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Bifocals

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15 replies to this topic

#1 Grousehunter49

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Posted 16 February 2024 - 03:41 PM

When wearing bifocals bottom for reading top for distance when looking through telescope what should you look with top or bottom..thanks



#2 kasprowy

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Posted 16 February 2024 - 03:45 PM

I look through the distance lens, on top. I suppose you could use either and focus accordingly. They correct the astigmatism which is what your scope cannot correct.



#3 TOMDEY

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Posted 16 February 2024 - 03:48 PM

Top is best because eyepieces are optimized for true afocal use aka one's eye (or eye with glasses) focused on far away infinity.    Tom


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#4 auroraTDunn

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Posted 16 February 2024 - 03:54 PM

"IF" I'm using glasses, I use my top half.

But most of the time I take my glasses off. I found I can see better by focusing to my eyes and I'm dang near blind without my glasses.

Noting that I'm near sighted with extreme astigmatism. Not sure if it would be the same for far-sighted.



#5 Donacton

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Posted 16 February 2024 - 04:38 PM

I find that as much as I try to use my glasses, I see better without them. It’s kind of a pain to look at my iPad with my glasses and then look through the eyepiece without them but the view is better.



#6 Starman1

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Posted 16 February 2024 - 04:43 PM

When wearing bifocals bottom for reading top for distance when looking through telescope what should you look with top or bottom..thanks

The top half, for distance, because that is what you use for looking at the sky and it will be close to the vision of other people with whom you might share the view.

 

However, if the eyepiece has a wide field, you will find yourself looking through the bifocal section at the bottom when you glance down.

Some labs, like Costco, can make bifocals with a very small lower section so the reading section can be outside your field of view when looking through the eyepiece.

This only works partially.  I finally found that single vision astronomy glasses worked best for naked eye and the telescope.

That, of course, means augmenting your vision for writing notes, reading charts, etc., which can easily be done with a pair of reading glasses or a large magnifying glass.


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#7 Starman1

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Posted 16 February 2024 - 04:47 PM

I find that as much as I try to use my glasses, I see better without them. It’s kind of a pain to look at my iPad with my glasses and then look through the eyepiece without them but the view is better.

You can either switch from distance vision glasses to readers when looking at the iPad, or use bifocals.  See the caution about that in my previous post.

 

"IF" I'm using glasses, I use my top half.

But most of the time I take my glasses off. I found I can see better by focusing to my eyes and I'm dang near blind without my glasses.

Noting that I'm near sighted with extreme astigmatism. Not sure if it would be the same for far-sighted.

With severe astigmatism, the stars will look like trash until you get to really tiny exit pupils.

You're better off wearing your glasses at the eyepiece and using eyepieces that work well with glasses, like Delites, Delos, Morpheus, etc.


Edited by Starman1, 16 February 2024 - 04:47 PM.


#8 JohnTMN

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Posted 17 February 2024 - 01:45 AM

When wearing bifocals bottom for reading top for distance when looking through telescope what should you look with top or bottom..thanks

The optical correction for your eyes with your lenses is/are your primary view through them.

The magnification value offered by a bi/or tri-focal adaptation to your lenses is rendered mute with eye piece selection and the focus value of any OTA.

 

The complication is the distance from the eye piece's focal point vs how close you can get while wearing glasses,,

 

What's the word for it guy's,, help me out??


Edited by JohnTMN, 17 February 2024 - 01:46 AM.


#9 Starman1

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Posted 17 February 2024 - 02:31 AM

The optical correction for your eyes with your lenses is your primary view through them.

The magnification value offered by a bi/or tri-focal adaptation to your lenses is rendered mute moot with eye piece selection and the focus value of any OTA.

 

The complication is the distance from the eye piece's focal point vs. how close you can get while wearing glasses,,

 

What's the word for it guy's; help me out?

The term you're looking for is "eye relief", the distance back from the glass surface of the eye lens the image reaches its minimum size.

Glasses compatibility requires a "long eye relief" in order to accommodate the fact the eye is pulled back away from the eyepiece when wearing glasses.

 

And you're right that the telescope can be focused for any part of a bi- or tri-focal lens.

The advantage of focusing for distance, however, is that you can share the view with others without requiring a lot of refocusing.

My wife and I focus at radically different places, for example, when not wearing glasses, but when we wear glasses, neither of us needs to refocus when sharing the view.



#10 NinePlanets

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Posted 17 February 2024 - 09:28 AM

 

The advantage of focusing for distance, however, is that you can share the view with others without requiring a lot of refocusing.

