Hasselblad H3D IR cut filter replacement

[antoine_k]

So my back has a few dings on the IR filter.    Sending it to Denmark is quite expensive.  New Jersey is even more expensive.

My question is this: Does anyone know the specification of the IR filter?   I can obtain Hoya CM-500, Schott BG39 and BG40 filters with AR coating cut to the correct size easily and at 1/10th the price. There is even an IR650 filter on ebay, from China, for the suspiciously stupid low price of $14.  But I have no idea if any of them is the correct filter.

Anthony.

[Joe Towner]

Yea, it's pricy, but unless you have a cleanroom environment to work within & all the other tools, I highly recommend sending it off.  Due to the age, it may be cheaper to purchase a replacement back, even a higher MP one.  Are you dealing with a 33x44 sensor, or the larger 36x48?

The cost isn't the filter, the cost is the tools & experience to do it right.

[antoine_k]

Appreciated.  It's the 33x44 sensor (H3D-31). 

The back was sent for cleaning and a new filter a few years ago, and it's still working just fine. So I don't really need the full service. I've already removed a few screws and lifted the black plastic cover, and I know it's only glued/caulked down and is easy enough to remove and place a new glass on top.  Plus I can prepare a clean space to work on it. I expect most of the cost for the service is the time spent calibrating autofocus etc., which it doesn't need since it's not being used on a hasselblad body.

[Joe Towner]

Sounds like you're far enough into it you can pull it out and measure.  Honestly I'd build something like this to do the repair in - mostly because dust is a .....  https://www.youtube.com/watch?v=xPEa0Wc9iUc    It's a box, with a clear window, and some air filtering. 

Also, never underestimate the value of a couple of sheet magnets for holding screws as you take it apart. Good luck, and take a video to share with the rest of us

[antoine_k]

That youtube link for the dust free enclosure is pretty cool, thanks.    I will have to rig-up an enclusure like that to be sure. The two videos I saw on youtube about the filter change just shows the presenter doing it out in the open, which is perhaps a little cringeworthy. 

I did measure the glass and found it to be 51mmx56mm.  Not surprisingly, there are a few vendors selling Schott and Hoya filters on ebay in those same dimensions. The issue is getting the correct model number for the glass as they all have different transmission curves.  If I had a loose sample of Hasselblad glass I might be able to take it to the university and find someone with a monochromator to measure the curve for me.  I did have a piece from the last time the guys in Denmark replaced the filter, but I cannot find it now and I figure I must have disposed of it since it was broken.

[Joe Towner]

Since they're cheap, why not get different filters and try them all?  You may even want to do a clear one, without the IR blocking, just to see what you get for an image

[antoine_k]

 

I might just buy one if I can't determine the correct one, at which point I would have to get a colorchecker and profile the back in Phocus.

And then there's this guy trying to come-up with a combination of filters to mimic Kodak IR Ektachrome.  https://next-eyes.blogspot.com/2018/11/my-history-re-inventing-digital-ir.html

[Dustbak]

There was a time that sending your back in for a cleaning of your IR filter they would replace the filter. This used to be a much cheaper option than sending it in for an IR filter replacement...

I have screwed up replacing stuff like this too often. 

[antoine_k]

They don't have a separate price for just IR filter replacement.

[antoine_k]

I'm going to start with the ridiculously cheap chinese filter.  It's on order and we'll see how long it takes to get here.

[antoine_k]

I received an email from the repair shop in Denmark telling me "the filters from Hasselblad are BG-39".   BG-39 is a Schott number. 

[Joe Towner]

I received an email from the repair shop in Denmark telling me "the filters from Hasselblad are BG-39".   BG-39 is a Schott number. 

NICE!

[balsop]

Did it work?

has anyone tried this with a Iq or Credo back?

[pemihan]

You need to take into account the thickness of the glass. It needs to be the same when it comes to focus as the light breaks differently depending on the thickness. At least that's what I have been told.

[balsop]

Thanks!

I was thinking that I would need to remove the filter and measure it for size and thickness, seems fairly straight forward with the hasselblad but haven't seen or heard if there are any tricks with the phase/leaf backs.

has anyone tried this with a credo or iq back or converted to for wide spectrum?