Beginners telescope and eye pieces

[CLOUD90]

Hi I've just brought a celestron nexstar 90 gt refractor not the WiFi version but the goto one unfortunately it only came with a standard 8mm ep which I struggle to look through the pin hole  I'm not to familiar on what what kind of eye pieces are recommended for this type of scope I'm looking to spend around £60 for a newish  ep maybe around 15mm or 20mm any help or advice would be great also should I buy a Barlow lense ? 

Edited July 31, 2022 by CLOUD90

[Zeta Reticulan]

Not sure whether this is the same OTA as the Synta 90mm Maksutov.

A 13 or 14mm Plossl should give around a 1mm exit pupil. A 14mm Bresser 'Plossl' gives me 89x in my 90mm Maksutov. My Orion StarMax came bundled with 10mm and 25mm Plossls.  It might be worth looking at the 10mm and 23mm SvBony aspherics. These are very good eyepieces, despite their inexpensive price. They have 60 degree fields of view so may be easier to view through for you. I am not convinced a Barlow will be of great benefit with a catadioptric scope as they are usually f/10 and slower. 

 

Oh yeah, avoid the 4mm aspheric, it exhibits a fair bit of chromatic aberration. The other two are fine though.

[CLOUD90]

 this is my scope are the svbony eps any good ?

[Zeta Reticulan]

Oh right. Yes, they are good.

[CLOUD90]

I do see alot of them on ebay but they seem very cheap and didn't know if they were ideal so you don't recommend getting a Barlow lens for my telescope ?

[DaveL59]

to give you a range of magnifications you might consider a zoom eyepiece. One in the 7-21/8-24mm range would probably be much easier in use than the one that came with your scope, tho zooms do tend to have a narrower field of view at the longer end of their focal length (21mm end). There's several options available, some quite pricey but good quality, like the Baader and others lower in price. This thread may give some more info

I have the SVBony 8-24 and the 7-21mm and I find both very useable and well made.

Edited July 31, 2022 by DaveL59

[Zeta Reticulan]

1 hour ago, CLOUD90 said:

I do see alot of them on ebay but they seem very cheap and didn't know if they were ideal so you don't recommend getting a Barlow lens for my telescope ?

Sorry, I thought it was a catadioptric. Yes, a Barlow would probably help. What's the focal length of your scope?

[CLOUD90]

I think it's 910mm  I don't know if that's good or bad lol 

[Zeta Reticulan]

28 minutes ago, CLOUD90 said:

I think it's 910mm  I don't know if that's good or bad lol 

About f/10 then, oddly the same focal ratio as most SCT's. It should be a good scope for lunar/planetary observing, and splitting doubles. It's not got a very wide field though. A 10mm eyepiece will give 91x. Add a 2x Barlow and you have 182x. A decent achromatic refractor should often be able to achieve that. Get a Barlow with a removable element and you can thread that element directly into the barrel of the 10mm eyepiece. 

Effectively making it a 6.25mm one. This will now give you a magnification of 145.6x. Although 182x and 146x will be near the highest for that scope. The 23mm SvBony will give a reasonable 39.5x with your scope. Again, with the Barlow you can make it into an 11.5mm eyepiece and a 14.3mm eyepiece. Getting very low magnifications on an f/10 scope is the tricky bit. I've threaded a focal reducer into the 23mm SvBony in the past to turn it into a 46mm eyepiece. Obviously it changes some of its visual characteristics and also shortens the eye relief. But you would get 19.7x as a low magnification, often useful for some open clusters.

I made this 25mm TV Plossl into a 50mm with the reducer. 

[Zeta Reticulan]

DaveL59's right about the SvBony zooms. They are very good for the money.

[CLOUD90]

Thanks for the info so if the telescope doesn't have very wide  fov  will getting an eye piece with bigger fov not work ? I am sorry I have very little clue how all this works I get how Barlow lens works which is a start lol does this mean I should stay away from eye pieces like 30mm 40mm 50mm ?

Edited July 31, 2022 by CLOUD90

[Ratlet]

Just be aware that the 8-24mm svbony is a heavy beast of a lens.  You have to slightly adjust focus when you change the zoom and the field of view alters depending on what zoom level you've gone for.

It is very well made though.

[globular]

6 hours ago, CLOUD90 said:

it only came with a standard 8mm ep which I struggle to look through the pin hole

Before considering buying more eyepieces, barlows or zooms I recommend you get to grips with what you have.

Looking through a pin hole is astronomy.

Yes you can get eyepieces with more glass and with easier eye placement.... but they all produce a tiny point image.... called an exit pupil.  And they'll range from something below 1mm to something around 3mm.

I recommend you point your telescope with your 8mm eyepiece at the moon and practise getting just the right eye placement to get the best image.  You'll get better the more you try.

Then you can point at other objects, learn your goto settings, see how they look with your 8mm EP, etc.

Then you can come back here with more idea about what you might need to improve your kit... and the folks here can help you out.

 

p.s. your scope is perfectly capable of getting wide field views.  With the right eyepiece you can get around 1.7 degrees of sky at about 38x magnification.... you don't need more than that for many things in the sky.

[Zeta Reticulan]

1 hour ago, CLOUD90 said:

Thanks for the info so if the telescope doesn't have very wide  fov  will getting an eye piece with bigger fov not work ? I am sorry I have very little clue how all this works I get how Barlow lens works which is a start lol does this mean I should stay away from eye pieces like 30mm 40mm 50mm ?

