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Affordable eyepieces to use with very fast Newtonian scope like GSO 8" F/4

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#1 shubham_chandravanshi

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Posted 25 October 2020 - 09:22 AM

Hey everyone, I recently purchased a GSO 8" F/4 Imaging Newtonian Telescope from Tejraj in India. It is currently on its way to be delivered. It is coming with a GSO 25mm Super Plossl eyepiece. As other eyepieces are not available due to covid, and will come by late November, I wanted to ask recommendations from you all. 

The biggest problem is the fast F ratio this scope has. I was looking for a medium power eyepiece to buy like the GSO 15mm but then found that how bad they perform at such a fast optics. For higher powers, I will be using GSO's 2.5x and 5x three element barlows with the 25mm and the other eyepiece yet to buy. With a 15mm, I would be able to go to 267x. 

I do not have much budget and Tele Vues are way too much expensive here. I don't think going with GSO 15mm would be a good option so I am looking for the Explore Scientific 52° 15mm LER eyepiece.

It is still 3times more expensive than the GSO. So is it worth that much money? Will it be good with my 8" F/4 for deep sky and planetary (with the above mentioned barlows)? 

 

Please help.

🙏



#2 Achernar

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Posted 25 October 2020 - 09:44 AM

Explore Scientific 82 degree eyepieces, and a coma corrector will work with an F/4 Newtonian. I use these eyepieces with my 10 and 15-inch F/4.5 Dobs with good star images across all but the outer edges of the field of view. The coma corrector I use is an original Paracorr with a tunable top. Those can be picked up on the used market and there's other options available too.

 

Taras


Edited by Achernar, 25 October 2020 - 09:58 AM.

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#3 havasman

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Posted 25 October 2020 - 10:29 AM

When we buy a Newtonian scope at f4 there are effects tied to the physics of operating at that fast focal ratio. The steep slope of the light cone at the focal plane must be managed to form the collimated pencil of light presented to your eye that should contain a manipulated but accurate copy of the waveform that entered the scope aperture. That more extreme bending of the light rays from the steep cone to parallel rays is a prime reason for better correction in eyepieces and for coma correctors. Eyepieces designed without consideration of these phenomenon will produce a less accurate image. But they will produce an image that can be useful and beautiful.

 

See if the GSO coma corrector is available to you in your market. It is effective. The outer part of the wide field your scope allows will be cleaner and prettier. Then you may want to investigate the ES68 16mm for instance. It performs well in my f4.49 scope with coma corrector and could be Barlowed easily. The quality of the image comes at some cost with fast Newtonian optics. The ES82 eyepieces would be even better.

 

But to be sure, your scope WILL work with GSO Plossl eyepieces.


Edited by havasman, 25 October 2020 - 10:30 AM.

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#4 SeattleScott

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Posted 25 October 2020 - 10:56 AM

At F4 you really want a coma corrector, but you might get by without one for awhile if you stick to 50-60 AFOV. Celestron Xcel LX Series 25, 9 and 7mm are well corrected and perform well at F4. Plossl should be pretty good too.

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#5 aeajr

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Posted 25 October 2020 - 03:59 PM

Hey everyone, I recently purchased a GSO 8" F/4 Imaging Newtonian Telescope from Tejraj in India. It is currently on its way to be delivered. It is coming with a GSO 25mm Super Plossl eyepiece. As other eyepieces are not available due to covid, and will come by late November, I wanted to ask recommendations from you all. 

The biggest problem is the fast F ratio this scope has. I was looking for a medium power eyepiece to buy like the GSO 15mm but then found that how bad they perform at such a fast optics. For higher powers, I will be using GSO's 2.5x and 5x three element barlows with the 25mm and the other eyepiece yet to buy. With a 15mm, I would be able to go to 267x. 

I do not have much budget and Tele Vues are way too much expensive here. I don't think going with GSO 15mm would be a good option so I am looking for the Explore Scientific 52° 15mm LER eyepiece.

