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Nexstar 8 Evo - EP selection

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#1 smasraum

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Posted 24 January 2021 - 08:15 PM

My previous scope (6+ years ago) was an 8" dob.  I liked the combination of FOV and magnification using Baader Hyperion and a 2.5x Powermate.  I had a range of 56x --> 325x.  I assume most of my viewing was probably in the 100-200x-ish range, occasionally down the the low end and when capable, I would occasionally push the high end.  I got a really nice view of Mars at 325x once that was great.

 

I've now got an older 8" Nexstar Evolution.  The guy that I got it from included a couple of random EP and a 2x Barlow. 

 

I think I'm looking for a range more like I had on my old Dob.  I had thought "I'll get a focal reducer corrector and then similar EP to what I had before," but then I realized that I could skip the f6.3 reducer/corrector and just get EP that gave me something similar.  Granted, to get similar FOV, I'm pretty sure I'm going to have to spend more, getting EP that have AFOV in the 76º-82º range instead of the 68º hyperions.

 

So, does that seem like a reasonable course of action?

 

I was thinking, something in the 24-31mm range would give me low power views, then maybe something in the 21-16mm range (AFOV to vary depending upon the option and availability).  Then maybe something in the 14-11mm range and again 10-8.5mm.  Then I could try the barlow for the rare times when I wanted to try pushing into the 250-350x range.

 

And for those ranges, if for instance, I went with a 16mm instead of 17 or 17.5, spend a bit more and get something with a wider AFOV to try to keep the views similar.  But if I went with 21mm instead of 16mm, then I could go with something like the hyperion at 68º.

 

Please point out flaws in my thinking or recommendations.

 

Thanks


Edited by smasraum, 24 January 2021 - 08:15 PM.


#2 ravenhawk82

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Posted 24 January 2021 - 09:16 PM

You don't need a wide AFOV eyepiece, they're just nice to have. For example, a 30mm eyepiece in a 2000mm scope will yield the same magnification (~66x) as a 15mm eyepiece in a 1000mm scope. If they're both 82* AFOV eyepieces the field of view in the sky will be the same too. The AFOV isn't affected by the telescope itself though, and the AFOV doesn't change the magnification.

To meet the criteria you're describing, I'd get a nice 30mm and 10mm to use with that barlow (I use a similar setup, but with an 8mm high mag eyepiece for my shorter FL scope). That'll effectively give you 30mm, 15mm, 10mm, and 5mm eyepieces and magnification options from 66x to 400x, which nicely rounds out most of the useful magnification range of that scope. If you have a barlow though, don't bother getting EPs that are half the focal length of one you already have unless you just want to avoid using the barlow lens. 30mm with a 2x barlow is effectively 15mm, so you're just doubling up on what you've already got if you buy EPs in both of those focal lengths. 

Which eyepieces specifically depend on what matters to you and what you want to spend though. Having an AFOV of 82* or higher quickly adds to the cost of each EP so it's up to you whether or not that's worth it. I personally think Explore Scientific has some of the best value for your money, so it might be worth checking out what they have to offer.
 



#3 smasraum

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Posted 24 January 2021 - 10:12 PM

You don't need a wide AFOV eyepiece, they're just nice to have. For example, a 30mm eyepiece in a 2000mm scope will yield the same magnification (~66x) as a 15mm eyepiece in a 1000mm scope. If they're both 82* AFOV eyepieces the field of view in the sky will be the same too. The AFOV isn't affected by the telescope itself though, and the AFOV doesn't change the magnification.

To meet the criteria you're describing, I'd get a nice 30mm and 10mm to use with that barlow (I use a similar setup, but with an 8mm high mag eyepiece for my shorter FL scope). That'll effectively give you 30mm, 15mm, 10mm, and 5mm eyepieces and magnification options from 66x to 400x, which nicely rounds out most of the useful magnification range of that scope. If you have a barlow though, don't bother getting EPs that are half the focal length of one you already have unless you just want to avoid using the barlow lens. 30mm with a 2x barlow is effectively 15mm, so you're just doubling up on what you've already got if you buy EPs in both of those focal lengths. 

