Custom variable NIR-pass filter with Hoya 80B

[enricosavazzi]

This post is related to my earlier thread https://www.ultravioletphotography.com/content/index.php?/topic/5686-a-few-nir-low-pass-filters-and-others-tested/ .

 

As reported in the older thread, I assembled a variable NIR-pass filter from a color filter, a reversed circular polarizer, and a linear polarizer. Only this time, instead of a red color filter, I used a Hoya 80B, which is a pale blue-cyan filter originally designed to use tungsten color film in natural daylight. From the transmission spectrum of this filter in the above thread, we know that it transmits NIR, but it also transmits (to a lower extent) across the whole VIS. Why not?

 

The weather here has been dreary for a while, so the only reason for me to go out is to walk the dog, but without carrying a camera. At last the fog has largely lifted, although the sky is featureless grey, so I can shoot from our terrace. Not an inspiring view, but enough for a quick test with the Olympus 12-40 f/2.8 Pro on full-spectrum E-PL6, then I let ThumbsPlus decide how to autobalance the JPGs. No changes in contrast etc. aside from this. At 40 mm FL , three different filter settings give interesting results. I am adding a shot at 12 mm FL, which obviously shows that the filter is not suitable for wideangle shooting, but gives far more false color than I expected, especially from the building in the background which is off-white and grey in VIS.

[lukaszgryglicki]

Looks like dichroic filter put opn wide angle lens. I like this effect.

 

 

[Wayne Harridge]

Really interesting effect from that filter combination.  So does ThumbsPlus perform the white balance based on a particular point in the image or integrated over the full frame?

 

[enricosavazzi]

9 hours ago, Wayne Harridge said:

Really interesting effect from that filter combination.  So does ThumbsPlus perform the white balance based on a particular point in the image or integrated over the full frame?

 

You can make a rectangular selection on the picture with the mouse, and ThumbsPlus calculates a white balance based on the selection and applies it to the whole picture. ThumbsPlus also allows manually adjusting the RGB components of the WB, saving the WB from an image, and applying it to other images. For these test images I selected the whole image (Ctrl + A).

 

Sometimes this white balance works, sometimes it fails miserably (especially often on false-color images). Also, I often shoot raw + JPG, and ThumbsPlus white balance tends to works on the JPG and to fail on the raw of the same shot.

 

The raw images of these test shots are almost totally green, like the following example (converted from raw to JPG in ThumbsPlus, which does not change the color balance and contrast during this conversion). Also, there is a visible vignetting in the corners in the raw images, which is not present in the JPGs straight-out-of-camera. The JPGs straight-out-of-camera are also slightly better color-balanced than the raw as displayed by ThumbsPlus. As a whole, the raw converter in ThumbsPlus is quite basic, compared e.g. to PhotoNinja. The lens I used is recognized by the camera, which corrects automatically for vignetting and geometric distortion in the JGPs, but the raw converter does not know how to do it.

 

[Doug A]

Excellent experiment. I like the effect. I'll have to give this a try.

 

Thanks for sharing,

Doug A

Excellent experiment. I like the effect. I'll have to give this a try.

 

Thanks for sharing,

Doug A

[Wayne Harridge]

Thanks for the details on the white balancing Enrico, I just checked ThumbsPlus and it seems to have some good features.

 

[enricosavazzi]

32 minutes ago, Wayne Harridge said:

Thanks for the details on the white balancing Enrico, I just checked ThumbsPlus and it seems to have some good features.

 

I use ThumbsPlus mostly as a picture organizer and for some simple post-processing, like reducing pixel count and JPG file size for web publishing. It is good for this type of work, but has its limits and does not seem to be developed any more. For sophisticated work it is better to use more powerful software.