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Canon SX40HS Force Aperture to F2.8 While At Max Zoom

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Offline blenderbach

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Canon SX40HS Force Aperture to F2.8 While At Max Zoom
« on: 05 / March / 2022, 23:57:22 »
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Guys? Is there a way to force the Canon SX40HS Aperture to be F2.8 while at maximum zoom? I noticed that while I zoom in, the Aperture goes from 2.8 to around F5.0...
I really want to know, if CHDK can forcefully make the Aperture go to F2.8 while at maximum zoom. I need this, so it lets more light in, so I can do Astrophotography, but whatever I try, the aperture gets smaller while I zoom in! Any ideas? I'm going crazy... :-X
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Offline reyalp

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Re: Canon SX40HS Force Aperture to F2.8 While At Max Zoom
« Reply #1 on: 06 / March / 2022, 14:18:10 »
Quote from: blenderbach on 05 / March / 2022, 23:57:22
Guys? Is there a way to force the Canon SX40HS Aperture to be F2.8 while at maximum zoom? I noticed that while I zoom in, the Aperture goes from 2.8 to around F5.0...
No, this is physically impossible. The f number is the focal ratio, so the same physical aperture position gives a higher f number when you zoom in to a longer focal length.
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Offline blenderbach

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Re: Canon SX40HS Force Aperture to F2.8 While At Max Zoom
« Reply #2 on: 06 / March / 2022, 14:28:03 »
Quote from: reyalp on 06 / March / 2022, 14:18:10
Quote from: blenderbach on 05 / March / 2022, 23:57:22
Guys? Is there a way to force the Canon SX40HS Aperture to be F2.8 while at maximum zoom? I noticed that while I zoom in, the Aperture goes from 2.8 to around F5.0...
No, this is physically impossible. The f number is the focal ratio, so the same physical aperture position gives a higher f number when you zoom in to a longer focal length.

Then how do I make the Camera take in more light at higher zooms? I need that big aperture but a higher zoom...
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Offline reyalp

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Re: Canon SX40HS Force Aperture to F2.8 While At Max Zoom
« Reply #3 on: 06 / March / 2022, 16:21:13 »
Quote from: blenderbach on 06 / March / 2022, 14:28:03
Then how do I make the Camera take in more light at higher zooms? I need that big aperture but a higher zoom...
Unless you physically change the optics, the only way to collect more light is to use a longer exposure. Of course, unless you use a tracking mount, the length of exposure you can use before trailing becomes a problem is limited, and the higher the zoom, the shorter the limit. You can take multiple exposures below the limit and stack them to get deeper images, but this becomes impractical at high zoom because the minimum exposure is so short.
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Offline blenderbach

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Re: Canon SX40HS Force Aperture to F2.8 While At Max Zoom
« Reply #4 on: 04 / April / 2022, 01:31:07 »
Quote from: reyalp on 06 / March / 2022, 16:21:13
Quote from: blenderbach on 06 / March / 2022, 14:28:03
Then how do I make the Camera take in more light at higher zooms? I need that big aperture but a higher zoom...
Unless you physically change the optics, the only way to collect more light is to use a longer exposure. Of course, unless you use a tracking mount, the length of exposure you can use before trailing becomes a problem is limited, and the higher the zoom, the shorter the limit. You can take multiple exposures below the limit and stack them to get deeper images, but this becomes impractical at high zoom because the minimum exposure is so short.

Alrighty, thanks for the information! :D
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