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12-29-2006, 10:39 PM   #16
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Nope, it's totally possible, technically!

If the Auto ISO feature is smart enough, the TAv mode is actually redundant!

Why, just set the camera in M mode and then with Auto ISO enabled also..

For the question you raised, technically it is totally possible. Camera's light meter first get the lighting level and the relationship of the 3 variable can be defined (as a 3-d curve, similar to the 2-d program curve).

For the case the OP and others who K10D user responded, it is simply not desirable for the Auto ISO which is dropped and then cannot be further raised. If the camera is "smart" enough, it should be able to GO BACK and fro with the mode dials, no matter how the user turns the wheels.

The logics is simple and it is very practical for this behaves, otherwise the Auto ISO function will be useless.

Of course, Pentax firmware engineers need to re-write their algorithms, though.

QuoteOriginally posted by klopus Quote
Isn't TAv mode desgined for this? It's exactly what you want - you set desired Aperture and/or Shutter and ISO gets adjusted for you (if you set ISO step to 1/3 stops you'll get it more precise).

To me using Auto ISO in Hyperprogram without some user definable rules seems like the most impossible algorithm that really doesn't have the correct (or at least predicatble) behavior. Just think of it. You have 3 variables but change at a time only one of them (e.g. Shutter). As a result you expect the other 2 variables (Aperture and ISO) to auto change in some predictable manner which's impossible unless you put obvious, simple (remember you're in a heat of taking a shot) and reasonable constraints on behavior of the other two variables.

Changing ISO only when AE reaches the metering limits isn't very usefull. Much better, is how Nikon wisely have done this on D200 (I believe) by allowing user to define Auto ISO constraints in terms of shutter speed, e.g. "Bump ISO when shutter slows below 1/60, decrease ISO when shutter gets faster than 1/60"." That's what you really want - bump ISO to mainatin handholding sharpness. Same can be applied to maintain DOF or lens best aperture, e.g. bump ISO only when aperture opens up past F4.5. I think Pentax on K10D tried to achieve something like this with this vague Hyperprogram Lines. They should've done this the Nikon way- let user control Auto ISO by explicit shutter or aperture threshold values.

Too bad Pentax didn't do this. TAv mode seems like a next best thing.


12-30-2006, 02:28 AM   #17
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Original Poster
QuoteOriginally posted by klopus Quote
Isn't TAv mode desgined for this? It's exactly what you want - you set desired Aperture and/or Shutter and ISO gets adjusted for you (if you set ISO step to 1/3 stops you'll get it more precise).
No. TAv mode is completely different. Hyper program allows you instantly switch to either Tv or Av modes.

QuoteOriginally posted by klopus Quote
To me using Auto ISO in Hyperprogram without some user definable rules seems like the most impossible algorithm that really doesn't have the correct (or at least predicatble) behavior. Just think of it. You have 3 variables but change at a time only one of them (e.g. Shutter). As a result you expect the other 2 variables (Aperture and ISO) to auto change in some predictable manner which's impossible unless you put obvious, simple (remember you're in a heat of taking a shot) and reasonable constraints on behavior of the other two variables.
Not true. Algorythm is very simple and predictable. I didn't study how does it work in Hi Speed, Depth and MTF program lines, I will describe how Tv and Av works with Auto ISO in Normal Program line.

So, Tv mode:
Camera is always trying to set lower ISO. So, generally you get ISO100. When you make shutter speed faster, camera opens aperture up to the point when aperture reaches it's widest limit for lens. Then when you make shutter speed even faster, camera increases ISO.

Example: 1/125-f5.6-ISO100 -> 1/180-4.5-ISO100 -> 1/250-f4-ISO100 -> 1/350-f4-ISO140 -> 1/500-f4-ISO200 and so on until ISO reaches it's defined upper limit.

In case you decrease shutter speed, camera first tries to lower ISO and when it reaches defined lowest limit, camera starts to close aperture.

Simple, isn't it?

Av mode works identically. When you close aperture, camera tries to keep ISO as low as possible, thus decreasing shutter speed. It decreases shutter speed until it reaches some speed X (talk about "X" later). When you further close aperture, shutter speed remains constant and ISO starts to increase. It increases up to the defined upper limit. Then shutter speed starts to decrease again.

Opening aperture works opposite way, camera first increases shutter speed to value X, then it decreases ISO until it reaches lowest limit and then starts to speed up shutter speed.

Also very simple, isn't it?

