I know about the "little" white spot on the shutter curtain from which the light is metered. I have two questions:

1. Why not put another spot on the second curtain like the CLE, such that one could meter w/o the shutter being cocked. No big complaint, but why not?

2. What is the angle of view of the lensed sensor? If it reads more than the spot, Leica, in the future may be able to alter the curtain markings - and calibration, of course - for averaging (again like CLE), center weighting, etc. Adding more reflecting to the curtain may increase low light sensitivity after calibration(?).

Another topic: Does the M7 measure exposure off the film in AE mode a la CLE? I too want to try one.

-- chris chen (chrischen@msn.com), March 21, 2002

Answers

The "angle of view" for the meter in the M6/M6TTL/M7 is totally dependent on which lens you have mounted on the camera at the time. The white metering spot represents approximately 13% (1/9th) of the total image area.

:-),

-- Jack Flesher (jbflesher@msn.com), March 21, 2002.

Jack,

I know what your saying. But, I don't think you know what i'm trying to say.

Take the lens off; look inside; do you see the little light sensor in the body cavity; there's a lens over it. What portion of the shutter curtain does this sensor "see"? Is it greater (certainly not less) than the 12 mm white spot? How much greater? Does it see the whole frame? If Leica changed the little lens (cheap) and the pattern on the curtain (cheap) and reprogramed the software (cheap) would any one want that?

-- chris chen (chrischen@msn.com), March 21, 2002.

The clip-on MR type meters are said to meter from an area similar to the 90mm lens field of view. Would it not be a safe bet to think the meter in the M6 and M7 is similar?

-- Tim Franklin (tim_franklin@mac.com), March 21, 2002.

Com'on Folks,

Do I have to stop this car and get the flame throwers out? 8^0

PLEASE read the question.

-- chris chen (chrischen@msn.com), March 21, 2002.

It seems to me that eveyone who responded above is taking time and trouble to try to be helpful to you. Your response is unkind. If they did not give an answer that satisfies you, you might try rephrasing the question in an attempt to make it clearer.

-- Ollie Steiner (violindevil@yahoo.com), March 21, 2002.

But Ollie,

I did try to put a BIG smillie w/my comment, I just can't get my keyboard to emulate teeth. Rereading, I think the question is pretty clear. 8*)

See post about self timers for an insite about taking the time to...I'm guilty.

-- chris chen (chrischen@msn.com), March 21, 2002.

Sorry folks, but Chris is right - what you're answering is NOT what he's asking. Forget clip-on meters and forget the white spot.

What is the angle of view of the light-sensitive metering cell combined with it's little lens (assume you've taken it out of the camera and are pointing it at a testing device of some kind).

Chris - I don't know. Here's a possible test scenario.

Take off the camera lens. Make sure the camera is cocked (so the meter will come on). Put something white inside the camera covering the entire film gate (white paper may be enough, or a low-tack white sticky label) as a 'full-frame' substitute for the white dot. Put ANY lens on the camera (except those that block the meter or have substantial fall- off). I'll come back to focal length choice.

Find a dark place with a single bright light source (light bulb, e.g.) Point the camera at the light source and take a bunch of meter readings with the light in different parts of the frame-lines (not the whole viewfinder) (zero the indicators and record the shutter speed at each point). Record the various readings and chart them on a rectangle representing the film area/framelines.

This will give you a rough idea of what the cell 'sees' all by itself - if the shutter speed needs to be real long with the light source out near the corners, then you've gone past the point where the light registers on the meter cell anymore. Maybe the cell sees all the way to the corners, but I'd EXPECT a circular pattern larger than the white dot's area, falling off at the edges. You'll find out (maybe) how MUCH larger than the dot.

Lens choice: A 35 will give the finest, most discreet readings, since the image of the light bulb projected will be smaller. But a 50 (NOT the fall-off prone Nocti) may have less fall-off. A 90 may have even less fall-off, but the image of your light source may get too big for fine determination of the meter's viewing angle.

-- Andy Piper (apidens@denver.infi.net), March 21, 2002.

Thanks again Andy,

I'll try it sometime; though, it's not on my to-do list yet, as it seems a bit OTT. I was hoping someone already knew the answer.

Cheers

-- chris chen (chrischen@msn.com), March 21, 2002.

