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What is the ultimate Calibration Board Material?

The place for questions, problems, comments and tips regarding the camera calibration.

What is the ultimate Calibration Board Material?

Postby Lunat1c » Fri Nov 29, 2013 4:03 pm

Dear Davidians,

This is the 3rd time I decided to change my calibration board.

The first was just a card board.
The second one was an alupanel, but a part from a junk alupanel, so was a little bent.
The third one was wood, made by a carpenter, but yesterday I've realized that the right wing is bowed! And it was the very thing that was causing me trouble for weeks!!!

the Carpenter advised me to use GLASS, he says it never bends and is damn straight.
I've decided to make a panel out of glass.
But first I like to hear your ideas and votes for which material owns...

Dear MagWeb you're the expert, would there be negative consequences of using glass? Do I have to coat the inside with mat black spray paint? Would it be bad to leave it like it is (no coating, bare glass) ?
Or is there a method other than coating it with spray paint?

Regards,
Mitsubishi xd 206u, logitech pro9000, acer 3820tg
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Re: What is the ultimate Calibration Board Material?

Postby MagWeb » Fri Nov 29, 2013 5:39 pm

In puncto form-stability glass is a good idea. You could also use grounded flagstones. ATM also pretty big formats are up to date...

I didn't use it until now (I´m using "Dibond" boards).
Times back I used AcrylicGlass. I coated the backside white, engarved the pattern from the backside with my CNC (just a little bit) and filled this engarving with black color. At that time, when DAVID wasn't as accurate as it is today, that worked reasonable well. I wouldn't do that anymore today.

Using glass brings some problems:
- opaque white glass will still have subsurface scattering;
- transparent glass with patterns on the back of the glass (as you get it with those frameless picture frames) will give a fraction of the light at its first surface - this should result in a calibration error (bowed results).
- The glasses' (of normal quality) first surface will mirror some light.

So you've to coat the first surface (towards the cam) either with paint (maybe a rather sensible surface > avoid scratches);
Think the best way is to print the pattern on selfadhesive waterprooved printer foil.
Waterproofed, for it is hard to apply selfadhesive foil without some bubbles in a dry way. There's an easy technic to do this: Spray a thin film of water on the glass, apply the selfadhesive foil. The water between foil and glass allows some corrections. To do the final fix, use a squeegee to press the water and maybe air from the foil's center to its edges.
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Re: What is the ultimate Calibration Board Material?

Postby argo » Fri Nov 29, 2013 7:08 pm

Hi,

I made my first calibration panel with 10mm thick glass. I did not paint it and also it was not precise 90 degrees(was difficult for me to make it 90) and also it was heavy. so totally i got disappointed with that material.
I then moved to acrylic plastic materials.
http://www.indiamart.com/assam-plywood- ... sheet.html
they are easy to glue(with using a Syringe and Chloroform and it takes only some seconds to dry and glued) and lightweight.
The only thing, most of these materials have shiny surfaces, so either you need to print on a thick Cardboard or paint the surface( I suggest both back and front side of it).
I am happy with this material but yet i could not figure it out, how to stick the paper on it so i can change the paper any time is needed and not make a new panel !!
there will be always a bow on papers if i dont glue whole the paper.

Regards,
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Re: What is the ultimate Calibration Board Material?

Postby MagWeb » Fri Nov 29, 2013 8:24 pm

Greg (aka Bongobat) suggested to cover the boards with magnetic paint and to use a print on magnetic foil (e.g. Posterjack.com)

Edit: there are also magnetic foils for standard printers available.
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Re: What is the ultimate Calibration Board Material?

Postby Lunat1c » Fri Nov 29, 2013 9:11 pm

Thanks a bunch guys, I will also search for that magnetic paint and foils. I was thinking if I could paint it properly, and after painting and sticking the self adhesive calibration paper, wouldn't it damage the paint if somehow I want to remove or change the paper.. That magnetic foil can do it if I one find some printable.. What should be the paint's color I don't know... I thought of mat black.
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Re: What is the ultimate Calibration Board Material?

Postby MagWeb » Fri Nov 29, 2013 10:40 pm

Paint e.g: http://www.motipdupli.de/en/products/du ... -1346.html
Color is not that important for you should cover the whole visible area with the magnetic foil.
Paper e.g: http://www.amazon.com/Avery-Magnet-Shee ... uctDetails
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Re: What is the ultimate Calibration Board Material?

