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10-10-2008, 01:11 PM   #1
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hyperprogram (P) and auto-ISO

I'm trying to understand how the camera adjusts the settings when I'm using a K10D/K20D in hyperprogram (P), with auto-ISO enabled. Actually, I think I have it figured out, but I would like somebody with some confidence to confirm my understanding - or correct it.

I've been experimenting here and it looks like it works this way. If I start out in P and then start stopping down the aperture by moving the rear e-dial. Doing so of course puts the camera effectively into aperture-priority mode. Now, the camera will respond to each change in the aperture (from f/4 to f/5.6, to f/8, etc.) by adjusting the shutter - until the shutter speed is roughly the reciprocal of the focal length. And then the camera will start adjusting the ISO instead, until the max aperture defined in the auto-ISO range is reached, at which point the camera returns to adjusting the shutter speed.

For example: Say I've defined auto-ISO's range as 200-800. I'm in P mode and I hit the green button to get an initial nominally correct exposure, and the camera returns f/5.6, 1/250th sec, ISO = 200. I'm using the Pentax FA 16-45 f/4 lens, with focal length set to 45mm. As I stop down the aperture, here's what happens:
  1. ISO 200: f/5.6, 1/250th sec
  2. ISO 200: f/8, 1/125th sec
  3. ISO 200: f/11, 1/60th sec
  4. ISO 400: f/16, 1/60th sec (ISO changes)
  5. ISO 800: f/22, 1/60th sec (ISO changes)
  6. ISO 800:f/32, 1/30th sec (shutter changes)
In short, it looks as if, in aperture-priority mode with auto-ISO enabled, the camera is going to use the lowest ISO and adjust the shutter instead, until the shutter is on the verge of violating the old reciprocal rule about the relationship of the focal length to shutter speed, and then it will adjust the ISO instead. And when the max ISO is reached, it will go back to adjusting the shutter speed, and the reciprocal rule is abandoned (out of necessity). By the way, I'm using the Normal program line (custom menu #1 in the K20D).

Have I got this right?

__________


Using shutter priority mode, things work a bit differently and I'm more confused here.

If I start with a nominally correct exposure and ISO at the minimum of 200, and I start increasing the shutter speed by adjusting the front e-dial, the camera adjusts the aperture in response to each change in the shutter speed - but when the max aperture is reached, the camera stops responding at all. That is, I can move from 1/250th sec to 1/500th sec and get a change in the aperture from (say) f/5.6 to f/4. But since the lens's max aperture is f/4, that's as far as that setting can be pushed. At this point I'd expect the camera to start adjusting the ISO upwards. But it doesn't. Instead, I just seem to get stuck at 1/500th sec, f/4 and ISO 200. That doesn't sound too problematic, but now let me report what happens if the light is low. Say I hit the green button and the camera sets the exposure to 1/10th sec, f/4 and ISO 800. (At this point it doesn't matter what the focal length is, because 1/8th is already less than the reciprocal of 16mm.) Note that the camera does bump up the ISO when I hit the green button.

Now if I try to move the front e-dial to increase the shutter speed, what happens? Well, what happens is weird. The first time I move the front e-dial to increase the shutter speed, nothing happens to the shutter speed (except that it gets the > sign next to it, indicating that I've moved into effective shutter priority mode). But if I keep trying to increase the shutter speed, what happens is the opposite of what I expect. The shutter speed actually starts decreasing, while the ISO decreases as well. Here's what happens:

ISO 800: f/4, 1/10th sec
ISO 560: f/4, 1/8th sec
ISO 400: f/4, 1/6th sec
ISO 280: f/4, 1/4th sec

And so on.

Except that it's weirder than that. Sometimes it doesn't work at all, I mean, I move the e-dial and nothing happens at all.

I notice that, if I switch to a fixed ISO (say, 800) and point the camera into a darkish area of the room, if the green button gives me a base exposure of 1/10th sec at f/4, and I try to increase the shutter, the camera won't go there. That makes sense. After all, this is P mode, and the camera is determined NOT to let me screw up the exposure, if it can help it. I assume that this is the chief goal of P mode, and it explains the strange results I note immediately above in shutter priority with auto-ISO.

Is my understanding of shutter priority + auto-ISO in hyperprogram mode correct?

__________


Here's why I ask. The more I use hyperprogram on the K10D/K20D, the more I like it. I have never found M mode especially difficult - I've been using it most of my life - but when light is abundant, hyperprogram mode seems a little easier. I can control things much of the time with a single e-dial, instead of having to move both dials, as I would in M if, say, I wanted to stop the aperture down but keep the same exposure balance. When the light is good, hyperprogram is great.

The problem is, much of my photography is done in marginal lighting conditions. Well, that's half of the problem. I'll get to the rest of the problem in a second.

Since so much of my photography is done in mediocre light - or in light that's downright bad - if I'm going to use hyperprogram mode, I need to understand how it reacts in these situations when the light gets bad.

The other part of the problem comes in when I consider how important it is to develop good shooting habits. That doesn't just mean doing things the same way (i.e. right) all the time, it also means thinking the same way all the time, at least as much as possible. Unfortunately, shooting in P mode may not be consistent with my goal of developing good shooting habits - and good thinking habits. The point of shooting in hyperprogram is to make things easier on myself - to allow myself to concentrate less on exposure and more on composition and timing. But it looks as if I'm going to have to worry, at least when the lighting is marginal, about moving from bad to worse and suddenly having the camera behave like a mule who's decided he doesn't want to go any further in that direction. Then I have to start thinking three times harder than usual about what's going on.

