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DAVID-Laserscanner Forum • View topic - add lense to projector?
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add lense to projector?

Problems, solutions and discussion about scanning with a video projector and stripe patterns.

add lense to projector?

Postby moog » Sat Sep 10, 2011 10:25 am

can someone advise me what type of lense to add to my projector?
i'd like to make my projector work a bit closer to my corner, i guess i want to widen it's projection,
would it be better to take the lense assembly apart and move it closer to the internals( or away)
or could i add another lense onto the outside of what i've got, I'm not up on optics, so any help appreciated.
I have a BenQ PB8220 DLP Projector
LC532-5-3-F(16x65), BenQ PB8220 DLP Projector, logitec quickcam PRO9001, Casio EX-FH20
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Re: add lense to projector?

Postby WalterMo » Sat Sep 10, 2011 10:43 am

Because I didn't want to remove the original lens (warranty !) I have added an adapter with an achromatic lens just in front of the lens of an ACER K11.
The specs are: f = 400 mm = +2.5 dioptre.
In so doing the working range to focus sharp changes from 0.6 m ......"infinite" to 26......52 cm.

The other possibility is to open the projector and try to mount the original lens a bit away from the internals.

Edit: For a coin scan I have used a lens of f= 130mm.
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Re: add lense to projector?

Postby MagWeb » Sat Sep 10, 2011 11:43 am

Hi,

I use Close-up lenses like these:
http://www.ebay.com/itm/37mm-Digital-1- ... 608wt_1318

glued to the tube of the projectors optics. You can get them in different diameters - maybe you find some that fit to your optics.

Gunter
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Re: add lense to projector?

Postby moog » Sun Sep 11, 2011 9:21 am

thanks guy's for your help, this is a great help
LC532-5-3-F(16x65), BenQ PB8220 DLP Projector, logitec quickcam PRO9001, Casio EX-FH20
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Re: add lense to projector?

Postby moog » Mon Sep 19, 2011 9:22 am

I've recieved my macro lens's but they don't make the view any wider, only closer up, would the addition of this
http://www.ebay.com.au/itm/58mm-0-45X-W ... 27bdbfc623
enable me to get closer and wider projection, or would this adversely affect Davids ability to correct for lens distortion?
LC532-5-3-F(16x65), BenQ PB8220 DLP Projector, logitec quickcam PRO9001, Casio EX-FH20
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Re: add lense to projector?

Postby andyjk » Wed Nov 16, 2011 10:33 am

Gunter

Have you literally glued this extra lens to the front of your projector ? Do you have a picture of this ?

I am interested in getting a similar projector but need to scan an area of around 50x50mm so would need to modify it too - I was concerned about introducing too much tangential lens distortion if I hadn't quite lined the lens up properly.

I currently use an optima pk201 (which is completely useless - very poor gamma) but will focus at a much shorter distance. I use it with Gray codes only - no sine wave patterns.

On a separate note - does anyone have comments on depth of field of the cameras they use - my logitec 9000 webcam has very poor depth of field close up so I was thinking of moving to a uEye or David camera - any comments welcome.

Andy
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Re: add lense to projector?

Postby WalterMo » Thu Nov 17, 2011 11:01 am

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Re: add lense to projector?

Postby moog » Fri Nov 18, 2011 3:28 am

Walter,
Would a F2.5 lens give less distorsion than a F1.4 lens?
Or is this size only telling us what the maximum size the iris will open up to?
LC532-5-3-F(16x65), BenQ PB8220 DLP Projector, logitec quickcam PRO9001, Casio EX-FH20
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Re: add lense to projector?

Postby WalterMo » Fri Nov 18, 2011 10:51 am

Andy,
F tells the luminosity of the lens, means how many entering light will pass the lens if its iris is maximally opened. Best is a low value, but I think for our scanning also "worse" values will work fine. Lasers or video projectors are normally powerful enough to illuminate the "scene".

