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09-18-2016, 10:06 PM   #1
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Spot metering and following AF Active Area 11 point grid?

So.. on the weekend I had a couple of gigs to attend to that I knew were going to be tricky lighting scenarios. One was my daughters ballet concert which involved black backgrounds and brightly lit dancers, the other a 'Science at the Local' event that features local scientists from around Sydney coming to give talks about their field of work among some the boozing locals

Ballet; Ballet | Flickr

Science at the local; Science at the Local | Flickr

(both albums are organised with newest ie this past weekends events as showing first).

The equipment used was my K-50 and either the 50mm 1.8 pentax smc or the 100mm 2.8 FA Macro lens (should tell you in the description of each pic etc). I set to TAv, with iso on Auto up to 3200.

Now my question is this. I had set my AF to being that 11 point active area, I even have my Raw/FX button to allow a quick toggle of where to place my focus point. Often I set the focus point to being top right or top middle, or even furthest right (near the edge of the screen), but I also had Spot Metering selected.
When using Spot metering, is it doing 'it's thing' only when the focus point is dead centre (ie the middle red square in that 11 point grid), or does it do the spot metering thing from where you choose the focus point to being in that AF Active Area grid?

I just felt as tho when aiming the camera at the subject, the iso blinking thing would be happening, like warning me its gonna be over or under exposed etc, yet the pics came out ok, often the iso of the photo perhaps being 2000 or so etc. I found myself (for the first time) just kinda ignoring any 'warnings' it was sending out, like I couldn't trust what it was tell me, not when I was shooting like this way...

So I found myself not really sure what aperture to set at, I think for some shots I coulda aimed much higher, but I was scared to because the camera was alerting me to such that it might not be a great pic.
I had review of picture for just 1 second, enough for me to have a quick look and see if everything looked ok, and basically just kept going, and then of course LR after to fix some things.

What could I have done better for this kinda scenario?

Cheers,

Bruce

09-18-2016, 11:37 PM - 1 Like   #2
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QuoteOriginally posted by BruceBanner Quote
When using Spot metering, is it doing 'it's thing' only when the focus point is dead centre (ie the middle red square in that 11 point grid), or does it do the spot metering thing from where you choose the focus point to being in that AF Active Area grid?
Unless you have set the metering to follow the focus point, the two systems work quite independently and even then I don't believe that feature works for the spot setting. That being said, I will share the usual spot metering bit:
  • There is nothing special or more accurate about spot metering
  • There is a significant risk of poor exposure with spot metering
  • Unless you have a reason to use spot metering and understand how to leverage the feature, it is not a good setting to use
The second point is the one that is critical to understand. The spot reading will result in exposure to that point to a middle gray value. That will work great if the spot is gray and not so great if it is white or black. For most scenes, the last two cases will result in gross underexposure or gross overexposure, respectively. That is why the conventional advice on this site is to use matrix metering unless you have good reason to use something else.

When is it appropriate to use the spot meter? I can give you a textbook example:

Subject is a dimly-lit stage with a dark wood table at right of center, a white cat on the table, and a narrow spot light on the cat. Your task is to preserve the details of the cat's fur while making sure that it looks white. With spot metering, the task is simple. Set exposure compensation to +3 and spot meter on the white cat. Use exposure lock, recompose, and take the photo. In the resulting image, the cat should be nicely white with detail in the fur and the rest of the scene should follow by being nicely dark.

If you had used matrix, the camera may have guessed your intent or maybe not. Most likely is a 1-1.5 stops overexposure with a blown out cat. If you where using spot metering to the (darkened) center of the stage, the overexposure would have been about 5 stops and the cat would have been a white blob. Not good.


Steve

Last edited by stevebrot; 09-18-2016 at 11:43 PM.
09-23-2016, 05:10 PM   #3
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So... consider this picture below;



If focus point is far right (red circle), and I have spot metering selected, then is the spot metering doing it's 'thing' from that point or is it calculating from the center (blue circle)?
09-23-2016, 05:20 PM   #4
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The spot meter ALWAYS measures the blue circle. It's best used with AE-L or the green button in M mode to set an exposure (often in conjunction with an EV adjustment) before composition, focus, and firing.

It's really powerful for some situations, but it's easy misuse, forget its active and ruin shots, etc.

