[Mark DeB]

Hi, I am a beginner learning all about histograms. As an experiment, I took a photo of a gray card, pretty much filling the frame, and I got the histogram attached. I am surprised that the spike is so far to the left, but should I be? Is that the way my camera is designed to work? I would have thought that the meter would put the average value closer to the middle. (If I understand correctly, IrfanView is telling me that the midpoint of the spike is around 82 on a scale from 0 to 255.)

I am using a *ist DS2, FA 50 f/1.4 lens (also tried manual A lens, not much difference). Set ISO to 200, white balance to Daylight. Aperture at f/1.4, Av mode. Center-weighted metering. Had camera on MF, manual focusing.

If this is unusual, maybe it's because I'm using a KatzEye focusing screen (not Optibrite).

So, basically, I am wondering whether my camera is metering as intended. Is it normal for a DSLR (or a Pentax DSLR) to meter in such a way that this is the histogram that results, in these circumstances? I realize that this is kind of an elementary question. I did do a search, but I wasn't able to find an answer, so thanks in advance!

Mark

Attached Images

   

[ProfessorBuzz]

With an 18% grey card, it will come in a bit below the midpoint (I would expect around 111-127), assuming the light source illuminating the card is daylight (eg sunshine, 5000K).

If you have a different light source, it's spectra will be different. eg it's probably a "warmer" color light source, giving you higher red values.

It also depends on whether the camera is set to AdobeRGB or sRGB (web) color space.

One time shooting, I was wearing a red sweater, and it was reflecting on the surface I metered. So white balance was off. I felt like such an idiot for not figuring it out at the time!

[photoptimist]

Yes, changing the focusing screen will affect meter through the viewfinder. Focusing screens with split-circles can let in more light while the exact texture of the 3rd-party screen could be darker or brighter than the original screen. Spot metering will be the most affected metering mode. (You can assess the amount by comparing the optical viewfinder metering value to the live-view metering value).

Also, the shape of the histogram will be smeared to the dark side if the lens has vignetting (which likely on a 50 f/1.4 being used wide-open).

[rogerstg]

And, the histogram represents the jpg, so in-camera processing such as saturation, brightness, etc will be reflected in the histogram.

[Mooncatt]

One time shooting, I was wearing a red sweater, and it was reflecting on the surface I metered. So white balance was off. I felt like such an idiot for not figuring it out at the time!

Try shooting while wearing a high viz orange shirt. That's something I'll never do again. Lol

[Mark DeB]

With an 18% grey card, it will come in a bit below the midpoint (I would expect around 111-127), assuming the light source illuminating the card is daylight (eg sunshine, 5000K).

If you have a different light source, it's spectra will be different. eg it's probably a "warmer" color light source, giving you higher red values.

It also depends on whether the camera is set to AdobeRGB or sRGB (web) color space.

One time shooting, I was wearing a red sweater, and it was reflecting on the surface I metered. So white balance was off. I felt like such an idiot for not figuring it out at the time!

Thanks, that's what I thought, like around 120, and this is well below it. The light was daylight coming in through the window. The camera is set to sRGB. I think that the card is an 18% card--I probably got it at a camera store years ago--but it shouldn't matter, right? It can be a 12% card, or a 90% card, and it should come out the same, correct? I turned the card over to the white side, and the histogram was approximately the same.

---------- Post added 12-11-22 at 11:26 PM ----------

Yes, changing the focusing screen will affect meter through the viewfinder. Focusing screens with split-circles can let in more light while the exact texture of the 3rd-party screen could be dark or brighter than the original screen. Spot metering will be the most affect metering mode. (You can assess the amount by comparing the optical viewfinder metering value to the live-view metering value).

Also, the shape of the histogram will be smeared to the dark side if the lens has vignetting (which likely on a 50 f/1.4 being used wide-open).

OK thanks. Yes, that's what I have read, that the screens can affect metering, but I'm wondering whether this would be normal anyway, or whether we should say that it's off and probably because of the screen. About the vignetting, if there is a light drop-off, then won't the meter compensate for that, and make the whole picture lighter? It doesn't know that there's vignetting, am I understanding this correctly?

[StiffLegged]

You’re over-thinking this. Grey card metering generally uses an 18% grey card, so where would you expect a camera’s meter to place it? At around 18% on the histogram, not the middle. That’s what it’s supposed to be calibrated to.

A grey card image with the peak at 50% would have it at 100% by just doubling the exposure time. That’s pure white. A quick experiment will show that’s not what happens in real life.

