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11-29-2009, 10:57 PM   #1
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K-X in video mode -- questions about setting f-stop

Hello all!

First post, so please be gentle...

It's been a while since I've played around with a manual lens so I'm hoping the answer to my questions are pretty simple. Basically, what I need to know is how to set the f-stop on my stock lens to whatever I want it to be. I turn the dial and the aperture numbers change, but the exposure never changes. Also, the numbers will flash red from time to time - why is that?

I've set my AF button to 'exposure lock,' so if I do get my exposure where I want it I'm able to lock it in place and I can push or pull it a stop or two using the +/- button and the dial.

How do I set it manually, though? How will it work when I put on an old 35mm lens that has its own f-stop ring?

Thanks!

11-30-2009, 12:45 AM   #2
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I haven't used video mode all too much, but I do know that if the aperture is flashing red, that means that the camera thinks the video will be underexposed (i.e. you should choose a wider aperture).

If you mount a lens that does not have the 'A' setting on the aperture ring, the video will be shot using whatever the aperture ring is currently set to. Metering should be done accordingly by the camera.

AFAIK the camera always tries to get correct exposure. So, even if you change the aperture, you're really just changing the DOF and possibly making the video brighter in low-light conditions. I'm not sure if you can do exposure compensation in video mode, but perhaps somebody else knows!

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11-30-2009, 09:23 AM   #3
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Thanks for the reply. I did see a thread in the video section of the boards about petitioning Pentax to allow full manual control in video mode, so I guess that answers one of my questions.

Here's the thing about the flashing red aperture numbers - the numbers respond when I turn the dial but the actual exposure doesn't change at all.
11-30-2009, 10:00 AM   #4
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The exposure doesn't seem to change until you have actually depressed the shutter - it seems to me that the 'live view' you are seeing when not shooting, and the scene you see once filming will change, sometimes fairly significantly. Since you can't control ISO, I think the metering system doesn't kick in until the camera begins filming. The only real trick around it is to start filming, get the live view image to an exposure you prefer (by pointing it around until the metering has chosen a balanced image overall) and then you can use exposure lock via the AE-L button to lock that particular exposure. I don't know a whole lot about it beyond that, but it has still been fun shooting occasional vids. I love going out at night with my 50mm f1.4 and hitting proper exposure (at least the camera is indicating it can get proper exposure) down a dimly lit street though!

11-30-2009, 10:09 AM   #5
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Have you enabled the setting to allow using older manual aperture ring lenses on the camera (Custom menu C4 > Item 22 - Using Aperture ring to 'Permitted' [K-x manual page 284)?

That would be the first thing I'd look into.
11-30-2009, 11:33 AM   #6
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QuoteOriginally posted by rawr Quote
Have you enabled the setting to allow using older manual aperture ring lenses on the camera (Custom menu C4 > Item 22 - Using Aperture ring to 'Permitted' [K-x manual page 284)?
That would be the first thing I'd look into.

I have, but I haven't gotten any of the new lenses I've ordered yet. Right now I'm just monkeying around with the stock lens. I've been getting worried that I'm not going to have the control I want over the older 35mm lenses, though.

I'll try setting my aperture and then letting it record to see if that changes anything.

If I lock the aperture in-camera with the AE-L button, can I then have free reign over the aperture with my 35mm lens?
11-30-2009, 01:06 PM   #7
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I was under the impression that if you have the video setting to pre-select the aperture (vs. the auto setting), that the aperture remains fixed throughout the video being shot, and that the camera then changes exposure via variable ISO, which is not a controllable setting regardless (I don't know if shutter speed factors in at all, anyone else know? I am assuming since it is 24p that it is running at 24 frames/second, at a fixed interval).

From using my 50mm f1.4 A lens, you are able to change the aperture manually - if you lock the exposure during shooting it will get darker or lighter accordingly - if you don't lock exposure then the ISO will be adjusted to compensate - the benefit of course being the change in depth of field (especially with wider aperture lenses).
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