NGC7662, Imaged with an
AP 10" f/14.6 Maksutov-Cassegrain
This past Monday night we had superb seeing here in northern Illinois.
Even though it was hazy and the full Moon was high in the sky, I thought
I would try imaging this tiny planetary through all that murk. I managed
a personal best in resolution of 1.5 arc sec FWHM at F11 and 1.3 FWHM at
F22. Normally around here it is tough to get better than 2 arc sec.
The wide field image was taken at F11 with my 10" F14.6 Mak-Cass,
ST10XE, color filter wheel, on AP 1200 mount. The closeup in the upper
right corner was taken with a Barlow at F22. The image is half size in
order to fit mostly on the computer screen.
RGB colors taken at 900 seconds total exposure, L was taken at 2400
seconds total exposure.
For those not familiar with the term FWHM, it is used in imaging to
describe the diameter of the star image half way between the base noise
level and the peak brightness of the star. It does not mean that the
resolution of the image is only 1.3 arc sec. In fact, two stars>
separated by half that number would be recorded as two stars with dark
between them.
The attached image shows how Maxim DL characterizes the resolution. The
image is one of many individual 5 minute unprocessed luminance
exposures. These are then stacked and sharpened before using in the
final LRGB.
Roland Christen
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