Louis D

Remember, you still need about 15mm of usable eye relief for the Dioptrx to work well.

The old Meade 4000 UWAs were quite good.  The Meade 4000 SWAs were equivalent to the Tele Vue Wide Fields (better than an Erfle, but not as good as a Panoptic), and the original made in Japan Meade 4000 Super Plossls in smooth side were excellent, having been made by Towa as a 5 element design.  If you can find these used at good prices and in good condition, they're quite decent performers.

The modern Meade 4000 series only refers to their Super Plossl line as far as I know and are simply 4 element symmetrics that are little different from all the other Plossls coming out of China.  I would get the GSO/Revelation Plossls from Taiwan due to better consistency from sample to sample at a better price.

It's quite likely the Dioptrx fit on the modern Super Plossls, but they also fit on most Plossls out there with removable eye cups.

Dioptrx still need about 15mm of usable eye relief on an eyepiece to work well.

It fits on eyepieces with an eye cup lip of about 41mm to 44mm in outer diameter.  This is assuming the eye cup is removable.  Many non-TeleVue eyepieces have an M43 top thread once the eye cup is removed.  Then it's just a matter of it's tall enough for the Dioptrx to cam down onto it securely.

I've got the 7mm XW and 5.2mm XL in an 8" Dob and tend to use the 5.2mm more.  However, given your longer focal length, the 7mm would probably make more sense.  You could get a 5mm BST Starguider  as temporary stop-gap to see if you need that focal length as well later on.

If you go to a wider apparent FOV (AFOV) while maintaining the same eyepiece focal length, you'll see a greater true FOV (TFOV) without increasing sky brightness which does increase contrast and makes it easier to spot faint fuzzies.  That's why the 21mm Ethos is more desired than the 31mm Nagler T5 which is itself more desired than the 41mm Panoptic (aside from the desirability of wider and wider AFOVs).  Each step yields slightly less TFOV, but the sky darkens noticeable at each step as well.  Alternatively, when using nebula filters, the lower the power, the larger the exit pupil, the brighter the nebula appears per unit area.  Since the filter blocks most of the light pollution, the contrast get higher at lower powers.

On 09/08/2020 at 02:31, Kirby301 said:

I have tried but the view isn't as good being further away.

Then you need to buy eyepieces with longer eye relief like Pentax XWs, Delos, DeLites, Morpheus, Vixen SLVs, etc.  Many long focal length eyepieces naturally have long eye relief.  If you use them with a Barlow or telecentric magnifier, you can get to higher powers while maintaining or even extending the long eye relief.

4 hours ago, Don Pensack said:

Mine was Japanese-made, 1993, not the current Chinese-made unit talked about in the linked thread.

I don't know if there is a difference or not.  Mine had 4 elements.

Like the original smoothie Meade Super Plossls and 8-24mm zoom, the older, Japanese made items are better apparently.

I read on CN where someone resorted to using a Starizona reducer to get decent images at the edges with their SCT after trying many standard reducer/correctors.  Perhaps you got really lucky visually?

Have you tried unscrewing the back cover plate to see if there's any adjusting screws hidden underneath?  Apologies if you've already tried this.

3 hours ago, blinky said:

would F6.3 reducer, 2” Visual Back, 2” Diagonal, 35mm ED eyepiece work?

Nope.  You'll get all sorts of vignetting.  A 32mm Plossl is about the max when using a reducer.

It's not like they are an international, official naming body; so who cares?

I recommend putting Sorbothane pads under each tripod foot to dampen the vibrations in short order.

6 hours ago, RobertI said:

I would think a 2" UHC or OIII would work really well for the extended nebulae - sadly I have just invested in 1.25" versions and will not be upgrading soon unless a cheap one appears.

Twist the eyecup all the way down and try using the 1.25" eyepieces between your eye and the eyepiece.  You should be able to hand-hold them and slide them into the light path.

My concern would be, will the Nirvana 7mm be any sharper on axis than the BST Starguider 8mm that disappointed you?  Has anyone done a comparison between these two?

I must be the metal tubes causing the issues.  My Dob's tube is Sonotube and has no such issues.  It also has no dewing issues, either.  It also never gets cold to the touch in winter.

If FLO paid extra to get them branded BST Starguider, I hope they got a discount back from their supplier for their mistake.

