Hoya Y2 vs K2 Filter

[thefizz]

Does anyone know what the difference is between the Hoya Y2 and K2 yellow filters?

 

[koraks]

Good question. Hoya's own product information is pretty opaque on it.

 

[loccdor]

Answered by B&H staff:

Both the Hoya 67mm Yellow #K2 (HMC) Multi-Coated Glass Filter for Black & White Film and the Hoya Y2 PRO Yellow Filter (72mm), BH #HOY2P72, have s similar affect, but the K2 is a little more intense as it is less opaque than the Y2. This gives the K2 a slightly more noticeable reduction in reds while making greens appear slightly brighter than they would appear when filtered through the Y2.

 

[Ian C]

Here are absorption/transmission graphs for both filters. The K2 and Y2 graphs appear identical.


Hoya Y2 spectral absorption/transmission graph

https://hoyafilter.com/product/y2_pro_yellow/


Hoya K2 spectral absorption/transmission graph

https://www.nikonians.org/reviews/using-a-full-spectrum-camera-part-ii


I own and use both types. If there are differences between the results, they are too subtle for me to perceive.

 

[Daniel Stuefer]

Looking at transmission curves, K2 transmits ever so slightly more light on the short wavelength end than the Y2 (based on intersect with the X0 and X1 curves, assuming those are the same; Y2 seems has a higher cutoff wavelength, but only barely). Practically, though, you might say their cutoffs are the same. The Y2 also seems to have slightly higher transmission around the peak at 600nm, where transmission seems to be around 98%, while the K2 seems to be flat at about 95% transmission from ~500nm upwards

So, as Ian has just said whilst I was writing this, differences would be very subtle.

 

[loccdor]

I've always treated them as interchangeable.

 

[koraks]

Thanks for digging up the K2 curve @Ian C and posting them side by side @Daniel Stuefer !
Here's an overlay of both:

It confirms what @Daniel Stuefer says above.
The K2 filter is a little 'less yellow' than the Y2 filter, so the Y2 will have a slightly stronger filter effect as it attenuates a bit more of the blue spectrum.
I doubt the difference is apparent in normal photography.

 

[thefizz]

Thanks all for your help, I'll order whichever one is available.