It is still 3times more expensive than the GSO. So is it worth that much money? Will it be good with my 8" F/4 for deep sky and planetary (with the above mentioned barlows)? 

 

Please help.

Can I assume you are in India?

 

If your budget is low but you want a good quality well corrected eyepiece, consider the Meade 5000 UWA 14 mm.  

https://www.amazon.i...e/dp/B005HSPUVO



#6 Voyager 3

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Posted 26 October 2020 - 06:45 AM

Can I assume you are in India?

 

If your budget is low but you want a good quality well corrected eyepiece, consider the Meade 5000 UWA 14 mm.  

https://www.amazon.i...e/dp/B005HSPUVO

It's a 130$ EP , come to India and get it for 300 bucks bawling.gif .

If you want these EPs better ship it from the west .


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#7 aeajr

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Posted 26 October 2020 - 08:46 AM

It's a 130$ EP , come to India and get it for 300 bucks bawling.gif .

If you want these EPs better ship it from the west .

That is the problem when the original poster doesn't give a budget.  I have no idea how to read prices in Indian currency or how they compare to the market.  In the USA, these are a great value.  I have two of them and recommend them often.


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#8 Voyager 3

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Posted 27 October 2020 - 07:34 AM

And to the OP ... I bet it isn't the case but...

Did you buy this astrograph for visual ? 



#9 shubham_chandravanshi

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Posted 28 October 2020 - 01:42 AM

I am from India and yeah, I do have a very tight budget. 1USD = 75INR. But, that formula doesn't work here! You get a thing worth 100USD for 150USD+ here in India and on top of that, the income of people is less! So, I have a budget only of about 80USD and I can only buy equipments from tejraj.com as it is the only vendor in India selling these products at reasonable prices. So for a 15mm, I do only have a choice to go with the GSO 15mm Super Plossl and the ES 15mm 52° LER eyepiece. The later one is 3 times more expensive. So is it worth buying? And I have read many threads discussing about the field stop issues in GSO 15mm so I am a bit skeptical about that eyepiece. And, should I buy the GSO CC? These things are very very expensive for me to afford but if they are worth it, then I will buy them.

Anyone here following Chuck's Astrophotography? Recently he uploaded a video in which he destroyed his Celestron Nexstar 8SE. I commented and said that although it wasn't in great condition, but there are some people, for example me (I am in 11th grade) who are fascinated by these things but can't afford to buy them. Then, a very nice person from Bulgaria, commented me to email him and said that he'll give me one! And that's how, I got this scope and it'll reach my doors in 3-4 days now. I don't have any other equipment like cameras & all and he said that he'll send me some accessories from Bulgaria like a simple planetary camera that can also be used to produce decent deep sky images (it has sony imx178 colour chip) and some barlows, and uhc filter and all.


And I was thinking to also use it for some visual if I can. And was interested in planetary as well as deep sky...

I know we cannot do everything in one scope but still, even if I could get something out of it, I will be happy.

#10 aeajr

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Posted 28 October 2020 - 07:17 AM

shubham_chandravanshi,

 

Thanks for that information.  Now we know how to help you.

 

First, you have an imaging telescope so it isn't made for visual use.  I presume you plan to use it for imaging most of the time.  I don't know anything about its characteristics as a visual scope.  I presume it can be used visually, but others will have a better idea.

 

Plossl eyepieces are good eyepieces, they are just not as wide field as other eyepieces. 

 

Plossls are very good eyepieces  – Good discussion
https://www.cloudyni...s/#entry8285208

 

In your first post you comment about how poorly a certain eyepiece performs at such a fast focal ratio.  Most inexpensive eyepieces will perform poorly at F4.  Even expensive eyepieces will likely not give you a perfect image across the entire field at F4.  In a scope like that we typically use a coma corrector to help with this in a Newtonian scope.

 

At your budget and the F4 of your scope and being limited to this web site, I would suggest you stay with the GSO Plossls which have about a 50 degree AFOV.  As you go wider the issue becomes worse and the better corrected eyepieces become quite expensive.

