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01-26-2008, 04:36 PM   #1
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Tweakable Auto ISO!

Hello!

I'm currently using a Nikon D50 but will most likely migrate to Pentax after the release of the new cameras. Now I have one question concerning the Auto ISO feature in Pentax DSLRs and a in my opinion great suggestion for a firmware improvement.

With Nikon Auto ISO requires you to enter the shutter speed limit at which ISO shall rise (unfortunately only in full EV steps). That's fine with primes as, for example, with a 35/f2 you set it to 1/60s and in Av-mode it will use the lowest ISO in good light, but will raise it when the shutter speed would hit 1/50s and thus blur could be introduced.

With zooms it starts to get messy. I have a Tamron 28-75/f2.8 and at the wide end the 1/60s I've set is very safe (28*1.5=42<60) but at the long end it produces images with low ISO but often also motion blur due to camera shake (75*1.5=113>60). So I can either set the Auto ISO to 1/125s and get unnecessarily noisy images or switch off Auto ISO in the menu whenever I'm zooming. As all modern zoom lenses send their focal length to the camera it is most sensible to automatically link the shutter limit to the current focal length.

Now I wonder how Pentax does it. As far as I understood there is no rule you can give the camera apart from the ISO range. So does it take focal length into account and if so: how? 1/f or 1/f*1.5 or something else? I've search this forum and found no definite answer. In this thread even Pentax USA seems to not know the algorithm and the whole matter seems like some kind of mystery. Can anybody elaborate on this reliably?

I really can't understand why this should be so intransparent, as exposure/ISO is no magic but fundamental physics/mathematics. I would like to see an approach where I can tell the camera which shutter speed I need depending on the relative focal length. For example 1/(f*1.7)s in order to ensure absolute sharpness.

Being able to adjust this multiplying factor becomes even more powerful if you consider Pentax' Shake Reduction. No need to limit the speed to 1/(f*1.5)s if SR can gain 2 or 3 stops consistently. As you know the results of SR vary between different users, depending on shooting technique or are. If someone believes to constantly gain 3 stops, he can set it to 1/(f*1.5/2^3)s=1/(f*0.2)s; if someone thinks SR makes only 1 stop for him then 1/(f*1.5/2)s=1/(F*0.75)s; and if someone has very shaky hands let him govern 1/(f*2)s!

That is a very powerfull and yet easy to implement (even via firmware upgrade for K10(0)d) feature which takes advantage of two of Pentax' greatest strengths (Auto ISO + SR) and gives you great flexibility. Now further add the ability to set an additional minimum shutter speed in order to rule out subject movement blur and your Auto ISO is just perfect.

Apparently Pentax is listening to its users so there is some hope in my longish post. But first there must be some users interested in it; so, what do you think? Is the current implementation of Pentax already clear and usefull enough? Or would you appreciate, if they introduced something like the aforementioned idea with the next firmware update?

Thanks for your patience,
Pareto

01-26-2008, 05:26 PM   #2
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From my experience the pentax cameras seem to work on the principle of keeping ISO up until yoou have a viable solution for the lens in terms of shutter speed and Fstop.

So for example if you have a zoom lens and are zoomed to 70mm and you have selected F4, the auto iso will try to insure you ahve at least 1/90 or something like that.

conversely if you are in shutter priority and set 1/90 it would keep the ISO high until you have a viable F stop.

I think in some cases it follows the program line that you can select.

To be honest, I don't use auto ISO. I find generally what I do is to pick up the camera, consider the lighting and then set ISO. Unless there is a serious change in lighting, or I put, for example a long slow lens on, once set for the day it never changes.

In my view, all these auto modes are a waste of time. My K10D spends most of its life in manual
01-26-2008, 06:03 PM   #3
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QuoteOriginally posted by Lowell Goudge Quote
In my view, all these auto modes are a waste of time. My K10D spends most of its life in manual

The mode is irrelevent. "M" is not "Magic" mode :-) It is how you allow the camera to interpret the metering that matters. You can compose on a slightly brighter or darker area to fool the camera, set exposure compensation, or set the aperture and shutter yourself in "M". If you don't get the exposure right, the M mode does not help.