P.S. As stevebrot said, the spot meter doesn't analyze the spot, figure out there's a white cat on a black tabletop, and adjust. Instead, it simply assumes you want whatever is in that spot to be 18% in the final photo. If what is in the spot is meant to be brighter or darker than 18%, then EV adjust is used.


Last edited by photoptimist; 09-23-2016 at 05:28 PM.
09-23-2016, 05:29 PM   #5
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QuoteOriginally posted by photoptimist Quote
The spot meter ALWAYS measures the blue circle. It's best used with AE-L or the green button in M mode to set an exposure (often in conjunction with an EV adjustment) before composition, focus, and firing.

It's really powerful for some situations, but it's easy misuse, forget its active and ruin shots, etc.
I got lucky then I guess with my pics over last weekend as I was treating it as such that the spot metered where I had the focus point selected in that 11 grid!
I don't normally focus with center then reframe the shot as I shoot sometimes high apertures (2.8 etc) and I know that even moving the camera slightly can skew the focus point and make the shot blurry...
I have to admit I don't use the AF/AE-L button at all... guess now's the time to start practicing...

Talking of practice, I wish there were actual specified practice scenarios/tutorials for noobies like me to try and get to grips with things haha.
09-23-2016, 07:29 PM   #6
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A couple more thoughts:

1. Check if your camera has "Link AE and AF Point" which uses the regular matrix metering setting but selects the data according to the AF point selection.

2. If you are lucky and the stage lighting is fairly uniform and does not change much during the performance, you can spend the first few photographs finding a good setting (one in which the lightest person/costume under the brightest part of the lighting is NOT overexposed) and then stay with that setting for the rest of the performance.
09-23-2016, 09:21 PM   #7
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QuoteOriginally posted by photoptimist Quote
A couple more thoughts:

1. Check if your camera has "Link AE and AF Point" which uses the regular matrix metering setting but selects the data according to the AF point selection.

2. If you are lucky and the stage lighting is fairly uniform and does not change much during the performance, you can spend the first few photographs finding a good setting (one in which the lightest person/costume under the brightest part of the lighting is NOT overexposed) and then stay with that setting for the rest of the performance.
I checked and mine was set to '1' ie not enabled.

Are you saying therefore if I set that setting to '2' (ie enabled) then how I was shooting ie select a different focus point on 11 grid, then the spot meter would take effect from that point?

It seems like the K-50 has given the user two ways to do it, either capture the subject in the middle, use the AF/AE-L button, then reframe, or enable that 'link' feature and do as I was doing?

Have i understood that right?
09-24-2016, 06:59 AM   #8
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QuoteOriginally posted by BruceBanner Quote
I checked and mine was set to '1' ie not enabled.

Are you saying therefore if I set that setting to '2' (ie enabled) then how I was shooting ie select a different focus point on 11 grid, then the spot meter would take effect from that point?

It seems like the K-50 has given the user two ways to do it, either capture the subject in the middle, use the AF/AE-L button, then reframe, or enable that 'link' feature and do as I was doing?

Have i understood that right?
I've never used the mode myself but I'm glad stevebrot mentioned it.

First, it's really important to realize that the "spot meter" is a physical light detector that only measures light in small area in the very center of the viewfinder. There's no way to change where it looks in the scene.

The "multi-segment meter" is a bigger light sensor with an array of detectors (77 of them probably in a 7x11 grid in the case of the K-50). Generally speaking (and with the link setting disabled), the camera's computer looks at all 77 measurements and automagically tries to estimate the best exposure. You can think of the matrix meter as a tiny 77 pixel thumbnail photo and the computer is trying figure out whether the image has bright white, pitch-black, or various middle gray parts and then adjust the exposure settings to get the image right. Matrix metering has gotten better and better over the years, but it can still make mistakes (e.g., a small ballerina in a bright-white costume on a very dark stage). And matrix metering does not factor in artistic choices such as high-key and low-key where the photographer is creating some dramatic overall brightness or darkness in the scene.

If you enable linking and use the multisegment light meter, the exposure computer will preferentially use multisegment light meter data from the segments near the focus point. It's not really a true spot meter and it's not using the physical spot meter but it will probably do a better job than the multisegment light meter would without linking. I strongly advise you experiment with the link enabled because I don't know exactly how the camera behaves. Put on a wide-angle lens, go into a dark room with a single desk lamp lighting up a small part of the wall or part of a table, and try the various metering modes. Pay attention to how the exposure value changes as the brightly lit part of the scene moves into the frame, across the focus points, or across the center spot meter.