2 hours ago, Gaurav Mk said:

Hello Louis D,

Your inputs about my prev question would be very helpful

Not sure which question you're referring to, but since you live on the coast, you probably have very good seeing, as long as you're not behind a coastal range.  As such, 150x to 200x with your scope should be quite doable.  However, I've often found that 100x to 125x yields better views of planets.  Pushing toward the higher powers is usually more useful on planetary nebula and globular clusters.  Highest powers above that can be used to split tight doubles.

5 hours ago, Gaurav Mk said:

Thankyou all.

I have two options in the eyepieces thay fit my budget-

1. Meade 6.5mm 5000 HD60 

2. Orion 6mm flat field edge on 

If someone has used or knows about these two eyepieces and would like to suggest me choose the best, it would be very helpful

No experience with the Orion, but the HD-60 is very good at f/6.  It has a wider apparent field of view than the Orion based on specs.  Ultimate resolving power?  Probably quite similar.  Here's a collage of test images I've taken through my eyepieces around the same focal length using a field flattened 72ED f/6 refractor.  It hangs right in there with the better eyepiece on edge of field correction.  I haven't tried to nail down how good it is at stray light control and contrast around bright objects.  It's probably not as good as the Pentax XW, but it's not terribly far behind, either.

And a diagonal unless you only plan on using it terrestrially as a spotting scope.

1 hour ago, John said:

On my SLR and now DSLR cameras position of the the focal plane of the camera is marked on the body with a symbol:

I wonder if it would be useful to have the field stop position (which has to be at the focal plane of the eyepiece) marked similarly on the body or barrel of the eyepiece ?

It might be useful.  In photography, one use is for panoramic stitching.  You need to pivot directly below the focal plane to avoid stitching issues with near/far objects.

For eyepieces, such a marking would need to be at the virtual field stop for eyepieces with lens elements between the objective and the physical field stop because those lenses generally move the focus position relative to the physical field stop just as a Barlow or focal reducer would.  For example, most positive-negative eyepiece designs have the physical field stop located above the focal plane (virtual field stop).

Another issue would be that it would have to be marked on the insertion barrel for eyepieces with a focal plane below the "reference surface".  A stamped marking on chrome or printing on Morpheus style kerfs might be difficult to read.

12 hours ago, Naveen said:

Hi all - looking for some

advice on eyepieces. I have seen beautiful views of Jupiter with its moons and Saturn and of course the moon. I have two extra 32mm and 10mm plossls but am looking for better lenses for planets which will show more detail? Which ones would you suggest? Many thanks in advance!

Back to the original question, I wouldn't go below an 8mm eyepiece.  I have a couple of 127mm Maks, and the power builds rapidly with a 1500mm focal length.  That, and you're only working with about 118mm of actual clear aperture due to the undersized primary mirror.  Thus, the exit pupil gets really tiny really quickly.  An 8mm eyepiece is only yielding a 0.63mm exit pupil, which is reaching the limit for extended objects.  The 8mm BST Starguider is quite good in that scope with very comfortable eye relief and a very usable 60 degree field.  I would also get the 12mm BST Starguider because ~190x is a bit high for Jupiter's low contrast details.  ~125x with the 12mm is usually much more usable.

3 minutes ago, Ags said:

I think it automatically adds info from each goto to its model, as you center the object then confirm. I can't the source where I read that though. The AZ GTi does a really good job of goto though regardless of whether it refines the model.

So, a rough initial alignment on two widely spaced stars as Don suggests should be good enough as a starting point.

How about "Insertion Barrel Termination Plane"?

Or "The point or plane of the eyepiece where the part you stick in the focuser suddenly gets wider and stops the eyepiece from going any further in" to be totally long-winded? 🤪

3 hours ago, Don Pensack said:

I'm in Los Angeles, and even here the bright stars are visible.

LA skies must have cleared up a bunch thanks to emission controls.  When I lived in the Mid-Hudson Valley in upstate New York 30 years ago, I could see the moon and 4 brightest planets, but almost no alignment stars thanks to the heavy smog layer.  There were clear days when I couldn't even see the sun due to the thick, gray smog.  I could only figure out where it was because it hurt my eyes when I was looking straight at it, so I figure either IR or UV light was making it through.  On some better days, the sun was a dull red orb.  If I drove 2 hours out into the nearby mountains to gain some altitude and lose some light pollution, the night sky was amazingly better.  The Hudson River acted like a super-highway channeling low altitude smog from the NYC metro area up to us.  I didn't take up astronomy until I moved to Texas 26 years ago.

Does it have "realign on current object"?  My Sky Commander DSC has such a feature to refine the alignment in each new section of the sky.  I find it helps quite a bit to realign on each object after I center it.