willemvelthoven
RD1 user
The blue dot on the M8 is a sensor for determining the actual aperture of each shot.
The camera needs a second light measurement to compare to the ttl measurement (and for angle of view and ultimate accuracy reasons, the known lens characteristics) to know the actual aperture setting.
Nice that they can write that info to the EXIF and/or show it in a display.
More importantly, Leica are promising us very specific image enhancements based on the characteristic of the lenses used.
Ever since they've shown us the 6bit lens coding, i've wondered how they were going to do any corrections withou knowing the aperture setting.
The aperture setting influences lens characteristics so dramatically that you cannot do automatic anhancements without knowing it.
The camera needs a second light measurement to compare to the ttl measurement (and for angle of view and ultimate accuracy reasons, the known lens characteristics) to know the actual aperture setting.
Nice that they can write that info to the EXIF and/or show it in a display.
More importantly, Leica are promising us very specific image enhancements based on the characteristic of the lenses used.
Ever since they've shown us the 6bit lens coding, i've wondered how they were going to do any corrections withou knowing the aperture setting.
The aperture setting influences lens characteristics so dramatically that you cannot do automatic anhancements without knowing it.
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willemvelthoven
RD1 user
Obviously Cool
Obviously Cool
Surely, the blue dot can be used for other things too. White balance for instance. Hell, it could even be made to blink when the self timer is running.
But Leica would never deface their company-saving new flagship with something that cheap.
Design wise, the BLUE DOTs prominent placing must be justified. IMHO, it can only be justified when it represents a really intelligent, cool, new function!
Imagine, it even reads the (effective) aperture of ANY piece of old glass mounted on the camera!
Obviously Cool
Surely, the blue dot can be used for other things too. White balance for instance. Hell, it could even be made to blink when the self timer is running.
But Leica would never deface their company-saving new flagship with something that cheap.
Design wise, the BLUE DOTs prominent placing must be justified. IMHO, it can only be justified when it represents a really intelligent, cool, new function!
Imagine, it even reads the (effective) aperture of ANY piece of old glass mounted on the camera!
willemvelthoven
RD1 user
Will Blue Dot aperture measurement work with non-coded glass?
Will Blue Dot aperture measurement work with non-coded glass?
Theoretically, the accuracy of the aperture measurement by comparing blue dot and ttl metering is dependent on the angle of view of the lens used.
Assuming that the blue dot has a fixed angle of view, the M8 could vary the size of the ttl measurement circle to match it. But only if the focal length is known. This requires a coded lens or somekind of prohibitively awkward manual identification procedure.
Sufficient argument for Leica to disable aperture recognition for non coded lenses!
And actually a nice extra argument to have your summicron 50 of 75 coded. (because those lenses really don't need any corrections in camera)
Here, the guys and girls that are in charge of marketing Leica glass might find the leverage to have the M8 designers switch off aperture detection for non coded glass.
I would regret that however, i'd rather have a slightly inaccurate reading than no ready on the 8 non-codable lenses that I use. (mostly voigtlaender and old german glass)
So please Leica:
If we are naughtly and use lenses that do not contribute to your organisations profit...
give us a slightly inaccurate reading in stead on no reading at all!
Actually, one of the reasons that I ordered an M8 is that i can use all kinds of optics on an M camera.
And yes Leica, i'll have my cron, lux and noct coded. I promise!
Will Blue Dot aperture measurement work with non-coded glass?
Theoretically, the accuracy of the aperture measurement by comparing blue dot and ttl metering is dependent on the angle of view of the lens used.
Assuming that the blue dot has a fixed angle of view, the M8 could vary the size of the ttl measurement circle to match it. But only if the focal length is known. This requires a coded lens or somekind of prohibitively awkward manual identification procedure.
Sufficient argument for Leica to disable aperture recognition for non coded lenses!
And actually a nice extra argument to have your summicron 50 of 75 coded. (because those lenses really don't need any corrections in camera)
Here, the guys and girls that are in charge of marketing Leica glass might find the leverage to have the M8 designers switch off aperture detection for non coded glass.
I would regret that however, i'd rather have a slightly inaccurate reading than no ready on the 8 non-codable lenses that I use. (mostly voigtlaender and old german glass)
So please Leica:
If we are naughtly and use lenses that do not contribute to your organisations profit...
give us a slightly inaccurate reading in stead on no reading at all!
Actually, one of the reasons that I ordered an M8 is that i can use all kinds of optics on an M camera.
And yes Leica, i'll have my cron, lux and noct coded. I promise!
