Why no f stops on the histogram?

[wag]

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I'm at a loss as to why the histograms don't show f stops in my copy of Lightroom 1.1, when they always appear whenever the program's histograms are shown. It appears below the histogram between focal length and shutter speed. My lenses are coded but aperture never appears. What am I doing wrong.

 

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BW

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[Shootist]

Nothing. The only way for the camera to know what the f/stop is you used for a shot is to have the lens tell the camera. The coding is only used for focal lenght and maximum f/stop of the lens. The lens would need to have a chip in it and electrical contacts between the lens and the camera. Not going to happen with M lenses.

[keithdunlop]

Because Leica M lenses have no electronic communication between the lens and the camera. The lenses are not "chipped" like say a Nikon D lens. My understanding is that the coding only serves to tell the camera what lens is being used so that the correct cyan vignetting in the corners is corrected.

[luigi bertolotti]

I'm at a loss as to why the histograms don't show f stops in my copy of Lightroom 1.1, when they always appear whenever the program's histograms are shown. It appears below the histogram between focal length and shutter speed. My lenses are coded but aperture never appears. What am I doing wrong.

 

_____________________________

 

BW

 

Sorry, just to understand... you write "when they always appear whenever the program's histograms are shown". : I suppose referred to histograms shown in documentation of the SW itself ? I do not think they can appear into a M8 RAW development session: the f stop information simply does not exist in the M8 image engine, for there is no way to acquire the info from the lens: the diaphragm ring on the lens barrel is a pure mechanical device... differently from the mechanical (cammes) and then electronic contacts used in Leica (and others) SLRs.

[wag]

Thanks, I now get it. I think I feel better.

It would have been helpful in understanding the relationship of aperture to shutterspeed.

Even though it's basic, I still struggle with that subject.

 

If I'm correct that AP uses a shutterspeed based on the aperture I've chosen, what criteria

is best used for selecting the appropriate aperture?

 

My apologies if this question is too obvious.

 

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BW

[larry]

Bradford,

 

I hope I'm not misinterpreting your question, but just the basics:

If you want to maintain a higher shutter speed (stop action), use a wide opening (i.e., f2.0).

If you want a slower shutter speed (blur action), use a small opening (i.e., f16).

If you want shallow depth of field (portraiture), use a wide opening.

If you want greater depth of field (landscape), use a small opening.

 

Larry

[luigi bertolotti]

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Bradford,

 

I hope I'm not misinterpreting your question, but just the basics:

If you want to maintain a higher shutter speed (stop action), use a wide opening (i.e., f2.0).

If you want a slower shutter speed (blur action), use a small opening (i.e., f16).

If you want shallow depth of field (portraiture), use a wide opening.

If you want greater depth of field (landscape), use a small opening.

 

Larry

 

... and, Wag, do not forget that for the f stop/time combination choosen in AE mode, you can also easily play also with the ISO sensitivity you can set very quickly in M8... 160/320/640 are all perfectly usable, 1250 is a little noisy (just A LITTLE imho) and 2500 is risky - to be used in extreme situation (want to try the excitation of a shot at 1/8000...)

[wag]

Are AE and AP not the same? And if so. how can one choose the speed if set on AP?

 

I'm beginning to understand the role of aperture now, thank you.

[larry]

Are AE and AP not the same? And if so. how can one choose the speed if set on AP?

 

I'm beginning to understand the role of aperture now, thank you.

 

Bradford,

 

The M8 has only one AE (auto exposure) choice, that's AP (aperture priority). Changing the f-stop will change your shutter speed. Or, use manual: select your shutter speed, then adjust the f-stop to the proper exposure.

 

Larry

[dante]

Nothing. The only way for the camera to know what the f/stop is you used for a shot is to have the lens tell the camera. The coding is only used for focal lenght and maximum f/stop of the lens. The lens would need to have a chip in it and electrical contacts between the lens and the camera. Not going to happen with M lenses.

 

Actually, that's incorrect. You could compute shooting aperture from (1) the maximum aperture (which is discernable from the 6-bit code) and (2) the differential between ambient light (as measured by a lens cell off the lens axis) and what's coming through the lens (via the TTL meter).

 

Leica actually uses the "third eye" on the M8 to do this for correcting vignetting. Leica's claim is that the third eye is not accurate enough to compute the shooting aperture for EXIF purposes.

 

I'm skeptical of that claim. Contax used that same technique (if I recall correctly, on the G2) to compute aperture information for data imprinting. It should get you to the nearest f/stop (or even half f-stop). Obviously, it wouldn't be guaranteed accurate where you hand-coded a third-party lens as a Leica lens of different maximum aperture.

[larry]

Actually, that's incorrect. You could compute shooting aperture from (1) the maximum aperture (which is discernable from the 6-bit code) and (2) the differential between ambient light (as measured by a lens cell off the lens axis) and what's coming through the lens (via the TTL meter).

 

Leica actually uses the "third eye" on the M8 to do this for correcting vignetting. Leica's claim is that the third eye is not accurate enough to compute the shooting aperture for EXIF purposes.

