Saturday, April 1, 2017

Comparison of the Celestron C5 telephoto and the Bushnell Northstar 90mm telescope

As I look forward to the solar eclipse in August, 2017 which passes through central Oregon I have been wondering how each scope's view will make the eclipse appear. 

Having just purchased an old school Celestron C5 (previous blog entry) 

and the Moon being visible last night, I mounted it and my Bushnell Northstar 90mm telescope

on tripods and using the same camera (Canon t3i) at prime focus I imaged the Moon for comparison shots. Here are the results:

                           Bushnell Northstar 90mm                             Celestron C5

Not only does the Celestron C5 have a wider view but the exposure difference was significant.

At ISO 100 the Bushnell required 1/5 sec exposure due to the fact that it is a f/14 lens
whereas the Celestron C5 only needed 1/20 sec because it is an f/6 lens.

That means that under low light the C5 will be easier to focus and can use a shorter exposure time than the Bushnell. However, the Bushnell gives a closer view of the subject, nearly twice the magnification of the C5.


As there is no such thing as a telescope that can be "all things to all people" it appears that, if possible, I will use both scopes during totality (if I have sufficient help from others).

The Bushnell might work well for a closer view of any prominences that may appear on the edges of the Sun during the eclipse and for imaging the Baily's Beads.

The red around the edges are prominences
and Baily's Beads (on the right hand side)
result from the Sun peeking through the
mountain peaks of the Moon during a solar eclipse.

The Celestron C5 will capture more of the surrounding corona due to a larger field of view. The fact that the corona is so dim will also play to the C5's ability to let more light come to the sensor in a shorter period of time.

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