The official Leica Press release on new lens info for M8

[Ken Ford]

I can see no way the aperture can be derived by the body with the current mount - sorry.

 

[Socke]

I am not sure what you are trying to say Volker. Perhaps I am dense on this matter, but doesn't the meter "see" only the amount of light coming through the lens and the shutter speed? Since the amount of light coming through the lens is dependent on the aperture, I don't see how the meter or camera can tell the difference between dim light and low shutter speed because the lens is at f/16 or f/22 and dim light and low shutter speed when the lens is at f/2 and the building is dark. Probability doesn't really enter into the question -- there are many times when you would be using f/2 if you were handheld, but f/11 on a tripod...
If someone can explain how the camera can differentiate between the two without some auxiliary meter or aperture reading device, I would be interested to hear it.

It does know the sensitivity, too.

With known ISO and known shutterspeed you can look up aperture here:

http://www.fredparker.com/ultexp1.htm#Introduction

Thats what the Contax G Databack did when it recorded an "estimated" f-stop, estimated because it could not know about filters.

 

[humanized_form]

i'm really really hoping Leica gets this right because i can't imagine anyone else putting this kind of investment into developing a digital rangefinder camera. not Zeiss. not Epson. nobody.

if they can carry over as much of the design and simplicity of operations from the M7, while minimizing the need for menu diving that would be great.

because i love my M7. i think it's nearly perfect and a digital version of it would make me very happy. so it may be crazy but i'm thinking it's worth spending the $5k to finally have a digital camera that i will really want to use. now i gotta start selling some stuff to get that 5k! hello ebay.

 

[CPF100]

I presume that Leica are doing something quite similiar to Hasselblad's H2D-39 system. This is taken from their website.

"Getting the most from every lens: digital APO correction
The H2D-39 captures an extended set of metadata and then performs an automated correction for color aberration effects with every shot. This means that your digital captures are automatically optimized to provide the finest detail that a given lens can resolve. We have named this feature “digital APO correction” (DAC), signifying the digital, APO-chromatic correction of the images that takes place. Implementation of this feature includes detailed mapping of each H system lens, ensuring that each image represents the best that your equipment can produce. We are confident that the image quality you achieve as a result of the DAC functionality will make you - and your customers - look twice."

 

[Ben Z]

With known ISO and known shutterspeed you can look up aperture...Thats what the Contax G Databack did

AFAIK there are 4 interdependent parameters to exposure: ISO, shutter speed, aperture, and ambient light level. Unless I'm mistaken you need to know 3 to divine the 4th. I can get an "ideal" histogram at ISO 200 and 1/125 at any aperture so long as the light is right for that combo. Since the aperture is between the ambient light and the meter cell, the only way the camera could tell what the ambient level is independent of the set aperture would be if there was an external metering cell.

AFAIK the Contax G bodies had such an external metering cell in addition to the TTL meter. Perhaps that's what was used to measure the ambient light for the aperture guess?

 

[StuartR]

It does know the sensitivity, too.

With known ISO and known shutterspeed you can look up aperture here:

http://www.fredparker.com/ultexp1.htm#Introduction

Thats what the Contax G Databack did when it recorded an "estimated" f-stop, estimated because it could not know about filters.

Isn't the lens's aperture functioning just like a filter in this case? In the case of the Contax G, the aperture was transmitted to the camera, if not the data back. In the case of the leica, the aperture on the lens is covering the meter, so it is functioning like a filter would in the example you described above. Think about it, the only light that reaches the meter is that which the lens lets through. ISO doesn't matter in this case. Sure, if you know ISO and shutter speed you can calculate aperture if you are actually IN the light you are shooting, but the meter is not seeing the full light of the scene, only the light that is being transmitted through the lens. So the question remains, how does the camera differentiate between a low light situation caused by small aperture and a low light situation caused by low light?

If I have not explained that well enough, I am sorry. But I do think I am understanding this correctly. If not, please just shoot me in the head so we can all move on.

 

[Socke]

The Contax G body uses the external meter cell only when a lens blocks the internal one and if the manual is right, the lenses don't pass aperture information to the databack.

So put it the other way around, my Gossen Sixtar measures EV14 and I could use 1/1000 f4, 1/500th f5.6, 125th f11 1/6th f16 for ISO100.

I shot it with a D60 at ISO100 with 1/125th at f11 (got the same reading from the camera set to centerweighted metering)

And I realy need to clean my window and a lenshood for the 24/2.8 would be nice, too 🙂

 

[varjag]

So put it the other way around, my Gossen Sixtar measures EV14 and I could use 1/1000 f4, 1/500th f5.6, 125th f11 1/6th f16 for ISO100.

