IR Blocking Filter Tests

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This page is a work in progress as I continue to test the effectiveness of two IR blocking filters as time permits:

The Filters:

Travis McNeal of  Sirius Optics Inc.(   8730 122nd Ave. NE Kirkland, WA 98033,  Phone - 425-803-6918, Fax - 425-803-6910 email - or ) sent out a couple of their IR Blocking filters (NIR1) for testing. I was fortunate enough to get one of these and have begun test/comparing it to a BG-40 filter which I am using in the F-IRBK filter I have made. I am trying to be subjective here, although you can be the judge of this.

The Sirius Optics filter came in a very nice hinged case mounted in a nice 1.25" aluminum frame. The filter is an interference type and is basically clear (visually). The surface (both sides) has some fine speaks on it. This does not appear to effect the image at all. For detailed specs on the filter goto Sirius Optics Web site at:

The Webcam Adapter filter uses a BG-40 absorption filter. These filters have a light blue cast visually. That is, when you look through them they look a bit light blue. They are absorbing some of the red light which causes the filter to look blue-ish. The filter specs for this filter can be found on my IR_BLOCK Proposal page. If you brought one from me it would come in a plastic sleeve raped in bubble wrap and tissue paper. A Delrin 1.25" filter frame, basically the same as the Sirius one functionally but not as nice. I wish I could get some of those nice filter frames.

Test 1: Solar Image

This test was conducted using a Meade ETX-60 Refractor and a Bader solar filter. The camera was a Vesta 675 (Unmodified) at prime focus. This is the first solar imaging I have attempted with a web cam and the first images with the ETX-60. Lets say the image quality is not under test here, OK. Focusing is critical for a comparison test. I just went visually on the sunspot detail. Hard to do without either IR filter. Not 100% precise in any case.

The images below are single frame raw from the Vesta via Vega. I then just cut a sample of the same area out and pasted it here. What I had planned to do was keep all the settings the same and just take three images and compare them. This worked OK for the two filtered images but not for the unfiltered. Without the filter I had to reduce the exposure time by 0.25 (400%) to get any kind of image that was not completely washed out (over exposed). So both filters reduce the available energy on the CCD significantly over having no filter. Another area to test.

So, same exposure for each filter, which one lets through more energy?

sun-none.jpg (398 bytes) sun-BG40.jpg (2760 bytes) sun-sirus.jpg (1093 bytes)
No Filter BG-40 Filter Sirius NIR1 Filter


There is no question that the both IR filters give much  better detail of the sun spots. Yes IR blocking filters give far better sun spot detail.

Ah, you are looking at the green tint to the BG-40 and thinking yes it is the blue color coming through. Maybe but I am no so sure. Playing with the exposure gave me this green ting on either filter. I couldn't say if the BG-40 had more or not. I plan on investigating this further . I couldn't draw any conclusions from these images having watched the effect of varying the gain and shutter speed. You can see the green in the corner or the NIR1 frame and this increased as you went to the edge of the sun.

While the NIR1 looks to give better detail I thing that without adjusting the exposure for each filter it is impossible to draw any conclusions. On the preview screen they looked very similar and where both easy to focus on the sun spot detail

What is clear to me from these images is that the NIR1 lets through more energy than the BG-40. It is a little hard to quantify at the moment but I would guess at about 20%. The green is due to exposure problems and is evident on both images. The BG-40 blocking more light got more green at this exposure setting.

That's it so far. I plan to update this page as I conduct more tests and check the results from this one.