IR with Sigma SD Quattro

[digitalhecht]

Hi All,

My new SDQ arrived yesterday. While I was able to get decent "aerochrome" shots via Kolari's IR Chrome filter in the T&O mode (with AWB), the results I get with ANY other filters across the board are just a red nightmare (470nm, 590nm, O-56). No matter which Mode or WB I try, the results are the same.

I have a dumb-adapted Pentax Asahi 50mm f/1.4 M42 lens, which works great with the aforementioned filters on my full spectrum converted Sony A7R II. (UNfortunately this is the only lens I have that I can use with this camera for now.)

My workflow is

1) Remove the internal IR filter

2) Place external IR filter on lens

3) CW with foliage or grey (Unfortunately, setting CWB mostly fails for me too.)

What I see is a muddy red mess-so muddy, I can't even focus properly-which may explain why my CWB attempts fail.

 

What am I missing???

TIA.

Ed

Thanks to @Gary for the aero tips here from TO, ONT-still my fav city on the planet!

[colinbm]

Great camera & GaryR on this forum has some good information & beaut photos.

Please remember that Foveon & Bayer cameras are completely different in their responses to IR.

I have many Sigma Foveon cameras including the Quattro, but I haven't got around to using it for IR.

I have converted a Sigma fp, which is a Bayer sensor camera, I that is my current go-to camera for UV & IR photos.

Between GaryR & Christoph both on UVP you will be in good hands.

[digitalhecht]

Great camera & GaryR on this forum has some good information & beaut photos.

Please remember that Foveon & Bayer cameras are completely different in their responses to IR.

I have many Sigma Foveon cameras including the Quattro, but I haven't got around to using it for IR.

I have converted a Sigma fp, which is a Bayer sensor camera, I that is my current go-to camera for UV & IR photos.

Between GaryR & Christoph both on UVP you will be in good hands.

Thanks, colinbm. It sounds like there may be some filter stacking technique(s). Hopefully, one of them can point me in the right direction.

[colinbm]

You can search the forum & read their posts.

[digitalhecht]

One thought just occurred to me....

 

Is it possible that the slightly yellowed tint (from Thorium) on my vintage Pentax M42 lens is causing these issues with Foveon?

 

Again, I don't have a single other lens I can mount on the SDQ for now. SA mount lenses are hard to come by: Special order from B&H, backordered at Adorama, and most eBay listings are coming from Japan. So I ordered a used Sigma 17-70 from Japan. I just need to ascertain there isn't a problem with this unit before Adorama's return window closes...

[Andy Perrin]

I would say that’s doubtful that the yellow tint is causing the problems with IR. It affects the blue end of the spectrum and only a little.

[dabateman]

No I highly doubt its the lens. Foveon sensors are extremely IR sensitive. Gary was using a Kg3 filter to cut it down to reasonable levels. Thus why I usually just use Foveon for IR black and white.

 

The 17-70mm is a nice lens. Its cut off is 378nm into UV. So it can be used for UV photography with the SDQ, but again this is only in the Blue channel, so setting the camera to monochrome would be best. The only downside is the 72mm filter thread leads to very expensive filters.

[eye4invisible]

Not sure if this will help you, but some cameras can be put into monochrome mode, which can help with focusing. If I shoot raw+jpeg on my Nikon D3200, I get a b&w jpeg, but the raw NEF file retains the colour info.

[GaryR]

Hi Ed,

 

Yes, the Quattro does produce a lot of red. You can CWB with no filter, but there's still a lot of red in the mix. I currently using a MidOpt DB850 to attenuate the reds, but I've also used the KG3 filter with good results. CWB works fine with those filters.

 

With the DB850 (or KG3) I do CWB on gray, export TIF from Sigma Photo Pro, then process in DxO NIK. In particular, the Pro Contrast menu in Color Efex Pro, has a profound effect on reducing the red haze and accenting the blues and yellows. That's about it.

 

I use my FS-Sony aR7 for more authentic looking Aerochrome colors, but I still like the unique look of Foveon colors. For bw IR, I use Monochrome Mode with a R72.

 

Here's one with sdQH + 75mm El-Nikkor + DB850