F has directly nothing to do with distortion, but perhaps indirectly. If the lens is more light powerful then the iris can be more reduced in its size. That means the depth of field will increase. :)

Walter
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Re: add lense to projector?

Postby _jack_ » Sat Mar 17, 2012 12:33 pm

Hi WalterMo,
can you suggest to me a website where I can find the achromatic f=400 +2,5 lens you used for the Acer k11 ?
Thanks in advance.
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Re: add lense to projector?

Postby WalterMo » Sat Mar 17, 2012 1:28 pm

The lenses came from a German dealer for odds:
http://www.macony-design.de/catalog/ind ... 55a0c37e8f

Important: Choose a not too small diameter, the projector's beam is angled upwards. 42-44mm should be ok.
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Re: add lense to projector?

Postby andyjk » Sat Mar 17, 2012 3:02 pm

What is the 'screen size' you can achieve with these ? Can you focus the screen at 8cm wide and therefore (theoretically) obtain 100 micrometer resolution from the acer K11 ?
If so what is the distance from the projector to target ?

(Could you even focus the screen at less - say 3cm wide or less for a coin scan ?)
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Re: add lense to projector?

Postby WalterMo » Sat Mar 17, 2012 5:50 pm

Without any additional lens the projector can focus from 63 cm to a target and the image is 28cm x 21cm.
Only one additional lens cannot fill the gaps below 63cm, therefore I have 3 different lenses:

Lens A (f=130mm) can focus from 13cm (4.6cm x 3.4cm) to 15.5cm (5.6cm x 4.2cm).
Lens B (f=145mm) can focus from 15cm (5.6cm x 4.1cm) to 19.5cm (7.5cm x 5.5cm).
Lens C (f=400mm) can focus from 26.5cm (11cm x 8cm) to 54cm (23cm x 17.5cm).

All values are just about. The image sizes are in brackets.

For a coin scan I had used lens A:
viewtopic.php?p=19429#p19429

And yes, 100µm (= 0.1mm) is attainable. But only if the object is small, like a coin or similar.
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Re: add lense to projector?

Postby andyjk » Sun Mar 18, 2012 8:32 pm

Thanks Walter - do you have a pic of the K11 with the added lens ?

I've seen your Dell M110 on another post - is it similar to this ?
Also have you had time to play much with the Dell ? Its brighter and higher resolution than the ACER but there were concerns about pixel alignment. Has this been a problem or are you getting better results with the Dell M110 that the ACER K11 ?

I ask because I will buy one or other of these projectors, for small object scanning. Obviously the specs of the Dell are better so this would seem the obvious choice if the pixel alignment isn't a problem.

Finally, could you stack lenses (or buy a different one) to go even smaller than the f130 (4.6cm x 3.4cm) - maybe down to half that again ( 2.3 cm x 1.7cm) ? This should still fit a coin in at an increased resolution, although maybe its preferable to keep the scan to the central part of the field of view to minimise radial distortion ?

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Re: add lense to projector?

Postby WalterMo » Mon Mar 19, 2012 9:29 am

Andy, the Dell M110 was only some days at my place. My primary job was to build two lens adapters. Of course I had made some scans to see if it's working but my goal wasn't to get best results regarding highest resolution and accuracy.

In the meantime you can see what Mattia (hal) has achieved with this Dell, e.g.:
viewtopic.php?f=15&t=2886&start=15

I have attached a photo of my Acer K11 with an attached lens adapter. You can see on the sketch that the Acer's original lens isn't "hidden" like at the Dell, but it's looking out for about 11 mm to enable a possibility to clamp the lens adapter.

Also other lenses with a less focal length, e.g. 100 mm can be used to get a smaller image of the projector.

Walter
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Acer mit Vorsatzlinse.jpg
Acer K11 with a 400mm lens
Acer Objektiv.jpg
Sketch of the original lens of the Acer K11
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