Louis D

5 hours ago, Geoff Lister said:

The encoders in the mount are "dumb", in that they do not register an absolute position, but just give rotational pulses; it's the software in the mount/handset/PC that turns these into a position. At power-up, the software sets the Az/Alt position to zero (OTA facing North and horizontal). If the mount is level, manual slews to the first Synscan alignment object will give a corresponding Az/Alt reading on the display. The Virtuoso software just needs to be calibrated with the mount's celestial latitude (angle to celestial N), to give reasonable tracking; whereas Synscan needs that value + longitude + date & time so that it can form an accurate reference for GoTo alignment. Aligning with 2, or more, celestial objects, preferably with about 90 degrees Az difference, should help the software to record any slight errors in mount levelling.

Geoff

So, will the mount slew to where it thinks the first alignment star is located based on the initial zero position?  I've heard that's how some of these mounts work, which is pretty neat for beginners who don't know alignment star names and locations.

I'd recommend checking the classifieds for a GSO 2" dielectric.  I've got three of them under various brands that I keep with various scopes.  They are not light, though.  I don't think I paid more the $70 for any of them.  Admittedly, used prices and availability may be different in the UK/Europe.

I wonder why the need to pre-align the mount?  I've never had to do leveling or aligning of my Sky Commander DSCs on my Dob, and it's fairly accurate after two star alignment and gets better with each object realignment once centered.

On 14/08/2022 at 09:40, spacegalaxy said:

Okay, honestly I have reverse apeture fever. That's why I am asking how good a 40mm and 60mm refractor are. I am obviously going to look at the moon with it.

(P.S. Also what else can you with both of them except the moon and Sun?)

Starry nights

 

Achro, ED, or APO?  A 60mm f/11 achromat was the traditional entry point for astronomy for most of the 20th century.  I have a 72mm ED that is much more compact with slightly more aperture.  I really like its compactness and ability to accept 2" eyepieces.  Wide field views are fabulous with it.

1 hour ago, Don Pensack said:

Note, however, all the ultra high-end planetary eyepieces have been multi-coated, so a single layer coating is more likely to be a cost-cutting decision.

Well, Brandon eyepieces didn't seem to pass on the cost savings of single coating.  These 4 element eyepieces are $280!

2 hours ago, Don Pensack said:

An inexpensive Twist-Lock adapter will work just as well, and works well with undercut barrels.  No snag going in or out.

Yeah, but all the cool kids have BCLs. 😉

6 hours ago, bosun21 said:

Is there any direct benefit to be found in using a 2” as opposed to a 1.25”.

I couldn't use my ES-92 eyepieces in my refractors or Mak without one, so there is that.  However, for binoviewing, I use a 1.25" diagonal to keep the optical path shorter than in a 2" diagonal.

Using my 24mm APM UFF or 32mm GSO Plossl as a widest field eyepiece instead of one of my 30mm to 40mm widest field 2" eyepieces seems unnecessarily restrictive just to keep an eyepiece collection simple or to avoid balance issues.  Sure, my A-team eyepiece case weighs in at over 20 pounds, but there's a lot of observing joy packed in there.  I know someday I won't be able to hoist that weight, so I may have to split it across multiple cases.

5 hours ago, bosun21 said:

Which 30 or 31mm eyepieces would you recommend i should be considering? Thanks in advance  

    Ian 

I prefer the 30mm APM UFF to my 30mm ES-82 for both eye relief reasons and for image quality.  The latter has a bit bloated stars on axis and severe CAEP at the edge.  The APM has none of this.  My 27mm Panoptic might be a tad sharper on axis, but the APM trounces it for eye relief, field flatness, and edge sharpness.

1 hour ago, Don Pensack said:

https://www.baader-planetarium.com/en/baader-2"-clicklock-eyepiece-clamps.html

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1 hour ago, Mr Spock said:

If you can find one, a 20mm T5 Nagler would be a great choice.

