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Bandpass Filter Simulation
Posted: 25 July 2008 06:49 AM   [ Ignore ]   [ # 16 ]
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Tks again Taha,
i wrote to omegabob2 as you sugested.

I’ve found the datasheet for the lens i own, Miniature Glass V-4301.9-2.0FT 1.9mm 1/4’’CCD . How do i know the diagonal of this? You’ve suggested a 25 26mm lens to have less distortion. Would it fit in a 12x0.5 CamerA?

Best Regards.

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Posted: 25 July 2008 11:31 AM   [ Ignore ]   [ # 17 ]
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behem0t - 25 July 2008 06:49 AM

Tks again Taha,
i wrote to omegabob2 as you sugested.

I’ve found the datasheet for the lens i own, Miniature Glass V-4301.9-2.0FT 1.9mm 1/4’’CCD . How do i know the diagonal of this? You’ve suggested a 25 26mm lens to have less distortion. Would it fit in a 12x0.5 CamerA?

Best Regards.

Sorry you misunderstood me, i talking about the diameter of the filter not the lens.. if you have a wide angle lens like i do (mine is 120degrees) and you have a small diameter BP filter you when you place the filter on top of the lens you get the barrel effect where you can see the internal edges of the filter. to minimse this you should get a larger filter (in diameter) so this doesnt happen

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Posted: 25 July 2008 11:43 AM   [ Ignore ]   [ # 18 ]
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Ok, thanks a lot.

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Posted: 24 January 2009 11:18 AM   [ Ignore ]   [ # 19 ]
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Hey great post regarding the simulation. I have a question hopefully someone can help me out with. I’m doing an LLP screen with 780nm lasers. I already have a bandpass filter, 780CWL 10FWHM and I’m encountering the blueshift problem with the edges fading out. If I were to correct it by redshifting my filter to 785nm and upping the FWHM to around 30, would that mean I would start to pick up a bit of the visible spectrum (red) with my camera since red is round 750nm?

Any help would be appreciated smile

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Posted: 15 February 2009 07:53 AM   [ Ignore ]   [ # 20 ]
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Sorry for the late contribution. I always want to add something and forget where to add it in the forum rasberry

The wavelength shifting that rdagger mentioned is mainly due to the fact that he is using the LLP method. As Seth asked (long ago smile ) why other ppl have not complained about this effect. The optical explanation would be that laser emission and led emission greatly differ. A laser output is monochromatic, the peak wavelength differs from the 0 emission wavlengths by only 0.5-1%. This means that a laser of 850 nm will emit mostly at this level.

A LED however has a greater wavelength spread that can be as large as 80 nm. When you combine the laser output to the (real) problem of the angle of incidence on the BP filter, you get the shifting effect. With LEDs you can still get 50-60% transmission efficiency even at the wavelength of the filter no matter how much it shifts. This is why FTIR users did not encounter this effect, or if they did, it is easily corrected through proper software filters.

In this case, FTIR users can opt for narrower band filters than LLP users.

I’m not sure that after so much time this explanation serves anyone but better late than never smile

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Posted: 19 March 2009 12:54 AM   [ Ignore ]   [ # 21 ]
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madian, thanks for the great explanation!  I’ve encountered the same problem with 780nm lasers and a 780nm 10W Bandpass filter.  While never having a problem with 850nm leds (ribbon flex) and a 850nm 10W bandpass filter on the same camera (and actually the 850 nm BP filter is much smaller in diameter).  I was wondering why this was happening and coudn’t find a good reason; I thought maybe it was the wavelength or another difference in the filters i didnt know about, but your explanation makes alot more sense smile

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Posted: 11 May 2009 12:25 PM   [ Ignore ]   [ # 22 ]
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this is an interesting discussion.. thank you for sharing smile
simulation rachat de credit

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Posted: 24 June 2009 03:19 AM   [ Ignore ]   [ # 23 ]
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why not just put the filter before the wide-angle lense? that seems like it’d solve the problem entirely.  since the blue-shift comes because of the lense, if you filter everything out beforehand, who cares if the infrared gets blueshifted after the filter.

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Posted: 31 July 2009 10:33 AM   [ Ignore ]   [ # 24 ]
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i search the IR bandpass filter on googlr, it come out Wide IR bandpass filter and narrow IR band pass filter...what is the different between them? which one i ned to use (let say my IR LED is 850nm)?

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Posted: 23 October 2009 08:04 AM   [ Ignore ]   [ # 25 ]
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ok i’m having this vignetting problem with my DI setup with wide angle lens.

So the workaround for this problem is to get a higher/wider FWHM band pass filter? because currently now i’m using a narrow pass filter with 10 FWHM.

Another workaround is to put the filter in between the CCD and lens? i dun think i can do that since my filter is too big to fit it in, but i dun mind trying out and see what is the effect.

is this the filter i’m looking at?

http://cgi.ebay.com/NIR-Optical-Filter-850DF55-25-4mm-painted-edge_W0QQitemZ310169023609QQcmdZViewItemQQptZCamera_Filters?hash=item483783b479

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