A huge part of photography is in learning how your equipment handles light. Although books, friends, and PF can give you lots of tips and ideas, the specifics of your camera, your lenses, your scenes, and your photographic interests mean that you really have to try it for yourself to learn how to accomplish what you want to accomplish with your equipment.

09-24-2016, 05:39 PM - 1 Like   #9
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QuoteOriginally posted by photoptimist Quote
I've never used the mode myself but I'm glad stevebrot mentioned it.

First, it's really important to realize that the "spot meter" is a physical light detector that only measures light in small area in the very center of the viewfinder. There's no way to change where it looks in the scene.

The "multi-segment meter" is a bigger light sensor with an array of detectors (77 of them probably in a 7x11 grid in the case of the K-50). Generally speaking (and with the link setting disabled), the camera's computer looks at all 77 measurements and automagically tries to estimate the best exposure. You can think of the matrix meter as a tiny 77 pixel thumbnail photo and the computer is trying figure out whether the image has bright white, pitch-black, or various middle gray parts and then adjust the exposure settings to get the image right. Matrix metering has gotten better and better over the years, but it can still make mistakes (e.g., a small ballerina in a bright-white costume on a very dark stage). And matrix metering does not factor in artistic choices such as high-key and low-key where the photographer is creating some dramatic overall brightness or darkness in the scene.

If you enable linking and use the multisegment light meter, the exposure computer will preferentially use multisegment light meter data from the segments near the focus point. It's not really a true spot meter and it's not using the physical spot meter but it will probably do a better job than the multisegment light meter would without linking. I strongly advise you experiment with the link enabled because I don't know exactly how the camera behaves. Put on a wide-angle lens, go into a dark room with a single desk lamp lighting up a small part of the wall or part of a table, and try the various metering modes. Pay attention to how the exposure value changes as the brightly lit part of the scene moves into the frame, across the focus points, or across the center spot meter.

A huge part of photography is in learning how your equipment handles light. Although books, friends, and PF can give you lots of tips and ideas, the specifics of your camera, your lenses, your scenes, and your photographic interests mean that you really have to try it for yourself to learn how to accomplish what you want to accomplish with your equipment.
I was thinking this would be the case, I intend to try this soon and see the different results, perhaps even post my findings in this post.

Once again thanks for the replies, feedback and suggestions =)
09-25-2016, 09:48 AM   #10
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QuoteOriginally posted by photoptimist Quote
1. Check if your camera has "Link AE and AF Point" which uses the regular matrix metering setting but selects the data according to the AF point selection.
I too have never used that feature (see further comment below), but it was my understanding that it is not available in AF select mode. I don't have a K-50 in hand, but on my K-3, the exposure does not follow the AF point in "SEL 1" mode.

Edit: I took some time to do a bit deeper testing and was wrong with my original assessment. AE metering will follow the AF point in all AF point modes in with multi-segment metering. I did not test for center-weighted or spot.

QuoteOriginally posted by photoptimist Quote
It's not really a true spot meter and it's not using the physical spot meter but it will probably do a better job than the multisegment light meter would without linking. I strongly advise you experiment with the link enabled because I don't know exactly how the camera behaves.
What you describe is true, but will result in the same potential problems as center spot metering, that being the camera will adjust whatever is in focus to middle gray. The advice to experiment is a good one, it may well be that the feature suits the OP's work flow well.


Steve

Last edited by stevebrot; 09-25-2016 at 02:27 PM.
09-25-2016, 01:29 PM   #11
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QuoteOriginally posted by stevebrot Quote
I too have never used that feature (see further comment below), but it was my understanding that it is not available in AF select mode. I don't have a K-50 in hand, but on my K-3, the exposure does not follow the AF point in "SEL 1" mode.
I'd don't have a K-50, but a few quickie/informal tests on the K-1 seemed to have the following behavior (using a 12mm lens, TAv mode, watching the ISO vary as I panned around a room that had both dark objects and bright windows):

1) The exposure did track the focus point even in "SEL 1" mode on the K-1. In fact, the exposure reading changed as I bumped the AF point across the frame which is kind of a cool feature if one has the camera locked down on a tripod but then wants to double-check the EVs in different parts of the image (e.g., zone system work on a landscape around sunrise/sunset)

2) In AE set to "Multi-Segment" mode, the AE logic seemed to evaluating the scene around the focus point rather than going strictly by the EV directly under the focus point.

