Tips for the Partially Sighted

[daniel991999]

Hi,

I'm after some advice.

Whilst might eyesight is moderately short sighted, my wife's is much worse. She's short sighted, but that's corrected with glasses. Her biggest problem seems to be a poor sensitivity to light.

During the day, she's fine, but as the Sun goes down, she struggles. Walking in the dark unaided means she can't even see the kerb by her feet.

Anyway, the reason for this post - as a result of this, she's never seen stars, something I always take for granted. Obviously she's seen pictures, but she's never seen them properly.

She did however manage to spot what she was a very bright star in the sky the other night whilst we were driving home - she thought it may have been a plane, but it was actually Jupiter.

So, before I start going down the route of buying a telescope (or even binoculars), does anyone have any simple tips or tricks for "enhancing" the night sky? It's almost like I need a way to change the contrast ratio of the night sky and make the stars just that little bit brighter.

Any advice appreciated.

Thanks.

[Siriusmeg]

Hello, I am sure that others will be along soon to offer more helpful advice; my best thought so far is to try sitting out in the dark for a while before observing (dress warmly!).  As your dark adaptation improves, then more can be seen - I wonder if that would work with your wife's eyesight?  My partner is dyspraxic & so finds going from light to dark very difficult to adjust - but after a while his eyes begin to adapt.  Alternatively, the Moon would be a good subject for her to observe, as it is very bright in the ep - plenty to see there.

[NGC 1502]

Hello, I am sure that others will be along soon to offer more helpful advice; my best thought so far is to try sitting out in the dark for a while before observing (dress warmly!).  As your dark adaptation improves, then more can be seen - I wonder if that would work with your wife's eyesight?  My partner is dyspraxic & so finds going from light to dark very difficult to adjust - but after a while his eyes begin to adapt.  Alternatively, the Moon would be a good subject for her to observe, as it is very bright in the ep - plenty to see there.

Good advice here.  I like to add that getting eyepieces with long eyerelief may help. That means a greater distance between your eye and the eyepiece, so glasses can be worn, and you can still see the whole field of view.  Look for 20mm eyerelief in the specification.  They often cost more, but make the observing experience so much better for spectacle wearers.

Good eyerelief is also desirable with binoculars for the same reason.

Regards, Ed.

[ronin]

Sounds like you will need a scope that collects a reasonable about of light, does not magnify greatly and produces a fairly sharp image.

So basically avoid the eternal temptation of magnification, might be bigger but dimmer and possibly less defined.

There are posts saying that you need 160x and more for Jupiter, which I would argue with, I have seen Jupiter at 60x very nice and sharp with 2 well defined dark bands.

What you get depends on what you intend and the budget.

Whatever you get what you see will not match the images that you see, the images are the result of many stacked and processed images.

In about a week it is Star Gazing Live and clubs will have public nights so locate one and get along to one, or two, and try to have a view through the assorted types of scope and see what the results are. Check the fedastro web site for clubs around you and check what is available.

[brantuk]

My first suggestion is that if you get a scope or binocs then she will stand a much better chance using the equipment from a really dark site - totally dark and full dark adaption of the eyes will maximise the likelihood she picks up light.

My missus has similar shortsighted problems - she wears bifocals whereas I just use regular prescription reading glasses. But it's a real pain at the eyepiece and I'm thinking of fitting a crank handle to the focuser cos the difference is our eyesight is so big that I have to refocus the tube about half an inch lol. I jest - but the point is she doesn't use her specs to view the night sky with a scope and can attain good views using just the focuser.

I have noticed she struggles to see fainter objects more so than myself, and has to use averted vision with the visually more challenging objects. So that's a technique your wife could employ. Finally investigate the use of filters some of which are designed to darken the area around certain types of object and maximise contrast in the center of the eyepiece making faint stuff stand out more.

What really gets me miffed though is that, just looking up at the sky, she see's the Milky Way long before I do - same thing with binocs - total contradiction in terms but I'm sure there's a technical reason somewhere lol. We both enjoy our astronomy together and, assuming your wife's light sensitivity isn't more dire, there's no reason why with a few adjustments, you shouldn't too. Hth and welcome to SGL

[NGC 1502]

More good advice above.  Couldn't agree more ( post # 4 ) that Jupiter is a fine sight at modest powers like 60x.  Bet Galileo would have been impressed with 60x and modern optics............

Regards, Ed.

[itmo]

I would suggest asking some kind of an eye doctor why she cannot see in the dark. It might be because of optical issues, or because of damaged/lacking dark vision nerve cells. If the latter is the cause, then you just need a large enough scope to make it possible to see stars with her color vision. This should not be a problem with brighter stars or planets. If the problem is with optics, then it is probably a bit easier to solve  as long as she can wear her glasses while using the scope. If the problem is with rod cells , then she might not be able to ever see deep sky objects or faint stars. 

