Louis D

I have the 14mm XL, 10mm Delos, 7mm XW, 5.2mm XL, and 3.5mm XW.  The Delos is flat of field and sharp to the edge with or without a coma corrector at f/6.  I have never had blackout issues with it.  The 14mm XL has field curvature, as does the 14mm XW as I understand it, but is otherwise flawless to the edge with refocusing.  The 7mm XW has a finicky exit pupil and weird chromatic aberrations at the edge.  I rarely use it because of these two strikes against it.  The 5.2mm XL is flawless edge to edge like the Delos with an easy exit pupil.  The 3.5mm XW is very well behaved as well, but rarely used due to seeing conditions and floaters in my observing eye.

It might help to list what eyepieces you already are using in this range to avoid recommending something you already own.  Also, are you using a tracking mount?  If not, then the hyper-wides can be advantageous.

You could also post your question to Cloudy Nights as it is US based.  You might even be able to connect with a local AZ stargazer and be able to borrow equipment for evaluation.

You could try the TS-Optics Skywatcher 2" adapter.

7 minutes ago, RobB said:

Hopefully I'll be able to take one with my own telescope this weekend although South Devon isn't particularly known for clear skies.

Maybe so about the clear skies, but from the looks of photos of the countryside, it appears to be a very beautiful place to live.

There's a pinned topic on Cloudy Nights with lots of input on just this subject.

I have both a late 90s era Lumicon and a Zhumell OIII filter.  The Lumicon shows the Veil nebula as bright, crisp, and detailed in a 15" f/5 Dob.  The Zhumell is more of a light pollution filter by comparison.  The Lumicon appears to be a mirror when viewed directly, the Zhumell looks more like a weird green filter.  I'm not even sure the Zhumell uses dichroic coatings because of this.  The Lumicon was over $150 20 years ago.  The Zhumell was $16 five years ago.  You make the call on manufacturing quality based on that alone.

The Celestron Omni eyepieces are average Plossls.  A very minor step up in quality.  If you were going to buy Plossls, I would recommend the Revelation line made by GSO in Taiwan.  I find them to have a bit better polish and coatings and better attention to stray light control.

The Baader Planetarium eyepieces are classic orthoscopic eyepieces which yield a nice jump up in planetary observing.

Other options for upgrades would include the various TMB Planetary eyepiece clones and the BST Starguider eyepieces.  They will have wider apparent fields of view with better eye relief, especially at the shorter focal lengths.

19 hours ago, Andy R said:

When having a drive round oz a few years back I went from Cloncurry to Noosaville in 22hours of solid driving in 1978 Hiace camper van. Well apart from 1/2 lunch and a several fuel stops. Something like 1800km. The experience has stayed with me as it doesn’t bother me driving from North Wales to Essex and back in a day just for a cup of tea and a catch up with my mates. 

It's what you're used to.  I can't believe people actually fly directly (not a connection flight, mind you) between Dallas and Austin or Dallas and Houston when it's actually quicker to drive when you count in all the time it takes to get to and from the airports and get through security and boarding, etc.  I've driven 900 miles and 18 hours solo with just quick stops for food and fuel as well.  We road-tripped 3000 miles in two weeks on vacations when my kids were younger, now they think nothing of driving 500 miles solo in their early 20s to get to or from college, friends, holidays, etc.

@parallaxerrThat's a mighty slippery slope you're heading down.  You better watch your wallet carefully.  I've got thousands of dollars tied up in eyepieces, and I'm no where close to done. 😁

6 hours ago, widotje said:

Hi there,

I've made a video to discuss the main differences between eq and alt az mounts here: 

https://youtu.be/Ii5Ey3MUbU

Perhaps useful for those who have similar questions.

Clear skies!

 

I'm getting "Video unavailable".  Can anyone else see it?

One thing I noticed about my 127mm Mak is that if you defocus a star, there's a black hole in the center of the light disk due to the central obstruction.  As I bring the star into focus, the hole gets smaller and smaller, but at best focus, it seems to be preventing all of the light energy from being focused to a pinpoint.  The star just won't collapse into a perfect pinpoint.  In fact, the focused star seems to twinkle, possibly due to thermal acclimation issues.  It reminds me of the black hole trying to push out all the light crowding in on it.  I'd swear I can still see glimpses of a tiny black pinpoint in the center of the star at best focus.

I then tried the same experiment with my co-mounted AT72ED.  A star defocuses to a perfect disk all the way to the center.  Then, as the star is brought to focus, it just goes down to a tiny pinpoint without any fuss.  There is no twinkle, either.  Perhaps due to better thermal acclimation.

On 03/09/2019 at 07:36, LukeSkywatcher said:

I cant justify the cost because of the traffic in my town. Its quicker to walk anywhere, and it's free.

Sounds like Manhattan.  Only 22% of the residents there even own a car.  That's not much of a surprise when it costs $300,000 to buy and maintain a parking spot there.