Chris, you've given me an idea. Leica could have a rotating knob or sliding switch that would change the existing sensor lens with another for true spot readings. It would be easy for them to design the lenses with different densities so the calibration would be the same. Thus an M-6/7 (M-6/7sp?) could have both spot and the existing (effectively center-weighted) metering. I find both types of metering to be extremely useful and often complimentary for a given situation. Leica could also have the spot coincide with the rangefinder patch to make this more predictable, but they'd probably have to build the spot-meter cell into the rangefinder to do this.

-- John Layton (john.layton@valley.net), March 21, 2002.

Chris, you've given me an idea. Leica could have a rotating knob or sliding switch that would change the existing sensor lens with another for true spot readings. It would be easy for them to design the lenses with different densities so the calibration would be the same. Thus an M-6/7 (M-6/7sp?) could have both spot and the existing (effectively center-weighted) metering. I find both types of metering to be extremely useful and often complimentary for a given situation. Leica could also have the spot coincide with the rangefinder patch to make this more predictable, but they'd probably have to build the spot-meter cell into the rangefinder to do this. By the way, I'll be curious to know how you resolve the bugeye lens recalibration issue!

-- John Layton (john.layton@valley.net), March 21, 2002.

Guess there were at least three questions here.

First on meter activation. Making it necessary to have the shutter cocked for the meter to operate, warns the shooter if the shutter isn't cocked. I'm sure that was more important to the Leica engineers than giving one the ability to meter a scene without being able to shoot it without then cocking the shutter. You could get into escoteric things like increased battery drain while the camera jostled around in the bag while walking to but the first was probably enough for them.

Secondly, having a pronounced spherical lens would seem to indicate that the sensor has a wide angle of view, certainly greater than the spot itself. How wide? I would suspect greater than 90 degrees, but it really doesn't matter, as the angle of "read" is only whats important, and that's the width of the spot.

And here is where the use of the "spot" that has most of the posters hung up somewhat with words. Using the 135mm lens, with an 18 degree angle of view (diagonally) will still give one a larger metered area than any 1-5 degree "spot" meter. For the bulk of lens usage of lesser focal length, the area metered is in effect more of the center weighted variety than any spot meter. Simply because you have a larger center to meter.

As to the question as to whether or not increasing the amount of white on the shutter curtain will increase the sensitivity of the meter. No. Take grey card and reflector meter (spot or otherwise) and hold it up to the card and take a reading. Now move it back, making certain you don't exceed the "field angle" of your meter. Same reading even though you are metering a larger area. Meters don't read the amount of light reflected, rather the strength of that reflected light.

Lastly I suspect the M7 in AE does measure light off the film plane with the second sensor devoted to that purpose, but only when you have the proper flash attached to make use of the TTL. I don't have an M7, but I can't imagine it's ability to shoot daylight fill flash in any other fashion and still leave a properly exposed scene.

How about hearing from new M7 owners on that one?

Best,

Jerry

-- Jerome R. Pfile, Jr. (JerryPfile@msn.com), March 21, 2002.

Chris,

I agree with your first point, which sounds practical. I don't like to have to cock the shutter just to be able to take a meter reading.

As to the second point, being able to read the whole shutter curtain surface instead of just the central "spot" area would enable centre- weighted average metering in the M7, which would be a very useful option in AE mode because it would save having to lock the exposure and recompose for every shot. The R camera designers have always understood this but I suspect they don't communicate with the M designers!

Incidentally, it doesn't matter what the angle of view of the photocell used for "spot" metering is: the camera could simply switch to the other photo cell for full-field average metering, the one that already exists to control TTL flash. That cell reads from the whole area of the film but it could also be made to read from the shutter curtain if the curtain was suitably patterned. All Leica has to do is to use a "checkerboard" pattern on the shutter curtain (as in Olympus OM), instead of the white spot, and adjust the sensitivity of the spot-metering cell accordingly.

In answer to your final question, no, the M7 doesn't measure OTF in AE mode and it couldn't do so, if you think about it. At speeds faster than 1/50 sec. the shutter is never fully open, so the camera would have to meter from the curtains and/or the film, as with Olympus OM cameras. The M7 meters exactly the same as the M6 TTL, i.e. from the white spot on the shutter curtain for non-flash and OTF (full field average metering) for TTL flash.

-- Ray Moth (ray_moth@yahoo.com), March 21, 2002.

