Canon SX230 HS

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Offline kollamraja

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Canon SX230 HS
« on: 27 / October / 2013, 04:16:17 »
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Hi,
I'm Raja, male, 54 yrs, from Kollam, a coastal town in the Southern part of India.
Just logged in. Looking forward to exciting experiments with my Canon.

Regards.  :)
For the sheer pleasure of experimenting....:-)

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Offline kollamraja

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Re: Canon SX230 HS Long Exposure
« Reply #1 on: 27 / October / 2013, 04:28:17 »
Hi,

I've been having the Canon for over a year now and stumbled upon CHDK. Totally fired up with the prospect of experimenting with Long Exposure. Have tried time lapse shots of Sunset and recording cloud movement over the sea with fairly good results. Now trying Long Exposure to capture star tracks :-)

Below I give the steps I do before shooting:
CHDK Main Menu> Enhanced Photo Operations>

Here I set the 'Override Tv type' to "Long Exp" and then Set values for the following 3 parameters,

Long Exp. Value
Override Av
Override ISO

For now, I'm seeking your help on 2 points. I find the Av value can be set between 3.19 and 16. How can I extend the range beyond 16 to say 32 or more?

Also, to record star tracks on a moonless clear night, can anyone give a set of values for the above 3 parameters that I can use as a starting point to my experiments?

Raja.
« Last Edit: 27 / October / 2013, 04:52:59 by kollamraja »
For the sheer pleasure of experimenting....:-)

Re: Canon SX230 HS Long Exposure
« Reply #2 on: 27 / October / 2013, 06:12:39 »
I find the Av value can be set between 3.19 and 16. How can I extend the range beyond 16 to say 32 or more?

Welcome Raja !
On the SX230hs the aperture is a physical hole so you cannot make it any smaller.

Quote
Also, to record star tracks on a moonless clear night, can anyone give a set of values for the above 3 parameters that I can use as a starting point to my experiments?

You need to use the Forum Search to find this and similar topics.

These will get you started :-

http://chdk.setepontos.com/index.php?topic=8750.msg91502;topicseen#msg91502

http://chdk.setepontos.com/index.php?action=profile;area=showposts;u=13458


David

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Offline kollamraja

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Re: Canon SX230 HS
« Reply #3 on: 27 / October / 2013, 08:37:41 »
Hi David,

Thanks for your response. Will certainly follow the links.

On the SX230hs the aperture is a physical hole so you cannot make it any smaller.
In that case, how is it that the aperture is adjustable between 3.19 and 16?!!   :'(
Thank God, I'm a certified Newbie, so I can get away with bombs like that  :haha

Raja.
For the sheer pleasure of experimenting....:-)


Re: Canon SX230 HS
« Reply #4 on: 27 / October / 2013, 10:29:02 »
Thanks for your response. Will certainly follow the links.
You might also find this script interesting :  http://chdk.wikia.com/wiki/Meteor_Intervalometer_with_Dark_Frame_Management

On the SX230hs the aperture is a physical hole so you cannot make it any smaller.
In that case, how is it that the aperture is adjustable between 3.19 and 16?!!
I checked the manual for your camera  - pages 109 & 198 :
http://gdlp01.c-wss.com/gds/7/0300004757/01/PSSX230HS_SX220HS_CUG_EN.pdf
The iris adjustment range for your camera goes from f3.1 to f8.0  ( depending on the zoom position, some aperature values may not be available.)

The values you see in the CHDK menu going outside this range are just generic CHDK values that CHDK will try to let you use.  Sometimes you can actually get an f-stop smaller than the official ones given in the Canon manual.  But there is no guarantee that CHDK will be able to get you different values - you need to take several pictures at the different settings and see if the resulting exposure changes in the images.

Edit : corrected earlier version of this post where I said the camera does not have a user adjustable iris.