3) Contrary to what I said (and what I expected), "Spot Meter" mode also tracked the focus point but the AE logic seemed use an extremely narrow measurement which would have the problem you mention if what's under the focus point is not 18% gray.

NOTE: I didn't try all the AF settings or AE modes, I didn't use an independent light meter to cross-check, and I didn't actually take any pictures. Also, this is on the K-1.

QuoteOriginally posted by stevebrot Quote
I
What you describe is true, but will result in the same potential problems as center spot metering, that being the camera will adjust whatever is in focus to middle gray. The advice to experiment is a good one, it may well be that the feature suits the OP's work flow well.


Steve
Good point!

Modern AE systems come with two curses. The first is that AE is usually so good that it's easy to get lazy, not pay attention to AE's likely interpretation of the scene, and get blown highlights or dark pictures.

The second curse is that it's too easy for first-time photographers to get good pictures without learning what the AE system is doing and how the AE system is setting exposure with the expectation that it's looking at something is 18% gray or might be affected by large bright or dark areas.

That said, "Multi-Segment" + "link" + selective AF would probably do a decent job of metering the tiny bright ballerina on big dark stage scenario.
09-25-2016, 01:48 PM   #12
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It might be the K-50 works like the K-5. And there the spot metering following the Af point chosen only
y worked in Matrix metering mode and with reduced weighing.
Just from the K-3 and K-1 I know that you definitely can have spot metering selected and then have the af point be the center of metering.
But that is actually in the manual for the custom setting. on k-5 there was mentioned it only worked in matrix.
09-25-2016, 02:22 PM   #13
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QuoteOriginally posted by photoptimist Quote
I'd don't have a K-50, but a few quickie/informal tests on the K-1 seemed to have the following behavior (using a 12mm lens, TAv mode, watching the ISO vary as I panned around a room that had both dark objects and bright windows):

1) The exposure did track the focus point even in "SEL 1" mode on the K-1. In fact, the exposure reading changed as I bumped the AF point across the frame which is kind of a cool feature if one has the camera locked down on a tripod but then wants to double-check the EVs in different parts of the image (e.g., zone system work on a landscape around sunrise/sunset)

2) In AE set to "Multi-Segment" mode, the AE logic seemed to evaluating the scene around the focus point rather than going strictly by the EV directly under the focus point.

3) Contrary to what I said (and what I expected), "Spot Meter" mode also tracked the focus point but the AE logic seemed use an extremely narrow measurement which would have the problem you mention if what's under the focus point is not 18% gray.
Wow! That is a significant departure from what I thought I saw on the K-3. It occurred to me that maybe I did not structure the test properly, so I went back and did another look-see and things are as you describe. I did not test the case for spot metering, but will assume it is the same on the K-3 as what your observed. I am not sure, but with multi-segment metering, it appeared that the full frame was evaluated, though with weight given to the AF point. Clearly this feature will require experimentation, though I can see some obvious applications where face exposure is critical, for example.


Steve
09-25-2016, 02:33 PM - 1 Like   #14
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QuoteOriginally posted by photoptimist Quote
The first is that AE is usually so good that it's easy to get lazy, not pay attention to AE's likely interpretation of the scene
You are so, so right. The system on the K-3 seems to have an uncanny ability to meter difficult lighting situations. I won't post the photo here, the link below goes to a "blue hour" photo of a lighted bridge. It is a straight shot with no EC needed.

High Strung | Nighttime on Portland's newest bridge. (Straig? | Flickr


Steve
09-25-2016, 02:40 PM   #15
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QuoteOriginally posted by beholder3 Quote
Just from the K-3 and K-1 I know that you definitely can have spot metering selected and then have the af point be the center of metering.
But that is actually in the manual for the custom setting.
??? I looked in the K-3 manual to find where this is explicitly state but with no luck. It is implied though. The K-1 manual completely lacks detail documentation on the feature. For the K-50, the manual states multi-segment mode only as you stated.


Steve
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