The official Leica Press release on new lens info for M8

[StuartR]

Varjag, unless my fundamental understanding of the universe is wrong, you, Ben and I are correct in this matter. Jaapv's idea of an external ambient reading would be the only way I can think they might do it, but even that could be tricked, as you can be standing in one light and shooting at something in another (i.e. standing in the shade and metering on the sunny mountain top 2 miles away).

 

[Socke]

And..? I know what aperture is 🙂 I don't see a way how you deduct an aperture from a value of TTL meter, not knowing the ambient light. Up to the point that I started to doubt my sanity and tried to put down it into math, but all I end up is one equation with two variables unknown, aperture and subject brightness.

Hm, how does the meter do it?

As far as I know it tries to represent the scene as 18% grey no matter what the color or illumination of the metered scene is.

But I may have cheated a bit, I started with a negative exposed to what a meter would read. Think autoexposure.

Thus I reduce it to the subject illumination as metered with a given sensitivity and shutterspeed, then only the aperture is unknown.

At the moment I have EV13, bright light but no shaddows sunset in about 2 hours, I shoot with ISO100 and the built in meter sets my shutter to 1/125th then my lens must be at f8. If it sets the shutterspeed to 1/250th the aperture must be at f5.6 and so on.

 

[Paul T.]

"At the moment I have EV13, bright light but no shaddows sunset in about 2 hours, I shoot with ISO100 and the built in meter sets my shutter to 1/125th then my lens must be at f8. If it sets the shutterspeed to 1/250th the aperture must be at f5.6 and so on."

If the camera/processor know the light level is EV13 then it can deduce the aperture. Otherwise, you might well have a lower light level, and a larger aperture. The ambient sensor, as used on many P&S cameria would allow the processor to deduce aperture, in that there will be two meter cells, one behind the diaphragm, one on board the camera, and it would be a reliable sustem unless you obscure the on-camera sensor.

In any case, I would doublt that deduction of the aperture is necessary. If the processor needs to know the lens type, in order to map for vignetting due to oblique light rays, I would think the vignetting is independent of aperture. Although I'd be interested to know if it varies slightly with subject difference.

 

[Socke]

Baaah! Now I get it! The camera has no way of knowing how much light is out there and if I try to shoot a supernova or the moon.

Damn! Sometimes it takes realy long until the obvious trickles down to my brain.

 

[Ben Z]

I would think the vignetting is independent of aperture..

From my own experience, which confirms what I've seen in print multitudes of times, vignetting very much does depent on aperture. Most lenses vignette less and less as they are stopped down, in fact some vignette significantly at maximum aperture and not at all by mid-apertures. My 21mm Elmarit pre-ASPH is a case in point (and one of the codable lenses according to the list). At 2.8 there's maybe 2-2.5 stops of vignetting which is all but gone by 5.6. How could software compensate without knowing the shooting aperture?

Of course we're talking about the vignetting inherent in the lens, which in fact would be lessend due to the cropped sensor. Perhaps there is some vignetting caused by the digital sensor/microlenses which is not aperture-dependent, but more severe with some lenses than others. That might be compensated for by the camera only knowing the specific lens that's mounted.

 

[StuartR]

Good point Ben. It would be interesting to know whether that type of vignetting is aperture dependent as well. Perhaps RD-1 users can speak to that...


And Volker, I am glad we worked that out...I thought I was going crazy there for a second...

 

[Paul T.]

Sorry Ben, should have made myself clearer; as you say, vignetting on a lens does vary with aperture.

However, I have read that vignetting due to light rays hitting the microsites (or microlenses) on the CCD sensor at an oblique angle does not vary with aperture to a significant degree. But I've only read this on the 'net somewhere, so you are within your rights to take this statement with a pinch of salt. If aperture did make a difference, I would have thought it's pretty easy to deduce what the aperture is using two light sensors as suggested earlier, and it wouldn't be hugely expensive.

 

[LCT]

...vignetting due to light rays hitting the microsites (or microlenses) on the CCD sensor at an oblique angle does not vary with aperture to a significant degree...

Yes digital vignetting does not vary much with aperture.
Best,
LCT

 

[herbkell@shaw.c]

I see that the 135 is "unsuitable" for the M8. Does this mean it can't be used at all or is is simply too difficult to focus. I would have thought that a smaller field of view was a bonus focusing a rangefinder lens but I am a rookie in the rangefinder world and may have this wrong

 

[Socke]

Yes digital vignetting does not vary much with aperture.
Best,
LCT

I just looked again into Sean Reids R-D1 lens review, and yes, most of the lenses don't improve much at f8.

Hopefully Leica found something more than a software tweak to improve this.

 

[StuartR]

I see that the 135 is "unsuitable" for the M8. Does this mean it can't be used at all or is is simply too difficult to focus. I would have thought that a smaller field of view was a bonus focusing a rangefinder lens but I am a rookie in the rangefinder world and may have this wrong

The ease of focus would not change, but their argument is that the framelines would be too small to accurately see what was in the picture. I think this is more or less a legal argument so that people won't say: "Hey, I just bought your damn 3000 dollar lens, and I can't get a single good shot!" The 135mm will work fine on the M8, but the framing would probably be very difficult, even with a 1.25 magnifier. Think of it this way, the 135mm frameline WITH the 1.25 magnifer will be smaller than the current 135mm frameline is without it. Just like they left the 135mm framelines out of the .58 Leica, they will probably leave them out of the M8.

 

[LCT]

I see that the 135 is "unsuitable" for the M8. Does this mean it can't be used at all or is is simply too difficult to focus....

Any 135mm lens should be usable on the M8 but assuming that the base length of the rangefinder and the finder magnification (.72x) will be the same as that of classic Ms, it should be difficult to focus at f/4.5 and wider apertures IMHO.
Best,
LCT

 

[Mark Norton]

My hope is there will be a frameline for the 21mm lens - which is no more than providing one for a 28mm on a film M.