The the OP - The K100D has no tweaks, and in fact Auto ISO is disabled when you use EV compensation...
01-26-2008, 06:17 PM   #4
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Just to give you some info on how our auto ISO prioritizes things.

In Av mode:
It will aim for a shutterspeed faster than 1/focal length. My 50mm prime, the target shutterspeed was 1/60. On my 50-200 DA, it depended on the focal length. It was around 1/125 when I was at about 100mm. 1/200 at 200mm. On my 18-55 DA, it ranged from 1/30 at 18mm range to 1/90 at 55mm.

If the aperture gets smaller, it will increase the iso to maintain the targeted shutterspeed rule until it has reached the maximum designated ISO. From then on, it will slow down your shutterspeed.

Going the other direction, if there's so much light that minimum ISO still lets in too much light, it will increase shutterspeed.

Turning on or off SR had no affect on the shutterspeed preference.

Oh, and our auto ISO can do 1/2 ev steps or 1/3 ev steps. Horray.


Last edited by AVANT; 01-26-2008 at 06:23 PM.
01-26-2008, 08:12 PM   #5
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QuoteOriginally posted by SpecialK Quote
The mode is irrelevent. "M" is not "Magic" mode :-) It is how you allow the camera to interpret the metering that matters. You can compose on a slightly brighter or darker area to fool the camera, set exposure compensation, or set the aperture and shutter yourself in "M". If you don't get the exposure right, the M mode does not help.

The the OP - The K100D has no tweaks, and in fact Auto ISO is disabled when you use EV compensation...
The point I was trying to make is that you use M (manual) mode and set the exposure exactly how you want it, Automatic modes, either Tv Av or in the K10D Sv all let the camera follow preprogrammed curves, and while usually the photo's turn out all right, I find it much more reliable in many situations to meter off a surface you want exposed properly, and the rest will follow correctly based on the exposure you set.

reliance on automatic modes including ISO is ok to get a quick result if you don't understand photography, but there is no replacement for learning the theory behind photography. once you do, you will use less and less auto features, because you want to decide most of these things for yourself.
01-26-2008, 08:22 PM   #6
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QuoteOriginally posted by AVANT Quote
Just to give you some info on how our auto ISO prioritizes things.

In Av mode:
It will aim for a shutterspeed faster than 1/focal length. My 50mm prime, the target shutterspeed was 1/60. On my 50-200 DA, it depended on the focal length. It was around 1/125 when I was at about 100mm. 1/200 at 200mm. On my 18-55 DA, it ranged from 1/30 at 18mm range to 1/90 at 55mm.

If the aperture gets smaller, it will increase the iso to maintain the targeted shutterspeed rule until it has reached the maximum designated ISO. From then on, it will slow down your shutterspeed.

Going the other direction, if there's so much light that minimum ISO still lets in too much light, it will increase shutterspeed.

Turning on or off SR had no affect on the shutterspeed preference.

Oh, and our auto ISO can do 1/2 ev steps or 1/3 ev steps. Horray.
So you're saying it tries to keep things on the right side of the 1/(35mm equiv) for shutter speed rule, and that when using a zoom it automatically adjusts for the chosen focal length, changing dynamically as you zoom through the values? Is this based on your experience or definite inside" type knowledge?
01-26-2008, 08:31 PM   #7
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QuoteOriginally posted by Arpe Quote
So you're saying it tries to keep things on the right side of the 1/(35mm equiv) for shutter speed rule, and that when using a zoom it automatically adjusts for the chosen focal length, changing dynamically as you zoom through the values? Is this based on your experience or definite inside" type knowledge?
Based upon playing with it a long time ago when I saw a similar post and got curious. BUT, I have never used it in the field, always go manual ISO setting.

I have also heard some complaints with respect to flash and auto ISO, and tested this also. Auto ISO will leave the ISO very high looking for a solution without flash and as a result, in a dark room, even with all the power of an AF540FGZ (more than enough to blister the paint 10 feet away) the camera will keep the ISO at the maximum range. As I said, I played enough to see what it did, and found I didn;t like how it behaved. I leave it off.
01-26-2008, 09:32 PM   #8
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QuoteOriginally posted by AVANT Quote
Just to give you some info on how our auto ISO prioritizes things.

