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Recommend an eyepiece for a very fast telescope for viewing planets

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#1 stevereecy

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Posted 12 September 2019 - 02:58 PM

Ok, I know you’re not supposed to use a very fast scope (like an f4 or less) to look at planets.  But suppose you’re about to pack up for the evening and you see Saturn clearing the trees.  Assuming that you’re absolutely certain that the amateur astronomy community will never find out, what eyepiece  do you use to view it?  Do you combine it wIth a specific Barlow?  With some other supplementary tool?  Money is no object answers and thrifty answers are encouraged. 



#2 db2005

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Posted 12 September 2019 - 03:32 PM

Don't worry, just enjoy the planetary views with a fast scope. We won't tell anybody... lol.gif

 

But seriously: Unless you go crazy with magnification, planets usually present fairly small objects in the eyepiece, so since even simple eyepieces tend to perform fairly well on-axis, you will be fine. As long as you keep the planet centered (on-axis) you can expect sharpness to be good. But for best off-axis performance you need to consider the scope as well as the eyepieces.

 

Scope: Some observers prefer to use a coma corrector in a fast Newtonian, providing much sharper views off-axis. The coma corrector will also improve views generally.

 

Eyepieces: As a useful rule of thumb, high-end (= expensive) eyepieces tend to be extremely well corrected for fast scopes. To name a few: Televue Delos, Delite, Pentax XW, Vixen SLV. Televue Plössls are also advertised to be well-corrected in fast scopes. However, IME, off-axis performance even in excellent Plössls is inferior to more high-end designs. One thing to be noted: I haven't tried any of these eyepieces in scopes faster than f/5, so your mileage may vary.


Edited by db2005, 12 September 2019 - 03:34 PM.

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#3 Richard O'Neill

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Posted 12 September 2019 - 03:43 PM

Ditto!



#4 photoracer18

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Posted 12 September 2019 - 04:18 PM

Well planetary viewing depends a lot of seeing conditions. Still, heavy air is best but that is actually a pre-fog condition. Rarely have I been under skies like that (once I can remember it was 2005 Mars Opposition). So normally you want about 200x-250x if the air can stand it and more if things are just right, so whatever gives you those numbers. Perfect conditions can be as high as 600x although that's stretching the limit especially if you are near sea level. At higher altitude anything is possible. Sadly I never paid attention to that when growing up at 5000'.

Yyou don't need a WA eyepiece for planets, and is why simpler designs are usually used for "planetary" eyepieces like TMB Monocentrics and similar ones like Pentax SMC O-x Orthoscopics. I used Orthos for decades (UO Professionals) before I went to wider FOV ones for all general observing. Vixen LV Lanthanums also work for me.


Edited by photoracer18, 12 September 2019 - 04:18 PM.

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#5 TOMDEY

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Posted 12 September 2019 - 04:18 PM

A good Barlow with a good shortish eyepiece should do. I would recommend pulling the coma corrector out, too... they introduce some spherical, and are unnecessary on-axis anyway. Spherical is an axial aberration, present even at center field... so get that thing outa the way.

 

Note to the techies: If you question my statement regarding spherical... just test your good Newtonian with and without the coma corrector (star-test and/or autocollimation interferometry). I did that on mine and the difference was not insignificant. That was an old Lumicon CC on a superb 12.5-inch F/6 Newt. It massively suppressed the field coma, but at the expense of introducing quite a bit of spherical. That motivated me to pull the CC when doing high-mag viewing, or imagery of small center-field stuff. The reason that I blithely assert that a coma corrector and/or field flattener must introduce (some) spherical... is because lenses comprising all spherical surfaces must introduce (some) spherical aberration (blend of all orders)... nature of the beast --- whereas, a naked Newt is entirely corrected for all orders of spherical. So, it becomes a question of how much. It is quite possible that some correctors introduce a truly insignificant amount of that aberration.  Tom


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#6 havasman

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Posted 12 September 2019 - 05:33 PM

The best planetary views I ever had were via f3.3 scope.  The 32" aperture didn't hurt anything nor did the fact that Jupiter was near zenith as viewed from rural Oz. I think the prejudice against sub-f4 planetary observing is entirely specious.

 

As posted above, the most effective planetary observing I've done with any of my scopes generally maxes out the mag around 250x.