[itmo]

And if you dont want to try buying optics first, then I would suggest going into a very dark place and letting her dark-adapt properly (30 minutes minimum) 

[cantab]

Somebody mentioned in another thread that they had some glasses specifically for stargazing, a different prescription to the normal ones. The eye can be different in low light. Even without that, I know my mum for example prefers an undercorrected prescription for her short-sightedness, so that it doesn't affect her near vision so much. So it may be worth speaking to an optician about.

There will I expect be some viewing sessions soon, run by local astro clubs under the banner of Stargazing Live. You might try getting to one of them. If your wife can see stars fine in a scope or binoculars, possibly after a fair refocus, that would suggest she just needs different glasses for night.

[bomberbaz]

Sounds like you will need a scope that collects a reasonable about of light, does not magnify greatly and produces a fairly sharp image.

Agreed with this. I am not 100% on best advice here but nothing faster then an F6 scope giving a good light gatherer and also agree with the long eye relief eyepieces if you intend wearing glasses at the eyepiece. Lacking any other information it is difficult to say more.

oh and +1 on the dark sight for any viewing.

[LukeSkywatcher]

I'm also short-sighted (whatever that means). I had an eye test 2 weeks ago and got two new pair of glasses. My optician told me that with my glasses on that i have better then 20/20 vision. She said my eyesight with glasses is "EXCELLENT". A few days ago i went out to have a look at how good the new glasses performed and after waiting 30-40 mins for my eyes to become fully dark adapted, i saw (for the first time in my life) all of the Seven Sisters.................just looking with the naked eye/glasses. When i am out and about, i can now read the reg plate of cars 4 car lengths away from me.

I still suffer from what is called "night blindness", which means lights from on-coming cars really do blind/dazzle me for a second or two.

Not sure what to suggest for your wife apart from there are glasses out there available which are basically designed to exercise the muscles in the eyes and strenghten them and improve vision. They look like a pair of cheap sun glasses with slits in them (think of a Bratinov mask). I dont think they are medically approved, so best to visit an optician for professional advice.

[Deadloud]

I'm new (very) to this game .. first telescope being delivered later in the week ... but I've had a decent set of bino's for years. I wear glasses for everything, except looking through the binoculars. If I try to use them with the glasses on then I can't see anything of any use. I can focus properly without them and see no problem. I have long sight (an optician once told me I was so long sighted there wasn't anything on this planet I would ever see without glasses) I know this isn't directly relevant to the thread but how do glasses effect other people ? Use them or lose them ?  

[m37]

Could you find a local astro society? I'm sure they would help out and chances are someone there will have a humongous dob she could have a look through. Some even have access to proper full size observatories. They are bound to be friendly and helpful.

cheers and good luck, that's a really nice thing to do for your wife.

[NGC 1502]

I'm new (very) to this game .. first telescope being delivered later in the week ... but I've had a decent set of bino's for years. I wear glasses for everything, except looking through the binoculars. If I try to use them with the glasses on then I can't see anything of any use. I can focus properly without them and see no problem. I have long sight (an optician once told me I was so long sighted there wasn't anything on this planet I would ever see without glasses) I know this isn't directly relevant to the thread but how do glasses effect other people ? Use them or lose them ?  

At 65 I'm fortunate not to need glasses for distance,  just need basic glasses for reading.  So at the telescope, only need the specs for star charts.

If you do need specs for general use, some find they only need them at the scope when using low power, because the exit pupil is larger, using more of the eyes dilated pupil.  At higher powers that will have a smaller exit pupil, using less of the eyes lens, you may perhaps dispense with the specs and be ok.

Some will find they need their specs at low and medium power, but do not need them at high power that will have a tiny exit pupil.

But it's an individual thing, try it and see how you get on.

To find exit pupil, divide the aperture by the magnification.  Example - 10 x 50 binoculars - 50 divided by 10 = 5mm exit pupil.

To use specs with a telescope or binoculars, most will be best served with long eyerelief, that means you don't need to get your eye right up close to the eyepiece, leaving room for the spectacle lens.

Regards, Ed.

[bomberbaz]

Don't know if anyone has mentioned this but if you stick to the lower magnifications, you get a larger exit pupil that gives a greater saturation of the nerves which receive the light. There is a calculator on here that helps, sorry can't remember where but that will tell you the exit pupil for eyepieces when married up to your chosen scope. IE my 31mm Axiom gives me a 6mm exit pupil on the 12" dob in my sig.

hth

steve

[NGC 1502]

Hi Steve.  The simplest way to find exit pupil is to divide aperture by magnification.

With my 10" Dob, my low power is with my 27mm eyepiece, mag = 1200 / 27 = 44x.  Exit pupil is 250 / 44 = 5.7mm exit pupil.

Works for any eyepiece / telescope combo.

Regards, Ed.

[cantab]

Also simple is to divide the eyepiece focal length by the telescope focal ratio. So a 27 mm eyepiece in an f/4.8 telescope will give a 27/4.8=5.6 mm exit pupil.