On 11/08/2022 at 11:07, bomberbaz said:

I have already checked each eyepiece has a minimum (for me) 15mm ER

TV eyepiece specs for 20mm NT5 (see the column right of C, 12mm ER):

So, not a good choice for the OP who seeks a minimum of 15mm eye relief.  I was going to recommend it myself until I checked TV's specs and ruled it out.

Are the types of fisheye mappings applicable to eyepiece distortion?

3 hours ago, michael.h.f.wilkinson said:

I had the TMB Paragon 40mm and that listed a "true" AFOV of 68 deg (as measured from the effective field stop, i.e. how much of the sky do you actually see), and an "apparent" AFOV of 69 deg (the angle of the image you see looking through the scope). This means the Paragon has negligible distortion and can as such be named orthoscopic (as it said on the barrel).

The Lacerta ED 40mm also claims to have a 69° AFOV while in fact it has a 65° AFOV and a 66° eAFOV.  It's focal length in the center is 40.1mm and 31.1mm radially at the edge by my calculations.  Once again, like the 35mm Baader Scopos Extreme (70° claimed AFOV, 66° measured AFOV, 68° eAFOV), and 26mm Meade MWA (100° claimed AFOV, 83° measured AFOV, 90° eAFOV), the 40mm Lacerta ED (TMB Paragon) is targeting the AFOV of its benchmarked competition (35mm Panoptic for the Baader, 25mm ES-100 for the Meade, and 41mm Panoptic/40mm Pentax XW/etc. for the Lacerta/TMB).

It's quite easy to see below that the Baader is not 70° and the Lacerta is not 69° despite claims on either their barrels or in their marketing literature:

The Baader has a center focal length of 34.8mm and a radial edge magnification of 28.8mm, so only a 17% difference versus 22.4% for the Lacerta.  Thus, even more "orthoscopic".

The 40mm Meade Series 5000 Plossl is also low distortion at a 21.2% difference (40.4mm vs 31.8mm).  The edge does get pretty blurry at f/6, but the moon looks quite naturally round across the field in it.

A bit more magnified, you can see that there is some magnification distortion in the Lacerta at the edge, so it's not perfectly orthoscopic.  It's less than the "competition", though.

Probably 65° eAFOV.  My Meade 5000 SWA, Pentax XW-R, and Lacerta ED 40mm's are all 65°/66° eAFOVs despite having 69°, 70°, and 65° AFOVs, respectively.  If the Vixen LVW has a field stop of around 46mm +/- 0.3mm, that's the most likely explanation.

I wonder if the Lacerta ED 40mm (TMB Paragon) is better, worse, or the same corrected as the 42mm Vixen LVW? 🤨

It's probably far enough above the focal plane that it won't be very visible.  On the other hand, I had a brand new 30mm APM UFF with debris on one of the lower lenses which is practically coincident with the focal plane, and boy was that visible.  In the far right schematic below, the debris was on either the top of the second lens from the bottom or the bottom of the third lens up from the bottom.  Both are rally close to the internal field stop.  Either way, I exchanged it for another that was clean.

Try smacking the eyepiece sideways into your open palm with the debris side facing downward.  You may be able to displace the debris to the side wall.

Search on CN.  There's lots of reports on them there.  Basically, extremely fine polish, low glare/scatter, high contrast.  However, the edge falls apart in sub f/8 scopes starting at 50% out from the center.  The faster the scope, the worse the edge looks.  If you simply look on-axis and use the outer field for context, they're reportedly great.  They're supposedly terrific in slower scopes (think f/10 and higher).

7 hours ago, Mr Spock said:

I don't know if it is intended or not, but I'm happy with the result

Yes, they were one of the earliest eyepieces with the dual fit barrel (1.25" and 2").  Of course, Tele Vue had their 2" skirts before that, which Meade copied, but boy were/are they annoying.  There's not enough 1.25" barrel left to securely fasten it into a 2" to 1.25" adapter, so you have to use it in 2" mode, even if that means having to crank the focuser way out to reach focus.  I fixed that with my 12mm NT4 with a 2" extension ring and 5 O-rings:

Which dovetails nicely with your topic because that lowest O-ring sits on the lower taper of the 2" skirt's undercut.  That made it impossible to get a parfocal ring to tighten on the slope where I wanted it to be.  It kept wanting to slide down into the undercut where it was too wide, so the ring wanted to tip.  I gave up on the parfocal ring and switched to the O-ring solution as a result.

