I have an Orion XT-10 250mm f/4.8. For overview I want to use an eyepiece with a field as large as possible. I saw this 38mm which is actually unsuitable for normal observing as the exit pupil is too large: 38 / 4.8 = 8mm but it boasts a field of over 2 degrees which is a nice overview. For $84 it is not bad.
Does somebody have experience with such long eyepieces on a short Newton ?
Unless you're at a very dark site you'll find the sky background too bright and therefore the objects will lack contrast. I had a 36mm eyepiece and sold it for those reasons. I now have a 28mm Explore Scientific and it works very well with my f/5 Newtonian.
I use an Orion 38mm Q70, which is basically the same eyepiece. I mainly use mine for star hopping, but I also use it on each side of The Veil Nebula with an O-III filter with excellent results. The 8mm exit pupil is fine and many people go on about the large exit pupil which is overblown. Sure the edges are soft and I get an 8mm exit pupil but what I really like about this eyepiece is that there are zero blackouts or critical eye positioning, and I get a really big field of view with it for really large targets. IMO, this is a great "bang for the buck" eyepiece. If you want a bit better correction but also want the 2 degrees of field, I recommend the 34mm ES 68 degree eyepiece, which I also owned but only sold to get two eyepieces to replace it.
Note the shot of the moon with just a hand held camera through this eyepiece!
These "Q70" EPs are the worst mismatch for use in Newtonians. I looked into these and showed the worst astigmatism I've seen in my fast Newt's - starting from 25% out from the centre of the FOV. The Q70 range is the same EP as that mentioned by Sky, just rebadged.
The GSO SuperView range leaves these for dead if you are after a modestly priced super wide EPs. The Superviews are cheaper too.
These Q70's are better suited to very slow SCTs & Maks.
There is nothing wrong in going BIG with the exit pupil. Sure, not all the possible light can enter your pupil, but it's not like you see jack. I use a 34mm Meade SWA in my f/4.5 & f/4 Newts for extra kick in the TFOV (I limit my AFOV to 70*), and it is still good using it from my home in Sydney.
I even have a 65mm plossl. I can only use it in my fast Newt's from a dark site, but it is a gorgeous EP, showing no aberrations at all as these all lie outside the critical optical point of the lens arrangement due to the barrel limited AFOV of 40*. Though small, it is comfortable to view with.
All long focal length EPs will start to show an increasingly bright back ground, particularly from urban skies - it is not limited to large exit pupils. What an over large exit pupil will do is effectively stop down the aperture of your scope (the bright background is a given from urban areas). It's not like you see nothing in a smaller aperture, is it?
A 40mm EP will still be very, very useful with a fast scope, and the sky glow won't be too much to render it useless (a 50mm will from the big smoke). Over large exit pupils is unnessarily over rated as a detriment. If you know what it does, and work with it, EPs that give these are still very useful.
There is one thing that will help you see more from urban skies too - use a smaller aperture. The smaller aperture will proportionately give less sky glow, allowing for better contrast. I saw this with comet Lemmon, where it was much easier to see its tail in an 80mm f/5 refractor than an 8" f/4 reflector.
I have to respectfully disagree with some of the first part of your post Alex. I have had, and tried the GSO Superview eyepiece and it was far worse off axis than the 38mm Orion Q70 I now own. I owned a 30mm GSO Superview for one night only and got rid of it the very next day because the off axis aberrations were so bad...and that was at F/5 !!! There *is* off axis astigmatism in the 38mm Q70, but it is a lot less than the GSO Superview. It also does not start at 25% out. Well, it doesn't in my 10" F/4.72 reflector. Aberrations in my 38mm Orion Q70 don't start until about 50-70% out. You probably tried it @ F/4 which is a big difference. I am on my second one, which should tell you something compared to what you said about the GSO Superview, lol.
I *do* agree that my eyepiece is better suited to a longer focal length telescope, but it does wonders on my 10" F/4.72 reflector as a finder EP and for viewing really big things like the Veil, M-45, and a few....and I mean *a few* deep sky objects, so I really see no point in spending a large amount of cash to star hop and view minimal targets.
The 38mm Q70 not black out on you and it is one of the easiest eyepieces to use eye-placement wise.
Another point I would like to add: If you want to spend heaps on a well corrected eyepiece, you could spend up to $300.00-$350.00 US on a used 35mm TeleVue Panoptic. I also tried one of those in my scope and stars are sharp to the edges. However, there is a trade off: Eye placement on it in a fast scope is extremely critical. I went back and forth between it and my 38mm Orion Q70 and in all honesty, the critical eye placement of the 35mm Pan drove me nuts and I liked my 38mm Q70 more believe it or not. I also owned a 34mm ES 68 degree eyepiece which basically works just like the 35mm Panoptic, but I sold that off because eye placement was critical as well.
