I recently purchased a Schott BG40 IR cut filter, so I thought I'd do a comparison to see how it stacks up against my B+W 486 UVIR cut filter and Tiffen Hot Mirror filter. The purpose (at least for me) of a UVIR cut filter is so I can use my full spectrum converted camera for taking 'normal' photos.

IR cut filters compared

Transmission graphs for the filters can be viewed at:

The BG40 does not cut UV (much), which you might think would cause a problem with UV contamination when shooting with a full spectrum camera. However the main light sources I use (full spectrum flash and the sun) output very little UV compared to visible and IR, and so in practice this is not a problem.

The Tiffen T1 was purchased after I started these tests, and so is not included in the 'studio' tests below, but is included in most of the later 'real life' tests. From the transmission graph you can see it isn't suitable for removing IR when shooting with a full spectrum camera, however for some reason I didn't think to check the transmission graph before I purchased it. It is marketed as a Breakthrough Solution for IR Pollution and it contains no dichroic coating; therefore, it will not vignette green, magenta or cyan at wide angles, so it sounded like a good filter.

Please note there are a lot of comparison images in this post!

Wide-angle test

To compare the filters I just photographed a large sheet of card. My first test was using a Fuji 14mm lens on my full spectrum X-M1 camera. I wanted to check with a wide-angle lens as I know this is where the B+W 486 filter has problems.

The photos were lit with a full spectrum modified flash. When processing they were white balanced using the grey patches on the colour card.

Photo of grey card with colour checker in centre, taken with full spectrum Fuji X-M1 camera and Fuji 14mm/2.8 lens without any filter
With no filter the image contains a lot of IR.

Photo of grey card with colour checker in centre, taken with full spectrum Fuji X-M1 camera and Fuji 14mm/2.8 lens with B+W 486 UVIR cut filter attached.
The B+W 486 filter gives strong cyan vignetting on wide-angle lenses like this.

Photo of grey card with colour checker in centre, taken with full spectrum Fuji X-M1 camera and Fuji 14mm/2.8 lens with Tiffen Hot Mirror filter attached.
The Tiffen hot mirror has some cyan vignetting, but not as bad as the B+W. On the other hand, it is passing more IR.

Photo of grey card with colour checker in centre, taken with full spectrum Fuji X-M1 camera and Fuji 14mm/2.8 lens with Schott BG40 filter attached.
The BG40 filter looks very good, no colour cast.

Flash test

I wondered what would happen if I filtered the flash rather than the camera. I have a cardboard snoot for my flash that takes 77mm filters.

Filtering the flash is only effective when the flash is the dominant light source. These tests were carried out in a dark room.

Photo of grey card with colour checker in centre, taken with full spectrum Fuji X-M1 camera and Fuji 14mm/2.8 lens. No filter was used on the camera / lens, but a Schott BG40 filter was attached to the full spectrum modified flash that lit the image.
BG40 looks much the same as when on the camera.

Photo of grey card with colour checker in centre, taken with full spectrum Fuji X-M1 camera and Fuji 14mm/2.8 lens. No filter was used on the camera / lens, but a Tiffen Standard Hot Mirror filter was attached to the full spectrum modified flash that lit the image.
The Tiffen also produces very similar results as when on the camera.

Photo of grey card with colour checker in centre, taken with full spectrum Fuji X-M1 camera and Fuji 14mm/2.8 lens. No filter was used on the camera / lens, but a B+W 486 UVIR cut filter was attached to the full spectrum modified flash that lit the image.
The B+W result is not directly comparable because my flash snoot is designed for 77mm filters, while my 486 filter is only 67mm. So we get some vignetting from the smaller filter size. However, again, the result still looks pretty similar to what we got when using the filter on the camera.

Standard test

This test was taken with my 27mm lens. This shows how the interference-based UVIR cut filters (B+W & Tiffen) compare to the absorbtive based IR cut BG40 filter on a lens that is not particularly wide and also passes UV (most lenses block UV).

Photo of grey card with colour checker in centre, taken with a standard Fuji X-A1 camera and Fuji 27mm/2.8 lens
To start with, here's how it should look, taken with a standard unconverted camera.

