Hyperstar Focal Reduction

When we were recently at Crossing Creeks RV Park in Georgia, I had a chance to capture images that I could use to compute the actual amount of reduction with the Hyperstar lens on my Celestron 8” telescope. 
​
The first night I used my DS10c on the C8 telescope without the Hyperstar installed to get a base line image using the camera with just the f/10 telescope.  Here is a picture of the setup and a captured image of the Lagoon Nebula with the DS10c on the 8” telescope.

I submitted the above image to nova.astronomy.net to have it compute the actual width of the field of view.  The red circled information below is the only information I need from this analysis. When this image was processed at nova.astronomy.net, it calculated the horizontal field of view size as 30.4 arcmin.

The remaining nights at Crossing Creeks I used the Hyperstar lens on the 8” telescope.  The Hyperstar + Camera replaces the secondary mirror of the telescope so the camera is at the top of the telescope rather than at the typical bottom location.  Here is a picture of the telescope with the Hyperstar lens and DS10c camera in place, and a captured image that contains the Lagoon Nebula in the bottom and the Trifid Nebula in the upper right.

When this image was processed at nova.astronomy.net, it calculated the horizontal field of view size as 2.51 deg (To convert to arcmin: 2.51 x 60 = 150.6 arcmin).  

The effective f value with the Hyperstar lens in place can be found by dividing the two field of views and multiplying by the original f value as follows: 
 
30.4 / 150.6 = 0.202 focal reduction
0.202 x f/10 = f/2.02      (assuming the first image is exactly at f/10)

or simply f/2

So with the Hyperstar lens installed on the Celestron 8” telescope, it changes the setup from f/10 to f/2.


For other examples of computing the focal reduction based on actual use, click here to see my 11/28/2017 post “Measuring Focal Reduction”.
​