Eyepiece use

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Eyepiece use

Postby cwardlaw » Sun Feb 07, 2016 1:44 pm

Can anyone suggest in beginners terms how I see/observe the wide range of objects up there to best advantage. I have a Celestron 9.25. I have a range of eyepieces form celestron including a Barlow lens. So far, with my limited experience and clear sky ops i have seen a fairly distant view of Jupiter , I did think i would be getting closer to objects like that??? I have not managed to pick out anything else... I know I have a lot to learn...so please forgive the range of my sillynes
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Re: Eyepiece use

Postby Aratus » Sun Feb 07, 2016 3:02 pm

Getting a range of magnifications for a telescope is important to getting the most out of it. You don't say which eyepieces you have but for average, good use the highest magnification shouldn't be more than 50 x for every inch of aperture. So using that rule theoretically you can get up to 463 x. In reality skies here are rarely that steady, and with those kinds of magnifications larger telescope don't perform better than smaller ones. 40 x 9.25 is probably more realistic so 370 x. Guessing your focal length is 2350mm, divide the magnification into focal length and the size eyepiece you need is . . . about 6mm. (Check your actual focal length)
A 2x barlow will give the same effect with a 12mm eyepiece.

Just bear in mind that what you can see is far more dependent on seeing conditions than it is for magnification. The above calculation will work for good seeing conditions. In poor seeing conditions you need to drop the magnification, or in very poor seeing conditions - give up! :(

(edit) Zoom eyepieces are another option. I have never used one, but the obvious advantage is that you only need one eyepiece for a range of magnifications.

Having said all that some people think it worth trying a higher magnification. 400x or even 500x (It never hurts to try - but be prepared to be disappointed most times. Magnifications at the top end of the range will yield dim, wobbly images on most occasions) Others are happy with a crisp bright image that you can get with an even lesser magnification, even if it seems quite small.

With my own 8 inch, magnifications of 250x - 320x seem to give a enough detail on Jupiter to keep me busy. Different thicknesses of the belts, satellite shadows, the occasional festoon or white spot, as well as the Great Red Spot can be seen in good conditions.
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
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Re: Eyepiece use

Postby The Man with the Corrugated Iron Roof » Sun Feb 07, 2016 10:58 pm

I would only use high magnifications, in excess of 100x on the Moon and planets. Many deep sky objects need low magnification to get the whole object in the field of view. I normally use 24x magnification to see the Messier objects.

I sometimes go above 300x when looking at fine detail on the Moon but I don't do this often, these days, concentrating on getting full disc images instead.
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Re: Eyepiece use

Postby Aratus » Mon Feb 08, 2016 10:55 am

It certainly is interesting (and understandable) that most people start off by wanting to know about the highest magnifications of their telescope, but actually with experience it is finding out the lowest magnifications, and greatest width of field which occupies most attention. :?

Lowest magnifications start at 3.7x the aperture in inches. So 9.25" gives a theoretical lower magnification of 34x. However with an SCT the secondary mirror starts to show as a black blob in the middle of the view if the magnification is made too small. Also eventually the pupil of the eye is just too small to take in the extra width and the increased light. There is also a point beyond which the eye cannot take in any more detail from the image even if it is wider. Individual eyes are slightly different in these respects. Also the increasing age of the observer doesn't help matters :(
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
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