53 replies to this topic

[Captain Quark]

My astigmatism is -1.75 in my viewing eye and -1.25 in the other. Any thoughts?

Here’s a chart at televue showing that a bit over 1mm exit pupil is your cutoff for 1.75.
https://www.televue....=54&Tab=_Choose

A 7mm eyepiece is a 1mm exit pupil in your f7 scope. I’m picky about my astigmatism and always use glasses at greater than my cutoff point. And then I’m picky about my glasses not mashing into the cup. Maybe you are or are not.

 

The APM UFF 24mm is supposedly good with glasses (haven’t tried it). It’s over $100, but not by a lot. If I had your scope I would want something in the 12-14mm range. I don’t know anything about $100 eyepieces and glasses in that range. At 7mm, you won’t have to use glasses.

 

The recommended spec for glasses is around 20mm eye relief, but the frustrating thing about that is manufacturers’ listed specs are often not accurate or don’t take into account how much distance is eaten up by the metal sticking up above the glass.

[B 26354]

For observation with the telescope, I purchased a pair of glasses that have distance and astigmatism correction for the entire lens (not progressive or bifocal). Is this what you mean by "standard" infinity-focus lenses?

 

My astigmatism is -1.75 in my viewing eye and -1.25 in the other. I have been told at a very small exit pupil, astigmatism disappears and glasses may not be needed for that 1 or 2 pieces?

Yep, that's what I meant... and after re-reading your post #5, I realized that you already had them.  

 

And it's also true about (possibly) not needing to wear your glasses when using short-focal-length (small exit-pupil) eyepieces. The exit pupil sizes that work, will depend on how severe your astigmatism is... so there's no way to definitively say what will or will not work, specifically for you.

 

As far as choosing a set of focal lengths is concerned... you've already gotten a lot of good advice. My Stellarvue SV080SD refractor is essentially identical to your AT-80EDL... and I now have seven eyepieces that range from 50mm to 4.7mm, with no duplicate focal lengths. If you have no eyepieces at all... I'd start with four single-focal-length ones: a 30-40, a 20-25, a 10-12, and a 4-6.

 

For four decades, my 1977 C8 was my only scope. I had four eyepieces for it: a 40, a 25, a 10 and a 6... and I succeccfully completed two Messier Marathons with that "meager" setup.

 

Edited by B 26354, 30 October 2024 - 07:09 PM.

[Nightskyman]

Thanks for all the input, I feel more prepared with what needs to be included when
considering sizes and the specifications that matter when choosing an eyepiece.

If I was willing to up my budget slightly, say up to around $150, would that open the
door to any additional recommendations?

Which focal length eyepieces should be wider than others. What sizes would say 60 degrees
be more acceptable if any?

When someone says “this or that eyepiece should work well with your scope” or probably
won’t work well, what do they mean and what determines that a particular eyepiece
would or would not work well with a specific scope? Is it a size, a style, a brand,
or something else? For that matter, what should you look for in an eyepiece?

I also want to thank everyone for taking some of your time to help with my questions
as your experience is invaluable to those of us just getting started on our journey.
For me, it is later in life but I guess better late than ever!

Edited by Nightskyman, 31 October 2024 - 10:29 PM.

[Oldfracguy]

For observation with the telescope I purchased a pair of glasses that have distance and astigmatism correction for the entire lens (not progressive or bifocal) is this what you mean by "standard" infinity-focus lenses? My astigmatism is -1.75 in my viewing eye and -1.25 in the other. I have been told at a very small exit pupil astigmatism disappears and glasses

may not be needed for that 1 or 2 pieces?

I am very nearsighted, and take my glasses off when looking in the telescope eyepiece, no matter if it happens to be a 1.25" 5mm Orthoscopic or a 2" 40mm eyepiece.  You just have to adjust the focuser a bit compared to where it would be with your glasses on.  Another thing I do is to use magnifying finder scopes that are focusable.  I adjust the focus by rotating the front objective lens so I can see clearly through the finder scope with my glasses off.  That way I can move from the finder to the main telescope eyepiece and back with ease.

Edited by Oldfracguy, 31 October 2024 - 10:45 PM.

[SeattleScott]

Wider AFOV is helpful for high power on manual scopes because it gives more drift time. Wider AFOV can be helpful with any scope, at any magnification, in order to frame extended objects. That being said, most objects are small and don’t require a wide view for framing.

