Ixus860/SD870 Setting Aperture - General Discussion and Assistance - CHDK Forum
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Ixus860/SD870 Setting Aperture

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Offline littlejohn

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Ixus860/SD870 Setting Aperture
« on: 03 / August / 2008, 23:59:28 »
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Hi,

I'm using Allbest CHDK.
My camera is Ixus860.
I would like to know if there is any way to override the aperture,
such as setting the aperture to any value, or just overriding the aperture to the MIN/MAX value.
Letting ND filter IN would minimize the aperture (f8), however, the screen becomes darker and needs slower shutter speed.

Thanks,
John
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Offline fvdk

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Re: Ixus860/SD870 Setting Aperture
« Reply #1 on: 04 / August / 2008, 01:56:23 »
Hi John,

The Ixus series don't have apertures. Try searching the forums, there are some treads about this.

Frans
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Offline littlejohn

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Re: Ixus860/SD870 Setting Aperture
« Reply #2 on: 04 / August / 2008, 02:41:05 »
Thank you, Frans.  :)

I've read the threads about the aperture topic.
It surprises me quite a lot, since in my opinion the aperture is the basic component in any camera.
Then, how does it "control" the aperture value when shooting  :-[
Some of my photos have aperture value 2.8, some have 5, some have 5.6, etc. (according to the EXIF)
Or Ixus860 can use the built-in ND filter to control the aperture shown in the EXIF?
It really confuses me.

John
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Offline fvdk

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Re: Ixus860/SD870 Setting Aperture
« Reply #3 on: 04 / August / 2008, 02:51:05 »
Quote from: littlejohn on 04 / August / 2008, 02:41:05
Thank you, Frans.  :)

I've read the threads about the aperture topic.
It surprises me quite a lot, since in my opinion the aperture is the basic component in any camera.
Then, how does it "control" the aperture value when shooting  :-[
Some of my photos have aperture value 2.8, some have 5, some have 5.6, etc. (according to the EXIF)
Or Ixus860 can use the built-in ND filter to control the aperture shown in the EXIF?
It really confuses me.

John

Hi John,

It still confuses me too :-)
I think that the values that are shown in the EXIF are the equivalent settings of shutter speed and aperture as they would be when the camera would actually have aperture settings.

I still wonder if the ND filter has one value or if the camera can electronically dim it so it can mimic different ND values.

Frans
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Offline PhyrePhoX

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Re: Ixus860/SD870 Setting Aperture
« Reply #4 on: 04 / August / 2008, 03:46:35 »
i think it maybe also has to do with zoom.
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Offline fe50

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Re: Ixus860/SD870 Setting Aperture
« Reply #5 on: 04 / August / 2008, 04:21:03 »
Quote from: PhyrePhoX on 04 / August / 2008, 03:46:35
i think it maybe also has to do with zoom.
Yes, the SD870 has F2.8 (ND filter out) - F8.0 (ND filter in) without zoom, with *EDIT: full zoom you'll get F5.8 (ND out) - F16 (ND in) under the same conditions.
The F-stops are "virtual", calculated from ND filter, exposure time / shutter speed...

The ND filter swings in/out, mechanical, you can hear this, no el. dimming...
« Last Edit: 04 / August / 2008, 04:38:29 by fe50 »
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Offline littlejohn

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Re: Ixus860/SD870 Setting Aperture
« Reply #6 on: 04 / August / 2008, 05:07:59 »
So is it the reason why 860 cannot take a picture just like this one?  :'(
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Offline fe50

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Re: Ixus860/SD870 Setting Aperture
« Reply #7 on: 04 / August / 2008, 05:27:08 »
No, littlejohn, you can take such a picture with every (CHDK-powered Canon) camera  :D

-> use a tripod, long time shutter, low ISO...

The pic looks like a HDR, multiple pictures with different exposures combined...
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Offline littlejohn

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Re: Ixus860/SD870 Setting Aperture
« Reply #8 on: 04 / August / 2008, 06:27:52 »
I mean the "star"-shape lighting coming from each street lamp.
It seems necessary to have small 'aperture' (in physics) to photo such a picture.
However, in 860, no physical aperture exists... @@
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Offline whoever

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Re: Ixus860/SD870 Setting Aperture
« Reply #9 on: 04 / August / 2008, 06:48:27 »
Quote from: littlejohn on 04 / August / 2008, 06:27:52
I mean the "star"-shape lighting coming from each street lamp.
It seems necessary to have small 'aperture' (in physics) to photo such a picture.
However, in 860, no physical aperture exists... @@
Precisely. The crosstar reflects diffraction in the hexagonal opening of 6-bladed iris aperture, the latter being absent in IXUS'es.
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