Postby pottersfriend » Sat Nov 30, 2013 1:39 am

The ultimate panel as far as flatness goes, would have to be (IMHO) honeycomb aluminum panels. These are typically used in the aircraft industry and are extremely strong and flat. Unfortunately, they are very expensive. I believe a 1/2" thick 4'x8' panel here in the US will cost about $600 USD.

I was fortunate to get some "scrap" off of craigs list relatively cheap but have yet to build a panel out of them. Out of curiosity I just checked on craigs list again and someone is trying to sell some more scrap pieces. Don't think it's really worth the price for a calibration panel, especially after what I have seen others do with much more basic materials. Like the saying goes, "It's the poor craftsman that blames his/her tools". Of course I'm no craftsman so I guess I'll still try using my fancy scraps some day when I have the time. I'll update when I do.

Good luck with your search, and keep us up to date on your progress.

Darin
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Re: What is the ultimate Calibration Board Material?

Postby moog » Sat Nov 30, 2013 9:05 am

I use the back of mirrors. re-paint the back white and paint on the markers with permanent felt pen
LC532-5-3-F(16x65), BenQ PB8220 DLP Projector, logitec quickcam PRO9001, Casio EX-FH20
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Re: What is the ultimate Calibration Board Material?

Postby Lunat1c » Sat Nov 30, 2013 9:12 am

Hi Moog,

Can you post a picture when you're available and the things are at hand?

I especially am curious about how you've painted the markers.

Not just for me,that would be useful for anybody.

Best regards,
Mitsubishi xd 206u, logitech pro9000, acer 3820tg
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Re: What is the ultimate Calibration Board Material?

Postby moog » Sat Nov 30, 2013 9:37 am

sure, no problem.....
you can see, I used a bathroom mirror with frame, then used the frame to mount the piano hinge, and lock bars,
then it can be folded away fairly flat for storage or transportation
Attachments
P1010921-1.jpg
P1010922-1.jpg
P1010923-1.jpg
LC532-5-3-F(16x65), BenQ PB8220 DLP Projector, logitec quickcam PRO9001, Casio EX-FH20
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Re: What is the ultimate Calibration Board Material?

Postby moog » Sat Nov 30, 2013 9:52 am

to transfer the markers accurately onto the corner panels, I had an aluminium sheet, laser cut with the marker pattern, for the big dots I use the "cartwheel" piece to draw , rotate, draw.
The calibration size for this board is 300mm.

if you'd like to make a template like this, I can attach a .dxf file (or any format you wish) as I have it modeled in 3D
Just tell me what size you want.
Attachments
P1010924-1.jpg
P1010925-1.jpg
LC532-5-3-F(16x65), BenQ PB8220 DLP Projector, logitec quickcam PRO9001, Casio EX-FH20
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Re: What is the ultimate Calibration Board Material?

Postby argo » Sat Nov 30, 2013 9:53 pm

Hi,

Today i did a research about these printable magnet foils. they are good but the problem is their maximum size is A4 (here just A4 available)
so in some cases maybe we need a bigger calibration panel so what to do? then here i got some information about Adhesive Magnetic sheets that are available at any sizes (either roll or sheet) (e.g http://www.anchormagnets.com/products/m ... c-sheet-2/)
so we can print our calibration paper and put it on adhesive side of this magnet sheet.
and also i guess we do not need the magnet paint. we can just use some of these tiny and strong magnets to stick the magnet sheet to the panel from back side.
http://www.amazon.com/Applied-Magnets-E ... B0012AUU84
and these magnet sheets are thick enough to not have bows on themselves!

will try and update here.

Regards,
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Re: What is the ultimate Calibration Board Material?

Postby MagWeb » Sat Nov 30, 2013 10:25 pm

Magnetic paint isn`t a magnet but contains some iron particals. That's all. You could also use some iron material for the corner.
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Re: What is the ultimate Calibration Board Material?

Postby argo » Sat Nov 30, 2013 10:49 pm

MagWeb wrote:Magnetic paint isn`t a magnet but contains some iron particals. That's all.


Oops
I thought you mean something like this by magnetic paint : http://www.greatart.co.uk/Paints/Acryli ... Paint.html
"ideal for turning cardboard, wood, metal, plaster and other surfaces into magnetic boards!"
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Re: What is the ultimate Calibration Board Material?

Postby MagWeb » Sun Dec 01, 2013 12:53 am

Seems that's the same kind of color, with embedded iron particles, I´m talking about
You can attach magnets onto a surface painted with that color and it will stick to. But it will not keep some simple iron or steal e.g a simple needle.
One magneted piece (in our case magnetic foil) is enough to hold it on a surface containing iron.
Thats the way all "magnetic" boards I know work.
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