Using glasses and eyepieces

[kinetic]

As per John's suggestion.....

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Hi John, all,

Sorry to sidetrack from the topic but you seem to have a good knowledge of eyepieces all round....
On the subject of wearing glasses, what exactly, in layman's terms, would
having to wear glasses mean to using eyepieces in general?

I have just entered my forties and recently found that what I thought was
exceptional 20/20 vision is now on a slow, gradual, typical deterioration
of a 40 plus person.
This is obviously frustrating at times and especially so when observing.
I find I have to sway between about 1.5 diopter cheapie $2 shop glasses
to read the monitor and see stars as pinpoints, to taking them off to
look through the eyepiece.
I have recently had my eyes tested and was told I have the raw deal out of
the two typical diagnoses.
I need glasses now for reading, and I also need a slightly different diopter
for distance vision.
Steve B.
Hi Steve,

If you care to start a new thread in the eyepieces section I will be happy to respond there. This is quite a complex topic which warrants a detailed reply and I don't think it entirely appropriate to divert this thread.

Cheers,
John B

[leon]

John, to make a long story short, glasses have no effect on seeing through any eye piece, or scope for that matter.

I always thought that i needed to focus my scope and camera with them on, because i figured that if i focused with them off my focus would be out because the camera didn't know i was half blind. However this was not the case. it makes absolutely no difference at all.

If I focus with the glasses on of or off the focus is still perfect, however I do have to wear them to see the stars clearly, just as a visual.

This may not be the answer you are seeking but that was my experience.

Leon :thumbsup:

[ausastronomer]

Hi Leon,

I wasn't asking the question. Steve actually adressed this question to me in a different thread and I suggested he start a new thread specifically on this topic and I would respond there.

Your comment above is not totally correct. See my detailed response to Steve below. Wearing glasses or having a need to wear glasses when you are observing can have a significant effect on observing. Your comment only holds true for people who wear glasses, but do not suffer from astigmatism. Most people who have myopic correction (shortsighted) also have astigmatism correction, particularly those over 40 yrs of age.

Cheers,
John B

[wavelandscott]

Did I miss a post?...I'm looking for your detailed response below...I expect it to be a worth while read...

[ausastronomer]

Hi Steve,

Before I begin let me explain eye relief and exit pupil. You asked about eye relief. The eye relief of an eyepiece is the distance from the front surface of the eye lens of the eyepiece that the image forms. In simple terms, how far away from the eye lens you need to place your eyeball to hold the exit pupil and comfortably view the image. The exit pupil is the diameter of the column of light that projects from the eyepiece and forms the image that you view. This is a function of the focal length of the eyepiece and the F-ratio of the telescope. You calculate the exit pupil by dividing the focal length of the eyepiece by the F-ratio of the telescope. eg. A 20mm eyepiece in an F5 telescope gives a 4mm exit pupil. A 10mm eyepiece in the same F5 telescope gives a 2mm exit pupil.

As Leon alluded to above, sometimes, having a need to wear glasses doesn't matter. If a person has no astigmatism, then any correction can be accomodated with focuser adjustment alone. Both for shortsighted people and longsighted people. If this is the case then the easiest option is to just remove your glasses and adjust the focuser to make the required focus adjustment. Alternatively, you can use long eye relief eyepieces combined with your glasses, or use contact lenses, which work well in the absence of astigmatism. Unfortunately, a lot of myopic people (shortsighted) over 40 years of age (me included), also suffer from astigmatism. This cannot be corrected with focuser adjustment alone. It manifests when you are seeing stars that you cannot focus to a point. They always have some degree of flaring. Many people attribute this to an eyepiece aberration, when in fact it is caused by the astigmatism in their own eye. The worse the astigmatism of ones own eye, the worse the flaring. The difficult thing for some people to understand is why the perceived flaring changes with different eyepieces. As the width of the exit pupil that is created is reduced, the amount of astigmatism observed is reduced. As the eyepiece focal length is reduced in any given telescope, the created exit pupil is reduced. As you use progressively shorter focal length eyepieces in any given telescope the amount of observed astigmatism is reduced because you have a smaller exit pupil and are using a progressively narrower light cone. Consequently, as the light cone narrows you are using a progressively smaller section at the center of your eye lens which introduces less aberrations (including astigmatism) than are introduced when you use the outer areas of the eyes lens. The degree of astigmatism in the observers eye will determine at which sized exit pupil it begins to manifest and at which point they need to wear their glasses. I have .75 diopters of astigmatism correction and my astigmatism manifests at exit pupils over 3mm. I have no problem removing my glasses for eyepieces which create an exit pupil of less than 3mm.

