Problem with focusing

[karlernst]

Hi!

I have a Astromaster 130md and have a hard time finding focus. Im using 20/10/6,5mm eyepieces and a 2x barlow. When looking at jupiter its impossible to get a sharp view with anything but the 20/10mm eyepieces. As soon as i use the barlow and/or the 6,5mm the planet get "smudgey", "pointy" and leaving lighttrails after it when viewed. I suspected that this was do to collimation error, but the "out of focus star - test" indicate everything beeing OK.

Looking at planet jupiter doesnt revelae any detail at all, just a smudged blobb and its moons. As i adjust focus around where "it should be", i really dont see any difference...

Am i having an issue with my optics, or am i just having to high expectations?

//Karl

[Jiggy 67]

I think you're just pushing the scope to its limit, with a 6.5mm + 2x barlow, that gives you 217x mag, with a relatively small aperture of 130mm, you are at the edge of what your scope can cope with..........enter....aperture fever!!!

[Tinker1947]

Proberly what Jiggy typed,,,time for a bigger scope........

[ronin]

The 130 will start to drop off at 150x if it can get that, that is a 6mm eyepiece.

The barlow that comes with it is usualy poor and so delivers an indistinct image.

The scope is I suspect a spherical mirror and at f/6.9 is too fast for a spherical to deliver a decent image, hence my reason for saying it may not deliver 150x.

You have I would say a poor image from what I think is a spherical mirror to start with, then adding a poor barlow just adds to the problems.

[karlernst]

Thanx for the answers!

Its a bit dissapointing, since the scope was specified by celestron as beeing capable of upto 300x. Even the usual 50x/inch rule gave me the impression that it would be capable of atleast 250x. I did some more tests today and even at 32x its hard to get Jupiter to not "flare out".

So i will need a bigger scope with a parabolic mirror?

[wookie1965]

Better eyepieces and better Barlow don't push mag and you will get some great views. You can always go bigger then but you will then have the added bonus of having a couple of good eyepieces and a good Barlow.

[astronymonkey]

Id agree that the level of magnification is probably too high for the scope and adding more glass in the light path by way of a barlow will probably only add to the problem. Often the maximum quoted level at 50x per inch requires pretty stable skys with little or not atmospheric turbulence otherwise the level of resolution that is possible drops off. On a perfect night, with cooled optics then you may be able to push the limit but often the view itself tells you if you if youve past the limit for the given conditions.

To view Jupiter I would let the scope cool for half an hour and select a non barlowed lens of approx 50x mag, get the best focus you can on a star (so you know its in focus !) and then swing it to jupiter and allow it to drift across the field of view whilst you watch ... dont touch the scope, just watch. Between the ripples in the atmosphere you will glimpse moments of good , stable air, where you can just make out two faint sandy coloured cloud belts on the disk . I find this low power approach often gives the best image in a small scope as it seems to concentrate the colours on the disk to give better contrast and so makes the cloud belts more obvious.

Clear skies,

Astronymonkey

[LeeB]

The 130md is a great scope, but I agree with most of the above, the viewing of jupiter is governed by seeing conditions, on a great night i will go to 400x + with a 10 inch scope but with the same scope on a bubbly/poor night 100x can be to much. Saying that I would check collimation ( no special tools at this stage just peek in the focuser without an eyepiece and check to see if it looks pretty symetrical ) then at somepoint invest in a cheshire collimator.

Better eyepieces will help as will allowing a good cooling off period, this takes longer if the temperature outside is vastly different from storage temp. which it tends to be this time of year.

Your scope will on a good night push 200x or even a little more but all things have to be in your favour.

Also as heating on houses tends to be full on this time of year, any roof near or under the target star or planet can, if poorly insulated cause a column of rising air which will ruin viewing.

[mareprah]

I use a similar scope, SW 130/900, and in a whole year, the seeing was good enough to view above the 150x mag only once. My favorite mag is the lowest one (36) maybe on some occasions the 90x... Still, regardless of the seeing, i recomend you to build at least a Hartzman mask if not a Bahtinov, and try to get a motorfocuser fitted up there. I spent cca 10-15€ on mine, but its very efficiant. Looks like this:

remote:

cheers,

Mare

[nicks90]

i have a celestron astromaster 130 as well and it DOES have a parabolic mirror - like the SW 130p etc

so it is not the optics per se that is the problem. It is a 'fast' scope at F5 and therefore it will show up rubbish eye pieces very quickly. I also found the celestron 10mm it came with is rubbish. the image correcting 20mm is also not particularly good either, although it is handy for finding things being horizontally and vertically correct - once i have what i want in the focusser, it gets changed to a 25mm plossl, as the views through that are much crisper!

However I find that anything over x125 starts to break down the image on all but one night I have had it out viewing. The skies just arent clear enough!!! Your 6mm ep is just about right at x110 - dont barlow it though as that will just kill anything you could possibly see!

As others have said, make sure its fully acclimatised to the cold for at least 30 mins before you start viewing, try to move away from viewing stuff over the roofs of nearby houses (heat haze!) and also gauge how much the stars 'twinkle' in the sky. The more they twinkle, the more turbulence in the atmosphere there is and the poorer the views you will get! On a good steady night with my 6mm meade 4000 series super plossl i can see the 2 main bands with good definition, and the odd band above and below - not particularly distinct smaller bands - more of a vague colour change in the background beige of the planet. But you should definitely see good solid banding x2 on a good evening!

also, the higher the mag from the eyepiece, the narrower the focussing range is and the more accurate you have to be when focussing. To aid this, try blutacking a golden syrup lid on to one of the focusser knobs. that means a 1mm movememt of the lid wll give less than a 0.5mm movement on the focusser knob - giving you more accuracy and making it slightly easier to find perfect focus (depending on seeing conditions and light pollution!)

you aint got a rubbish scope - but the eyepieces are fairly low rent and really need upgrading, Dont spend a fortune, £20 second hand plossls do the job nicely, or shell out a bit more of a tmb planetary. Believe it or not, I find one of my most used eps is a cheap second hand 12mm ortho! poor eye relief and poor field of view - but the images are absolutely pin sharp and it cost a tenner!