Generally you want eyepieces that will provide around 5-6mm exit pupil at low power, and down to 0.5mm at high power. (Or 300x magnification, possibly more depending on your seeing conditions and aperture). Exit pupil is the focal length of the eyepiece divided by the F ratio of the telescope.

Cheap wide AFOV eyepieces typically don’t work great with F5 scopes. However Plossls are cheap and work fine at F5. They just aren’t wide.

Scott

[Max Headroom]

How do you "copy" portions of somebody's previous post as others above have done so that I may respond directly to the person's question?

Use the quote button

[Starman1]

I am relatively new to this hobby and would like a basic understanding of
choosing appropriate eyepieces suited for my telescope. I am using an
AT-80EDL refractor on a Skywatcher AZ5. I am interested in viewing the moon,
planets, doubles, and clusters. I read that eyepiece selection needs to
take into account the scope you are using. My 80mm scope has a focal length
of 560 and a f7 ratio.

1. Can anyone explain what type of eye pieces should
I be looking at and why?

2.What focal lengths should I be considering
and why? I do have a 2x Barlow. I am inquiring more in general, not necessarily
for brand recommendations at this point.

3. If price affects your answers,
I would like to spend up to about $100 per eyepiece which I realize is
likely considered budget or low end.

I numbered the points above.

1. Just about all eyepieces will work OK in your scope.  Since it has a 2" focuser and you are probably using a 2" diagonal, my suggestions are for at least the lowest power eyepiece to be a 2" eyepiece because the maximum

field 2" eyepieces yield a significantly larger true field than 1.25" eyepieces.  Apparent Field determines how wide the true field is at any given power, so if you'd like wider true fields, then wider apparent fields would be preferable.

How wide?  That's up to you and related to your own personal experiences.  If all your eyepieces are 50°, getting one 70° eyepiece to try would quickly tell you if you prefer wider true fields at any given power.

 

2. It depends how much you have to spend.

With an 80mm scope, a set of 25x/50x/75x/100x/125x/150x would be considered a fairly complete set.

Since you have a 2X Barlow, that reduces the need to 25x/50x/75x/125x eyepieces.

Since eyepiece focal length = telescope focal length / magnification, that is eyepieces of 22mm, 11mm, 7.5mm, and 4.5mm.

Since not all eyepieces come in every possible focal length, a +/-1mm on each focal length would be fine.

The 22mm can be a 2" eyepiece, and I can recommend this one:

https://astromaniaop...ariantsId=10092

It is a far better eyepiece than its price suggests.  It won't work with your Barlow, but you wouldn't be Barlowing your lowest power eyepiece anyway.

 

3. You wear glasses, so you need eyepieces capable of being used with glasses, which means at least 15mm of Effective eye relief from the rubber eyecup.

Since most eyepieces have their eye lenses recessed into the body of the eyepiece an average of 5mm, that means you should look for eyepieces having 20mm of design eye relief (design eye relief is what is quoted as eye relief on eyepieces, usually).

So you are looking for long eye relief eyepieces.  That will rule out a lot of inexpensive eyepieces, but they're there if you research it.

[Oldfracguy]

I think the OP mentioned somewhere in one CN thread or another that he uses an Astro-Tech AT1D 1.25" Dielectric Mirror Diagonal with his AT80EDL.

[Starman1]

I think the OP mentioned somewhere in one CN thread or another that he uses an Astro-Tech AT1D 1.25" Dielectric Mirror Diagonal with his AT80EDL.

Well, if he's reading this, the maximum field of view is probably OK with 1.25" eyepieces.

In which case the aforementioned 24mm Ultra Flat Field would be nearly ideal--widest 1.25" field, glasses-compatible, can be obtained for $137 under the Sky Rover name on Ali Express.

True field with that eyepiece: 2.82°, which is actually a bit more than the 22mm 70° SWA I was suggesting earlier.

Good catch.

[Nightskyman]

I think the OP mentioned somewhere in one CN thread or another that he uses an Astro-Tech AT1D 1.25" Dielectric Mirror Diagonal with his AT80EDL.

Yes, it is an Astro-Tech AT1D 1.25" Dielectric Mirror Diagonal

[Nightskyman]

Well, if he's reading this, the maximum field of view is probably OK with 1.25" eyepieces.

In which case the aforementioned 24mm Ultra Flat Field would be nearly ideal--widest 1.25" field, glasses-compatible, can be obtained for $137 under the Sky Rover name on Ali Express.

True field with that eyepiece: 2.82°, which is actually a bit more than the 22mm 70° SWA I was suggesting earlier.