Photo of grey card with colour checker in centre, taken with full spectrum Fuji X-M1 camera and Fuji 27mm/2.8 lens with Schott BG40 filter
The BG40 looks pretty good, but the reds aren't as deep, as the BG40 has lower transmission in the deep reds than the standard hot mirror filters used in cameras.

Photo of grey card with colour checker in centre, taken with full spectrum Fuji X-M1 camera and Fuji 27mm/2.8 lens with B+W 486 UVIR cut filter
The B+W 486 has a slight cyan vignetting, but is pretty decent at this angle of view.

Photo of grey card with colour checker in centre, taken with full spectrum Fuji X-M1 camera and Fuji 27mm/2.8 lens with Tiffen Standard Hot Mirror filter
The Tiffen Hot Mirror still has its problem of passing too much IR.

Resolution

First test is on my A7R II, which is not a full spectrum camera. But it does have quite a high resolution, so should be a good test of any degredation in resolution caused by the filters. Lens used was the Canon 100mm macro at f/7.1. I photographed the printing on a cardboard box, below are 100% crops.

100% crop of an image of a cardboard box, taken with 100mm macro lens on Sony A7RII and with Tiffen Standard Hot Mirror filter on the lens.
Tiffen hot mirror looks good

100% crop of an image of a cardboard box, taken with 100mm macro lens on Sony A7RII and with B+W 486 UVIR cut filter on the lens.
The B+W 486 gives a good result, the same as the Tiffen

100% crop of an image of a cardboard box, taken with 100mm macro lens on Sony A7RII and with Schott BG40 filter on the lens.
Pretty good result from the BG40, but seems to loose a bit of resolution compared to the other two filters. The image was also heavily cyan tinted, but that's not really an issue since you wouldn't use this filter with an unconverted camera in real life.

Second test is with my full spectrum converted Fuji X-M1, which 'only' has 16MP to test with. This time images were taken with a 75mm N El-Nikkor, a lens that passes UV, at f/8. A similar subject (cardboard box) and 100% crops again.

100% crop of an image of a cardboard box, taken with 75mm EL-Nikkor on full spectrum Fuji X-M1 and with Tiffen Hot Mirror filter on the lens.
Tiffen Hot Mirror

100% crop of an image of a cardboard box, taken with 75mm EL-Nikkor on full spectrum Fuji X-M1 and with Tiffen T1 filter on the lens.
Tiffen T1

100% crop of an image of a cardboard box, taken with 75mm EL-Nikkor on full spectrum Fuji X-M1 and with Schott BG40 filter on the lens.
BG40

100% crop of an image of a cardboard box, taken with 75mm EL-Nikkor on full spectrum Fuji X-M1 and with B+W 486 UVIR cut filter on the lens.
B+W 486

Not a lot of difference.

Unfortunately it's hard to conclude anything from this test, other than all 3 filters are pretty similar. If I get a higher resolution full spectrum camera at some point I'll be able to do a more meaningful comparison.

Flare

First test with flash out of frame and pointed towards the camera.

Image of a cardboard box with flash just out of frame and pointed at camera to create lens flare, taken with 75mm EL-Nikkor on full spectrum Fuji X-M1 and with Tiffen Hot Mirror filter on the lens.
Tiffen Hot Mirror

Image of a cardboard box with flash just out of frame and pointed at camera to create lens flare, taken with 75mm EL-Nikkor on full spectrum Fuji X-M1 and with Schott BG40 filter on the lens.
BG40

Image of a cardboard box with flash just out of frame and pointed at camera to create lens flare, taken with 75mm EL-Nikkor on full spectrum Fuji X-M1 and with B+W 486 UVIR cut filter on the lens.
B+W 486

Next test with flash in the frame.

