Exit Pupil / Magnification / Help

[The Frog]

I have recently bought a Skywatcher 127 maksutov cassegrain on the Synscan Av. I decided to get this as I am really keen on viewing the moon and planets to start.

I am trying to pick some eps for this. I read about exit pupil and so on because I want these eps to perform so I don't have to buy more.

Can anyone recommend a good couple of eps along with a 2 x barlow. I don't have mega bucks and I am really looking for personal experience. I was thinking a 10mm and a 6mm plus a Barlow.

Any help would be really appreciated.

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[Owmuchonomy]

A quick comment from me is to watch the limits of your seeing vs. magnification.  I would be wary of pushing it too much over 200x so that means with your scope 6mm should be more than enough.  You could achieve this native or with a 2x barlow and a 12mm ep for example.

[Alien 13]

One of the most useful eyepieces for a Mak is a 32mm which is about the limit for a 1.25 inch focusser.

Alan

[Peter Drew]

I would be looking at a zoom for starters, this would give you a better idea of what magnification suits the telescope and the objects viewed before investing in further eyepieces. The inexpensive Celestron/Seben type 8mm-24mm zooms would work well on your '127mm. 

[Alan64]

You made a very good if not excellent choice in a telescope, and for lunar, planetary and stellar(double and variable stars), along with the smaller and brighter deep-sky denizens: planetary nebulae, smaller galaxies and globular clusters.

It's always good to see that one is not in a hurry to get one eyepiece after another, as in the form of an eyepiece kit, but instead in a manner tailored to an individual's telescope(s) and eyes. 

With your Maksutov being of a long focal-length, you do not have to invest in costly oculars to get pleasing views.  Such are preferred and perhaps even required for the much faster parabolas of Newtonians 200mm and up.  A 32mm, as suggested, will give a magnification of 47x, and will be the lowest power available for a 127mm Maksutov.  A 40mm(38x), whilst at the lowest practical magnification, however will exhibit a narrower field-of-view, and limited by the physical size of the 1.25" barrel.

The 32mm... http://www.firstlightoptics.com/skywatcher-eyepieces/skywatcher-sp-plossl-eyepieces.html...or... http://www.rothervalleyoptics.co.uk/skywatcher-sp-series-super-plossl-eyepieces-125.html

There's no need to be concerned about the exit-pupils of any oculars utilised with a 127mm f/12 Maksutov.  However, if you're curious...

40mm: 3.3mm

32mm: 2.7mm

6mm: 0.5mm

The dark-adapted pupil of the human eye ranges from 8mm or more in one's youth, to 5mm or less in advanced age, generally speaking, and more than enough to accommodate said oculars' exit-pupils.

Insofar as the shorter focal-length oculars, your bundled 10mm specifically, think nothing of getting one of better quality and increased eye-relief/comfort at or near the 10mm, and without costing a small fortune.

I'd strongly consider this 16mm(94x), and combined with the barlow listed below, which would then simulate an 8mm(188x)... http://www.firstlightoptics.com/skywatcher-eyepieces/skywatcher-extraflat-125-eyepieces.html

It is sold here as well... http://www.rothervalleyoptics.co.uk/skywatcher-extraflat-eyepieces-125.html...as is the barlow itself listed below.

You'd have a 16mm to fill the gap between the 10mm and 25mm, and a simulated 8mm as the next step up in magnification from the 10mm.  You can then try to barlow the 10mm for a simulated 5mm(300x), but don't expect much.  The barlow can also be combined with the bundled 25mm, and to fill the 12.5mm(120x) slot.  The barlow...

I have the non-twist lock version of this 2x barlow, and I highly recommend it... http://www.rothervalleyoptics.co.uk/antares-x2-twist-lock-barlow-lens-125.html

The body is made in Canada utilising Japanese-made lens elements, and the price, for what you get, can't be beat.  I recommend not combining a lesser barlow with the better eyepieces, as the images may suffer as a result.  A 2x barlow only requires purchasing once, and for life.

This gentleman is perhaps a bit too conservative regarding the limits of magnifications for differing telescopes, or perhaps not... http://www.rocketmime.com/astronomy/Telescope/MaximumMagnification.html

You be the judge.

[Stu]

The 32mm Plossl is a good finder eyepiece giving about the widest field of view in a 1.25" format. Not necessarily what you are looking for for Lunar/planetary observing. It would give a 1 degree field which would show the whole of the moon, which is 0.5 degrees across roughly, framed nicely against the background sky.

You mention exit pupils. There is much discussion about this, and it's a very useful measure for choosing eyepieces. For higher power, many stick to a 1mm exit pupil minimum, which basically means using the same power as the aperture of your scope eg yours is a 127mm scope so x127 gives a 1mm exit pupil. To achieve this you use an eyepiece of the same focal length as the focal ratio i.e. Your scope of f11.8, so a 12mm eyepiece gives your 1mm exit pupil at x125.

