What I learned from Gollywop -- and what I wonder

Started Mar 26, 2013 | Discussions thread
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Anders W Forum Pro • Posts: 21,465
Re: What I learned from Gollywop -- and what I wonder

richarddd wrote:

Anders W wrote:

richarddd wrote:

Anders W wrote:

richarddd wrote:

Anders W wrote:

Practice makes perfect though. That's why it is important to think and talk about it. Some people are wont to say that "theoretical" discussions of the present kind are of no help in the field. I think it's exactly the other way. Only by thinking and talking about it will you eventually know exactly what to do in the field, and do so intuitively and instantly. For example, I know "without thinking" when it's the proper time to switch from ISO 200 to ISO 400 on my E-M5 when I am out taking pictures. But I do so only because I have exercised my thinking about the matter quite a bit beforehand.

There are two ways to figure out how to proceed in the field (1) have a good set of rules telling you how to behave and (2) have a good set of underlying principles from which you can derive such rules.  They are clearly not mutually exclusive.

As an illustration, please summarize when you would and when you would not increase from ISO 200 to 400 on your E-M5. For example, are there cases in which you would increase ISO to 400 even though you could increase exposure without sacrificing desired DOF or blur control, or cases when you would not increase ISO to 400 even though you are at maximum exposure consistent with desired DOF and blur control and could increase ISO without clipping highlights with detail you would like to preserve?

My answer to the two questions at the end would be no. So I think you have already indirectly summarized what the rule is: If you can't reach the highlight clipping point at ISO 200 without exceeding your f-stop and shutter speed requirements, go to ISO 400.

If, on the other hand, we have the same scenario but a choice between ISO 1600 and ISO 3200, I would normally prefer to remain at ISO 1600 since the read-noise gain from going higher would be close to zero and staying at 1600 means that I have to worry less about any highlight clipping

All of which appears to lead us back to a rather simple set of rules for the E-M5:

Start at base ISO

Set aperture and shutter speed to get the most light on the sensor, consistent with desired DOF and lack of camera or subject motion blur, so long as we don't clip highlights in which we wish to preserve detail

If we are not clipping desired highlight details, increase ISO until just before clipping point. Skip values between 200 and 400 and stop at 1600.

If we can't hit targets (e.g., desired DOF or fast enough shutter), then decide on best compromise, which may involve bracketing.

Use orange blinkies to determine clipping.  Alternatively, spot meter on brightest point with detail, then increase exposure (and then ISO) by 3.3 stops.

Have I missed something?

At least you haven't missed all that much. I am not sure what you mean by the point which begins with "if we can't hit targets". Please elaborate that point a bit and I'll be happy to react.

By "if we can't hit targets" I mean that we can't get all of (a) desired DOF, (b) a fast enough shutter speed to stop undesired motion blur and (c) being just below the clipping point for highlights in which we wish to preserve detail without increasing ISO above 1600. If so, we have to compromise.

OK. I see what you mean. But I wouldn't agree that this particular condition is some kind of "break point" where we have to start thinking "out of the box", one of several reasons being that there is nothing special about ISO 1600 except that this is approximately where read noise (as measured in electrons) stops falling as you crank up the ISO on the E-M5.

That fact makes it redundant (and slightly counterproductive) to crank up ISO beyond 1600. But it won't guarantee that we will "hit targets" in the sense of meeting reasonable quality requirements. Depending on the scene, we might well fail to "hit targets" in that sense even if we follow the rules and by so doing manage to stay at ISO 200.

But let's finish "Exposure 101" before moving on to "Exposure 102".

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 requirementes 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 sufficent 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, follow the guidelines in the post to which I link below. Note that rule 5, like rule 2, is E-M5-specific.


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 2 by using an ND filter.

Does this look OK with you, Richard?

An additional rule would be to bracket for HDR if we are at the clipping point for highlights in which we wish to preserve detail and shadows in which we preserve detail are blinking blue.

Yes. Something like that. But I think we should save that for "Exposure 201".

The main point is that none of this is very difficult at the practical level.

Right. Following the "normal" rules as I have spelled them out above isn't very difficult.

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