Louis D

Here's one last check for eye astigmatism.  Rotate your head around the optical axis of the eyepiece as you view through it to see if the star spikes rotate with the rotation of your head.  If so, it's your eye causing it.

My employer's insurance covers one free eye exam and one free pair of eyeglasses every year, so I've been very diligent about keeping my prescription up to date.  It's also good to go to check for glaucoma, cataracts, retinal tears, etc.

No, astigmatism makes point sources spiky.  Extended objects will appear blurry due to all the point source spikes overlapping, but point sources like stars will be starbursts.

Astigmatism focuses light into lines.  The human eye can have multiple axes of astigmatism of varying strengths.  Eyeglasses attempt to correct the most egregious offender, so there's always some remaining uncorrected astigmatism unless you get LASIK which corrects all defects at once.

Have you had an eye exam in the last year?  If so, check your CYL or cylinder correction number on your prescription.  If it's above 0.5, you'll probably see spiky stars at large exit pupils as with this 40mm eyepiece.

Also, don't expect the outer field to be in focus at the same time as the center of field unless you're using a visual field flattener with that scope.  Short focal length refractors have strong field curvature.

Were you wearing eyeglasses?  It sounds like you might have astigmatism in your eye if you weren't.

How did the view compare to other ~40mm eyepieces you own?

That's the exact scope I did my testing in, and stars looked sharp out to about 75% from the center to the edge.

If cost and weight is no object (and if Don is still making them), the Clement focuser would probably work for you with the appropriate adapter.  It's natively a 3" focuser.

I've got a 2.5mm Planetary TMB II Eyepiece on order from China via ebay.  For $35+tax I thought it would be worth a try.  Once I get it, I'll compare it to my 3.5mm Pentax XW and my 5.2mm Pentax XL Barlowed.  It might end up being a project eyepiece where I have to blacken or flock the interior to control stray light if the optics pan out.  If the optics are bad, I'll do an exposé on it here on SGL and write it off as a learning experience.  If I like it, I might get the 4mm version as well.

I have the Astro-Tech 72ED (original version), and it easily comes to focus with 2" accessories.  However, the focuser slips under heavy 2" loads, so I wouldn't recommend it.  If you're going to use heavy 2" diagonals and eyepieces near zenith, makes sure to look for an R&P focuser to help control slip.

As @Ricochet says above, it takes a long dovetail bar to reach balance.  It just barely works with a 6" and is better with an 8".  However, the focuser knobs then need to be at an angle to avoid hitting the bar.

I doubt the 45 degree Amici prism would cause backfocus issues with most eyepieces with the Sky-Watcher version.  They don't require all that much more infocus relative to 90 degree mirror diagonals.

There's nothing stopping you from putting both the EQ platform and Dob on a cart together.  To make the stack more compact, the Dob's original ground board can be replaced by the EQ platform's upper board.  You just have to transfer or replicate the sliding materials from the ground board to the EQ's top board.  Depending on the design, you may need to use tie-downs of some sort to lock the upper and lower platform boards together during transport so the upper board doesn't slide or slip off the lower board.

My attic here in Texas regularly hits over 130° F in the summer.  In my experience, certain thermoplastics shrink (like those clear, custom fitting display packages) and some glue types dry out and crumble (like hardback book bindings) up there.  My A/C-Furnace electronics seem unfazed, though.  However, they were designed for those conditions.  Foam, rubber parts, and urethane finishes seem unfazed as well.  As long as it's a dry heat (the usual case here), I haven't noticed any other problems with things stored up there.  It's well ventilated, so there's no mustiness.

17 hours ago, Dave scutt said:

would it work just as well as an EQ platform.

That's a DSC kit which is intended to help locate objects.  You still have to push the Dob about to find the object and to continue tracking it once found.

Maybe you were thinking of a GOTO kit?

@WJC Is that true regardless of where the magnification originates?  If a BV is used with the same eyepieces in a 400mm versus a 2000mm telescope, will collimation error be 5 times more obvious in the 2000mm telescope?