Now, Jupiter can often take around x180, and the moon considerably more under good conditions. Below 1mm exit pupil you are likely to start to see the floaters in your eye which can be distracting, but down to 0.5mm can be worthwhile. This would suggest a 6mm at x250 ish. The reality is that probably would not get used that often, too much power.

Personally I would probably go with the 10mm you suggested giving x150, but add an 8mm at x187, and then something lower, perhaps the 32mm Finder or a 12mm at x125

[Piero]

Some time ago I wrote this short thread which might provide you with some indication:

http://stargazerslounge.com/topic/251506-a-guide-for-choosing-a-sensible-eyepiece-collection-using-the-exit-pupil/

[Mak the Night]

My 102mm Mak has a f/l of 1300mm. Which makes it f/12.7. The maximum exit pupil I can get is with a 40mm eyepiece (3.1mm). This only gives me a magnification of 32.5x but allows me a bright enough image to sometimes use a UHC nebula filter.

However, the sky's almost the limit with high magnifications and I can easily get 200x plus (241x limit) magnifications. A 127mm Mak should easily magnify well to 250-300x for lunar/planetary observations.

My advice would be to get a 15 or 20mm eyepiece and a decent 2x Barlow to give you a choice of magnifications. For lunar/planetary about a 150x is the minimum magnification to see decent detail.

My favourite eyepiece combinations for high power (lunar especially) on my Mak are:

1/ 16mm Nagler T5 plus TeleVue 2.5x Powermate ~ 203x, exit pupil 0.5mm. 

2/ 10mm Delos plus Barlow (1.6x) element ~ 208x, exit pupil 0.49mm.

3/ 15mm TeleVue Plossl plus Barlow (2x) nosepiece ~ 173x, exit pupil 0.59mm (binoviewer pair). 

4/  9mm William Optics SWAN plus Barlow (1.6x) nosepiece ~ 231x, exit pupil 0.44mm (binoviewer pair).

As you can see, a combination of wide angle eyepieces combined with a Barlow or equivalent can give the same magnification as a 6mm eyepiece on its own but with a better field of view.  

[Alan64]

Sky-Watcher offers these interesting planetaries, and instead of having to resort to the use of a barlow... http://www.firstlightoptics.com/skywatcher-eyepieces/skywatcher-uwa-planetary-eyepieces.html

The 9mm and 7mm might be of interest.

Dedicated oculars are always preferable, but only if comfortable at the higher and highest magnifications, with greater eye-relief and larger eye-lenses.

Barlows are utilised for a number of reasons.  One being that with a fast telescope, the higher magnifications are more easily realised, and without having to resort to 3mm or even 2mm oculars.  Another being that it serves to multiply, to double the number of magnifications with, say, three eyepieces.  Three eyepieces and a barlow will produce the same levels of magnification as six dedicated oculars, therefore without the cost incurred by two additional oculars. 

Still another factor being that if one already has a fine set of eyepieces, yet the shorter focal-lengths of which possess tiny eye-lenses and tight eye-relief, then one extant, of a longer focal-length with greater eye-relief along with a larger eye-lens, can be barlowed instead, and so to retain said comfort whilst eliminating the less-comfortable ocular being simulated.  To illustrate, here is a 4mm orthoscopic...

...and with a tiny eye-lens and short eye-relief; most uncomfortable.  However, with a barlow, a 2.8x in this case, a much more comfortable 12mm becomes a simulated 4.3mm...

That said, with the 127mm Maksutov's focal length at 1500mm, the need for a barlow isn't as critical as it would be for an 80mm f/6 achromat, or a 150mm f/5 Newtonian.

[ronin]

It is a Mak so will be around f/15 or f/13.

I would suggest no smaller then 12mm, so a 10mm and 6mm and I assume the barlow is for these would be close to unuseable, as I think only the 10mm would be of some use and that only occasionally.

To find things you want a 32mm plossl or 40mm plossl - owing to everything they actually come out with almost identical fields of view.

So following others a 32mm plossl to generally find things.

For magnification then a 12mm or maybe better a 15mm, suspect the 12mm as in a few month Saturn will be making an appearance and 12mm will be useful on that. At present a 15mm should be OK for Jupiter.

Bit difficult to say  too much as for looking at planets it really is not unusual to get several eyepieces in small increments, believe me 1mm increments is not unusual. You could find a 7mm does not deliver well one night but an 8mm does. Again a 10mm may not work but a 12mm could well.

Plossl's are the obvious and with the assorted makes you can get a fair range.

If you wanted "better" then for planetary viewing I tend to point people at the Celextron X-Cel LX's, simply because they have 7mm, 9mm, 12mm, 15mm.

The BST's cost less and are as good but they have "only" 8mm, 12mm, 15mm. Less choice and bigger jumps.

For my little Mak I use the 12mm, 15mm, 25mm BST's. Don't think I have ever tried the 8mm in it.