[steephill]

When your camera was new there was a raging debate on DPR about this, I may not remember this correctly but there seemed to be two different sets of results for the same camera models, one batch peaked to the left and the other batch had a more central peak. There were lots of competing theories such as Pentax were deliberately underexposing to preserve highlight headroom. There was also a lot of noise about whether the original Kodak grey card was 12%, 17% or 18% reflectance. It also opens up the can of worms that is ETTR - expose to the right. The pragmatic solution is to use the EV compensation on your camera to get the histogram placed where you want it.

[photoptimist]

OK thanks. Yes, that's what I have read, that the screens can affect metering, but I'm wondering whether this would be normal anyway, or whether we should say that it's off and probably because of the screen. About the vignetting, if there is a light drop-off, then won't the meter compensate for that, and make the whole picture lighter? It doesn't know that there's vignetting, am I understanding this correctly?

"Center-weighted" metering, by definition, pays less attention to the dark vignetted corners in calculating the exposure.

There's also some complex optical interactions between large aperture lenses (e.g., an f/1.4 lens) and the surface of focusing screen. The exact percentage of light from each bit of the scene, coming through the lens, refracting/diffusing on the focus screen, and reaching the light meter can vary with lens design and f/stop. Thus vignetting on the focusing screen may be different than the vignetting on the image.

[normhead]

It would be so much easier to just show us an image. Regardless of what the histogram shows, a good picture is still a good picture.

[normhead]

I'm still not seeing much in the way of images...so I'll just add my two bits....



Taken with my *istD. If you're getting decent images, I wouldn't worry about the histogram. If you're not, then we can't tell from a histogram why you are not.

[Mark DeB]

When your camera was new there was a raging debate on DPR about this, I may not remember this correctly but there seemed to be two different sets of results for the same camera models, one batch peaked to the left and the other batch had a more central peak. There were lots of competing theories such as Pentax were deliberately underexposing to preserve highlight headroom. There was also a lot of noise about whether the original Kodak grey card was 12%, 17% or 18% reflectance. It also opens up the can of worms that is ETTR - expose to the right. The pragmatic solution is to use the EV compensation on your camera to get the histogram placed where you want it.

Thank you--I saw some of this but I didn't know about the different batches. Much appreciated.

---------- Post added 12-12-22 at 11:00 AM ----------

I'm still not seeing much in the way of images...so I'll just add my two bits....



Taken with my *istD. If you're getting decent images, I wouldn't worry about the histogram. If you're not, then we can't tell from a histogram why you are not.

That is a great picture!

---------- Post added 12-12-22 at 11:05 AM ----------

"Center-weighted" metering, by definition, pays less attention to the dark vignetted corners in calculating the exposure.

There's also some complex optical interactions between large aperture lenses (e.g., an f/1.4 lens) and the surface of focusing screen. The exact percentage of light from each bit of the scene, coming through the lens, refracting/diffusing on the focus screen, and reaching the light meter can vary with lens design and f/stop. Thus vignetting on the focusing screen may be different than the vignetting on the image.

That is interesting about the interaction with the focusing screen. Certainly my use of a third-party screen introduces a new variable!

[Bob 256]

The primary use of the histogram is to make sure the photo's brightness range is not being clipped on the top or bottom ends. If it's all mushed to the left or all mushed to the right, that means you are probably losing some of the shadow or highlight detail, respectively. Shooting a gray card tells you little, so as mentioned in many of the posts above, it is usually of more importance in actual photos for making sure you aren't losing shadow or highlight information (and even then, there are exceptions that you can live with).

[BWG]

When your camera was new there was a raging debate on DPR about this, I may not remember this correctly but there seemed to be two different sets of results for the same camera models, one batch peaked to the left and the other batch had a more central peak. There were lots of competing theories such as Pentax were deliberately underexposing to preserve highlight headroom. There was also a lot of noise about whether the original Kodak grey card was 12%, 17% or 18% reflectance. It also opens up the can of worms that is ETTR - expose to the right. The pragmatic solution is to use the EV compensation on your camera to get the histogram placed where you want it.

I was a new digital photographer around then with my Pentax *istDL. The way I remember it, the “discussion” got pretty heated for the DPR forum at that time (it was generally friendly forum). I learned a lot about histograms from that forum thread.

[Lowell Goudge]

The *istDxx series cameras metered much better than this. With average greyscale being between 100 and 120 for F1.4 through F5.6.

Are you sure there is no ev compensation set or auto bracketing, with first shot under exposed?

As far as impact, it depends on what you are hoping for this level of under exposure isOK if you really want detail in any highlights, but it is about 1 full stop under exposed