53 replies to this topic

[Nightskyman]

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

[Nightskyman]

Sorry, I didn’t realize asking a lot of questions means you can no longer be considered new.
I thought experience comes from doing. My questions are to learn and I thought that was the
point of the forums. Considering the years that many here have spent in the hobby is
Why I respectfully consider myself relatively new.

Edited by Nightskyman, 30 October 2024 - 01:11 AM.

[havasman]

Yes, your scope is to be considered when you choose eyepieces. So should your observing locale with particular attention to typical conditions ranging from light pollution to jet stream influence. What you plan to and/or like to observe factors in strongly too.

 

I had an AT80ED out in good rural darkness last July showing a small group of inexperienced observers prominent open and globular clusters, galaxies, nebulae and colored and double stars. I had a complete compact kit that included 13, 5, & 3.5mm T6 Naglers, an Astro-Tech 7mm UWA and an ES68 24mm eyepieces. All our observing was well supported by the ES68 widefield, the 13T6 and the A-T 7mm. We just didn't need any others and all my guest observers saw all the objects easily. The next day I set the scope up with Herschel wedge for some white light solar observing and used only the 7mm.

 

What I recommend for you are an Astro-Tech UWA 7mm and 13mm. Each is $99 and they will be extremely useful for most of your observing, providing very fine images in a comfortably wide field. All you need beyond that pair is a good widefield ep to match the strongest capability of your scope. Despite blowing right by your budget limits I suggest you consider the $199 A-T UWA 28mm that is so highly thought of by some respected, experienced members here. That set has such a logical spread of focal lengths it would almost certainly remain useful in most second scopes you may choose in the future and are definitely a lifetime kit in your AT80EDL.

 

some simple arithmetic that should illuminate much about eyepieces for you - 

 

MAGNIFICATION  =  SCOPE FOCAL LENGTH / EYEPIECE FOCAL LENGTH

EXIT PUPIL  =  EYEPIECE FOCAL LENGTH / SCOPE FOCAL RATIO

TRUE FIELD OF VIEW  = (EYEPIECE FIELD STOP DIAMETER / SCOPE FOCAL LENGTH) * 57.3                 note here that AFOV is NOT part of the most accurate TFOV calculation

 

eyepiece field stop diameters can be found here  -  https://www.cloudyni...e-buyers-guide/

Edited by havasman, 30 October 2024 - 01:24 AM.

[B 26354]

Sorry, I didn’t realize asking a lot of questions means you can no longer be considered new.
I thought experience comes from doing. My questions are to learn, and I thought that was the point of the forums. Considering the years that many here have spent in the hobby is Why I respectfully consider myself relatively new.

It is. Please never stop asking questions.

 

I've been a dedicated DSO visual observer for seventy years. But I only started trying to take astrophotos seven years ago... and I still consider myself to be relatively new at that aspect.

 

And thank you. Those of us who've spent decades pursuing this wonderful hobby, appreciate your respect.

[Nightskyman]

I do wear progressive eyeglasses but based off of a recommendation from Starman1 for
observing, I use a pair that has only distance correction. I somewhat understand wearing
eyeglasses requires more eye relief, what is the minimal amount that I should look for and
how does exit pupil factor in as well?

Edited by Nightskyman, 30 October 2024 - 07:25 AM.

[havasman]

I do wear progressive eyeglasses but based off of a recommendation from Starman, for
observing, I use a pair that has only distance correction. I somewhat understand wearing
eyeglasses requires more eye relief, what is the minimal amount that I should look for and
how does exit pupil factor in as well?

This too is a very important consideration. All of the ep's I recommended are spec'd at only 12mm ER and that's probably a bit tight for glasses wearers but some can get away with 12mm. It has to do with face shapes. I think I'll let others suggest LER units. I don't use them. There are A LOT of very good ep's out there and a bunch of them are in your price range. You'll be fine.

[Jon Isaacs]

Sorry, I didn’t realize asking a lot of questions means you can no longer be considered new.
I thought experience comes from doing. My questions are to learn and I thought that was the
point of the forums. Considering the years that many here have spent in the hobby is
Why I respectfully consider myself relatively new.

 

 As far as I'm concerned, the number of posts you have is irrelevant. What's important is that you are asking questions that are "beginner's questions." 

 

I had an 80 mm F/7 apo for about 15 years. Now I have a 90 mm F/6.2, same focal length.

 

You to an buy some good quality eyepieces for $100 or less. I like the Astro-Tech Paradigm series, I have the full set except the 15 mm. The 25:mm and 18 mm are not as sharp at the edge of the field as the others but they're still enjoyable. The 5 mm, 8 mm and 12 mm are the best. With your 2x Barlow, they could be the  core of your set. Do you have a 1.25 inch or a 2 inch diagonal?