I suspect the 127 Mak will not deliver the magnifications that many manufacturers claim, none really do. Your max will be around 180x to 200x I would say.

If you have in effect no eyepiece then at this time, or start up a specific set for the scope) a 32mm, 15mm and 12mm, although I would like to see a 20mm (maybe 18mm) in there as well. Working on: 1 at low power, 1 at medium, 1 at medium/high, 1 at high.

[ollypenrice]

I can't see much point in a Barlow for this scope, myself. Nor am I much into having a vast choice of magnifications. In my non-planetary big Dob I only ever use two and in scopes which do deep sky and planets I use only three. I feel that finessing on perfect magnification can become a distraction from concentrating on the object.

Olly

[bingevader]

 Because I'd disagree with Olly on the barlow.

They're great for travelling and, if lunar is your thing, then the moon takes way more magnification than would be suitable for anything else, so a barlow rather than a high magnification EP makes sense to me.

From FLO btw: Telescope Focal Length: 1500mm (f/11.81)

So it shouldn't be too fussy on EPs, the BSTs might give a more comfortable ride than plossls.

[chiltonstar]

I've used the same scope for 6 years, mainly for planetary and double stars. In practice, my most useful EP is 8mm (BST), followed by 12mm (BST), with a cheap (Meade 4000 series) 32mm EP for a wider field. On exceptional nights (exceptional seeing that is), I also use a 6mm (Celestron) EP which is good for eg Saturn and double stars, but does not have much eye relief - a problem for some people. I've never found much use for a Barlow for visual observing because of the extra optical surfaces for light loss, dewing up and reflection.

Clear skies!

Chris

[Putaendo Patrick]

If this telescope is new, it should come with 10mm and 25mm EPs. Some vendors include a x2 Barlow in the bundle. This gives you a satisfactory range of magnifications out of the box.

If you have these three items, I personally would use them first before adding any more EPs. Over a few months of use, you will find out what additional magnifications will be most useful to you as well as deciding whether the supplied EPs would benefit from being upgrades.

If you have an astronomy club near you, their members will probably be very happy to let you try out their EPs. This can be vey helpful, as ultimately buying an EP is a very subjective choice which depends on you.

Check the diameter of the focuser and diagonal. The local supplier in Chile apparently provides a 2" diagonal with adaptor, rather than the more normal 1.25". Should this be the case, you have the interesting option of a 2" EP for wider views at low magnification.

[Mak the Night]

The standard Sky-Watcher give away Barlow is unusable in my experience and is almost completely plastic (I suspect the lens element is plastic also). The Sky-Watcher 'De-Luxe' Barlow is almost certainly the same (made by Synta) as the Celestron 2x Universal Barlow as sold by FLO for £23: http://www.firstlightoptics.com/celestron-eyepieces/celestron-2x-universal-125-barlow.html

This is a very usable Barlow for the money and I still have mine even though I usually use my TeleVue Barlows costing over four times the price nowadays. It doesn't degrade the image in a very noticeable way. It may not be TeleVue, but it is well worth 23 quid, and should be perfectly adequate for bright planetary/lunar observing. I recommend the Celestron Barlow.

The Celestron Omni eyepieces are also very good value for money IMO: http://www.firstlightoptics.com/celestron-eyepieces/celestron-omni-plossl-eyepiece.html

I used the 12mm, 15mm Omni Plossls and the Omni Barlow a lot on my Mak before I upgraded my eyepiece collection. 

They are still carried in my EP case. I found them to be excellent for planetary and lunar observing and should work well on a 127mm Mak with a 1500mm f/l. The 15mm Omni should give an easy 200x combined with the Barlow. The 12mm Omni (actually 12.5mm) will give 240x although (depending on conditions) you should be able to push a 5" Mak to near 300x. Maksutov telescopes tend to excel at high magnifications with bright planetary objects as a whole.

There are also some Celestron kits. The AstroMaster has a nice 15mm wide angle Kellner eyepiece that I always thought worked superbly for lunar observations on my Mak combined with the 2x Barlow. It gives a very pleasing wide view of the lunar landscape for a relatively inexpensive eyepiece.

http://www.celestron.com/browse-shop/astronomy/visual-accessories/eyepieces/astromaster-accessory-kit

It also has a 6mm Plossl eyepiece but it is quite uncomfortable to use IMO as the eye relief and field stop/AFOV are so small.

Two Celestron Plossls shown, the AstroMaster 6mm is on the right.

All in all, in my experience, a small Maksutov can deliver very good high magnification images especially for planets and the Moon, with a combination of around 12mm to 15mm relatively inexpensive eyepieces and a Barlow. The downside to Mak's is getting a bright low magnification with a large enough exit pupil to enable the use of a filter. But if high magnification planetary observing is what you are interested in they really do well.

[The Frog]

Thank you all very much for the advice.

This forum is brilliant. I have asked the same question on other forums and got nothing..... so thank you very much.

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[Mak the Night]

You're welcome.