A New Diagonal: Correct Image and The Advantages

I really enjoy observing with my 102 mm refractor, but don’t like the mirror-reversed image view, due to the 90º diagonal.  

On many occasions I chose my Newtonian, as I want my sketches to be correctly oriented.  For many years, I’ve wanted to try a correct image 90º diagonal, but thought the views might suffer.  I’ve been using a 96% enhanced reflectivity mirror diagonal for many years.  

Why do I dislike a mirror-reversed view?  

When making a sketch, it does not match the object as it is truly oriented in the sky.   And I also like to compare my sketches with photographs, as APer’s “for most part” make their images scientifically correct.   North should be up, and west to the right.    

It can also be easy to confuse the cardinal points when using a standard diagonal, with the mirror-reversed image.    

While looking through an Orion Telescope and Binocular catalog, I noticed a 1.25-inch, correct image diagonal for only $49.95.  After years of wondering how this type of diagonal would perform, I made the decision to order, and give one a try. 

Last night (March 5th, 2014) I set up my refractor for its first test. 

I started with a high magnification of 200x.  I then examined the Trapezium stars in the Orion Nebula to see how the view would compare with my current enhanced mirror diagonal.  The stars were beautiful and sharp in both, and even the “E” star could be glimpsed. 

I then went to my favorite galaxy pair, M81 and M82 at 57x.  I immediately liked the non-reversed and correct image view, and couldn’t really see any difference between the two diagonals.  The next test would be Jupiter, and again, both diagonals performed comparably with the cloud bands appearing very sharp.   

One thing I should mention:  When observing a bright star with a correct image prism diagonal, a very thin thread of light will be seen crossing from edge to edge.  This is not a defect, but is inherent to this type of diagonal, but I found it to really not be a problem.  

I purchased this diagonal, not to observe the brightest of stars, but to observe the faintest of deep-sky objects possible, with a 102 mm refractor.  

Roger Ivester

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