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Old 11-11-2020, 07:29 PM
Hans Tucker (Hans)
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Eyepieces and Glasses

Stupid question time ... but ... for those that have transitioned to wearing glasses later in life .. has this affected your selection of eyepieces particularly the Focal Length selection. Eyepieces that you may have purchased and been your favourite pre glasses era are now no longer preferred. Have you had to revamp your collection to accommodate your decline in sight. I don't wear glasses for viewing through a telescope .. only reading and computer based activities. Previously I would used eyepieces in the shorter FL below 10mm but now I find it difficult.
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Old 12-11-2020, 02:53 AM
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wavelandscott (Scott)
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Yes and no...yes, I find some eyepieces less enjoyable (although still usable) but no in that I have had a number of long eye relief (glasses friendly) Pentax XW for some time and I still find them enjoyable even in my evolving sometimes glasses wearing state of being.
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Old 12-11-2020, 04:03 AM
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I also use glasses at the computer and reading (slightly different script because of distance to viewing object). I also need glasses for star charts at the telescope but prefer not to view through an eyepiece with glasses on, even through long eye relief eyepieces. I also need to take them off when viewing the sky unaided.

My astigmatism is mild so I can get away without glasses at higher powers and smaller exit pupils but if that changes I may have to use glasses at the telescope (or Dioptrx) but my preference is still to observe without glasses when possible.

Long eye relief (20mm eye relief) eyepieces are available in short focal lengths from a number of suppliers. Tele Vue now has Delos and DeLite and used to have Radians which I have down to 3mm focal length. The Radians make for very comfortable viewing with or without glasses as Im sure the Delos and DeLite would do to.

I once compared a 6mm Radian, 6mm Clave Plossl, 6mm Brandon and each time I swapped out the eyepiece I thought that I could see more detail (if seeing were better perhaps the difference in detail seen would be more obvious), but I did preferred viewing with the Radian because it was so comfortable with the 20mm eye relief (no glasses). I usually leave the click stop on the Radian all the way down or up one or two clicks at the most.

I can still view through the 6mm Clave and Brandon but they often stay in their case in favour of the Nagler 6-3mm and 4-2mm zooms. These have 10mm eye relief and 50deg apparent field and variable focal length which is all just about perfect for viewing planets (tracking preferred and no glasses).
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Old 19-11-2020, 05:18 AM
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Quote:
Originally Posted by Hans Tucker View Post
Stupid question time ... but ... for those that have transitioned to wearing glasses later in life .. has this affected your selection of eyepieces particularly the Focal Length selection. Eyepieces that you may have purchased and been your favourite pre glasses era are now no longer preferred. Have you had to revamp your collection to accommodate your decline in sight. I don't wear glasses for viewing through a telescope .. only reading and computer based activities. Previously I would used eyepieces in the shorter FL below 10mm but now I find it difficult.
Yes, due to increasing astigmatism, I've had to sell my beloved 21, 17, and 13mm Ethos and replace them with long eye relief eyepieces:
30mm APM Ultra Flat field
22mm Tele Vue Nagler
17.5mm Baader Morpheus
14mm Baader Morpheus
12.5mm APM Hi-FW
11mm TeleVue Apollo 11
But, fortunately, I can still observe from 10mm down without glasses, so kept the 10, 8, 6, 4.7, and 3.7mm Ethos eyepieces.
If they end up getting replaced in the near future, I'll replace them with Baader Morpheus or TeleVue Delos or Pentax XW eyepieces.
I think the 12.5mm eyepiece will soon leave my collection, but the others are staying. All the above except the Ethos eyepieces are compatible with glasses.
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Old 19-11-2020, 06:12 AM
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I have to wear glasses while observing with longer focal lengths (15mm+) due to astigmatism. Also I wear a transitional glasses for long vision and reading. They are almost unusable for observing so I have to switch to non-transitional glasses. And because of glasses I need at least 16mm of usable eye relief on a eyepiece. "Usable eye relief" = from the very top of the rim and not from the eye lens (this is the one makers specify). So choosing eyepiece is difficult.

If you don't have astigmatism or it's very minor then you might not need eyeglasses with eyepieces.

To identify what max exit pupil you can use for observing without being affected by astigmatism you need to use the following formula:

Max Exit Pupil = SQRT (2.3 / Cylinder)

Where Cylinder is a positive value of your "Cylinders" in diopters from your eyeglass prescription.

In my case:
My cylinders: -0.75D (while my eyesight is -6.5D)
Max Exit Pupil = 1.75mm = SQRT (2.3/0.75)

If I have 100ED f9 then it's 15.8mm eyepiece. Which is pretty much true. I need glasses if I'm using any eyepieces longer than 15mm and don't need glasses if shorter than 15mm.
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Old 19-11-2020, 07:51 AM
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Tele Vue has this chart:
Attached Thumbnails
Click for full-size image (DioptrixAstigmatismVis.gif)
14.7 KB20 views
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Old 19-11-2020, 08:59 AM
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They've got quite "relaxed" graph I'd say. With my -0.75D the graph says I shouldn't see astigmatism with my 24mm (2.67mm EP) without glasses, but I clearly see it even with my 18mm (2mm EP) and it disappears with my 13mm (1.44mm EP). So I suspect that the formula is more correct than the graph.
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Old 19-11-2020, 10:14 AM
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There is a difference between detecting astigmatism and seeing astigmatism in the in-focus image.

For example, I can detect astigmatism in the eyepiece down to 5mm (0.9mm exit pupil) by defocusing a star on both sides of focus, looking for ovality in the star, and evaluating for a 90 change in orientation from one side of focus to another.

But I do not really see astigmatism in a focused star image in a 10mm eyepiece (1.7mm exit pupil), but I do in a 12.5mm eyepiece (2.2mm exit pupil).

I have 1.0 diopter of astigmatism, so their chart predicts I will see astigmatism above a 11.5mm focal length (2mm exit pupil).
Your formula suggests I would see it at an exit pupil of 1.5mm and larger.

I can see it in an out of focus star image at a smaller exit pupil than that, but don't see it in an in-focus star image at that exit pupil.

I recognize that if it is even detectable in an out of focus star image on either side of focus, it is affecting the in-focus star image in a deleterious manner, but if you see the star as a point with a single diffraction ring around it, how badly could it be damaging the star images?
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Old 19-11-2020, 01:13 PM
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I'm talking about seeing astigmatism without eyeglasses and in the in-focus image.

YMMV I guess. We all have different eyes and eye conditions at the end. Personally for me I've found the formula is much close to what I see in real life than the graph. I cannot test exactly as I do not have 15mm eyepiece - only 13mm and 18mm ones.

Also it's a bit difficult to judge by the graph as diopters are not linear on the X axis. Where is exactly 0.75?
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