Quote:
Originally Posted by Brycepj
Rom you are correct I still have questions for you Jeremy (Anyone else ).
Let's start with eye pieces. The unit comes with 10mm & 25 mm So to be a bit techno should get magnification of 120x and 48x (Focal length scope/ focal length eye piece?? )
Is that enough ? there is a celestron kit for $100 the has 6mm and 15 mm plus a 2x "Barlow" and a few filters. Doesn't sound like a bad deal.
But I await your opinions.
Next question is powering the syn scan can you use 240v using the correct adapter. What about batteries for remote locations?
Don't have anything else to question think that's about it please let me know if I have anything else to consider.
To recap Skywatcher 10" Goto Dob is what I will look at getting bit over budget but what the hell.
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Here is a little write up as to how you may select a range of magnifications and eyepieces for a start. after this we could talk about the actual eyepieces.
Over budget eh? Peter. Well you only live once.
About powering the Synscan outfit. I use a 12v, 20ah gel battery - lasts about 10 hours per charge ... I have not run it down yet
The thing to watch out here is that if the battery is large, like mine, and cannot ride on the turn table you have to keep an eye on the cable. A point can be reached when the mount is slewing in azimuth when the cable will be stretched and pull out of the connector or worse damage the connector.
Eyepieces? Do Not go over board.
Stick with the supplied eyepieces but attend a viewing night organised by the local astronomy club or society and test everyone else's eyepieces on your 'scope before making a decision! Selecting eyepieces can be daunting and the cost can be very high.
How to select an eyepiece range:
Firstly look at a range of magnifications that you may require, say from x40 to x400
Ie. a range of 10 : 1 and how many steps (eyepieces) you may require. Say you require 5 eyepieces to cover the range. To make a range of eyepiece focal lengths use the following, choose any two points (A and B) and calculate the middle point as being the geometric mean ie. SquareRoot( A.B)
1) Choose the end points , x 40 and x 400, and obtain the magnification for the centre of the range as follows :
Magnification at the middle: SquareRoot (40 x 400) = 126.49
2) Calculate the next lower magnification : SquareRoot(40. X 126.49) = 71.13
3) Calculate the next higher magnification: SquareRoot (400 x 126.49) = 224.94
So we have a range of magnifications:
x40 x71 x126.5. x225 x400
Note how each magnification may be obtained by multiplying the previous magnification by 1.77 or say 1.8.
That is why we have a commonly available Barlow Lens of x 1.8
Now calculate the eyepiece focal lengths:
30 mm , 17mm, 9.5mm, 5.3mm, 3mm
Select a "good" x1.8 Barlow Lens and Voila, You have a 10 speed telescope with good transition between speeds.
Interestingly the range of resistors follows this rule and so does the ratio of gears in a manual 4WD
Notice the eyepiece range of Televue , Vixen, Takahashi etc. correspond to the rule above.
We can talk about types of eyepieces next if you like.
Jeremy
