Question on Off the Film Metering

[raytoei@gmail.com]

Hi,

I received my Olympus OM2SP today.

Without putting in a roll of film I noticed that shutter speed (by sound) is different between Program/Auto and Manual. Program and Auto seem to be a stop slower. The Viewfinder shutter speed indicator showed 1/30 but sounded like 1/15. Testing this in Manual mode in 1/30 sounded like 1/30. I was paranoid after a while and tested this against my OM1n, and manual mode in the SP sounds okay as indicated by the shutter indication in the VF.


I have put in a roll of film and speed sounds normal again. I have not developed the film yet.

Question: could off the film metering (or lack of film) be the cause of the different shutter speed in Program / Auto priority ?

thanks much.

raytoei

 

[sevo]

Without film, you are metering off the black surface of the pressure plate, so yes, you'd end up with longer exposure times.

 

[unixrevolution]

Without film, you are metering off the black surface of the pressure plate, so yes, you'd end up with longer exposure times.

I was going to say...film has a different reflectivity than the pressure plate. As an LX owner I know that the auto speeds are not accurate without film loaded.

 

[Fraser]

It can also change between when you meter and the actual exposure in program etc (I think). Olympus cameras when new were supplied with a piece of card that sat where the film goes to test exposures.

 

[raytoei@gmail.com]

thanks much! learn something new everyday.

 

[p.giannakis]

I don't know if the 2S model is different than the 2N but the OTF metering does not work like that for speeds higher than 1/30. It measures the light reflecting from the first curtain, not the film so it should sound pretty accurate.
In low light (below 1/30) shoot a picture without a film in it and then put silver foil and take another pic. It should sound very different. The changes of having problems with the OTF sensors are quite slim though.

 

[oftheherd]

Wasn't there a camera that had a pattern on the shutter that was supposed to have the same reflectance as film, for otf metering? I seem to remember it was one of the more popular brands. It might have been Olympus, but I think it was another, mayBE Contax?

Anybody recall/

 

[Dwig]

Wasn't there a camera that had a pattern on the shutter that was supposed to have the same reflectance as film, for otf metering? I seem to remember it was one of the more popular brands. It might have been Olympus, but I think it was another, mayBE Contax?

Anybody recall/

The OM-2 series had a white spot on the first shutter curtain. This provided a metering target for a reasonable portion of the metering when in automatic varying from a modest proportion (at very long exposures) to 100% at the higher shutter speeds. A completely separate meter "lives" in the VF and is used for manual exposure and exposure prediction when in automatic.

This type of metering was patented by Minolta (or one of their combined companies) and licensed by Olympus. Minotla didn't use it themselves. I seem to remember that there were other licensees, but I don't remember which.

 

[Photog9000]

I had two OM-2S bodies that I used for about a decade (back in the 1980s and 90s) before upgrading to OM-4T's. Seems like I remember the first shutter curtain had a number of black spots on it for the OTF metering circuits as oftheherd suggested. Great little cameras but I loved my OM-4T even more with its spot metering system!!

 

[sevo]

This type of metering was patented by Minolta (or one of their combined companies) and licensed by Olympus.

IIRC it went quite a long way - the earliest patents for metering off film, during exposure and off a (then white) curtain appear to have originated at Pentacon and various parts of it were widely licensed. Minolta developed a more advanced system (reportedly from work passed on to them by Leitz when these abandoned the CL), which they used in the CLE and sub-licensed to Olympus (OM2) and Pentax (LX).

The concept was neat, but not perfect, needing correction factors for film types. The mass of patents must have hampered it (I remember that the LX booklet listed licenses from pretty much every competitor). And it did not mix that well with other innovations - by the next generation of cameras after 1980, everyone used at least one of matrix metering, program AE (apertures do not respond fast enough for live exposure correction) and digital exposure processors (then not real-time ready other than the analogue computers these live TTL systems used), all of which were incompatible. Only the flash TTL subsystem of it remained popular and became standard across all brands for the last twenty years of film SLRs.

 

[David Hughes]

Hi,

The OM10 had a random pattern on the shutter blind and I think it is pretty accurate. From memory there's a little logo of the pattern on the front of the camera.

Regards, David

 

[oftheherd]

Hi,

The OM10 had a random pattern on the shutter blind and I think it is pretty accurate. From memory there's a little logo of the pattern on the front of the camera.

Regards, David

You have me curious. I will have to check. I have a thrift store OM10 that I'm having trouble trying to bond with.

 

[p.giannakis]

Yes, the OM-10 offers the same OTF metering.

 

[David Hughes]

Hi,

They - OM10's - are also a source of prisms for the OM-1's and OM-2's but they are hard to beat as a superior P&S, my one gets a lot of use.

Regards, David

 

[oftheherd]

Yes, the OM-10 offers the same OTF metering.

Including the pattern on the 1st shutter, and the little logo on the front of the camera. David Hughes was right. Thank you sir.