Image of a flash pointed at camera to create lens flare, taken with 75mm EL-Nikkor on a standard Fuji X-A1.
Unconverted camera

Image of a flash pointed at camera to create lens flare, taken with 75mm EL-Nikkor on full spectrum Fuji X-M1 and with no filter on the lens.
No filter

Image of a flash pointed at camera to create lens flare, taken with 75mm EL-Nikkor on full spectrum Fuji X-M1 and with filter on the lens.
Tiffen Hot Mirror

Image of a flash pointed at camera to create lens flare, taken with 75mm EL-Nikkor on full spectrum Fuji X-M1 and with Schott BG40 filter on the lens.
BG40

Image of a flash pointed at camera to create lens flare, taken with 75mm EL-Nikkor on full spectrum Fuji X-M1 and with B+W 486 UVIR cut filter on the lens.
B+W 486

In these tests, the filters perform pretty much the same in terms of flare. These were taken with the 75mm N El-Nikkor on the full spectrum X-M1, and a full spectrum flash was used.

However, I found I was getting a ring of flare when shooting with the Fuji 14mm lens, with all of the filters.

Image of a flash pointed at camera to create lens flare, taken with Fuji 14mm on full spectrum Fuji X-M1.
No filter

Image of a flash pointed at camera to create lens flare, taken with Fuji 14mm on full spectrum Fuji X-M1 and with Tiffen Standard Hot Mirror filter on the lens.
Tiffen Hot Mirror

Image of a flash pointed at camera to create lens flare, taken with Fuji 14mm on full spectrum Fuji X-M1 and with Tiffen T1 filter on the lens.
Tiffen T1

Image of a flash pointed at camera to create lens flare, taken with Fuji 14mm on full spectrum Fuji X-M1 and with Schott BG40 filter on the lens.
BG40

Image of a flash pointed at camera to create lens flare, taken with Fuji 14mm on full spectrum Fuji X-M1 and with B+W 486 UVIR cut filter on the lens.
B+W 486

Image of a flash pointed at camera to create lens flare, taken with Fuji 14mm on standard Fuji X-A1 and with B+W 486 UVIR cut filter on the lens.
Unconverted camera with B+W 486

The solution was to use a ring of black paper between the lens (well actually between the step-up ring) and filter. This was a circle of black paper the same size as the filter with a hole in the middle just large enough for the lens to 'see' through without vignetting.

Image of a flash pointed at camera to create lens flare, taken with Fuji 14mm on full spectrum Fuji X-M1 and with Tiffen Hot Mirror filter on the lens. A ring of black paper was sandwiched in between the step-up ring and the filter in an attempt to reduce flare caused by reflections from the underside of the filter.
Tiffen Hot Mirror

Image of a flash pointed at camera to create lens flare, taken with Fuji 14mm on full spectrum Fuji X-M1 and with Tiffen T1 filter on the lens. A ring of black paper was sandwiched in between the step-up ring and the filter in an attempt to reduce flare caused by reflections from the underside of the filter.
Tiffen T1

Image of a flash pointed at camera to create lens flare, taken with Fuji 14mm on full spectrum Fuji X-M1 and with Schott BG40 filter on the lens. A ring of black paper was sandwiched in between the step-up ring and the filter in an attempt to reduce flare caused by reflections from the underside of the filter.
BG40

Image of a flash pointed at camera to create lens flare, taken with Fuji 14mm on full spectrum Fuji X-M1 and with B+W 486 UVIR cut filter on the lens. A ring of black paper was sandwiched in between the step-up ring and the filter in an attempt to reduce flare caused by reflections from the underside of the filter.
B+W 486

My guess is that light hits the front of the lens, bounces up, reflects back off the underside of the filter, and ends up creating this ring of flare. I've only found this problem with the Fuji 14mm, however I haven't tested with a large number of lenses. I also tested my Olympus 24mm/2.8 with the B+W 486 on my Sony, and that didn't have the flare. So it doesn't seem an effect you'd see on all wide-angle lenses, just the Fuji 14mm so far as I can tell.

Wide-angle 'real-life' test 1

This first example was taken using the wide-angle Fuji 14mm lens on my converted X-M1.