 

Or look to the used market.  I can't advise you there for the Indian market. 



#11 daniel_h

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Posted 28 October 2020 - 08:30 AM

just grab the 15mm GS plossl, make sure you don’t get the 15mm super view, the ES 15mm isn’t 3 times better


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#12 Spartinix

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Posted 28 October 2020 - 10:53 AM

I'd go for the Plossl too. Over time you might be able to get some coma corrector to make larger apparent field eyepieces perform better.
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#13 aeajr

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Posted 28 October 2020 - 11:05 AM

Now that Plossls are the likely best choice, what focal length should you get?

 

The focal length of that scope is about 800 mm.  The 25 mm eyepiece will give you 32X.

 

FL scope / FL eyepiece = mag

 

A 15 mm eyepiece wll give you 53X.  If you were buying a full set of eyepieces, that would be good to have. But I would consider that too closer to the 25 mm if you are only going to have two or three.

 

First I would get a 2X barlow - 

https://tejraj.com/barlow-lenses.html

 

This will give you two magnifications for each eyepiece.  So the 25 mm will also act like a 12.5 for 64X so you don't need the 15 mm.


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#14 shubham_chandravanshi

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Posted 28 October 2020 - 02:20 PM

Oh. I forgot to mention that I will be using the GSO 2" 2x Apochromatic Barlow to magnify the image. And in future, the CC on top of that barlow will become 1.1x2=2.2x and that will provide me 32, 53, 70 & 115x. Now I have two low powers and two medium powers.

That guy who bought me this telescope is giving me a 5x barlow. So, that will give me 160x with the 25mm eyepiece and 265x with the 15mm eyepiece. I don't want to go further than this as the atmosphere already limits the maximum magnification. At average to good seeing nights, I would be able to see crisp views of the planets at 265x.

I do not want to go any below than 15mm because of the eye relief factor which is already a mere 13mm in the GSO 15mm Super Plossl. Regarding Plossls, I know that these are very good eyepieces but I have read on CN that GSO 15mm Super Plossl do not have a field stop at all and thus, causes very blurry field stop while viewing. That thread was very old, probably 7-8 years. I hope GSO has corrected the mistake. Does anyone has experience with that particular eyepiece?

#15 Miranda2525

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Posted 28 October 2020 - 03:49 PM

Can I assume you are in India?

If your budget is low but you want a good quality well corrected eyepiece, consider the Meade 5000 UWA 14 mm.
https://www.amazon.i...e/dp/B005HSPUVO


Not well corrected at F/4. Field curvature will be really dominant, especially at F/4.

#16 Miranda2525

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Posted 28 October 2020 - 03:50 PM

The best eyepieces for an F/4, and affordable will be used Vixen LVW's.

#17 SeattleScott

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Posted 28 October 2020 - 04:18 PM

The ES is more expensive because it has long eye relief for glasses wearers.

Can’t speak to whether or not the GSO has a field stop.

Scott

#18 Tank

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Posted 28 October 2020 - 04:37 PM

Sounds like your on a budget budget
I would highly recommend a zoom meade 8-24 with a barlow 3x
Covers pretty much everything dirt cheap

#19 shubham_chandravanshi

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Posted 28 October 2020 - 10:23 PM

The 80$ budget I mentioned was for a 15mm eyepiece (if bought the ES one). Ofcourse ES one is not 3 times as good, but if there still are those field stop problems with the 15mm then there will not be any point in investing in 15mm GSO.
The barlow that I mentioned and the CC are not included in that budget ofcourse.

If the GSO 15mm performs well in F/8 and above telescopes (without the field stop problems I mentioned) then it should be good to use with a CC.

So this becomes the root question of this thread that does GSO 15mm eyepiece still has those problems that it had years ago? If no then I'll go with the GSO if yes then I will be using the ES eyepiece.

