Help a newbie - eyepiece question

[Grippo]

Hi everyone, I'm a novice at this game and I have some very basic questions!

 

I have an Orion Starblast ii as a Christmas present.  It's a reflector with a 450mm focal length and 114mm diameter.  f/4.0.  It came with Sirius Plossl eyepieces at 10mm and 25mm.  Had some excellent experience so far looking at the moon, but my youngest is absolutely crazy about planets (Saturn in particular) so I'd like to get the right accessories to help us look at the planets in more detail (Saturn's rings, jupiter moons, maybe even colours/spot on jupiter?). 

 

If I'm understanding things correctly (And Warthog's pinned post about eyepieces was really helpful) then I should be thinking about accessories to improve the magnification in order to see the things we're interested in, but on a fast f/4.0 scope it seems like a Plossl smaller than 10mm wouldn't be a particularly good idea?  So, I'm after a bit of help to make sure I don't make any silly errors with what I do next!!  I guess my current thinking would be to try to find a short eyepiece (~6mm) that has decent eye-relief, and maybe add a Barlow lens at some future point?

 

• Would a 6.2mm Plossl be too uncomfortable with the limited eye-relief?
• If 6.2mm is a sensible size for what I want to do, are there any EPs that would be recommended?
• Should I just get a barlow to go with the 10mm EP?  2x or 3x?
• What should I be thinking about that I'm currently overlooking?

 

Long term, this will def be used for looking at the moon and planets.  It would be nice to expand that to interesting stars and other stuff later.  As for budget up to £50 would be easy, I could stretch to £100, maybe a little more for the *right* accessory if it makes a big difference to what we're trying to achieve.  Can easily get a few different things over a few months if that is the best use of my time and money too!

 

All help and advice very gratefully received!!!

[Grippo]

I mean, is it as "simple as these?

https://uk.telescope.com/Telescopes/6mm-Orion-Expanse-Telescope-Eyepiece/rc/1306/p/109904.uts

https://uk.telescope.com/Telescopes/Orion-Tri-Mag-125-3x-Barlow-Lens/rc/1306/p/109891.uts

 

Is there a catch with the wide-view Expanse type lens?  There's always a catch isn't there?... 🤣

[Pixies]

The catch - especially with a fast scope like  yours, is that you have to pay big bucks for an eyepiece with a wide field of view that will be sharp out to the edges. Your scope has a wide angle  of incoming light rays, which is hard for a simple eyepiece to focus at the extremities. The good news is, if you are interested in planets, they are small and if you can keep them cantered in the view, most reasonable eyepieces will be fine. However, with a manual dob at high powers, the target will be moving across your field of view quite rapidly, so this is where wide angle views can help.

You'll find everything is a compromise, including with cost! With eyepieces, especially if you can purchased good quality used ones, if you find they aren't your cup of tea, you can sell them on without losing too much money.

[Zermelo]

Hello, and welcome to SGL.

If you haven't already seen it, do have a read of this: https://stargazerslounge.com/topic/196278-what-can-i-expect-to-see/

I don't have experience of your particular telescope, but certain things apply across the board.

F/4 is a very "fast"scope, which has some advantages (wide fields of view) and some disadvantages. Two of the latter are:

- it will show an optical aberration called coma, which will distort objects towards the edge of the field of view (not an issue for planets, if you keep them centred)
- it will tolerate cheaper eyepieces less well than would a telescope with a slower F ratio

The eyepieces supplied with most telescopes tend to be quite cheap and do not show their capabilities very well. In your case, plossl designs are actually not bad, as stock eyepieces go. You may find the 25mm more usable than the 10mm.