 

Jon

[Mike Q]

So a 80mm scope will max out around 160x, maybe 200x.  Your skies in Pa are probably like most mid western states and will limit you to 200x most nights.  I would have a 3mm as my max mag eyepiece and a 25mm at the low end.  You can fill in between  as you see fit.  I would use a 2mm spread so for me it would be 3, 5, 7.......down to 25mm.  While i have barlows i rarely use them as the midwest is so seeing limited.

 

I will definitely second the astro tech paradigm line.  At 65 bucks a pop they are a steal.  

[Razz]

Ok, I get it and can share info to help,,

But how can you be "new" and have over 500 posts?

Instead of making a pointless comment, why don't you just share the info you have to help the OP? 

[Nightskyman]

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?

[SeattleScott]

Celestron Xcel LX have just enough eye relief for most glasses wearers and fit your budget. The 25, 9 and 7 (6.5) are particularly well regarded.

Amazon had some Vixen SLVs on sale for $90. Not sure if that’s still the case.

A vixen 30mm NPL would work nicely for low power and be affordable.

Eyepieces around 13mm, 7mm and 4mm would round things out nicely.

[kathyastro]

What focal lengths should I be considering and why?

As a general rule of thumb, you should be looking at focal lengths from 1x to 7x the focal ratio of your scope.  So, with an f/7 scope, you would look for eyepieces in the 7mm to 49mm range.

 

Most people find that they can push those limits a bit.  So it is common to have an eyepiece (or eyepiece + barlow combination) that has half the focal length of the rule of thumb.  In your case, that would be 3.5mm.

 

At the short focal length (high magnification) end, you are running up against the optical limits of your scope.  Shorter focal lengths (i.e. more magnification) will not show more detail, because the details start to get blurry with too much magnification.  More magnification also makes the image darker, because you have the same number of photons spread out over a large apparent field of view.  And if the exit pupil is too small (magnification is too high), the tight beam of light will highlight any "floaters" in your eye, which is annoying.

 

At the long focal length (low magnification) end, the exit pupil of the scope/eyepiece combination becomes larger than the pupil of your eye.  (The rule of thumb number of 7x is based on an average dark-adapted pupil size of 7mm, but that gets smaller as you age.)  At longer focal lengths, some of the light will not enter your eye, and you will lose one of the main advantages of lower magnification.

Edited by kathyastro, 30 October 2024 - 07:57 AM.

[WillR]

This too is a very important consideration. All of the ep's I recommended are spec'd at only 12mm ER and that's probably a bit tight for glasses wearers but some can get away with 12mm. It has to do with face shapes. I think I'll let others suggest LER units. I don't use them. There are A LOT of very good ep's out there and a bunch of them are in your price range. You'll be fine.

A couple of things. To quote another poster, there is a quote button on the lower right of their post. You’ll get a box in your reply like the one above.

 

Have you tried focusing with your glasses off? Do you have an astigmatism? I was very nearsighted (I have since had cataract surgery) and always observed without my glasses. 
 

For that reason, I can’t tell you which eyepieces have long enough relief. However our sponsor does make a very good line of eyepieces with a wide 82 degree FOV for about $100 each. I have the 7mm and 10mm and they so make a 4mm that would be a good maximum power eyepiece for that scope. But it only has 12mm eye relief.

 

https://astronomics....2-1-25-eyepiece

[Nightskyman]

 As far as I'm concerned, the number of posts you have is irrelevant. What's important is that you are asking questions that are "beginner's questions." 

 

I had an 80 mm F/7 apo for about 15 years. Now I have a 90 mm F/6.2, same focal length.

 

You to an buy some good quality eyepieces for $100 or less. I like the Astro-Tech Paradigm series, I have the full set except the 15 mm. The 25:mm and 18 mm are not as sharp at the edge of the field as the others but they're still enjoyable. The 5 mm, 8 mm and 12 mm are the best. With your 2x Barlow, they could be the  core of your set. Do you have a 1.25 inch or a 2 inch diagonal?

 

Jon

I have an AT-1D 1.25” dielectric diagonal.

[Nightskyman]

A couple of things. To quote another poster, there is a quote button on the lower right of their post. You’ll get a box in your reply like the one above.

 

Have you tried focusing with your glasses off? Do you have an astigmatism? I was very nearsighted (I have since had cataract surgery) and always observed without my glasses. 
 

For that reason, I can’t tell you which eyepieces have long enough relief. However our sponsor does make a very good line of eyepieces with a wide 82 degree FOV for about $100 each. I have the 7mm and 10mm and they so make a 4mm that would be a good maximum power eyepiece for that scope. But it only has 12mm eye relief.

 

https://astronomics....2-1-25-eyepiece

I do have an astigmatism

[B 26354]

I do have an astigmatism

I'm farsighted, and have a moderate astigmatism, so I must wear glasses when using optical instruments. I find that for the most part, I need at least 15mm of eyepiece eye-relief in my scopes and binoculars.

