• Ultraviolet Photography
  •  

Mystery IR filter - transmission spectra and images

Infrared
128 replies to this topic

#121 dabateman

    Da Bateman

  • Members+G
  • 2,767 posts
  • Location: Maryland

Posted 23 March 2021 - 22:37

Nah just label it fake and be done with it.
At least you have a nice new IR spectrometer.
My Jaz spectrometer is funny. I bought it with two detectors. One with grating #2 and one with grating #4. The #4 gratings has a lp filter and was to be used for fluorescent detection.

Then when testing a xenon pulse module the one with grating #2 stopped working, it was still under warranty so returned for fix. He had one with grating #1, which for me was perfect as now can see the 185nm Mercury line. So I have that module but its 4x more sensitive than the one originally for fluorescence with #4 grating. So haven't used the IR #4 grating module yet for original purpose. But it is better to eliminate stray light.

Have fun looking into the IR world.

I now like to scan stuff with the light I intend to use to get idea for the signal variation.

#122 JMC

    Member

  • Members+G
  • 1,270 posts
  • Location: London, UK

Posted 24 March 2021 - 12:03

Can of worms indeed.

My 'R72' came from someone who used to do forensics work, and there was no mention of if not being what it said it was, and the filter ring is an R72 one. Looking at the spectra it looks to be something like an 89B, but that is just speculation. I have bought myself another R72 to test - hopefully this one will be a good one.

Does make me wonder how many people don't have what they think they have?

For now I'll update the graph I shared yesterday, to remove the suspect filter.
Jonathan M. Crowther

http://jmcscientificconsulting.com

#123 colinbm

    Member

  • Members+G
  • 2,405 posts
  • Location: Australia

Posted 24 March 2021 - 13:17

" Does make me wonder how many people don't have what they think they have? "

Filters, Lenses & lights....that is why I bought a spectrometer... :cool:

Edited by colinbm, 24 March 2021 - 13:18.


#124 dabateman

    Da Bateman

  • Members+G
  • 2,767 posts
  • Location: Maryland

Posted 24 March 2021 - 16:19

View Postcolinbm, on 24 March 2021 - 13:17, said:

" Does make me wonder how many people don't have what they think they have? "

Filters, Lenses & lights....that is why I bought a spectrometer... :cool:


Oddly you almost need one.
The advantage of buying a spectrometer that I see is after purchasing it everything I have purchased is what it says it is. To make you feel like you don't need it. But if you don't have one than its all questionable.

#125 Andy Perrin

    Member

  • Members+G
  • 4,084 posts
  • Location: United States

Posted 24 March 2021 - 16:34

Surely the message of this thread is that it might still be questionable even if you DO have one!

#126 JMC

    Member

  • Members+G
  • 1,270 posts
  • Location: London, UK

Posted 26 March 2021 - 10:57

Just when I thought this couldn't get more weird, it does.

So I had a quick look on ebay and saw another Hoya R72 for sale, for about £20 so bought it for testing. This looks to be an older one based on the style of the writing on the side of it. I now have data on 3 different filters marked up as Hoya R72. These are;

No1 - my original one, bought a few years ago, second hand, but from someone involved in forensics/scientific photography.
No2 - bought second hand, tested by me and then sent to Ulf for testing, so we could look at the same filter. Ulf - looks like I sent you a good one.....
No3 - bought from ebay in the last few days, a second hand one, and looks to be an older one based on the writing style.

I have transmission data from the FX spectrometer and the STS-NIR one, and here is how they all look between 650nm and 750nm.
Attached Image: R72 comparison.jpg

Here's what's odd. Only filter No2 looks to have the cutoff in the area expected for an R72 filter.

So, No1 and No3 are fakes and are not Hoya R72, right?

I did a search for fake Hoya filters, and it lead me to a thread on a forum from 2002 - https://www.dpreview...um-post-3161709

This is what struck me (quoted from the thread);

"Most IR experts on filters DON'T believe the Hoya numbers, it seems.

The R72 is supposed to start blocking visible light beyond 720nm, but many web sites claim that the numbers from Hoya don't add up, and the R72 is closer to the 89b. Other reports, from Will at H&H, say the 72 lands between the 88a and the 87. I really don't know who to believe. The R72 cuts visible at either 690nm, 720nm, or 745nm, depending on the source."

Perhaps the question of "is this filter actually R72 or is it a fake?" is not that straightforward to answer, and maybe some of the older ones had cut-offs in different places. All very strange.
Jonathan M. Crowther

http://jmcscientificconsulting.com

#127 dabateman

    Da Bateman

  • Members+G
  • 2,767 posts
  • Location: Maryland

Posted 26 March 2021 - 12:22

I got my first full spectrum converted Canon S5 back in 2008. At that time many supposed R72 filters were not real Hoya.
It came with a "R72" filter. But it almost like your other fakes. However if you actually use its quite nice.
Now I will have to spec it as I can't remember what it looks like.

#128 Andy Perrin

    Member

  • Members+G
  • 4,084 posts
  • Location: United States

Posted 26 March 2021 - 15:13

My “NEEWER” R72 is clearly a different filter from my Hoya brand R72 and white balances quite differently. I always just said “Chinese filter” and threw up my hands at that observation.

#129 UlfW

    Ulf W

  • Members+G
  • 1,607 posts
  • Location: Sweden, Malmö

Posted 26 March 2021 - 16:55

I think most"R72"-filters on the common photo-equipment market are only R72-ish.
The R72 is often used as an approximative indication for an IR-pass filter that gives images with some colour differences.
The vast majority of the users will never notice as they do not use spectrometers to verify their filters.

It is just like the Hoya-branded filters are not produced by Hoya if I remember correctly.
To get real R72-type glass you have to get it from a scientific filter supplier, and then there can still be mixups and confusion due to human error.

Edited by UlfW, 26 March 2021 - 16:56.

Ulf Wilhelmson
Curious and trying to see the invisible.