View Full Version here: : TeleVue Dioptrix

04-09-2006, 11:44 AM
I have slight astigmatism in both eyes - though not enough to cause significant distortion in the eyepiece. (I don't need glasses except for nocturnal myopia). I keep seeing the TeleVue adverts for their Dioptrix gadget. Has anyone used this? Does it work well?

Conversely, has anyone tried a simple correcting lens stuck over an eyepeice to achieve the same effect?


Don Pensack
05-09-2006, 12:33 PM
They work, and work well, though they don't fit most eyepieces. They do fit some non-TeleVue eyepieces. They are better than any glasses for viewing faint objects through.
If your astigmatism is less than, say, 1.5 diopters, you'll probably be OK viewing without glasses. Just refocus to obtain sharpness.
If you are like most people, the astigmatism in your eyes ceases to be noticeable around an exit pupil of 2-2.5mm and disappears completely at around 1mm of exit pupil. This is because the irregular curve of your eyes becomes less as the field used diminishes in size. If your astigmatism is slight (less than 1 diopter), you'll probably not notice it at the telescope except with your very lowest power eyepiece.
Remember the formula:
Exit Pupil = focal length of eyepiece/f-ratio of scope.