The supplied EPs will give you magnifications of x18 and x45. You say that planets will be a particular focus. Well, two things that will limit your views of planets are :
(a) their altitude in the sky - Jupiter and Saturn in particular take a long time to navigate round the constellations, which determines how far up in the sky they are (the higher the better); at the moment they are not positioned very well for the UK (you don't say, but I'll assume that) in the next few years they will get better
(b) the conditions - this limits the magnification you can use, and the detail you can see. If conditions allow, you might want to go up to perhaps x150 for Jupiter and x200 for Saturn, though you will be able to see some features at lower magnification. The rings of Saturn and the four main moons of Jupiter will be visible at modest magnification. But planets will look small, and Saturn won't show much in the way of surface detail (Jupiter does start show distinct bands at medium magnification).

So your 25mm EP won't show you much on planets, the 10mm will do, if it's OK.

A decent barlow is a very useful accessory. As well as giving you extra focal lengths (hence magnifications) it preserves (or even extends) the eye relief of the EP it's used with. In some cases it can even reduce some of the defects inherent in the EP design. But should you barlow your 10mm stock plossl on an F/4 scope? I'm not sure - someone with direct experience of your kit may comment. You are correct that the eye relief of Plossls is dependent on their focal length, so you may well find that a 6mm ish plossl is uncomfortable to use, especially for children.

The rule of thumb for maximum magnification would suggest around x230 for your scope in excellent conditions. That would equate to an EP of around 2mm, which is very agressive. I think you could look to getting a decent x2 barlow and try it with your 10mm first. That would give you x90, which would be enough to show you some reasonable views of the planets if the EP plays ball. If not, you could perhaps look at a BST Starguider 8mm, which is a decent model. That would give you x56, and x112 with the barlow. The BST range have a decent eye relief and a 60 degree field, so would also be useful on other targets larger than planets.

A range of opinions would be useful, I hope you get some other responses.

Edited May 9, 2022 by Zermelo
typo

[Louis D]

I would also recommend getting a decent 2x Barlow to "slow down" the f/4 light cone so your stock eyepieces will perform better and at a higher power.

The 6mm Expanse is supposedly decent, but suffers from kidney beaning (SAEP) and poor stray light control from what I've read.  I'd probably get the 5mm Starguider instead.  They're also known as the Astro Tech Paradigm and Agena Starguider Dual ED.

If you can get your power up to around 75x to 90x, you should be able to easily see the moons and major bands of Jupiter, their shadow transits, the rings of Saturn, and perhaps some of its brighter moons.  Thus, a 5mm to 6mm eyepiece, or its equivalent with a Barlow would do.

A Barlowed zoom might also be a good choice to allow you to seek out the highest usable power without spending a fortune on individual eyepieces.

[Grippo]

Thanks everyone - these are really helpful responses and I'm very grateful.  Nice to see that I wasn't to wide of the mark, and to get some recommendations too.  I shall lurk on this friendly and fascinating forum to see what elese I can pick up!

 

Thanks again  for the help and warm welcome

[Mr Spock]

For a fast Newt like that a Barlow slows it down enough to use inexpensive eyepieces. The BST's already mentioned would be perfect. You could start with a Barlow at £45, add an 8mm at £49 either now or later. Then if you decide you want more, you could add a 5mm, which with the Barlow would give x180 and about as much as I'd recommend for that scope.

You can find the BSTs here 
https://www.firstlightoptics.com/bst-starguider-eyepieces.html

[PeterStudz]

I have a very similar telescope - a Skywatcher Skyhawk 1145p. One thing I would say is get a white light solar filter. I’ve had more fun with this than anything else. And with the solar cycle hotting up it’s a good time. 

I’d also echo what has been said already and get a 2x Barlow. I had a stock 2x Barlow with the telescope but it was rubbish. Replacing it with something reasonable was a good move.

For high power I find that the 5mm BST StarGuider plus 2x Barlow works well, especially on the moon. I wear glasses when observing and the eye relief has been fine for me. For planets like Jupiter and Saturn 170x is the max I found possible when the seeing was good.  I was even able to see the Great Red Spot on a good night although it was small. And you’ll easily be able to see Saturns rings. You should be able to get a little more magnification on the moon. 

The telescope is really best at wide field and I’ve had better views of things like the Pleiades and Beehive Cluster with this telescope than the much larger Skywatcher Skyliner 200p Dob which I also own. 