There are several solutions to the problem and all of them have inherent issues.

1) Leave glasses on. The issue here is that you need to use long eye relief eyepieces to accomodate the glasses and take in the full field of view and also to avoid scratching your glasses and your eyepieces. I will expand further on this option below.

2) Use a Televue Dioptrix. I don't like this option. I do a lot of outreach work where other people share the view through my scope. No one else can use the eyepiece with the dioptrix fitted unless they have an identical astigmatism correction to me.

3) Use contact lenses. I have tried this option on and off over many years and it isn't the answer for me. The issue here is that contact lenses are weighted at the bottom of the lens to correctly orientate the lens on your eye and correct for your astigmatism. Unfortunately when you observe you often get your head on funny angles which means the contact lenses don't align correctly to the right position on your eye every time.

I have found over many years that using glasses combined with long eye relief eyepieces (16mm to 20mm) is the best way to go. The convenience here is that you never have to remove your glasses when you alternate between, eyepiece, star chart, laptop display, argo navis display and naked eye viewing of the sky. It also leaves both hands free all the time. This may not sound important but when you are up the ladder of a 25" or larger scope you want to hang on with at least one hand, while you adjust the focuser with the other. It is important when you get glasses for observing to get good quality ones with high grade anti reflective coatings. If your glasses do not have good anti reflective coatings you will get reflections back into the eyepiece from the glasses themselves and off your own eyeball. You will think you have "moths" flying around inside your eyepieces. Moreso, if you combine cheap poorly coated glasses with cheap poorly coated and internally baffled eyepieces.

I think I have covered most things. If not ask away. I have suffered astigmatism and observed with glasses for over 30 years and tried every available option known to modern (and ancient) science :)

Cheers,
John B

[ausastronomer]

Got sidetracked watching TV while I was in the middle of typing it out :)

Cheers,
John B

[wavelandscott]

No worries, I just thought my kids might be right and I might actually be losing it in reality!

Lots of good information in your post...

[kinetic]

John,

Wow, thanks for the reply,
A good overview of everything!

I don't think I have much, if any, astigmatism.
There are a few online tests etc and my optometrist didn't find any
worth noting.
However when you say it shows itself as flares around stars and you
can't see stars as pinpoints, did you mean with the correct glasses
on for distance vision or with glasses off?

Up until my forties I could totally 'relax' my eyes and they would
focus stars as pinpoints. As if in a total rest state, my eyes focused
on infinity naturally.
When I hit forty I needed to apply a bit of noticeable effort to focus
the stars and if I 'relaxed' they would turn to a flare....like a dandelion
flare...equally flared in 360 degrees around the star.
Astigmatism shows as unequal flaring around a pinpoint, because the eye
lens is not a perfect lens any more but 'pulled' out of shape.
At least thats my understanding of it.
When driving at night also, I could see a very distant pinpoint street lamp
as a set of beautiful diffration rings if I relaxed my distant vision back to
out of focus
If I had astigmatism, wouldn't the rings be distorted?

Now as for using eyepieces, you recommend the use of long eye relief
eyepieces and glasses on as your preference.
Obviously you need the glasses as you say, to correct for the astigmatism
component of your defect and leaving them off would introduce some
residual flaring even though you could focus and correct the myopic
component.
For me, I feel very uncomfortable having any gap (the gap that eyeglasses
cause) between the eye and the eyepiece.
I have had no exposure to high end eyepieces like you have and so
probably can't comment about their benefits WRT eyeglasses and
eye relief.

Also I don't like the way that gap introduces secondary reflections from
external sources (dome LEDS etc) buggering up the contrast of the
view from the eyepiece.

When I have friends over of varying ages, and kids for example, with
perfect vision, the setting that I leave the eyepiece at (corrected for
myopia and no glasses left on) is still in focus for them too.
I sometimes think they are just being polite and then dial in a bit of
out-of-focus and then they say "hey no, now it's blurry"

Once again, thanks John for the insight,

regards,
Steve B.

