Eye Pieces for Planetary Viewing?

[Dave1]

Hello people

 

I am still fairly new to using telescopes. I intend to make my telescope into a planet killer. So I need advice with this in mind. I have read this artical http://www.cloudynights.com/documents/planetaryeyepieces.pdf  and taken on board what it conveys.

So the two eye pieces I am going for is an TeleVue Plossl for Jupiter and Edmund RKL for Saturn and Mars.

My question is one of performance not in your typical sense. I use this telescope calculator http://www.stargazing.net/naa/scopemath.htm . I find it the best. First off, if by this point you have not read the first link posted in this topic, you will be at a loss from now on. You need to study both links, to see where my logic and current understanding come from.

So in the first link it says for Jupiter best viewing ( depending on earth atmosphere conditions of course ) I need an eye piece which would produce 45x per inch power, which is 213 magnification in my 120mm aperture, F8.33 telescope. But using the scope calculator the exit pupil at this mag is only 0.56mm, which is less than optimum of >1mm, so the image will be dimmed?

So my question is at 45x per inch, how dimmed is the image going to be with 0.56mm exit pupil? Am I am going to notice? Or is this all theoretical? 

Ditto again for Saturn and Mars, except the Cloudy Nights article mentions 50x per inch power. Which results in an exit pupil size of 0.5mm. 238 magnification. Which is very close to the maximum magnification for my telescope.

 

Thanks 

Dave

 

 

[John]

With my Skywatcher ED120 refractor (F/7.5) I've found 180x - 200x the most effective on Jupiter. Occasionally 225x bought a few benefits but most often the slightly lower magnifications allowed the surface details of the planet to be sharper and more easily defined.

Saturn and Mars seem to benefit from slightly higher magnifications so I've found 225x and 256x effective on those targets when the seeing conditions allow.

If you don't mind a 40-50 degree field of view and don't wear glasses when observing, it's very hard to improve on the optical quality that orthoscopic eyepieces such as the Astro Hutech, Fujiyama or the discontinued Baader Genuine Orthos deliver. The slightly less expensive Baader Classic orthos and the matching 2.25x barlow lens do a great job on the planets as well

[Putaendo Patrick]

I really don't think there is one definitive magnification to view any particular planet. So much depends on the atmospheric conditions on the night.

I tend to try out different magnifications, ranging from x100 to x200 or very occasionally more before finding one that seems the best at the time. I certainly don't want to suggest that optical theory is rubbish - it's not! But today's good quality EPs give quite a lot of leeway and are only part of the equation. Conditions, conditions, and conditions is the rest

[Dave1]

Thanks for your answers guys,

 

Yes John I've thought about acquiring the KK Fujiyama, and the Baader genuine and classic Orthos. Don't know much about the Astro Hutec. I was also considering getting an Ortho for comparisons against the Plossl and RKE, since these will be my first aftermarket eye pieces. I had narrowed down my choices to either the KK Fujiyama or Baader Classic Ortho.

I read a lot of the articles on the internet which either you John or BillP over at Cloudy Nights write, I think you are both experts. So I am glad you have replied to this topic.

 

[John]

No problem - love the avatar by the way

 

[Roy Challen]

Don't read too much into the calculations. I've used this one you linked to, and it is useful - as a guide.

You will notice dimming as the exit pupil gets smaller, but it's still up to you to decide at what point it becomes a hindrance to observing. I'm happy with a  0.4mm exit pupil as my minimum, although anything larger is going to yield a brighter image. As already mentioned, conditions are everything in visual observing, and it also depends very much on your target. As I only really do planetary and lunar, a small exit pupil is fine (for me). DSOs benefit from a much larger exit pupil.

The orthoscopics mentioned above will be great performers, but don't rule out plossls or eyepieces such as Vixen LV/NLV/SLV, TeleVue Radians (or any TeleVue for that matter), Pentax eyepieces and many others.

[Stu]

I regularly use exit pupils down to around 0.5mm for planetary observing with a 4" frac. The issue I face is not dimness of image but visibility of floaters in my eyes which become worse at those exit pupils. The scope can take more but my eyes can't!

I find that if the scope is decent and conditions are good then it is worth using mags at these levels. Do note that this applies to smallish fracs in the 2.5" to 5" range. You wouldn't need to use a 0.5" EP on a 12" dob for instance because you would be at x600!

[Dave1]

Thanks Roy Challen and Stu. Its good to have two peoples views on exit pupil size in field use.