An eyepiece with a bigger AFOV would probably be better in many respects. It's just that an f/10, 90mm refractor isn't going to have a widefield view like a fast short tube refractor. A 15mm GSO SuperView would give you 61x and about 1 arc degree, 30 arc minutes of field. That's equivalent to around the diameter of three Full Moons. I don't know if your scope has a 2" visual back or not. To get very low power wide angle views you may need to use heavier 2" eyepieces.

 

 

[Zeta Reticulan]

3 minutes ago, globular said:

 

 

p.s. your scope is perfectly capable of getting wide field views.  With the right eyepiece you can get around 1.7 degrees of sky at about 38x magnification.... you don't need more than that for many things in the sky.

We may have a difference of opinion on what widefield views are lol. 

 

[CLOUD90]

Thanks all I think I might look at the svbony zoom and give that ago I was wrong it's not an 8mm it's a 4mm that came with the scope  i feel it maybe easier to align the scope with a better ep rather than the 4mm as I have to point it at 3 bright stars unfortunately haven't managed to do that yet as it's been cloudy ever since I brought the scope lol typical

 

[CLOUD90]

I don't know if it has a 2inch back all I know is that it fits 1.25 eye pieces could I not get an 2 inch adapter or is that not possible for my type of scope ?  https://www.astroshop.eu/telescopes/celestron-telescope-ac-90-910-nexstar-90-gt-goto-sun-planet-set/p,57599

[globular]

16 minutes ago, CLOUD90 said:

i feel it maybe easier to align the scope with a better ep rather than the 4mm as I have to point it at 3 bright stars

You should do the alignment using the finder, not an eyepiece and the main scope.  The EP is only used once you get close using the finder.

Edited August 1, 2022 by globular

[Zeta Reticulan]

5 minutes ago, CLOUD90 said:

I don't know if it has a 2inch back all I know is that it fits 1.25 eye pieces could I not get an 2 inch adapter or is that not possible for my type of scope ?  https://www.astroshop.eu/telescopes/celestron-telescope-ac-90-910-nexstar-90-gt-goto-sun-planet-set/p,57599

I think it can only use 1.25" accessories. 

[globular]

1.25" only with that scope - but there is lots you can see with it with a range of 1.25" EPs or a zoom - don't think of it as a negative 

Sort out aligning using the finder and get a 8-25 or 7.1.21.5 zoom and you'll soon start making progress.

[Zeta Reticulan]

15 minutes ago, CLOUD90 said:

Thanks all I think I might look at the svbony zoom and give that ago I was wrong it's not an 8mm it's a 4mm that came with the scope  i feel it maybe easier to align the scope with a better ep rather than the 4mm as I have to point it at 3 bright stars unfortunately haven't managed to do that yet as it's been cloudy ever since I brought the scope lol typical

 

I think I understand what you mean now.

Small 4mm eyepieces are not easy to use without some practice. I'd still consider the 23mm SvBony aspheric as it has a 62 degree FOV. The 7-21mm SvBony zoom is lightweight and has good visual acuity. It really is worth the money. 

[CLOUD90]

Lol yer I will probably get the 7-21mm I see you have the orion one what's that like ? 

[Zeta Reticulan]

11 minutes ago, CLOUD90 said:

Lol yer I will probably get the 7-21mm I see you have the orion one what's that like ? 

They are identical and almost certainly made in the same Chinese factory. They are probably sold under other brand names. 

These Meade, Celestron and Astromania zooms are basically identical. The Meade has an aluminium barrel as opposed to the chromed brass of the other two. I can use two of them in a binoviewer.  

[CLOUD90]

That's crazy are the prices all the same? And with the alignment I'm pretty sure it asked for both. first with the finder and then through the eye piece for each star. would I need to check to see  if the finder scope is in  line with the actual scope as I did take it off to replace the battery I didn't know if I have to adjust it or will it be at a fixed position probably a silly question I know but have no clue lol

[Zeta Reticulan]

I think the Meade was the most expensive. The 'Astromania' was almost half the price of the other two. Sometimes you pay for the name. Astronomy has a lot of ridiculous mythology. Something distributors can often take advantage of with disingenuous advertising. One of these myths is of the 'incredible' Meade zoom. Which supposedly was super brilliant with outstanding contrast and bionic abilities with super brilliance or something. Like an idiot I fell for this ridiculousness. Apparently Vixen originally made these super brilliant Meade zooms. Meade actually manufacture very little. 

So I acquired a Vixen zoom with this alleged super brilliance. They were made in Japan. Where all optics are super brilliant. Supposedly. I returned three in a row due to visible debris in the field of view. They weren't super brilliant either IMO. I don't own a Vixen zoom now. I wasn't that impressed to be honest and I preferred my other zooms. The myth of the superiority of Japanese optics is another that quite frankly mystifies me. Tele Vue eyepieces are actually manufactured in two factories. BASO in the ROC and a factory in Japan (I suspect Ohi Optical). BASO is the oldest optical company in Taiwan, originally an offshoot of a German company I believe. I have no idea where in Japan Tele Vue have their eyepieces made. The only TV eyepieces I've had to return due to being faulty  were Japanese made. There's no difference in quality between Japanese made TV eyepieces and Taiwanese made TV eyepieces. Except in mythology. I still recommend the SvBony aspherics, although the Meade versions look quite reasonably priced (avoid the 4mm). There are a plethora of distributors and brand names. Most actual original equipment manufacturers are based in the PRC and elsewhere in Asia. Everything else is marketing, suggestion, mythology and advertising. Caveat emptor!

 

Edited August 1, 2022 by Zeta Reticulan