Too many slots in my eyepiece case!

[Ags]

I foolishly made an eyepiece case with 12 slots, and now I am struggling to fill it! Empty slots are not acceptable! 

My telescopes are a small F6 refractor and a small SCT, which is usually F6.3. If I add a telescope, it might be a 102mm F7 refractor.

From left to right, top to bottom: Vixen NPL 30mm, ES 68 20mm, Speers WALER 13.4mm, Speers WALER 10mm, ES 82 6.7mm, Speers WALER 4.9mm. I have only two slots to fill - something around the 24mm mark, and something around the 3.5mm mark. Note the 4.9mm Speers WALER does double duty as a 3.1mm with an extension ring, but it doesn't seem sharp in that configuration. 

I was thinking about the APM UFF 24mm as a widefield dark sky workhorse - does the "ultra flat field" mean the field curvature of my Zenithstar 66 will be less apparent?

For the other slot I am considering the Nirvana 4mm and the TS-Optics XWA 3.5mm. I had a Nirvana 16mm that I most definitely did not like, but I hear the 7mm and 4mm are better eyepieces. The TS XWA would let me play with 110° AFOV and would show a full degree of sky with my Zenithstar. It would also have to go in the case lying down, which means I will need to do more carpentry and several empty eyepiece slots will be blocked, which will be a mercy.

But assuming I fill those slots, how can I fill the remaining slots? I think there would be at least one slot, maybe four? I've tried SLVs and plossls, but the AFOV is too narrow. Maybe a zoom? 

[badhex]

Might be an issue with eye relief but have you considered a BCO or other ortho for planetary? The BCOs represent great bang for buck, and the 10mm or 6mm would be lovely in your C6.

Again, eye relief can be a bit tight though.

Edited November 4, 2021 by badhex

[Franklin]

Get a Binoviewer, then you can just double up your existing eyepieces?

Nice case btw.👍

[Ags]

53 minutes ago, Franklin said:

Binoviewer

Genius! The only problem is I don't get on with binoculars.

@badhex I have been thinking of getting some Starbase orthos for fun.

[badhex]

Interesting! I don't know much about these, although I'm sure I read a thread somewhere that they aren't true orthos, but not sure of the design. I could be mistaken though. Either way, definitely interested to hear more about them!

[Louis D]

15 hours ago, Ags said:

I was thinking about the APM UFF 24mm as a widefield dark sky workhorse - does the "ultra flat field" mean the field curvature of my Zenithstar 66 will be less apparent?

No.  It just means it won't add or subtract any OTA field curvature.

Get a TSFLAT2 and put it ahead of your 2" diagonal if you want to flatten your Zenithstar 66's field.

[Don Pensack]

15 hours ago, badhex said:

Interesting! I don't know much about these, although I'm sure I read a thread somewhere that they aren't true orthos, but not sure of the design. I could be mistaken though. Either way, definitely interested to hear more about them!

orthoscopic means "without distortion".  The 3:1 design for the Abbe orthoscopic eyepiece is only one of the orthoscopic designs.

Though the Starbase orthos are a 2:2 design, that doesn't mean they're not orthoscopic.  So long as the field is under 42-45°, many designs could be described as orthoscopic.

[badhex]

5 hours ago, Don Pensack said:

orthoscopic means "without distortion".  The 3:1 design for the Abbe orthoscopic eyepiece is only one of the orthoscopic designs.

Though the Starbase orthos are a 2:2 design, that doesn't mean they're not orthoscopic.  So long as the field is under 42-45°, many designs could be described as orthoscopic.

Thanks Don. I had mistakenly thought that only a couple of designs were generally considered orthoscopic. Also, it's entirely possible I'm misremembering whatever I read anyway 😅

[Ags]

8 hours ago, Louis D said:

No.  It just means it won't add or subtract any OTA field curvature.

 

I thought the typical eyepiece curves opposite to the telescope, so surely a flat eyepiece is likely to be an improvement?

Edited November 5, 2021 by Ags

[Louis D]

1 hour ago, Ags said:

I thought the typical eyepiece curves opposite to the telescope, so surely a flat eyepiece is likely to be an improvement?

Maybe in that case (like the 14mm and 20mm Pentax XWs) it would be.  In my experience, the 10mm Delos, 9mm Morpheus, 30mm ES-82, both ES-92, and 9mm Vixen LV all appear flat to my eye.  The 27mm Panoptic might have a bit as do some of the Nagler T4s (17mm springs to mind).  The 14mm Morpheus has a bit as well, although Don P. doesn't see any in his copy.  The worst are the 80 degree, 30mm WideScan III clones.  They have several millimeters of curvature center to edge.

[Voyager 3]

Several mm ? Then is it even possible to focus the field together at once even in a flat scope ? 

[Louis D]

9 hours ago, Voyager 3 said:

Several mm ? Then is it even possible to focus the field together at once even in a flat scope ? 

Nope.  However, I added enough spacing in front of my TSFLAT2 in my AT72ED to flatten its field once as an experiment.  Once I did that, it actually has only mild astigmatism to the edge.  That eyepiece design holds great promise if the designers would simply add a field flattening group ahead of the field stop.

