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davhei

Low power eyepiece - Fast 10” dob

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Hi all,

Have been pondering low power eyepiece options for some time and would really appreciate some good input.

A few parameters:

I’m using a 10” f4.7 dob without paracorr.

As this will be used to find objects by star hopping I believe I need a minimum tfov of around 1.3 degrees.

Have had balance issues with EPs weighing in at 1 kg so it needs to be lighter than this.

I do not observe with eyeglasses but have long eyelashes and would like more than 15 mm eye relief if they are not to brush against the glass.

Good contrast. Compared the ES 82 30 mm to the ES 68 24 mm and the difference in contrast was striking. Really appreciated that.

As well corrected as possible. I am not hyper sensitive to coma though.

 

Have had an ES 82 30 mm and tfov was great. Weight, contrast and off axis less so.

Just got a Pan 24 that might be a good match, eye relief causes some concern though and I need to evaluate it a bit more (when I get clear skies, sigh).

Pan 27?

22 Nagler?

The other EPs in my case are Delos 14, 10 & 6 mm plus a x2 TV barlow. All of these are great, it’s the low power finder EP that I need to nail.

Edited by davhei

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First, I highly recommend getting a GSO/Revelation coma corrector and adding a 25mm extension to it or put the optics section on a Baader 2" ClickLock with 2" CL Extension 47mm.  It will massively improve edge performance on wide field eyepieces on your f/4.7 scope without breaking the bank like a Paracorr II would.

As far as wide fields at f/4.7, you'll want to stay below 33mm to keep your exit pupil at 7mm or less to avoid cutting off some of the light coming from your 10" mirror as it enters your eye and to keep the sky a little darker.  That leaves you with the 31mm NT5 and 30mm ES82 for widest field.  If you're willing to give up a bit of TFOV, there's the 30mm APM UFF.  You could jump up to a 21mm Ethos or 20mm APM XWA HDC Hyperwide to maintain a TFOV similar to the 30mm APM UFF but have a much darker sky background.  The 22mm Nagler has a TFOV more like a 27mm Panoptic or 28mm ES68, so not even close to widest TFOV.

Below are some photos I took through my f/6 AT72ED refractor of some of my wider and widest field eyepieces using a yardstick as a target and keeping the scope/target distance constant.  Your f/4.7 primary would be much more demanding on the eyepieces, so expect poorer edge correction on your scope.  They'll give you some idea of the differences you can expect (except that I don't have any 100° AFOV eyepieces).  The "full view" images were taken with an ultrawide, lower resolution camera and rescaled to match the on-axis image scale of the other camera's images.

1833175478_18mm-22mm.thumb.JPG.b2a9f1289172154a138f3813b09da0a4.JPG1381562251_18mm-22mmAFOV.thumb.jpg.88386d195597c48c65f2953c28d718d7.jpg905587778_23mm-28mm.thumb.JPG.5b345039b074716312b3ea6b26a46bed.JPG1124725079_23mm-28mmAFOV.thumb.jpg.af71e7f883fc2552cfae36880a508c9c.jpg1503910180_29mm-30mm.thumb.JPG.beb0e0b0d494a0fb027e38e2a180acef.JPG1270098715_29mm-30mmAFOV.thumb.jpg.b72cf50a97eb28a4217fd5188677c85a.jpg1633940429_32mm-42mm.thumb.JPG.bef44bf60fe3e68cfbac5e7ed8712d66.JPG2142447751_32mm-42mmAFOV.thumb.jpg.dead789621328694a186dcce97a21653.jpg

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Thanks Louis, much appreciated!

Problem with the 31 mm NT5 and I guess Ethos 21 as well is the weight. Just unbalances my scope too much att certain angles. I would trade some tfov for a lighter EP. With Ethos there’s the question of eye relief as well.

Realise I may have to compromise with a few things, no such thing as a perfect ep I guess.

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Hiya. If you're not too bothered about a little coma, and it's just for star hopping/finding objects, how about using a 0.5x focal reducer? I too have a fast 10in scope, and sometimes pop my (admittedly pretty cheap one) on my 16mm 68 degree ES MaxVision (turning it into a 32mm EP). The view is actually pretty reasonable.

