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exit pupil, eye releif & tri focals??

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#1 klxdrt

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Posted 26 May 2013 - 11:19 AM

Hi,

Getting back into astronomy (if my wife lets me) after about a 60+ yr hiatus.

Need some savvy advice about how to determine the best exit pupil, eye relief for use with tri-focals.

Had cataract surgery about 1 yr ago, wnet from 20/800 to 20/30, but I still use/need glasses. Do a lot of computer business, analysis work plus I'm bicyclist and glasses keep bugs, debris out of my eyes.

Is their a formula? Rule of thumb? Or do I need to ask the surgeon who did my cataract surgery or my optometrist or an ophthalmologist. If anyone knows House's" phone or email addr, I'm sure he will know the answer.

cheers,

klxdrt

#2 howard929

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Posted 26 May 2013 - 11:56 AM

My wife wears tri-focals but since she has no 'tisms she can view just fine without them. i'm not sure that cataracts count, got any?

#3 TexasRed

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Posted 26 May 2013 - 12:34 PM

If you don't have astigmatism, you may find that you can view fine without your glasses. Many people compensate for glasses by just refocusing their eyepieces. If you can't do that and have to leave your glasses on (or just prefer to leave them on), you'll want eyepieces with at least 19-20mm of eye relief. Low power eyepieces will usually have that much anyway and keep all their eye relief when used with Barlows.

I wear bifocals and sometimes find it a little awkward to keep the line below my field of view at the eyepiece. Trifocals may be an even bigger problem. You might consider getting a extra pair of glasses with only one or two focal regions for use at the telescope. Avoid progressive lenses, though.

#4 SeattleScott

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Posted 26 May 2013 - 06:16 PM

16 to 20mm of eye relief, keep the exit pupil between 5mm and 0.5mm.

#5 Jon Isaacs

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Posted 26 May 2013 - 07:05 PM

Is their a formula? Rule of thumb? Or do I need to ask the surgeon who did my cataract surgery or my optometrist or an ophthalmologist. If anyone knows House's" phone or email addr, I'm sure he will know the answer.



Hello and welcome to Cloudy Nights... :whee:

You may find that you don't need to wear your glasses while observing, you need the trifocals because the lens in your eye was replaced and the replacement lens cannot be focused.

However, a telescope has a focuser and so if one is just near sighted or far sighted, glasses are unnecessary. The only issue is if you still have astigmatism, probably not so likely because you do have those brand new eye lenses.

You could find out what your prescription is and whether you still have significant astigmatism but it might be better just to look through a scope and see.

Jon

#6 GeneT

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Posted 26 May 2013 - 07:19 PM

With 20/30 vision, I don't believe you will need glasses to view. I recommend attending your local astronomy club's outing and view through their telescopes. That way you will know for sure. If your schedule will not allow to attend one of their scheduled outings, go to their web site, and e-mail one of the points of contact. Explain your situation and ask if you could visit one of the members and view through their telescope. You would not have to get to a dark sky site for this test. You could go out in the back yard and look at some of the brighter stuff such as the moon, Saturn, or any visible stars. Doing this will answer the question whether or not you can focus the eyepiece into an acceptable non-eyeglass view. Should you need to wear glasses while viewing, I recommend a minimum of 17mm of eye relief (19 or 20 is better) for your eyepiece selection.

This is out of date, but you might want to read the information I posted on this topic a few years ago. The general material might help you think through this situation.
http://www.cloudynig...rd=Eyepieces...
By the way, I do 98 percent of my viewing while wearing glasses.

#7 klxdrt

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Posted 27 May 2013 - 07:40 AM

Thanks for all the good tips, ideas.

I have to wear tri-focals all the time to function with my lifestyle. With 20/30 after cataract surgery, I'm sure I will be able to view thru a scope fine w/o glasses. But since I have worn glasses over 55 yr, if I take then off, I'll lose them or sit on them. At least this is what Murphy's Law predicts.

I probably am going to buy a Celestron, so after the Holiday, I give them and my cataract surgeon a call and see what the experts have to say.

Cheers,

klxdrt

#8 izar187

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Posted 27 May 2013 - 09:11 AM

Thanks for all the good tips, ideas.