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Ben Z
Veteran
Did I miss something, like an official statement from Leica that there actually is a "blue dot" on the real M8 and an official announcement of its function?
Palaeoboy
Joel Matherson
I cant see how it would work as you have described.
For example if you are standing in direct sunlight shining on the camera top and pointing the lens into the shadows it would think the lens is set at a different aperture to if you were pointing the lens to another area also in sunlight.
Self timer LED is my guess.
For example if you are standing in direct sunlight shining on the camera top and pointing the lens into the shadows it would think the lens is set at a different aperture to if you were pointing the lens to another area also in sunlight.
Self timer LED is my guess.
willemvelthoven
RD1 user
The Blue Dot is a little telelens...
The Blue Dot is a little telelens...
Not just a sensor. It is actually precisely measuring a portion in the middle of the image. Does it have mechanical parallax correction? It could be mechanically achieved... but just as easily electronically at the moment of selecting the corresponding image circle in the RAW data.
again, assuming that the M8 knows about the lenses angle of view through the 6 bit coding info of course...
I'm also assumin that tha camera is electronically registering the focus distance of course... would that be too much for a $ 5000 camera?
The Blue Dot is a little telelens...
Not just a sensor. It is actually precisely measuring a portion in the middle of the image. Does it have mechanical parallax correction? It could be mechanically achieved... but just as easily electronically at the moment of selecting the corresponding image circle in the RAW data.
again, assuming that the M8 knows about the lenses angle of view through the 6 bit coding info of course...
I'm also assumin that tha camera is electronically registering the focus distance of course... would that be too much for a $ 5000 camera?
Mark Norton
Well-known
I think you're dreaming and should go and lie down in a dark room until the feeling passes...
ywenz
Veteran
will. I thought you were talking with inside information... now I just think you're crazy 
rvaubel
Well-known
Palaeoboy said:
You'd be right if the blue dot functioned as an incident light meter. But if it worked as a reflected light meter, it would work fine,,,,,in theory. The problem is the light intensity comparision must be done between areas of similar included angles of view. However, the lens coding does take care of that problem for Leica lenses and, for that matter, with any lenses that have been coded.
This would be a really useful feature. I would love to have the F# info recorded in the EXIF file. Also, having the F# displayed in the viewfinder would be handy, especially in low light situations.
Since the F# would be a calculated number based on two light readings which are not totally similar (in the geometric sense), there might be a slight disagreement between the actual apeture setting and the reported one. But, still the information would be a lot better than nothing.
Rex
sf
Veteran
What kinds of automatic enhancements are they planning on putting in this thing? I wouldn't want any camera automatically enhancing my images - especially a Leica. Seems just wrong...
AusDLK
Famous Photographer
>Self timer LED is my guess.
Absolutely. Just like the dot on the front of the Hexar RF.
Same thing.
Absolutely. Just like the dot on the front of the Hexar RF.
Same thing.
rvaubel
Well-known
shutterflower said:
I don't want any automatic enhancements either. I just want the the F stop to be recorded on the EXIF data and displayed in the camera viewfinder. Others will want automatic enhancements but not me.
Rex
jlw
Rangefinder camera pedant
I don't know whether or not the blue dot is it, but the original poster is 100% correct about needing a second sensor to determine the actual aperture of the lens.
The Contax G1 and G2 use a very similar system. The external meter cell was provided primarily for exposure setting when using the 16mm Hologon lens (which sits too deep for TTL metering to work) but also is used to derive the aperture setting in use. The only use made of this data in the G cameras was to imprint the exposure data on the G2's data back, but obviously with a digital camera more can be done with it.
Here's the background of why an external sensor is needed to determine the f/stop in use:
All SLRs that feature full-aperture metering communicate the aperture setting from the lens to the metering system in the camera body, either by a mechanical linkage (e.g. the prong on Nikon F lenses) or an electronic contact (as used on most modern SLRs.) This coupling reads the actual setting of the lens' aperture ring and passes it along to the metering system in the camera body.
The metering system needs to know the aperture setting so it can determine the correct shutter speed without having to stop down the lens, which on an SLR would cause the viewfinder to get dim. (Owners of stop-down-metering SLRs such as Pentax Spotmatics are all too familiar with this.)
Rangefinder camera lenses (including Contax G-mount lenses) have never had this kind of aperture coupling system. They always meter at the actual working aperture, with the lens stopped down. It's a simpler and theoretically more accurate system, and there's no reason not to use it, since you're not viewing through the lens and don't have to worry about the finder getting dim when you stop down.
