A question about the OM spot meter with various screens.

[Keith]

Since getting my OM-3 and experimenting with spot metering (I like it!) I'm curious about the various screens Olympus offered.

The OM-3 came with a screen with the central split image focusing aid and a surrounding fresnel circle and the size of this relates directly to the spot area I gather. My favourite type of OM screen is a plain matt one that comes with only the fresnel circle and no split image and the circle is a little larger overall from what I can see ... I'm curious if this type of screen has any effect on the spot metering system of the camera? How does the camera's metering system actually read such a narrowly defined area and where does it take it's reading?

If John Hermanson reads this maybe he can give me an explanation?

 

[FrankS]

Keith, from what I've read, the meter needs to be adjusted (or exposure compensation made) when changing between the earlier screens and the later series brighter screens. Just based on what I remember reading.

 

[alistair.o]

Have you seen this link before Keith?

http://www.star.ucl.ac.uk/~rwesson/esif/om-sif/findergroup/focusingscreens.htm

 

[FrankS]

So based on the info in Alistair's link, some cameras give incorrect exposure readings using brighter screens, and other cameras including the OM3 do not.

 

[dtcls100]

Since getting my OM-3 and experimenting with spot metering (I like it!) I'm curious about the various screens Olympus offered.

The OM-3 came with a screen with the central split image focusing aid and a surrounding fresnel circle and the size of this relates directly to the spot area I gather. My favourite type of OM screen is a plain matt one that comes with only the fresnel circle and no split image and the circle is a little larger overall from what I can see ... I'm curious if this type of screen has any effect on the spot metering system of the camera? How does the camera's metering system actually read such a narrowly defined area and where does it take it's reading?

If John Hermanson reads this maybe he can give me an explanation?

The spot meter readings are not affected by the screen used, as the light measurement is not based on light passing through the focusing screen, but rather the light passing through the primary mirror and reflecting off of the secondary mirror to the metering cells in the mirror box. The spot metering area closely corresponds to the split image/microprism area. The circled area in the original 1-4 screen (which you appear to have) is somewhat larger than this metering area and this resulted in Olympus coming out with the 1-4n screen with a smaller circular area that better corresponded to the spot metering area. So if you are using a 1-4 screen, you have to take this fact into account; but the screen itself doesn't affect the spot metering's accuracy per se.

 

[dtcls100]

Keith, from what I've read, the meter needs to be adjusted (or exposure compensation made) when changing between the earlier screens and the later series brighter screens. Just based on what I remember reading.

This is only correct with regards to an OM-1, OM-1n, OM-2 and OM-2n cameras in manual mode. This is NOT TRUE for OM-4, OM-4T, OM-4Ti, OM-3, OM-3Ti, and OM-2S cameras, as these models do not measure the light passing through the focusing screen, but rather measure light using metering cells in the mirror box. Same is true for OM-2 and OM-2n in auto exposure mode, as the light is not measured from the focusing screen for ACTUAL exposure (although the meter needle indicator does measure light from the focusing screen in providing an estimated shutter speed to be used).

 

[dtcls100]

Since getting my OM-3 and experimenting with spot metering (I like it!) I'm curious about the various screens Olympus offered.

The OM-3 came with a screen with the central split image focusing aid and a surrounding fresnel circle and the size of this relates directly to the spot area I gather. My favourite type of OM screen is a plain matt one that comes with only the fresnel circle and no split image and the circle is a little larger overall from what I can see ... I'm curious if this type of screen has any effect on the spot metering system of the camera? How does the camera's metering system actually read such a narrowly defined area and where does it take it's reading?

If John Hermanson reads this maybe he can give me an explanation?

The spot meter readings are not affected by the screen used, as the light measurement is not based on light passing through the focusing screen, but rather the light passing through the primary mirror and reflecting off of the secondary mirror to the metering cells in the mirror box. The spot metering area closely corresponds to the split image/microprism area. The circled area in the original 1-4 screen (which you appear to have) is somewhat larger than this metering area and this resulted in Olympus coming out with the 1-4n screen with a smaller circular area that better corresponded to the spot metering area. So if you are using a 1-4 screen, you have to take this fact into account; but the screen itself doesn't affect the spot metering's accuracy per se.

 

[Keith]

Have you seen this link before Keith?

http://www.star.ucl.ac.uk/~rwesson/esif/om-sif/findergroup/focusingscreens.htm

I hadn't stumbled across that! Thanks Alistair.


So it appears any screen can be used on the OM-3.

I'm still curious about how the camera's metering actually defines the spot. EDIT (I see that has been answered ^^^)

Hmmm ... I'd love one of those plain matte 2-4 screens. Im not really into those split image rangefinders in the centre circle.

 

[Trius]

As stated, you are fine. A 2-series screen installed in an OM-1 or OM-2 requires the camera's meter circuitry to be adjusted. Mr. Zuiko (aka John Hermanson) can perform such a sex change, but it is not reversible! 😀

 

[Keith]

I've noticed that the 2 series screens seldom appear for sale on eBay and when they do they go for ridiculous money. How does the Beattie screen compare ... not that its particularly cheap either.

How the hell can a little piece of plastic be worth close to two hundred dollars ... the manufacturing process must be more complex than I suspected?

 

[Keith]

Economics 101: supply & demand. 😉

Well that doesn't make me feel any better! 😀

I would seriously love the extra stop of brightness in the OM-3 finder ... focusing SLR's is definitely getting harder these days and I intend fighting off auto focus for as long as possible! 😛

 

[Keith]

Rick (can't remember his user name) who posts here and is a long time OM user seems to think the Beattie screens are pretty much on par with the series 2 OM ones.

I've been checking out the Beattie screens and the one I'd like would end up costing me nearly $240.00 AUD with post ... they can't be serious!!! (channeling John McEnroe) 😛

 

[dtcls100]

Having both, I would say that the Olympus Series 2 screens are definitely better, as they snap into focus noticeably better although the Beattie screens are of approximately equal brightness.

 

[sevo]

I've been checking out the Beattie screens and the one I'd like would end up costing me nearly $240.00 AUD with post ... they can't be serious!!! (channeling John McEnroe) 😛

There seem to be many people for whom spending outrageous amounts on add-ons is a important part of pimping their gear. This is no exception.

The difference between the hypothetical ultimately diffusive sanded screen and the aerial image (with zero light loss) is little more than three stops (more accurately, pi stops exactly - diffusion is in a spheric relation to the ground glass).

Focusing on a aerial image is hard to do and error prone, nor does an aerial image allow for inspection of off-axis parts of the finder image, so any "fast screen" has to be a trade-off between brightness, focusing and visibility. In my experience, all practically useful screens tend to be within a stop or two in brightness, and the usually superior screens for cameras that were professional enough to have interchangeable ones tend to be even closer.

That is, Beattie screens will buy you a half to one stop at the very best. A difference probably only noticeable if you keep a body with the old screen about for constant comparison... ;-)

Old Rolleiflexes/Rolleicords are a notable exception - many of these had a truly horrible screen out of factory. But there, even a home-made screen will be almost as much of an improvement as a Beattie...

 

[ColinW]

How does the Beattie screen compare ... not that its particularly cheap either.

Keith,

I don't have a series 2 Olympus screen but have various series 1's. I also use two Beattie's; an (equivalent) 1.4n and an (equivalent) 10 with the grid lines, and compared the series 1's there is all the difference in the world.