[montman]

I have two ME Supers. I am metering them off the same object both with the M 50 1.7 lens. They meter 1/250 at 2.8
I meter my LX with the same lens and it meters 1/60 at 2.8
I meter my EOS 1V with the Sigma 50 and it meters 1/60 at 2.8

That's seems like a pretty big difference. The EOS was on spot metering so that could have effected it but the LX is a Center Meter camera should not it have read closer to the ME Supers? Any ideas?

[amoringello]

Are they all metering in the same method? Was the ME also on center-weighted or spot?
Or was it perhaps on Matrix?

I would try against a solid evenly lit wall to make sure the metering won't have much effect and that any slight position change wouldnt cause a change either... although slight movement shouldn't cause that much difference without bing an obvious cause. :-)

[SOldBear]

The LX has OTF (Off The Film) metering. It measures the light reflected from the film during exposure.

Without the film inside the camera, the LX measures the light reflected from the pressure plate, which has different reflectivity from that of film. This may account for the difference compared to the ME. When I still had my LX, its metering (without film) didn't match my Minolta light meter either (my LX had just been calibrated by Eric).

As you mentioned, the difference between the EOS 1V and the ME may be caused by metering method (spot vs center-weighted).

[montman]

The ME and LX can only meter center-weighted. But ya, even if I moved the point a little bit it would not change.

[montman]

The LX has OTF (Off The Film) metering. It measures the light reflected from the film during exposure.

Without the film inside the camera, the LX measures the light reflected from the pressure plate. This may account for the difference compared to the ME. When I still had my LX, its metering (without film) didn't match my light meter either (my LX had just been calibrated by Eric).

As you mentioned, the difference between the EOS 1V and the ME may be caused by metering method (spot vs center-weighted).

That might just be it, I will have to try it with a roll in the camera.Thank you!!!

[foto guy]

This may be too obvious, but just in case...
Is the ISO (ASA) set to the same value on all cameras?

[Nesster]

Without the film inside the camera, the LX measures the light reflected from the pressure plate, which has different reflectivity from that of film.

surely you mean it meters the shutter for the in-viewfinder indication. The pressure plate in the OP would start off at 1/60 and adjust from there...


the two stop difference between two sets of two cameras is kind of strange. Like Foto Guy says, check the ISO

[montman]

ISO is the same on all four cameras.

[stevebrot]

Meter against an evenly lit blank wall. If the LX is in the mix for the comparison, use the pre-exposure reading as the basis for the comparison. As a sanity check, meter the same blank wall with a hand-held meter or even better, take an incident reading from the target area with the meter pointed at the camera.

The total spread should be no more than about a stop from longest to shortest time within your group. If you have an outlier, a good camera repair shop can check your meter against their calibrated light source and tell you in short order whether it is accurate. They may also do a shutter check at the same time. (Usually for free...good for business, you know...)


Steve

[PPPPPP42]

So something that just occurred to me, how does an LX meter off the film before the shutter is opened to expose it?

[stevebrot]

So something that just occurred to me, how does an LX meter off the film before the shutter is opened to expose it?

It doesn't. The system is complex and is a coordination of conventional and off-the-film systems. Based from what can be gleaned from the owner's manual the picture looks something like this:

• There are two metering systems, conventional TTL and OTF
• What is displayed in the viewfinder is from the conventional meter
• Av mode uses OTF at exposure time, though not always purely OTF. High speed measures are taken off the front of the shutter curtain, not the film.
• M mode uses conventional TTL

This distinction allow for an additional clarification regarding LX meter sensitivity. According to the manual, the conventional TTL meter used in M mode has a fairly standard range of EV 1(100) - EV 19(100). Due to the nature of the OTF system, the published and often quoted range in Av mode is calculated at EV -6.5(100) - EV 20(100) when used with the 50/1.2 lens. The lower end of the range is somewhat less with a slower lens. Likewise, the upper end of the range might be somewhat higher with a lens capable of narrower apertures.

Probably more than what you wanted to know


Steve

[Not a Number]

There is a second mirror behind the main mirror (half-mirror area) that is used for TTL metering (pre-exposure). This flips up with the main mirror out of the light path. Final exposure as noted above is from OTF measurement.

The Olympus OM-2 used measurements off the shutter blind in auto mode.

Pentax LX - How does its metering works
Pentax LX - How does its metering works

[stevebrot]

The Olympus OM-2 used measurements off the shutter blind in auto mode.

Thanks for the links. They are helpful, though both the linked article and the owner's manual state that the LX meters off the shutter curtain at higher shutter speeds (> 1/75s). This makes sense when you consider that at greater than the X-sync speed, the full frame is never fully exposed. The shutter opening is a traveling slit and the "speed" is determined by the width of that slit. Settings for fast speeds must be determined in advance of actual shutter actuation.


Steve

[PPPPPP42]

Hmm, that actually kills the only advantage useful to me that the LX had over my Super Program.
That saves me a ton in CBA.