Image of sunset over a field taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens.
No filter

Image of sunset over a field taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Tiffen Standard Hot Mirror filter.
Tiffen Hot Mirror

Image of sunset over a field taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Tiffen T1 filter.
Tiffen T1

Image of sunset over a field taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Schott BG40 filter.
BG40

Image of sunset over a field taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and B+W 486 filter.
B+W 486

Image of sunset over a field taken with standard Fuji X-A1 with Fuji 14mm lens.
Unconverted camera

Despite using the black paper ring to avoid the ring type lens flare caused by the filter(s), you can see the effect is still quite bad on the B+W and the Tiffen Hot Mirror. Both the B+W and Tiffen Hot Mirror use the same type of IR blocking technique (dichroic coating to reflect IR).

Everything else is pretty much what we'd expect based on the earlier 'studio' tests. The Tiffen T1 is additionally featured here, but as you can see, doesn't do a very good job. The reason for this is that it is designed for use on cameras that have a weak IR blocking filter in place, rather than no IR blocking filter at all. It starts passing IR again around 840nm, so there is quite a lot of IR contamination (I don't know exactly how deep into the near-IR my camera can see, but likely it is up to around 1000nm).

Wide-angle 'real-life' test 2

Another test with the Fuji 14mm. Similar results to the previous image, except no sign of the ring of flare. The black ring of paper to try and avoid flare was used again.

Image of sunset over a pond in a field taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens.
No filter

Image of sunset over a pond in a field taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Tiffen Standard Hot Mirror filter.
Tiffen Hot Mirror

Image of sunset over a pond in a field taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Tiffen T1 filter.
Tiffen T1

Image of sunset over a pond in a field taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Schott BG40 filter.
BG40

Image of sunset over a pond in a field taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and B+W 486 filter.
B+W 486

Image of sunset over a pond in a field taken with standard Fuji X-A1 with Fuji 14mm lens.
Unconverted camera

Wide-angle 'real-life' test 3

Final test with the Fuji 14mm. Black paper to reduce likelihood of flare was used again. This time I am including the out of camera images, so you can see what they are like before white balancing, and also corner fixed images. CornerFix is a piece of software you can run your images through to remove the cyan vignetting such as produced by the B+W 486 and Tiffen Hot Mirror on wide angle lenses.

Out of camera:

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens. Out of camera image (not whitebalanced).
No filter

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Tiffen Standard Hot Mirror filter. Out of camera image (not whitebalanced).
Tiffen Hot Mirror

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Tiffen T1 filter. Out of camera image (not whitebalanced).
Tiffen T1

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Schott BG40 filter. Out of camera image (not whitebalanced).
BG40

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and B+W 486 filter. Out of camera image (not whitebalanced).
B+W 486

Image of a building on an overcast day taken with standard Fuji X-A1 with Fuji 14mm lens. Out of camera image (not whitebalanced).
Unconverted camera

White balanced:

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens.
No filter

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Tiffen Standard Hot Mirror filter.
Tiffen Hot Mirror

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Tiffen T1 filter.
Tiffen T1

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Schott BG40 filter.
BG40

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and B+W 486 filter.
B+W 486

Image of a building on an overcast day taken with standard Fuji X-A1 with Fuji 14mm lens.
Unconverted camera

White balanced & Corner fixed

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens. White balanced and run through CornerFix to remove any vignetting.
No filter

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Tiffen Standard Hot Mirror filter. White balanced and run through CornerFix to remove any vignetting.
Tiffen Hot Mirror

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Tiffen T1 filter. White balanced and run through CornerFix to remove any vignetting.
Tiffen T1

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and Schott BG40 filter. White balanced and run through CornerFix to remove any vignetting.
BG40

Image of a building on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 14mm lens and B+W 486 filter. White balanced and run through CornerFix to remove any vignetting.
B+W 486

Normal 'real-life' test 1

This test was taken with the Fuji 27mm. The cyan vignetting on the B+W 486 and Tiffen hot mirror images is hardly noticeable.

