Does anyone know of a good place to buy a IR bandpass filter use with a for Pt. Grey firefly MV and Osrahm SFH485 (880NM)?  Currently I am using two pieces of photo negative, but my projector is also producing a IR hotspot (small circle) in the middle of the projected image.

Hey thomas,

I’m guessing you need something like this : Optical Filter for the projector hotspot.

The hotspot is because the projector also emits some amount of IR light that causes the ‘hot spot’. cerupcat apparantly placed this over the projector to avoid it.

hope it helps,

I will order one of these tomorrow.  This takes care of the hotspot right?  Do I still need a bandpass filter for optimal performance, or do the photo negatives i use now perform just as well.  As I said I am using osrahm LED and know their wavelength.

If anyone has experience with the difference between a real bandpass filter and photo negatives I would love to hear about it.

be careful to get a filter that covers your projector output completely. this basically blocks IR light from the projector..

My experience shows that a good bandpass filter does make a huge difference. It shouldn’t make your blobs much brighter, but it will definitely filter out most ambient IR.
I had a couple photo negatives on a MS VX-6000 webcam which would work alright at night with all the lights off, but suffer greatly at the presence of daylight.
Now I’m trying a Thorlabs bandpass filter with a very narrow spectral width (+-10nm) on a FireflyMV and boy, is my table sensitive. It really doesn’t make a difference if I use the table during the day with the room windows open or at night with all lights off.
It should be noted that I upgraded pretty much all of the table components from one setup to the other, so the bandpass filter is just one of the elements that made that difference. But I have an impression that it was an important one.
Also, I have here a +-40nm filter that I have yet to try. It should give me brighter blobs though filtering less ambient light. I guess the +-10nm filter should only be used with a high sensitivity camera and lens, plus powerful leds (SFH485s are ok).

midwest optical system can custom cut a filter that fits in the CS mount for $20.

Link

that sounds perfect.  Is it $20 for just the cutting, or does that include the lens?

Thats the filter and cutting. What wavelength are your LEDs? 850nm? if so just as for a BP850 14mm x 14mm x 1mm that will fit in the space where the IR cut filter is not in the CS mount.

I actually checked the point grey site for an IR filter for the firefly and there seems to be something called “ ACC-01-5001 - RoHS M12 Micro Lens Holder with IR Filter”.  I was planning on calling the sales number and asking what this is, but it is made for the firefly MV.

I believe this Point Grey filter is the one that lets visible light in and blocks IR light.

Point Grey FFMV camera…

Point Grey has lens mounts, with and without filter filters. The one with IR filter (visible pass) is very easy to remove, but you don’t need to because the $300 development kit for the FFMV includes both (also, get the 4mm and 8mm as well the default 6mm lens for a range “panel in frame” distances). These microlenses are not CS mount (remove cs mount from camera and install microlens mount). Microlenses also do not have threads for mounting filters (see last comment on filter mounting).

Regarding the bright spot…

Put to both projector and camera off-axis to get rid of the glare (of course NOT on opposite sides of the axis!). You get a little trapezoid, but most projectors are designed to be off-axis (ceiling or table mount). But the IR radiation from the projector may still be slightly picked up by the projection via the diffuser. So some means of getting rid of the projected IR is nice. You CAN use a filter or hot mirror that is SMALLER than the lens, it will then act as an aperture (like changing the F stop in a traditional camera lens) with slight attenuation to the projected image (which is only a problem for dim projectors, rarely for most, especially for ftir tables).

Also consider a COLD MIRROR !!!

One single cold mirror can both filter IR from projector to panel AND filter visible from panel to camera. This is done by mounting Projector and camera are 90 degrees to each other with projector reflecting off of mirror to panel and camera seeing through it straight to the panel. There is a small cross-over region in the spectrum where some IR is reflected and some visible is transmitted.

FILTERS, irLEDs and SPECTRUMS…

I tried a 890PB10 on a FFMV with a panel using Optek OP290 LEDs (spectral output similar to SFH485) and had to replace the filter with a wider pass 880BP70. Along with a large and cheap hot mirror it is working well with good tolerance to ambient lighting.

Remember that LEDs actually emit a fairly wide spectrum of radiation. The SFH485 is 80nm wide between 50% points, and don’t assume it is symetrical - check out the “Relative Spectral Emission” plot in its datasheet - use this as your reference when comparing plots of filters. General rule of thumb is to pass at least between the 50% points (has anyone really had success with very narrow 10nm pass filters?)

The specific filter I am using with the FFMV now is from Thorlabs…
http://www.thorlabs.com/thorProduct.cfm?partNumber=FB880-70

The specific hot mirror I am using is a Rosco #38000
http://www.rosco.com/us/filters/protect.asp#IR-UV
(I highly recommend an “extended IR” hot mirror over a regular hot mirror)

CHEAP IR-PASS

Ebay has some great deals, otherwise on a budget you can get a 4"x5" resincast and cut it into many 1” x1” pieces and stack them up for a decent IR-pass on the cheap.
http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=1918
(don’t get the 1” round one, it is a different material and sucks)

FILTERS MOUNTING DOES NOT HAVE FIT EXACTLY

As long as the filter is at least as large as the camera lens, it will work - silicone glue! You may have to make an adapter ring out of black plastic (actually, I made an aluminum bracket for mine). Just glue it up with silicone and it is done, but removable if you need to. The microlens on the FFMV do not have threads for mounting filters - not a problem. Don’t waste your money cutting down filters.

Wow roger, thanks for the great info!

Thanks for the great post Roger! Looks like the table will be working even better when I get back in the lab

-Seth

thank you roger!!

Seth, I thought that might be you.
Actually it is the same filter that has been there for a while, but I do have some new surfaces.
I think there is a general lab meeting tomorrow/wednesday morning at 10:30am.

brettf - 25 March 2008 02:52 PM

midwest optical system can custom cut a filter that fits in the CS mount for $20.

Link

brettf (and also everybody else),

can you tell which Midwest Optical filter you have and how it performs in comparison to photo negatives?