring).


i use "M" modality, i choose the diaphragm (for example f4), i push the "green button" and so i know the shutter speed (for example 1/125).

but i find problems for exposure: because i change aperture (before f4 and then f8 or another aperture) but the shutter speed is always the same!

where is my error?
Hmmmm. . . for M42 lenses with a manual aperture mode (e.g. the auto/manual switch near the base of a Super or SMC Takumar) you can just put the camera into Av mode (as suggested above).

However, some M42 lenses are auto-aperture only. You set the aperture using a ring, but the aperture stops down only when the pin at the base of the lens is depressed.

I think the Zenitar M is auto-aperture only. There's no mechanism in a K mount body to depress the pin, so all exposures will be taken with the lens wide open. (You really don't want to do that.) In this case you will need to modify the lens to disable the auto-aperture mechanism.


The "manual mode + green button" technique is useful for K-mount lenses without an "A" aperture setting (such as the Zenitar K); it's not usually what you want for an m42 mount lens.
09-10-2008, 09:25 AM   #7
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QuoteOriginally posted by troyz Quote

I think the Zenitar M is auto-aperture only. There's no mechanism in a K mount body to depress the pin, so all exposures will be taken with the lens wide open. (You really don't want to do that.) In this case you will need to modify the lens to disable the auto-aperture mechanism.
Unfortunately, I think Troy is correct. I have never seen the M-42 Zenitar, but it would not surprise me if it lacked the manual/auto switch. My understanding is that M-42 adapters are available that have some sort of tab to depress the aperture actuator pin.

Steve
09-10-2008, 09:35 AM   #8
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QuoteOriginally posted by troyz Quote

However, some M42 lenses are auto-aperture only. You set the aperture using a ring, but the aperture stops down only when the pin at the base of the lens is depressed.

I think the Zenitar M is auto-aperture only. There's no mechanism in a K mount body to depress the pin, so all exposures will be taken with the lens wide open. (You really don't want to do that.) In this case you will need to modify the lens to disable the auto-aperture mechanism.

yes, my Zenitar M42 has the pin at the base of the lens! and if i press (with my finger) the pin, the aperture changes!

I didn't know that "There's no mechanism in a K mount body to depress the pin".
now i understand why the shutter speed is always for 2.8.

how i can modify the lens?
but if modify it, than i can open\close diaphragm using this lens on K10D?

09-10-2008, 09:48 AM   #9
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dude

dont

use

M

mode

put the camera in AV and be done with it.
09-10-2008, 10:23 AM   #10
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platinum,
With the lens off the camera, does the appeture change when you rotate the appeture ring? Does it have a manual/auto switch in the lens barrel? If the appeture doesn't change and it doesn't have a manual/auto switch, you will need to lock the auto diapham pin in the depressed position. The easiest way to do this is to apply a very small drop of epoxy in the hole at the base of the pin, with the pin depressed. tape the pin down until the epoxy sets. Now the appeture will work correctly and you can us AV mode or manual mode. AV will automaticly adjust the shutter speed for you and will allow exposure compensation too. I have to do this with some of my M42 and converted lenses. Good luck.

Dave

QuoteOriginally posted by platinum Quote
i use a K10d + Zenitar 16mm f2.8 (fisheye): it is a M42 lens and so i must use an adapter ring (i have an original pentax ring).


i use "M" modality, i choose the diaphragm (for example f4), i push the "green button" and so i know the shutter speed (for example 1/125).

but i find problems for exposure: because i change aperture (before f4 and then f8 or another aperture) but the shutter speed is always the same!

where is my error?
09-10-2008, 10:31 AM   #11
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QuoteOriginally posted by Big Dave Quote
platinum,
With the lens off the camera, does the appeture change when you rotate the appeture ring?
no. i must press the pin (with my finger)

QuoteOriginally posted by Big Dave Quote
Does it have a manual/auto switch in the lens barrel?
no. only the manual focus ring and diaphragm ring.

QuoteOriginally posted by Big Dave Quote
If the appeture doesn't change and it doesn't have a manual/auto switch, you will need to lock the auto diapham pin in the depressed position. The easiest way to do this is to apply a very small drop of epoxy in the hole at the base of the pin, with the pin depressed. tape the pin down until the epoxy sets. Now the appeture will work correctly and you can us AV mode or manual mode. AV will automaticly adjust the shutter speed for you. I have to do this with some of my M42 and converted lenses. Good luck.

Dave
this is a good idea, but if then i want to remove epoxy?
it is possibile about your experience?
09-10-2008, 10:34 AM   #12
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QuoteOriginally posted by Gooshin Quote
dude

dont

use

M

mode

put the camera in AV and be done with it.
That wont make any difference with this problem. Besides, you cant manually control everything in AV mode.
09-10-2008, 10:36 AM   #13
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QuoteOriginally posted by Gooshin Quote
dude

dont

use

M

mode

put the camera in AV and be done with it.
Gooshin,
The lens is stuck wide open...NO MANUAL SWITCH

Steve
09-10-2008, 10:42 AM   #14
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QuoteOriginally posted by stevebrot Quote
Gooshin,
The lens is stuck wide open...NO MANUAL SWITCH

Steve
understood.. altho, thats rather weird
09-10-2008, 10:55 AM   #15
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QuoteOriginally posted by stevebrot Quote
Gooshin,
The lens is stuck wide open...NO MANUAL SWITCH

Steve

Gooshin is right. As Platinium said when he presses the pin the diaphragm will operate correctly. Since he is using a genuine Pentax screw-K adapter, that pin is kept pushed permanently. Now the OP must focus wide open then stop down before pushing the green button to meter. Besides, he has to change in Custom Settings " Green Button in TAV/M modes" to TV shift. If he uses AV mode, he's to focus wide open then stop down to whatever he wishes, then the metering is automatically done, no need to green it.

Rui
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