Interesting piece of Lunt/Coronado solar history

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randcpoll
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Interesting piece of Lunt/Coronado solar history

Post by randcpoll » Fri Aug 21, 2015 1:17 am

I recently acquired a very interesting piece (to me). This is a solar filter set from when Lunt was just starting Coronado as a mass-market manufacturer. This is called a Gemini 2.5 filter and is a 40mm <.6A unit with a 40mm ERF and a BF15 blocking filter. It has lots of documentation about the company going from a custom filter manufacturer to offering general market filters. The documentation says this set was shipped 11/1/2000 and the serial # for the main filter is 0019 and for the blocking filter the serial # is 0035! The set was manufactured in Isle of Mann and looks to be in excellent condition. The blocking filter has a screw for the tilt detuning instead of having it on the main filter. I took some quick photos with it on a 480mm focal length OTA to see how it would "handle." Photos included

As I was doing so, I made an interesting discovery. The BF-15 has the blocking filter and a precision mirror, but without the secondary filter that I have seen in more modern blocking filters. When I was taking photos I noted quite a bit of dust and thought that my IR cut filter on my camera was dirty. I removed it to see what difference it made. It didn't make any difference with the dust (I later realized it was on the CCD itself) but I did notice that the image was now overexposed. I cleaned things up and tried again with the IR cut and the former settings on the camera worked just fine. (Photo with this setup included too.)

So were the manufacturers counting on users having an IR cut filter on their cameras at that time? Perhaps later they started adding them to the image train?
I'm interested in any comments/ideas.
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IMG_9874.JPG
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IMG_9876.JPG
Sun 40mm Coronado.jpg

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Merlin66
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Re: Interesting piece of Lunt/Coronado solar history

Post by Merlin66 » Fri Aug 21, 2015 1:41 am

I had one of those early IOM blocking filters....an interesting concept.
Unfortunately it didn't work too well with the SM60 - sold it on.
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Re: Interesting piece of Lunt/Coronado solar history

Post by Montana » Fri Aug 21, 2015 9:34 am

I suspect the coatings on the blocking filter were not that great a long time ago, in those days the cameras were not as sensitive to IR as they are now. If your camera can see it, make sure you use an IR cut filter before looking down it.

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Re: Interesting piece of Lunt/Coronado solar history

Post by marktownley » Fri Aug 21, 2015 9:36 am

An interesting piece of filter history indeed!
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Re: Interesting piece of Lunt/Coronado solar history

Post by Solar B » Fri Aug 21, 2015 12:01 pm

I did see a similar 90mm up for sale once ... it was also black and came with tilting
BF15 as I recall to ... and also was interestingly rated as a <0.6a , I had an early
SV50 (2003) which had a tilting internal BF and the etalon had to be tilted by a
very small Allen key before Ken moved to the now common wheel.

Brian
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