 

About twenty-five years ago, I tried wearing progressive-lensed eyeglasses, and absolutely hated them. For observing with a telescope or binoculars, I would recommend getting a pair of glasses in your prescription that have "standard" infinity-focus lenses.

 

[noisejammer]

I do have an astigmatism

This is when things become a little complicated.

 

Let's start with the idea of exit pupil. In essence, this is the diameter of the beam of light that emerges from the eyepiece. You can calculate it by dividing the eyepiece's focal length by the effective focal ratio of the scope.

 

This means a 10 mm eyepiece used without a Barlow lens would have an exit pupil of 10/7 = 1.4 mm (57x). If you insert a 2x Barlow and use the same eyepiece, the exit pupil is now 10/(2*7) = 0.7 mm (114x).

 

This can be helpful because inexpensive short focal length eyepieces tend to have relatively short eye relief (which makes them difficult to use with glasses) but your astigmatism may be tolerable when you have a small exit pupil. Alternatively, using a Barlow and a longer focal length eyepiece may allow you to use your specs, yielding a well corrected image.

 

I tend to keep my exit pupils between 0.6 mm and 6 mm. This would make your shortest eyepiece 7*0.6mm = 4 mm or (if you use i with a 2x Barlow) 8 mm.

 

Final thought - this is considerably out of your price bracket but TeleVue makes a lens called the Dioptrx which corrects for astigmatism. They can be used with some third party eyepieces.

[Kefka1138]

In addition to the valuable advice shared, if you’re a data enthusiast, creating an eyepiece database can enhance your understanding of your equipment’s capabilities (e.g., below). I find it helps tremendously when identifying gaps in mag and optimizing the overall kit. 

[KBHornblower]

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?

Click on the "Quote" icon in the lower right corner of the post you wish to quote.  That will open a "Reply to this topic" field at the bottom of the page, with the quoted post embedded in it.  Now click in the field below the quote.  That will place your cursor there and you can begin typing your reply.

[Captain Quark]

What’s your astigmatism prescription in your observing eye? At shorter eye piece focal lengths, you don’t see your astigmatism. Mine becomes invisible at a 2mm exit pupil which is a 12mm to 10mm eye piece depending on which scope I’m using.

 

You could get an APM 24mm UFF which would fit your 1.25” diagonal, is supposedly good with glasses, is a good eyepiece, and isn’t a budget buster. Then for your shorter focal length eyepieces, maybe one around 10mm and one around 7mm, if you know the point at which your astigmatism doesn’t matter, you could get eye pieces with shorter eye relief within your budget and view without glasses.

[Dave Mitsky]

The eyepieces in the 60-degree apparent field of view Celestron X-Cel LX line that SeattleScott mentioned may have enough eye relief to be usable.  One of the astronomy clubs of which I am a member has the entire set.  I've used them in a number of different telescopes and find them to be good performers for the price. 

https://astronomics....endor=Celestron

Members of Cloudy Nights get a small discount from Astronomics on non-sale items.

https://www.cloudyni...y_discount.html

[sevenofnine]

Sometimes it's best to actually "see" what focal lengths you like best in your telescope on the objects you like to view. For that, I recommend an inexpensive zoom eyepiece like the SVBONY 7-21. It's a budget favorite on this forum. Best of luck to you! 

 

https://www.amazon.c...254&sr=8-1&th=1.

[Nightskyman]

I'm farsighted, and have a moderate astigmatism, so I must wear glasses when using optical instruments. I find that for the most part, I need at least 15mm of eyepiece eye-relief in my scopes and binoculars.

 

About twenty-five years ago, I tried wearing progressive-lensed eyeglasses, and absolutely hated them. For observing with a telescope or binoculars, I would recommend getting a pair of glasses in your prescription that have "standard" infinity-focus lenses.

 

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?

[Nightskyman]

What’s your astigmatism prescription in your observing eye? At shorter eye piece focal lengths, you don’t see your astigmatism. Mine becomes invisible at a 2mm exit pupil which is a 12mm to 10mm eye piece depending on which scope I’m using.

 

You could get an APM 24mm UFF which would fit your 1.25” diagonal, is supposedly good with glasses, is a good eyepiece, and isn’t a budget buster. Then for your shorter focal length eyepieces, maybe one around 10mm and one around 7mm, if you know the point at which your astigmatism doesn’t matter, you could get eye pieces with shorter eye relief within your budget and view without glasses.

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

[vtornado]

Astigmatism is subjective.

 

I have roughly .75 dipoters of of astig in my viewing eye.   I can notice it around a 4mm exit pupil.  If I am just bouncing around I can live with it.  If I want the best stars possible for a prolonged view I put the glasses on.

 

Here is  chart from televue regarding astigmatism.

 

https://www.televue....=54&Tab=_Choose

 

My resistance to glasses is that they allow stray light to leak in from the sides and that diminishes the view.  I have AR coatings on them, but they still seem to scatter light.

Edited by vtornado, 30 October 2024 - 06:22 PM.