SD500 stuck on f2.8?? - General Chat - CHDK Forum
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SD500 stuck on f2.8??

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Offline jbourgui

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SD500 stuck on f2.8??
« on: 08 / July / 2008, 15:11:59 »
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OK, maybe somebody can help me with this...  I've used the SD500 for years, probably taking in excess of 8k images with it...  I had retired it for a while (~1 year) due to my G9 purchase, but then I found CHDK, and now the SD500 is back up and running with hacks, scripts, etc. 

The weird thing is that it appears to only be shooting at f2.8, in every focus mode, and with the dial on A or M.  I have verified with EXIF data, as well as CHDK's on screen display that the only thing that changes when exposure needs adjusting is shutter speed.  As a result of the camera always being in f2.8, it almost always pops up the "shaky camera" warning icon, and will have exposure times of 1/6" to 1/4" in a relatively brightly lit room...

For the SD500, Canon lists these aperature ranges: f/2.8-7.1 (W), f/4.9-13.0 (T)   

I read somewhere that some Canon P&S cameras only have one aperature and "fake it" with an ND filter to come up with others...  is this what is happening?

Help me out!!  Has my aperature been stuck for a while, and I just now noticed it, due to CHDK's awesome OSD?   Is there another way to test this out?  Is my out of warranty camera just screwed?  Do I get to take apart the case and mess with it?  :)

Cheers!

-joe
« Last Edit: 08 / July / 2008, 15:28:16 by jbourgui »
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Offline cyril42e

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Re: SD500 stuck on f2.8??
« Reply #1 on: 08 / July / 2008, 16:08:43 »
Quote from: jbourgui on 08 / July / 2008, 15:11:59
The weird thing is that it appears to only be shooting at f2.8, in every focus mode, and with the dial on A or M.  I have verified with EXIF data, as well as CHDK's on screen display that the only thing that changes when exposure needs adjusting is shutter speed.  As a result of the camera always being in f2.8, it almost always pops up the "shaky camera" warning icon, and will have exposure times of 1/6" to 1/4" in a relatively brightly lit room...

For the SD500, Canon lists these aperature ranges: f/2.8-7.1 (W), f/4.9-13.0 (T)   

I read somewhere that some Canon P&S cameras only have one aperature and "fake it" with an ND filter to come up with others...  is this what is happening?

f2.8 is a wide aperture, so it shouldn't be related to the "shaky camera warning icon" or long exposure times. ND filter simulates narrower apperture, in your case f7.1 (W) to f13 (T), by blocking some light. When you head your camera toward a strong light you should hear a noise in the lens that corresponds to the ND filter coming in place (OSD and EXIF should then show f7.1), and the same noise when you head the camera back to darker area (ND filter coming out).
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Offline jbourgui

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Re: SD500 stuck on f2.8??
« Reply #2 on: 08 / July / 2008, 16:13:30 »
cyril42e, thanks for the quick reply!   Looks like my camera needs to basically be pointed at the sun to have the ND drop in (the clunk noise you mentioned), at this point it does read f7.1    Thanks for the clarification!

-joe
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Offline fe50

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Re: SD500 stuck on f2.8??
« Reply #3 on: 08 / July / 2008, 17:16:02 »
Quote
I read somewhere that some Canon P&S cameras only have one aperature and "fake it" with an ND filter to come up with others...  is this what is happening?

Yes, the Ixus series has no iris (aperture), they have a ND filter instead.

They have #define CAM_HAS_ND_FILTER  1  in the camera.h (in the sources).

You can also see the ND filter swinging in / out (on the reflexions in the lenses) when you focus into a strong light.
The ND filter is always "in" (=active) in the Canon fireworks scene mode, there the highest F stop is selected (F8.0 on my SD870).
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