 

Eyepieces in rotation at those exit pupils include 10mm Ethos, 8 & 6mm Delos, 6mm Tak Abbe Ortho, 5T6, 4.7 & 3.7mm Ethos, 3.5 & 2.5T6's. In the 16" Starmaster that yields 210 - 839x and the 10mm Ethos is probably the one most used. With the AT115EDT I get to use the 2 Ethos SX for 171 and 218x. Those two may be my overall favorite eyepieces.

 

I favor high and very high magnification observing but planetary observing is not where I find it particularly rewarding. Planetary nebulae, by all means. Extragalactic details, you betcha. Even white light solar back when there were sunspots is, for me, more effectively done at really small exit pupils than planetary. 


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#7 SeattleScott

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Posted 12 September 2019 - 06:48 PM

What eyepiece you use will depend on the scope. The Vixen HR or Tak TOE lines would be well suited to an 6”-8” F4 on a tracking mount, but generally useless on a 20” Dob. A TV Delos or Baader Morpheus would be suitable for the 20” Dob, but not really enough magnification to top out a 6”-8” unless you barlow them. And if you do that you are adding even more glass to the light path.

Tracking versus manual is important because you might think twice about a TMB Supermono with 30 AFOV if you are manually tracking. A 3.7 110 AFOV might be more practical even if you lose some contrast.

So we really need to know a bit more to make suitable recommendations. Assuming this is the Comet Catcher, HR or TOE will give probably the best views, but I fear their optical excellence would be wasted on a Comet Catcher. So maybe a Paradigm 3.2?

Scott

Edited by SeattleScott, 12 September 2019 - 07:05 PM.


#8 areyoukiddingme

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Posted 12 September 2019 - 07:17 PM

A good Barlow with a good shortish eyepiece should do. I would recommend pulling the coma corrector out, too... they introduce some spherical, and are unnecessary on-axis anyway. Spherical is an axial aberration, present even at center field... so get that thing outa the way.

 

Note to the techies: If you question my statement regarding spherical... just test your good Newtonian with and without the coma corrector (star-test and/or autocollimation interferometry). I did that on mine and the difference was not insignificant. That was an old Lumicon CC on a superb 12.5-inch F/6 Newt. It massively suppressed the field coma, but at the expense of introducing quite a bit of spherical. That motivated me to pull the CC when doing high-mag viewing, or imagery of small center-field stuff. The reason that I blithely assert that a coma corrector and/or field flattener must introduce (some) spherical... is because lenses comprising all spherical surfaces must introduce (some) spherical aberration (blend of all orders)... nature of the beast --- whereas, a naked Newt is entirely corrected for all orders of spherical. So, it becomes a question of how much. It is quite possible that some correctors introduce a truly insignificant amount of that aberration.  Tom

 

I've compared my 12.5" F5 on planets with Paracorr 2 and Paracorr 1, and the P2 seems to be the sharper.

 

Also done the same comparison in 8" F7, and the 'average' quality across the field is better with the P2 than without around 200-250x. Right on axis (as the planet moves across the field), it's actually hard to say (and the scope has excellent optics).

 

So I'm guessing the P2 does a better job correcting for spherical aberrations than the P1.

 

I have also heard it claimed that the 15% of magnification with these coma correctors is there to decrease spherical aberration.


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#9 Spikey131

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Posted 12 September 2019 - 08:13 PM

Tele Vue designs all their eyepieces to perform well in scopes down to f/4.  Their 5” f/4 MPT (multipurpose telescope), from which the NP101 and NP127 were derived, was designed test their EPs.  They still test their eyepieces with it.

 

So pick the Tele Vue EP that gives you the magnification you want and you should have good views of the planets.  At least the eyepieces won’t get in the way.


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#10 SeattleScott

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Posted 12 September 2019 - 11:47 PM

Not untrue, but TV isn’t the only company that designs eyepieces that perform well at F4. So the key is to look for the features, performance and price. If looking at a premium eyepiece for a fast scope, there is a good chance a TV will be the best fit, simply because they have several eyepiece lines to choose from. But at the same time, I wouldn’t just pretend TV was the only game in town and ignore the others.

Scott
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#11 Jon Isaacs

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Posted 13 September 2019 - 05:15 AM

Note to the techies: If you question my statement regarding spherical... just test your good Newtonian with and without the coma corrector (star-test and/or autocollimation interferometry). I did that on mine and the difference was not insignificant. That was an old Lumicon CC on a superb 12.5-inch F/6 Newt.

 

 

Honestly, the Lumicon is not a Paracorr 1 or 2.  It's an old design meant for astrophotography where spherical aberration is not much of an issue.  