Your Gossen is not behind a lens with stopped-down aperture though. A TTL meter measures light available *in camera*, not outside, and I too fail to see how one can derive working aperture from that.

 

[Socke]

Your Gossen is not behind a lens with stopped-down aperture though. A TTL meter measures light available *in camera*, not outside, and I too fail to see how one can derive working aperture from that.

Does sunny 16 work? Are shutterspeed and aperture direktly linked to the amount of light reaching the sensor?

If yes, then it will work within the limits of the sunny 16 rule under the assumption that no filtes where used.

Since most digital cameras can indicate under- and overexposed areas, you could even make a good assumption wether the photographer under- or overexposed the picture.

Have a look at the histogram, the handheld meter, the TTL meter and the histogram aren't too far from each other.

This can be fooled, yes, but Sunny 16 is a good indicator of what the aperture should have been, without filters, and the sensor data show what they got, with filters and intentionaly "wrong" exposure.

 

[varjag]

The histogram is not in any way related to working aperture, I don't see how it is relevant: it is an issue of building distribution of pixel values.

Sunny 16 trick could maybe work if there was an external meter available for reference. I don't see how can it work in case of TTL metering with non-automatic aperture: you don't know the actual EV, the exposure you get is the amount of light you have through the lens (which can be stopped down to unknown amount).

 

[Socke]

Ok, I must be wrong. I thought exposure is the amount of light hitting the film and the amount of light can be controled by aperture and shutterspeed (and filters).

 

[Socke]

Come to think of it, has anybody here ever used a Rolleiflex where you could couple aperture and shutterspeed?

That's exactly what I mean.

EV14 on ISO100 can be 1/1000th f4, 1/500th f5.6, 1/250th f8, 1/60th f16 and so on.

 

[varjag]

Ok, I must be wrong. I thought exposure is the amount of light hitting the film and the amount of light can be controled by aperture and shutterspeed (and filters).

Of course it's true. It's just that I don't see a way to derive aperture from shutter speed, ISO and TTL metered amount of light, unless you know what amount of light is actually on the subject (i.e. how much light was lost in transmission through the lens).

 

[rxmd]

It's just that I don't see a way to derive aperture from shutter speed, ISO and TTL metered amount of light, unless you know what amount of light is actually on the subject (i.e. how much light was lost in transmission through the lens).

Transmission losses aren't a problem. On one hand with modern lens coatings there isn't really all that much light lost in transmission, probably not on the order of magnitude of half a stop. On the other hand the camera more or less knows what lens is attached and can compensate by using a lens database, since transmission losses are lens specific.

Philipp

 

[varjag]

Phillipp, my point was about the loss due to lens effective aperture (and that's what we were trying to figure out), not coating reflections which are indeed neglectible. As others pointed out, from a given luminosity value on a TTL meter we can't really tell if is a subject that dark or just a lens stopped down.

 

[jaapv]

The Digilux2 has an external lightbalance sensor. Such a thing could easily read ambient light levels and then the camera could calculate the f-stop through TTL. I think it very possible the M8 will have an external lightbalance sensor as well, as it works exceedingly well on the Digilux2

 

[rxmd]

As others pointed out, from a given luminosity value on a TTL meter we can't really tell if is a subject that dark or just a lens stopped down.

Yes, that way it's true, of course.

Philipp

 

[Socke]

Phillipp, my point was about the loss due to lens effective aperture (and that's what we were trying to figure out), not coating reflections which are indeed neglectible. As others pointed out, from a given luminosity value on a TTL meter we can't really tell if is a subject that dark or just a lens stopped down.

But I rely on the luminosity beeing the same with a varity of lenses, the Gossen Sixtar I mentioned was bought by my father for his Robot with a Schneider Kreuznach lens, a Rolleiflex with a Tessar and a Linhof Technika with a Rodenstock lens. I used it with a Zorki and a Kiev and somehow it agrees with my Contax SLRs with, hard to admit, Contax, Yashica and even Soligor lenses.

So I just assume by observed evidence that a Contax lens at a given aperture transports as much light as a Yashica lens at the same aperture, same from my two Jupiter-8 and one Jupiter-12. It works.

 

[varjag]

So I just assume by observed evidence that a Contax lens at a given aperture transports as much light as a Yashica lens at the same aperture, same from my two Jupiter-8 and one Jupiter-12. It works.

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.

 

[varjag]

For example, we know the shutter speed is 1/125, and film speed ISO 100. TTL sensor shows 100 Lux/second.

Now, how exactly you determine aperture?