25 replies to this topic

[twilliams8187]

I'm looking for suggestions for my first 2" eyepiece.  I have a 8" Meade LX200 GPS. Recently ordered a 2" diagonal from High Point Scientific.  My current mish-mash of eyepieces:

 

Manufacturer Type              FL  2000mm FL X
OMCON        Plossl            32         63
Meade        Plossl            26         77
Sirius       Plossl            20        100
Meade        Super Plossl      15        133
Meade        Illuminated Ret.  12        167
Unknown      Kellner           10        200
Meade        Super Plossl     6.4        313

 

Eventually I plan on adding a 10" or larger Dobsonian to my telescope collection.  I'd like to eventually switch to using 2" eyepieces exclusively but, as we know, it's an expensive undertaking...

 

Thanks in advance for your suggestions.

 

--Tracy

[vtornado]

Hello Tracy and welcome to CN.

 

Is the diagonal you ordered an SCT diagonal?   Or do you already have a 2 inch visual back?

 

How much do you want to spend per eye piece?

 

There is no need for all 2 inch eyepieces.  Typically they make sense for low power wide field of view.  High power can remain in the 1.25 inch format.

 

Your SCT is f/10, lower priced 2 inch eyepieces like Orion Q70 series will operate fine.

However in your path toward a 10 inch dob the lower cost eyepieces will show bloated stars in the outerfield of view.  This is because the Dob will be f/5.  

 

Additionally long focal length eyepieces like the Orion Q70 38 mm which is fine

for the long focus SCT (2000mm) will not be optimized for the (1200mm dob), 

the exit pupil will be too large to allow a fully illuminated view.

[JohnBear]

FYI - Svbony seesm to have 20% off on all their Amazon stuff for CyberMonday!

This seems to include thier 2" EPs and other excessories!

[doole]

I think in your place I would try them out on the Dobsonian before making any permanent choices. Since I started actually observing, I don't have any favourite eyepieces that are 2" - not kidding. (Except the Baader zoom, and it still fits in a 1-1/4" sleeve...) I actually find the extra field kind of distracting.

Edited by doole, 28 November 2022 - 03:16 PM.

[twilliams8187]

Thanks for the welcome!

 

I bought an SCT diagonal. This one.  I'm a bit concerned that it's not going to work with the zero-shift micro focuser but we'll see...

 

Budget: If I'm okay spending $ on quality glass.  I'm getting the impression, however, based on yours and others responses, that I may be dreaming if I think I can buy quality 2" glass that will work on both an f10 and an f5 (or f4!) telescope.  Hmmm...

 

I think a lower cost long FL 2" is probably the way to go. I like big bright views...

[twilliams8187]

Do I maybe have this wrong: A 2" eyepiece would be better a shorter FL / higher power than a 1.25"?  Short FL 1.25" EPs tend to be pretty dim. Would the view be brighter with a 2" barrel?

[KWB]

Thanks for the welcome!

 

I bought an SCT diagonal. This one.  I'm a bit concerned that it's not going to work with the zero-shift micro focuser but we'll see...

 

Budget: If I'm okay spending $ on quality glass.  I'm getting the impression, however, based on yours and others responses, that I may be dreaming if I think I can buy quality 2" glass that will work on both an f10 and an f5 (or f4!) telescope.  Hmmm...

 

I think a lower cost long FL 2" is probably the way to go. I like big bright views...

A high quality 2 inch eyepiece such as a Nagler, ES or UWA will be well corrected using an F/5 telescope and of course we do well at F/10. No dream but reality.

 

A budget wide field such as the Q70 will display a lot of astigmatism at F/5 but should be fine at F/10.

 

A long focal length 2 inch eyepiece is my favorite type for any telescope that has a 2 inch focuser.

[pj_thomas]

Additionally long focal length eyepieces like the Orion Q70 38 mm which is fine

for the long focus SCT (2000mm) will not be optimized for the (1200mm dob), 

the exit pupil will be too large to allow a fully illuminated view.

