eye piece

[KAYCE]

Hi,just acquired a skywatcher 127,so early day's.last night managed to use the view finder okay but not managed to

get the moon very well in the small eye piece using the hand device was not so easy to get a good result.

Not sure which lens to start with,how to use the lenses,any help would be great,

[cloudsweeper]

Start with the biggest focal length (widest angle), then when on target, reduce FL for greater mag..

Doug.

[ronin]

Usually big/long as in 30mm or 32mm plossl, Could opt for a 40mm plossl (my first was this) but the field ends up about the same and the actual object image is smaller - not necessarily a bad thing. Owing to the design and the long focal length you will get highis magnification and so narrow(ish) fields of view from the scope. For me dropping 12mm is likely to be the lowest for now, but do not run off and get a 12mm yet.

Main consideration s budget and expectations. In approximate order of number of new pence you have:

Assorted bugdet plossl's, (Try Skies the Limit, Alan has a fair choice), then GSO/Revelation plossls, Then Vixen NPL plossls, then come the BST Starguiders (Skies the Limit for these), then Celestron X-Cel LX's. The Starguiders and X-Cel LX's seem to perform identically and have the same field. Difference comes down to the offered eyepiece focal lengths.

Above these in cost (over the £100 mark generally) come the ES 68's and ES 82's then assorted TV and ES eyepieces

Think that Rother Valley do the GSO plossl's, FLO do the Celestron's and Vixens, StL do the BST's. Also check out 35Astronomy as they have other makes (not sure which so cannot give names), Lacetera I think is one.

When/If you get a long plossl be aware that the exit pupil location may be a problem, it is well away from the actual eyepiece so getting your eye in the right place and stable can be a problem.

In terms of field a 25mm Starguider or X-Cel will give the same as a 30mm plossl and either are better for eyeball location. Just something to be aware of.

If the "small" eyepiece was a 10mm then you get 150x magnification which in a 50 degree eyepiece means 1/3 degree view so 0.333. As the moon is 0.5 degree in size it will not all fit in. Also the supplied eyepieces may be less the 50 degree items, likely 40 or 45, so narrower still. Generally a "safe" idea is to end up with a field of view in an eyepiece of twice the object size - frames the oject reasonably. Take any claims of maximum magnification with a pinch of salt.

[noah4x4]

All good advice, but in simple terms don't be tempted to chase too high magnification except for solar system objects. I made the early mistake of finding that the magnificent M11 (Wild Duck Cluster) fitted nicely in my 25mm Televue Plossl and 8inch F10 scope. That (81x magnification in that scope) lured me into using the same EP when seeking most other DSO'S. Hence my lesser quality 40mm that was supplied with the telescope rarely saw the light of day (or night).  

Then all I  often saw of DSOs was blurred dusty smudges  that I attributed to poor seeing conditions. The penny didn't even drop when I went to dark sky sites with my Nexstar SE4 "grab and go" in which a 25mm produces merely 51x. Then one night I was showing my larger scope to some pals on a night when there was so much cloud that alignment was tricky. So I simply aimed my 'scope at the smallest gap and dropped in the 40mm  knowing that offered a wider FOV. It was a Eureka moment! Suddenly I was seeing amazing sky patterns that mirrored what I was supposed to see according to those sensible guides that don't use Hubble images to tease us. I had previously been viewing DSO's but at such high magnification I was seeing only small sections of them. Of course in less powerful telescopes the ratios for each EP will differ. But do work out the magnification of each EP and start observing stuff at 50x or even less. You can always increase magnification once you have found your target, but too high and you may miss it, even if using the excellent Starsense.

[Cosmic Geoff]

I have the Celestron Nextstar 127mm SLT, a telescope very similar to yours. 

For looking at the moon I usually use the 25mm eyepiece that came with the scope, and occasionally the 9mm.

I had the scope for nearly two years before considering buying any other eyepieces. 

Most people agree that these scopes will not benefit from eyepieces higher powered than those supplied.

If you don't have a good moon map, you can call up an online moonmap on a tablet and take it outside. 

