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poor focusing in a plane

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Offline reyalp

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Re: poor focusing in a plane
« Reply #10 on: 12 / July / 2014, 20:13:20 »
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Quote from: rkomar on 12 / July / 2014, 19:35:22
I've only been using one of them so far when shooting the book pages.  I remember focus problems with both when shooting albums, but that was about a year ago, so my memory may be off.  I'll test the second camera in the book rig, and report here later.
This is just curiosity, so no need to go out of your way if you don't feel like it. It would not surprise me that low end cams are variable and quite bad, but it would be interesting if they were consistently bad in the same way.
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Offline Hardware_Hacker

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Re: poor focusing in a plane
« Reply #11 on: 12 / July / 2014, 20:25:28 »
You could try attaching a weak "Macro" supplementary lens via an adaptor see

oronocova post on DIY 37mm filter adapter for SX260, and others... 21/April/2012,
http://chdk.setepontos.com/index.php?topic=8021.msg84509#msg84509

Then continue to Here "Compact Digital Cameras" near the bottom http://www.kenrockwell.com/tech/macro.htm

and here "Close-Up Lenses" http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/A95/Close-Up/Close-Up-Lenses.html

H-H

Also, but slightly off topic, for improving the "Quality" of the images. see:-

http://en.wikipedia.org/w/index.php?title=File%3AMyBookScanner%2CJune12%2C2011.JPG

You then could try attaching Polaroid filters to the light sources and to the cameras.

With OCR it is very important to have high "Quality" grey scale images.

ALSO for very old books, with age spots, try a 4 camera setup with two of the cameras that have InfraRed filters attached.
« Last Edit: 12 / July / 2014, 20:27:55 by Hardware_Hacker »
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Offline rkomar

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Re: poor focusing in a plane
« Reply #12 on: 12 / July / 2014, 20:54:53 »
I've set up the second camera on the other side of the rig (to photograph the opposite book page from the first camera).  It's about the same distance (maybe 3mm less).  I used the same script to capture a set of photographs with the focus setting ranging from 190 to 250mm.  It does appear that the focus changes differently over different parts of the page, but it's not as straightforward as with the other camera.  I've uploaded the images to http://www3.telus.net/rkomar/focus2/.  So, it does look like the two cameras aren't consistently wrong the same way.
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Offline waterwingz

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Re: poor focusing in a plane
« Reply #13 on: 12 / July / 2014, 20:57:34 »
While the early A series CHDK Powershots were quite good,  it has always felt to me like the A1000-A4000 were produced as "impulse purchases".  Adequate for taking snapshots and vacation pics.  Not that great for serious work.

I'm just happy that my initial fear - something else wrong with set_focus() or the kap_uav.lua script - set off by the subject of this thread - was not realized.
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Offline rkomar

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Re: poor focusing in a plane
« Reply #14 on: 12 / July / 2014, 21:11:10 »
Quote from: waterwingz on 12 / July / 2014, 20:57:34
While the early A series CHDK Powershots were quite good,  it has always felt to me like the A1000-A4000 were produced as "impulse purchases".  Adequate for taking snapshots and vacation pics.  Not that great for serious work.

I'm just happy that my initial fear - something else wrong with set_focus() or the kap_uav.lua script - set off by the subject of this thread - was not realized.

I'm still using the "MoveFocusLensToDistance" hack that srsa_4c suggested a while ago in the A4000 thread.  I believe that it's working well.  You reminded me that I should test the latest set_focus() changes on the A4000.  That model is a bit of an oddball, so my expectations are low and I've been putting it off.

