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Hello and a camera MF question

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Offline JohnW

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Hello and a camera MF question
« on: 01 / January / 2014, 08:43:11 »
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First off, hello and Happy New Year! :)

I'm new to CHDK but I have been playing primarily with the motion detection scripts. 

For the last couple of days I have been trying to photograph fireworks on a G15, F5, 6sec exposure.  My issue is the focus - if I set MF and then rail the focus right to the end the focus is very out  ??? its nowhere near infinity (I would assume its a long way beyond for a reason below) I haven't been using CHDK for this.

If I set the camera to AF and take the same shot, and its nice and sharp.  The camera is screwed to the balcony railing so it isn't moving.

Is there an 'easy' way to figure out where infinity really is in terms of focus so that I can have a script which simply preps the camera for fireworks?  I wrote a simple script which sets the focus at 65535 and then shoots, reduces to 65534 shoots etc....

But that's going to take ages so while the cameras happy snapping away is there and easy way to get the camera properly focussed at infinity?  With or without CHDK?

Thanks!!

Re: Hello and a camera MF question
« Reply #1 on: 01 / January / 2014, 10:50:14 »
First off, hello and Happy New Year! :)

I'm new to CHDK but I have been playing primarily with the motion detection scripts. 

For the last couple of days I have been trying to photograph fireworks on a G15, F5, 6sec exposure.  My issue is the focus - if I set MF and then rail the focus right to the end the focus is very out  ??? its nowhere near infinity (I would assume its a long way beyond for a reason below) I haven't been using CHDK for this.

If I set the camera to AF and take the same shot, and its nice and sharp.  The camera is screwed to the balcony railing so it isn't moving.

Is there an 'easy' way to figure out where infinity really is in terms of focus so that I can have a script which simply preps the camera for fireworks?  I wrote a simple script which sets the focus at 65535 and then shoots, reduces to 65534 shoots etc....

But that's going to take ages so while the cameras happy snapping away is there and easy way to get the camera properly focussed at infinity?  With or without CHDK?
I really don't understand why you are having problems getting the G15 to focus at infinity using the built-in MF capability.   But what happens if you set the focus at 10 of 15 ft and take some night shots ?  (Those are the MF distance steps before infinity on my G10 - the G15 might be different).

The reason I ask is that the little lens systems in P&S cameras have amazing depth of field.  Typically, if you focus a few feet away from yourself,  everything from there to infinity will also be in focus.

So I'd suggest taking some more test shots at night in Canon MF mode as you gradually adjust the setting wheel back from infinity and see what the images look like.

If you really want to use a script,  the set_focus setting is in units of millimeters   ( 25.4 mm = 1") so changing the setting in steps of 1 mm is not really useful.    I'd suggest simply using a few discrete settings :  1000 5000 10000 20000 30000 40000 50000 and see what happens.

More info on CHDK manual focus is here :  http://chdk.wikia.com/wiki/CHDK_Manual_Focus_and_Subject_Distance_Overrides

and there is an active thread here right now :  http://chdk.setepontos.com/index.php?topic=11078.0

Both are still a "work in process"


Update :  I took a look at the EXIF data embedded in your images.  Other than the timestamp and filename, the only difference between the two images is as follows :

Code: [Select]
IMG_2921.jpg
Focus Mode :            0x0008
Focus Distance Upper :  1617 mm

IMG_2922.jpg
Focus Mode :            Continuous
Focus Distance Upper :  6553 mm
which I believe tells us that the first shot was in MF mode and the second in AF mode.  AFAIK, Canon EXIF do not contain the actual focus distance - what they give you is an "in focus" range via Focus Distance Upper  (FDU) and Focus Distance Lower (FDL). The MF  shot had its FDU set at 1.6 meters (~ 5 ft )  while the AF shot was at 6.6 meters ( ~21 ft)!   So it looks like your MF setting is actually short by a quite a bit rather than too far out as you originally guessed. 

Note that on some cameras, the MF setting works in a dual range mode - you have to keep rotating the dial to get it to switch to the longer distance settings ...