7 hours ago, Mr Spock said:

I've had enough of them. It's bad enough swapping eyepieces without trying to drop them without having to wrestle them out of compression rings as well.

Right there with you.  I've had eyepieces become nearly inextricable after snagging the compression ring and pulling it up and out of its channel, jamming the eyepiece in the tube in the process.

14 hours ago, Zeta Reticulan said:

In my experience, the only discernible differences between TV Plossls and NPL's are ergonomics, build quality, and focal lengths. 

 

 

And price. 😆

10 hours ago, Astroscot2 said:

I was a few miles north of Verdun.  What a sight. I recall a bus full of passengers drove past with its lights on? All I could think of was why is he not stopping.

In Nebraska, we were observing from the center line at a liquid fertilizer depot.  They had workers moving tanks around.  As long as we stayed well away from them and left no trash, they were okay with us being there.  As more people showed up closer to noon, the business owner gave all his workers an impromptu couple of hours off so they could get their families and observe the eclipse as well.  They were oblivious to what was going to happen right above them.  I picked the tiny town on purpose figuring that would be the case, and I was right.

18 minutes ago, cajen2 said:

To get more than 'you pay for in terms of results', consider a Vixen NPL 20mil, assuming its narrow FOV doesn't bother you. Best value for money range out there.

How well does the Plossl design of the NPL hold up at sub-f/5 focal ratios in your experience?  Tele Vue's Plossls are modified with slightly concave outward facing surfaces to get better correction at shorter focal ratios:

The field reducer is not going to play nice with widest field 2" eyepieces like the 41mm Panoptic or 40mm Pentax XW.  It might play fine with shorter focal length 2" eyepieces, though.

2" eyepieces are mostly useful for when the (effective) field stop approaches or exceeds the inner diameter of a 1.25" barrel.  They are also useful for securing big, heavy eyepieces like the 12mm ES-92.  Otherwise, there's no important reason not to go with 1.25" eyepieces at the shorter focal lengths.

Having an f/10 scope makes having a wide range of exit pupils difficult.  To get to even a 6mm exit pupil requires a 60mm eyepiece.  The closest would be a TV or Meade 55mm/56mm Plossl.  An exit pupil this large is mostly useful with narrowband nebula filters like an OIII.

If you start at 40mm as suggested above, you would have a 4mm exit pupil as your widest.  Next, a 30mm such as the APM UFF would yield a 3mm exit pupil.  A 20mm/21mm such as the StellaLyra 80, Ethos, or APM XWC HDC would get you to an optimal 2mm exit pupil.  At 1mm exit pupil, you could go with a range of eyepieces from 9mm to 11mm.  There's the 9mm Morpheus or APM XWC, 10mm Delos or Ethos, 11mm Nagler T6 or Apollo.  Below 1mm exit pupil, your options become extensive.  You could go with Morpheus, Delos, Ethos, Delite, Nagler, Pentax XW, Nikon SW, or various orthos.  I would not go below 5mm for a 0.5mm exit pupil, though.  My limit is closer to 0.7mm with a 7mm eyepiece.

5 hours ago, vagk said:

Do you know the 3 focal lengths and if there is a possibility of making them in the future?

Here's an old post on CN by Don related to this.  He mentions 22mm, 8.8mm and 6.5mm future focal lengths.  That 22mm would be huge and heavy!

As I say in this post in my Svbony 20mm thread, they do make for a excellent pairing in a binoviewer at long f-ratios, so keep that in mind.  You're not going to be able to pair up the StellaLyras in a 1.25" binoviewer. 😁

The StellaLyra UWA 20mm might be your best bet for long eye relief and excellent correction, possibly better than the APM XWA 20mm.  I've been happy enough with my 22mm NT4 to not feel tempted to buy one to find out first hand, though.

Here's a report on one here on SGL: