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UltravioletPhotography

Mystery IR filter - transmission spectra and images


JMC

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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.

post-148-0-29441600-1616755352.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.com/forums/thread/296693#forum-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.

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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.

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Andy Perrin
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.
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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.

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