Eyepiece recommendations for a 10" Dob

[eifionglyn]

So I've got the 10 inch Skywatcher Dob, and I love it. Now for some eyepieces. I know that at f/4.7 it's a fast scope, and as such is not that kind to cheaper eyepieces, but "cheaper" is all relative. What is cheaper to one person might be top of the range unattainable luxury for another. So where in terms of price or make / model should I be looking at for more eyepieces.

I've got the 25mm / 10mm skywatcher Plossls, as has everyone, and the 2x barlow. And they work about as well as expected. They create an image, but it's not great. It's not rubbish, but not great. Most of my time was spent looking through my 18mm BST Explorer, as the image quality is that much better, even if it wasn't the optimum magnification for my target.

What should I get to extend my eyepiece case? More BST Explorers? Are the OK with a f/4.7 scope? The 18mm performed alright, certainly better than the Skywatcher Plossls stars at the edge of the field were noticeably not sharp. Not that I'd expect them to be edge to edge pin sharp, but wondering if there's another model that's a better match to the 10 inch tube.

I've also been looking at the Baader Hyperion 8-24mm zoom. Would this be any good with this scope? I know from photography that zoom lenses, while convenient don't have the IQ of a similarly priced prime. Would this be true with eyepieces too?

Thanks in advance,

Eifion

[brantuk]

The Baader zoom is great in this scope but the fov is a little narrower at lower magnifications - it's smashing on planets, moon, and doubles though. I also like the 8mm Baader Hyperion eyepiece which is a cracker in my 12" dob. Bear in mind single field stop eyepieces usually are better than zooms.

You might like to consider a reasonable quality low power widefield eyepiece for looking at large objects. But as you rightly say - the edges do suffer the cheaper you go - and the edges are what you want when looking at larger objects. Around 30mm eyepiece would be nice - and for your budget something like a s/h Panoptic between 24mm to 35mm isn't out of range. Hth

[Eastridge]

I'd recommend that you look at the Maxxvision 24mm - the range are on amazing offer at the moment ( see threads in Discussion - Eyepeices ) and it's a class above anything else we have in the 10" dob.  There is a thread running right now saying they are better than the BST's for fast scopes and they have a greater field of vision.

I'd have got some at lower focal lengths as well but |I need good eye relief. 

[Andy_E]

It all depends what you want out of your EP to be honest. If it's wide angle your after then I have nothing but good words to say about the ES 82s and WO UWANs... both perform very well at f4.7. If FOV isn't your concern then your options are a little more open. TV plossls are great if you can cope with the reduced FOV and eye relief (probably should mention ES and WO also have a moderately tight eye relief). The maxvisions get pretty good write ups though I've no first hand experience with them myself.

The BSTs will perform ok, but that depends on whether you want a higher or lower power EP (preference given to the higher power BSTs)

There's also orthos, but that's a different story.

[Qualia]

Forgive me if I'm repeating myself but I’ve seen a number of enquiries on EP choosing for 10" f/5-ish scopes and wanted to set out a brief and rough working guide that I've found useful.

My journal has a number of observations on exit pupil (EP's focal length / telescope’s f/ratio) which concludes:

• 6mm - 4mm - nice wide field, handy for star hopping, really nice for star fields and large open clusters.
• 4mm to 3mm - nice contrast, good on star-fields.
• 2.5mm to 1.5mm - nice for most DSOs and general planetary viewing.
• 1.6mm to 1mm - nice contrast and resolution on planets, Moon and globs.
• 1mm to 0.5mm – finer detail on planets tweaked, Moon work, tight doubles split - dependent on seeing conditions.
• 0.5mm to 0 – not any occasion to justify an assessment.

In terms of a 10" f/5, we're talking general magnifications between:

• 40x - 60x
• 60x - 85x
• 90x - 170x
• 150x - 250x
• 250x – 500x
• 625x

And in terms of EP focal length for a 10” f/5, we’re looking at:

• 30mm to 20mm
• 20mm to 15mm
• 14mm to 7mm
• 8mm to 5mm
• 5mm to 3mm
• 2mm to 0mm

In practical, everyday terms, on most evenings I'm not pushing 250x. And find that 90% of my DSO viewing - as opposed to planetary and Lunar work - relies upon  just 3 eyepieces, viz. 24mm, 14mm and 10mm. From this pattern taken over the last 7 months, a number of observations have been made:

At the beginnning, I feel one only needs one decent long focal length, wide field EP, something around the 50x which can give you about 1.3 to 1.5 true field of view. And that small focal lengths for DSO viewing are not going to be used that much, if at all.

However, the range of possibility between 2.5mm to 1.5mm exit pupil is huge. What looks relatively tiny in terms of exit pupil is in fact a wide range of magnifications dependent on the given object being observed, atmospheric conditions, one’s state of mind, level of fatigue and so on. That tiny 1mm covers most DSOs and a good general level of planetary viewing.