Which eyepieces specifically depend on what matters to you and what you want to spend though. Having an AFOV of 82* or higher quickly adds to the cost of each EP so it's up to you whether or not that's worth it. I personally think Explore Scientific has some of the best value for your money, so it might be worth checking out what they have to offer.
 

Right, I just want the FOV to be similar to what I was used to with the old scope.

 

Good point on not buying a 30 and a 15, no point in that when I've got the barlow.  It's a Celestron Ultima 2x, btw.

 

Thanks, for the response.



#4 spereira

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Posted 25 January 2021 - 08:14 AM

Moving to Eyepieces.

 

smp



#5 SeattleScott

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Posted 25 January 2021 - 02:23 PM

The widest realistic FOV with an 8” SCT is about 1.2 degrees. You can get there with a 40mm 70 AFOV 2” eyepiece, or with a reducer and 32mm Plossl (or 24mm 65 AFOV if preferred).

If you liked 68 AFOV before and want to stick with it, there are certainly options, including the Hyperion series. APM UFF/Meade UHD/Celestron Ultima Edge are options as well. Or you can go with wider AFOV but it will typically cost more.

At 100x magnification, the view through a SCT with a 68 AFOV eyepiece will be just as wide as the view through the Dob with a 68 AFOV eyepiece.

I would go maybe 36-42mm for low power. Then maybe a 21, 13, 10 and 8 Hyperion. If you liked those at F6 you will love them at F10-11. Certainly there are other options if you want better and wider AFOV and plan to spend more. I’m not saying Morpheus, ES 82, Meade PWA and Naglers aren’t better. If you want to spend $200-$400 per eyepiece you can do better than the Hyperions.

Scott

Edited by SeattleScott, 25 January 2021 - 02:32 PM.


#6 smasraum

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Posted 25 January 2021 - 03:34 PM

The widest realistic FOV with an 8” SCT is about 1.2 degrees. You can get there with a 40mm 70 AFOV 2” eyepiece, or with a reducer and 32mm Plossl (or 24mm 65 AFOV if preferred).

If you liked 68 AFOV before and want to stick with it, there are certainly options, including the Hyperion series. APM UFF/Meade UHD/Celestron Ultima Edge are options as well. Or you can go with wider AFOV but it will typically cost more.

At 100x magnification, the view through a SCT with a 68 AFOV eyepiece will be just as wide as the view through the Dob with a 68 AFOV eyepiece.

I would go maybe 36-42mm for low power. Then maybe a 21, 13, 10 and 8 Hyperion. If you liked those at F6 you will love them at F10-11. Certainly there are other options if you want better and wider AFOV and plan to spend more. I’m not saying Morpheus, ES 82, Meade PWA and Naglers aren’t better. If you want to spend $200-$400 per eyepiece you can do better than the Hyperions.

Scott

Right, got it, thanks.  I keep thinking about the same EP with the new scope, and, of course, that will give a different TFOV because the mag will be very different, but if the AFOV of the EP is the same, and I compare 2 different focal length EP that yield the same mag on the two scopes (ie 100x via 12mm and 100x via 20mm), then the TFOV will be the same.

 

I probably won't be going to any 2" EP, so I'll probably stick to 31mm or less.  I should be able to get a good range of EP starting at 31mm and going up from there.  I'll probably max out at somewhere between 300 and 350 since it's rare to get to push that high anyway.  I'm thinking of sticking with the hyperion for the wide angle stuff and then maybe going to morpheus for the higher mag stuff.  I've also heard good stuff about the ES 82.  Then of course, anything Televue seems to be highly regarded.
 


Edited by smasraum, 25 January 2021 - 03:37 PM.


#7 SeattleScott

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Posted 25 January 2021 - 04:10 PM

So you could do 32mm Plossl for lowest power, widest FOV (I might go a different direction if you get a focal reducer). Then maybe 17 and 13 Hyperion, followed by 9 and 6.5 Morpheus (or similar focal lengths of other brands, like 10 and 7 Pentax XW, etc.).

