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G12 - Subject Distance Bracketing mode query

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Offline Andy Y

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G12 - Subject Distance Bracketing mode query
« on: 13 / November / 2011, 11:04:16 »
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Hi all,

Day 1 of CHDK for me!

One of my main reasons for trying out CHDK was the capacity to make use of the subject distance bracketing in a fair amount of stacking shots I take.

I *think* I've set everything up correctly but the shots all seem to be of the same initial focal point and do not progress any further through the desired increments.

I've attached a couple of screenshots to show how I've got the settings configured.

Any guidance gratefully received!


G12 -100e

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Offline Microfunguy

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Re: G12 - Subject Distance Bracketing mode query
« Reply #1 on: 13 / November / 2011, 12:28:22 »
Hello and welcome !

Have you tried turning off autofocus and 'safety manual focus' and also enabling manual focus ?



David
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Offline Andy Y

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Re: G12 - Subject Distance Bracketing mode query
« Reply #2 on: 13 / November / 2011, 12:37:52 »
Thanks for the welcome David.

I was trying to shoot in M with MF or are the autofocus and 'safety manual' another setting with CHDK?

Thanks,

A
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Offline Microfunguy

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Re: G12 - Subject Distance Bracketing mode query
« Reply #3 on: 13 / November / 2011, 13:15:10 »
Quote from: Andy Y on 13 / November / 2011, 12:37:52
are the autofocus and 'safety manual' another setting with CHDK?

They are Canon settings as described on page 99 of your camera manual.

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Offline Andy Y

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Re: G12 - Subject Distance Bracketing mode query
« Reply #4 on: 13 / November / 2011, 13:32:19 »
Thanks David,

Confirmed as AF off, no 'safety manual' and MF is enabled.

No success yet.
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Offline SkyWalker9

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Re: G12 - Subject Distance Bracketing mode query
« Reply #5 on: 13 / November / 2011, 15:23:12 »
@Andy_Y

You may be having the same problem that others have experienced when trying to use subject distance bracketing  (http://chdk.setepontos.com/index.php?topic=7061.msg75398#msg75398 )

It may be a case of the option not working for some cameras or simply that we haven't found the right sequence of events needed for the option. The posting above has a simple script that will allow you to experience/check DOF stacking on your G12 to see the different focus changes on your camera (and photos). Small changes in the focus units are usually hard to see, so I'd start with about 5 shots to make sure you can see the changes the first time. If the script works similar to what you wanted, then you might want to search the completed scripts forum for other DOF Stacking scripts -- each has it's Pros & Cons.

Although it would be nice to findout how to use the CHDK subject distance bracketing option, scripts or SDM can fill the 'void' until then. Good luck and welcome to CHDK!
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Offline philmoz

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Re: G12 - Subject Distance Bracketing mode query
« Reply #6 on: 13 / November / 2011, 15:24:38 »
Quote from: Andy Y on 13 / November / 2011, 11:04:16
Hi all,

Day 1 of CHDK for me!

One of my main reasons for trying out CHDK was the capacity to make use of the subject distance bracketing in a fair amount of stacking shots I take.

I *think* I've set everything up correctly but the shots all seem to be of the same initial focal point and do not progress any further through the desired increments.

I've attached a couple of screenshots to show how I've got the settings configured.

Any guidance gratefully received!


G12 -100e



The G12 does not have a continuous focus motor - there are only a discrete number of focus positions available.
See the graph in this post that shows requested focus distance (X) versus actual focus distance (Y).
http://chdk.setepontos.com/index.php?topic=6570.msg69571#msg69571

Depending on your starting position +10mm will not change the actual focus distance.

Try this test:
- enable focus bracketing with +6000mm settings
- set the camera to manual focus, focus on something very close to the lens (<10cm)
- take 3 shots in continuous mode

You should be able to easily see the focus change in these shots.

Phil.
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Offline Microfunguy

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Re: G12 - Subject Distance Bracketing mode query
« Reply #7 on: 13 / November / 2011, 15:51:04 »
Quote from: philmoz on 13 / November / 2011, 15:24:38

The G12 does not have a continuous focus motor - there are only a discrete number of focus positions available.

Depending on your starting position +10mm will not change the actual focus distance.

This has nothing to do with the G12 or not having a continuous focus motor, it is completely normal behaviour based on the lens equations.

Quite simply, it is the focus stepper motor that can only move a certain distance.
(that can actually be a fraction of the steppers native step, doubt if that is done on cameras).
For each change of stepper position, you calculate an assumed focus distance, it is unlikely to be a 'nice' round number.

Small sensor digital cameras with short focal length lenses have tremendous depth of field, especially at wide angle.
Starting at 10mm, a single step may correspond to a 1mm change of focused distance.
That soon changes to 3mm, 10mm, 100mm etc.
After about one or two metres with the wide-angle lens, the depth of field already extends to infinity.
The next step takes you to 65535mm , in Canon and CHDK terms.

Focus at 10mm and try bracketing again.
Even better, zoom to next setting and start at whatever near focus applies.

You should then see focus change.


David
« Last Edit: 13 / November / 2011, 16:07:29 by Microfunguy »
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Offline Andy Y

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Re: G12 - Subject Distance Bracketing mode query
« Reply #8 on: 13 / November / 2011, 15:55:32 »
Thanks all, I shall test some more tomorrow and advise of the findings.
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Offline achillies

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Re: G12 - Subject Distance Bracketing mode query
« Reply #9 on: 13 / November / 2011, 16:16:18 »
I would not be able to help you because of my lack of understanding of the focus settings/zoom range, but recently I have been working with manual focus in the GUI's (ptpcamgui and sdmcongui), and have learned quite a lot.  If I have this wrong, someone will correct me (I hope).

The focus increments you select depend ENTIRELY on the zoom range that you are at, and the focus values that are currently set.  In other words, if you are at full wide zoom, and focused at 10mm, the next focus step will be (perhaps) 11mm. BUT if you are focused at 3000mm, the next focus step will be more like 3800mm, because the focal plane when at that zoom and focus range does not change in a small increment.  It would not make any difference in the focus on the image.

So you will have to think about where your focal plane will be and adjust your focus values in your script to match that.  You simply will not be able to move at 10mm increments from 3000 to 3100mm, but you would be able to move at 10mm increments from 10mm to 100mm. And again, this is highly zoom dependent.
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