[UniPol]

I suffer from astigmatism and long sightedness and do not always have to wear glasses depending on which scope I am using, both eyes requiring a 2.00 diopter correction. I can just about use any eyepiece on my f15 refractors without glasses as the exit pupil is relatively small, say between 1.00 - 1.5mm. On my f5.9 - f7.7 refractors I have to wear my glasses or in the case of Televue eyepieces, a Dioptrx is used. Glasses can be worn at anytime with long eye relief EP's as has already been stated.

A useful guide to eyepiece exit pupils and other useful information can be checked out on Televue's website.

http://televue.com/engine/calculate3b.asp?NoBack=True&_2in=yes

[Starkler]

This has been my experience when attempting to use glasses for observing, along with the distraction of reflections from local light sources. I gave up on the idea.



Are such coatings available as an option from the larger optical franchises, or is this only available from a specialist shop? What coatings are recommended?

[ausastronomer]

Hi Geoff,

Any optometrist can supply the right glasses and coatings. However, someone that spends a lot of time prescribing reading glasses to older people may not be as conversant with the newer materials and coatings as someone who deals with a generally younger clientele, that demand the latest and greatest.

My glasses use Hoya EYNOA lenses which have an index of 1.67, which compares to the standard polycarbonate lenses with an index of 1.5.

http://65.161.187.167/index.php?SID=48770e674137885894754 5&page_id=7878

My previous glasses used Hoya EYAS material (1.6 index)and they were also very good. EYNOA was not available at that time.

http://65.161.187.167/index.php?SID=48770e674137885894754 5&page_id=7879

Similar high quality lense materials are available from Zeiss, Nikon and Rodenstock. My optometrist advised against some of the super duper higher index lenses (>1.7) because of "possible" chromatic aberrations.

Without question the best coatings available at present are Crizal Alizé® These are absolutely superb and unsurpassed at the present time. They can be applied to lenses from several different manufacturers.

http://crizal.com/Consumer/Crizal+Technology/

Now the bad news.

1) Be seated when you ask, "how much".

2) Don't visit the optometrist on an off pay week.

Not sure what the cost would be now but with 1/2 decent frames my present glasses were well West of $1k. However, that was nearly 3 years ago and EYNOA was a new product. With changes in the exchange rate and rapidly advancing technology, they may be somewhat cheaper now.

Cheers,
John B

[erick]

Very interesting reading, thanks guys. I took this thread along when I visited my optometrist yesterday.

Good news - I have zero astigmatism in my right eye, which is my observing eye for a single eyepiece. My left eye has 0.5 astigmatism.

I'll continue to observe without glasses, but still need them to observe the sky and point the scope. I use them for straight-through finderscope since I want to watch sky and finderscope view simultaneously. But I'll experiment again. My left eye isn't too bad for distance.

I also asked her to measure my dilated pupil diameter. 4mm she reckons! That's probably reasonable for my advanced years and worth knowing!

ps. I've also decided - stuff these multifocals - been driving me crazy for a few years now. I'm getting to pairs of single lenses, one for close and one for long.

[Starkler]

Ouch!
Thanks for the great info John. I think I'll put up with it for now :doh:

[Wavytone]

There's an even better solution. I'm also on the wrong side of 50, very long sighted (I wear glasses full time and have a lazy right eye). In my early 40's I tried the two pairs thing - a second pair for reading and computers - but soon lost them. I also tried the multifocal thing etc etc...

For the past 6-7 years I wear ultra light titanium frame "convertibles" which have a magnetic clipon -normally this is used for sunglasses - however I have the optician fit these instead with positive lenses that are the dioptre difference between long distance and close up (for reading etc). Made in high index plastic and coated, these cost $110 a pair - far less than prescription reading glasses.

Even better is that these clipons fit very unobtrusively in shirt/coat pockets without damaging the shirt and without looking like an ugly lump, and I have two pairs in case I lose/break one.

This way i can keep my long distance glasses on my nose all the time and am never hunting for "the other pair".

While the complete set of convertibles and the clipons with good coated lenses etc can cost north of $1k, IMHO the convenience beats the alternatives hands down and is well worth it. And you can have the sunnies too..

I'll tell you who the optician is that does these (they are in Sydney), you could ask yours to contact them for the details in optometrist-speak.

If you really want to get fancy you could probably opt for two different types of plastic and have them designed to reduce chromatic aberration. In principle you could probably come up with an achromatic doublet but it would be thick and heavy...

PS I also have a pair of 2X glasses (galilean telescopes in frame) - bit of a party trick more than anything else
http://www.eschenbach.com/preview.php?pid=702

Now when digital eyeballs become available I want one...