dai_sieh1

I did some discussion on the M6 metering pattern in a previous thread. Glad to see you noticed same thing.

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=005h3W

I cycle competitivly. Most of my training are done in the mountains, or cross the mountain to the Pacific coast and back. I always wished to photograph the spectacular views along my training rides. But the sad conclusion I reached was that photograhy couldn't coexist with serious cycling.

Stopping to take picture interrupts the rhythm during the ascent and is unwise during the descent. I would never risk anything more than a cheap P&S camera to the vibrations experienced on a roadbike. While everything will be saturated with sweat on the body.

Having said all that, I did witness one guy snapping picutures with a disposable camera while racing. But that was during the neutral start, and didn't fit with the mood of the rest of the bunch. Because there were 6 giant climbs in the eastern Sierras and 200 miles waiting for us that day and the next.

BTW 80 PSI seemed low. 115 PSI is what I use. I have seen others use 120 PSI. For very poor pavements, use 105 at the front and 110 at the rear. But I heard highways in Europe are better paved than the ones in the states. Maybe the road will be so smooth in the Alps that you can store camera on the bicycle.

Have a good ride,

Thanks for your responses. The majority opinion seems to be to keep the tool simple, but use plenty of experience and judgement. I guess I need to try harder to forget the technology laden EOS stuff. BTW, I did compare my M6 and EOS in front of a evenly lit wall. And their readings agree. The M6 meter is doing what it's supposed to do.

(Putting my enginner's hat back on) If the Leica designer moved the frame selector cam to a different position, and put the photo cell at the 12 o'clock position (where the frame selector cam used to be), the metering pattern will be ..... But in order to maintain compatibility with the legacy system .... Typical technology headache.

Best Regards,

SHORT STORY:

The weighting (or gain) of the light measurement varies across

the metering area. I observed a variation of over 2 stops in an area

around the RF patch with 35mm lens. The highest gain (most

sensitive)

spot is just outside of the lower left corner of the RF patch which

reads 1 stop higher than the center of the RF patch. Some area just

above the RF patch and to the right of the RF patch read more than 1

stop lower than the center.

LONG STORY:

The light metering in M6 is accomplished by sensing the light

reflected from the white disk in the middle of the 1st shutter

curtain. The photocell aims at the white area from outside the edge

of the film frame at about 11 o'clock position. (I guess this

arrangement is true for all later models such as M7 and MP).

The light traveling from the white metering disk to the photocell

behaves like free space propagation (not being focused by any lens).

So the light intensity decreases with the square of the

distance. The distance from the photocell to the different points of

the white disk vary quite significantly. The point that's closest to

the photocell is the upper left hand portion of the white area, which

corresponds to the lower left hand section in the viewfinder

image. Which agrees with my observation of the most sensitive spot.

The angles of reflection between the incoming light and the reflected

light propagating to the photocell will be different at different

points on the white disk. This may or may not contribute to the

variation of the light intensity detected by the photocell.

There is some discussion of shutter reflected light metering in

Stephen Gandy's Bessa L and Bessa R pages at www.cameraquest.com.

There is a plot of metering pattern showing the variation of the

metering weight. Which kind of agree with my explanations above.

DISCUSSION:

The non-uniformity of the light measurement is to be expected from

the

design and is present in most in camera metering system. What I

regret is that the pattern is not symmetric (favors the lower left

hand corner). I kind like the pattern in the Besser system, which is

symmetric and more like a normal center weighed metering pattern (at

least

in the horizontal direction).

I would like to supply this information to the community and hear

back

any confirmation or correction. Hopefully, someone will do a more

quantitative survey of the M* system's metering behavior. What I

really want to hear is how one use his M6/7/P's metering system in

actual photo shooting situations. Can one meter more intelligently

and reliably than measuring the back of one's hand? What does one do

knowing the metering pattern has asymmetric weighting?

Having a couple of handheld meters, I was planning to use the M6

without battery. How many of you out there are using your M6 without

battery?

Cy,

You are welcome. Let me also point out that the color I was talking about was the reflected color. Any reduction in reflection does improve the transmission. But since the amount of reflection is small to start with, the effect of the coating on transmission is very small. The color one sees when looking thru the lens has very little to do with the anti-reflection coating.

Good luck and have fun with the lens.

Try looking at the color of the reflection off the lens surface. Dull brownish color is typically seen on MC lens. I have seen Single-Coated lens typically has blueish colored reflection.

The lens surface is coated to minimize the reflection and maximize the transmission of light. A single layer of coating at the glass-air interface will prevent the reflection of a narrow band of light spectrum having wave length (in the coating not air) approximatly equal to 4x the thickness of the dielectric coating. Multi-Coating is more engineering than physics, where different layers of dielectric are stack on the glass surface in order to supress the reflection over a broader band of light spectrum. MC probably reflects a bit more light at the frequency where Single-Coating was designed to work. But MC supresses most of the reflection over a wider range of frequency. So it workes better in practice, that's why I call it engineering.

Hope I havn't bored you.

The color of the reflection off a single-coated lens is white (full spectrum) with a narrow band of color spectrum missing. I have seen blueish color myself.

The color of the reflection off a MC lens is white with lots of color spectrum missing (or reduced). Ideally it shuld appear black, but in reality it's more like dull brownish color. The darker the better.

What color do you see?