Barlow and eyepieces for Skywatcher Evo 80ED

[Horatio]

Just purchased a Skywatcher ED80 refractor and apart from the supplied 2" 28mm LES eyepiece I have the Ultrawide 6mm Skywatcher 1.25" and the Skywatcher Super Plossl 40mm.

I am looking at purchasing a 2x or 2.5x Barlow and was after any recommendations?   Also have I read somewhere that I have to have a certain 'type' for the supplied 2" star diagonal?  Would I better be off purchasing one that can fit both 2" and 1.25" eyepieces or for optical quality sticking with just a 1.25" (does it affect optical quality even?)  Celestron Luminos for example

My other question is can this scope take (visually acceptable) a 2.5mm eyepiece and take it to the max possible magnification if I required max even.

Last question is Sky-Watcher SWA 70° Eyepieces on offer at FLO at the moment, anybody have any thoughts or feed back as I was thinking about an Hyperion to add to the eyepiece collection.  (thinking about 13mm-17mm)

Sorry, a load of questions but I live in West Wales and have no local suppliers within 100 miles, I'm happen to be going past FLO at the end of the week and I've a credit card .....gulp!

[Louis D]

6 hours ago, Horatio said:

Just purchased a Skywatcher ED80 refractor and apart from the supplied 2" 28mm LES eyepiece I have the Ultrawide 6mm Skywatcher 1.25" and the Skywatcher Super Plossl 40mm.

I am looking at purchasing a 2x or 2.5x Barlow and was after any recommendations?   Also have I read somewhere that I have to have a certain 'type' for the supplied 2" star diagonal?  Would I better be off purchasing one that can fit both 2" and 1.25" eyepieces or for optical quality sticking with just a 1.25" (does it affect optical quality even?)  Celestron Luminos for example

Using barlows with refractors is problematic because they usually require quite a bit of back focus (ability to rack the focuser inward) to reach focus.  The work-arounds are to use a shorty type barlow, a barlow with a nosepiece that is threaded to screw onto either a 1.25" or 2" filter thread and then thread it onto the front of the diagonal, or use a telecentric type magnifier like a TV Powermate that shifts focus very little.  If you have a 2" diagonal, then you would need a 2" barlow to take the middle approach.  The GSO ED 2" 2X barlow is very good and can be used in this manner.  I find quality 2" barlows work better with 1.25" eyepieces than quality 1.25" barlows.  Sure, there are the super premium 1.25" barlows costing hundreds of dollars, but I'm not going down that route to see how good they might be.  To be honest, I'd hold off on the barlow and fill in some of your eyepiece gaps first.  You need a good anchor eyepiece for mid power in the 10mm to 14mm range.  You'll end up using it the most because they yield an exit pupil close to 2mm which tends to be ideal (15mm in your case).  Given the 600mm focal length of your scope, you might want to err toward the higher power, smaller exit pupil end of things.

My other question is can this scope take (visually acceptable) a 2.5mm eyepiece and take it to the max possible magnification if I required max even.

You could try, but the exit pupil becomes vanishingly small at 2.5/7.5=0.3mm.  You'll definitely be having issues trying to look past the floaters in your eye.  I don't recommend going below an exit pupil of 0.7mm, or about a 5mm eyepiece in your case.  Get a scope with a larger objective for higher powers.  An 8" reflector with a 1200mm focal length would immediately double your magnification and increase your exit pupil with each eyepiece.

Last question is Sky-Watcher SWA 70° Eyepieces on offer at FLO at the moment, anybody have any thoughts or feed back as I was thinking about an Hyperion to add to the eyepiece collection.  (thinking about 13mm-17mm)

These are the same as the Celestron Ultima LX, Olivon 70, AT AF70, and many others.  I have the 22mm, 17mm, and 13mm AF70 versions.  The 22mm is nearly as good as the Pentax XL/XW lines.  It shows minor astigmatism in the last 10% of the field, but has a flat field and is comfortable with eyeglasses.  Unfortunately, FLO appears to be sold out of them.  The 17mm has astigmatism starting about 25% from the edge along with chromatic aberration and gets worse near the edge than the 22mm.  The 13mm starts at about the 35% mark falling apart and shows stars as nice rainbow seagulls near the edge.  It's odd that this line seemingly gets worse with decreasing focal length.  Most eyepieces lines are just the opposite.  For instance, the Meade HD-60 12mm is quite good, the 18mm worse, and the 25mm not much better than the 18mm.  The Hyperions are reportedly similar, though I haven't looked through any, with the exception of the 21mm which is supposedly not that great, particularly when compared to the 22mm mentioned above or the 22mm Vixen LVW.

Sorry, a load of questions but I live in West Wales and have no local suppliers within 100 miles, I'm happen to be going past FLO at the end of the week and I've a credit card .....gulp!

Ask if you can try out the eyepieces in store in some of their scopes prior to purchase.  Camera stores let you mess around with lenses and camera bodies in store prior to purchase, so I would hope a telescope store would be as accomodating.  Focus objects in the center and then move them to the edge.  Look at subjects with a sharp bright/dark division as an acid test.  You should also try out any barlows first to make sure you can reach focus with them.

 

[Horatio]

Thanks Louis for your response that has helped me loads, really appreciate your time answering my post in such depth. 

I've had scopes before but never a refractor, so I knew there be new rules...