Digital Spot Meter

[williamtheis]

here goes a rant: I use a Betterlight (BL) back and I use film with a spotmeter. When taking a picture, you need to set the exposure: shutter speed (line capture time on BL) and the f/stop on the lens. If you knew L, you still don't know how to set these values in the field. the usual number used is the "EV" or exposure value that is translated into these quantities and you usually measure such that you don't block up either the high or low values (true for film, true for BL) unless your'e on of them digital HDR guys.... the fact that the Minolta will display L does not mean it is useful in the field even with a tethered Laptop like I have with the BL since the time to open an image and convert to LAB (YES the CAPTURE is RGB, just like film... it does not natively capture in LAB--this is true of conventional dSLRs as well) takes so long that knowing the values is not truly useful. Theoretically, you could analyze the L values to see that something is not blocked up and adjust the shutter speed/capture time or the f/stop to refine it but you can do the same with the EV scale... just MHO

[bob carnie]

I am having my business partner look into this on the phase, You are absolutely right , he knows he can give me RGB values, and he will see how long it takes to covert to LAB to see the numbers... Probably the time it takes is not practical.
I am interested in the Betterlight as I think it has many attributes that are compelling to me.

I am moving into a whole new area of print making where each process will have aimpoint specifics , whether RGB, Greyscale or in my preferred LAB.
most of my output require RGB but I look at the L numbers for working in PS.

I would love to be able to purchase some type of high end back that allows me to see the numbers from beginning to end.

Please excuse my ignorance , but how exactly does the EVscale spot meter work , will it give you readings in a 0-100 scale??

here goes a rant: I use a Betterlight (BL) back and I use film with a spotmeter. When taking a picture, you need to set the exposure: shutter speed (line capture time on BL) and the f/stop on the lens. If you knew L, you still don't know how to set these values in the field. the usual number used is the "EV" or exposure value that is translated into these quantities and you usually measure such that you don't block up either the high or low values (true for film, true for BL) unless your'e on of them digital HDR guys.... the fact that the Minolta will display L does not mean it is useful in the field even with a tethered Laptop like I have with the BL since the time to open an image and convert to LAB (YES the CAPTURE is RGB, just like film... it does not natively capture in LAB--this is true of conventional dSLRs as well) takes so long that knowing the values is not truly useful. Theoretically, you could analyze the L values to see that something is not blocked up and adjust the shutter speed/capture time or the f/stop to refine it but you can do the same with the EV scale... just MHO

[tlitody]

I know you want to control the L value but apertures only go in one third stop and time in one third stop increments. When camera is in auto mode you may be able to control it finer but I'm not sure about digital backs. The lens is not always connected for control by camera back settings. What I'm saying is that whilst you have very fine aim points, the limitations of setting lens and shutter controls may not allow it. Therefore controls as they already exist have to be lived with. You can probably adjust exposure to be within limits but that is no more than you can already do if you know what you are doing with a standard spot meter.

[bob carnie]

Thanks

I know my ignorance in Spot meters is showing, I am looking for 1point accuracy within a 0-100 scale.

bob

I know you want to control the L value but apertures only go in one third stop and time in one third stop increments. When camera is in auto mode you may be able to control it finer but I'm not sure about digital backs. The lens is not always connected for control by camera back settings. What I'm saying is that whilst you have very fine aim points, the limitations of setting lens and shutter controls may not allow it. Therefore controls as they already exist have to be lived with. You can probably adjust exposure to be within limits but that is no more than you can already do if you know what you are doing with a standard spot meter.

[williamtheis]

1/3 stop on f/stop, factors of two (1/25, 1/50, 1/100, ...) on the shutter for film, slightly better for the betterlight since scan times are 1/8 sec, 1/10, 1/15, ...

nothing approaches 1 part in 100 and it is not necessary to get the capture to this accuracy IMHO. you should do setting of final endpoints in CMYK or RGB but LAB is a little too brute force. (yes, I am VERY VERY VERY familiar with LAB having taking Dan Margulis's classes)

EVs are for 0 to about 20, each represent a doubling but spot meters conveniently read in 1/3 EV (so 2 1/3 is 1/3 stop more than 2) which matches lenses but not shutters

[bob carnie]

I know I am nitpicking here and asking for something that is probably not required.
I am just concerned about the top five shades of highlight detail and the bottom five shades of shadow detail.
I have never used a spot meter and do not own a camera with a meter , other than the phase that is available to me , which btw I have no idea how to work.
So taking my preference of LAB numbers out of the equation, my probable naive goal is to find a system that can give me exacting measurments that I can then transfer to print.
Thanks for your explanation on EVs.

1/3 stop on f/stop, factors of two (1/25, 1/50, 1/100, ...) on the shutter for film, slightly better for the betterlight since scan times are 1/8 sec, 1/10, 1/15, ...

nothing approaches 1 part in 100 and it is not necessary to get the capture to this accuracy IMHO. you should do setting of final endpoints in CMYK or RGB but LAB is a little too brute force. (yes, I am VERY VERY VERY familiar with LAB having taking Dan Margulis's classes)

EVs are for 0 to about 20, each represent a doubling but spot meters conveniently read in 1/3 EV (so 2 1/3 is 1/3 stop more than 2) which matches lenses but not shutters

[tlitody]

I know I am nitpicking here and asking for something that is probably not required.
I am just concerned about the top five shades of highlight detail and the bottom five shades of shadow detail.
I have never used a spot meter and do not own a camera with a meter , other than the phase that is available to me , which btw I have no idea how to work.
So taking my preference of LAB numbers out of the equation, my probable naive goal is to find a system that can give me exacting measurments that I can then transfer to print.
Thanks for your explanation on EVs.