[YKSE]

Have you tried any higher power eyepiece with your scope? chromatic aberrations in an achromatic refractor can be quite distracting in high power view.

[Rick Towns]

I agree that theory is nice, but what works in the field relies much more on the conditions and even how the observer is feeling. I have an 8" SCT (f/l: 2000mm) and I use only a few eyepieces: 8mm (250x), 11mm (182x), 15mm (133x) and 20mm (100x) Tele Vue Plössls. When observing a planet, I start with the 20mm and work my way up. On a bad night of seeing, I might pop the 11mm in and decide the 15mm gave me a crisper, more detailed view. Recently, we've had some really nice skies here (Ontario, Canada eh!) and I've been using the 8mm with great success. I just bought a Fujiyama 6mm (333x) Ortho for those really nice nights. I hope to get it out soon!

As far as glass is concerned, I am a practical minimalist. The Plössls and Orthos are 4-element lenses, and I find light scatter isn't an issue with them. The eyepieces I've had in the past (Orion Edge-On Planetary, BST Planetary) exhibited light scatter which annoyed me. But that's just my experience. I've heard of observers using more complex eyepieces like Naglers on the planets with great success.

[Moonshane]

If your scope is an achromat then in all truth (based on my experience) it will be a good all round scope but never a planet killer. My best planetary views have been with newtonians but with fracs I was never happy until trying ed scopes.

Good eyepieces will always be appreciated in any scope though.

[Dave In Vermont]

For planets an orthoscopic eyepiece is very hard to beat - or even match. As long as the user doesn't need to wear glasses while observing. As regards the brand to get - I've never met an 'ortho' I didn't like. Hence my collection is of several names/brands.

Old ortho-fan here,

Dave

[ronin]

I would suggest that you forget the rules of avaialble magnification it is rare that they work at the extremes. I have also noticed that manufacturers are claiming higher also, not so oddly on the cheap and not so good scopes.

Jupiter I have seen very nicely at 50x and 60x, best view of Saturn was at 125x. Mars you need more, usually up at the 200x-250x region, and beyond. Does depend on what your viewing expectations are. I am happy to use binoculars on Mars (8x42's) . Sort of "Yes, thats Mars. Now what else is there?"

An 8mm in your scope will or should allow Saturn and Jupiter therefore, you have BST Starguiders and TV plossl at this focal length. You might try a 5mm for Mars but I have doubts that the view will be that good. A 120 achro will show CA and some SA and both detract from the image quality at the higher options.

One other aspect is that if the 8mm works but the 5mm does not do you have a 6mm to try in case that works. On planetary observing it is close to normal to have eyepiece increments in about 1mm steps. I have 3.2, 4, 5, 6, 8, 9, 10, 11, 12mm eyepieces (no 7 as yet - although might have in the Antares set if I check). The conditions may make a 5mm poor but allow a 6mm to deliver.

 

120mm aperture, F8.33

[Mr Spock]

I have a 120mm achro and I can say from experience x200 is pushing its limits. CA becomes objectionable and along with some SA causes image softness.

[Louis D]

I never got good, high magnification views of planets until I invested in a used 15" dob with a high quality mirror (Nova in my case).  It loafs along at 200x most nights here in Texas.  It will take 300x with ease.  I find that aperture makes a much bigger difference than eyepiece choice.  Don't over invest in high end orthos trying to eek out the last little bit of image scale from a small aperture telescope.

[michael.h.f.wilkinson]

I also tend to go for bigger aperture to get out more detail, possibly at the expense of contrast (at a given exit pupil), but the EP also comes into play. Especially viewing comfort. If you have to strain to see the image (e.g. through lack of eye relief) you are probably going to lose some detail. Apart from the extra strain causing trouble, it is harder to observe for a long time if you are uncomfortable. Sticking at it is important in planetary observation, because you have to wait for those fleeting moments of the best seeing to get the most out of the optics. Like others, I start out fairly low (14mm Delos at 145x, as a rule at the moment, and then work my way down the EP focal lengths to XW 10, Delos 8, XW 7, and on Mars and the moon sometimes the XW 5 (which gets much more use in the little 80mm F/6). At each step up, I wait for quite a long while to see if there are moments of sufficiently good seeing to merit perhaps an even higher magnification. AT some point I decide enough is enough, and move back to a lower magnification. Sometimes I find that conditions improve, and I might move up again.