« Last Edit: 27 / October / 2013, 11:04:53 by waterwingz »
Ported :   A1200    SD940   G10    Powershot N    G16

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Offline kollamraja

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Re: Canon SX230 HS
« Reply #5 on: 28 / October / 2013, 10:56:22 »
Hi Waterwingz,

Thanks.

 
The values you see in the CHDK menu going outside this range are just generic CHDK values that CHDK will try to let you use.  Sometimes you can actually get an f-stop smaller than the official ones given in the Canon manual.
I tried this out by taking similiar shots by setting CHDK with Av 8 and Av 16. I found it indeed made a difference. So CHDK is able to achieve values beyond the Av 8. However I don't know of any way to actually find out how much its able to achieve although its set at Av 16.
Anyway I think what its doing now is more than sufficient for most situations.
Thanks again for your help.

Raja.
For the sheer pleasure of experimenting....:-)

Re: Canon SX230 HS
« Reply #6 on: 28 / October / 2013, 11:10:59 »
Would you use f90 on a 35mm camera if it had such a tiny aperture (which it does not) ?

Well, that is what f16 on the SX230hs is equivalent to as far as depth-of-field is concerned.

Image sharpness will be VERY poor.

I suggest you do tests to prove it  ............   I have.


David

Re: Canon SX230 HS
« Reply #7 on: 28 / October / 2013, 11:28:34 »
However I don't know of any way to actually find out how much its able to achieve although its set at Av 16.
If you want to roughly calibrate this,  manually override the Tv, Av & Sv settings to 1/60, f8 and ISO 100, and take a reference shot. 

Then set the Av at f16 and take several shots using different Tv values until the resulting image appears to have the same exposure as your reference shot. 

Each doubling of the Tv value corresponds to one f-stop so you can roughly calculate what f-stop the camera was able to achieve that way.
Ported :   A1200    SD940   G10    Powershot N    G16


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Offline kollamraja

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Re: Canon SX230 HS
« Reply #8 on: 29 / October / 2013, 02:57:18 »
If you want to roughly calibrate this,  manually override the Tv, Av & Sv settings to 1/60, f8 and ISO 100, and take a reference shot.
Then set the Av at f16 and take several shots using different Tv values until the resulting image appears to have the same exposure as your reference shot.

Good idea, must get down to do it one of these nights. Would like your views on what I have said below.

.....Well, that is what f16 on the SX230hs is equivalent to as far as depth-of-field is concerned.
Image sharpness will be VERY poor.
Actually, I was a bit intrigued that a night scene I shot using f/8 turned out better than the same shot taken using f/16 ( of course with appropriate Tv setting, ISO maintained at  100). I expected the f/16 to be better with greater depth. Could it be that, extending the f stop beyond an optimum (and adjusting Tv appropriately) could be counter productive?

Raja.
For the sheer pleasure of experimenting....:-)

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Offline philmoz

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Re: Canon SX230 HS
« Reply #9 on: 29 / October / 2013, 04:16:38 »
.....Well, that is what f16 on the SX230hs is equivalent to as far as depth-of-field is concerned.
Image sharpness will be VERY poor.
Actually, I was a bit intrigued that a night scene I shot using f/8 turned out better than the same shot taken using f/16 ( of course with appropriate Tv setting, ISO maintained at  100). I expected the f/16 to be better with greater depth. Could it be that, extending the f stop beyond an optimum (and adjusting Tv appropriately) could be counter productive?

Raja.

http://en.wikipedia.org/wiki/Diffraction-limited_system

Phil.
CHDK ports:
  sx30is (1.00c, 1.00h, 1.00l, 1.00n & 1.00p)
  g12 (1.00c, 1.00e, 1.00f & 1.00g)
  sx130is (1.01d & 1.01f)
  ixus310hs (1.00a & 1.01a)
  sx40hs (1.00d, 1.00g & 1.00i)
  g1x (1.00e, 1.00f & 1.00g)

 

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