#20 RichA

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Posted 29 October 2020 - 11:44 PM

Explore Scientific 82 degree eyepieces, and a coma corrector will work with an F/4 Newtonian. I use these eyepieces with my 10 and 15-inch F/4.5 Dobs with good star images across all but the outer edges of the field of view. The coma corrector I use is an original Paracorr with a tunable top. Those can be picked up on the used market and there's other options available too.

 

Taras

  "LEAST expensive."  Not $300 for a coma corrector and a $200 eyepiece.



#21 CeleNoptic

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Posted 30 October 2020 - 02:47 AM

Oh. I forgot to mention that I will be using the GSO 2" 2x Apochromatic Barlow to magnify the image. And in future, the CC on top of that barlow will become 1.1x2=2.2x and that will provide me 32, 53, 70 & 115x. Now I have two low powers and two medium powers.

 
If you mean this  GSO 2" 2x  ED Barlow, be aware that it works as ~2.2x with most EPs like any other telenegative Barlow. I had it. And it's not "apochromatic", just usual 2-element telenegative Barlow. So your math is a little bit off because 1.1 * 2.2 = 2.42x. Probably, not a big deal, but worth consideration. The claimed magnification factor maintained more strictly only by telecentric Barlows like TV Powermate, ES Focal Extender etc. And this GSO Barlow has a removable nosepiece that works like ~1.4-1.6x being screwed directly into eyepiece filter thread.



#22 shubham_chandravanshi

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Posted 30 October 2020 - 10:28 AM


If you mean this GSO 2" 2x ED Barlow, be aware that it works as ~2.2x with most EPs like any other telenegative Barlow. I had it. And it's not "apochromatic", just usual 2-element telenegative Barlow. So your math is a little bit off because 1.1 * 2.2 = 2.42x. Probably, not a big deal, but worth consideration. The claimed magnification factor maintained more strictly only by telecentric Barlows like TV Powermate, ES Focal Extender etc. And this GSO Barlow has a removable nosepiece that works like ~1.4-1.6x being screwed directly into eyepiece filter thread.



Oh yeah. I am ok with 2.2x magnication. But you also said that it is not Apochromatic, does that mean that it does not perform well? Do the yellow and blue colours split up? Please tell me about that barlow's quality.

#23 Eddgie

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Posted 30 October 2020 - 04:20 PM

Not well corrected at F/4. Field curvature will be really dominant, especially at F/4.

Actually, an f/8 f/4 reflector has a pretty flat field.  It is actually almost as flat as an EdgeHD 8".  Field curvature is not going to be a problem at all.  Coma will be as will using eyepieces that are poorly corrected for astigmatism, unless Barlows or higher power eyepieces are used so that the outside of the field is not seen, but the field curvature will be so low that in essence, it is flat. 



#24 havasman

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Posted 30 October 2020 - 04:24 PM

Oh yeah. I am ok with 2.2x magnication. But you also said that it is not Apochromatic, does that mean that it does not perform well? Do the yellow and blue colours split up? Please tell me about that barlow's quality.

Please check your messages - the envelope icon at the top of the page. If you respond, please do so via that message reply tab.



#25 Miranda2525

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Posted 31 October 2020 - 10:31 AM

Actually, an f/8 f/4 reflector has a pretty flat field.  It is actually almost as flat as an EdgeHD 8".  Field curvature is not going to be a problem at all.  Coma will be as will using eyepieces that are poorly corrected for astigmatism, unless Barlows or higher power eyepieces are used so that the outside of the field is not seen, but the field curvature will be so low that in essence, it is flat. 

I was referring to the 14mm Meade Series 5000 UWA, which is notorious for showing lots of FC in fast reflectors, and also astigmatism.

Same glass as the 14mm ES 82, which is also notorious for the same thing.

 

I've tried both and seen it for myself. Both were loaded with FC.

 

http://www.iceinspac...45-0-0-1-0.html

 

https://www.cloudyni...ries-5000-r2463

 

https://www.cloudyni...-uwa/?p=7681925

 

https://www.cloudyni...-uwa/?p=7685738


Edited by Miranda2525, 31 October 2020 - 10:45 AM.



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