QuoteOriginally posted by klopus Quote
Changing ISO only when AE reaches the metering limits isn't very usefull. Much better, is how Nikon wisely have done this on D200 (I believe) by allowing user to define Auto ISO constraints in terms of shutter speed, e.g. "Bump ISO when shutter slows below 1/60, decrease ISO when shutter gets faster than 1/60"." That's what you really want - bump ISO to mainatin handholding sharpness. Same can be applied to maintain DOF or lens best aperture, e.g. bump ISO only when aperture opens up past F4.5. I think Pentax on K10D tried to achieve something like this with this vague Hyperprogram Lines. They should've done this the Nikon way- let user control Auto ISO by explicit shutter or aperture threshold values.

Too bad Pentax didn't do this. TAv mode seems like a next best thing.
Pentax did better! Remember that shutter speed X? So, this speed depends on focal length of your lens. I have 16-45 mounted. When I change focal length to 16mm, X is 1/30 on my K10D. When I zoom it to 45mm, X becomes 1/60. I.e at 16mm in Av mode when aperture is being closed K10D starts to increase ISO when shutter speed gets as low as 1/30. When I zoom to 45mm, ISO gets increased when shutter speed gets as low as 1/60.

In my opinion very clever. In Nikon D200 theoretically you have to change that minimal shutter speed when you mount some 300mm lens instead of some wide angle lens. Pentax just does this automatically for you.
12-30-2006, 07:48 AM   #18
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QuoteOriginally posted by Edvinas Quote
No. TAv mode is completely different. Hyper program allows you instantly switch to either Tv or Av modes.
Right.

QuoteQuote:
Not true. Algorythm is very simple and predictable. I didn't study how does it work in Hi Speed, Depth and MTF program lines, I will describe how Tv and Av works with Auto ISO in Normal Program line.

So, Tv mode:
Camera is always trying to set lower ISO. So, generally you get ISO100. When you make shutter speed faster, camera opens aperture up to the point when aperture reaches it's widest limit for lens. Then when you make shutter speed even faster, camera increases ISO.

Example: 1/125-f5.6-ISO100 -> 1/180-4.5-ISO100 -> 1/250-f4-ISO100 -> 1/350-f4-ISO140 -> 1/500-f4-ISO200 and so on until ISO reaches it's defined upper limit.

In case you decrease shutter speed, camera first tries to lower ISO and when it reaches defined lowest limit, camera starts to close aperture.

Simple, isn't it?
Crystal clear logics and super clear explanation. I really hope that you were one of the Pentax firmware engineers!

QuoteQuote:
Av mode works identically. When you close aperture, camera tries to keep ISO as low as possible, thus decreasing shutter speed. It decreases shutter speed until it reaches some speed X (talk about "X" later). When you further close aperture, shutter speed remains constant and ISO starts to increase. It increases up to the defined upper limit. Then shutter speed starts to decrease again.

Opening aperture works opposite way, camera first increases shutter speed to value X, then it decreases ISO until it reaches lowest limit and then starts to speed up shutter speed.

Also very simple, isn't it?
Ditto!

QuoteQuote:
Pentax did better! Remember that shutter speed X? So, this speed depends on focal length of your lens. I have 16-45 mounted. When I change focal length to 16mm, X is 1/30 on my K10D. When I zoom it to 45mm, X becomes 1/60. I.e at 16mm in Av mode when aperture is being closed K10D starts to increase ISO when shutter speed gets as low as 1/30. When I zoom to 45mm, ISO gets increased when shutter speed gets as low as 1/60.

In my opinion very clever. In Nikon D200 theoretically you have to change that minimal shutter speed when you mount some 300mm lens instead of some wide angle lens. Pentax just does this automatically for you.
Agreed also. Pentax Auto ISO is a great invention and useful feature. So, I really hope that the bug can be fixed very soon (but unlikely, according to their past track records..)
12-30-2006, 09:52 AM   #19
MnR
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Hi Edvinas,

You said you were in P mode and the program line was normal. Did you try using a different program line like high speed?

Rudy

12-30-2006, 09:54 AM   #20
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The program line has nothing to do with this bug. n/t

No text. See the subject line.

QuoteOriginally posted by MnR Quote
Hi Edvinas,

You said you were in P mode and the program line was normal. Did you try using a different program line like high speed?

Rudy
12-30-2006, 11:48 AM   #21
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Great explanation and resource

Thank you, Edvinas!

It's information like this that will allow me to better utilize my K10D.
12-30-2006, 05:47 PM   #22
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NOT a "whatever" type bug.

This information should help Pentax become aware of something that must be fixed in firmware as it is unacceptable on any camera, much less on somethig $1000 was invested in. Period. This information is NOT meant to have Pentax owners accept it like sheep and use it ONLY to work their cameras better.

Has ANYONE physically spoken to a Pentax tech, and gotten a "Yeah, we know what you mean, we acknowledge this problem exists and now we will fix it in a firmware update."?

OR what reaction DID you get?

Larry
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