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10-21-2011, 02:56 AM   #1
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Auto EV Compensation

Hi there,

in the K10 / K20 Custom menu there is a selection for Auto EV Compensation for over exposed pictures.

The default if OFF but I had set mine to on (apparently - I don't remember). There is nothing in the manuals about it other than to say there is a setting to do it.

So, does anyone have an insight as to the operation of this feature? Does a Manual EV compensation setting turn it off?

Any help would be appreciated.

Bill

Edit

Have just found this answer from Alph Dog in a 2008 thread:-

"Email response from Pentax

--------------------------------------------------------------------------------

This is the main part of the email I got when asking what "auto EV Compensation" does.

---------------------------------------------------------------

Thank you for contacting Pentax.

Auto EV would work in any mode other than Bulb or M.

Normally, a camera tries to balance an image to 18% gray.
With auto-EV the camera looks at the scene and applies EV compensation based what it thinks is supposed to be correct.
It may look at a scene of all snow and think, hey, 18% gray is probably not right for this, lets balance it to a brighter level.
This system is of course imperfect, but can help out a newer photographer to get shots correct more often, or help even an experience photographer who might just be in a hurry.

If you are in need of further assistance, please respond to this email or call our technical support center at 800-877-0155.

-------------------------------------------------------------------

I guess this would make it a type of "idiot" mode, but I've tried to push my k20d to make some type of auto ev adjustment and it doesn't seem like it's doing anything.

And just to re-clarify, this is the setting in the custom menu, NOT the setting when you do multi-exposure. "

But I wonder if there has been any more light shed on it since then.

Bill


Last edited by Billgscott; 10-21-2011 at 03:05 AM. Reason: More info
10-21-2011, 07:02 AM   #2
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Have you looked at your exif? The camera will probably indicate that an ev shift has occurred.

Btw, if you're looking for a more permanent way to avoid over/under exposing, you should look in to shooting in raw.
10-21-2011, 07:58 AM   #3
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I can't imagine how this is feasible.

Camera meters scene - it does not know if it is snow or coal.

With Auto EV on, it now somehow smartens up to know what the scene is?
10-21-2011, 08:19 AM   #4
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Hi Adam,

I do shoot RAW + and use the jpgs as a contact sheet on my PC.

The K20 I have has seemed to be fighting me when I was dialing in a bit of +EV manually.

I have turned it off now but would like to understand how it works.

It looks like no-one knows though.

Bill

10-21-2011, 03:25 PM - 1 Like   #5
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I do know how it works. Its a feature that does just a little to help in real life and probably why its off by default. But it can help sometimes. To see what it does put on a fully auto lens such as the kit DA18-55mm. Set the camera to Av mode and wide open (f/3.5), set ISO to ISO6400. Now with Auto EV off take a pic of a light bulb or other strong light source (not the sun!), make sure the shutter speed is pegged at 1/4000 and the camera is saying your over exposed (flashing shutter speed number in OVF). Turn on auto EV and take the pic, or just hold down the shutter in half press position and you will see the aperture go up by itself to avoid a seriously over-exposed pic! Same with speed, set it to Tv mode and experiment with it on and off. With is off you can take a over exposed pic, with it off you will not be able to take an over exposed (I think under as well) pic in some modes as Av.

It works when you need more than 1/4000 shutter speed to avoid over exposure; or higher f/stop. The K20D will automatically set the aperture from f/3.5 to f/5.6 or some value that works. Remember try taking pics that exceed the 1/4000 shutter limit. If your in Av mode and set the aperture to f/3.5 and the K20D can go to 1/2000 without over exposing that's where it will go. But if your at the same and it needs 1/5000 to avoid being over exposed with EV Comp off you will over expose, with it on the K20D will set a high f/stop number to avoid over EV.

When I am testing I turn off EV Comp so it does not fool me e.g. if I want f/2.8 I don't want the K20D to set it behind my back to f/5.6. When general shooting I turn on EV comp because it can save a pic.

Last edited by jamesm007; 10-21-2011 at 03:31 PM.
10-22-2011, 02:36 AM   #6
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QuoteOriginally posted by jamesm007 Quote
I do know how it works.
Thnks, very interesting. It would explain why some of my f2.8 shots were at f4 in the metadata.

I'll have to have a play I think.

Cheers - Bill
10-22-2011, 09:41 AM   #7
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Thanks Bill.

I to played with it more. Auto EV Compensation does in fact correct under exposure as well. So this IMO is a nice not so known feature it seems, I hope you or other don't mind me speaking of it some more. I would be glad to read your (Bill) results as well. Its useful if your just shooting and not paying attention to what the numbers are telling you. If you shooting in low light and are in Tv mode with ISO set to 400 and shutter speed at 1/200 and this is not slow enough to get a proper exposure the Auto EV Comp feature will lower your shutter speed accordingly for you (say to 1/50). As soon as you half press the shutter button it will lower the speed, and if you were not paying attention you will never know the camera changed shutter speed on you becuase it goes right back to 1/200 were you had it. That can trick you

Auto EV Compensation is in the Custom Menu number 10 for the K20D. Keep it on if your just taking pics. The only reason I can see turning it off is if you want full control. I remember doing BF/FF testing on my Sigma 17-70mm. Of course I test at f/2.8. I guess I was not paying attention to what the camera was telling me and I go in look at them and they are all at f5.6 (about). I thought WTHeck. So I double check everything and found I had Auto EV Compensation on. I had to turn it off and find a darker area to shoot in. But other than stuff like that I can't think of a reason not to use it. Most of the time you will be within the cameras settings you chose. But if you get it wrong the camera can save the pic!
10-26-2011, 11:07 AM   #8
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Had a play

Had a play over the weekend and it is as you said.

Thanks for pointing me in the right direction.

Bill

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