Scott

#8 smasraum

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Posted 25 January 2021 - 08:11 PM

So you could do 32mm Plossl for lowest power, widest FOV (I might go a different direction if you get a focal reducer). Then maybe 17 and 13 Hyperion, followed by 9 and 6.5 Morpheus (or similar focal lengths of other brands, like 10 and 7 Pentax XW, etc.).

Scott

Seems like this is the direction that the other thread is leading me as well. 
 



#9 smasraum

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Posted 27 January 2021 - 11:52 AM

I'd like to revisit this thread a bit.

 

I'd like to stick with 1.25" EP.  I don't have a specific budget, but I'd like to stick to no more than about $1000.

 

I've seen some mention that older folks often can't see all of the view in an EP with an AFOV wider than 68º.  Can someone explain that limitation.  I'm not young, but I'm also not that old either.

 

I'm wondering about a 24mm panoptic.  How much better is the TV Pan than the Meade 5k, Celestron and ES?  I want to get really good stuff, but I don't want to spend 50% more money for an EP that's 5% better.

 

Then I have been thinking something along the lines of Morpheus 17.5 or maybe Nagler 16.  And then something like Morpheus 12.5 or Nagler 13.  And then I'd use a 2x Barlow on the 17.5/16 and 12.5/13 for my high powers. 

 

Then I realized that the 2x Barlow that I have is an old Celestron Ultima SV which looks like a shorty.  I don't know how nice that is and if it would degrade the views through something as nice as the Naglers.  Would I need/want to get a better barlow?  I used to have a 2.5x Powermate.  Is there something that's a good quality that is closer to 2x.  2.5x seems like a lot for what I've been thinking and with this scope.

 

Then I thought "maybe I should just get an Ethos 13mm" which would give me higher magnification but the same TFOV as the 17.5 Morpheus and 16 Nagler.  Then I thought "what's the deal with old eyes not being able to take full advantage of high AFOV EP?  Would I be wasting money on the Ethos?

 

How do the Nagler's compare to the Morpheus?  It seems like TV is the gold standard, but are they really that much better?

 

current option1

24mm 68º (TV Pano or alternate)

17.5mm 76º (or 16mm Nagler)

12.5mm 76º (or 13mm Nagler)

2x Barlow

 

current option2

24mm 68º (TV Pano or alternate)

13mm Ethos

2x Barlow (or would I need something better/different)

 

Other options?



#10 SeattleScott

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Posted 27 January 2021 - 11:57 AM

I hear those old Ultima barlows are quite good.

Scott

#11 smasraum

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Posted 27 January 2021 - 11:59 AM

I hear those old Ultima barlows are quite good.

Scott

Good to hear. 

 

I'd hate to put questionable glass in front of a top notch EP.
 



#12 SeattleScott

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Posted 27 January 2021 - 12:39 PM

According to Ernest’s bench tests, the spot sizes for the ES 24 68 at F10 are 4 on axis, 7 at 70% and 13 at edge of field. The 24 Panoptic tests at 2, 4 and 6. So about 50% better for 50% more. That being said a spot size of 10 looks more or less pinpoint so you might only see a significant difference in the last 10% or so of the view at F10. Yes the Panoptic is better corrected but at F10 it is a bit overkill and the human eye might not fully appreciate it.

Another option is the APM 24 UFF and clones. Supposedly it comes closer to Panoptic performance at about the same price as the ES. Haven’t used one myself. There are a few clones available from Meade, Celestron, Orion, etc. But Orion made theirs 2”.

Scott

#13 smasraum

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Posted 27 January 2021 - 12:47 PM

According to Ernest’s bench tests, the spot sizes for the ES 24 68 at F10 are 4 on axis, 7 at 70% and 13 at edge of field. The 24 Panoptic tests at 2, 4 and 6. So about 50% better for 50% more. That being said a spot size of 10 looks more or less pinpoint so you might only see a significant difference in the last 10% or so of the view at F10. Yes the Panoptic is better corrected but at F10 it is a bit overkill and the human eye might not fully appreciate it.