I have to wear tri-focals all the time to function with my lifestyle. With 20/30 after cataract surgery, I'm sure I will be able to view thru a scope fine w/o glasses. But since I have worn glasses over 55 yr, if I take then off, I'll lose them or sit on them. At least this is what Murphy's Law predicts.


Welcome aboard.

Rig your glasses with a neck cord, or strap, so that they hang from your neck when you're observing, or can be held up on your head. Another method is a specific pocket on your upper body, for your glasses and only your glasses. Some combination of this that you come up with will work. In my experience, much better than simply taking them off and setting them somewhere nearby in the dark. Keep 'em on you at all times. Up on my forehead works better for me, rather than dangling from my neck. But the frame of the glasses must be up to the tension needed to hold them there with an adjustable cord or an elastic strap, if they won't stay up there on their own.

#9 Jon Isaacs

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Posted 27 May 2013 - 09:28 AM

I have to wear tri-focals all the time to function with my lifestyle. With 20/30 after cataract surgery, I'm sure I will be able to view thru a scope fine w/o glasses. But since I have worn glasses over 55 yr, if I take then off, I'll lose them or sit on them. At least this is what Murphy's Law predicts.



This is an issue many of us deal with, you will need your glasses for reading charts and naked eye viewing of the night sky. I keep mine in a shirt pocket or just flip them up on my forehead.

Wearing glasses at the eyepiece is best avoided if at all possible, they get in the way, limit the field of view, cause unwanted reflections, require extra long eye relief...

Jon

#10 howard929

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Posted 27 May 2013 - 09:52 AM

Thanks for all the good tips, ideas.

I have to wear tri-focals all the time to function with my lifestyle. With 20/30 after cataract surgery, I'm sure I will be able to view thru a scope fine w/o glasses. But since I have worn glasses over 55 yr, if I take then off, I'll lose them or sit on them. At least this is what Murphy's Law predicts.

I probably am going to buy a Celestron, so after the Holiday, I give them and my cataract surgeon a call and see what the experts have to say.

Cheers,

klxdrt


Most of the time, after becoming as dark adapted as I can, I do everything by touch and feel since I can't see anything but the night sky and the view through the eyepiece. It's a little disconcerting to become used to, not being able to see things close around yourself but not so rough that it can't be learned. I wear reading glasses that "seem" to help with all visuals regardless of distance and a lot of times, they're the last thing I find after the lights come on during tear down. My point is, it's not too unlikely that you won't need your glasses when viewing or gain anything from their use so put them somewhere safe beforhand. ;)

#11 GeneT

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Posted 27 May 2013 - 04:23 PM

I'm sure I will be able to view thru a scope fine w/o glasses. But since I have worn glasses over 55 yr, if I take then off, I'll lose them or sit on them. At least this is what Murphy's Law predicts.


I wanted to view, wearing glasses throughout the viewing cycle, not just at the eyepiece. Glasses on, glasses off, glasses on and so on would create a situation where I might lose or damage my glasses. The solution is to study the eye relief, and buy eyepieces with at least 17mm or eye relief, with 19 or 20 being better. The web site listing the eyepieces you are interested in will carry the eye relief.

https://www.astronom...-delos-eyepi...

https://www.astronom...iece_p3399.aspx

https://www.astronom...iece_p3302.aspx

#12 cn register 5

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Posted 27 May 2013 - 04:49 PM

I wear glasses all the time and for my observing just flip them onto my forehead.

The trick is to remember that if you are doing outreach leave your glasses on and focus with the glasses, this will be close for people who don't need glasses.

Chris

PS smallish amounts of astigmatism don't matter, especially if you are using highish magnification and hence a small exit pupil.

C

#13 klxdrt

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Posted 29 May 2013 - 02:58 PM

Thanks for all the help & tips. FYI: there are other issues in play here besides glasses, etc. Not a good idea to discuss here.

I fond 1 astro club in my county, and am going to talk to them. Next meeting 1 mo away, & I will but o.o.t at that time.

I'm thinking of starting with a Celestron C90 Maksutov spotting scope, 90mm, 1.25" 38x at BH link: http://www.bhphotovi...C90_MAK_Spot...

I know it's a spotting scope as I intend to use it for astro & spotting.

cheers,

klxdrt






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