Another tip is to use an erecting 45deg diagonal in place of the astro 90 degree diagonal  which you probably got with the scope. This will take out a mirror-reversal and make your brain hurt less when looking at moon maps.

[John]

20 minutes ago, Cosmic Geoff said:

...Another tip is to use an erecting 45deg diagonal in place of the astro 90 degree diagonal  which you probably got with the scope. This will take out a mirror-reversal and make your brain hurt less when looking at moon maps.

Generally the 45 degree diagonals are not good for astronomy. The arrangement of prisms in them adds unwanted artifacts to star images and also introduces contrast reducing light scatter.

I would stay with the 90 degree mirror diagonal and get used to the left-right reversal.

If we are talking about the maksutov-cassegrain 127mm scopes here, they are quite capable of delivering sharp views at 200x so an eyepiece with a focal length of around 7mm-8mm will be useful. The provisios are:

- that the scope has been allowed to cool to the ambient temperature, which can take 30-60 minutes depending on the temperature difference between where it's stored and the observing site.

- that the seeing conditions are reasonably good.

- that the intended targets will benefit from high magnifications. Generally this means the Moon, planets, double stars and small deep sky objects such as planetary nebulae. Many other tatrgets such as nebulae, clusters and galaxies look much better at low to medium magnifications.

It's a good plan to build up a set of 3-5 eyepieces to give you a range of magnfication / field of view options. For the mak-cassegrain 127mm you could consider:

- something around a 30mm focal length for low power / wide(ish) views.

- something around 16mm and something around 12mm for medium power views

- something around 8mm for high powers

- for really good nights, something around 6-7mm but this will be too much power quite often.

There are plenty of options for eyepieces from around £25 (standard plossls) and these will perform better than the stock 25mm and 10mm eyepieces supplied with the scope. For a touch under £50 apiece you can get eyepieces such as the BST Starguiders which will really perform well in the scope and will enable it to realise it's full potential.

This guide is worth a read:

http://www.swindonstargazers.com/beginners/eyepieces.htm

It's written by one of our members

 

[Mak the Night]

I tend to agree about not using 45° Amici prism diagonals, as they are primarily intended for terrestrial use, but there are good 90° Amici diagonals nowadays that are perfectly capable for astronomical use.

The Advantages of Observing with Correct Image Diagonal

The stock 25mm 'SUPER 25 Wide Angle Long Eye Relief' is quite useable and I sometimes used a couple as a bino pair on my 102mm Maksutov. I'd probably recommend an inexpensive Plossl  over the stock 10mm eyepiece usually supplied with most Sky-Watcher scopes though. FLO sell Sky-Watcher UWA (manufactured by Barsta/BST) eyepieces which are very good for what they cost and have a slightly greater field of view than a regular Plossl.

Sky-Watcher UWA

With a 5" Maksutov high magnifications won't be difficult to achieve, but as was said earlier, lower magnifications of around 30x to 50x will require longer focal length eyepieces.

These eyepieces above are all 25mm and vary in cost. The top four are the wide angle reversed Kellner type, the others are either Plossls or Abbe orthoscopics. I believe a 25mm eyepiece will give you 60x magnification on a 127mm Skymax. It might be worth considering a longer focal length eyepiece such as a 30mm or 32mm Plossl for even lower magnifications. I often use a 40mm Plossl on my 102mm Skymax.

Most people dislike 40mm Plossls because of their long eye relief and slightly narrower field of view, but they are inherently useful on Maksutov scopes I find, especially when you want a fairly low magnification.

Basically, it's usual to have a spread of magnifications and eyepieces. On various scopes I have a range of around 30x-40x at the bottom range, 50x-90x mid range and 150x to 300x at the top end.

[Cosmic Geoff]

3 hours ago, John said:

Generally the 45 degree diagonals are not good for astronomy. The arrangement of prisms in them adds unwanted artifacts to star images and also introduces contrast reducing light scatter.

 

I did notice that the 45 degree diagonal (borrowed from a SW Startravel) caused some loss of performance, so I only use it for the Moon now. I can't get on with a mirror-reversed Moon at all. Fortunately there seems to be an alternative (see post above).