Eyepieces

Only two weeks after buying the #395, I ordered an Alstar 40mm Plössl eyepiece. It gives 1000 / 40 = 25x and an exit pupil of 3.65mm. At this magnification is rather easy to find objects in the sky without the finder, so I use it a lot because using the finder is a big pain for objects placed high in the sky, due to in that situation the ocular and finder are placed below your waist level. The Alstar 40mm. gives a high relief exit pupil, so you must take a time to get used to it. Also, if you shift your eye only a little from the optic axis then the image turns black. This is common to Plössl designs. Messier objects like M42 in Orion or M41 in Canis Major are beautifully rendered with this eyepiece.

A friend of mine lend me his Celestron Ultima 7.5mm eyepiece from time to time. With this unit, the #395 gives 1000 / 7.5 = 133x. For newcomers to astronomy this figure starts to sound very good, since they believe that the more magnification, the better. This is not true. The reality is that as magnification increases the problems to get sharp images start to appear. First, you must be in a site under perfect observing conditions (very clear and dark sky, no wind) and second, the images you get are not as bright as with the other eyepieces, because with a 7.5mm eyepiece you get a exit pupil of only 0.68mm. Also the eye relief distance is very short, so you must put your eye very close to the eyepiece. Due to those optic characteristics, you must use this eyepiece only for observing planets, double stars and details of the Moon. Anyway, with this eyepiece and under good observing conditions you can read the number of a car plate from 1 km of distance.

Alstar 40mm (25x), Meade MA25 (40x) and Celestron Ultima 7.5mm (133.33x)

The following tables show eyepieces data made by several makes. When choosing eyepieces you must keep in mind that you must always be under 50 magnifications per inch of aperture. This means that the "ceiling" of out #395 is about 180x. The headers for each table have the following meanings:

Series: Several series of eyepieces are listed. Some manufacturers have different series ranging from economy eyepieces to first-class ones. For example, Meade MA's are the cheapest ones yet yielding acceptable images, Meade Orthoscopic'c are a step better than MA's and they give excellent planetary views and Meade Super Plössl's are that: Super!. Anyway, for Celestron, Televue and Vixen LV's, I only reference here the best eyepieces.

Focal length: Is the focal length in mm. of the eyepiece.

Apparent FOV: Is the apparent Field Of View as seen thorough the eyepiece in degrees.

Eye Relief: Distance in mm. from the eyepiece to your eye. Short relief eyepieces are difficult to use to glass wearers.

Magnification: The word says it all. This is not a very important issue in astronomy. Aperture is the game here.

Magnification/Inch: Ratio of magnification against number of inches of the frontal optical element of the #395 (3.6"). I repeat: This figure must be always under 50!

Pupil-Exit: Diameter of the circle of light projected in your eye. Higher figures yield brighter images.

Table of 1 1/4" Meade eyepieces

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Table of 1 1/4" Celestron eyepieces

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Table of 1 1/4" Vixen eyepieces

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Table of 1 1/4" Televue eyepieces