11 replies to this topic

[lucam]

I have recently bought a used Denk II with the A38 OCS and Power Switch for use primarily with an AP 130GTX and less frequently with a Starmaster 14.5in. I'll be viewing planets and the moon from home and DSOs (with the Dob) from dark skies.

 

Relevant 1.25in eyepieces I already own are:

 

TV Plossl 32, 25 (pair)

TV Nagler 9

Tak LE 7.5

Tak Abbe Ortho 12.5 (pair)

Pentax XW 7

 

I am interested in one eyepiece pair for low power, large FOV viewing and something to push the magnification a bit further than the Tak Abbe Ortho 12.5 when conditions allow.

 

Low power: I have seen the recommendation for Pan 24 often but given that the field is almost identical to Plossl 32 and magnification with the low-power OCS is 26x vs 34x, are there significant optical advantages? The difference in cost is substantial (2 Pan 24 vs 1 Plossl 32).

 

Medium power: I don't have any 1.25 eyepieces in the 15-20mm range, I am thinking a pair of TV Delite 18.2 or TV Pan 19 may be a nice addition. Thoughts?

 

High power: In my first test (seeing was pretty crummy), the Tak 12.5mm was excellent on Jupiter in the middle power OCS but not so great with the high power OCS. It could just have been seeing - I didn't take the binoviewer out and compare in mono mode - but I'd like to have something that gives me 200x or so in the middle OCS position, so roughly 9mm. What are the thoughts on the N9 for binoviewing? Alternatively, I would consider a TV Delite 9 or even the Tak Abbe Ortho 9 but I'd like to keep a slightly bigger FOV if possible. Slightly lower power, what about Pentax XW 10? Anything else that comes to mind?

 

Thank you for the advice!

 

Luca

 

 

 

 

 

 

[The Ardent]

My favorite low power pair is the Panoptic 24. The wide apparent field and sharp correction are very satisfying .

An alternative to the plossls is the Ultima 30 (Eudiascopic, Parks, Tak LE equivalent) I feel these give better views than a plossl.

The other one I like is the Tak Abbe 32mm .

For higher power I like the 18 Delite over the 19 Panoptic for eye relief. Remove the outer shell for easy IPD.
See https://www.cloudyni...noviewing-r3110

[noisejammer]

Although I mostly use Baader Mk V's, I still have my pair of Denk II binoviewers.

 

I found that the Denkmeier collets did not work well using the turkey-leg style of Pentax XW or TV Delos eyepieces. The problem was interaction with the undercuts & I could not resolve this using the commonly advised tape tick. They are fine with lighter TV eyepieces.

 

I really don't like the 24 Pans - they exhibit a lot of pin-cushion. This doesn't matter for a driven mount but it's horrible when sweeping the sky. I have pairs of 35 Masuyama & 30LE which do very nicely. The TV 32 Plössl has an equivalent field to the 30LE. I also use 26mm Plössls but tend to skip over these.

 

Medium power - get an AP BARADV & screw its optic into the binoviewer or diagonal nosepiece. Then use your Plössls. Alternatively, 16T5, 13T6,  Noblex 12.5 or APM 12.5 Hi-FW all work fine.

 

On the high power side, I have pairs of 5LE,  7T6, 7.5LE and A-II 10's. These all work well but my orthoscopics get used most on the best nights.  I chase magnification using a 1.6x or 2x Barlow. That said, the sky usually dominates things and I suggest your first pair should allow a larger apparent field.

 

To sum up, you will probably be well served if you add a second 32 Plössl and 9T6 to your set.

 

Post scriptum  - I haven't used the PxS in many years - it requires a lot of focuser travel which upset the balance on my mount (currently a FTX v2 for my 4.5" & DM6 for my TOA150.)

[ngc7319_20]

Comments:

 

Lower power:  I recommend a some sort of 32 Plossl to start since the view is easy (good eye relief) and image is bright.  The TV 24 Pan is very nice also, and has wider apparent view, which gives a bit of a "space walk effect."  Eventually you will probably want both a 32 PL and 24 Pan in your collection.  Images will be brighter in the 32 vs the 24 -- which is useful for faint stuff like North American Nebula, Veil Nebula, etc., with narrow band nebula filters.

 

Medium power: TV 19 Pan are ok, but the eye relief gets tight.  It gets more challenging to keep both eyes at the correct spacing from the eyepiece eye lens.  TeleVue says 13mm eye relief, but they are measuring from the center of a deeply concave glass lens -- not the metal work.  The effective eye relief is much less.  I really like the Baader Morpheus 17.5mm in this range -- very long 20mm eye relief.   They are a bit heavy but not terrible.

 

High power:  The Nagler 9 Type 6 is very nice.  The wide apparent field is nice from an aesthetic point of view, and helps when tracking planets with an undriven Dob.  Issues with eyepiece alignment in the holders, etc., image merge, etc., increase as the eyepiece focal length decreases.  Also optical issues in the bino prisms also become more apparent.  So I would not go much below 9mm on the eyepieces.  It is better to use Power Switch / OCS / Barlows to get the very high powers by magnifying the image ahead of the bino.  A pair of Pentax XW are going to be pretty heavy.  I also like the Baader Morpheus 9mm -- again a bit large and heavy, but the view is very comfortable (but you already have one TV Nagler 9 T6).