 

Try it with your Paracorr 2.  I imagine you have one.

 

Jon


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#12 25585

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Posted 13 September 2019 - 05:24 AM

Stop down your aperture with a simple mask. That will give you a larger focal ratio. The smaller aperture may be beneficial depending on seeing.


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#13 Spikey131

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Posted 13 September 2019 - 06:53 AM

Not untrue, but TV isn’t the only company that designs eyepieces that perform well at F4. So the key is to look for the features, performance and price. If looking at a premium eyepiece for a fast scope, there is a good chance a TV will be the best fit, simply because they have several eyepiece lines to choose from. But at the same time, I wouldn’t just pretend TV was the only game in town and ignore the others.

Scott

I did not mean to imply that eyepieces from other makers would not work well at f/4.

 

But Tele Vue performs the due diligence at f/4, so if one is particularly concerned about EP performance at this f/ ratio, their EPs are a good choice.


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#14 Sarkikos

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Posted 13 September 2019 - 08:37 AM

Ok, I know you’re not supposed to use a very fast scope (like an f4 or less) to look at planets.  But suppose you’re about to pack up for the evening and you see Saturn clearing the trees.  Assuming that you’re absolutely certain that the amateur astronomy community will never find out, what eyepiece  do you use to view it?  Do you combine it wIth a specific Barlow?  With some other supplementary tool?  Money is no object answers and thrifty answers are encouraged. 

What is the f number and aperture of your telescope?

 

Mike


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#15 George9

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Posted 13 September 2019 - 08:47 AM

I happen to have settled on Delos, but many are useful.

 

My point is that you DON'T limit yourself to 250x unless that is the only seeing you ever get. If your seeing varies, also support 400x or 600x or whatever your aperture supports in theory. You may use 200x more often, but a real shame to miss out on once-in-a-lifetime seeing opportunities that may crop up unexpectedly. Those are the nights you will remember forever if you just have the power available.

 

George


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#16 Spartinix

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Posted 13 September 2019 - 11:34 AM

Honestly, the Lumicon is not a Paracorr 1 or 2. It's an old design meant for astrophotography where spherical aberration is not much of an issue.

Try it with your Paracorr 2. I imagine you have one.

Jon

Same here, with the PCII the view was better. I tested this on Jupiter and Saturn.

Edited by Spartinix, 13 September 2019 - 11:35 AM.


#17 Hesiod

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Posted 13 September 2019 - 11:46 AM

I'd keep a good Barlow lens at hand...

If that fast telescope has to be my main visual tool however could think to get a couple of somewhat "awkward" eyepieces (I like to have sets of nearly parafocal eyepieces, and here the Barlow lens does not fit very well), but the actual focal length would depend on the whole telescope's specs and expected average seeing; were I not sure about committing myself to a specific focal, there is always the Nagler zoom, and the aforementioned Barlow lens.


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#18 izar187

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Posted 13 September 2019 - 09:06 PM

Ok, I know you’re not supposed to use a very fast scope (like an f4 or less) to look at planets.  But suppose you’re about to pack up for the evening and you see Saturn clearing the trees.  Assuming that you’re absolutely certain that the amateur astronomy community will never find out, what eyepiece  do you use to view it?  Do you combine it wIth a specific Barlow?  With some other supplementary tool?  Money is no object answers and thrifty answers are encouraged. 

Often just clearing the trees for me means it's down in the soup.

The ep isn't going to make much difference there.

However, Siebert SS3's play well with fast focal ratios.

Down into some short focal lengths too, for short focal length scopes.

Comfortable, affordable, better than my barlow combinations. 


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#19 noisejammer

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Posted 14 September 2019 - 03:11 AM

The easy way would be with a Barlow - this would allow less expensive eyepieces to shine. Let's assume this isn't on the cards.

 

I'd go for something  that will deliver an exit pupil of 0.7 - 1 mm and (unless you're far from the jet stream) produce a maximum magnification of 250-300 x.

 

So on that basis an f/4 scope wants something 3-4 mm (or longer), f3.5 wants something 2.5-3.5 (or longer).

 

Now go to the usual suspects - Pentax XW, Delos, Ethos, Nagler, Nagler zoom (if you can find one) and make your choice. You could also try something from ES - I have used several of their premium eyepieces at f/3.3 but I haven't tried for such a small exit pupil.