Ray,

I still think for the vast bulk of shooters, having the meter inoperable unless the shutter is cocked is far more rational than having the meter operable whether it is cocked or not. If one has camera in hand and takes the trouble to "meter a scene" the obvious presumption is that one is going to take a photo, either at that moment or fairly soon. If you do choose to take the photo at that very moment, its nice to know if the camera is ready to comply instantly when you press the release. If not at that very moment, chances are more than great that you will expose a frame soon....and your camera will be ready.

I'm not familiar with OMs you mention but am curious regarding the ability of a full shutter, geometric "checkerboard" arrangement on the shutter curtain, to yield a center weighted metering result for exposure. It would seem that the strength of the reflected light passed to the sensor would again be determined by the strength of the total light from the whole of the white (or whatever color as long as it isn't black) checkerboard squares on the curtain. That certainly wouldn't appear to be "center weighted", but equally weighted across the whole of the frame.

I would think that if one wished to have a weighted (in any fashion) reading from the whole of the frame, you would accomplish that either in the design of the sensor itself, or to forego the sensor altogether, and have the shutter curtain itself wired to yield what ever pattern chosen to serve as the only sensor. Certainly don't mind hearing if I'm wrong, but wasn't the latter the way the CLE computed exposure?

Again as I noted before, all I know about the M7 is what I've read. However, apparantly it does have the ability to synch flash at speeds greater than 1/50 (1/125 through 1/1000 with only the pulsating Metz model for the moment). I'd certainly be more than curious to know how it determines not the rapidity of the pulses, but their strength without reading not off the shutter curtain, but the film surface itself through use of its flash sensor. Without using the AE mode and first sensor to determine shutter speeds greater than 1/50 for a daylight scene, and the second sensor reading the portion of the film open to its view thoughout slit travel to determine the proper pulse strength for fill, how would automated daylight fill flash be possible? Understand the M6 TTL can't even do this at 1/50 without manually manipulated flash strength.

Inquiring minds...etc., etc.

Best,

Jerry

-- Jerome R. Pfile, Jr. (JerryPfile@msn.com), March 22, 2002.

Jerry,

What I called a "checkerboard" pattern (for want of a better description) is actually a "random" pattern of very small white rectangular dots on the OM's black cloth shutter curtains, which gives a pseudo-gray area from which to meter. You could build the weighting into the distribution of the dots on the curtain or you could achieve it through the design of the sensor; the latter is the way Olympus does it.

My point was, mainly, that both the M6 TTL and the M7 ALREADY have a secondary photocell that is used for TTL flash control. It reads from the entire film surface but I'm not sure if it's centre weighted. It probably should be. Whatever, it wouldn't take a genius to arrange for that cell to be selectable, as an alternative to the one used for "spot metering", to provide the option of pre-exposure full-field average metering, provided that the shutter curtain has the necessary pattern for such metering. I suppose this could be in addition to the white spot or instead of it. Leica could experiment with a paint- brush to get the best results!

It would mean, though, that the photocell used for "spot" mode would have to have a narrow angle of view, restricted to the size of the spot; with the present M6/M7 design, it doesn't matter because the white spot's surrounded by black. If it were surrounded by a pseudo grey area, it would be important. That was one of Chris's questions.

As I understand it, the M7 can control the flash using TTL metering only at or below the synch. speed of 1/50 sec, with an SCA 3000 compatible flash unit. For higher flash synch. speeds of 1/250 sec or faster, with a Metz 50 type unit, the flash is used in strobe mode WITHOUT TTL control. Sounds a bit basic to me!

-- Ray Moth (ray_moth@yahoo.com), March 22, 2002.

Jerry: The 'checkerboard pattern' of light squares in the OM cameras is center-weighted - there are more light-colored squares per surface area near the center than at the edges. Take a real checkerboard, randomly paint a few of the black squares near the center red, and a few of the red squares near the edge black, and you'll get the idea.

This "weights' the amount of light reflected to the metering cell, which 'sees' the whole curtain more or less evenly. A bright highlight near the edge of the frame, projected onto cloth that is mostly black, will not not send much light on to the meter - the same highlight projected onto a portion of the shutter curtain with LOTS of bright spots (the center) to reflect it will have more influence (weight) on the exposure (hence centerweighted).