 

My scope is an 8" SCT, and it delivers better planetary detail than my old (planet killer) 6" F/8 Newtonian (with a very good mirror and small central obstruction). Things got even better when I got myself EPs with long eye relief (first Vixen LVs, then Radians, Now Pentax XW and Delos), to replace the orthoscopics and (quality) Plossls I had been using (and which kept banging into my glasses). I have also tested a couple of the Vixen SLVs and they are like a long eye relief ortho, I find. Close, if not equal to XW performance, except for FOV

[Rick Towns]

I would agree somewhat with what Michael says above. I sold my 4" APO and got an 8" SCT because I felt I gave up too much aperture when I got the APO (the previous scope to those was a 10" SCT). Although I have given up some contrast and sharpness in the star points, I see more detail with the 8" than I did with the APO.

Where I disagree is with straining when using short eye relief eyepieces. I guess that's more of a personal thing - different people have different tolerances for eye relief. I use my 8mm Plössl for hours and at no point have I felt discomfort or strain using it. All of my Plössl eyepieces are a joy to use (for me). I have picked up a 6mm Fujiyama Ortho, and it also is not a burden to use for me. YMMV I guess. Cheers!

[John]

I've used loads of orthos and other eyepieces with tight eye relief / small eyelenses / narrow(ish) fields of view over the years. If you wear glasses when observing these are very troublesome or impossible to use but I've enjoyed using most of them. Having found eyepieces that deliver similar optical quality but without those constraints now though, I prefer those on the whole. Must be getting older !

 

[Dave1]

Thanks for the lengthy responses guys, yes I'm not completely new, and like others here I start with a relatively low powered eye piece. Then work my way up in power.

As I've just got back into Astronomy, I am currently limited to a 5,10 mm eyepieces. With a 3x Barlow.

So as I'm still relatively new and taken on board everything that has been said above. I have decided to go with a Baader Hyperion Zoom with matching Baader 2.25x Barlow.

That way I get to try the equivalent of 3.5 to 25 focal length eyepieces. To see what works best for me. Then invest in individual eyepieces at the length I use, if I feel the need to.

Dave

[John]

That sounds a good strategy Dave

 

[Roy Challen]

1 hour ago, Rick Towns said:

 

Where I disagree is with straining when using short eye relief eyepieces. I guess that's more of a personal thing - different people have different tolerances for eye relief. I use my 8mm Plössl for hours and at no point have I felt discomfort or strain using it. All of my Plössl eyepieces are a joy to use (for me). I have picked up a 6mm Fujiyama Ortho, and it also is not a burden to use for me. YMMV I guess. Cheers!

Can't say I've 'strained' when using ortho/plossl eyepieces either!

[michael.h.f.wilkinson]

2 hours ago, Rick Towns said:

I would agree somewhat with what Michael says above. I sold my 4" APO and got an 8" SCT because I felt I gave up too much aperture when I got the APO (the previous scope to those was a 10" SCT). Although I have given up some contrast and sharpness in the star points, I see more detail with the 8" than I did with the APO.

Where I disagree is with straining when using short eye relief eyepieces. I guess that's more of a personal thing - different people have different tolerances for eye relief. I use my 8mm Plössl for hours and at no point have I felt discomfort or strain using it. All of my Plössl eyepieces are a joy to use (for me). I have picked up a 6mm Fujiyama Ortho, and it also is not a burden to use for me. YMMV I guess. Cheers!

If an EP is comfortable for you, then there is no problem whatsoever. With glasses, however, an 8mm Plossl is hardly comfortable (10 mm is horrible already).

[Louis D]

2 hours ago, Dave1 said:

That way I get to try the equivalent of 3.5 to 25 focal length eyepieces.

Eddgie over on CN extols the virtues of using zoom eyepieces during nights of continuously variable seeing.  When the atmosphere settles for a few seconds, he can dial up the power almost instantly to the maximum that seeing conditions allow at that moment, and then dial it back just as quickly when they degrade.

[Louis D]

51 minutes ago, Roy Challen said:

Can't say I've 'strained' when using ortho/plossl eyepieces either!

I've got some decent 3 element eyepieces with narrow fields of view and small eye lenses.  While they don't cause eye strain, they do cause exhaustion trying to hold the tiny view with eyeglasses because I'm pulled back so far from the proper exit pupil location.

[John]

9 minutes ago, Louis D said:

Eddgie over on CN extols the virtues of using zoom eyepieces during nights of continuously variable seeing.  When the atmosphere settles for a few seconds, he can dial up the power almost instantly to the maximum that seeing conditions allow at that moment, and then dial it back just as quickly when they degrade.

The Nagler zooms are great for just that