But because the aperture ring setting isn't communicated to the metering system, the meter doesn't know (or care) what aperture you've set. It just measures the amount of light passing through the lens, and determines what shutter speed is appropriate for that amount of light. It has no way of knowing whether you're metering a dimly-lit scene at f/2 or a brightly-lit scene at f/16... and it doesn't need to know that to give you a correct exposure.
However, if you're trying to record your exposure data (on a data back or in an EXIF file header) you'd naturally like to know the aperture to which you had set the lens. So, Contax came up with a clever trick which Leica apparently is adopting as well: Measure the brightness of the scene using a NON-through-lens meter, and compare that to the brightness read by the through-lens meter. By comparing the two, the camera can compute what lens aperture would be needed to account for the difference in brightness. The result will only be approximate, but it should be close enough to help you evaluate your exposures.
To give a simple example I thought up for another mysterious-blue-dot thread, suppose you see me taking a picture and ask what settings I'm using. I reply, "My ISO is 400 and my shutter speed is 1/125, but I'm not going to tell you the aperture." (I must be crabby that day.) Still, if you happen to have a hand-held meter with you, you can set it to ISO 400, meter the scene, and then see what aperture lines up against 1/125 on the calculator dial, and you know approximately what f/stop I would have been using. The Contax G2 data back and presumably the Mysterious Blue Dot work exactly the same way.
As to the question of automatic enhancements, I can think of one example right off: vignetting. Most of us have observed that vignetting is worst at full aperture, and improves as you stop down. If you're Leica and you want to include automatic vignetting compensation, you'll need to know the lens' working aperture as well as its focal length, so you can apply an appropriate amount of correction for the aperture in use.
It will be interesting to see how they use this data: whether the camera includes a lookup table of correction values derived for various Leica lenses and applies correction to the images "on the fly" (which might mean that third-party encoded lenses could give inaccurate corrections) or whether they just store the coding data in the file header and then use it for post-processing via raw conversion software.
Picking apart this kind of stuff will be lots of fun for technically-minded RF enthusiasts, even if we can't afford to buy an M8 ourselves!
The Contax G1 and G2 use a very similar system. The external meter cell was provided primarily for exposure setting when using the 16mm Hologon lens (which sits too deep for TTL metering to work) but also is used to derive the aperture setting in use. The only use made of this data in the G cameras was to imprint the exposure data on the G2's data back, but obviously with a digital camera more can be done with it.
Here's the background of why an external sensor is needed to determine the f/stop in use:
All SLRs that feature full-aperture metering communicate the aperture setting from the lens to the metering system in the camera body, either by a mechanical linkage (e.g. the prong on Nikon F lenses) or an electronic contact (as used on most modern SLRs.) This coupling reads the actual setting of the lens' aperture ring and passes it along to the metering system in the camera body.
The metering system needs to know the aperture setting so it can determine the correct shutter speed without having to stop down the lens, which on an SLR would cause the viewfinder to get dim. (Owners of stop-down-metering SLRs such as Pentax Spotmatics are all too familiar with this.)
Rangefinder camera lenses (including Contax G-mount lenses) have never had this kind of aperture coupling system. They always meter at the actual working aperture, with the lens stopped down. It's a simpler and theoretically more accurate system, and there's no reason not to use it, since you're not viewing through the lens and don't have to worry about the finder getting dim when you stop down.
But because the aperture ring setting isn't communicated to the metering system, the meter doesn't know (or care) what aperture you've set. It just measures the amount of light passing through the lens, and determines what shutter speed is appropriate for that amount of light. It has no way of knowing whether you're metering a dimly-lit scene at f/2 or a brightly-lit scene at f/16... and it doesn't need to know that to give you a correct exposure.
However, if you're trying to record your exposure data (on a data back or in an EXIF file header) you'd naturally like to know the aperture to which you had set the lens. So, Contax came up with a clever trick which Leica apparently is adopting as well: Measure the brightness of the scene using a NON-through-lens meter, and compare that to the brightness read by the through-lens meter. By comparing the two, the camera can compute what lens aperture would be needed to account for the difference in brightness. The result will only be approximate, but it should be close enough to help you evaluate your exposures.
[At first I thought it also would be necessary to know the lens' maximum aperture, as it is on SLR full-aperture metering systems -- but further thought made me realize this isn't actually necessary, so I've deleted that part of this post.]
