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03-13-2011, 04:13 PM   #1
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Green button -- Optical preview ?

Is it normal for the optical preview to only be available with certain settings? It seems like it's malfunctioning, as I can't find any real rhyme or reason to when it works and when it doesn't.

03-13-2011, 04:36 PM   #2
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Which camera do you have? What lenses are you using? Which settings affect the optical preview?
03-13-2011, 05:16 PM   #3
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Oh, sorry! K-x with the kit lens. It seems random. For instance, right now I have it set to Manual, 1/15, F4.5, and it stops working just past 35mm. Change to F32, and it works from 18-55.

Is there a technical reason?
03-13-2011, 05:24 PM   #4
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Optical preview is achieved (on most bodies) by moving the on-off button all the way to the end, so that the lens stops down. I'm pretty use it can be used in any mode.


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03-13-2011, 06:11 PM   #5
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We were on a pentax event with Nicole and her Kx had Opti Preview set on the green button. Problem was it messed with her e-dial in P mode for some reason, I think it is as P mode uses the Green button to suggest an exposure.
Unfortunatly Kx can only use optipreview this way as there is no facility near the power button.
03-13-2011, 06:49 PM   #6
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QuoteOriginally posted by Brenda Lee Quote
Oh, sorry! K-x with the kit lens. It seems random. For instance, right now I have it set to Manual, 1/15, F4.5, and it stops working just past 35mm. Change to F32, and it works from 18-55.

Is there a technical reason?
It should work as you describe.

If the lens is set to F4.5 then the max. aperture of the lens will become F4.5 (and eventually F5.6) as you zoom towards a longer focal length (since the lens is a variable aperture F3.5 - F5.6 lens). At about 35mm the lens is thus by default already stopped down to F4.5 and the optical preview has no effect, since "full open" is the same as the aperture you've set.

I realize that my explanation is convoluted
03-13-2011, 08:39 PM   #7
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Thanks for the replies. I'll have to do some reading to fully understand the last post, but it's always good to know my K-x is working as it should.
03-14-2011, 12:08 AM   #8
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Look at it this way..

1. Optical Preview stops the lens down to your chosen aperture.

2. If you're using your kit lens (18-55) it has a maximum aperture of f3.5 at 18mm to f5.6 at 55mm (IIRC). If you assume every thing is linear then mid range on your zoom will have a maximum aperture of f4.5 at 36mm (it will be pretty close to that).

With optical preview you are expecting to see the viewfinder darken when you activate it, Correct?

3. If you set your zoom to 36mm and ask for f4, the camera is going to adjust for whatever the maximum aperture is. In the case of tic 2, that is f4.5. Wide open. When you activate the optical preview, the lens is already at it's chosen (adjusted) aperture and will not stop down any further.

If you want to see the effect across the entire zoom range, set your camera to something smaller than f5.6, like f8. Then at each zoom point, your camera viewfinder will darken when you activate the Optical Preview.



04-17-2011, 10:56 AM   #9
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I've had your issue before as well, but I haven't used optical preview since. I couldn't put my finger on any particular cause, but I think I might have learned that it was less of an issue when I put some recharged batteries in.
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