[Aavso-photometry] binning considerations

[Jeremy Shears]

I have used a Tak FS102, a C8 and a C11 (the later two with the f/6.3 reducer) for photometry. The light gathering efficiency that I have measured in photometric runs is approx 1x, 1.8x and 4x respectively. This shows how relatively "efficient" the Tak is: the SCT's should have put in a much better performance if you take into account their areas (even allowing for the loss due to the secondary). Presumably the extra optical surfaces in the SCTs account for part of this (the focal reducer accounts for about 10% light loss), not to mention the excllence of the Tak fluorite optics (and I won't even start on the magnificent build quality...). However, it still means that I can do decent photometry on fainter stars with the C11 than with the Tak. Hence, I use the Tak FS102 for my CV outburst patrol (which gets me down into the 17's limiting magnitude most nights and occasionly below 18 if it's very dark and transparent, with a 1 min CCD exposure), where the aim is to spot an outburst rather than do accurate photometry, and the C11 for t/series on fainter targets (say below mag 15). Which brings me to the question of whether anyone has tried the f/3.3 reducers on SCT's for photometry. They appear to have one element less that the f/6.3 reducers (plus allowing a greater choice for comp stars given the larger FOV with my rather small CCD chip). Arne's recent postings about gradients etc suggest that the uneven illumation I have heard about with such reducers may preclude this, however. Go well!Jeremy> From: lolife at bitstream.net> Date: Mon, 11 Jun 2007 13:37:44 -0500> To: David at tinyblue.com> CC: aavso-photometry at mira.aavso.org> Subject: Re: [Aavso-photometry] binning considerations> > Lots of people use and love the SCTs. I'm a Tak man, myself. The > optical and mechanical quality is superb. The main drawback for the > SCTs, IMHO, is they are slow (f/10). I'm running a Tak CN-212 in > Newtonian mode at f/4. It's a great scope for photometry. It can also > switch to Cassegrain mode at f/12. I looked at the Mewlons, too, but > was scared that it was too slow, giving me a really small FOV. Having > a large FOV has a lot of advantages for finding suitable comp stars > and guide stars.> > Your point about no glass is a good one, too. My CN-212 has a glass > corrector after the secondary.> > M.> http://www.lolife.com/astronomy/> > > On Jun 11, 2007, at 1:14 PM, David Trowbridge wrote:> > > Thank you Gary and Arne for your very helpful comments.> >> > Mike, yes actually I had been looking at the Meade LX200R series. I > > could> > get a bigger aperture for the same money with the Meade. But I > > thought maybe> > I could do better CCD photometry (presently BVR, but extending to U > > and I> > filters) and possibly infrared photometry (Optek's SSP-4) or > > spectroscopy> > over a wider range of wavelengths, on a system like the 10" Tak > > Mewlon which> > has no glass secondary (Only two mirrors in the Dall-Kirkham > > Cassegrain). Do> > you know anyone with experience using the LX200R for photometry?> _______________________________________________> > Aavso-photometry mailing list> Aavso-photometry at mira.aavso.org> http://www.aavso.org/mailman/listinfo/aavso-photometry
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