To give a simple example I thought up for another mysterious-blue-dot thread, suppose you see me taking a picture and ask what settings I'm using. I reply, "My ISO is 400 and my shutter speed is 1/125, but I'm not going to tell you the aperture." (I must be crabby that day.) Still, if you happen to have a hand-held meter with you, you can set it to ISO 400, meter the scene, and then see what aperture lines up against 1/125 on the calculator dial, and you know approximately what f/stop I would have been using. The Contax G2 data back and presumably the Mysterious Blue Dot work exactly the same way.
As to the question of automatic enhancements, I can think of one example right off: vignetting. Most of us have observed that vignetting is worst at full aperture, and improves as you stop down. If you're Leica and you want to include automatic vignetting compensation, you'll need to know the lens' working aperture as well as its focal length, so you can apply an appropriate amount of correction for the aperture in use.
It will be interesting to see how they use this data: whether the camera includes a lookup table of correction values derived for various Leica lenses and applies correction to the images "on the fly" (which might mean that third-party encoded lenses could give inaccurate corrections) or whether they just store the coding data in the file header and then use it for post-processing via raw conversion software.
Picking apart this kind of stuff will be lots of fun for technically-minded RF enthusiasts, even if we can't afford to buy an M8 ourselves!
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LCT
ex-newbie
Neither me. Raw will be free from those gadgets hopefully.rvaubel said:
ghost
Well-known
ausdlk said:
too bad they didn't put it in the same place.
rvaubel
Well-known
jlw said:
That's true in an open-apeture metering system. But the M8 doesn't have an open-apeture metering system so doesn't need to know the maximum apeture of the lens.
For arguments sake suppose the external metering system (AKA Blue Dot) has an effective field of view of a 50mm lens and an apeture of F4.0. Now if you have a 50mm Summicron on the camera set at an apeture of F4.0, the relative brightness of the two readings will be the same. So the cameras brain says " Oh this must be a F4.0 lens". If you decide to open the lens apeture to F2.8 the camera says "mmm, the internal meter is reading twice the brightness as the external meter... that must mean the apeture of the lens must have been opened up to F2.8"
Their is no need for the software to know what the maximum apeture of the lens is. It will soon find out when you open the lens to the maximum but if you never do, so what?
The only problem comes with the use of filters. If you put a filter with a 2X factor on the lens, the software has no way of knowing whether the camera has been stopped down by one stop or you reduced the light input by 2X by use of the filter.
Of course you don't really need to use filters on a digital camera but that opens up a can of worms that best be left closed for this discussion.
I'm I missing something here? This seems so intuitive and Leica like that I know I am missing something that will make it all complicated and screwed up.
Rex
AndyPiper
Established
"The aperture setting influences lens characteristics so dramatically that you cannot do automatic anhancements without knowing it."
The main optical effect that will need correcting with the M8 is darkening of the corners with wide-angle lenses due to angle-of-incidence between the incoming light and the sensor surface.
And that kind of darkening (unlike classical vignetting of the type one sees on film) IS NOT affected by aperture. I used my R-D1 and the Cosina 15mm to test this, shooting a scene at all apertures - and there was NO CHANGE in the pattern or amount of 'vignetting' from f/4.5 to f/16.
So the M8 needs to know WHICH lens is mounted (because each lens has a different pattern) but has no need to know which aperture was used.
The "blue dot" could still be a meter for aperture determination, even if only for EXIF.
Or a self-timer signal.
Actually, I think it's just a secret sign (for those in the know) that Zeiss bought out Hermés' and ACM's stake in Leica 3 months ago - to be revealed Sept. 15
8^)
The main optical effect that will need correcting with the M8 is darkening of the corners with wide-angle lenses due to angle-of-incidence between the incoming light and the sensor surface.
And that kind of darkening (unlike classical vignetting of the type one sees on film) IS NOT affected by aperture. I used my R-D1 and the Cosina 15mm to test this, shooting a scene at all apertures - and there was NO CHANGE in the pattern or amount of 'vignetting' from f/4.5 to f/16.
So the M8 needs to know WHICH lens is mounted (because each lens has a different pattern) but has no need to know which aperture was used.
The "blue dot" could still be a meter for aperture determination, even if only for EXIF.
Or a self-timer signal.
Actually, I think it's just a secret sign (for those in the know) that Zeiss bought out Hermés' and ACM's stake in Leica 3 months ago - to be revealed Sept. 15
8^)
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Ash
Selflessly Self-involved
radar...
John Camp
Well-known
Maybe the blue dot signals Homeland Security when you take a picture of a tall building or a bridge...say like the building in Ash's avatar...
JC
JC
jlw
Rangefinder camera pedant
rvaubel said:
I realized you're right shortly after I posted that, and have deleted that paragraph from my post above.