Image of a row of houses on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 27mm lens.
No filter

Image of a row of houses on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 27mm lens and Tiffen Standard Hot Mirror filter.
Tiffen Hot Mirror

Image of a row of houses on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 27mm lens and Tiffen T1 filter.
Tiffen T1

Image of a row of houses on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 27mm lens and Schott BG40 filter.
BG40

Image of a row of houses on an overcast day taken with full spectrum converted Fuji X-M1 with Fuji 27mm lens and B+W 486 filter.
B+W 486

Image of a row of houses on an overcast day taken with standard Fuji X-A1 with Fuji 27mm lens.
Unconverted camera

Normal 'real-life' test 2

Another test with the Fuji 27mm. The Fuji 27mm passes UV light quite well, but the BG40 (which passes UV) image doesn't appear to affected by UV contamination. This is simply because so little UV light gets through the atmosphere.

Image of a track across a field taken with full spectrum converted Fuji X-M1 with Fuji 27mm lens.
No filter

Image of a track across a field taken with full spectrum converted Fuji X-M1 with Fuji 27mm lens and Tiffen Standard Hot Mirror filter.
Tiffen Hot Mirror

Image of a track across a field taken with full spectrum converted Fuji X-M1 with Fuji 27mm lens and Schott BG40 filter.
BG40

Image of a track across a field taken with full spectrum converted Fuji X-M1 with Fuji 27mm lens and B+W 486 filter.
B+W 486

Image of a track across a field taken with standard Fuji X-A1 with Fuji 27mm lens.
Unconverted camera

Normal 'real-life' test 3

This test was with the Nikon 50mm/1.4 D @ f/2. Despite shooting into the sun, flare is no worse with the filters than no filter at all. The unconverted camera image does have less veiling flare, however the veiling flare appears to be down to the sensor / (lack of) filter stack in the converted camera, since the same level of veiling flare can be seen in the no-filter image.

Image of a backlit field taken with full spectrum converted Fuji X-M1 with Nikon 50mm/1.4 D lens.
No filter

Image of a backlit field taken with full spectrum converted Fuji X-M1 with Nikon 50mm/1.4 D lens and Tiffen Standard Hot Mirror filter.
Tiffen Hot Mirror

Image of a backlit field taken with full spectrum converted Fuji X-M1 with Nikon 50mm/1.4 D lens and Schott BG40 filter.
BG40

Image of a backlit field taken with full spectrum converted Fuji X-M1 with Nikon 50mm/1.4 D lens and B+W 486 filter.
B+W 486

Image of a backlit field taken with standard Fuji X-A1 with Nikon 50mm/1.4 D lens.
Unconverted camera

Macro / Close-up 'real-life' test

These were all white balanced on the white portion of the lowest petal. The BG40 image appears much duller than the Tiffen & B+W. This is because it doesn't transmit so much light, especially at the red end of the spectrum.

You can see IR contamination in the Tiffen Hot Mirror image, the coloured part of the flower is brighter, but it is most noticeable in the leaves. The B+W 486 image is clearly the best.

Photo of a cyclamen flower taken with full spectrum converted Fuji X-M1 with 75mm EL-Nikkor lens and Tiffen Standard Hot Mirror filter.
Tiffen Hot Mirror

Photo of a cyclamen flower taken with full spectrum converted Fuji X-M1 with 75mm EL-Nikkor lens and Schott BG40 filter.
BG40

Photo of a cyclamen flower taken with full spectrum converted Fuji X-M1 with 75mm EL-Nikkor lens and B+W 486 filter.
B+W 486

Conclusion

Unfortunately there doesn't appear to be a 'good' visible light filter. The B+W 486 (and Tiffen Hot Mirror to a lesser extent) are a pain to use on wide-angles due to the cyan vignetting. The BG40 doesn't have this problem, but looses deep red colours and has a strong cyan cast (though this is easy to correct).

The B+W 486 is clearly better than the IR leaky Tiffen Hot Mirror. And the Tiffen T1 is pretty useless - obviously it wasn't designed with full spectrum cameras in mind.

So for the moment I think you're still best off with two cameras - one for visible work and one for UV / IR work. I will continue using the B+W 486 for my macro / close-up Vis-UV-IR comparison images (it's not practical to switch cameras between full spectrum and visible only for that work).

One last thing to mention is the Kolari Vision Hot Mirror filter. While I haven't used this filter, from its appearance, description, and transmission graph, it looks like it should perform similarly to the BG40, perhaps with slightly less red reds.

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