From this, over a few months playing around with different combinations, I found that if I took the telescope's aperture, say, the 250mm, and divided it by 2 , I ended up with 125. If I looked at that in terms of magnification I would need a 10mm EP. I then divided that 10mm by my scope's focal ratio and ended up with an exit pupil of 2mm. This I figured would be the general work-horse for the 10" and indeed it has been so.

From this reasoning, I figure little steps could be made on a 1.3 or 1.4 ratio.

So, for example, from the hypothetical 125x mag, or 10mm workhorse EP, I'd divided the mag or multiplied the EP's focal length by 1.3 and 1.4. So, I end up with 96x to 89x, or an EP of around 13mm to 14mm, or an exit pupil of between 2.6mm to 2.8mm.

And there it was. 90% of my observations for DSOs are conducted with just 3 eyepieces: 24mm, 14mm, 10mm. And I wonder how different that is for most observers here?

I'm not into them, but with a 2x Barlow, that gives a useful range of magnifications: 50x, 90x, 100x, 125x, 180x, and 250x (weather and atmospheric conditions permitting). Sure, there is room for improvement, but you get an idea of what is possible with just 3 EPs.

I've found planetary and lunar work to be a completely different ball game and here we would need a completely new thread. Needless to say, I need a decent run of high power eyepieces, jumping with about 10% to 15% power increments. For this purpose, I use a set of decent Orthos running along 9mm, 7mm, 6mm, & 5mm and even with that gap between the 9mm and 7mm I feel I'm losing out on occassions!

I'm not sure if this helps, but I feel the numbers offered do help get a general gist of what is possible and some kind of map to work around. Being a fast scope, if eye relief isn't a concern, I'd stick with good quality plossls or orthos, those that will give you the best possible view even if the field of view is tight.

Either that, or I'd consider jumping the mid-range bracket of eyepieces altogether and instead start buying into premium EPs. If that requires more saving, so be it. Spain has about 30% unemployment, the market here is going crazy and in consequence I'm on a very, very low wage with a very precarious working contract and at best can only buy one or two premium eyepieces a year, but so be it. Such is the condition of man.

But I have found from experience that in the long term it is cheaper for the poor man to buy decent quality eyepieces knowing that these eyepieces will be 'lifers' and will fit a range of different telescopes and will retain their market value better, than going for some quick fix cheaper eyepieces that will eventually need upgrading and will inevitably lose a wack on the secondhand market. 

Seriously, it is rarely a bad move to buy premium, you just need to slow down a little to save up for them but I feel it will save you money, time, doubt and heart ache in the long term.

[YKSE]

Very good summary from Qualia. Maybe some newcomers will feel overwhelmed by amount of info, but it really worth to read through and through again to understand it, and don't hesitate to raise questions if you have any.

[eifionglyn]

Wow, really interesting and informative Qualia, thanks for going to the trouble of typing all that out. I've gone for the 24mm Maxvision. They're at such a good price at the moment, and if true that they are equivalent to Meade SWAs then that is just about knocking on the door of premium for mid-range money. With not much in the way of planets visible in the evenings at the moment I'm holding off on the high power eyepiece for a while, and will continue with the BST 18mm for medium power for the time being. I'm also of the view that ultimately quality doesn't cost  - it pays. Here's hoping the Maxvisions are all they're cracked up to be.

[laowho]

Kudos on your first upgrade. Qualia's post could be a primer on EP selection. Even Al Nagler says you only really need two or three EPs. So now you've begun with a 24mm, and if your skies are typical for light pollution, the exit pupil this EP produces will help a lot toward giving darker background and better views. Being at f/4.7 you may some day decide on a Paracorr--some folks swear by them, others don't care so much about coma. If you replace your 10mm next, consider the wide-fields...82 degree or better will keep your object in view longer, frame it better, etc. And consider a Barlow that is (or will convert to) 1.5 x to give you the best magnification spread. If you got a 2x Barlow that converts to 1.5x by the removal of an element, your 24mm can be a 16...next would be a 12mm to replace your current 10mm, and that would also be an 8mm. If, say, on a night of planetary nebulae viewing or great seeing, you wanted more power, convert the Barlow back to its original 2x configuration for a 6mm EP. Just a thought. But this way you'd have everything you'd need in just two EPs for most nights in most places.

But yeah, your instinct to upgrade your EPs is dead on. Kudos. As Bill Paolini says, the eyepiece is king.

[Qualia]

Thank you for the kind comments. It certainly sounds like the Maxvisions are the business and I hope all goes well on your next purchase. Please don't hesitate in asking more questions if they so happen to arise