Wow, the top of the BHZ is totally different from the Celestron Regal 8-24mm zoom:

There's nothing flimsy about its eyecup once it's screwed on.  It has an inner plastic track that the outer ring twists up and down on.  I'm surprised Baader chose such a flimsy eyecup attachment method.  I've read that the Leica ASPH also has an easily broken eyecup.

The problem for me with this particular zoom is that at high powers on manually tracked alt-az mounts, wide fields of view become much more useful for extended dwell time to examine your object between nudges and settling times.

I'll probably stick with my Speers-Waler 5-8mm in that range despite it being wildly non-parfocal throughout its range.  That is, unless this zoom is inexpensive.  If it comes it at $200 to $350, I'll have little to no incentive to buy it.

I have one of these I stash in the back of the van when moving boxes:

165 lbs. Capacity Aluminium Folding Dolly Push Hand Truck in Black

It might work well for you as an alternative.

On 05/09/2022 at 01:41, TheLookingGlass said:

but at the expense of very noticeable chromatic aberration on bright stars at higher powers

Probably due to spherical aberration.  I remove it for planetary observations as well.

5 hours ago, wookie1965 said:

How did you mount your phone please I would like to do that.

The 6mm and 9mm Red/Gold line Expanse clones are supposed to be pretty decent in faster scopes thanks to the integrated Smyth/Barlow lens slowing down the light cone.  However, they are poorly matched to the upper positive section leading to strong SAEP (kidney-beaning).

I would lean toward a 7mm as well given your scope's focal length and typical UK seeing conditions.

I can't answer that question, but with the addition of a low cost #8 Yellow filter, you could cut out a lot of the purple fringing of the achromat and substantially sharpen up the image in the process.

Is the red Hα?  You'll have to compare visually to see if it shows up at all to the human eye with the UHC filter.

I've measured the 30mm APM UFF's AFOV at 73°.  Its eAFOV is 70° due to some edge distortion.

If you're only going to be using it an f/10 SCT, I'd recommend the various 30mm WideScan III clones.  The field curvature isn't so bad for younger eyes at slow focal ratios.  It's very sharp in the central 50% even at f/6.

Here's a comparison image taken through my f/12 Synta Mak for several 30mm wide field eyepieces:

Notice how well behaved the 30mm (ignore the 20mm marking) Agena UWA 80° eyepiece is.  There's no SAEP or CAEP, and 18mm of usable eye relief.  It also shows significantly more TFOV than the 30mm APM UFF and about the same as the 30mm ES-82, but with significantly less edge distortion and no CAEP.  It's sold under many brand names.  Here's the APM Eyepiece UW 30 mm 80° version.  Here it is from an ebay seller.  I can highly recommend it for slower scopes.  I passed mine along to my daughter for use in her Synta 127 Mak.

23 minutes ago, cajen2 said:

Are you sure you're happy with the FOV? According to the photos, they're 46°. At that price, far wider fields of view are possible.....the 82° ES 30mil, for example.

It's this one I'm sure.

Try reading the Cloudy Nights threads returned by this google search to see if they answer some of your questions and concerns.

For an unobstructed system, you should be able to use the 41mm Pan in faster scopes as long as you don't mind losing a few photons to your iris and dealing with a brighter sky background.

Since the 30mm APM UFF's field lens is a bit over 40mm in diameter, it should be possible to scale the design upward a bit before it completely fills the inside diameter of a 2" (~46mm) barrel.  Perhaps a 35mm might be a possibility?

Other than the Pretoria eyepiece, a couple of Brandon eyepieces, and an APM Barlow, eyepieces and Barlows don't correct the coma of the primary.  You'll need to buy a coma corrector for the f/4.7 primary mirror.  Coma will be quite strong in most wide field eyepieces in that scope without a CC.

The 12mm and below Starguiders will still perform well with your scope in all likelihood.  At 15mm and above, I'd be looking at other designs better suited to fast scopes.