Hookeye Posted October 16, 2007 Share #1 Posted October 16, 2007 Advertisement (gone after registration) Coming from the M6 and M4p to the digital world M8 has been quite a trip for me. I also enjoy this forum very much. Reading about the "pink viewfinder" syndrome in the "Mirror lock-up on M8" thread made me curious: The little square window is for the rangefinder and the square corrugated window is for illuminating the bright-line frames, but what on earth is the tiny circular window above the rangefinder window for? Link to post Share on other sites More sharing options...
Advertisement Posted October 16, 2007 Posted October 16, 2007 Hi Hookeye, Take a look here What is that small circular window for?. I'm sure you'll find what you were looking for!
delander † Posted October 16, 2007 Share #2 Posted October 16, 2007 Brightness sensor according to the manual, Jeff Link to post Share on other sites More sharing options...
sandymc Posted October 16, 2007 Share #3 Posted October 16, 2007 It provides an approximate aperture reading.... Sandy Link to post Share on other sites More sharing options...
Guest tummydoc Posted October 16, 2007 Share #4 Posted October 16, 2007 Sandy would you please be so kind as to post the URL location of the official statement from Leica that the blue window effects an aperture approximation? The owner's book only states that it is a brightness sensor for the finder display. Thanks so much. Link to post Share on other sites More sharing options...
2Bébèrt Posted October 16, 2007 Share #5 Posted October 16, 2007 Is this maby the sensor for the automatic white balance? Link to post Share on other sites More sharing options...
fotografr Posted October 16, 2007 Share #6 Posted October 16, 2007 Is this maby the sensor for the automatic white balance? What automatic white balance? Link to post Share on other sites More sharing options...
Hookeye Posted October 16, 2007 Author Share #7 Posted October 16, 2007 Advertisement (gone after registration) Thank you for a lot of interesting suggestions . I believe "Tummydoc" has the right answer, I vaguely remember reading about it in the manual. But it does not fully answer the question. What does it do? What functions does it control? If it is a sensor of sorts - the signal from that sensor should affect some camera function.. but which? Link to post Share on other sites More sharing options...
sandymc Posted October 16, 2007 Share #8 Posted October 16, 2007 Sandy would you please be so kind as to post the URL location of the official statement from Leica that the blue window effects an aperture approximation? Vinay, You are of course right, Leica has never officially stated that the brightness reading is used for an aperture estimate. However, (a) it's difficult to postulate any other useful role for a "brightness sensor" and ( my view is that if we all waited for "official" communications from Leica on what the M8 does or does not do, we'd still have purple blacks..............me, I'll go with the knowledge base of the folks on this forum. Sandy Link to post Share on other sites More sharing options...
Hookeye Posted October 16, 2007 Author Share #9 Posted October 16, 2007 It provides an approximate aperture reading.... You know, Sandy, that when combined with the light sensor on the shutter and calculating the lighting ratio on the white stripe on the shutter blade and the ambient light through the small circular window - you COULD actually get an approximation of the aparture Link to post Share on other sites More sharing options...
cme4brain Posted October 16, 2007 Share #10 Posted October 16, 2007 Coming from the M6 and M4p to the digital world M8 has been quite a trip for me. I also enjoy this forum very much. Reading about the "pink viewfinder" syndrome in the "Mirror lock-up on M8" thread made me curious: The little square window is for the rangefinder and the square corrugated window is for illuminating the bright-line frames, but what on earth is the tiny circular window above the rangefinder window for? I believe it is used to compare the brightness from the lens to the scene to estimate what the f/stop of the lens is set on (since there is no way to send this information to the camera from 50 year old lenses). This info may be usefull in estimating degree of vignetting program application to the final image, or something useful. Link to post Share on other sites More sharing options...
jlm Posted October 16, 2007 Share #11 Posted October 16, 2007 didn't the M7 have adjustable finder display brightess w/o the need for a blue detector? Link to post Share on other sites More sharing options...
