Archive for the ‘A 4-inch (102mm) Refractor Can be An Excellent Deep-Sky Telescope’ category

A 4-Inch (102mm) Refractor Can Be An Excellent Deep-Sky Telescope: Finally Sirius B, Barnard’s Galaxy, and Much More….

May 23, 2010

All Observer’s Challenge Reports to-date: 147 consecutive months as of April 2021.

      Walter Scott Houston, most often used his 4-inch Clark refractor for his observations of deep-sky objects while writing the monthly “Deep-Sky Wonder’s” column in “Sky & Telescope Magazine” for 46 years until his death in December, 1993.  

     When Sue French picked up DSW’s where Houston left off, she seemed to favor the use of her 105mm refractor for so many observations over her twenty years writing the column.  

      I purchased my 102mm f/9.8 refractor in 1997, and have enjoyed using this scope over the years.  It provides for a nice velvety black background with excellent contrast of faint deep-sky objects within its reach.  

      On nights of good seeing, it will easily exceed Dawes Limit:  

       One thing I especially like about this scope:  It’s compact and portable enough to take out for those short observing sessions, when time is limited. 

      Double and multiple stars have always been of interest to me, and I’ve observed hundreds of close double and multiple stars over the years with this telescope.  At current, I’m working my way through another double star list with the refractor, taking my time to sketch each double, noting the colors, checking the position angle and also drawing a few field stars. 


The value of a correct image diagonal:

I’m now using a correct image 90º diagonal.  The view through a standard 90º diagonal, whether using a refractor, Schmidt-Cassegrain or Maksutov-Cassegrain makes it impossible to correctly draw “scientifically” a deep-sky object.  

I like to make my sketches as they are truly oriented in the sky, with north at the top and west to the right on my sketch card.  (See some sketches using my 10-inch reflector below) 

From Orion Telescope and Binoculars:

I finally purchased an Orion 1.25-inch correct-Image diagonal for my Orion/Vixen 102mm Refractor. The precision 90º diagonal provides a right-side-up, non-reversed image. 

I have really enjoyed observing with my refractor, but didn’t like the reversed mirror image, due to the 90º standard diagonal. On many occasions I would choose my Newtonian, as it’s so easy to make a correctly oriented pencil sketch. For many years, I’ve wanted to try a correct image 90º diagonal, but thought the views might suffer.  I’d been using a 96% enhanced reflectivity mirror diagonal for many years.  

A correct image prism diagonal, also known as an Amici:

Within a few days after making my purchase, the diagonal arrived, and on March 5th, 2014, I set up my 102mm refractor for the big test. I started with a very high magnification of 200x, to examine the Trapezium stars and see how the view would compare to my current enhanced standard 90º mirror diagonal.

The stars were beautiful in both, and even the “E” star could be glimpsed intermittently in both diagonals.  

I then went to my favorite galaxy pair, M81 and M82 at 57x, and immediately loved the non-reversed and correct image view of these two beautiful galaxies.  I really couldn’t see any difference between the quality of the two diagonals. The next test would be Jupiter, and again both diagonals presented excellent views. The cloud bands appeared very sharp with an incredible amount of detail visible in both diagonals. 

It is my opinion, the correct-image diagonal, seemingly passed all tests with flying colors.  I plan on using this diagonal for all of my observations and pencil sketches in the future.