In Av mode:
It will aim for a shutterspeed faster than 1/focal length. My 50mm prime, the target shutterspeed was 1/60. On my 50-200 DA, it depended on the focal length. It was around 1/125 when I was at about 100mm. 1/200 at 200mm. On my 18-55 DA, it ranged from 1/30 at 18mm range to 1/90 at 55mm.
So it uses something between 1/focal lenght and 1/focal length*1.5 without a transperent guideline!? I think that's better that the Nikon approach but still suboptimal considering the possibility to handhold longer shutter speed with the help of Shake Reduction and thus get lower ISO. Too bad there's no way to really make use of this and get cleaner images by adjusting the Auto ISO to one's individual experiences with SR.

I know that many prefer to adjust ISO manually, but if you have a transparent and sensible algorithm there is no point in bothering yourself about ISO, because it is not so much of a creative decision but rather deterministic and only a function of focal length and maybe subject movement.

Getting rid of this clear-cut ISO decision by automaticly adjusting it to the personal needs would enable the photographer to concentrate on the critical parts of his art. At least in my case.

Well, thank you anyway,
pareto.

01-27-2008, 01:27 AM   #9
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QuoteOriginally posted by Arpe Quote
So you're saying it tries to keep things on the right side of the 1/(35mm equiv) for shutter speed rule, and that when using a zoom it automatically adjusts for the chosen focal length, changing dynamically as you zoom through the values? Is this based on your experience or definite inside" type knowledge?
Based on experience. I just tested it again using my various lens pointing at a 60w light bulb just now (and no my eye did not thank me during this ordeal ). All my lens are Pentax branded and are new enough to carry communicate lens information with the camera. I do not know how this will hold true for third party lens, but I would love to find out if Auto ISO works the same for someone else using their 3rd party lens.

To pareto, I don't disagree that a more customizable Auto ISO can be beneficial. To be honest though, I haven't missed any photo opportunities because of this feature (and that's what matters in the end right?), so it's not a complete loss. With adjusting ISO so easy on my K10D, I spend more time in manual ISO than Auto ISO, even though I do use the feature at times.
01-30-2008, 07:28 AM   #10
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QuoteOriginally posted by pareto Quote
Too bad there's no way to really make use of this and get cleaner images by adjusting the Auto ISO to one's individual experiences with SR.
There is. It's called the TAv mode on the K10D. Set your shutter and aperture however you like and the ISO will automatically adjust to keep the exposure.
01-30-2008, 09:34 AM   #11
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QuoteOriginally posted by Jodokast96 Quote
There is. It's called the TAv mode on the K10D. Set your shutter and aperture however you like and the ISO will automatically adjust to keep the exposure.
One week with a K100D and already I want a K10D, since the auto-ISO feature is useless.

It's all rather simple to me. There are three basic parameters to a shot: shutter speed, aperture and ISO. All three need to be be easily adjustable. The current settings for all three must be easily visible. And there should be modes that allow us to set any two and let the final parameter be controlled automatically. Everything else (exposure compensation, fill flash, auto modes) is gravy.

From what I can see the K10D allows all this but the K100D makes it difficult. Anyone want to trade?
01-30-2008, 09:47 AM   #12
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QuoteOriginally posted by Jodokast96 Quote
There is. It's called the TAv mode on the K10D. Set your shutter and aperture however you like and the ISO will automatically adjust to keep the exposure.
I just want to emphasize this point made by Jodokast96. I read the OP's post and then scrolled down to see if anybody mentioned TAv on the K10D.

I think TAv mode is one of the most brilliant features of this brilliant camera. When I have plenty of light, I shoot M. But when the light gets low (say, shooting indoorr sports), I switch to TAv. I set the aperture to f/2.8 and shutter speed to whatever (say, 1/300th) and let the camera adjust the sensitivity from one shot to the next so that I get the photo. Great feature and I could not imagine living without it.

Will
01-31-2008, 09:03 AM   #13
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QuoteOriginally posted by WMBP Quote
Great feature and I could not imagine living without it.
Yeah, yeah, ok, rub it in!
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