Astigmatism

[Manok101]

I may be misspelling it but it's where the eyes move back and forth really fast and impares the vision I did not think that there would be a problem when I ordered a telescope but now after reading on eyepieces will I be able to see anything? How far away must one have their eye to look through an eyepiece?

[barkis]

I'm not sure rapid eye movement is connected with astigmatism.

Eyepieces do have differing distances of Eye relief, whereby the focused image distance can vary according to the type.

If you wear glasses, then a distance of around 15 mm eye relief would be suitable. If the eye relief is below the rubber eyecup of an eyepiece, then spectacle wearers would be unable to see the focused image.

Astigmatism is a fault that can exist in the human eye, and likewise in the optics of a telescope.

Ron.

[FraserClarke]

Astigmatism is where one axis of the eye focuses at a different point to the other axis of the eye (usually because they eyeball is a bit squashed in one direction). It means you can never get a sharp focus for any object.

I have it, and my glasses correct it (they're stronger in one direction than the other). Whether I wear them when I observe or not is a bit random. Mostly I tend not to, and don't notice much difference in the image quality. Sometimes I do notice a difference, and my glasses fix it.

How close you need to be to the eyepiece depends on the eyepiece (it's called 'eye relief' -- the more the better!). Some short focus eyepieces have very very little eye relief -- you need to be right up against them to use them; pretty impossible with glasses. Longer focal length eyepieces tend to be better. You can also get (more expensive) eyepieces which are specifically designed to have long eye relief (~25mm), and those you'll be able to use with your glasses on.

What you're describing sounds different from astigmatism -- but I don't know what it's called. However, remember that you're just looking at an image -- if you can see things normally, you'll be able to see things through a telescope.

[Doc]

My wife suffers from this. When I view the double cluster for example I say to her "look at all those wonderful stars" when she looks she says it looks like a jumbled mess and she cannot make out very well individual stars.

[michael.h.f.wilkinson]

I always wear my glasses behind the telescope, because I do notice astigmatism (more in low magnification, but still persistent at high magnification). I always select eyepieces with long eye relief.

[Digz]

I also have an astigmatism but havent noticed it affecting my observing. Its interesting to see what people say and Ill take more note next time I am out to see what the issue is. BTW I tend to observe without my glasses as well.

[michael.h.f.wilkinson]

Stars can become elongated, switching between | and - shapes as you focus. That is the tell-tale sign of (cylindrical) astigmatism.

[Talitha]

If you wear glasses, just use eyepieces with a long eye relief and you'll be fine. If you don't wear glasses (and don't want to get them just to correct this condition), find out if you can get contact lenses to exclusively correct the astigmatism.

[Merlin999]

Hi Manok01, I wonder if it is Nystagmus you mean rather Astigmatism. Astigmatism is where the image is focused to one side of the eye and can be corrected with glasses/lenses. Nystagmus is an involuntary eye movement which causes the image viewed to jump around and can cause difficulty with reading etc. If you have this, for some sufferers thereis a an angle the person can tilt their eyes to where the jumping stops so if you do have this, I don't know if you could tilt your eyes to find that point.

I'm pretty sure there is a Nystagmus society who may also be able to help (my friend's teenage boy has Nystagmus).