Celestron make incredibly good telescopes and have been for years but when it comes to eyepieces their record is somewhat blotchy, eyepieces are often optically good but are let down with poor comfort. The Omni is Celestron’s answer to the Super Plossl but how does it compare to eyepieces of comparable focal lengths?
The Omni follows a classic Plossl design employing the use of 4 lenses (or elements as they are known) in a symmetrical configuration, 2 groups of 2 lenses spaced closely together. Keeping the amount of lenses between the object and the observer down to a minimum ensures no excess glass to potentially degrade images. The down side is a smaller field of view when compared with 7 or 8 lensed optical systems. The Omni has a 52 degree field which places it squarely in the middle where Plossl field sizes are concerned. As the Omni is of low to medium magnification this restrictive field won’t be as much of an issue, as objects will take a little longer to pass through the entire field.
Optically the Omni does produce crisp and sharp images across the entire field, light scatter is present but is only visible on the brightest objects and is not so bad as to be of serious issue. Contrast is high due to the blackened edges of the lens elements making it especially useful on the fainter deep sky objects. Colour rendition is unfortunately quite poor so while images are sharp and contrasty objects can look a little bland when compared to some other eyepieces.
Visually the Omni is capable but there are similarly priced eyepieces out there that out perform it, with warmer colour rendition and less light scatter (even though the Omni’s light scatter is marginal).
Quite surprisingly the 15mm Omni isn’t uncomfortable to look through, it has 13mm of eye relief (the maximum distance one can position ones head away from the objective lens). 13mm is enough so you don’t feel like your eyeball is super glued to the lens and also means this eyepiece is suitable for anyone who wears spectacles. The objective lens is also of a good size so you don’t get the feeling you’re peering through a pin prick whilst observing through it.
In conclusion the 15mm performs well optically although it’s not the best eyepiece in it’s price range. To put it into a quantitive measure it gives a 7 out of 10 on overall image quality. Thankfully though it isn’t a nightmare to look through with an acceptable eye relief and a decently sized objective.