One of little group that used to observe together included a guy with severely wild focusing needs. As we moved between telescopes sharing views we would always make him wait to look last.  ;)


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#11 brionl

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Posted 17 February 2024 - 01:02 PM

I've been wearing multi-focal lenses for more than ten years now, and they mostly work pretty well. I'm near sighted so I can read just fine w/o my glasses.

The last time I got glasses though, I had them make me up a set of computer glasses that are one prescription for "medium" distance vision. They work so well that I wear them around the house 90% of the time, and only put on my full up 3-way glasses when I'm going out somewhere.

 

One complicating factor is that lately my eyeballs don't line up quite correctly so they had to add some Prism factor to the Rx. When I'm using my binoculars I have to wear some glasses, usually the computer glasses. But when I'm using the scope I can do either with or without.



#12 Buford7

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Posted 24 February 2024 - 09:20 PM

This is a great discussion—eyeglass wearers have an interesting set of challenges to deal with and at the eyepiece.

This may be a long shot—but does anyone know a good optometrist in the Edmonton Alberta Canada area that has good knowledge with working with amateur astronomers? I am finding challenges talking with optometrists about dealing with aberrations in the field of view and trying to solve issues with eyewear.

I am using a 10” f5.4 coma corrected Dob, with decent eyepieces that should be well corrected (APM30mm, Morpheus 17.5mm etc). I am taking into account Collimation, Cooling and Conditions (atmospheric).

Still seeing tendency to spikes coming off brighter stars, often in bottom left or right or both. They move locations when moving in and out of focus, and can change location when I move my head angle—so I’m quite sure this is astigmatism from my eye and glasses.

Trying to find someone to work with on lenses (hopefully without paying thousands of dollars trying different products!)

Thanks if anyone has any thoughts on this!

#13 Buford7

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Posted 24 February 2024 - 09:26 PM

I should add that I am using single vision round lenses (Essilor Accolade 4.0 from Costco) lenses corrected for both myopia and astigmatism.

#14 Hwunkzeep

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Posted 24 February 2024 - 10:48 PM

The term you're looking for is "eye relief", the distance back from the glass surface of the eye lens the image reaches its minimum size.

Glasses compatibility requires a "long eye relief" in order to accommodate the fact the eye is pulled back away from the eyepiece when wearing glasses.

 

And you're right that the telescope can be focused for any part of a bi- or tri-focal lens.

The advantage of focusing for distance, however, is that you can share the view with others without requiring a lot of refocusing.

My wife and I focus at radically different places, for example, when not wearing glasses, but when we wear glasses, neither of us needs to refocus when sharing the view.

+1.  In a group setting it's just so much easier if everyone has 20/20 vision - either naturally or corrected.  I (as an eyeglass wearer) have an additional complication - there's times/configurations where my scopes don't have enough focus range to even WORK for me naked eye - my uncorrected vision is 20/220 in my left eye and 20/240 in my right.  I'm over half way to legally blind without glasses.

 

Going back to the bifocal topic - since I hate them I have two pairs of glasses - one for everything beyond 5 feet or so, and another for more close up work (single vision lenses, basically the "bifocal" on an entire lens).

 

But my "near field" glasses still don't work so well for telescopes, let alone sharing in a session.  BUT, with my "regular" glasses I see everything about 40% smaller than everyone else.  People say "Jupiter was the size of a nickel" and to me it's the size of a pea...

 

When I got my single visions I was amazed at how much bigger things (within 5 feet or so) looked.

 

So I'm planning on getting a THIRD set somewhere in between someday (but in terms of telescope sharing I'll still stick with my "regular" glasses...).

 

I'm planning on having an optometrist make me a THIRD set ranging somewhere between the two.


Edited by Hwunkzeep, 24 February 2024 - 10:50 PM.


#15 Hwunkzeep

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Posted 24 February 2024 - 10:53 PM

One of little group that used to observe together included a guy with severely wild focusing needs. As we moved between telescopes sharing views we would always make him wait to look last.  wink.gif

If I wasn't wearing my glasses I'd be that guy.  But worse, as I posted here my uncorrected vision is so bad there's lot's of configurations that I can't even use at ALL due to lack of focuser range.  I'm talking Dobs here though, I'm thinking if I want to get into viewing without glasses I probably need to get into refractors...


Edited by Hwunkzeep, 24 February 2024 - 10:54 PM.


#16 CHASLX200

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Posted 25 February 2024 - 02:42 AM

When wearing bifocals bottom for reading top for distance when looking through telescope what should you look with top or bottom..thanks

I can't use them for anything but reading.




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