The Sun and 16 Mag Star Images with Focal Reducer

Blogged by Xiao Sun on May 3, 2010 and tagged with Sample Images, Moon, Saturn, Mosaic, Sun.

Combining different equipments and setting them up for optimal astronomy photos are complicated but fun to many astro-photographers. Last month, Piotr Maliński did some homework with a bunch of kits, including DMK 21AF04.AS astronomy camera, and sent us a review afterwards.

The paragraphs in blue are quotes from his e-mail:

I've made some interesting pictures recently. First of all I wanted to test a 1,25″ filter threaded 0,5 focal reducer with DMK 21AF04.AS (to get wider field). As I have f/5 newtonian the standard DMK C/CS nose was to long and it would reduce the image too much (unfocusable. It would be good for telescopes with focal ratio 9 and more). So I've got short C/CS nose (15 mm, which gives 30-33mm reducer to CCD distance and not 60 mm as with standard nose) and low profile 1.25″ eyepiece holder:

The results are quite interesting. From f/5 newtonian I've got about f/2,75 Newtonian nearly at the end of back focus. Imaging Sun I could make the mosaic with just two images (DMK 21AF04.AS, focal reducer, green RGB filter, false yellow color):

The Sun

Coma is getting noticeable at such extremely fast focal ratio (no coma corrector used). With a coma corrector it should look much better. Such fast focal ratio also give the possibility to catch very faint objects. On f/5 setup I could get Saturn moonHyperion at 2 sec exposures barely. With the focal reducer I can get nearly 16 mag star close to big bright Saturn:

Many Thank to Piotr for his details review!