Sony a7rii - wavelength of internal IR cut filter?

Hi, does anyone know the wavelength at which the internal IR cut filter of the Sony a7rii kicks in? To be clear, i am talking about a standard camera. 

Thanks. Joerg

It starts to roll off rapidly above 700nm but you can still do some IR photography with long exposures with something like a 720nm filter.

E.J. Peiker wrote:It starts to roll off rapidly above 700nm but you can still do some IR photography with long exposures with something like a 720nm filter.

Thanks EJ. Do you know where one might find the transmission curve for this internal filter? I've looked but no success so far...

Joerg

Joerg Rockenberger wrote:

E.J. Peiker wrote:It starts to roll off rapidly above 700nm but you can still do some IR photography with long exposures with something like a 720nm filter.

Thanks EJ. Do you know where one might find the transmission curve for this internal filter? I've looked but no success so far...

Joerg

Sony does not disclose transmission curves.  Even Phase One was not allowed to disclose the the transmission curve for the 101mp Sony MF sensor to me even though they made an official request for me and I was willing to sign an NDA so I just had to test it myself to find out what it will and won't see.  I have a 695 filter I can stick on an a7R III to see what it looks like - stand by!

OK, just a quick and dirty test in my backyard.  The loss is 9 stops on the a7R III with the Singh-Ray 695nm filter.

Here it is straight out of the camera: And then with just a really quick and dirty conversion in C1 Pro: Note that the sun was not out so it's less contrasty than it would be if it were...

I don’t see the advantage over converting to b&w in these samples. The IR just doesn’t make it pop. Maybe it’s simply the lighting or the cutoff is much higher than 695nm.

Joe

SantaFeJoe wrote:I don’t see the advantage over converting to b&w in these samples. The IR just doesn’t make it pop. Maybe it’s simply the lighting or the cutoff is much higher than 695nm.

Joe

Like I wrote - the sun was not out!  This was purely to show that the a7R III does have some sensitivity in the IR part of the spectrum.  You  get that IR pop when the sun is out.  Additionally, the biggest part of presenting an IR photo is actually the post processing and as I said, this was a simple quick and dirty B&W conversion.  Something like the Heliopan 715nm filter would be much better than the Sing Ray 695 which is not a great IR filter for mono work as it's tail into the visible spectrum is too long and even lets some green through.  For B&W IR you definitely do not want any green.

Thanks EJ. You da man, as always. Now, I am not too familiar with IR filters/photography and I am not sure I understand your statement "The loss is 9 stops on the a7R III with the Singh-Ray 695nm filter". My guess is that it means that in order to record the scene with the 695 in place you needed to increase the exposure by 9 stops. But how is that relevant to the wavelength at which the internal IR kicks in?

Thanks. Best, Joerg

Joerg Rockenberger wrote:Thanks EJ. You da man, as always. Now, I am not too familiar with IR filters/photography and I am not sure I understand your statement "The loss is 9 stops on the a7R III with the Singh-Ray 695nm filter". My guess is that it means that in order to record the scene with the 695 in place you needed to increase the exposure by 9 stops. But how is that relevant to the wavelength at which the internal IR kicks in?

Thanks. Best, Joerg

Because the camera has an IR cut filter and you are now adding a visible light cut filter on top of that you need to increase exposure by 9 stops to properly expose the scene with the a7R III.  Basically you are accounting for the transmission loss of those two filters to render the scene by adding 9 stops.  If instead of using a filter you were to get the camera converted, the company doing the conversion removes the IR cut filter and replaces it with a visible light cut filter.  The result of that is that the sensor is now very responsive to the IR spectrum and not the visible light spectrum so that your exposure values return to normal but in the IR part of the spectrum.

Thanks E.J.