 

I'm skeptical of that claim. Contax used that same technique (if I recall correctly, on the G2) to compute aperture information for data imprinting. It should get you to the nearest f/stop (or even half f-stop). Obviously, it wouldn't be guaranteed accurate where you hand-coded a third-party lens as a Leica lens of different maximum aperture.

 

Dante,

 

I used a very early M8 with firmware 0.64 (if memory serves me correctly) at a demo last October. The metadata showed the f-stops for all the shots I took with a coded 35 f1.4 Lux. So yes, I think you're correct.

 

Larry

[luigi bertolotti]

Intriguing... so there was a "beta" firmware that WROTE the f stop to the EXIF data... I also made Dante's consideration, thinking of the "third eye" role... and wondered why thy didn't add a simple function that, anyway, could have given them another add-on reason to have THEIR coded lenses... a selling argument for them. Strange they have not prosecuted this... maybe the mean grade of precision about the "written" f stop was unsatisfactory... or maybe they thought that many times people use intermediate stops, and this could be really difficult to manage... who knows ?

[Shootist]

Intriguing... so there was a "beta" firmware that WROTE the f stop to the EXIF data... I also made Dante's consideration, thinking of the "third eye" role... and wondered why thy didn't add a simple function that, anyway, could have given them another add-on reason to have THEIR coded lenses... a selling argument for them. Strange they have not prosecuted this... maybe the mean grade of precision about the "written" f stop was unsatisfactory... or maybe they thought that many times people use intermediate stops, and this could be really difficult to manage... who knows ?

 

This is all well and good but it isn't in the firmware we now use. So my answer still stands.

Whether Leica puts this feature back in the firmwarwe is besides the point. At present a guess of what aperture is used is not included. And the reason I say guess is it will always be a guess of what the aperture is. There is no way to read what the true aperture is.

[scott kirkpatrick]

Dante,

 

I used a very early M8 with firmware 0.64 (if memory serves me correctly) at a demo last October. The metadata showed the f-stops for all the shots I took with a coded 35 f1.4 Lux. So yes, I think you're correct.

 

Larry

 

I can't find my copies of very early .DNG files (the lady with the HP badge at PhotoKina, some of RPOttaviani's pictures in his magazine) which were taken with firmware 1.06x or even earlier. They may be on a backup somewhere, but I would appreciate it if anyone who still has these could send me the DNG's. Or a pointer to where they have been posted on the LUF. I believe the information about guesstimated aperture is still in the EXIF, just moved to a harder to read place.

 

scott

[luigi bertolotti]

Ok, Shootist, you're sure correct; as often happens, a thread starts with a question and then goes its own way... I simply felt curious about this issue of the "ur firmware" that calculated and wrote the stops.

[Shootist]

Ok, Shootist, you're sure correct; as often happens, a thread starts with a question and then goes its own way... I simply felt curious about this issue of the "ur firmware" that calculated and wrote the stops.

 

 

Right the older.original firmware did that but I guess Leica decided to remove it because it wasn't accurate.

 

Luigi I'm not trying to start a argument. None of the M8's Ive had wrote the f/stop used for the image.

[dante]

And the reason I say guess is it will always be a guess of what the aperture is. There is no way to read what the true aperture is.

It might be an approximation of the aperture (f/stop), but it would be a pretty good measurement of the T/stop of the lens.

[carstenw]

Scott, I still have that image, but it doesn't appear to have any extra info. I can send it to you. I am not sure if my version is original, because it is only 5 MB...

 

The reason for not using the blue eye is probably that it has a fixed "focal length", and so depending on the focal length of the lens, the guess can be arbitrarily bad, because the eye may not see half of the present information, or it may see too much, both of which could dramatically change the perceived f-stop.

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[scott kirkpatrick]

Scott, I still have that image, but it doesn't appear to have any extra info. I can send it to you. I am not sure if my version is original, because it is only 5 MB...

 

The reason for not using the blue eye is probably that it has a fixed "focal length", and so depending on the focal length of the lens, the guess can be arbitrarily bad, because the eye may not see half of the present information, or it may see too much, both of which could dramatically change the perceived f-stop.

 

5MB sounds like it has been through ACR and restored to what Adobe considers a basic standard DNG form. That reprocessing has side effects on the metadata.

 

The "guesstimated" aperture, as someone mentioned above, does a fine job of measuring the T-stop, or actual transmission, of the lens as long as the scene is uniformly illuminated, since it is the comparison of two wide spotmeter readings, one fixed focus and the other depending on whatever the lens is. I wouldn't think it would be very useful for available light work, but I've checked on outdoor scenes with the M8 and a 24 or 35mm lens and it tracks the actual aperture perfectly. The information is currently in the MakerNotes and is hard to pull out. Adobe reprocessing leaves out the MakerNotes in this case.

 

scott

[larry]

Scott,

 

I tried to find the files I shot at the demo, but with no luck -- must have tossed them. Another unusual thing I remember about these shots was the 20-meg RAW file size.

 

Larry