Which is driving me to the conclusion that it may be about time to end my experiment with hyperprogram and go back to shooting M most of the time, which is what I used to do. Or if not M, at least TAv - which is one of the more brilliant features of the K10D/K20D cameras. In most of my photography - weddings and events - I have a fair amount of latitude regarding ISO. I'm not shooting magazine covers and a little bit of noise is not a problem: not getting the shot, is. So I'm starting to think I should start using TAv more than I ever have in the past.

But - and please forgive me here - I'm driven back to P because, when it works - which is a lot of the time - (a) it's awfully convenient and (b) because I get better results on average with it when I'm shooting a lot of pictures than I do using M or even TAv. How can this be? Well, getting the right exposure is a lot like juggling three balls. The balls are aperture, shutter speed and sensitivity. When light is controlled (as in a studio) or very abundant, I can take sensitivity out of the equation by fixing it at 100 or 200 and just deal with aperture and shutter speed. But when the lighting is variable, then the problem is usually how to make the best compromise between the three settings, and that can't be done by making ONE setting do all the work. If I have time to think, I can do as good a job as the camera every time and occasionally I can do better. But when I am in a hurry to shoot, the compromise that the camera negotiates in a hurry is, I must confess, very often better than the one I could negotiate in the same split second. I might think I need to keep the aperture at f/5.6 and the shutter above 1/100th sec, when the camera will decide to open the aperture a bit, slow down the shutter a bit too and increase the ISO only slightly - resulting in a better overall shot.

This no doubt means that I'm not as good a photographer as I would like to be. I'm certainly not like one of those chess masters who can beat all but the most sophisticated computer programs game after game. But I do have a couple of strengths that the camera still doesn't: I know where to point the camera and when to click the shutter. Perhaps it just makes sense to work with the camera, letting it do what it can do well, and letting me what I can do well, and sharing the credit.

What do you think?

Will

10-10-2008, 02:29 PM   #2
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I read it with interest I have never evaluated the P mode to such an extent. I stay in Av mode most of the time and I know what the camera will do except if I have "auto Ev" in the menu enabled then the camera will take control sometimes without you knowing because it does not work until you half press the shutter, then if you have something way off the camera will correct it. Believe it or not I leave it on, because it helps avoid mistakes when in a hurry. With auto EV on you have full control as normal but say you set the iso to 1600 and the aperture to f2.8 and its sunny out, not even 1/4000 is enough shutter speed to avoid a grossly over exposed pic. So with it on when you half press the shutter button you may see (if you notice) the shutter jump up to f5.6 or something to correct your mistake. It is very transparent in operation and not just for beginners IMO, it helps anyone avoid mistakes when not thinking. It does not work in M mode, and I am not sure if it works in regular P mode but program line does.

So you may want to see if auto EV is on, and what you have Program line set to, normal, depth, h.speed, MTF, those will determine what the camera picks in P mode. Did you have P mode set to normal and was auto EV set to off? If so great findings and I also like P mode sometimes because I have it set to MTF and it picks a f number if there is enough light that corresponds to the lens best MTF at the focal length your set at, and it works and it works with other lens than Pentax. My Sigma 17-70mm works well with it, it will pick f5.6 at 17mm and f8 at 70mm if the minimum shutter speed is OK. Thats the key with program line, if you use MTF then your other settings must be OK and the camera will set the aperture to the setting Sigma provided for best MTF at any given focal length, nice!
10-10-2008, 02:58 PM   #3
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QuoteOriginally posted by jamesm007 Quote
So you may want to see if auto EV is on, and what you have Program line set to, normal, depth, h.speed, MTF, those will determine what the camera picks in P mode. Did you have P mode set to normal and was auto EV set to off? If so great findings ...
Embarrassed to admit that I didn't know the answer to your question off the top of my head. Had to check to find that Auto EV compensation is indeed enabled. Now I have to play around some more to understand better what exactly this is doing.


QuoteQuote:
and I also like P mode sometimes because I have it set to MTF and it picks a f number if there is enough light that corresponds to the lens best MTF at the focal length your set at, and it works and it works with other lens than Pentax. My Sigma 17-70mm works well with it, it will pick f5.6 at 17mm and f8 at 70mm if the minimum shutter speed is OK. Thats the key with program line, if you use MTF then your other settings must be OK and the camera will set the aperture to the setting Sigma provided for best MTF at any given focal length, nice!
I have never used MTF. I probably just don't understand it. But here's what I think it does: I think it's supposed to encourage the camera to use settings that will favor the lens's best aperture. This is fine, I guess, but I have more important reasons to set the aperture here or there. If I want paper-thin depth of field I'm not going to set the aperture to f/8 just because that's where the lens does its best work!

I keep the program line on Normal because anything else seems to work against the idea of hyperprogram. I just played around with the program line and found the results kind of interesting. Pointing the camera out my back door, here's what P calculated as a good exposure (with a fixed ISO of 800):

1/250th sec @ f/5.6 for high speed program line
1/180th sec @ f/6.7 for normal program line
1/125th sec @ f/8 for aperture program line

It's not bracketing, because they're all using the same base metering value. But it looks like normal program line is sort of a compromise, while high speed (which I think ought to be called "shutter") program line and aperture program line simply move the settings a half a stop in favor of one or the other.

I put the camera back to normal just now, because when I hit the green button, I want the camera's most unbiased calculation about the settings. If I think 1/180th sec is too slow, I'll move the front e-dial to make it faster. I assume that, once you've used the front or rear e-dial to move into effective shutter or aperture priority mode, the program line is no longer an issue.

Will
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