CLPEX Chat Board

Got an email from Arrowhead advertising their new FF1.0 Filter, supposedly a narrow bandpass filter that might enhance contrast when photographing prints developed with Indanedione and I'm assuming Zinc Chloride or DFO as well. Anybody want to explain why they're charging $2100+ for what looks like just an ordinary green filter? Is there something I'm missing? https://arrowheadforensics.com/a-ff-1-f ... ilter.html

Well, it is a pretty shade of green.

https://web.s.ebscohost.com/abstract?di ... 3d76502013

Probably something that Brian Dalrymple first published on in the 80s. We were able to purchase the same filter he used in this article around 2012 or 2013 but it is now unavailable. It drops reflected background fluorescence tremendously and does make the prints easier to see. It does require a slight shift in focus as the filter slows light down enough to cause a blurry image if not rectified.

Since we have one, I haven't had to look for one in a while. I think we paid around $300 for ours. While $2100 seems steep, they might only be making these in one size in very limited quantities. Brian said this filter is like a seatbelt, you don't always need it but when you do, you're really glad you have it! For those of you that know him, this would come as no surprise!

Filters that are meant for Laser's are going to be more expensive than regular filters plus bandpass filters are more expensive than cutoff filters. If you were able to get the specs you might be able to get a quote from a filter company like Alluxa.

Our lab has the filter and it does improve the photos. Also the filter is a one time cost so we thought it was worth it the price did go up since we bought it though.

Is this the article?

Use of Narrow-Band-Pass Filters to Enhance Detail in Latent Fingerprint Photography by Laser, B. E. Dalrymple, Journal of Forensic Sciences, 27:4 (1982) Various filters on porous and non-porous surfaces used with argon-ion LAS PHOTO

Thanks for the replies everyone! I will probably throw it on a wish list. Seems a good item for grant money.

Call me crazy, but according to the youtube video by ArrowHead on this very filter, they're showing the background noise range of 600+ nm
According to pass through charts of various filters we find that the Tiffen #11 allows a 60% pass through at a range that seems to occlude the background noise by rolling off by about 600 nm.
And this all for the low low price of 29.99
Shout out to Steve who busted out the old Wratten pass through chart we used to hang on the wall but had to take down since it was not a controlled document. (Thanks, ANAB)

Boyd Baumgartner wrote: ↑Mon Apr 11, 2022 7:50 pm Call me crazy

You should have a day off from this once in a while.

Shout out to Steve who busted out the old Wratten pass through chart we used to hang on the wall but had to take down since it was not a controlled document. (Thanks, ANAB)

We've had a nice selection of many different Kodak wratten screw-on (62mm) filters since before I started. I guess you don't realize how fortunate you are until you find out this isn't always the case.

I've got a couple of different Kodak Spectral Transmittance Charts that I found in an old Kodak filter book and online. There's a little crossover, but it covers a lot of ranges. This numbering system seems to be pretty consistent with the Tiffen document I found online, where Boyd sourced the #11 and #58 graph from. Also, for screw-on Tiffen filters, the number convention is TI[wratten number][filter diameter]. So, for a #11 in 62mm size, it's TI1162 as you can see in Boyd's image.

One more addition. When Fuji was releasing their UV/IR cameras (based off the S3 and S5's), Peca had a series of filters to use with them. Their website still exists with the information, but it looks like they no longer sell filters. Their Bandpass page shows several options they had available. Some of their IR kits still show up on sites like B&H, but either are discontinued or says they're shipped by manufacturer.

Somebody could call and see if there is any old stock availability. There is a number at the bottom of the page, although all of their social media buttons are unlinked.

Oh Steve and Boyd, you two are awesome, thank you for weighing in. I think I remember the Peca filter from when I was using one of the converted Fuji cameras and it wasn't green, it had a mirror like coat on it, probably to compensate for the removed filters in the body of the Fuji. I decided to just email Arrowhead Forensics and ask them how it's different from a regular Tiffen #11 filter, we'll see if they get back to me. I'm sorry, but I just don't understand how it would be $2100 except for "because we can" and "it's forensic!".

WIth the bandpass filters, It's a very narrow range that is passed. If you look at the chart for the Peca 535, you can see it's mostly in a defined range: http://www.ir-uv.com/535.html However, they also let light through in the UV and IR. But the 11 and 58 don't let in 100% of the light in the fluorescent range, and there's also more spread where a lower percentage of light is transmitted (especially with the 11 compared to the 58).

SConner wrote: ↑Tue Apr 12, 2022 7:11 am Oh Steve and Boyd, you two are awesome, thank you for weighing in. I think I remember the Peca filter from when I was using one of the converted Fuji cameras and it wasn't green, it had a mirror like coat on it, probably to compensate for the removed filters in the body of the Fuji.

Peca had a set of UV/IR filters that you could buy. They blocked most of the visual spectrum, but let in different areas (mostly in the IR range). You didn't known which one would do the trick. There's also the lens being used and if it would pass those ranges.

When the FBI was hosting their in-service classes 10+ years ago, we were shooting on 35mm IR film. But the instructor (Mike Brooks) at the time had an IR viewer that we could use on the "evidence" and put the different filters in front to see which worked the best/allowed the most reflected light to pass. Then that's the one we'd use with the camera, taking multiple "blind" exposures.

I think he had one of the new, at the time, Fuji cameras to show how to use it with the live view. The problem with it, at the time, was sensor heat on the DSLR as you left the sensor open to test the filters. It would introduce noise if left active too long. The viewer he had worked great, though.

If you want to geek out, here's another article you can read through. I only skimmed it at this point: http://www.ultravioletcameras.com/pdf/R ... ics_V3.pdf

Here you can see B&H's page for the Peca UV/IR kit: https://www.bhphotovideo.com/c/product/ ... r_Kit.html

They also had the 916 filter that would block UV/IR and took the place of the internal filter so that you can use the camera for visible light photography.

The Arrowhead website links JFI-2017-2-206 (Dalrymple) under 'Downloads>User Manual’ on the FF-1.0 filter page. It is indeed a narrow bandpass filter, designed to suppress background fluorescence, and is intended to be stacked with a cutoff filter (the cutoff filter suppresses the reflected light from the light source) . This is described under the ‘Brochure' link on the same page.

From the JFI article:

“The final filter (FF-1.0) selection for all subsequent activities was a 10 nm bandpass filter centered at 560 nm (Figure 3). This filter has 98% in-band transmission and transmits approximately 39% of the fingerprint fluorescence when stacked with a curved orange long pass barrier filter.”

I really loved my MP-4 using CPO sheet film in 4" X 5" format. CPO (contrast process orthochromatic film) was made by Kodak and was sensitive only to blue light. No filters were necessary and especially with superglue developed prints, a crisp white image was produced on a background in which colors lacking any blue component came out as black.

We bought the film in boxes of 100 sheets and hand loaded two sheets each into reversible film holders. We mixed our own chemicals, developed the negatives, and printed our negatives on contact sheets. For court, we printed enlargements on 16" X 20" photographic paper and mounted the prints on heavy poster board and, later, on ¼" white foam board after that was invented. We drew red lines to the points with a Sharpie marker, and used press-on letters and numbers to number the points and label the enlargements.

I really miss my old MP-4 and CPO film.

"Those were the days, my friend; we thought they'd never end!"
--Gene Raskin