[Grippo]

1 hour ago, PeterStudz said:

I have a very similar telescope - a Skywatcher Skyhawk 1145p. One thing I would say is get a white light solar filter. I’ve had more fun with this than anything else. And with the solar cycle hotting up it’s a good time. 

I’d also echo what has been said already and get a 2x Barlow. I had a stock 2x Barlow with the telescope but it was rubbish. Replacing it with something reasonable was a good move.

For high power I find that the 5mm BST StarGuider plus 2x Barlow works well, especially on the moon. I wear glasses when observing and the eye relief has been fine for me. For planets like Jupiter and Saturn 170x is the max I found possible when the seeing was good.  I was even able to see the Great Red Spot on a good night although it was small. And you’ll easily be able to see Saturns rings. You should be able to get a little more magnification on the moon. 

The telescope is really best at wide field and I’ve had better views of things like the Pleiades and Beehive Cluster with this telescope than the much larger Skywatcher Skyliner 200p Dob which I also own. 

This is really interesting - my 7 year old is all about the planets and that's what got us started down this route, but the more I learn about all of this the more I can see what you mean about wide field objects, which are really exciting too!

[Grippo]

3 hours ago, Mr Spock said:

For a fast Newt like that a Barlow slows it down enough to use inexpensive eyepieces. The BST's already mentioned would be perfect. You could start with a Barlow at £45, add an 8mm at £49 either now or later. Then if you decide you want more, you could add a 5mm, which with the Barlow would give x180 and about as much as I'd recommend for that scope.

You can find the BSTs here 
https://www.firstlightoptics.com/bst-starguider-eyepieces.html

Thanks!!  The BSTs sound like a perfect balance of budget and upgrade for where we're at right now.

[wulfrun]

Another vote for a Starguider or two. I have a 5mm and it performs quite well in a similar scope (114/500). You'll probably pay more than the scope cost for anything majorly better.

One thing to be aware of, besides coma etc: the aperture of the scope is fairly small...meaning that if you go much higher power the view becomes dim due to a small exit-pupil. Not too bad for something like Jupiter/Saturn or the moon though. Additionally, following a target manually as it moves becomes increasingly difficult.

[PeterStudz]

9 hours ago, Grippo said:

This is really interesting - my 7 year old is all about the planets and that's what got us started down this route, but the more I learn about all of this the more I can see what you mean about wide field objects, which are really exciting too!

I started out in a similar way. My then 9yr old was showing an interest in the night sky and I thought it would be a great  thing for us to do together, which it is. Although until we both started using a telescope it was hard to tell what we’d be interested in looking at. I imaged more deep sky objects than planets but I didn’t appreciate the practical aspects. Deep sky objects require a lot of patience - you need to get your eyes use to the dark; it’s more of a winter thing and it can literally be freezing cold; because of light pollution here the best views tend to be around 1-2am… all of these things work against children. Well, they work against anyone! After a while it was obvious that she preferred planets and I was happy with it all. Although we were lucky in that a member on here gifted us an old 200p Dob which required some work. This did help with viewing the likes of Jupiter & Saturn which my daughter wanted to view at every opportunity.

However, we are still using the 1145p. We got a solar filter for it mainly for viewing last years partial eclipse but of course it was cloudy! But we discovered how much fun looking at the sun was. In fact Alice prefers solar to the majority of deep sky. And of course it’s during the day when it can be warm; no late nights & no need to get eyes use to the dark. Wide field views of objects like star clusters can be a little more work. For star clusters ideally you want to find something that you can view with a good about of surrounding black space. It’ll then look more impressive than simply filling the eyepiece with stars. Often they will have a shape and you want to be able to see the whole thing in order to appreciate that. And when surrounded by black space issues with a fast scope like coma/edge distortions aren’t so apparent. To make it more interesting for Alice I try and make sure I know some interesting details about the object - not just it’s name and the fact it’s a load of stars!

Sorry for rambling on and I hope this helps.