Contact lenses

[Steve1976]

My eyesight is not the greatest and so ideally I should be wearing contact lenses. They make such a difference when trying to see stars with the naked eye but I'm coming against a problem when viewing through the EP. A star will tend to break off with its light going in different directions. It's kinda hard to explain but i reminds be of looking at venus when its near the horizon. This only happens in my right eye (I know an easy solution would be to use my left!) when the contact lens is in. Any suggestions / thoughts?

[brantuk]

Interesting question Steve.

Are you positive the "star break-up" isn't something to do with seeing conditions? The atmosphere can make stuff go in and out of focus somewhat randomly. Also heat currents in the tube can affect the view. Does this happen with both eyes? Does it happen all the time.

It would be informative to know what equipment you're using - maybe better quality ep's would help here?

Did you ever consider binoviewers? Somehow the brain compensates for the slightly different views in each bv eyepeice and creates a more interesting image - often better resolved than with one eye.

More info might help find a solution.

Cheers

[Steve1976]

Thanks for the reply mate.

I'm pretty sure it must be the contacts because after I noticed the problem I took them out and all was fine. It seems to happen with every EP I have and also through the finderscope. I'm using the MAK 127 and EP's are the standard ones that come with the scope but also a TAL 7.5 mm and a SW wide angle 15mm. And it only happens in the right eye not the left.

I could always just take the contacts out but the stars would just be blurs with the naked eye and so not so good.

[brantuk]

How long have you had the contacts Steve? It might be a simple as you're due for a new prescription. My specs are due for renewal cos my left eye is not so sharp as it was lol.

The standard ep's aren't usually up to much - usually just good enough to make the scope fit for purpose.

If you're in an astro soc or attending a star party you should try get a look through higher quality ep's. You'll be amazed at the difference it can make. If you're anywhere near the East Mids you'd be welcome to come experiment at our dark site.

And with the Mak - you just have to try some bv's - if someone can lend you a pair to try you'll never give them back lol

[xmal]

I also tend to find that when looking thru the scope it is (presently) quite late at night and my contacts have been in all day. Try putting your lenses in an hour or so before viewing and see if that helps.

[RichieP]

I find that my contacts dry up when observing because I forget to blink!

[Wurzil]

I agree - have a go at cleaning the contacts before viewing - maybe your right eye reacts to the contacts more than the left eye and is producing some eye-gunk.

alternatively, give a different sort of contact lens a try. I love my monthly night-and-days!

I use Systane lubricating eye drops with my contacts when the get manky or irritated - they come in packets of 28 individual use vials for a few quid - i get them from specsavers.

w

[Vega]

I too get this problem. especially as I use Torric contact lenses (these lenses have to be orientated a certain way up to be in focus sometimes requiring a little rotation). It can be a pain as the effect closely resembles a badly collimated newtonion or a scope slightly off perfect focus (As if collimation and focus wern't bad enough!).

I guess most of us have the same problem if wearing them all day, by the end of the day when darkness falls, the contacts start to 'complain' a little. Also we are allowing the air to dry the contacts for longer periods than normal.

Only advice I can give is blink often, maybe delay putting them in through the day (or keep a fresh pair to swap in before observing). They still beat glasses any day IMO.

Matt

[Steve1976]

Thanks for all the replies.

Usually I don't wear contacts because my eyesight isn't SO bad and I just get by. I only started wearing them for astronomy. As a result I only put them on just before observing and at first its ok. After an hour or so the problem starts so I think your right in saying its not blinking enough and they dry up a bit.

Matt - you mentioned glasses. I was actually thinking of trying them for the first time. That way I could use them for naked eye viewing and then just quickly take them off when looking through the EP. It's just too uncomfortable with the contacts but if I don't use them then with the naked eye its very hard for me to make out stars and in some cases even see them at all. What do you think?

[Steve C]

I found a similar problem with contact lenses, again only with my right eye. After consultation with the optician who supplied them he suggested it may be due to the fact that as I have an astigmatism, more pronounced in my right eye, the contact lense does not fully correct this & therefore can present itself especially when viewing very bright objects against a dark background.

[Skuber]

I have quite a strong prescription, +7.5 diopters in each eye.

At this magnification, my glasses have got very pronounced spherical and chromatic aberration off the centre line of the lenses. This seems to only be a problem in the scope when I don't look directly into it.

With my contact lenses, I have no problems at all. The stars are very clear and stable with no artefacts at all.

However, I've noticed something else that I didn't expect - I can see more stars ('naked' eye) with my glasses on than I can see with my contacts in.