Shootist Posted October 16, 2007 Share #12 Posted October 16, 2007 Vinay, You are of course right, Leica has never officially stated that the brightness reading is used for an aperture estimate. However, (a) it's difficult to postulate any other useful role for a "brightness sensor" and ( my view is that if we all waited for "official" communications from Leica on what the M8 does or does not do, we'd still have purple blacks..............me, I'll go with the knowledge base of the folks on this forum. Sandy It also controls the brightness of the LED's in the viewfinder window. It was rumored to also suggest an approximate aperture based on room/area brightness reading from that sensor and knowing what aperture lens was attached and the meter reading for a given ISO but that feature was removed in the release firmwares. Or so it has been suggested on this forum. Link to post Share on other sites More sharing options...
sean_reid Posted October 16, 2007 Share #13 Posted October 16, 2007 Sandy would you please be so kind as to post the URL location of the official statement from Leica that the blue window effects an aperture approximation? The owner's book only states that it is a brightness sensor for the finder display. Thanks so much. It's an exposure metering cell that is used by the M8 to estimate aperture (and for some other functions). I published that information early in 2007 and it is from the horse's mouth. So one source for this information is either "Leica M8, Part 4" or "Leica M8 Updates", both are RR articles. Cheers, Sean Link to post Share on other sites More sharing options...
sean_reid Posted October 16, 2007 Share #14 Posted October 16, 2007 Vinay, You are of course right, Leica has never officially stated that the brightness reading is used for an aperture estimate. Sandy Yes, they have - in response to my questions for an article. It is not rumor and I have no idea why people would think it was removed in firmware. Leica needs to this brightness information to approximate corrections. Cheers, Sean Link to post Share on other sites More sharing options...
pelikan1931 Posted October 16, 2007 Share #15 Posted October 16, 2007 can it also be designed to read the aperture value on the lens? it would be nice to have that value on the exif too. Link to post Share on other sites More sharing options...
sean_reid Posted October 17, 2007 Share #16 Posted October 17, 2007 can it also be designed to read the aperture value on the lens? it would be nice to have that value on the exif too. No, I'm afraid that would require some sort of mechanical or electronic lens coupling that does not exist on M lenses to date. Cheers, Sean Link to post Share on other sites More sharing options...
gearoido Posted October 17, 2007 Share #17 Posted October 17, 2007 Actually, though not specified in the manual, that small window is for inspecting the status of the imager. I know this for a fact as I have spent many hours looking into that very small window. Link to post Share on other sites More sharing options...
J_Brittenson Posted October 17, 2007 Share #18 Posted October 17, 2007 I'm curious why they couldn't use it for flash exposures as well, to approximately set the aperture on an auto flash. Or use it as an auto sensor with a TTL flash in combination with the pre-exposure aperture approximation. Link to post Share on other sites More sharing options...
Guest tummydoc Posted October 17, 2007 Share #19 Posted October 17, 2007 According to Stefan Daniel the blue window houses a brightness sensor that does one thing and one thing only: adjusts the brightness of the viewfinder display diodes according to ambient light. He responded specifically that it does not provide any input for corrections to image parameters whatsoever. Sean, would you please name your source at Leica who gave you your information to the contrary, so I that I may foward it to Stefan? Link to post Share on other sites More sharing options...
marknorton Posted October 17, 2007 Share #20 Posted October 17, 2007 Here is a picture of the metering circuitry. Trace the tracks and you can see centre main metering cell and the "blue-dot" cell both connect to the top integrated circuit. It's reasonable to assume that this is a dual channel logarithmic current to voltage converter so that the main metering and "ambient" metering are handled similarly. The output voltage will be linearly related to EV value sensed by each cell. The main metering cell will be a higher quality device with lower noise, wider dynamic range and more accurate response. Taking the difference between the two outputs (log base 2(ambient) - log base 2(TTL)) and you get a value which is directly related to ratio of light levels and lens f-stop, approximately. For example, if the direct light level was EV 14 and the TTL light level was EV 9, the difference would be 5; raise 2 to the power of the difference and take the square root and you get an estimated aperture value of 5.6. The two photo-diodes either side of the main metering cell are for flash metering and they connect to the integrated circuit on the right which I remember reading was developed specifically for the M8. Not clear what the circuitry bottom right is for, might be sample-and-hold circuitry to capture the brief flash exposure level. Compared to the main metering cells, these have to react extremely quickly to changing light levels. Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/35880-what-is-that-small-circular-window-for/?do=findComment&comment=378955'>More sharing options...
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