#20 Jon Isaacs

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Posted 14 September 2019 - 04:10 AM

Stop down your aperture with a simple mask. That will give you a larger focal ratio. The smaller aperture may be beneficial depending on seeing.

 

This reduces the resolution and the contrast as well as the brightness, all important for getting the good planetary views at high magnifications.  

 

When it comes to planetary eyepiece choice for a fast Newtonian, I think the first thing that we need to know is whether the scope is tracked manually or if it's driven.  If it is manually tracked, then a wide, well corrected field is a top priority and a coma corrector is also important.  If the scope has some sort of motorized tracking, then a narrower field eyepiece can be used.

 

Regarding the Pentax XW's, I am not sure how well the work at F/4 and faster but I see reports that they're better at more moderate focal ratios. 

 

Jon


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#21 vdog

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Posted 14 September 2019 - 09:22 AM

Ok, I know you’re not supposed to use a very fast scope (like an f4 or less) to look at planets.

I used to use my f/4 Starblast all the time to look at planets, with the pack-in plossls and Barlow no less.  The amateur astronomy secret police never came for me, so I think you'll be ok. Heck, the slowest scope I've ever used is an f/4.7.

 

Money is no object:  Anything Televue

 

Thrifty:  Meade 5000 UWA

 

In the meantime, enjoy those planets with whatever you got.

 

Oh man, was that a knock at the door? shocked.gif


Edited by vdog, 14 September 2019 - 12:26 PM.

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#22 Miranda2525

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Posted 14 September 2019 - 06:07 PM

I used to use my f/4 Starblast all the time to look at planets, with the pack-in plossls and Barlow no less.  The amateur astronomy secret police never came for me, so I think you'll be ok. Heck, the slowest scope I've ever used is an f/4.7.

 

Money is no object:  Anything Televue

 

Thrifty:  Meade 5000 UWA

 

In the meantime, enjoy those planets with whatever you got.

 

Oh man, was that a knock at the door? shocked.gif

Anything Televue? False. Diff types show diff results. 



#23 Miranda2525

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Posted 14 September 2019 - 06:07 PM

Ok, I know you’re not supposed to use a very fast scope (like an f4 or less) to look at planets.  But suppose you’re about to pack up for the evening and you see Saturn clearing the trees.  Assuming that you’re absolutely certain that the amateur astronomy community will never find out, what eyepiece  do you use to view it?  Do you combine it wIth a specific Barlow?  With some other supplementary tool?  Money is no object answers and thrifty answers are encouraged. 

Vixen LVW's. Televue Delos. Pentax XW's. Would help to know the size of scope and exact focal ratio though. 

 

The higher power ones above will show you great images when viewing planets.


Edited by Miranda2525, 14 September 2019 - 06:09 PM.


#24 SeattleScott

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Posted 14 September 2019 - 09:04 PM

Agreed, we have been making suggestions for days now without actually knowing what the scope is. Or receiving any more guidance from OP. Based on signature I am assuming it is a Comet Catcher which would eliminate several of the suggested eyepieces simply because the FL do not go low enough for high power planetary viewing with a Comet Catcher (at least without using a barlow). And yes he is asking for everything from cheap to money is no object, but is one really going to spend $330 or whatever on a Tak TOE to view planets with what, a 50 year old budget scope with something like 70% CO? Ok I exaggerate but putting a TOE in a Comet Catcher feels like putting a 500 hp engine in a Honda Fit. The Comet Catcher is going to be the limiting factor. So a bit of guidance from the OP to specifically identify the scope, and a realistic budget for what he might spend on a planetary eyepiece for one of the worst planetary scopes ever made, would be quite helpful.

Scott

#25 MartinPond

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Posted 14 September 2019 - 09:39 PM

Since planetary is done at higher powers usually....

 

If anyone wants a very sharp view for

minimal cost,  a 1.5x Barlow setup makes 

Plossls,

 Orthos,

RKEs,

 Brandons,

 1,2, 1,1,2 or 1,2,1 Konigs

very happy with F4...........

 

Take a  SVBONY Barlow, take the cell off, throw it away,

 , and add a Burgess 1.9x  OCA to replace the cell.

   Incredible results,  excellent contrast.

    (makes a 1.5x barlow/corrector in that layout).

  just in case someone has under $100 rather than over $300 in pocket.

  Or in case, like some plantary enthusiast, you are an eyepiece glass minimailst

    (don't worry, the OCAis not noticeable)

 

It doesn't take much...

 

 

 


Edited by MartinPond, 14 September 2019 - 10:04 PM.



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