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Author Topic: Spot metering & HDR?  (Read 2899 times)
russellsnr
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« on: February 10, 2013, 07:22:08 AM »
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Hi, I use or am trying to use the Sekonic L358 with the spot meter attachment to get a base reading for an HDR shot but I am getting a little frustrated with it.
If like today I take a reading for white clouds and get 1250 at F11 and the dark area gives me 60th at F11 that's about 4 & 1/3rd stops correct? So what would I have to set as a base reading to get my 7 shots -1,-2,-3,0,+1,+2,+3 to merge for HDR.
Hope someone understands my question.
Thanks
Russ

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SZRitter
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« Reply #1 on: February 10, 2013, 08:18:18 AM »
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If you are covering a 4 stop range, you don't need 7 exposures, which would be 7 stops if you did 1 stop steps.

If I was using AEB, I would set -2, -1, 0, -1, 2.

That said, you could make a fine image from a single RAW in that narrow of a situation.
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russellsnr
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« Reply #2 on: February 10, 2013, 08:38:42 AM »
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Hi, Thank you for the reply.
I understand I would not require the 7 exposures but the 1Ds Mk II only allows the factory set 3 exposures or as set via connection to a computer to set 5,7 or 9 exposure brackets, I have set mine to 7 AEB
so I need to no the base exposure to get even brackets either side of the base, in this case 3 up, zero, and 3 down, the +1 and -1 are only really for examples. it maybe a 14 stop requirement  at = or + 2.
Thanks again
Russ
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BartvanderWolf
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« Reply #3 on: February 10, 2013, 09:44:17 AM »
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Hi, I use or am trying to use the Sekonic L358 with the spot meter attachment to get a base reading for an HDR shot but I am getting a little frustrated with it.
If like today I take a reading for white clouds and get 1250 at F11 and the dark area gives me 60th at F11 that's about 4 & 1/3rd stops correct? So what would I have to set as a base reading to get my 7 shots -1,-2,-3,0,+1,+2,+3 to merge for HDR.
Hope someone understands my question.

Hi Russ,

If your clouds read 1/1250th at f/11, that would put them at an average exposure level which is too dark. You could use that reading and expose up to 3 stops longer to put the clouds near the raw data clipping limit. All other exposures will then be longer exposure times. The more you add, the better the shadows rendering will become. IOW, you could use your cloud measurement as middle exposure, and use the default -3 to +3 EV bracketing range with a 1 stop interval. When you want to preserve specular (brighter than the clouds) highlight colors, you could shift the whole range to a slightly shorter base exposure.

Cheers,
Bart
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russellsnr
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« Reply #4 on: February 10, 2013, 11:12:05 AM »
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Hi, Bart, Can I just confirm this with you?
When I take the cloud reading with the spot are you saying that I should increase that reading by 2 or 3 stops (as you would do with snow maybe) and use that as a base reading?
Thanks
Russ
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BartvanderWolf
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« Reply #5 on: February 10, 2013, 06:01:52 PM »
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Hi, Bart, Can I just confirm this with you?
When I take the cloud reading with the spot are you saying that I should increase that reading by 2 or 3 stops (as you would do with snow maybe) and use that as a base reading?

Hi Russ,

Yes, that's correct. When you take a lightmeter reading of a uniform area, it will place that area approx. 3 stops below the raw sensor data clipping point (the exact number of stops will depend on the calibration that the meter uses). So when you meter of the lightest area of a scene (sun lit clouds, snow), then you can boost the exposure for the shortest exposure time bracket by that amount of stops (if there are no specular highlights that need to be preserved), to maximize the number of captured photons. All other exposure times in the bracketing sequence will be longer than for that highlight preserving exposure.

You can also use a 2 stops longer exposure time instead of 3, which will automatically include a safety for brighter than measured highlights, but then your shadows exposure in the bracketing sequence also gets a stop less exposure (which may, or may not, be an issue). For high contrast scenes I usually take 7 exposure brackets with an interval of 1 1/3rd stops. That will still produce good results with my preferred HDR exposure blending software, SNS-HDR (even a 2 stop interval would work, but that's pushing the acceptable limits for SNS-HDR).

Cheers,
Bart
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russellsnr
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« Reply #6 on: February 11, 2013, 01:04:29 AM »
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Thanks again Bart, I also use SNS-HDR Smiley so that really is helpful.
Russ
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stamper
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« Reply #7 on: February 11, 2013, 03:16:03 AM »
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A couple of years ago Michael had an essay about bracketing if you can find it. What you don't do is to use an image that represents a mid tone and use it as your middle - of three - image. Bart has it right. I am not sure if using a meter has any point to it because you aren't looking for a mid tone.
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bwana
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« Reply #8 on: February 13, 2013, 02:23:15 PM »
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Bart said

If your clouds read 1/1250th at f/11, that would put them at an average exposure level which is too dark. You could use that reading and expose up to 3 stops longer to put the clouds near the raw data clipping limit. All other exposures will then be longer exposure times. The more you add, the better the shadows rendering will become. IOW, you could use your cloud measurement as middle exposure, and use the default -3 to +3 EV bracketing range with a 1 stop interval.

OK, so the idea is to spot meter a highlight. I understand how this makes sure you capture the top end. But what if -3ev below the clouds doesnt get all the shadow info? How does one know how low to go?
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BartvanderWolf
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« Reply #9 on: February 13, 2013, 04:20:40 PM »
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OK, so the idea is to spot meter a highlight. I understand how this makes sure you capture the top end. But what if -3ev below the clouds doesnt get all the shadow info? How does one know how low to go?

Hi,

That depends on the scene. The easiest way is to keep an eye on the histogram of the longest exposure in the bracketing series. When that exposure shows some signal in the middle of the histogram (and the LCD preview is overall very light, except for those now medium gray shadows), then the shadows have recorded enough photons for an improved SN ratio.

Then there is also experience. After having done several HDR sequences, it should become apparent how much of a range one can cover with e.g. 7 exposure brackets (with a 1 EV or 1 1/3rd EV interval). Contrasty scenes will then use a 1 1/3rd EV interval which will cover 2 1/3rd stop more with 7 exposures than a 1 EV interval would. Just make sure the shortest (e.g. -3 EV) exposure is an ETTR for non-clipped highlights, all other exposures are longer.

The 1Ds3 I use can show the Live View histogram when I stop down the aperture manually to dial in that first shortest exposure (I have the bracketing sequence set to -,0,+). Other cameras may have other useful settings.

Cheers,
Bart
« Last Edit: February 13, 2013, 04:36:40 PM by BartvanderWolf » Logged
Rendezvous
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« Reply #10 on: February 19, 2013, 02:53:06 PM »
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I often use spot metering in manual mode on the camera. I'll point the camera at a bright bit of the sky then adjust the exposure until it is 2-3 stops over exposed for that point. Seems to work out pretty well. This is essentially the same as what's been said above.
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l_d_allan
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« Reply #11 on: March 03, 2013, 07:23:39 PM »
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That said, you could make a fine image from a single RAW in that narrow of a situation.

Agree. If I read the OP correctly, the scene is relatively low contrast. I would think you could possibly use the "sunny 16 rule" and the histogram might fit with room to spare on the left and the right.

By "dark area", does the OP mean the darkest portion of the scene (like someone sitting under a shade tree that isn't supposed to turn out as a silhouette), or the darker part of the cloud?
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russellsnr
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« Reply #12 on: March 04, 2013, 12:55:55 AM »
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Hi, Thank you again for all the replies.
When I say darkest area I am talking about for example the gap in a bush where you now there is information but it's just to dark in there to see with the camera.
Again thank you for the help
Russ
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