IR with Sigma fp on a whim

[Akira]

Hi, this is my first post after a while.

 

I bought Sigma fp with the kit lens 45/2.8 a couple of month ago. I liked the combo very much so far, and the well known caveats are not much of problems for my shooting style.

 

Of course, I had never intended to shoot UV or IR with the combo, taking it granted that the current digital cameras have very efficient UV/IR cut filters and would never allow photography outside of the VIS range.

 

That said though, it came to my mind that this Sigma fp without either an AA filter or a dust shaker could shoot IR. Here are the result of the impromptu trials. I simply attached Cokin Z007 resin filter (equivalent of Kodak 089B or Hoya IR72) in front of the kit lens. There is a noticeable hot spot in the center of the image.

 

Shot at ISO3200, f4.0, 1/10sec,

 

#1: This is how the RAW (DNG) file looks (simple conversion from DNG to JPEG).

#2: A B&W conversion.

#3: A color version by my crude, inexperienced processing.

[dabateman]

Very interesting,

What would your guess be for the visible exposure?

To me it looks like a 9 stop drop in IR sensitivity.

I really hope Sigma goes back to placing the UV/IR block filter on a removable filter.

 

Do you have a Baader venus U filter?

Can you try an exposure in daylight to see if you see anything.

The Olympus cameras have very weak UV blocking. Would be good to know if the Sigma is strong like a Canon or weak like an Olympus.

 

My old Kodak SLR/n had just a 1mm S8612 filter to block IR. But would do some odd internal camera calibration to kill the UV signal. Sometimes it worked to shoot UV if you caught it before a calibration cycle.

I have since sold that camera though.

[colinbm]

Congratulations on getting the Sigma fp.

I am wanting one too, but I will remove the hot mirror & make it full spectrum.

How did you get the white balance ?

What are the Kelvin degrees that can be selected Please ?

Good to see your results.

Col

 

PS, I have found that magenta & cyan are a sign of over-exposure & perhaps you could reduce them in processing ?

[Akira]

Very interesting,

What would your guess be for the visible exposure?

To me it looks like a 9 stop drop in IR sensitivity.

I really hope Sigma goes back to placing the UV/IR block filter on a removable filter.

 

Do you have a Baader venus U filter?

Can you try an exposure in daylight to see if you see anything.

The Olympus cameras have very weak UV blocking. Would be good to know if the Sigma is strong like a Canon or weak like an Olympus.

 

My old Kodak SLR/n had just a 1mm S8612 filter to block IR. But would do some odd internal camera calibration to kill the UV signal. Sometimes it worked to shoot UV if you caught it before a calibration cycle.

I have since sold that camera though.

 

Thank you for your interest. I would agree that the IR sensitivity seems to be (very) roughly 9 stop lower than the sensitivity to the visible spectra. The image was brightly lit by the sunlight.

 

My last hands-on experience with an IR capable camera was the ancient unmodified Nikon D40, and one of the last image was shot at ISO400, f8.0 or 11.0, 10sec. Judging from the excellent high-ISO performance of the latest BSI 24MP full frame sensor of Sigma fp, it should be safe to assume that fp is more capable than D40 even without modification. The live view with the IR72 equivalent or even the denser IR84 filter looked crisp and clear, the AF worked very well and the manual focusing with the 8x magnification is a breeze.

 

I do have an 1 1/4" Baader U and the chrome-base EL Nikkor 105/5.6 and necessary adapters. So, I'm able to see how the camera performs in UV.

[Akira]

Congratulations on getting the Sigma fp.

I am wanting one too, but I will remove the hot mirror & make it full spectrum.

How did you get the white balance ?

What are the Kelvin degrees that can be selected Please ?

Good to see your results.

Col

 

PS, I have found that magenta & cyan are a sign of over-exposure & perhaps you could reduce them in processing ?

 

Thank you for kind words. I just use the "click white" method on the brightest part of the leaves in ACR. The original, untouched DNG file (#1) shows healthy amount of data in all RGB channels with no highlight clipping. If you are referring to the image #3 for the overexposure of magenta and cyan, that should be the result of the excessive tweaking in the channel mixer.

 

Also, I found that the image #1 was converted after I had applied the "click white". The true original DNG looks like this. The color temperature shows 5350k. Sorry for the confusion!

[OlDoinyo]

Foveon cameras are natively quite sensitive to IR, but somewhat more limited in the UV. You won't get much chromaticity in your images, though--the images are basically monochromatic once the tint is removed.

[dabateman]

Foveon cameras are natively quite sensitive to IR, but somewhat more limited in the UV. You won't get much chromaticity in your images, though--the images are basically monochromatic once the tint is removed.

 

Sigma Fp is not a Foveon sensor! Its the same Sony A7m3, Panasonic S1 and Nikon Z6 sensor, with Bayer pattern.

So totally new direction for Sigma.

 

Also Foveon are actually quite sensitive to UVA, they just cut off at 335nm, from my tests with SDQ, SD14 and Jonathan's tests with SD14. 350nm is strong, similar exposure to other converted cameras. Issue is they are only monochrome.

 

Akira,

I look forward to the UV test. Even though the 1.25" baader leaks IR the UV/IR block filter might help you if the UV blocking is weak. So I look forward to seeing your tests. Also since sadly Sigma just scrapped the L-mount Foveon camera. So the Fp line maybe it for awhile.

 

I too am interested in the fully selectable range of kelvin in Custom white balance. As in can I dial in 2000k to 14000k? Or just 3000k to 10000k.

The manual does not indicate the range.

[Akira]

Yes. Fp uses Bayer sensor. I'm not sure if it is the same one as used in Panasonic S1. Is the Panasonic one also of BSI type?

