Louis D

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.

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.

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.

6 minutes ago, parallaxerr said:

Stop it now gents. At least let me ride the 82° wave before you drag me deeper!

You don't know the power of the Green & Black side:

Resistance is futile:

On 19/08/2019 at 08:27, 2STAR said:

It still gets Cloudy lol, we manage around 12 to 15 nights good sky per year.

Eric

Dang, move to west Texas or New Mexico and multiply that by at least 10.  That, and you'll be quite a bit further south with much darker and drier skies.

On 14/08/2019 at 18:05, JamesF said:

I'm not sure I like the look of the undercut on that, I have to say.

James

I'm glad they finally went with a screw-off 2" inch skirt like the ones on the AstroTech AF70 and similar eyepieces (Omegon Redline SW, etc.).  I despise the Televue dual skirt design that dates back to the original 13mm Nagler T1:

What a beauty!    I can't wait to hear how it works under the stars.

@WavseekerBe aware of how big and bulky the xx12i is.  It weighs 84 pounds assembled and the heaviest component weighs 50 pounds.  If you don't have a decent sized car to transport it, it will only get used from your light polluted backyard.  If you do transport it by car, it will take up quite a bit of space.  This isn't such a big issue in the US if you own a Chevy Suburban, but most cars in Europe tend to be somewhat smaller.

For travel, I would recommend either a 3" or 4" ED refractor or a 5" to 8" Mak or SCT.  Remember that Maks and SCTs have long focal lengths, so you won't be able to achieve low power views of larger objects.  I would start smaller because the smaller scopes tend to get used more.  If you find you like astronomy, then move up to a bigger scope in the future if you want to see more planetary and DSO detail.  You'll still have the smaller scope for grab and go usage.

5 hours ago, Cosmic Geoff said:

Or did you mean do we have experience of Optcorp? They don't disclose their location. That's enough reason not to buy from them.  They appear to be based in the USA, so you should add international shipping, taxes and duties to the price they quote. I'd advise you to buy in Belgium or the EU.

Optcorp is OPT, Oceanside Photo and Telescope.  They're one of the oldest and best astro retailers in the US.  The recently closed their retail store, so now they only do in person visits by appointment only.  They list their new address as 2245 Camino Vida Roble, Suite 102, Carlsbad, CA 92011.

They are now no different from Agena Astro and FLO in having no physical retail presence, so I don't understand why that makes them shady.  You might as well lump Amazon in that group.

As far as taxes and duties, I'm glad Texas doesn't collect sales tax on international sales and the US federal government exempts imports under $800 from tariffs.  What with the current weakness of the GBP relative to the USD, there are quite a few bargains for Americans to be had cross-importing from the UK.  For instance, if I were to buy all 7 BST Starguider eyepieces from FLO, they work out to $40 each with international shipping compared to $60 each bought locally from Agena Astro with free shipping.  Vixen SLVs are also considerable cheaper from the UK.  They're $109 each shipped to the US from FLO compared to $169 each shipped from Agena.

On 08/08/2019 at 10:59, JeremyS said:

And before you know it, you will have 3 cases 🙂

Nice solution, you've come up with.

And then another case for the binoviewer and eyepiece pairs when the binoviewing bug bites.

On 05/08/2019 at 03:03, M55_uk said:

older newbies also need a stool /chair, I can confirm

 

I can also confirm that an observing chair is important even for the younger set.  I started observing in my early 30s, and I used a chair from the first day.  It makes observing so much more relaxing.

Now, my older back aches after 4+ hours of being hunched over eyepieces during observing.  It can take several days for it to recover.  Anybody else have similar bback issues?

1 hour ago, Scott42 said:

Thanks for setting me straight!  I've used the WIdescans-types before.  So the UFF has some more lenses to flatten things out.   I see that there is no "safety groove" on the APM which is fantastic.   Weight is very reasonable at 19 ounces.

It's actually an entirely new approach to lens design to keep it slim enough for binoscope usage as well as being flat field.  The lowest elements actually form a telecompressor instead of the more typical Smyth or Barlow tele-extender.  The physical field stop (30.4mm as shown in the lens diagram) is smaller than the effective field stop (36.4mm as I measure it based on the above photo) as a result.

8 hours ago, M55_uk said:

Being a newbie myself, I have realised that one important bit that you need to factor in (if you havent already) is set aside some budget for eyepieces & telrad (optional). Hope this helps

 

Add in collimation tools for Newts in particular.  A well collimated Newt is beaten only by an APO refractor in my experience.

While learning the skies, an old fashioned planisphere is handy to have.  Sure you can use phone apps, but the older method helps you to understand the progression of the sky night by night and hour by hour.

For older newbies with presbyopia and strong astigmatism like myself, they might also want to invest in a dedicated pair of distance only eyeglasses to correct their astigmatism across the entire field of view.  This isn't possible with bifocals or progressive lenses.  Luckily, there are plenty of online places that make quality eyeglasses for very reasonable prices.

