Ixus 115 hs = Elph 100 hs: Why CHDK doesn't have aperture control?

2frugal

12

« on: 02 / May / 2018, 16:09:11 »

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Hello!

Just curious, why CHDK doesn't have aperture control (Av override) for Ixus 115 hs = Elph 100 hs? I first thought the aperture is non-controllable (always open as is), but I see two apertures for wide zoom, F2.8 and F7.9 (example two DNGs; and it's not mistake: the two images give same exposure of same object). So canon firmware controls it. Why CHDK doesn't?

Thanks

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waterwingz

12140

Re: Ixus 115 hs = Elph 100 hs: Why CHDK doesn't have aperture control?

« Reply #1 on: 02 / May / 2018, 16:13:54 »

Because as you guessed, the camera does not have a adjustable aperture. You will however see different f-stop values reported in your images as you either change the zoom lens position or as the camera inserts or removes an internal neutral density (ND) filter from the light path as needed.

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2frugal

12

Re: Ixus 115 hs = Elph 100 hs: Why CHDK doesn't have aperture control?

« Reply #2 on: 02 / May / 2018, 17:05:36 »

Quote from: waterwingz on 02 / May / 2018, 16:13:54

... or as the camera inserts or removes an internal neutral density (ND) filter from the light path as needed.

Oh, ok, thanks, I didn't understand what ND is when I was reading the manual (and skipped it).

Could you explain a bit more, how to manually enable/disable this ND? I just tried its setting, "In" and "Out" (with overriden fixed Tv), and I see no difference in the visual brightness of the two jpegs (on the camera screen). The reported aperture is also same, F2.8.

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2frugal

12

Re: Ixus 115 hs = Elph 100 hs: Why CHDK doesn't have aperture control?

« Reply #3 on: 03 / May / 2018, 12:30:33 »

Ok, I found what I was doing wrong: I did not wait for auto-focus and auto-exposure during the half-shutter press. Works fine. Thank you!

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reyalp

14119

Re: Ixus 115 hs = Elph 100 hs: Why CHDK doesn't have aperture control?

« Reply #4 on: 03 / May / 2018, 12:42:19 »

Quote from: 2frugal on 03 / May / 2018, 12:30:33

Ok, I found what I was doing wrong: I did not wait for auto-focus and auto-exposure during the half-shutter press. Works fine. Thank you!

It's supposed to work in both cases, so this is probably a bug. There is a common bug like this, but the ixus115 code appears to already have the workaround

Can you check whether shutter overrides when you shoot without waiting for AF?
To test, half press to see what shutter speed the camera picks, use the CHDK "Enhanced Photo Operations" to override to something very different, then check the exposure of the resulting image.

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Don't forget what the H stands for.

2frugal

12

Re: Ixus 115 hs = Elph 100 hs: Why CHDK doesn't have aperture control?

« Reply #5 on: 03 / May / 2018, 13:08:53 »

Yes, Tv gets overridden in both cases, wait and no-wait. And I just tried again, the ND does not get overridden during a quick (no-wait) press.

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