 

The sensors in Sony A7III and Nikon Z6 are of the BSI type, but they have PD photosites whereas Sigma sensor is CD only. I'm not sure if they are identical either.

 

The "Temperature" slider of ACR ranges from 2000k to 50000k. Quite wide.

[dabateman]

 

 

The "Temperature" slider of ACR ranges from 2000k to 50000k. Quite wide.

 

Sorry for the confusion Akira. But Colin and I were asking for the Kelvin selection directly in camera on the Fp.

[colinbm]

Thanks Dave

Akira, in the camera you can select a 'White Balance', there are 12 options....

(Auto, Auto (Lighting Source Priority), Daylight, Shade, Overcast, Incandescent, Fluorescent, Flash, Color Temperature, Custom 1, Custom 2, Custom 3)

In Color Temperature what is the Kelvin range in the camera menu please ?

[Akira]

Sorry for the confusion Akira. But Colin and I were asking for the Kelvin selection directly in camera on the Fp.

 

I see. Sigma fp allows the color temperature to be set from 2500k to 10000k in 100k step.

[Akira]

And here is the result of quick and dirty test.

 

1 1/4 Baader U taped (!) on Industar-50 from 1960s wide open. Industar-50 is a 50mm f3.5 lens of Tessar type. The camera was set to ISO25600. The shutter speed is 1/50. The scene was shot under the bright sunlight.

 

The second image is a screen capture of ACR processing the DNG file shot under the above mentioned condition. In order to make the histogram easier to be seen, I raised the exposure by 1.5 stops. The test image was processed without the exposure boost.

[colinbm]

Thanks Akira

[Akira]

Colin, I edited one of the doubled posts and uploaded the sample image for UV. Please refer to it.

[colinbm]

Yes Akira

That is looking similar to what I got with the Sigma Foveon SD15, with-out the hot mirror......:-(

The hot mirror in the Sigma fp is doing good work at suppressing the UV.

I am waiting for a used Sigma fp so I can remove the hot mirror & try it for UV & IR photography, I don't want to experiment with a new camera.

Col

[dabateman]

Thank you for the image and details.

I typically use ISO 200, f8 and 2 seconds with my full spectrum converted camera and a 365nm led light source.

Your exposure settings are interesting. You have 1/50, which is 6 stops faster than I would set. But also ISO 25600, which is 7 stops more than I would set.

 

So you seem to be 2 stops slower. Not bad really and looks like its violet. So maybe mostly 385nm getting through. Overall not bad. I am not seeing a sharp blue color, which would be from the IR. So the UV is definitely more than the IR leak.

[Akira]

Thank you for the image and details.

I typically use ISO 200, f8 and 2 seconds with my full spectrum converted camera and a 365nm led light source.

Your exposure settings are interesting. You have 1/50, which is 6 stops faster than I would set. But also ISO 25600, which is 7 stops more than I would set.

 

So you seem to be 2 stops slower. Not bad really and looks like its violet. So maybe mostly 385nm getting through. Overall not bad. I am not seeing a sharp blue color, which would be from the IR. So the UV is definitely more than the IR leak.

 

Thank you for examining my humble data. That would be rather encouraging. My Baader U filter has been put on my TK-566 UV flashlight to cut the visible portion, but I may want to put the Baader U for more proper purposes. :)

[colinbm]

Your Baader U on the TK-566 UV flashlight will give you fluorescence in the visible light.

We call it Ultra Violet Induced Visible Fluorescence, UVIVF, here on this forum, so you can search that here.

Col

[Akira]

Your Baader U on the TK-566 UV flashlight will give you fluorescence in the visible light.

We call it Ultra Violet Induced Visible Fluorescence, UVIVF, here on this forum, so you can search that here.

Col

 

Yes, UVIVF experiment was the initial reason for my purchase of TK-566.

[colinbm]

Akira, can you tell me if there are any problems with using the Sigma fp with older manual lenses please ?

Col

[Akira]

Akira, can you tell me if there are any problems with using the Sigma fp with older manual lenses please ?

Col

 

Colin, sorry for my belated reply.

 

As yet, I have used mount adapters for M42 and Nikon F lenses. Both are made by Novoflex. I have encountered no problems with using pre-Ai Nikkor-H 50/2.0, Ai 200/4.0 and Industar-50. Both the A- and M-modes works just any other cameras used with the mount adapters. The 2MP LCD screen on Sigma fp and 8x magnification with or without focus peaking enables me to focus effortlessly, even with the IR 72 or IR84 filters.

 

If you have any other questions about my humble experiences with fp, please feel free to ask.

[colinbm]

Thanks very much Akira, good news.

I am looking for a secondhand fp to convert.....?

[Akira]

As the weather is fine today, I tested Fuji TAC IR84 (Wratten 87C equivalent) and Cokin Z007(Wratten 89B equivalent) on the Nikkor-H 50/2.0 which is known to be immune to the hot spot.

 

#1: IR84 straight out of the camera. (ISO400, f5.6, 0.8sec.)

#2: Tweaked the DNG file to taste for B&W

#3: Z007 SOOC (ISO 800, f5.6, 1/8sec)

#4 Tweaked the DNG file.

[Akira]

I found an even denser Fuji IR90 TAC filter.

 

#1: SOOC (ISO400, f5.6, 2.5sec.)

#2: Tweaked the DNG file to taste for B&W

 

Overall, I like the B&W images yielded from a denser IR filter: they look more surreal and tranquil.

[colinbm]

Very nice to see Akira, thanks for showing us.

Keep safe.

Col