Telescope Reviews: eyepiece opinions ?

Welcome to the hobby and a fine choice for your first telescope. The C8 was my first serious telescope when I returned to the hobby in the '80s.

Eyepiece choices are many, and you will want to consider many things before jumping in and buying them such as:
- Do you wear glasses? Why? If it's for astigmatism, then you may need/want to wear them observing. Near/Far sightedness does not require they be worn.
- What are your observing goals? Planets? Double stars? Galaxies? Planetary nebulae? All of the above?
- What are your plans for future telescope purchases, if any? Specifically speaking, do you see fast (f/5 or less) optics as a possibility? If so this may influence your selection.

The good news is at f/10 the C8 is very forgiving. It does not place huge demands on the eyepiece. You will do quite well to conserve cash and buy any of the many fine offerings that are available from Explore Scientific, University Optics, Astro-Tech, Meade, GSO and others have available. On the other hand if you plan to add a large, fast Dob down the road, you might be inclined to narrow your vendors/products to those that have better edge corrected designs such as Televue, Explore Scientific, University Optics Orthos, etc. The "right" choice now may well serve you a lifetime irrespective of the telescopes you choose to buy and sell down the road. (Well, until Televue introduces the 180degree AFOV Megos eyepiece design anyway

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If you wear eyeglasses for astigmatism Then eye relief will be important assuming you need to wear them to observe. I do have mild astigmatism, however, this is not noticeable for eyepiece/OTA combinations yielding an exit pupil smaller than about 2mm. This would be a 20mm or longer focal length eyepiece in the C8. And for those Televue offers the Dioptrx.

Though magnification is an obvious consideration, so is Total Field of View, or TFOV. Larger TFOVs can be achieved with eyepieces that have larger AFOVs. So it is with the 82, 100, 110 degree and larger AFOV products from Televue, Explore Scientific, and others. I prefer wide fields of view, some do not. You will need to decide what you like.

There is one basic rule of thumb to keep in mind, and that is that the maximum usable magnification for a telescope is around 50 to 60 x Aperture in inches, or 480x for the C8 and this would be on a near perfect night of seeing, and only good for resolving tight double stars, planetary nebulae, and planets. Typical seeing will reduce this by a third or more. That said, at a power of 812x, the 2.5mm Nagler is not well suited to a C8. You would be buying an eyepiece that you would be very disappointed in.

My high power eyepiece for use with my C8 was a 7mm Nagler and I found myself using the 11mm Nagler more often than the 7mm. I probably would recommend a 9mm or 11mm in lieu of a 7mm as there would be more nights you could use it. A 17mm would be an ideal mid-power eyepiece, great for DSOs, and your 40mm is a fine low power eyepiece. Add a quality 2x Barlow or Powermate and you will have a good selection of usable powers.

A great site for evaluating eyepiece and Barlow combinations is found here: http://www.davidpaulgreen.com/tec.html

Edited by GaryJCarter (09/19/12 10:27 PM)