It's worth getting an big inexpensive 2 inch to use just as a finder in an SCT, straight through finder are a pain near zenith.  I have the Q70 32mm in a 6" ACF.  There is some astigmatism in the outer edge that make the stars a little fuzzy.  In the f/10 ACF its not horrible and I only see the actual astigmatism by going to either side of focus.   There is also some vignetting but again not bad and only noticable by defocusing a star and seeing a bite taken out of the donut.  I was concerned about vignetting so went with 32mm, a 38mm is probably better for an 8".  Finally there is some field curvature.  I can bring the outer stars into a soft focus but then the center stars are fuzzy.  This may not be the best view view but it still is a good view and very useful as a finder.  There are also other "superview" erfle designs, like the Q70, that are less expensive than Q70 that would work for a finder.

[Ihtegla Sar]

Do I maybe have this wrong: A 2" eyepiece would be better a shorter FL / higher power than a 1.25"? Short FL 1.25" EPs tend to be pretty dim. Would the view be brighter with a 2" barrel?

The view will be no brighter with a 2" eyepiece of the same focal length as a 1.25" eyepiece.

Why do you want a 2" eyepiece? The only advantage of a two inch eyepiece is that it can have a larger field stop than what would be possible in a 1.25" eyepiece due to the larger barrel. So, a 2" eyepiece can provide a wider field of view than what is possible with a 1.25" eyepiece.

However for eyepieces with a focal length under about 14mm, maximum field of view can be achieved in a 1.25" barrel. So, if you are looking to maximize field of view with a 2" eyepiece, you would want to look at longer focal length 2" eyepieces.

[MJB87]

Moving to Eyepieces Forum.

[twilliams8187]

Oh. Sorry. Didn't know there was an Eyepieces forum.  ;-)

[Mark Lovik]

Implied from previous comments

 

You can buy cheaper 2" wide field eyepieces at F/10.  If you are not constrained by budget get some higher quality eyepieces that can work on a Dob. 

 

You may want separate finder eyepieces for these 2 scopes, just be aware of the SCT fov limits and Dob maximum exit pupil measured for your eyes.

[twilliams8187]

However for eyepieces with a focal length under about 14mm, maximum field of view can be achieved in a 1.25" barrel. So, if you are looking to maximize field of view with a 2" eyepiece, you would want to look at longer focal length 2" eyepieces.

That makes sense. Thank you.

[SeattleScott]

If you were looking for a single 2" eyepiece to rule them all, it would be a quality 30/31mm ultrawide. About 90% of maximum FOV possible in 2" format, yet small enough exit pupil to use at F5. Also very big, heavy and expensive.

 

Maybe the most practical runner up would be the 28mm UWA. About 90% as wide as the 30/31mm. Cheaper and lighter. But now you are down a little more in terms of max FOV. Interestingly it sounds like the field stop is only a mm or two less than the 30/31mm ones so maybe not a significant difference. 

 

And yes the other approach is something like a 38mm SWA for the SCT, and some 20-30mm for the future Dob (hard to make recommendations until you decide on a particular model and know the actual F ratio).

 

Scott

[Elroy]

The 2inch eyepieces that get the most discussion on this board I believe are the AstroTech UWA 28mm and the APM UFF 30mm. The AT 28mm can be bought here on Astronomics for a very reasonable price. The APM 30mm UFF can be purchased at EyepiecesEtc.com. Can't speak for the Meade 8", I've never used one, but both of the eyepieces should work very well in a 10" or larger dob. I really enjoy my 2" EPs in my 12" dob.

Good luck to you!!

[davidgmd]

Welcome to CN Tracy.

 
Long focal length wide field 2” eyepieces can serve two purposes as I see it.
 
One: The longer focal length and lower mag result in a larger exit pupil that can make extended objects like nebulae (and background sky) brighter.
 
Two: The longer focal length and larger field stop combine to produce a wider true field of view that can better frame larger extended objects. The field remains somewhat limited in a long focal length SCT compared to that of a fast dob. You can still get close to 1 degree which should encompass all but the largest DSOs. The really big ones are what a dob or rich field refractor are for.  

   
I have the APM 30 mm UFF. It works very well in my 8” SCT at f/10 and in my 4” refractor at f/5.4. It has enough eye relief to use with glasses and it’s easy to find and keep the entire field of view visible. Weight is listed at 556 gm. I see prices ranging from €172 direct from APM to $250 but it’s backordered at many shops. Eyepiecesetc has them in stock.

  

The AstroTech 28 mm UWA has a wider apparent field than the 30 mm UFF and about the same true field at a slightly higher mag. That will give a slightly darker background under less than dark skies. Eye relief is shorter than the UFF but some report being able to use it with glasses. Weight is listed at 680 gm. It’s available at $200 from Cloudy Nights’ sponsor Astronomics.

