Louis D

Yes, you probably need more spacing.  The shorter the focal length, the greater the field curvature in a refractor.  That flattener is optimized for a certain focal ratio range, but curvature mostly varies by focal length.  I use a TS - 2'' Field Flattener - Universal Field Flattening Lens visually on my 72ED and have to space it out to about 127mm to get about the best correction for most of my eyepieces that focus at the shoulder.  Their values suggest the following:

• Achromatic refractor f/5: 100mm to 105mm
• Refractor f/6.6: 103mm to 109mm
• Refractor f/7.5: 105mm to 110mm

For the very short 72ED, these values are no where near long enough.  As a guess, I'd say to try adding 8mm additional spacing to start with.  I'm basing this on your corrector doing the same work as mine in half the distance (55mm vs 110mm) and I needed to add about 17mm additional spacing.

Pick up a used 8" or 10" Dob for a quick grab and go option.  Sure, you'll have to manually track, but it's manageable.

6 hours ago, Paz said:

I've made one last addition to my heavy set, a 10mm Delos as I found over time I was missing something at that focal length for the VX14. The problem is it would not fit in my case in the same way as the others and the out of place problem isn't easy for my eyepiece-case-ocd to handle!

The 10mm Delos is the only Delos I own.  It is a terrific eyepiece.  I'm thinking I might get the 6mm and 8mm Delos to slot in between my Pentax 5.2mm XL, 7mm XW, and 9mm Morpheus.  Right now, my old Speers-Waler 5-8mm zoom covers those gaps.

On 30/08/2018 at 01:21, Jean-Luc74 said:

Hello Mislav,

Great work on this Skywatcher Telescope! I'm looking into buying one.

Do you think that prime focus is achievable without voiding the warranty using a raspberry cam, described here: ?

https://www.instructables.com/id/Raspberry-Pi-Astro-Cam/ 

Is the prime focus location inside the original focuser or just on top of it?

Kind regards,

Jean-Luc

 

Prime focus is generally located well above the most inward travel position of a focuser to allow various eyepieces to come to focus.  The problem for the OP was that it wasn't at least 55mm, the required distance for a T-mounted DSLR.  That Raspberry Pi imager should have no problems coming to focus in that scope (or any other for that matter).

2 hours ago, garryblueboy said:

Slight update to green case thanks Gavstar almost there now 

I swapped out my venerable 27mm Panoptic of 20 years for the 30mm APM UFF this summer.  All good things must come to an end.

Unless you absolutely insist on having 82 degrees of field, the 30mm APM UFF is an excellent eyepiece with 73 degrees of measured AFOV and 16mm of usable eye relief.  With the possible exception of on-axis sharpness, it outperforms my venerable 27mm Panoptic in all areas.  It's considerably smaller and lighter than the 28mm Nirvana UWA if weight and size are an issue, and yet it only gives up 9 degrees of AFOV.

The main downside to it for me relative to the older 30mm ES-82 mushroom top that I own is that the 28mm WO/Nirvana's recessed eye lens vastly reduces eye relief for eyeglass wearers.  Why even have a twist up eyecup if you're going to start by removing 5mm or more of eye relief in the fully down position?  The 24mm APM UFF does the same thing, so I'm taking a pass on it as well.

@StuCan you check for central sharpness of stars in both?  I can't get my original style 30mm ES-82 to focus stars to pinpoints on axis like just about every other eyepiece I own.  They're always a bit bloated trying to find best focus between the blue and red sides of focus.

6 hours ago, Peter Drew said:

A Porro prism is a "spike free" arrangement but won't give you the angled benefit of a diagonal, where are they now?, they used to be a poular item years ago. A Pentaprism is a constant deviation prism, it will give an angled viewing position as per a PST which employs one, however it doesn't alter the input orientation so in use it maintains the original astronomical orientation.

What about about two diagonals at 90 degrees to each other?  The first would flip left for right while the second would flip top for bottom, or am I missing something?  Would that yield the 180 degree rotation needed for a refractor image to correctly orient it?

Yes, I have heard that this is the norm due to the roof edge in the Amici erecting prism causing a diffraction spike.  It's also my understanding that a porro prism or pentaprism would not cause a diffraction spike.

4 hours ago, balzer said:

I'll look into 40mm. Seems interesting thing. Thanks for your advice.

Having been observing for over 20 years, it's kind of exciting to see familiar patches of sky in a new way.  You pick out relationships between objects you don't notice while panning about.