[lucam]

Thank you all for your thoughts, I'll try to borrow a 9T6 from fellow local astronomers and see how it goes. The PxS works fine with the big focuser on the GTX and a RST135, which is very insensitive to balance. I can use all three magnifications if I add a short extension to the binoviewer and thread the OCS to the diagonal. Otherwise, I either run out of in-focus or out-focus depending on whether i thread the OCS to the Maxbright diagonal or to the binoviewer neck and can only use two out of three PxS positions.

Edited by lucam, 15 January 2024 - 03:12 PM.

[betacygni]

Here is what I recommend you do. Write out (or use a spreadsheet if you’re fancy) all of the effective focal lengths/magnifications/exit pupils resulting with all the different eyepieces you’re considering, including at all 3 power switch settings. Doing this might surprise you and prevent you from duplicating focal lengths at certain power switch settings.

With my powerswitch I’ve settled on 32mm, 25mm, and 18mm eyepieces. This covers all my needs in all my scopes.

Only thing you seem to be missing (after you double up the 32mm plossl) is an 18mm pair. I’d highly recommend the new Takahashi TPL. For planetary detail they have bested all I’ve put them up against, including some high end eyepieces such as brandons, tak orthos, and Delites. They are perfect eyepieces for binoviewing ergonomically and an ideal AFOV for two eyes.

I wouldn’t get any shorter focal lengths than the 12.5mm you already have, they will result in too high of power at higher power switch settings, and it’s recommended to achieve higher powers with the powerswitch, not short focal length eyepieces (shorter focal length eyepieces are harder to merge and more likely to be negatively effected by prism defects).

Edited by betacygni, 15 January 2024 - 03:33 PM.

[Sarkikos]

Here is what I recommend you do. Write out (or use a spreadsheet if you’re fancy) all of the effective focal lengths/magnifications/exit pupils resulting with all the different eyepieces you’re considering, including at all 3 power switch settings. Doing this might surprise you and prevent you from duplicating focal lengths at certain power switch settings.

With my powerswitch I’ve settled on 32mm, 25mm, and 18mm eyepieces. This covers all my needs in all my scopes.

Only thing you seem to be missing (after you double up the 32mm plossl) is an 18mm pair. I’d highly recommend the new Takahashi TPL. For planetary detail they have bested all I’ve put them up against, including some high end eyepieces such as brandons, tak orthos, and Delites. They are perfect eyepieces for binoviewing ergonomically and an ideal AFOV for two eyes.

I wouldn’t get any shorter focal lengths than the 12.5mm you already have, they will result in too high of power at higher power switch settings, and it’s recommended to achieve higher powers with the powerswitch, not short focal length eyepieces (shorter focal length eyepieces are harder to merge and more likely to be negatively effected by prism defects).

Have you compared the 18 Tak TPL's to the 18 Tak LE's?   The 18 Tak LE's have been popular for mono and binoviewing.  

 

Mike

Edited by Sarkikos, 21 January 2024 - 12:20 PM.

[betacygni]

Have you compared the 18 Tak TPL's to the 18 Tak LE's? The 18 Tak LE's have been popular for mono and binoviewing.

Mike

Unfortunately no, had some 30mm LE’s many years ago. I wasn’t all that into eyepiece comparisons back then, but ended up selling them preferring other eyepieces I had at the time. Just judging by how well my TPLs have done against my existing eyepieces I’d be surprised if the LE’s would have been better, but no way to know without actually comparing side by side of course.

[Sarkikos]

Unfortunately no, had some 30mm LE’s many years ago. I wasn’t all that into eyepiece comparisons back then, but ended up selling them preferring other eyepieces I had at the time. Just judging by how well my TPLs have done against my existing eyepieces I’d be surprised if the LE’s would have been better, but no way to know without actually comparing side by side of course.

I recall BillP liked the 18 LE's, particularly when Barlowed.  IIRC, he compared them favorably to ZAO's.  Binoviewers tend to require a Barlow/OCS to come to focus, and these would be needed in any case to reach magnifcations sufficient for planet viewing.  Just saying. 

 

Mike

[Kutno]

I'll try to borrow a 9T6 from fellow local astronomers and see how it goes.

 

Wise decision to try before you buy.  I love the Nagler Type 6s for binoviewing, and 16mm Nagler Type 5s, as well.

Edited by Kutno, 22 January 2024 - 06:46 PM.

[ABQJeff]

+1 to getting a second 32mm Plossl AND 2x 24mm 68 degree TV or ES (or APM UFF)

 

If you have the funds the TV 18.2mm Delite is reportedly fantastic.  I have an ES68-20 and Baader Morpheus 17.5mm, both also excellent in this range and of higher end.

 

For high mag, either use a Baader glass path corrector (corrects prism issues, reduces needed backfocus), and/or get another Pentax 7XW.  The TV Delite series, Pentax XW series and Baader Morpheus (6.5mm and 9mm) are all excellent as well.

Edited by ABQJeff, 26 January 2024 - 04:19 PM.

[Nerd1]

I have a set of Denk 2s with power switch and same ocs, and a 125mm f7.8 apo. I went with 32mm possls,  18.2 Delites and AT 7mm UWAs. Very pleased with all of my choices. Jupiter is pretty big with the 7s on full power. The 18.2 Delites are just beautiful,  no other way to say it. I think they are perfect for the Denk 2s. If only the seeing would cooperate. Just picked up a Celestron 8se ota today, unfortunately we are socked in with clouds until Sunday.  New scope curse strikes again.  But this coming Sunday evening is looking very promising for us in North Texas.