  
The “money and weight are no object” choice is the Tele Vue 31 mm Nagler type 5, at 1 kg and ~$700.

  
All should work well in a fast dob.

  

They also probably all have a larger field stop than the opening on the back of your SCT, so the scope won’t be able to deliver all of the light that the eyepiece is capable of using. That results in some drop off in brightness at the edge of the field (vignetting). It’s not a smaller field of view with a sharp cutoff edge but a gradual reduction in brightness in the periphery. It’s not noticeable to me in the SCT. The eyepieces still deliver the widest field I can get out of the scope.

[Adam Long]

 

The AstroTech 28 mm UWA has a wider apparent field than the 30 mm UFF and about the same true field at a slightly higher mag.

I've got both (well the Meade version of the 28). I'd say the AstroTech 28 mm UWA has a much wider apparent field than the 30 mm UFF and a significantly bigger true field at a slightly higher mag.

 

AFOV is 70^o for the UFF vs 85^o for the AT.

 

Field stop is 36mm vs 40.6mm ( i.e. AT28 is closer to the 31mm Nagler at 42mm). The True Field of the 30mm is similar to my 20mm XWA. In use, the 28 is an obvious and worthwhile increase.

 

Weight is 545gm vs 675gm, so the 30 is lighter but not light.

[doole]

The view will be no brighter with a 2" eyepiece of the same focal length as a 1.25" eyepiece.

Why do you want a 2" eyepiece? The only advantage of a two inch eyepiece is that it can have a larger field stop than what would be possible in a 1.25" eyepiece due to the larger barrel. So, a 2" eyepiece can provide a wider field of view than what is possible with a 1.25" eyepiece.

However for eyepieces with a focal length under about 14mm, maximum field of view can be achieved in a 1.25" barrel. So, if you are looking to maximize field of view with a 2" eyepiece, you would want to look at longer focal length 2" eyepieces.

THANK you. Plus they're about 4x the weight, a concern in normal-sized scopes. <ducking & running...>

[twilliams8187]

Thank you, all, for the great feedback. I've ordered a "starter" SVBONY 26mm EP from Amazon for $52.  I'll keep this thread handy for my next purchase.

 

It's snowing in the Seattle area. I'm looking forward to solid overcast for the Mars/Moon occultation next week.  

[Ihtegla Sar]

 

One: The longer focal length and lower mag result in a larger exit pupil that can make extended objects like nebulae (and background sky) brighter.

 

This is true but a larger exit pupil can also be had in a long 1.25" eyepiece, such as the 32mm Plossl that the OP already has, so you don't need a 2" eyepiece for a larger exit pupil, only for wider fields. 

[SeattleScott]

Thank you, all, for the great feedback. I've ordered a "starter" SVBONY 26mm EP from Amazon for $52. I'll keep this thread handy for my next purchase.

It's snowing in the Seattle area. I'm looking forward to solid overcast for the Mars/Moon occultation next week.

You are barely taking advantage of 2” format with that eyepiece. It really works better as a medium low power, with a 40mm as low power and then the next step up is the 26mm and it is even 2” format for convenience. If you want to visually see the difference between a max FOV 2” eyepiece and your 26mm (I have one too), you could meet up with Seattle Astronomical Society. Or hop a ferry and join me on Vashon for somewhat darker skies and I can show you what my max FOV eyepiece would look like in your scope. Suddenly it will become clear why they call it Double Cluster and not Pair of Clusters Near Each Other. Yes mine cost more than $52 so you will have to pay more, but if you want to maximize your FOV, you have to pay more than $52. If you think about it , right now, you just invested what, $200 in a 2” diagonal and 2” eyepiece? To get maybe 10% wider view? So spending another $125 to get maybe 25% wider view is actually economical by comparison.

I sent my cousin in Indiana a picture of our first snow. He laughed. Basically gone now.

Scott

Edited by SeattleScott, 29 November 2022 - 04:53 PM.

[davidgmd]

I've got both (well the Meade version of the 28). I'd say the AstroTech 28 mm UWA has a much wider apparent field than the 30 mm UFF and a significantly bigger true field at a slightly higher mag.

 

AFOV is 70^o for the UFF vs 85^o for the AT.

