educate me on 2" eps

[nicks90]

I’m about to take the plunge and buy my ‘scope for life’ – a 12” flextube dob with aftermarket hilux coatings

Presently I have a small 130mm fast newt, and therefore to get useful magnification I use eps mostly in the 6-15mm range, with my 25mm plossl as a finder ep to compliment my finder scope. The 25mm currently gives me a mag of 26x and a good fov.

Obviously with the new scope having a FL of 1500, most of my eps are now in the high power range! So I am looking for a nice low power ep for cruising about and finding stuff. I’ve been told the maximum field of view achievable with a 1.25” barrel is a 32mm ep. This still would mean a mag of 48x which is a bit high for a finder! But as this scope accepts 2” eps, this opens up a whole new world which I am unfamiliar with.

So the question is, what is the widest field of view I can get with a 2” ep? And to start my 2” ep collection I was looking at just getting a 40mm 2” skywatcher modified kellner, as its cheap and buying the scope is wiping me out – for now

Is it worth getting something like this to assist in widefield finding, or am I wasting my cash?

Any help greatly appreciated

Nick

[John]

Hi Nick,

The 2" format can offer wider fields of view than the 1.25" one so it's common to have a 2" eyepiece or two in the set. The catch is that cheap 2" widefield eyepieces show quite a lot of distortion in the outer parts of the field of view when used with, say, an F/5 scope. The 40mm Skywatcher kellner would fall into this category with a vengence I'm afraid. A 32mm Skywatcher Panaview would be better (though still not ideal) but as you see, better widefield performance in fast scopes drives the cost up dramatically.

If the budget is tight It might be best to get a decent quality 30mm / 32mm plossl in the 1.25" fitting which will show as wide a view as a 1.25" eyepiece can show.

Edit: I mention 30mm / 32mm as an ideal low power focal length as the exit pupil (the bundle of light that exits the eyepiece) gets large and unwieldy with an F/5 or faster scope when used with longer focal length eyepieces.

[swamp thing]

Hi Nick

I'd go along with John here. A good 32mm 1.25" plossl is gonna be nice and sharp right across. No point in buying a cheap 2" wide field only to lose half the field of view due to distortion.

[Breakintheclouds]

Is there any chance for you to borrow an EP from anybody nearby? John's point about distortion is a good one, but having said that, I've used a 38mm Skywatcher Panaview with an f/5 scope and loved the views. Yes, there was a bit of distortion round the edges, but the views were so good I just didn't care, especially as the EP was reasonably priced. If at all possible, it might be worth trying something of the sort to see how much the distortion bothers you.

[Moonshane]

one option is these https://www.astronomics.com/explore-scientific-68-degree-wide-field-eyepieces_c495.aspx which I think are very good? personally I'd agree that unlessyou pay big money then you'd be better with a good quality 32mm Plossl but trying is a good idea.

[bingevader]

I have the 32mm Panaview and still love it!

I start observing with it most times before moving up to a higher magnification.

Yes, it's a little soft towards the edges, but not terribly so.

Here's a link in Europe for Maxvisions. There's a 28mm, 34mm and a 40mm all in 2" and they'd be super, maybe worth saving for rather than the other options!

There's another thread all about these Meade re-brands.

Cheers

[rl]

f/5 AND 2" eyepieces...hmmmmm..a similar set of choices forced me to spend some big money a few years ago. Trouble is, you will want the best out of a large expensive scope thike that. If you can afford it, i'd get an ES 82 deg 30mm s/h off astro B+S or a 28mm UWAN. I have the UWAN myself and can vouch for the performance. They go for about £170 s/h, but watch the weight. If that's still not good enough I'm afraid you will have to start saving for the dreaded coma corrector, but don't do this until you have one really good eyepiece in this range of focal lemgth. Coma correctors do nothing for cheap 2" eyepieces with off-axis astigmatism.

The low power widefield views are worth it.

RL

[Moonshane]

Indeed, they are coma correctors and don't correct other flaws. good quality eyepieces reveal coma whereas poorer quality often hide the coma with other flaws.

[ollypenrice]

I know they're very expensive but the high end widefield EPs clean up the edges on our 20 inch F4.1 to an incredible degree. Even good Plossls at long FL are very edge-distorted. I use a 26 Nagler but I'm sure there are less expensive 2 inch widefilds. I don't think I've tried any so I can't comment, but the 26 Nagler is the default EP in our big scope.

Olly

[cs1cjc]

Larger telescope do result is larger magnification and smaller field of view! Maximum field of view for a 1.25" eyepiece with a field stop of 27mm is about 1 degree (57.3*27*/1500). A 24mm Panoptic or ES68 or the very affordable Maxvision would be nice, giving a magnification of 63x. Maximum field of view with a 2" eyepiece with a field stop of 45mm is about 1.7 degree (57.3*25/1500). I find the Baader 36mm Aspheric to be satisfactory giving for you a magnification of 42x, though I realise that the exit pupil would be on the high side at just over 7mm.

With my F/4.5 and F/4.6, I like the improvement that the Altair Astro (aka Astro-Tech, GSO) makes to the view, though the effective focal length is increased by about 10%, so the field of view decreases (and exit pupil) decreases by the same amount.