Another option is the APM 24 UFF and clones. Supposedly it comes closer to Panoptic performance at about the same price as the ES. Haven’t used one myself. There are a few clones available from Meade, Celestron, Orion, etc. But Orion made theirs 2”.

Scott

Just based on context, I think I have an inkling of what you're saying with respect to spot sizes.  Is there a link or thread that you can direct me to so I can dig a bit deeper?
 

Thanks for the info about the APM. 



#14 SeattleScott

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Posted 27 January 2021 - 01:12 PM

Spot size is kind of the size of a star. Smaller the better, smaller the tighter a star looks. If it gets up to 20 or 30 (some eyepieces can be worse especially in fast scopes), that is an indication of some abberation bloating star images. Normally worse near the edge. I don’t know of a link offhand. Ernest’s site is in Russian so that probably doesn’t help you much.

Scott

#15 SeattleScott

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Posted 27 January 2021 - 01:18 PM

It is interesting in that the ES 24 68 used to be THE low cost alternative to a 24 Panoptic. (I guess you could throw the 22LVW in the mix but it was basically the same price as the Panoptic.) People seemed pretty happy with it, although it was naturally acknowledged to be less sharp than the Panoptic. As the price of the ES has gone up and competitors like Meade HD60, Xcel LX and APM have emerged, I hear more complaints about the FC in the ES. Granted I haven’t used the ES but it has been intriguing to see a once popular eyepiece now being criticized more.

The 24 Panoptic is great though, as is the HD60/Xcel LX although they are only 60 AFOV.

Scott

#16 smasraum

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Posted 27 January 2021 - 01:25 PM

Thanks, lots of good info.



#17 Echolight

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Posted 27 January 2021 - 01:40 PM

I would have to get a 0.63 reducer for a C8 if I were sticking to 1.25 eyepieces.

 

The view and ability to find stuff in the eyepiece at 1.2 degrees true field of view just blows away a 0.78 degree true field of view.



#18 SeattleScott

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Posted 27 January 2021 - 02:03 PM

And using a reducer makes Panoptic versus ES a different dynamic.

Scott
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#19 Echolight

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Posted 27 January 2021 - 02:04 PM

With a 0.63 reducer, the 24-68 eyepiece will be a good wideview and finder. And a good brightness level with a 3.8mm exit pupil.

 

A 13mm will be the main DSO eyepiece with the magic 2mm exit pupil and about 100x.
If you go for the 100 degree AFOV, it'll give you around 1 degree true field of view. So a good place to try a 100 I believe. Although an 82 will give you a sharper defined field stop, and a smaller form factor. The 13-100 is a very large eyepiece and I probably wouldn't quite feel right about putting one in a 1.25 barlow.


Edited by Echolight, 27 January 2021 - 02:06 PM.


#20 Echolight

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Posted 27 January 2021 - 02:28 PM

And using a reducer makes Panoptic versus ES a different dynamic.

Scott

I guess one of the biggest problems I had with a 0.78 degree true field of view was finding stuff in the eyepiece to do the goto alignment.

 

I will admit that when I was doing this I did not have a finder scope on the C8.

So with a properly aligned finder scope I'm sure it would be much easier. But still slow. And speed of acquisition while doing a 2-star alignment has been rumored to affect the go-to's accuracy.

 

And of course I like the option of the wider 1.2 degrees true field of view for fitting and framing some mid-size DSO.

1.2 degrees is just enough for M42, the Orion nebula. And who doesn't want to look at that?


Edited by Echolight, 27 January 2021 - 02:31 PM.


#21 brentknight

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Posted 27 January 2021 - 03:35 PM

Just curious why you don't want to use any 2" eyepieces?

 

I didn't like the idea myself because of the extra weight, but I've since changed my mind on that.