Good catch.

That is correct, and thanks for the great advice and recommendations! I continue to look forward to any input of and all of the great 

insights that keeps coming from the seasoned observers, especially as it pertains to my specific scope.

Edited by Nightskyman, 03 November 2024 - 05:10 PM.

[Nightskyman]

Are there any thoughts on the Astro-Tech UWA 82° 1.25" eyepieces that are available in
in 4mm, 7mm, 13mm and 16mm? Yes they are UWA but otherwise how do they compare to the
Paradigms?

Edited by Nightskyman, 04 November 2024 - 06:51 PM.

[Starman1]

Are there any thoughts on the Astro-Tech UWA 82° 1.25" eyepieces that are available in
in 4mm, 7mm, 13mm and 16mm? Yes they are UWA but otherwise how do they compare to the
Paradigms?

PM sent.

[Tony Flanders]

Which focal length eyepieces should be wider than others. What sizes would say 60 degrees
be more acceptable if any?

People's tastes differ considerably with respect to apparent field of view. I find 60 degrees to be wonderful in any focal length, and more than 70 to be annoyingly wide. Other people, obviously, feel differently.

In general the benefits of a wide apparent field of view are arguably biggest at the longest and shortest focal lengths that you use.

At the long (low power) end of the spectrum, the size of your eyes' fully dilated pupils limits the longest focal length that you can use while still taking full advantage of the telescope's aperture. For instance, my pupils open a smidge narrower than 5 mm. That means that the longest focal length eyepiece I can use in an f/6 scope is 30 mm, because 30/6 = 5. If I use, say, a 42-mm eyepiece in that scope, it delivers an exit pupil of 42/6 ~= 7 mm, and have of the light collected by the scope falls on the iris rather than the lens. Many young people have pupils 7 mm wide, in which case they can use the 42-mm eyepiece with no light loss. But even they can't use a 50-mm eyepiece.

Given my 5-mm pupils, the only way for me to get a wider true field of view without "wasting light" is to get a 30-mm eyepiece with a wider apparent field of view. So I'm seriously contemplating buying a 30-mm eyepiece with a 70-degree apparent field of view despite the fact that I find a 65- or 60-degree field of view more comfortable and convenient.

As for the high-power end of the spectrum, if you're using a telescope without motor drive, objects drift out of the field of view alarmingly quickly at 200X and higher. The wider the eyepiece's apparent field of view, the less often you have to re-position the scope.

[Dave Mitsky]

Are there any thoughts on the Astro-Tech UWA 82° 1.25" eyepieces that are available in
in 4mm, 7mm, 13mm and 16mm? Yes they are UWA but otherwise how do they compare to the
Paradigms?

The A-T UWA eyepieces are not known for their ample eye relief so wearing prescription eyeglasses to correct for astigmatism will be a problem.  You might not need to wear your glasses with the shorter focal length UWAs, however.

[WillR]

Are there any thoughts on the Astro-Tech UWA 82° 1.25" eyepieces that are available in
in 4mm, 7mm, 13mm and 16mm? Yes they are UWA but otherwise how do they compare to the
Paradigms?

Better, IMO. I had the paradigms and upgraded to the Astro-Tech UWA.  I have the 7mm and 10mm. But the big incentive was the UWA, 82° vs. 60°. That's a big difference, especially with the shorter focal lengths. You want to keep things in the FOV as long as possible.

 

Edit. I forgot you wear glasses. The eye relief may not be enough for you, especially to get the maximum FOV.

Edited by WillR, 04 November 2024 - 09:52 PM.

[Nightskyman]

I am considering the 4mm and 7mm Astro-Tech UWA eyepieces since with my f/7 scope
they both would yield an exit pupil of 1mm or less and according to the earlier
referenced charts, with my astigmatism, I could view an exit pupil of 1mm or less
without glasses. Am I correct in my thinking or am I not understanding it correctly?
Maybe the 10mm with a 2x Barlow as well since it would increase the eye relief. For
low power, the 24mm UFF mentioned above seems like a good choice. If I go this
direction, is there any downside to having all eyepieces being wide fields?

Edited by Nightskyman, 05 November 2024 - 03:23 AM.

[Oldfracguy]

I am considering the 4mm and 7mm Astro-Tech UWA eyepieces since with my f/7 scope
they both would yield an exit pupil of 1mm or less and according to the earlier
referenced charts, with my astigmatism, I could view an exit pupil of 1mm or less
without glasses. Am I correct in my thinking or am I not understanding it correctly?
Maybe the 10mm with a 2x Barlow as well since it would increase the eye relief. For
low power, the 24mm UFF mentioned above seems like a good choice. If I go this
direction, is there any downside to having all eyepieces being wide fields?

