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09-02-2012, 01:54 PM   #1
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Experience with Pentax - trying to understand Olympus

Sorry about asking here about Olympus, but I'm coming from a Pentax experience, so someone might be able to understand my confusion.

I'm very use to using a Pentax-M series lens, both on a digital K110D and a 35mm film ME Super. To set aperture, I simply rotate the aperture ring, and the diaphram opens/closes etc. The light meter looks through this? On my K110D I press the AE-L button and it sets the shutter speed for me according to its light metering. On the ME Super - the light meter readings through the viewfinder, respond as I operate the aperture ring, adjusting the shutter speed - increasing speed as I open it up, slowing it down as I close the aperture. Simple.

I bought a bargain Olympus OM10 35mm film SLR today at a car boot sale. The system is different and confuses me. It has the kit Zuiko OM 50mm lens. If I adjust the aperture ring - nothing happens. The diaphram only adjusts if I press what I understand to be a DoF preview button on the bottom right of the lens. It seems as though the body only closes the diaphram to the ring setting - when it takes an exposure. But the light meter doesn't seem to understand this, so gives a false reading in the viewfinder. If I look through the viewfinder, the light meter indicates the same shutter speed regardless of what I do with the aperture ring.

A different philosophy to the contemporary Pentax-M series? Can someone please put me out of my misery and give a dummie explanation?

Thank you so much.

09-02-2012, 03:02 PM   #2
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Unless somethings is broken, when an M series (as well K and others) is mounted and locked in, the diaphragm of the M series lens does not open or close by moving the aperture ring. Like the OM you have, it only closes down when firing the shutter or activating the DOF preview.
09-02-2012, 10:39 PM   #3
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Apart from Pentax I have the OM1 and OM4Ti. And I don't know the OM10 very well. Here a link to it as something may ring a bell for another member: OM-10, OM-10 QD, OM-10 FC

Have you installed new batteries?

Last edited by Hilo; 09-02-2012 at 10:45 PM.
09-03-2012, 09:23 AM   #4
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I can see a possible source of confusion since you have a Pentax K110D as it uses the KAF2 mount which doesn't have coupling for aperture ring. With this arrangement, the manual Pentax lenses works as you say - turning the aperture ring will stop it down. However, unless there is something wrong with your ME Super, your M series lenses mounted on it will not stop down as you turn the aperture ring.

09-03-2012, 10:08 AM   #5
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On Pentax dslr in M Mode with Pentax-M lenses, the diaphragm only physically stops down:
1.For half a second or so when the exposure metering button is pressed.
2. Continuously while the DOF lever is pressed, and here the aperture can be adjusted and the view will dim down at small apertures.
3. When the shutter is released and the lens diaphragm will snap down to the setting on the ring and then will open wide again .

At other times the diaphragm is held wide open for composition by the camera using the lever on the right side looking down, and the view does not dim down as the aperture is adjusted
09-03-2012, 11:47 AM   #6
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Maybe you have an M lens with a cut aperture lever.
09-03-2012, 01:10 PM   #7
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As mentioned unless modified a Pentax-M lens diaphragm should not close with change in aperture setting,
except with DOF preview or shutter release. FWIW the Olympus OM lens also has an automatic diaphragm.

To clarify, which body's meter doesn't respond correctly with it, the Olympus OM10 or your Pentax DSLR?

Chris

Last edited by ChrisPlatt; 09-03-2012 at 02:28 PM.
09-03-2012, 01:34 PM   #8
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QuoteOriginally posted by Trojan_Llama Quote
I bought a bargain Olympus OM10 35mm film SLR today at a car boot sale. The system is different and confuses me. It has the kit Zuiko OM 50mm lens. If I adjust the aperture ring - nothing happens. The diaphram only adjusts if I press what I understand to be a DoF preview button on the bottom right of the lens. It seems as though the body only closes the diaphram to the ring setting - when it takes an exposure. But the light meter doesn't seem to understand this, so gives a false reading in the viewfinder. If I look through the viewfinder, the light meter indicates the same shutter speed regardless of what I do with the aperture ring.
This ought not to happen, as my understanding is the OM10 is open aperture reading aperture priority auto exposing. That is, the camera should be registering the aperture changes, but not stopping down until the moment of exposure. It should be working, in fact, just like your ME Super. I only have experience with the OM1/2/2s... but some things you need to check: 1) the batteries, as Hilo mentions. 2) on the lens, unmounted, test the operation of the aperture indicator lever. 3) ditto in the OM10 body, there will be a follower to go with the one on the mount.

Ultimately, even if the exposure indication does not work, if the camera figures the correct exposure at the time you press the shutter, it's not ideal but at least it works!

09-06-2012, 11:22 AM   #9
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I have a new to me OM-10. It handles much like a ME in that readings are taken at full aperture, the camera shows the selected speed on the left side of the VF. On my Olly the bayonet seems stiff; if your lens is not fully seated it may not talk to the meter or it might fall off the camera. Check that the 2 cells are good, if they are dead so is the camera, indeed the mirror may freeze in mid-cycle.* Mike Butkus has a manual for this Olly: Olympus OM10 instruction manual, user manual, PDF manual, free manuals

A couple items of interest: AFAIK the only way to use flash with the OM 10 (without the Manual Adapter) is with either of two dedicated flashes: the T20 and the T32. These are "auto" and are available second hand at reasonable prices, as is the Winder 2. The Manual Adapter fits on the left side of the camera and lets you set shutter speeds yourself. With this you could presumably use any flash, although since the shutter is electronic some of the older units with high trigger voltages might fry the innards!

Its nice that the Olly has depth of field preview, I don't know why the ME-Super doesn't. All in all the OM-10 is a nice piece.

BTW, from what I've seen in the manual the Olly reads light off the film or the shutter curtains for exposure; the indications in the VF are a separate system strictly for user convenience. *When I got mine it needed new cells and with the mirror in mid cycle I could see a dot pattern on the shutter curtain. Kewl! And just like the Pentax LX.
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