 

2" pieces will open up many more options.  The Ethos 13mm would work great with the 2" 2x Powermate.  Getting an APM 30mm UFF, an APM 20mm HDC, or even an Ethos 17mm would give you about max TFOV, and you could still use all your 1.25" with the adapter.  The cost of a 2" diagonal and back is probably cheaper than the F/6.3 R/C too.

 

I'm 61, and I have no issues viewing the FOV in an Ethos.  I'm nearsighted with astigmatism.  Normally it just requires a little movement of the eye to see the edges, but I usually just enjoy the view without seeing any edges.


Edited by brentknight, 27 January 2021 - 03:45 PM.

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#22 smasraum

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Posted 27 January 2021 - 03:45 PM

Just curious why you don't want to use any 2" eyepieces?

 

I didn't like the idea myself because of the extra weight, but I've since changed my mind on that.

 

2" pieces will open up many more options.  The Ethos 13mm would work great with the 2" 2x Powermate.  Getting an APM 30mm UFF or the APM 20mm HDC would give you about max TFOV, and you could still use all your 1.25" with the adapter.  The cost of a 2" diagonal and back is probably cheaper than the F/6.3 R/C too.

 

I'm 61, and I have no issues viewing the FOV in an Ethos.  I'm nearsighted with astigmatism.  Normally it just requires a little movement of the eye to see the edges, but I usually just enjoy the view without seeing any edges.

It sounded/looked like it would be a pain in the rear to swap from 1.25" diagonal to 2". 

I've already (mostly) decided against the focal reducer/corrector (but I was still open to persuasion if someone came up with a good reason to have it)

It's good to know about you being able to see the view in the Ethos.

 

OK, 2" diagonal now a possibility.  If that's the case, is there any reason not to use the Celestron 2" diagonal?
 



#23 SeattleScott

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Posted 27 January 2021 - 04:13 PM

It takes about 30 seconds to swap the diagonal, maybe 60 if you get an SCT diagonal. You do it once and leave it there forever.

There can be a little nuisance with swapping a 1.25” adapter in and out. A number of 1.25” eyepieces have an optional 2” barrel to eliminate this hassle. You can also buy the adapters for $15 and just leave one on each of your 1.25” eyepieces.

Scott

#24 Echolight

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Posted 27 January 2021 - 04:47 PM

It sounded/looked like it would be a pain in the rear to swap from 1.25" diagonal to 2". 

I've already (mostly) decided against the focal reducer/corrector (but I was still open to persuasion if someone came up with a good reason to have it)

It's good to know about you being able to see the view in the Ethos.

 

OK, 2" diagonal now a possibility.  If that's the case, is there any reason not to use the Celestron 2" diagonal?
 

If you're talking about the one that's made to screw on the SCT without using a visual back, then yes there is a reason not to use it.

It only has a 37.9mm clear aperture. And being so close to the field stop of the eyepiece, it could cause noticeable vignetting when used with eyepieces that have a larger field stop, like any of the eyepieces that would provide the largest true field of view in a C8.

Also, some have reported that they were unable to thread it all the way on. Only getting about 3/4 of 1 thread on to the OTA.

 

Another reason to use a 2 inch visual back and 2 inch refractor style diagonal is they are much easier to adjust the angle of the diagonal and eyepiece.

Say you want to view low near the horizon. Instead of standing up to look down into the eyepiece that would be pointed near 90 degrees up, you could rotate the diagonal to the side for easier access to the eyepiece.

 

And last, the twist lock feature can be difficult to turn in cold weather... or so I have read.


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#25 smasraum

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Posted 27 January 2021 - 04:54 PM

It takes about 30 seconds to swap the diagonal, maybe 60 if you get an SCT diagonal. You do it once and leave it there forever.

There can be a little nuisance with swapping a 1.25” adapter in and out. A number of 1.25” eyepieces have an optional 2” barrel to eliminate this hassle. You can also buy the adapters for $15 and just leave one on each of your 1.25” eyepieces.

Scott

OK, I'll look into it.  Wouldn't I need an SCT diagonal since I have an SCT?




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