Quote:
Originally Posted by mikerr
John, I think the Barlow may just be physically too long to allow the focuser to reach focus. In other words, if you could get a few more turns of the focus knob it would probably come into focus.
You may just need a different brand or physical size Barlow.
Did you purchase the scope from a local dealer? If so they can probably help.
Hopefully others will chime in and offer other possibilities.
Michael.
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This would make sense. It was a gift so no money lost, sounds like we may just need a bigger Dob
Might have to shelve this Barlow until we get some experience under our belts.
Quote:
Originally Posted by barx1963
John
The 50 per inch is a "theoretical" maximum assuming very dark skies and perfect seeing. In reality is is closer to 10 or 20 per inch and in a small scope like yours, 50x would be usually adequate for reasonable views.
A 130mm scope at 50x will show quite a few DSOs nicely, EG M42, Omega Cent, NGC 2070 and should be able to pick up Cent A Galaxy with little problem.
Malcolm
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Thanks Malcolm, that's encouraging.
Quote:
Originally Posted by mental4astro
G'day John, to IIS!
Like Michael said, some barlow lenses may not work, needing too more in-travel than your focuser may allow.
However, by the sounds of it, you did achieve focus, which leaves one of two possibilities.
The first was that the prevailing atmospheric conditions didn't allow for 195X to be used. The typical maximum possible is only 100X to 120X, REGARDLESS of the size of the scope you've got! 250X is pot-luck to achieve with minimal "boil" of the image. Anything more and you should be buying lottery tickets. My 5" scope gave fantastic images at 250X, but only when the atmosphere was stable, but it too was a very, very good scope.
The other thing it could be is that the mirror of your scope is spherical in shape, and not parabolic. Spherical mirrors are cheaper to produce, and if your scope has a long focal ratio, these spherical mirror can perform well. However, with the fast focal ratio your Heritage scope has got, if the mirror is spherical, you've got no chance of pushing the scope's magnification. The light from the primary mirror just won't come to the one focal point.
The GOOD news is that it sounds more like it was the prevailing atmospheric conditions that were the problem. A quick test would be to use your 25mm eyepiece with your barlow. If the image was still good, I'd suggest it is the atmosphere.
If things don't improve, I'd then suggest you talk to the folks who sold you the scope. If it is spherical, all the scope will be good for is low powers. You will not be able to get a good high power image from it.
I hope this makes sense.
Mental. |
Thanks for your response, it makes sense. I have overestimated the magnification capabilities of the scope (probably a common problem so I'll console myself with that). I didn't actually achieve focus with the Barlow even with the super wide 25mm eyepiece so it may be atmospheric conditions or the Barlow simply isn't compatible. The mirror on the scope is a parabolic mirror (at least that's what is says) so that doesn't seem to be the problem. I'll reassess tonight as it looks to be a reasonable night for observation. Thanks all.