 

Field stop is 36mm vs 40.6mm ( i.e. AT28 is closer to the 31mm Nagler at 42mm). The True Field of the 30mm is similar to my 20mm XWA. In use, the 28 is an obvious and worthwhile increase.

 

Weight is 545gm vs 675gm, so the 30 is lighter but not light.

  
Thanks Adam. I’m tempted to try the AT 28 mm UWA. I think I could handle the eye relief with glasses, but I’m finding it hard to justify the purchase.

 
The UWA’s 82 degree apparent field should look much wider than the UFF’s 70 degrees. That and to a lesser degree (no pun intended) the slightly higher mag/darker background are what’s tempting me. The weight doesn’t bother me.
 
I’m not sure how significant the difference in true field would be in the OP’s 8” LX200.  I haven’t done the math using the field stops. The approximation using AFOV/magnification says it’s 1.79 vs 1.64 degrees, illustrated here:

  

[SeattleScott]

The reason to get the 30mm is the extra eye relief, especially if you wear glasses for astigmatism at those exit pupils. Otherwise the 28mm is the more logical choice, especially since you don’t have to worry about balance.

[Adam Long]

 

 

  
Thanks Adam. I’m tempted to try the AT 28 mm UWA. I think I could handle the eye relief with glasses, but I’m finding it hard to justify the purchase.

 
The UWA’s 82 degree apparent field should look much wider than the UFF’s 70 degrees. That and to a lesser degree (no pun intended) the slightly higher mag/darker background are what’s tempting me. The weight doesn’t bother me.
 
I’m not sure how significant the difference in true field would be in the OP’s 8” LX200.  I haven’t done the math using the field stops. The approximation using AFOV/magnification says it’s 1.79 vs 1.64 degrees, illustrated here:

  
astronomy_tools_fov.png

I'm not sure that illustration is accurate. The 28mm's AFOV has been measured as actually 85^o, whereas the 30mm is accurate at 70^o. Likewise the field stops I've quoted above have been measured by drift timing - the 28 doesn't have a published spec but the 30mm's is smaller than the specs. When I've compared them the increase in AFOV feels huge, and the gain in TFOV is not insignificant.

 

As Scott says, wearing glasses does tip the balance back towards the 30 though. The extra field is only worthwhile if you can see it.

[Sixptelk]

I  have both SCTs from 8" to 11" and DOBs from 10" to 16". I had a line of Meade UWA 82 degree eyepieces that I liked quite a bit. For some reason Meade killed off that line. I've moved to Explore Scientific and have most of their UWA eyepieces and a couple of SWA at 68 degrees AFoV. They are great for the price. I like them better than the Meade only due to the fact that the Meade's were like baseballs. The ES has a better grip in my opinion.  Optically I won't compare them to the TVs. I've owned a few but for the cost, hever got serious about them even though my scopes are very high quality I don't think that with ES or the Meade's I was ever left wanting. I also have the entire collection of the Celestron X-CEL eyepieces. I've found those very good as well in a wide angle 60 degree AFoV at a very reasonable price. The adjustable eyepiece shade is second to none on those and images are what you'd expect in an eyepiece costing around $90. I have found that the branded 2" SWA 70 degree AFoV like Orion's Q70s are also a bargain for a large eyepiece. Made under several names all from the same Synta shop. For very low powered viewing with my SCTs I really like the Meade 56mm 2". Great low powered views...another DCd eyepiece. That being said, while it depends on the magnification I want to use I will give a slight nod to the ES eyepieces although the DCd Meade's had a sharper edge in the AFoV. Not a sharper image but the field stops were sharper, that's all. Some will say they didn't like the grease applied to the Meade's eyepiece used to provide an eye shield. I didn't find that objectionable. I do find the overly simple eye shield on the ES series a liability. I have to clean the oculars all the time. Again the less expensive twist up/down feature on the Celestron X-CEL eyepieces is the best I've found to date. All of the aforementioned eyepieces afford good eye relief and under dark skies a rich black background with no discernable internal glare. Note: Under dark skies. If you're looking at the moon or have stray light there may be some internal ghosting or glare. I typically view in a Bortle 2 or 3 sky so no issues. If you must have a zoom then I did buy a Hyperion Mk 4. Great on the planets for use of a single eyepiece, well corrected and no complaints unless you consider threading a filter into the 1 1/4" barrel with the 2" adapter in place a liability. My $.02 cents worth.