I find doubling my aperture shows a noticeable increase in resolution and limiting magnitude visually.  So, for your 130p, that would be 260mm.  The closest scope available would be 250mm or 10".  For your budget, I'd have to second @Victor Boesen's recommendation of the Sky-Watcher Skyliner 250PX Dobsonian.  You'd be hard pressed to see much difference visually between the 130p and 150pds.

It kind of depends on how wide you want your apparent field of view to be and how well corrected you want it to be to the edge.  Wider and better corrected is going to cost more.

It also depends on how fast your scope is.  Lower f-ratios put more demands on eyepiece design to maintain good correction across the field of view.

It also depends on whether or not you have a tracking mount to keep objects centered.  If you always observe on-axis, many low cost eyepieces do quite well against the higher cost alternatives.

Then, there's the issue of poor contrast and ghost images in some low cost eyepieces that many beginners fail to even notice because they've never seen better.

And then there's the issue of sufficient eye relief for eyeglass wearers that tends to add to the cost.

Add it all up, and premium eyepieces end up costing a lot more because you get wider fields of view, better correction to the edge, better ability to handle steep light cones, better polish/coatings/stray-light-control, and longer eye relief.  An example of this differential would be the 17mm ES-92 compared to a 17mm ebay Plossl.  The ES-92 is breath-taking from edge to edge while peering into with eyeglasses.  The Plossl is frustrating to use with eyeglasses providing a straw-like view.  I won't even get into the other differences, as they become apparent with use of each.

4 hours ago, andrew s said:

Reminded me that NASA was given two spare Hubble class mirrors by the US military.  Although they might have a tendency to point the wrong way.

Now if anyone has a spare...

Regards Andrew 

As a matter of fact, Mike Clements in Utah did buy such a spare blemished spy mirror and built this.  Apparently, it has a permanent home now.

Does this make you wish the UK had a constellation of spy satellites with lots of spare mirrors?

As far as getting another eyepiece, I'd get a mid-power, work-horse in the 16mm to 20mm range to achieve a good, general magnification of 75x to 100x.  There are so many choices in this space.  Because you don't need to wear eyeglasses, you can save money, weight, and bulk by buying eyepieces with shorter eye relief.

I would get a GSO/Revelation coma corrector before I'd get a barlow.  The CC will help flatten the field as well as correct coma.  I added a 25mm M48 spacer ring to mine to achieve very good correction for eyepieces focusing within 5mm of their shoulder.  It is also useful for achieving focus with only a 10% increase in magnification.  I used it to take the following Mercury transit image with my 8" Dob:

I would get an FPL-53 doublet over an FPL-51 triplet.  The correction is nearly indistinguishable and the doublet cools down quicker, is less front heavy, and tends to have fewer collimation issues.

Have you considered using an off-axis mask on your 16" Dob to make it a 6" to 7" unobstructed system?  It would also help with punching through seeing conditions.

Any scope with a central obstruction will have poorer double star performance aperture for aperture.  It's a simple matter of optical physics.  Stars are much more pinpoint in my little AT72ED than in my 127 Mak or 8" Dob.  For instance, the E component is much more apparent in the Trapezium with the 72ED than with either obstructed scope.  The main four stars bloat too much in the obstructed systems to see the E component.

On 01/09/2019 at 15:39, davekelley said:

Given that the Hyperion provides the maximum FOV possible for this scope and the sharpest most contrasty image, it gets the thumbs up here! 

I often find that backing off on the power to the lowest amount that still resolves details works best.

Here's a review by Bill Paolini of the first three Vixen HRs released.  I apologize if you've already read it.

The Takahashi TOE eyepieces are also considered another good alternative in this space.

14 hours ago, Kronos831 said:

thanks for the help!, however, when i tried to take a picture of one lens, it slipped of my hand and broke,so i guess there goes my eyepiece

lesson learned:Never take your eyepiece apart...

 

Just be more careful in the future.  The lower barrel often holds the lenses in the upper barrel in place, so remove it upside-down to prevent the upper lenses from falling out.  If you want to remove the upper lenses, support them with a wide dowel and flip it over and slowly remove the upper barrel.  When putting the stack back together, reverse the procedure and slowly lower the upper barrel over the assembled stack to avoid a tipped lens that can jam in the barrel and chip an edge.

13 hours ago, Geoff Barnes said:

Now we're in Australia we too think nothing of 200 mile trips, it's just up the road!  

Yep, Australia dwarfs Texas:

But it's about the same size as the continental US:

6 hours ago, John said:

One thing to bear in mind is that I think fuel in the UK costs a whole lot more than it does in the USA. I don't know what the current price is in the USA but here it is around £1.25 per litre for unleaded petrol which equates to £4.73 per US gallon or £5.68 per UK gallon. 

 

I just paid $2.11/US gallon for gas (petrol?).  It's higher in New York and especially California, but still under $4.00/US gallon.  Maybe y'all have higher gas taxes.