Celestron 6mm 1.25" Eyepiece ReviewConclusion: Stay clear of this dog
We bought the Celestron 6mm focus low profile eyepiece to use in a set of oculars for our small limited budget Celestron FirstScope and other telescopes.
I thought the small profile would weigh less and be ideal for small preset telescopes that are affixed to their mounts. Unfortunately I was wrong.
The heavy 6mm Celestron eyepiece is a dog. It has added weight and contributes to offsetting the fine balance of the telescope. It has one tiny itty bitty coated lens with a tiny diameter of a mere 4mm - it does not let enough light through to see much of anything. The exit pupil of 1mm is almost nonexistent! You're sure to see nothing through this useless accessory.
The worst problem happens with either visual observing or photo imaging because the limited FOV is severely restricted . On top of that, it does not produce good images. The color is off and the objects are dim. The worst problem is the exit pupil. It's only 1mm with the Celestron FirstScope, and much too small. A human eye cannot get close enough to the tiny opening to see anything, either with or without glasses.
The interior is coated flat black and the housing is threaded for filters. You'd definitely want to use a filter to help clean up the achromatic and chromatic color aberrations with fringing around the FOV.
Advertising has no specs and no information about the one tiny lens design. It's probably just a spherical mass produced uncorrected lens. It has a ring of color aberrations and fringing. The only redeeming features are the lens is made from glass and the housing is metal so it won't melt like the other two plastic Celestron eyepieces that were included with the Celestron FirstScope. It's hard to believe a company would put out such trash with a high cost. Caveat Emptor - let the buyer beware!
Recommendations: do not buy this eyepiece, it's a real dog
Advantages
* threaded for filters
* glass lens won't melt
* metal barrel is durable
* interior coated flat black
* anti-reflection coated lens
* low profile
* screen printed with type and focal length
Disadvantages
* Too Heavy
* too expensive for poor performance
* Bad exit pupil barely 1mm
* Difficult to use, results are bad
* eye cannot get close enough to see anything
* lens diameter is too small
* achromatic aberrations are severe
* Bad chromatic abberations
* images are soft and not sharp
* images are dim
* the FOV is too restricted
* bad single lens poor design
* lens is likely uncorrected
* introduces image distortion
* Optically poor
* Barrel threads jammed and won't disassemble for cleaning
* old discontinued product
Tip: To calculate the exit pupil of a telescope, divide the focal length of the eyepiece in millimeters by the focal ratio of the scope. For example, a 25mm eyepiece used in an f/5 scope delivers an exit pupil of 25/5=5mm, while a 35mm eyepiece in the same scope delivers an exit pupil of 35/5=7mm.