I don't see a point in spending $300-$350 for an eyepiece that will only be used as a finder eyepiece for star hopping or in looking at a few targets like the Veil etc. I spent just over $100.00 Canadian for my 38mm Q70 and I had $200.00 left over to get more gear.
I also did the comparison between my 30mm SuperView & a 38mm Q70 I was looking to buy, and found the exact opposite of yours!!!!
I was looking to buy it from a fellow IIS member who brought it over one night. He too looked through both EPs and saw the same thing.
I will say that the SuperView I have now I only use at outreach occasions as it is a very easy EP to use for novices. I don't use it for my own observing any more. Alas there is only so much inexpensive EPs can do for us right now. In another 10, 15 years could be another story.
If you do want a better age, then yes, a few more $ do need to be spent. But I don't subscribe to the big $$$ either. It comes to be a balance between AFOV, human eye physiology, mass of the EP, it's intended use, and what you are happy to use.
But if all you want is an inexpensive finder EP, either the 'Q70' or Superviews will do.
The reason you experience "blackouts" (also known as "kidneybean") with some eyepieces is that some particular designs have a lot of spherical aberration at the exit pupil. The larger Panoptics and a few of the Naglers were well known for this.
If you want a premium well-corrected (ie sharp) big eyepiece that doesn't suffer from this there are others, in particular Vixen's LVW 22, 30 and 42mm don't suffer from this and are otherwise similar to Panoptics, as well as the older LV30 and LV50. For something closer to 38mm, there's the TMB Paragon 40mm though Alex's experience suggests its not so well corrected in fast scopes.
Regarding your application vs price, I agree completely - there is no point spending big $ on a premium eyepiece if its only used a a finder.
Lastly 38mm is too long for an f/5 scope, the exit pupil will be too big. The longest eyepiece you should be considering is 30mm.
Another cause of `blackouts' is using a large exit pupil and the secondary mirror obstruction is actually blocking your eye pupil. If you use an 8mm pupil in a light polluted sky and your real eye pupil is only 4mm and the secondary obstruction is 33% ( the dark disc being 3.75mm diameter ) then you are only getting to see a sliver of your mirror as it is mostly obstructed by your eye pupil and the inner part by the central obstruction.
Just a reminder for the beginners that exit pupil is calculated by the aperture in mm divided by the magnification.
Most appraisals of off axis performance of eyepieces used that deliver exit pupils above what your eye can handle are actually apprasials of performance at slower ratios. If your eye can only take in half the delivered pupil then your scope is effectively stopped down to twice the F # . ie a an 8" F4 scope with half the pupil admitted is actually behaving as an 4" F8 - so you would expect some increase in edge sharpness despite the very large pupil coming from the eyepiece.
an 8" F4 scope with half the pupil admitted is actually behaving as an 4" F8 - so you would expect some increase in edge sharpness despite the very large pupil coming from the eyepiece.
... and a big black blob floating in the middle which is the shadow of the secondary mirror, out-of-focus.
I have been into astronomy for over 30 years. I am well aware that a 38mm EP gives a large exit pupil. That theory is overblown in my case as the exit pupil is just over 8mm and I use it as a finder eyepiece and for looking at The Veil with my O-III filter, and for other large objects.
The 38mm Q70 does not exhibit blackouts like other eyepieces do...it suits me just fine.
PS: Look at my sig line......it shows that I already have a 22mm Vixen LVW, and I already explained what the 38mm EP is for.
Totally true that there is no "perfect" eyepiece. There are eyepieces that will match certain types of scopes! As for the O-III and my 38mm Q70, I have used it and my O-III on the Veil and a few more targets. That eyepiece alone does wonders on both halves of the Veil with an O-III.
The drawings attached are not a work of art, but it gets the idea across as to what I saw with an O-III and my 38mm Orion Q70, and also two other objects I saw in that eyepiece. The filter was a 2" Celestron O-III, which has a narrow bandpass at 8.5nm. I have since sold that filter and obtained a 2" DGM Optics O-III, (15 nm bandpass), instead which I will be trying on the Veil again when summer comes.
Also, note the pics I took through this eyepiece of the moon and M-45 by just holding my camera against the eyecup of the eyepiece. If the edges were more corrected, this eyepiece would be all around excellent. Even though the 35mm Panoptic has a bit tricky eye placement, doesn't mean I wouldn't buy one! I have an observing friend who has one and I intend to keep on bugging him to try it out and one day I might pick one up because the correction is really nice in a fast scope.
