What I learned from Gollywop -- and what I wonder

Started Mar 26, 2013 | Discussions thread
Anders W
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Re: What I learned from Gollywop -- and what I wonder
In reply to bowportes, Mar 28, 2013

bowportes wrote:

richarddd wrote:

This is Anders' post slightly edited:

Exposure 101 only covers what I would normally do and leaves out both the question of when I'd try to do something else and what else I'd try to do. So for the normal case, my advice would be the following:

1. Set the widest f-stop that satisfies your DoF requirements and the slowest shutter speed that satisfies your need to control subject motion and camera shake.

2. Set the lowest ISO within the ISO 200 to ISO 1600 range that brings the brightest highlights that you care to preserve just up to the clipping point. In so doing, skip intermediate ISOs between 200 and 400 (250 and 320) since going directly to ISO 400 when ISO 200 is insufficient is usually preferable. Note that rule 2 is E-M5-specific and might look different for other bodies.

3. If it turns out to be impossible to follow rule 2 because you are still clipping highlights even at ISO 200, use a smaller aperture or a faster shutter speed than you need according to rule 1. In so doing, be aware that peak aperture for MFT lenses is usually somewhere between f/4 and f/8 (about f/4 for fast primes, about f/8 for slow zooms at the long end where "wide open" means f/5.6 or smaller) and that it is not generally advisable to use a smaller aperture than the optimal unless you need it for sufficient DoF.

4. If it turns out to be impossible to follow rule 2 because you are not yet at the highlight clipping point when you reach ISO 1600, shoot anyway (at least if the highlight clipping point would be reached if you continued to ISO 3200, possibly ISO 6400, depending on your quality requirements).

5. In order to determine when you have reached the clipping point, check the orange blinkies, subject to:

Exception 1. Hidden blinkies, type A: If the scene you try to capture passes below a certain threshold in terms of contrast, the blinkies will never appear no matter how much exposure you dial in. These scenes are as a rule not photographically interesting and if, nevertheless, you want to capture them, they can easily be handled by my alternative strategy, i.e., that of metering on the brightest area and dial in +3.3 EV exposure compensation based on that reading.

Exception 2. Hidden blinkies, type B: If, in a scene that passes the contrast threshold mentioned above, you point the spot meter at the brightest highlights, the blinkies will again not appear when they should. In this case too, the situation is unproblematic once you are aware of how the camera behaves. Just avoid pointing the spot meter directly at the brightest highlights when observing the reaction of the blinkies, or, alternatively, point the meter at the brightest highlights (if they are large enough to be isolated by the spot) and dial in +3.3 EV exposure compensation based on that reading.

Exception 3: Phantom blinkies: If, in a scene that passes the contrast threshold mentioned above, you instead point the spot meter at the very darkest parts of the frame (black or near black), you are likely to see blinkies on the highlights that will never disappear no matter how much you try to restrict the exposure level. In this case too, there are easy work-arounds available of essentially the same kind as for exception 2.

Note 1: There are of course shortcuts that simplify the above under certain conditions. Suppose, for example, that you know in advance that ISO 200 will be sufficient because you are shooting in broad daylight and don't have particularly high shutter-speed requirements and/or use a fast lens. Then you would of course have the camera set to ISO 200 all the time and just adjust the f-stop and/or shutter speed so as to be in line with rule 3 (without violating rule 1).

Note 2: If you actually want to use a wide aperture because you want to maximize background blur for subject isolation or if you actually want a low shutter speed to simulate subject motion (e.g., that of moving water), you can alternatively comply with rule 3 by using an ND filter.

Looks good to me, although I don't have much experience with the Exceptions.

Regarding Exception 2, blinkies change depending on where you point the camera, not whether you are using spot metering or another metering mode, at least in the brief testing I've done. Are you suggesting something else?

Could Richardd or Anders or someone else take a stab at a small rewrite based upon the sensor data for the G5?  Specifically...

1. How far up should ISO go? (I'm thinking 1600)

Yes 1600.

2. Should it go up in a 160, 320, 640, 1280 sequence (because these are "real" ISOs, like with the GH2), or should it go 160, 200, 400, 800, 1600?

Can't answer that question. For the GH2, you would use 160, 320, 640 (no reason to go further). But the G5 might work differently. The read-noise data reported by Sensorgen suggest it does.

It would take someone with access to a G5 (you perhaps) to check out the entire read-noise curve, including the intermediate ISOs. DxO/Sensorgen gives us data for the main ISOs only.

Based on the few G5 RAWs I have looked at, it doesn't look as though it clips the read-noise distribution at the black level, as does the GH2. If that observation is correct, you could do it by simply shooting a series of black frames (capped lens, dark room, shortest shutter speed, smallest aperture), one at each ISO including the intermediate ones. You then open the files in RawDigger, move the black level backwards to zero, and observe the standard deviations, which in this case should reflect pure read-noise. This is what I did to see how the E-M5 behaved with regard to the intermediate ISOs. See here:

http://www.dpreview.com/forums/post/41988325

3. Are there any ISOs to be avoided?

See above.

There's been so much emphasis upon the "rules" with the EM5 that I'd like to know what changes with the G5 and the EPL5.

I would guess, but don't know for sure, that the E-PL5 behaves just as the E-M5 in this regard.

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