« Last Edit: 01 / January / 2014, 11:18:40 by waterwingz »
Ported :   A1200    SD940   G10    Powershot N    G16

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Offline JohnW

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Re: Hello and a camera MF question
« Reply #2 on: 01 / January / 2014, 21:21:34 »
Hi waterwingz,

Thanks for the feedback - I did a quick experiment this morning, setting the camera as per last night and this time in MF mode and AF mode I get the FDU to be 6553, having tried photographing fireworks a couple of times now (they love them here) I always get images out of focus when MF to infinity...

I shall investigate some more tonight.  Why should day MF be different to night MF, or it might still be user error  :lol

Re: Hello and a camera MF question
« Reply #3 on: 01 / January / 2014, 21:47:02 »
Why should day MF be different to night MF, or it might still be user error  :lol
When you are shooting during the day,  the camera is probably selecting a smaller lens opening (larger f-stop number) due to the brighter illlumination which will give you a greater depth-of-field (DOF) and thus a farther FDU.
Ported :   A1200    SD940   G10    Powershot N    G16


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Offline JohnW

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Re: Hello and a camera MF question
« Reply #4 on: 01 / January / 2014, 21:55:55 »
But I'm shooting in M mode, or is M not truly M? (I had to reduce the shutter time a lot to not be hideously over exposed obviously...)

Re: Hello and a camera MF question
« Reply #5 on: 01 / January / 2014, 22:24:15 »
But I'm shooting in M mode, or is M not truly M? (I had to reduce the shutter time a lot to not be hideously over exposed obviously...)
Yes - M is M.   Attach a couple of the pictures .  How did you select the f-stop when you put it into M mode?

Might be interesting to try a small CHDK script set for focus at infinity.  It seems very strange that you are not able to make that adjustment manually though.

Ported :   A1200    SD940   G10    Powershot N    G16

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Offline JohnW

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Re: Hello and a camera MF question
« Reply #6 on: 02 / January / 2014, 01:40:53 »
I'll play tonight and post some photos, one thing I found odd, is the AF light seems to go even if you have the camera in M and MF mode  :blink:

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Offline JohnW

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Re: Hello and a camera MF question
« Reply #7 on: 02 / January / 2014, 07:41:01 »
Ok I've tried pressing up to get the focus to infinity and then going round and round with the wheel and it definitely focuses at 6553.

If I just go with the up arrow it seems to get there too.

One block back on the UI shot is in focus, so is two and three at F5.

I can only assume I ballsed something up (twice) when I was turning off the display to shoot and setting up CHDK - at the time I had a super simple script that just shoots over and over again - now I have a not quite so super simple script which sets the focus at infinity first and then shoots over and over, so I'll be set for next time at Chinese New Year  :xmas

Thanks for your help, I'll have a look at the links you reference tomorrow :)


Re: Hello and a camera MF question
« Reply #8 on: 02 / January / 2014, 09:46:39 »
Ok I've tried pressing up to get the focus to infinity and then going round and round with the wheel and it definitely focuses at 6553. If I just go with the up arrow it seems to get there too. One block back on the UI shot is in focus, so is two and three at F5.
I assume this means that your image in Canon MF are now focused correctly?

Quote
now I have a not quite so super simple script which sets the focus at infinity first and then shoots over and over, so I'll be set for next time at Chinese New Year  :xmas
I don't know how much you have tested that script but there are some "tricks" to getting CHDK to set focus via a script.  This is discussed here : http://chdk.wikia.com/wiki/CHDK_Manual_Focus_and_Subject_Distance_Overrides

In fact, we are looking for more information about this and do not have a dump from the G15.  If you have a few minutes to help out, can you download the script post here :
http://chdk.setepontos.com/index.php?topic=11078.0
and run it on your camera?  Post the resulting mf_test.csv file either here or the forum thread I just linked.  If you'll help us out that way,  I will look at the file and let you know how to make sure your G15 actually focuses when you issue the set_focus() command.

It would also be good if you'd attach your script if you'd like me to look at that too.
Ported :   A1200    SD940   G10    Powershot N    G16

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Offline JohnW

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Re: Hello and a camera MF question
« Reply #9 on: 02 / January / 2014, 21:06:50 »
I've added the CSV to the thread - it seems to have many fails written in there though !

 

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