AutoISO Limits

Marsu42 · February 17, 2013, 09:49:17 PM

The shiny new cameras like 6d & 5d2 have an advanced auto-iso function that lets you set lower and upper limits. It'd be mighty useful to backport this feature to older and lesser camera bodies, for example on my good ol' 60d it's only possible to set some crude upper iso limits. Esp. a lower iso limit is important to prevent the camera going down to iso100 and setting too slow shutter or too large aperture.

Yes, this can be somehow circumvented by using the fixed "ML Auto ISO" settings, but it works only in Av/Tv mode, but a more flexible solution would be very useful. The alternative solution to a 5d3/6d backport would be to improve "ML Auto ISO" to use *minimal* shutter/aperture values which would also prevent the camera using unnecessary low iso values.

epozar · February 23, 2013, 11:38:04 AM

Nikon has it done very well. Why not just copy the idea? D800/600

Marsu42 · February 23, 2013, 04:15:45 PM

Quote from: epozar on February 23, 2013, 11:38:04 AM
Nikon has it done very well. Why not just copy the idea? D800/600

I don't have a d800/600 here right now :-p ... can you describe how Nikon's approach works, maybe in constrast to what the 6d/5d3 do?

epozar · February 23, 2013, 07:49:46 PM

Just made a simple check:

D600, M mode, AUTO-ISO set

1/15, f3.5 ambient exposure correction set = 0 (ISO100)
1/15, f3.5 ambient exposure correction set = +1.7 (ISO250)

And the second image is visibly lighter than the first.
Note, in the viewfinder there is always "needle in the center", only when I press the correction button I can see the amount set.

1% · February 23, 2013, 08:12:39 PM

Would have to check the props on 600D, lower limit prop might be there. Compare with 60D then 6D/5d3.

Marsu42 · February 23, 2013, 08:51:33 PM

Quote from: epozar on February 23, 2013, 07:49:46 PM
D600, M mode, AUTO-ISO set

What you describe is more like "ec on m" that I have requested here and that's really sourly missing from Canon: http://www.magiclantern.fm/forum/index.php?topic=4514.0

This feature request is simply about setting upper and lower(!) iso limits like Canon allows for on the 6d/5d3, but lesser or older camera bodies only have an upper limit so the camera often falls back to iso 100 with an unnecessary low shutter speed or a too large aperture (= too shallow depth of field).

But all these auto-iso/shutter/aperture dependencies are interwoven, another (dismissed) feature request is a lower shutter speed limit that's also available on 5d3/6d but not for the rest of us: http://www.magiclantern.fm/forum/index.php?topic=4672.0

Personally I would like to have all of these because they all make sense in different shooting conditions, shutter speed limit (5d3/6d), lower auto-iso limit (5d3/6d), ec on m (Nikon).

epozar · February 25, 2013, 08:55:59 AM

In Nikon D600/800 you can set minimum allowable shutter speed either by specifying a fixed value or a value based on a focal length. However, the second option also has a further option: +/- two stops so you can prefer faster shutter speed for "shaky hands" or a slower one if you shoot say landscapes and/or use a stabilised lens.
In Canon 6D this "focal-length linked" minimum shutter speed is rather bad implemented - choosing 1/50 for my fixed 100mm lens for example. Also a range of fixed speeds are limited (1/125-1/250.. only full stops).

epozar · February 25, 2013, 09:48:15 AM

One more thing: Canon 6D chooses a lower speed if the AUTO-ISO runs out of "available ISOs" (e.g. max), I think this cannot be changed.
But it is frustrating - I wish the minimum speed be "fixed" (because better to have a darker image than a blurry one!).
At least an option will be fine..

Marsu42 · February 25, 2013, 09:59:18 AM

Quote from: epozar on February 25, 2013, 08:55:59 AM
In Canon 6D this "focal-length linked" minimum shutter speed is rather bad implemented - choosing 1/50 for my fixed 100mm lens for example. Also a range of fixed speeds are limited (1/125-1/250.. only full stops).

This is Canon deliberately crippling the 6d firmware (thanks, Canon!) - on the 5d3 there are more selectable values, even more on the 1dx. So if you want Canon to change some bytes in the firmware you have to pay a couple of thousand $$$ ... I'm glad we have ml. I never have shot Nikon, but it seems their firmware is less conservative and more thought through.

1% · February 25, 2013, 04:59:28 PM

I bet some of this behavior can be altered with cache hacks.

QuoteI think this cannot be changed

Cache hack the decision point that says to lower shutter into NOP. The minimums can probably be changed too. Just needs some looking into the functions/props.

6D didn't get much TLC, just look at the convoluted canon menus. Just looks like a bunch of the same icons at the top... and they complained about ML menus being all over the place...

Found: PROP_LIMITED_TV_VALUE_AT_AUTOISO so maybe on 6D this limit can be changed to whatever.

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AutoISO Limits