1 hour ago, balzer said:

I thought of 24mm panoptic. Don't you think the 40mm is a overkill. It gives a me approx 14x magnification. My fl is 558

I use my 40mm Meade 5000 SWA all the time in my 430mm 72ED yielding 11x.  I love sweeping star fields, looking at large OCs like the Pleiades, Hyades, Collinder 70, etc.  I can almost take in the entire Orion complex at once with the 6.3 degree TFOV.  The exit pupil is still quite reasonable at 6.7mm as well.  My thinking is when you've got a short focal length, play to its strength, wide fields.  For higher powers, I use my 127 Mak on the other side of my alt-az mount.

8 hours ago, balzer said:

Which Ep should I replace for my Megrez90 ? Or are they fine?

I would probably add a widest field 2" eyepiece like a 41mm Panoptic, 40mm ES-68, or 40mm Maxvision.  Balance can be a challenge in a refractor with them, though.  After that, you might consider swapping out the 24mm Hyperion for a 24mm Panoptic and the 10mm Hyperion for either a 10mm Pentax XW or Delos.  I have the 10mm Delos and consider it to be near perfection across the field.

Here's a comparison review of the Zeiss E-PL 10x25 vs 24mm Panoptics in a binoviewer.

There's a pair of these Zeiss eyepieces on CN classifieds right now.

Denis on CN posted a long series of descriptions of Zeiss microscope eyepieces and his experiences using them in telescopes a couple of years back.

2 hours ago, 25585 said:

That is some seriously old school eyepiece construction technique.  Exposed retaining ring with spanner wrench notches?  It's probably why they covered it with that rather extensive rubber eye cup.

6 hours ago, 25585 said:

Going by CN; Orion Ultrascopic, Antares Super Plossl, Parks Gold & Baader Eudiascopic all have the same optics 35mm for the pseudo-Masuyama. Celestron should be the easiest to acquire due to brand, in theory. 

Here's a link to Don Pensack's excellent post on the subject from 2013.

15 minutes ago, DRT said:

I have had to let all of my TV eyepieces go

Some my reactions to your news:    

51 minutes ago, carastro said:

What about the 130P on one of those pronto mounts?  They look pretty easy to use, much better than a cheap EQ mount.  It's like having a standing height dob. (ish). 

Carole 

 

The problem comes in with that particular design that you can't leave the altitude clutch loose or the scope will tip backward above a certain altitude.  You have to keep it pretty tight which causes pretty jerky motions when not using the slow motion controls.  The AZ-5 (and AZ-4 before it) mount eliminates most of this issue by keeping the altitude pivot point passing through the telescope's center of gravity, rather than well below it as with the AZ-Pronto mount.  I say mostly eliminates because as the telescope tips backward with a tall, heavy eyepiece like a 17mm ES-92 in the focuser, the horizonal center of gravity shifts farther and farther away from the OTA's center of gravity causing the telescope to again tip backward above a certain altitude.  To counteract this, you need to have an equal weight protruding outward from the bottom of the OTA an equal distance away from the CG toward the objective.

15 hours ago, 25585 said:

Good idea for foam. I expect camping mats are similar.

And those interlocking mats clerks stand on.

Hmmm, I've never tried photography with my 72ED.  I'll have to give it a go sometime to see if I can reach infinity focus without a diagonal or extension tube installed.  You'll definitely want a field flattener.  It has so much field curvature, I rigged up a TSFLAT2 on the front of my 2" diagonal to flatten the visual field.  Without it, it reminds me of using a fast Newt without a coma corrector.

16 hours ago, R26 oldtimer said:

The bgo's have arrived, so has an ES 24/68. All of these plus finder, eaa cams, adapters, camera, 2" diagonal, filters and cables where in desperate need of a new case, so here it is...

Did you layer things on top of each other?  How are you going to get to various bits and pieces that aren't in the top layer in the dark while observing?

Are the axes clutched on that AZ Pronto mount in some manner such that you don't have to turn the slow motion controls to move the scope from one target to another in the sky?

Before buying my first telescope 20 years ago, I asked for buying advice from the astro community.  I was steered toward a very nice Dob that I use to this day.  I had originally been interested in a Meade DS-10 on a pier mounted GEM from Walmart.  It would have been horrible trying to deal with it's myriad issues.  The fact that that particular telescope and mount have practically zero resale value 20 years later because no one would buy it except as parts speaks volumes.

4 minutes ago, britto765 said:

Would the Celestron PS1000 Newtonian Reflector be any good? 

That's a Jones-Bird design which is notoriously difficult to collimate and doesn't yield all that great of images even when properly collimated.  The design uses a fast spherical mirror of 500mm focal length at a low focal ratio (remember, fast scope, losts of issues with a spherical mirror).  It then places a "corrector" below the eyepiece holder to double the focal length to 1000mm.  The corrector doesn't do a whole lot to fix the spherical mirror issues, though, so the images aren't all that great.

I'd also be wary of any telescope including a 3.6mm eyepiece.  It will be all but unusable in this scope because it will yield too high of a power for that scope.