The CLE worked the same way - the pattern on the shutter was NOT light sensitive itself - it was just a reflector to send a weighted amount of light from different parts of the shutter curtain on to the metering cell. The only difference between the OM-2/CLE metering and the Leica M6 (or Contax G or Hexar RF for that matter) is that the latter three use a solid shape (circle/rectangle) of gray/white for the reflector, while the 1970/80's cameras used a scatter pattern of smaller dots to modify the metering pattern and give SOME weight to the outer portions of the frame.

"I'd certainly be more than curious to know how it [the M7 High Speed Sync flash] determines not the rapidity of the pulses, but their strength..."

The M7's HSS sync mode is NOT automatic

8^(

but fully manual - you personally have to pick an aperture based on subject distance. The flash will show you different scales based on the shutter speed in use so it does some of the calculation - but it does not vary the flash power to suit your aperture - you must vary the aperture by hand to suit the flash's output. Therefore the M7/Metz combo does NO flash metering in the HSS mode - it just puts out a constant stream of light of a factory-determined amount.

Auto-metered flash will not work in the HSS mode regardless of how/ where it's metered. Autoflash works by shutting down the flash once the sensors have 'seen' the correct amount of light. But with the HSS - shutting down the flash this way will leave part of the frame unexposed - the flash turns off before the curtain has moved all the way across (just as with 'normal' flash sync). And the early parts of the frame will probably be overexposed - there is no way for the flash to go back in time and reduce the exposure for film that is already under the second shutter curtain.

..which leads us back to Chris' last question - no, the M7 doesn't meter ambient light off the film. In fact (as you noted) it quits metering once the first shutter curtain and dot have disappeared. The second cell (as with the M6TTL) DOES meter off the film, but only at the normal 1/50th sync speed.

-- Andy Piper (apidens@denver.infi.net), March 22, 2002.

Ray - what cosmic connection allows us to say exactly the same thing at exactly the same time from 8000 miles (10000 Km) apart?

-- Andy Piper (apidens@denver.infi.net), March 22, 2002.

Andy,

LOL! Actually, it's more than 8000 miles because Internet uses satellites. We're not saying exactly the same thing, however. Olympus, in the initial OM-2 model, did, as you say, print a pattern on the shutter curtains that was weighted toward the centre. The pattern was designed to have the same reflectance, overall, as a typical film but had more white dots in the middle than at the edges. Interestingly enough. Olympus found that the reflectance of different types and makes of slide, colour negative and black-and-white films was pretty consistent.

However, because OM cameras (in AE mode) do real-time metering, they have to use a combination of both off-the-film and off-the-curtain measurement, the proportion of light measured from each being dependent upon the shutter speed the camera chooses. Slow shutter speeds measure mostly from the film, while high shutter speeds measure mostly from the shutter curtain.

The problem was that, because a film has, of course, a uniform reflectance over its entire surface, it appears differently to the photocell than a curtain having non-uniform reflectance. This led to light metering inconsistencies in the early OM-2 and Olympus had to change to an even, unweighted shutter curtain pattern in subsequent models to be consistent with film reflectance. they built the weighting into the design of the photocell.

-- Ray Moth (ray_moth@yahoo.com), March 22, 2002.

"However, because OM cameras (in AE mode) do real-time metering, they have to use a combination of both off-the-film and off-the-curtain measurement, the proportion of light measured from each being the shutter speed the camera chooses. Slow shutter speeds measure mostly from the film, while high shutter speeds measure mostly from the shutter curtain." In the OM2, when the shutter curtain is open to take exposure, light is measured directly from the film, disregard high or slow shutter sppeds. The readings taken off the surface of the shutter curtain is to provide (approx.)exposure information in the viewfinder prior to you fire the shutter. So the actual exposure measurement is not a combination of reading taken from the shutter curtain and off the film. Regards,

-- tom tong (tom.tong@ckh.com.hk), March 22, 2002.

Thanks for the explanation guys. However, within that explanation rises another question for me at least.

I have no equipment that meters off the film in either flash or regular mode. In that various film emulsions would appear to have a range of reflectance, how does the OTF sensor compensate for that?

Perhaps the question is worthy of a thread of its own but it arouses my curiosity.

Thanks,

Jerry

-- Jerome R. Pfile, Jr. (JerryPfile@msn.com), March 22, 2002.