I wonder if this is because my glasses act as a telescope in themselves, with an aperture of the size of the glasses, whilst the aperture of the contact lense is that much smaller?

Does this make sense?

[Wurzil]

thats is an interesting theory!

I wonder if a minus prescription would have the same or the opposite effect.

[great_bear]

I wonder if this is because my glasses act as a telescope in themselves, with an aperture of the size of the glasses, whilst the aperture of the contact lense is that much smaller?

No - the absolute aperture of a lens matters only in relation to where it is placed in the optical chain.

There are a number of potential reaons why the glasses are giving you a better image - but aperture isn't one of them.

[Moonshane]

I have been considering this too. I think I'd prefer to observe without any correction myself but glasses are a pain - although I cannot see much without them (just short sighted).

is it possible in theory to just wear a left contact and then observe with my bare right? anyone tried this?

[xmal]

Usually I don't wear contacts because my eyesight isn't SO bad and I just get by. I only started wearing them for astronomy. As a result I only put them on just before observing and at first its ok.

I think that might be your problem.... If you do not wear contacts regularly then your eye does not fully get used to them and they can get dry(ish). Maybe wear them longer to try and get your eye more used to them. Some of the modern lenses are 55%+ water and they act like a sponge in your eye.

[roundycat]

I don't understand this. I read somewhere that astigmatism is not a problem once the magnification is high enough to give you an exit pupil smaller than the dark adjusted eye. Also can't you adjust focus for the with and without glasses situation? I can.

Dennis

[great_bear]

I read somewhere that astigmatism is not a problem once the magnification is high enough to give you an exit pupil smaller than the dark adjusted eye.

That's not quite right - i.e. the size of the dark-adjusted pupil is not relevant to the issue. The exit pupil simply needs to be small enough to mitigate the problem. The size that is required, will vary depending on how bad the astigmatism is.

There will be a size at which it shouldn't be a problem for anyone - but I don't know what that size is. In any case, you don't really want that to be what drives the selection of magnification

Also can't you adjust focus for the with and without glasses situation? I can.

You're right about that - there is more than enough focus in every telescope to cope with the variances between people's eyes. However, I think some people like to keep glasses on, or contact lenses in, so that they can enjoy the naked-eye view when not looking through the telescope, and also see their charts and thermos flask

My own experience is that my soft contact lenses are completely unsuitable for astronomy. The narrow-angle light-scatter they produce on bright planetary targets and the moon, makes them unusable. I just have to accept bad eyesight when not at the scope (I have no glasses)

[Steve1976]

GreatBear your spot on about wanting to enjoy naked eye views as well as the view through the telescope. For me its more tricky to pick out the constellations without the contacts.

Went to the opticians and got myself a really cheap pair of specs. I'll just be using them for astronomy and watching TV so I didnt care what they looked like. So I will try with the specs a few times and see if it isnt too much hassle taking them on and off.

Thanks for your thoughts folks, much obliged.

[LukeSkywatcher]

I need to wear glasses for watching tv and driving. I can read fine without them. Over the yrs i have slowly adopted the habit of wearing glasses all day every day so i dont have to keep removing them and putting them back on. This has made my eyes VERY lazy (not in the sense of having a "lazy eye"). NOW if i remove my glasses it takes a couple of hours for them to refocus properly so that i can see things clearly (or as clearly as i can with my eyesight).

Given that we can not really plan any observing session in advance (due to unpredictable weather) i have two choices:

1/ Observe with my glasses on

2/ Observe with the glasses off

Observing with the glasses on is out of the question. Its something i have tried and just can not get used to. My eyes are too far from the EP lens and i cant see anything.

Observing without the glasses is my usual method but i am sure it is hampering my views due to my eyes needing a couple of hours to refocus after removing the glasses. This also cant be good for my eyes because i am sure i am straining the muscles in the eye/socket etc which could cause lasting damage as well as hampering my views.

I have no complaints about the views i get while observing without the glasses. Objects are sharp and focused (as far as my brain can tell).

The alternative is to have an eye transplant because i sure as hell am not gonna let any doctor go near my eyes with a laser, although my dad had laser eye surgery many moons ago when it was in its infancy and he said it was the best thing he ever did. He wore glasses all his life until he had the laser treatment.

[tomys]

Try aiming with specs on then take them off and center in the finderscope and view also without specs. focus can be adjusted to your eye anyway, unless you have alot of friends with you...

[Steve1976]

Tomys

Thats what I had in mind. After a few times trying now I can say that it is probably the best solution to the problem. Off course its still a bit of a hassle taking the glasses on and off but hey thats life!