Other good accessories to invest in are a high quality OIII filter first and a quality UHC filter second, especially if you observe under light polluted skies.

7 hours ago, Scott42 said:

It looks good - not too heavy - and the price is right, I'd like to try one....the body looks similar to the TMB Paragon series.  Only 5 elements and 80 degrees, sounds interesting.   I did like the XW40mm better than the Paragon 40mm but the XW40 is far heavier.

https://www.apm-telescopes.de/en/eyepieces/more-74-ultra-wide-angle/apm-lunt-eyepieces/apm-eyepiece-uw-30-mm-80.html

Wrong 30mm APM.  That's the much older Widescan III clone.  It has severe field curvature leading to blurry edges.

This is the 30mm APM UFF I'm referring to.  It has 9 elements in 5 groups:

I did compare it to the Agena Astro version of the 30mm Widescan clone in this thread.  If you page down, I have several comparison reports.  Here's what they look like side by side.  The 2nd eyepiece from the left that says 20mm is really a 30mm Widescan clone that comes with a removable barlow element to make it 20mm.  The 3rd eyepiece from the left is the APM UFF.  The leftmost one is a decloaked original 30mm ES-82 when they had a twist-up, mushroom shaped eye guard.  The 27mm Panoptic on the far right is self-explanatory.

And this field of view comparison image includes all of the above eyepieces:

43 minutes ago, Scott42 said:

No one has mentioned Pentax XW's so I will....30mm and 40mm.  Currently only available on the used market.  I did a grand face-off contest between the TV offerings and these two - 41mm and 35mm Panoptics, 31mm Nagler.  The XW's are a bit lighter which was the first reason to try them.  They weigh about the same as the 35mm Panoptic, which is lighter than the 41mm Pan and 31mm Nagler.

After many comparisons I became a big fan of the XW's.  Under careful examination I got the impression that all 3 TV eyepieces imparted a yellowish tone to the stars, where the Pentax appeared pure white.  Also the XW's do not employ rectilinear distortion, so the stars appear normal when panning around, instead of visibly bending as the FOV moves across the sky.

Because there is no rectilinear distortion, the 40mm doesn't work so great at lower f-ratios typical of big Newts - you see the field curvature at the edges where the Tele Vue keep the stars as points to the edge.   However the 30mm XW has better edge correction and it's worked well for me at f/5.6.  Between the two of them you have a great high-contrast eyepiece that works well on long & short f-ratios.  I've avoided the ES eyepieces because of heavier weight.

Have you tried comparing the 30mm Pentax XW to the 30mm APM UFF?  areyoukiddingme on CN claims the latter is optically better than the former, but he still prefers the former due to the sharper field stop.

It hasn't been made clear enough in the above posts, but a push-to scope will require you to periodically nudge your scope to allow your object to drift across the field of view of your chosen eyepiece.  At higher powers, this nudging happens more often.  To get more "hang-time", you'll soon be upgrading from simple 50 degree Plossls to super/ultra/hyper wide eyepieces to get longer "hang-time" between nudges.  To get well corrected wide field eyepieces that work well at f/4.7 gets expensive in a hurry.  The goto scope's tracking will allow you to use narrower field of view eyepieces because it will keep the object centered on axis where even simple eyepieces have very good performance.

The goto scope may come with its own host of issues.  Being mass produced, it may require some tweaking to get the tension between the drives and axes perfected.  There are even reports of having to have parts replaced or rebuilt to get them to operate properly.

The collapsible tube has the advantage that you can do prime focus DSLR photography of solar system objects by not extending the struts all the way, and the goto tracking will keep the object centered for short exposures that can be derotated and stacked later.

To add tracking to a push-to scope later, an equatorial platform can be added underneath it and the push-to system put into a tracking mode.  The goto system is a more integrated solution.

On 01/07/2019 at 14:46, Captain Magenta said:

... I’ve thus temporarily evicted my Astrotrac to accommodate them plus my new 3.5mm...

 

I'd be terrified having a cat lurking about behind an open eyepiece case perched on the edge of a table. 😱  The cats I've known over the years have a tendency to bat at things with their paw at random times.

8 hours ago, vlaiv said:

Indeed! I'm in the market for ~ 5mm-7mm eyepieces for planetary and simply love my ES82 11mm, but at present time, given that ES82 LER would cost me total of about 185e (shipping, import duties, tax, you know, all the nice things government makes you pay ) - that is a bit steep for me.

The US, and Texas in particular, have been minimizing taxes and tariffs on imports to encourage trade.  Too bad it's not being reciprocated.  Off my soap box before John knocks me off of it. 🤐

1 hour ago, vlaiv said:

Bump up ...

Anyone has any news on these now?

I see them stocked again at TS - they were in stock at some point at the beginning and were pulled out of stock - in all likelihood related to first faulty batch. They are back again, but I don't seem to see any further mention online of this "line" (or rather addition to existing line of EPs?).

 

I just bought a set of Paradigms to compare to the HD-60s.  It's your turn to buy some equipment to check out for the rest of us. 😁