focusing at high mag

[algol]

So last night I was outlining at saturn, looked very nice. My ten mm eyepiece gives me 120x zoom, but I fancied pushing it so I put my Barlow in too giving me 240x zoom.

However I couldn't quite get it focused, it got quite near but then got worse as if the focus point wasn't there. Is this just a case of too high mag?

[ronin]

Quite possibly but also the barlow may spread the image so you no longer have a well defined focal plane.

Also not sure about the 10mm eyepiece, it will be a Huygens or Kellner design and although they are reasonable there is better but most relevant is that they will not be "good". Skywatcher put them in so you can see something when you get the scope, they do not unfortunately include high quality items.

I would guess that you have simply surpassed the comfort zone of the barlow and eyepiece combination. The solution being to go forth and buy some better eyepieces. It is easy, there are thousands to choose from :evil6: .

Just be carefull about asking for suggestions for better eyepieces. The recommendations start at GSO/Revelation Plossl's (£30), then BST Starguiders and X-Cels (£50), then it moves the ES (£200) then TV's at (£300-500).  Stating a limit (£'s) is generally ignored by people giving suggestions also. :ohmy:

[alexog]

At this time of year in the UK the ecliptic is low down in the sky (better than June though). Saturn is very low in the sky at the moment. With so much more turbulent air to look through things always look more blurred. Also in the evening at low altitudes the heat of the day is rising from the Earth also ruining the view. With a 200mm reflector 240x is easily within reach when the sky is cooperating. Thankfully the nights are drawing in and the ecliptic is rising. I'm looking forward to Jupiter in the New Year, nice and high in the sky

[algol]

Cheers fellas you helped to reaffirm what I already thought, think my next buy will be a revelation eyepiece kit and a new Barlow

[alexog]

If this is the one you're looking at it seems a great deal

http://www.telescopehouse.com/acatalog/Revelation_Photo_Visual_Eyepiece_Kit.html

This is pretty similar

http://www.firstlightoptics.com/eyepiece-sets/celestron-eyeopener-eyepiece-and-filter-kit.html

And both come with Barlows. The Celestron one comes with a 6mm but the Revelation has a niftier 32mm...

[algol]

Yeah mate that's the one, the rev seems like a better spread of focal lengths and the Barlow will expand that. Gonna be on the Xmas list me thinks in time for jupiter

[ollypenrice]

Personally I'd rather have two good EPs than four ordinary ones. You've seen that the ordinary ones do have their limits...The boxed sets are good value but not necessariy ideally suited to the needs of an individual scope and an individual observer. I've bought several premium EPs second hand, too. This is the best of all worlds.

Olly

[algol]

Aren't those a noticeable step up on the basic ones supplied with scopes though? Plus being able to have a good planetary and the 32mm for widefield is good?

[John]

Aren't those a noticeable step up on the basic ones supplied with scopes though? Plus being able to have a good planetary and the 32mm for widefield is good?

A slight step up would be more accurate. For £50 apiece you can have a really good eyepiece such as the BST Explorer or a Baader Classic Orthoscopic which would let your scopes show their potential much better than the eyepiece sets would I believe.

[alexog]

Personally I'd rather have two good EPs than four ordinary ones. You've seen that the ordinary ones do have their limits...The boxed sets are good value but not necessariy ideally suited to the needs of an individual scope and an individual observer. I've bought several premium EPs second hand, too. This is the best of all worlds.

Olly

You make a good point. With my OMC140 I use the supplied 25mm plossl and a barlow, plus a standard 40mm plossl but for high magnification (when seeing allows) I spent good money on a Vixen LV 7mm (280x).

[Moonshane]

this sounds more like seeing to me. as you use higher power (150x or more, sometimes less if the seeing is quite poor) the focus pops in and out despite being in the correct position for 'best' focus. i.e. if you have 'perfect focus', the seeing/focus will move in and out of sharpness with the atmospheric disturbance. poor seeing is indicated often by very clear skies and bright stars that scintillate (flicker/twinkle). no matter how good your eyepieces, bad seeing will mean longer waits between sharp views. once you find the correct focus position, just wait and observe, you'll eventually start to 'accrue' or store what you see and will build a mental picture of the planetary detail. this sounds like complete tripe but try it.

[algol]

this sounds more like seeing to me. as you use higher power (150x or more, sometimes less if the seeing is quite poor) the focus pops in and out despite being in the correct position for 'best' focus. i.e. if you have 'perfect focus', the seeing/focus will move in and out of sharpness with the atmospheric disturbance. poor seeing is indicated often by very clear skies and bright stars that scintillate (flicker/twinkle). no matter how good your eyepieces, bad seeing will mean longer waits between sharp views. once you find the correct focus position, just wait and observe, you'll eventually start to 'accrue' or store what you see and will build a mental picture of the planetary detail. this sounds like complete tripe but try it.

I'll give it a go mate

[alexog]

this sounds more like seeing to me. as you use higher power (150x or more, sometimes less if the seeing is quite poor) the focus pops in and out despite being in the correct position for 'best' focus. i.e. if you have 'perfect focus', the seeing/focus will move in and out of sharpness with the atmospheric disturbance. poor seeing is indicated often by very clear skies and bright stars that scintillate (flicker/twinkle). no matter how good your eyepieces, bad seeing will mean longer waits between sharp views. once you find the correct focus position, just wait and observe, you'll eventually start to 'accrue' or store what you see and will build a mental picture of the planetary detail. this sounds like complete tripe but try it.

+1

In my (heavily) light polluted skies I tend to look at solar system objects. I mentioned I use my high power eyepiece when seeing permits but in reality I sit looking at a highly magnified image hoping for a moment of clarity.

Have you tried double star observation? It's fun, will test your kit (including oculars), your observing skills and collimation of your 'scope. Good practice for that moment when Jupiter/work/cloud/seeing/commitments/etc. come together.

[LukeSkywatcher]

I have in the past bought the Celestron Eye Opener kit. It cost me 200 squids and all i used for a long time was the 32mm EP and the Moon filter. Not worth the money.

You really would spend your money better by buying a couple of better quality EP's.

240x mag in a 130mm scope is unthinkable in the British isles.  240x in a 200mm scope is the best you can expect on any given great night.

It boils down to "seeing" and transparency.

My rule of thumb is: whatever is the aperture of the scope is the magnification you should use. On absolute crystal clear nights, you can push say 200x up to about 260.