I did the same with my Pentax XL 14mm and found it to be perfectly corrected edge to edge.  Again, I wish the designers had added a field flattening group to it.

[Don Pensack]

23 hours ago, Louis D said:

Maybe in that case (like the 14mm and 20mm Pentax XWs) it would be.  In my experience, the 10mm Delos, 9mm Morpheus, 30mm ES-82, both ES-92, and 9mm Vixen LV all appear flat to my eye.  The 27mm Panoptic might have a bit as do some of the Nagler T4s (17mm springs to mind).  The 14mm Morpheus has a bit as well, although Don P. doesn't see any in his copy.  The worst are the 80 degree, 30mm WideScan III clones.  They have several millimeters of curvature center to edge.

The scope in question is a 1587mm focal length with a field-flattening coma corrector.  Resultant focal length is 1826mm, and slightly flatter than a non-corrected newtonian with that focal length.

If you look at field curvature in a newtonian, where the ROC = the focal length, anything longer than 1.5m is very flat.

It is typically the shorter focal length refractors, with a ROC of 1/3 the focal length, that field curvature is an issue.

Evaluating FC of an eyepiece in a strongly curved field telescope has to take the scope into account--otherwise the report of FC is simply confined to one observer on one scope.

I've spent a lot of time now with the 9mm, 12.5mm, 14mm, and 17.5mm Morpheus eyepieces, and I see no obvious FC in any of them.

Stars exit the field with tight focus.

I do have to say, the 9mm is special--almost the RKE 28.7mm phenomenon--where the eyepiece disappears, leaving you looking at an image hovering about the scope.

It's amazing.

[Piero]

35 minutes ago, Don Pensack said:

I do have to say, the [Morpheus] 9mm is special--almost the RKE 28.7mm phenomenon--where the eyepiece disappears, leaving you looking at an image hovering about the scope.

It's amazing.

Interesting. That is the kind of feeling I have when looking through my Docter 12.5mm. I did not feel similarly for the Morpheus 9mm, even though I consider it a very good eyepiece.

Regardless of brands, observing whilst forgetting about the optical path, is a truly beautiful experience, a connection with the universe.

[Alan White]

9 hours ago, Piero said:

Interesting. That is the kind of feeling I have when looking through my Docter 12.5mm. I did not feel similarly for the Morpheus 9mm, even though I consider it a very good eyepiece.

Regardless of brands, observing whilst forgetting about the optical path, is a truly beautiful experience, a connection with the universe.

Interesting thoughts and agree with the second part from experience, it’s just wonderful.

On the special eyepiece, well for me that’s the APM UFF 30, it’s got something special about it, sometimes it’s the only one used for the session.

[Ags]

I do have some nonutilitarian ideas for filling the case. I could try and get a full set of Speers WALERs - I am missing the 7.2mm and 17mm, and it would be a nice project to try and get them all in the classic orange lettering incarnation. I also like the ES eyepieces, and maybe I can add the 4.7mm and 11mm. But this duplicates focal lengths and it's hard to justify to my Vulcan half. 

Edited November 7, 2021 by Ags

[Ags]

Just had a charming session with my SLV 6mm. The narrow field reminded me of being a kid with a toy scope, although this time I can find targets, there isn't any CA, the mount is less wobbly, and the eyepiece isn't an SR4. Maybe I will remove the SLV 6 from the Sell List and buy a few more... Also the eye relief is pretty good with the SLVs and keeping my glasses on does sharpen things up a bit.

[Ags]

Well, I have decided on a "final" collection of eyepieces, and I have placed the necessary advert in the Wanted section.

First a series of 6 widefield eyepieces:

 - ES 68° 20mm
 - Speers WALER 80° 13.4mm
 - Speers WALER 82° 10mm
 - ES 82° 6.7mm
 - Speers WALER 82° 4.9mm
 - Nirvana 82° 4mm

Of these I only need to acquire the Nirvana 4mm. I was considering an APM UFF 24mm as well, but with local light pollution I would only be able to use that eyepiece on rare trips to darker skies. 

To that I am adding a set of nostalgic Plossl-likes, all Vixen:

 - NPL 30mm
 - NPL 20mm
 - SLV 12mm
 - SLV 9mm
 - SLV 6mm
 - SLV 2.5mm

When I started this thread I had hardened my heart against the three I already have (NPL 30 & 20, SLV 6) on the grounds of their restrictive field of view, but one magical chance session later and I have turned on a pin and now I am on an SLV buying spree!  My logical Spock half tells me that the widefields offer the best framing and darkest sky backgrounds, but the Plossls take my human half back 40 years in an instant.

Edited November 8, 2021 by Ags

[apaulo]

not much wrong with the slvs  im happy with mine

[Ags]

I've never heard a bad thing said about the SLVs. If you can live with the retro field, they are ideal.

[Don Pensack]

The early ones (so: caution buying used!) had a bright shiny spacer under the eye lens that reflected the light of anything bright.

Later versions more adequately blackened this spacer.

I don't know when the change occurred.

[Ags]

Thanks for the reminder! I will check purchase date if I find any on the used market. But I suspect I will have to buy new, SLVs don't often come up for sale.

[Ags]

Well, I managed to pick up two NLVs second-hand - 9mm and 12mm, so my case is filling up!