It is true you can view without your glasses on at higher magnifications using 7 mm and shorter focal length eyepieces, or a combination of a 2x Barlow and longer focal length eyepiece, so that Exit Pupil is 1 mm and smaller.  However, the only way for you to learn how small an Exit Pupil you will be able to work with is by trying things out.  It is entirely within the capability of your AT80EDL to go over 200x magnification, which would result from using a 2.5 mm focal length eyepiece. But, in many cases, when the Exit Pupil gets smaller than a certain level--and it varies from one person to the next--a person's own eye imperfections start to become noticeable.  For example, at small Exit Pupils some people start to see spots and floaters that degrade the image.  In those cases they either have to a) put up with them; or b) use a lower magnification to get a larger Exit Pupil.

 

There really is no downside to having all wide-field eyepieces, except for one possible exception.  They have been a real asset for many observers since their development.  Advantages include longer Eye Relief so they are easier to look through, and the wider field allow you to watch a target move across the field of view without having to adjust the telescope's position controls as often with a manual Alt-Az or GEM mount.  Modern wide-angle eyepieces can be just as sharp as the older Plossl and Orthoscopic eyepieces, and so much more confotable to use.  The one aspect of these wide-angle 82° AFOV eyepieces that some people do not like is that is can be difficult to see the edge of the field of view.  Some people just prefer a smaller AFOV, such as 70° or less, because they can see the field stop that encircles the entire field of view in the eyepiece.  It all boils down to personal preference.

Edited by Oldfracguy, 05 November 2024 - 10:48 AM.

[SeattleScott]

If you don’t mind mixed and matching, the 7 Luminos is a better gap filler than the 7 UWA. You are trying to fill a gap between 4 and 10. The 7UWA is closer to 8mm, nearly double the 4mm. By comparison, the 7 Luminos is about 6.6mm. 6.6 is 65% more than 4mm. And 10mm is 52% more than 6.6mm. A 6.3mm would be precisely in the middle. The Luminos comes much closer, and has better correction at the edge of the field (per Ernest’s tests).

It is a bit wider/heavier, and generally wouldn’t aesthetically match the AT UWA series. And the Luminos are usually a bit more expensive. But if you don’t mind paying a small premium and mixing and matching, technically it is a better fit.

[Starman1]

The Luminos is available in a smaller format with other labels, like:

https://astromaniaop...ariantsId=10072

It's still larger than the UWAs from KUO (Astrotech, Sky Rover, etc.), but smaller and lighter than the Luminos.

[Tony Flanders]

There really is no downside to having all wide-field eyepieces, except for one possible exception. They have been a real asset for many observers since their development.  Advantages include longer eye relief ...

Long eye relief is an entirely separate issue. There are plenty of eyepieces with long eye relief and relatively narrow fields of view. For instance, my 4-mm Vixen Lanthanum has 20 mm of eye relief and a 45-degree AFOV. Conversely, there are plenty of wide-field eyepieces with short eye relief. In fact I have never found any eyepiece with an AFOV bigger than 70 degrees that I can use while wearing glasses. Short eye relief is one of the main reasons I dislike ultrawides.

Three other important disadvantages are high cost, large physical size, and weight.
 

The one aspect of these wide-angle 82° AFOV eyepieces that some people do not like is that is can be difficult to see the edge of the field of view.

To clarify this, there are two practical problems with being unable to see the field stop, over and above my aesthetic issues. When observing a faint deep-sky object near a bright star, it's very advantageous to put the star out of the field of view. That's a lot less fun if you have to strain to see the DSO because it's so far from the center of the field.

Also, I routinely estimate objects' sizes by comparing them to the eyepiece's field of view. That's tough if you can't see the whole field stop.

 

Just to be fair, ultrawide eyepieces do also have some pretty important benefits. I find them particularly useful for observing the major globular clusters in big Dobs. That's a case where you really, really want the whole thing to fit in the field of view, but also want enough magnification to show faint stars. It's a challenging balancing act, and ultrawide eyepieces can help a lot.

[Starman1]

Long eye relief is an entirely separate issue. There are plenty of eyepieces with long eye relief and relatively narrow fields of view. For instance, my 4-mm Vixen Lanthanum has 20 mm of eye relief and a 45-degree AFOV. Conversely, there are plenty of wide-field eyepieces with short eye relief. In fact I have never found any eyepiece with an AFOV bigger than 70 degrees that I can use while wearing glasses. Short eye relief is one of the main reasons I dislike ultrawides.

Three other important disadvantages are high cost, large physical size, and weight.
 

To clarify this, there are two practical problems with being unable to see the field stop, over and above my aesthetic issues. When observing a faint deep-sky object near a bright star, it's very advantageous to put the star out of the field of view. That's a lot less fun if you have to strain to see the DSO because it's so far from the center of the field.

Also, I routinely estimate objects' sizes by comparing them to the eyepiece's field of view. That's tough if you can't see the whole field stop.

 

Just to be fair, ultrawide eyepieces do also have some pretty important benefits. I find them particularly useful for observing the major globular clusters in big Dobs. That's a case where you really, really want the whole thing to fit in the field of view, but also want enough magnification to show faint stars. It's a challenging balancing act, and ultrawide eyepieces can help a lot.

Suggestions to try:

Baader Morpheus eyepieces--usable with glasses and ultrawide fields(4.5-14mm are 78-79°, 17.5mm is 72°) and lightweight.

Explore Scientific 92° eyepieces--usable with glasses and ultrawide+ fields   Very heavy, though.

[Nightskyman]

I’m thinking I may have missed something that I should have asked about first. My areas of interest are planets,, double stars, and a few particular stars, but I also am interested in clusters and nebula as well. Should I be using the wide fields with the lower powers on the clusters and nebula but not necessarily for the higher powers used for planets and doubles?

[Dave Mitsky]

I’m thinking I may have missed something that I should have asked about first. My areas of interest are planets,, double stars, and a few particular stars, but I also am interested in clusters and nebula as well. Should I be using the wide fields with the lower powers on the clusters and nebula but not necessarily for the higher powers used for planets and doubles?

There are relatively few large deep sky objects and thousands upon thousands that are small.

I typically employ magnifications similar to the ones I use for observing the planets on many star clusters, especially globular clusters. 

 

Planetary nebulae for the most part are rather tiny in apparent size.  I've observed several of those with high surface brightnesses at over 1000x through large aperture telescopes.

[Starman1]

I’m thinking I may have missed something that I should have asked about first. My areas of interest are planets,, double stars, and a few particular stars, but I also am interested in clusters and nebula as well. Should I be using the wide fields with the lower powers on the clusters and nebula but not necessarily for the higher powers used for planets and doubles?

Correct.

Planets, Moon details, planetary nebulae, and double stars, are the smallest objects you will view in a telescope.

To see them well requires that you use higher powers.

Nebulae are typically faint and large, and require lower powers to see them well (and usually nebulae filters as well).

Star clusters range in size from huge (Pleiades=low powers), to very small (small globular clusters = higher powers).

 

Objects vary in size a lot, which is one of the reasons you need to have a variety of eyepieces in your kit.

The objects I've observed range from < 2" to 4°.  Needless to say, the magnification appropriate for the first is not the same as the magnification appropriate for the latter.

In the scopes and binoculars I've used, I've used a range from 7x to 1050x, so you can see that magnifications should suit the objects and the details you want to see in them.

 

Take a Planetary like the Saturn Nebula, NGC7009, in Aquarius.  It's easily visible at 100x and is bright and stands out well from the background sky.

But the details in the nebula become apparent around 400x, and it displays an almost photographic image at 500+x if you have the aperture, the seeing conditions, and the sky darkness to see them.

The point is that the magnification required to see the object may not be the magnification needed to actually observe the object well.

Jupiter's 4 Galilean moons can be seen in 7x binoculars.  But it takes 150-200x to see details on the surface of Jupiter, and 400-500x to see the moons as discs of different sizes, with different colors.

So experimentation in magnification is desirable, to see where you get the best view.

 

How far apart the magnifications can be is pretty much related to the aperture of the scope.

In a 25", having magnifications 100x apart can work.  In an 80mm scope, having magnifications 25-30x apart can work.

Wide fields aren't necessary for high powered views of small objects IF the scope's mount tracks.

But if the scope doesn't track, wider fields are advantageous for high powers so you get more time to observe the object before it drifts out of the field.

It's the reason I find a 70° field fine at 60x in my 12.5", but use a 110° eyepiece at 500x.

Edited by Starman1, 06 November 2024 - 04:58 PM.