I think if the problem was that the focus was just getting set to the wrong value, I'd see a problem over the whole image.  Instead, the fact that the part of the image that's in good focus moves around makes me think that it's not a problem with the value of the focus, but that the hardware can't physically focus on the whole page at all.
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Offline rkomar

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Re: poor focusing in a plane
« Reply #15 on: 12 / July / 2014, 21:15:39 »
Quote from: Hardware_Hacker on 12 / July / 2014, 20:25:28
You could try attaching a weak "Macro" supplementary lens via an adaptor see

oronocova post on DIY 37mm filter adapter for SX260, and others... 21/April/2012,
http://chdk.setepontos.com/index.php?topic=8021.msg84509#msg84509

Then continue to Here "Compact Digital Cameras" near the bottom http://www.kenrockwell.com/tech/macro.htm

and here "Close-Up Lenses" http://www.cs.mtu.edu/~shene/DigiCam/User-Guide/A95/Close-Up/Close-Up-Lenses.html

H-H

Also, but slightly off topic, for improving the "Quality" of the images. see:-

http://en.wikipedia.org/w/index.php?title=File%3AMyBookScanner%2CJune12%2C2011.JPG

You then could try attaching Polaroid filters to the light sources and to the cameras.

With OCR it is very important to have high "Quality" grey scale images.

ALSO for very old books, with age spots, try a 4 camera setup with two of the cameras that have InfraRed filters attached.

Thanks for the links.  The A4000 cameras I have are even cheaper than the PowerShot S series, and I don't think I can attach any kind of external lens to them.  There's nothing there on the lens assembly with a screw thread.  Perhaps I'm going to have to buy new cameras in the PowerShot S series to get this to work well, in which case, I'll take another look at these lens attachments.
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Offline Hardware_Hacker

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Re: poor focusing in a plane
« Reply #16 on: 12 / July / 2014, 21:37:21 »
With simple "L-Brackets" adapters you can attach most of these types of close up lenses.

ALSO, an additional after thought thought #1, try to avoid non BSI canon cameras
i.e. go for "HS" canon cameras. The offer two advantages:-

* No, internal, reflections off the sensors (internal) metallic contact grids.
* Makes up for the light losses in the Polaroid Filters.

This applies to "..... the early A series CHDK Powershots..."

Edit #1

And, after thought thought #2, May be the reflection from the glass is confusing
the camera focus, try again but without the glass.

H-H
« Last Edit: 13 / July / 2014, 00:58:18 by Hardware_Hacker »
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Offline blackhole

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Re: poor focusing in a plane
« Reply #17 on: 13 / July / 2014, 03:36:36 »
Quote
I think if the problem was that the focus was just getting set to the wrong value, I'd see a problem over the whole image.  Instead, the fact that the part of the image that's in good focus moves around makes me think that it's not a problem with the value of the focus, but that the hardware can't physically focus on the whole page at all.
It is quite normal when the camera is so close to the object that you photographing. Depth of Field in this case is extremely small and the focus can not be the same in the middle of the page and on its ends.
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Offline rkomar

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Re: poor focusing in a plane
« Reply #18 on: 13 / July / 2014, 12:45:03 »
Quote from: blackhole on 13 / July / 2014, 03:36:36
It is quite normal when the camera is so close to the object that you photographing. Depth of Field in this case is extremely small and the focus can not be the same in the middle of the page and on its ends.

Yes, I was expecting that this would happen to some degree.  However, I would expect that all four corners would be out of focus the same way, which is definitely not the case in the photographs I took with the first camera.  The focus settings for the two opposite corners are very different.
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Offline rkomar

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Re: poor focusing in a plane
« Reply #19 on: 13 / July / 2014, 12:52:53 »
Quote from: Hardware_Hacker on 12 / July / 2014, 21:37:21
With simple "L-Brackets" adapters you can attach most of these types of close up lenses.

ALSO, an additional after thought thought #1, try to avoid non BSI canon cameras
i.e. go for "HS" canon cameras. The offer two advantages:-

* No, internal, reflections off the sensors (internal) metallic contact grids.
* Makes up for the light losses in the Polaroid Filters.

This applies to "..... the early A series CHDK Powershots..."

Edit #1

And, after thought thought #2, May be the reflection from the glass is confusing
the camera focus, try again but without the glass.

H-H

When I bought my A4000 cameras over a year ago, I chose it over the HS models because the latter were more expensive and had lower resolution.  I figured the higher resolution (16MP) of the A4000 would help when applying OCR to text.  I'll take a look to see if there are any newer HS models with more resolution available now.

As to the reflections, I'm using CHDK to set the focus manually, so there isn't an issue with the camera getting confused. 
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