Kev

Screen Shot 2019-11-08 at 15.34.43.png

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I have the Nagler 31T5 and it is indeed a beast. I also have the Nagler 22T4, which is my main galaxy hunting EP, and a wonderfully comfortable EP to use. I have used it in Olly's 20" F/4.1 Dob, and it performed magnificently. It is a lot lighter than the 31T5 (a.k.a. "Panzerfaust").

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7 minutes ago, kev100 said:

Hiya. If you're not too bothered about a little coma, and it's just for star hopping/finding objects, how about using a 0.5x focal reducer? I too have a fast 10in scope, and sometimes pop my (admittedly pretty cheap one) on my 16mm 68 degree ES MaxVision (turning it into a 32mm EP). The view is actually pretty reasonable.

Kev

 

A focal reducer, that’s interesting. Never thought of that Kev, thanks. What are the drawbacks of those? I’ll have to read up a bit I think!

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Hiya. I'm probably not the best person to ask about their relative disadvantages as I have very limited experience with them. I was gifted one recently (I believe it only cost about 15-20 quid). I assume there are better quality ones out there, which might not cause as much distortion as mine (which as I said, is there, but isn't too bad).

I'm sure others can offer better advice ...

Kev

 

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1 hour ago, davhei said:

Thanks Louis, much appreciated!

Problem with the 31 mm NT5 and I guess Ethos 21 as well is the weight. Just unbalances my scope too much att certain angles. I would trade some tfov for a lighter EP. With Ethos there’s the question of eye relief as well.

Realise I may have to compromise with a few things, no such thing as a perfect ep I guess.

The 20mm APM HDC XWA is only 24 ounces, 12 ounces lighter than the 21mm Ethos and the same as the 22mm NT4.  According to what I've read, it's better corrected than the 20mm ES-100 and not that far off the 21mm Ethos.  Eye relief is 15mm designed and 12mm-13mm usable.  How much eye relief do you prefer when using eyepieces?

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48 minutes ago, Louis D said:

The 20mm APM HDC XWA is only 24 ounces, 12 ounces lighter than the 21mm Ethos and the same as the 22mm NT4.  According to what I've read, it's better corrected than the 20mm ES-100 and not that far off the 21mm Ethos.  Eye relief is 15mm designed and 12mm-13mm usable.  How much eye relief do you prefer when using eyepieces?

I’ve never looked at Lunt EPs before, certainly never through them. Have heard them mentioned a lot though so worth considering for sure. Thanks!

As far as eye relief goes, no less than 15 if there is to be no lens contact, more would be even better. ES 82 30 mm is listed as having over 20 mm and that felt good. Delos as well obviously.

Edited by davhei

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Getting eyepieces that are wide, well corrected at F/4.7, have decent eye relief and are light in weight is a tough order. To get the well corrected performance at fast focal ratios and good eye relief, quite a lot of large glass elements are needed with some radical curves on them and those are what weighs the most of course.

Of those discussed here, I've owned the Nagler T4 22mm and thought it a very good performer and comfortable to view though. 

I now use the Ethos 21 and a Nagler 31 but those are definitely in the heavyweight category.

 

 

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The Pan24 was my choice for my 10" f4.7.  No balance issues... just trim your eyelashes!! :D

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4 minutes ago, niallk said:

The Pan24 was my choice for my 10" f4.7.  No balance issues... just trim your eyelashes!! :D

I was also thinking that the Pan 24 ticked all the OP's boxes with the exception of eye relief !

Plus he already owns one .....

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10 hours ago, John said:

Getting eyepieces that are wide, well corrected at F/4.7, have decent eye relief and are light in weight is a tough order. To get the well corrected performance at fast focal ratios and good eye relief, quite a lot of large glass elements are needed with some radical curves on them and those are what weighs the most of course.

Of those discussed here, I've owned the Nagler T4 22mm and thought it a very good performer and comfortable to view though. 

I now use the Ethos 21 and a Nagler 31 but those are definitely in the heavyweight category.

 

 

Yes the 22 T4 Nagler keeps coming up, would love to try it out. Perhaps pick it up on the used market and compare it to the Pan 24 for a while, see which one (if any) comes out on top for me.

I guess somewhere down the road I’ll arrive at a point where I can better understand what aspects are most important to me and which ones are easier to make compromises on.

