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The last thing I want anyone to feel in these posts is that I am in any way criticising the TEC branded refractor. That is far from my intent. They are amazing scopes! But, it's well known that Yuri figures the optics for visual. Now if one puts a camera on the scope that perhaps mimics the frequency response of the human eye the blue channel will have a vanishingly small problem as witnessed by my own photos with the KAF8300 and Greg's many photos. But, put a camera on that has such a highly accentuated response to blue/violet/UV and we have an issue. As Greg has said one must match the camera to the optics. This is something I tried to do when making a purchasing decision about the Trius, but I failed to appreciate this one particular issue in blue. I spent a lot of time agonising over pixel size, etc. And, looking for similar posts such as this one...well, I couldn't find one which I find a bit odd given the popularity of the TEC140 and the Sony chip. I do think that this issue is likely to be raised more and more as the Sony chip takes on ever more popularity. Perhaps opticians will begin to rethink how they figure APO optics in reaction to this issue. Who knows? Time will tell.
I guess some people will take a swipe at the need for a -violet type of filter on an APO. My response is that's pretty much a garbage argument! I try to think of it this way: we don't blame DSLRs for having an IR cut filter do we (unless we are doing astrophotography)? We accept that a filter is necessary to compensate for the CCDs increased sensitivity (compared to the human eye). I think a -violet filter is exactly the same, just at the other end of the spectrum! Now, I suppose the argument isn't particularly helped when one considers that many reflecting type scopes can maintain critical focus into shorter wavelengths and thus manage to avoid blue fringed stars. But, I would argue that this light is no more "real" (by real I mean to the human eye in terms of colour) than IR. Maybe my argument is self serving. I don't know, but I do know that I'm not stressed about using a filter if in the end I can take a great photo with tight stars!
Peter
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