Basically the zone system or variant will do it. What you do is find a flat evenly illuminated surface which is a mid grey. Doesn't have to be exactly 18% but just middleish grey. Could be another middling colour. Nothing to vibrant or dark.
Align camera with it and focus. 10ft away should be plenty. Then standing behind camera point spot meter at centre of surface and take a reading. If reading says for example 125th sec at f8, then set digital camera to 7 stops less exposure than that. So that would be 1000th at f32. make image at that exposure. Then open up 1/3rd stop and make image. Repeat another 7 times. Then set exposure to intial reading + 7 stops and make exposure. So that would be 1/8th at f2.8. Then close down 1/3 stop and make image. Repeat another 7 times.
Now you have 18 images. open in PS and check which of the dark ones is the first one with an L value higher than your low limit. You can then work out how many stops that is from the metered reading. So it may be 5 1/3rd stops for example. You now know that whatever you meter that you can't close down more than 5 1/3 stops without it going out of range. You then find from the light images which is the first image which is within your range. Say that is also 5 1/3rd stops more exposure than your metered reading for example. So now you know that whatever you meter, you can't open up more than 5 1/3rd stops without it going out of range.
You also now know that you have 10 2/3 stops useable dynamic range with detail if your end points in printing show detail at those high and low values.
You should then always be within a 1/3 stop of your high or low value. And given that 10 2/3 stops is 32/3 and each 1/3 is approx 3% of that, then you should always be between 0 and 3 points of hitting either your high or low target values which is pretty darn close for most practical purposes. And if you take the mean, then on average you will be within 1.5 points of hitting your target values. If that is not close enough for you then I think you will have to do your photography in Lab conditions (pun intended).

It then becomes easy to check if you are in range. You may have to change levels a tad in PS but thats OK. You can also make decisions where in the dynamic range to put the exposure if the subject is say only 6 stops in range. You can pick higher key or lower key in the knowledge that you are staying within your limits.

essentially all you have done is to check the dynamic range of your camera sensor and provided yourself with limits on playing with exposure. Basically thats zone system metering only in digital you don't control it through film speed and development like you do with film. Call it the zone system for digital.

Note I have assumed the dynamic range of your camera is at least 10 2/3rd stops. It may be less in which case you should do the repeats an additional 3 times at each end and that would give values for a sensor with only 8 2/3 stops dynamic range.
Also the lighting and camera position must constant through the test.
And also if you use daylight for the test then the test is only valid for daylight. If you use tungsten then its valid only for tungsten etc. So don't use strobes for the test if you are going to be shooting in daylight.

So then if you are photographing storm clouds you just meter the absolute lightest part of the clouds and open up 5 1/3 stops from that reading and expose. Of course check that deepest shadow is not more 10 2/3 stops less than metered reading of clouds and if it isn't then all will be in range and you can adjust shadows with levels to get to your low point of 4.
A digital spot meter can tell you this. The minolta spot meter or spotmeter F allows you to store the initial reading and then scan the subject telling you the number of stops difference from the original reading in 1/10th stop increments. i.e. it is very accurate.

[bob carnie]

Wow, I am impressed
thank you for that thats a lot of info to digest. I made ring arounds in College that were of the same scope, I am going to ask for a spot meter for christmas.

[tlitody]

Wow, I am impressed
thank you for that thats a lot of info to digest. I made ring arounds in College that were of the same scope, I am going to ask for a spot meter for christmas.

Yes but you only have to do this once for any lighting type and then you have the limits of you sensor. Not sure what you will find.

[D. Bryant]

A digital spot meter can tell you this. The minolta spot meter or spotmeter F allows you to store the initial reading and then scan the subject telling you the number of stops difference from the original reading in 1/10th stop increments. i.e. it is very accurate.

Minolta meters are no longer manufactured though Kenko purchased the rights to that product line and markets meters under their name.

I prefer Sekonic meters though I still use my Minolta Flash Meter II for B&W work; it is durable, very feature rich and relatively inexpensive on the used market.

As for connecting LAB values to exposure meter readings - I just don't see the point. To each their own. Once you can predict how and how well a sensor will record light, metering becomes straight forward.

Do digital backs use LAB color space? Perhaps I'm just ignorant. Since I primarily use ACR/Lightroom3 for RAW processing I have adopted xRite ColorChecker to calibrate my cameras and as a WB tool. I wish Capture One Pro would support DNG profiles for that reason. I think C1P is perhaps the best image processing utility around, particularly for RAW processing. I know from experience the output scaling works better than Adobe's for 10 to 12x enlargements (don't know about bigger personally but I've heard that it is awesome.)

LAB in post can be very powerful but there are certainly split camps out there about it's utility as a way of living.

Don Bryant