Robert Ostrander

4 posts

Diagram of a telescope and eye piece focal plane.

Magnification in astrophotography and EAA

About a year ago, I wondered what magnification I was getting with my astrophotography set up.  The best answer came from an article on Cloudy Nights.  That article said that there really isn’t any answer to the question of magnification in photographs, but you might approximate the magnification by considering your eye as the eyepiece at the main focal plane of your telescope.  The human eye has a focal length of 22 mm, so the magnification your eye would see can be calculated by dividing the focal length of the telescope in millimeters by 22 millimeters.  Using that algorithm gave […]

NGC7293, August 5th-9th, 2021, 41 frames at 300 seconds each,180 gain

Astrophotography through smokey skies

There was a little bit of “Smoke Gets In Your Eyes” last night at the DHO, but it was much drier, so no constant use of the hair dryer to keep everything from getting soaked. Overall, the seeing went from baleful red Saturn and Jupiter, to fair conditions as the smoke cleared somewhat. I started with something nearly straight overhead to help reduce the effects of the smoke and started over with M13 so I could change the composition to include the galaxy NCG 6207 (bottom left in the picture). That means you also have to include the bright red […]

M13, August 8th, 2021, 10 frames at 300 seconds each, 180 gain taken with a guided 5" Maksutkov

Comparing images of M13 between a 10″ SCT and a 5″ Mak

Here is last year’s pic with the M13 taken with a 10″ Meade SCT. Exposure was 22 frames at 60 second. It was probably one of the best pictures I got from the Meade. Because of being able to guide with the 5″ Mak, I was able to get ten 300 second subs to stack (for a total of 50 minutes instead of just 22 minutes). Here is the result. The magnification of the second image is only about 60% of the older picture, but better focus and guiding give a much higher resolution end product. Funny how a 5″ […]


Experiments with LP Filters on M101

Some of you know that I have been taking way too many subs of M101 recently.  If you don’t want to know what I learned about light pollution filters, then just skip to the fourth photo and enjoy M101.   The idea was to see how well the Baader Light Pollution Moonglow filter with IR cut works.  I was also wanting to compare taking shorter subs (60-90 seconds) at 240 gain with longer guided subs at 90 gain.    Here are the results:   Looking very closely at the details, I think the second and fourth pictures are very similar. […]