At the moment I think comfortable viewing and good correction across the visible field trumps tfov. Pincushion would be ok. Not keen on having to add a paracorr because of the cost and added weight.

I have heard many state you ”need” a paracorr with the 22 mm T4 Nagler in fast scopes but I think that would push the total weight to over a kilo.

If the Pan 24 just had better eyerelief I think it would be a nice fit. With that said, since I haven’t put it through its paces properly yet I shouldn’t be so quick to judge. Perhaps I’m exaggerating the problem. The process of choosing is pretty fun though.

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7 hours ago, niallk said:

The Pan24 was my choice for my 10" f4.7.  No balance issues... just trim your eyelashes!! :D

I thought about it but I would never hear the end of it from my wife 😆

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Another viable option could be the ES68 24 mm. Longer eye relief than the Pan but perhaps a bit less well corrected, heavier, but still light of course. Doesn’t hurt that it gives some cash to spare.

Edited by davhei

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I used to have the T4 22mm. Very nice, very sharp. I sold it in favour of an LVW 22mm which is much more comfortable to look though. It's so good I didn't mind the drop from 82° to 65°.

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Baader Morpheus are superb and the 17.5mm will give you a spectacular high contrast view with a nice dark sky background. 

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1 hour ago, mikeDnight said:

Baader Morpheus are superb and the 17.5mm will give you a spectacular high contrast view with a nice dark sky background. 

Thanks! The tfov will be pretty close to my limit where I start to get lost when starhopping though. Will have to try and see how narrow a field I would be ok with. Given that this would be my higest focal length EP I would like a bit larger field of view.

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The best low power eyepiece w/o a coma corrector, in a 10" f/4.7 is the 22mm Vixen / Orion LVW. Try looking for a used one on the used market. 

Cheers!

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2 hours ago, TheLookingGlass said:

The best low power eyepiece w/o a coma corrector, in a 10" f/4.7 is the 22mm Vixen / Orion LVW. Try looking for a used one on the used market. 

Cheers!

Thanks! Do you know the differences between the Vixen and the 22 mm T4 Nagler? I would assume there would be similarities and the Naglers are always held in high regard. Do the Nagler need coma corrector to get sharpness across the full field while the Vixen albeit with a smaller tfov has sharp stars almost to the edge?

Edited by davhei

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On 08/11/2019 at 16:15, Louis D said:

First, I highly recommend getting a GSO/Revelation coma corrector and adding a 25mm extension to it or put the optics section on a Baader 2" ClickLock with 2" CL Extension 47mm.  It will massively improve edge performance on wide field eyepieces on your f/4.7 scope without breaking the bank like a Paracorr II would.

Very interesting! How good is the GSO/Revelation coma corrector? Obviously I am not expecting Paracorr performance but how does it compare to other cheap coma corrector (SW, baader,...)?

Would you care to eleborate?

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1 hour ago, davhei said:

Thanks! Do you know the differences between the Vixen and the 22 mm T4 Nagler? I would assume there would be similarities and the Naglers are always held in high regard. Do the Nagler need coma corrector to get sharpness across the full field while the Vixen albeit with a smaller tfov has sharp stars almost to the edge?

I've owned both the Nagler 22mm T4 and the Vixen 22mm LVW. They are quite different designs but peform equally well in terms of sharpness across the field of view. In a F/4.7 newtonian the Nagler will show more coma though because it shows more off axis field than the LVW. Not the fault of the eyepiece but the nature of fast newtonian optics. Both comfortable eyepieces with good eye relief and large eye lenses. Quite a bit difference in price though.

 

 

 

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3 minutes ago, Raph-in-the-sky said:

Very interesting! How good is the GSO/Revelation coma corrector? Obviously I am not expecting Paracorr performance but how does it compare to other cheap coma corrector (SW, baader,...)?

Would you care to eleborate?

I realise that there is some relevance with this thread but I'm keen that we don't go off on a tangent on coma correctors when the original question was about eyepieces :smiley:

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7 minutes ago, John said:

I realise that there is some relevance with this thread but I'm keen that we don't go off on a tangent on coma correctors when the original question was about eyepieces :smiley:

Fair enough. I'll start a new topic.

 

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22 minutes ago, Raph-in-the-sky said:

Fair enough. I'll start a new topic.

 

Thanks Raph :smiley:

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