(Sometimes) there is no aperture. - Hotwire! Hardware Mods, Accessories and Insights - CHDK Forum
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(Sometimes) there is no aperture.

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Offline daniel_reetz

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(Sometimes) there is no aperture.
« on: 17 / August / 2009, 08:17:29 »
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Inspired by this and this, I disassembled a broken Powershot A530 to understand the aperture mechanism.  

In the Powershot A530, there is no separate aperture mechanism. That leaves two possible outcomes:

1. There is no true aperture adjustment, and "aperture" as set by the camera is faked with some combo of shutterspeed and amplifier gain + ND filter;

2. The shutter is somehow opened only partially in order to serve both roles. There should be a way to identify this, either by watching it with a videocamera, or seeing its signature shape in the bokeh.

Here are the videos:
Canon Powershot A530 shutter mechanism.

Canon Powershot A530 lens assembly overview.

I took hundreds of disassembly photos, but unfortunately my memory card ate them. I tried Photorec and other apps, but they are really gone.

I know that the CHDK community has known about the ND filter thing for a while, but there is just one... how do we account for the many aperture settings?
« Last Edit: 17 / August / 2009, 08:55:00 by daniel_reetz »
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Offline daniel_reetz

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Re: There is no aperture.
« Reply #1 on: 17 / August / 2009, 08:31:44 »
fbonomi points out:

Quote
Other cameras have a real Iris, and aperture is a real aperture

Cameras with an Iris
G7
a540 a570
a610 a620 a630 a640 a650
a700 a710 a720
s2 s3 s5
tx1
sx100

Cameras without an Iris
a450 a460
a530 a550 a560
sd300(ixus40) sd400(ixus50) sd450(ixus55) sd600(ixus60) sd630(ixus65)
sd1000(ixus70) sd1100(ixus80) sd500(ixus700) sd550(ixus750) sd700(ixus800)
sd800(ixus850) sd870(ixus860) sd850(ixus950) sd950(ixus960)

(info from the CHDK source, include\camera.h)
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Offline Ailurus fulgens

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Re: There is no aperture.
« Reply #2 on: 17 / August / 2009, 08:40:46 »
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I know that the CHDK community has known about the ND filter thing for a while, but there is just one... how do we account for the many aperture settings?
many? it's either ND filter in or out. and then it's the zoom. zooming changes the amount of light coming to the sensor, so in a way it is changing aperture. thats about it :)

so, after you found out stuff everybody already knows, did you manage to put it back together again and it still works? :D
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Offline daniel_reetz

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Re: There is no aperture.
« Reply #3 on: 17 / August / 2009, 08:45:35 »
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so, after you found out stuff everybody already knows, did you manage to put it back together again and it still works? Big Grin

I fix Powershots all the time, but if you read my post, you would see that I said the camera was broken to begin with.

I have never seen a video, pictures, or anything more than discussion of what "aperture" means, and as pointed out above, that info is only accurately available in source code (the wiki is off and the forums are dense).
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Offline Microfunguy

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Re: There is no aperture.
« Reply #4 on: 17 / August / 2009, 09:08:57 »
On camera with no aperture diaphragm, 'aperture' refers to how much the incoming light is attenuated.
This is affected by whether the ND filter is in or out and the zoom setting.
The ND filters do vary slightly in their precise attenuation, even on the same model of camera.

Effective aperture changes with the zoom because the position of the exit pupil changes position and size as you zoom.

As far as fitting external lenses is concerned there are so many problems that I do not think it worth the effort, though I have tried.

You have to defeat three or four feedback sensors at the appropriate times to fool the firmware.

Secondly, most lenses for other formats simply do not have the resolution.
Even relatively small format like CCTV lenses are quite poor quality.

Thirdly, for most digital camera the chief rays should approach the sensor as near perpendicular as possible, this requires special design.

If you want to play around with legacy lenses from C-mount to 35mm size, buy a micro 4/3 camera.

I think that I might  :)

David
« Last Edit: 17 / August / 2009, 10:24:10 by Microfunguy »
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Offline daniel_reetz

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Re: (Sometimes) there is no aperture.
« Reply #5 on: 17 / August / 2009, 12:24:11 »
Thank you for taking the time to put all that information in one place.

It's not old lenses I'm interested in -- I need some general purpose small sensors. Was hoping to do better than webcams, but that looks like where I'll be taking this...
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Offline Microfunguy

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Re: (Sometimes) there is no aperture.
« Reply #6 on: 17 / August / 2009, 13:08:14 »
Quote from: daniel_reetz on 17 / August / 2009, 12:24:11
I need some general purpose small sensors.

Image below shows a (genuine) 2MP webcam that I converted to C-mount.
There are various no-name Chinese and Taiwanese cameras that do not require a mechanical shutter so are easier to play with.

You still have the problems mentioned previously and need to obtain small, thin, IR-blocking filters.

Even after all that, they are let down by the quality of the firmware.
We are so used to seeing the good quality and accurate-colour JPG's produced by the Canon cameras.
These other options are normally of quite poor quality, depending on the lighting.

I have given-up, life is too short  ;)

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Offline fbonomi

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Re: (Sometimes) there is no aperture.
« Reply #7 on: 17 / August / 2009, 13:33:29 »
Quote from: Microfunguy on 17 / August / 2009, 13:08:14
Image below shows a (genuine) 2MP webcam that I converted to C-mount.

Ohh... that is wizardry!!!

Anyway yes, image quality with those things is awful...

I know you would take away the crappy lens that comes with them, but Iguess the overall quality is commeasured with the lens!
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Offline RaduP

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Re: (Sometimes) there is no aperture.
« Reply #8 on: 17 / August / 2009, 14:15:29 »
Some Logitech cameras are quite good though, especially in low light. But yes, I really, really wish some Chinese camera makers would open source their firmware so that we can do more fancy stuff with them :)
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Offline Microfunguy

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Re: (Sometimes) there is no aperture.
« Reply #9 on: 17 / August / 2009, 14:23:06 »
Quote from: fbonomi on 17 / August / 2009, 13:33:29
I know you would take away the crappy lens that comes with them

To be fair, that is a CCTV lens that I attached just for the photo.
The lens on the webcam is made by  Carl Zeiss.

I never tested it but imagine it would be better than the lens shown.
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