....................                                              My Meade 2080 Schmidt-Cassegrain telescope Notes to remind myself
HOME My astronomy page with description of my Refractor telescope
   
 

I bought my Meade 2020 about 30 years ago. It does not have the computerised GoTo capability that is now available.
Specifications

8" (203 mm) mirror
Focal length 2000 mm
8x50 viewfinder

Inbuilt Right Ascension motor

Eyepieces, magnification and true field of view (FOV).
Magnification is the telescope focal length (2000 mm) divided by the focal length of the eyepiece. The maximum useful magnification is  2 x objective diameter (2003 mm) that is about 400x
.

The true field of view of an eyepiece is the number of degrees it shows in the telescope. It is the apparent field of view divided by the magnification.

My eyepieces

40mm. Celestron
24.5 mm Meade super wide angle multicoated.
12 mm Celestron X-CEL LX series. 
5mm Celestron X-CEL LX
8x50 viewfinder
Canon binoculars.

50x. FOV, 0.86 deg.
80x FOV, 0.79 deg
170x. FOV, 0.4 deg
400x. FOV, 0.15 deg
FOV 5 deg
15 x 50. FOV = 5 deg

           Note:  theX-CELL eyepieces give 60º apparent field of view.  The premium six-element optical set is finished with multiple layers of high-transmission coatings for clear, sharp images.   The edges of the optics are blackened for increased contrast.  16 mm of comfortable eye relief – very beneficial for spectacle wearers.



                         'Shop' picture of the Meade telescope.
 

This is the Telrad viewfinder.

The diameters of the illuminated rings are 4 degrees, 2° and 0.5°

 

Finding stars and Field of View
A useful website for this:
https://telescopicwatch.com/field-of-view-astronomy-calculate/
An eyepiece has an Apparent Field of View value. This is the number of degrees of sky the eyepiece would show you when held directly up to your eye, without the use of a telescope. The true field of view is the number of degrees the eyepiece shows in the telescope. To calculate this, you divide the apparent field of view by the magnification.

Finding a particular star. Use Telrad and/or viewfinder.

Many say that setting circles cannot be effective (minimum diameter 8”) because the accuracy of the circles cannot get to within the eyepiece field of view.
The full moon is about 0.5 degrees. A star at Equatorial equator travels 1 degree in 4 mins.

FOV of my eyepieces
Celestron     40mm       50x      Field   0.86 deg.
Meade         24.5mm    80x.     Field   0.79 deg
Celestron    12 mm      167x.   Field    0.4 deg.
Nagler           7mm.       290x
Celestron      5mm       400x.    Field   0.15 deg
Viewfinder                                  Field   5.0 deg.

Telrad diameter of illuminated rings of 4 degrees, 2° and 0.5°   So 40mm is bit more than halfway between inner circle and next one.

Setting circles  (8”” diameter)
Declination: 1 division is 1 degree. So if the setting is within 4 degrees it should be seen in Telrad.
If setting is out by only 0.5 deg then the object will probably be seen in 40mm.
Right Ascension: 1 division is 5 minutes. So difficult to be accurate.
So, using setting circle, go to the coordinates then moves RA knob slightly to find in Telrad or viewfinder or 40mm.

Simple Sky Measuring Guide Hold out hand at arms length.
1º   The width of the end of your little finger (pinky) is about one degree. (2 moon diameters)
5º  The width of your three middle fingers, tip-to-tip,
10º  The hand width as a clenched fist
15º  The width between your index and little finger, tip-to-tip,
25º That width between your pinky finger and thumb, tip-to-tip

Betelgeuse to Rigel in Orion is 19º.
Orion’s belt is a bit less than 3º.
End star of Big Dipper handle to end star of the bowl is 25º.
Between two end stars of the bowl: 5º.
The Great Square of Pegasus sides on average: 15º.
The W of Cassiopeia, from one end to the other: 13º.
Alpha Cass to eta is 8min RA and 1.3 deg dec.

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