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Binaries with a Newtonian.


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Great article Nick! The info about splitting stars in the small coma free area of the center of the FOV is hugely important, my f4.8 is a prime example. It does split stars very well though if cooled and collimated.

Hey aren't you a refractor guy? :grin:

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I'm going to have a shot. I've got an f6 8" OO and a lovely sharp f8 6" SW. I prefer the SW views of planets and the Moon.

Collimation is pretty tight using a collimated Barlowed laser on the night. Sadly , I have been known to count squares on the reticule to get it spot on.

Certainly will expand the experience !

Nick.

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Using a friend's 200P, I've never had too much problem with close-ish doubles, but it struggles a bit with very unequal brightness doubles (I assume because of the poor Strehl ratio of many cheap newts, and maybe quality control??). Anyone any experience with eg Delta and Lambda Cyg? I note that Neil got a decent split on these on at least one occasion with his SW scope.

Chris

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My 12" F/5.3 dob can "out split" my ED120 refractor as you might expect but the star images are not as satisfyingly tightly defined as they are in the refractor. It's an aesthetic thing but I really like the star images that refractors produce. The 12" dob remains the only scope I have which has split Sirius though, not that it's a particularly close pair, but the immense brightness difference and pulling the mag 8.5 "Pup" through the glare of the primary star is a job that the 12" aperture and reasonably well figured mirror have proved adept at.

I'd like to try a really nicely figured 8" F/8 or similar newtonian sometime :smiley:

When I had a Skywatcher 200P dob I cen recall that it was better at splitting doubles than I was expecting it to be.

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I need to give my OO 10" f6.3 more of a go on some doubles soon, have only really used it for planets so far. It's 1/10th wave so in theory should be pretty good. Will report back when I get a chance

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One thing I've noticed with my dob is that clean mirrors offers much less scatter than a dirty ones... of course this depends on how dirty it is. We obviously don't want to make the mirror worse by cleaning and damaging them :smiley:.

This scatter can really impact double viewing IME. I always clean my secondary now too. Slight miscollimation can also make for some pretty lousy dob star splits as can an unequalized mirror system. Having all this in line allowed Sirius to be split in the 10" and the Double Double at less than 70x, Pi Aquilae no problem etc.

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One thing I've noticed with my dob is that clean mirrors offers much less scatter than a dirty ones... of course this depends on how dirty it is. We obviously don't want to make the mirror worse by cleaning and damaging them :smiley:.

This scatter can really impact double viewing IME. I always clean my secondary now too. Slight miscollimation can also make for some pretty lousy dob star splits as can an unequalized mirror system. Having all this in line allowed Sirius to be split in the 10" and the Double Double at less than 70x, Pi Aquilae no problem etc.

With my fracs or my Mak, I find the worst area for dust/dirt is the surface of the diagonal - I suppose the effect of any dust is more significant here because the light beam is reduced to a much smaller circle than eg the front of the objective (or corrector).

As an aside, worth reading some of the other blogs on Neil's site.......

Chris

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I think it's really nice to see the linked article highlighting much of what has been said over the years on SGL and the advice we try to give to new comers.

Firstly, that Synta's 8" Newt is a cracking scope for beginners and seasoned observers alike. There's also the idea that there is no one telescope type which can monopolise on double stars, Saturn or Jupiter, for example, and that performance derived from a given session isn't determined by the amount of money one has spent on their gear but will depend on the observer's skill, patience and knowledge of the night sky and the given conditions of his or her environment.

The worrying case would be an artcle calling into question the performance of a telescope type per se (refracting, reflecting, or catadoptric). Almost by definition, certainly by the simple fact of existing, each telescope type has strengths and weaknesses; the creator or designer of the instrument working on a tight rope of compromises. As stargazing aficionados, playing and advising only to one side, would reveal more about the speaker than it would about the telescope type.

Thankfully, SGL rarely, if ever, gets involved in such debates as frac vs newt, or mirror vs glass etc and if such an issue does arise, we generally bring to the boards our experience and insights without delving upon rhetorical banality. The telescopes we use are instruments to reach further than our naked eye - nothing more - and some of the pleasure derived from this will not always be grounded on what can be resolved, split, tweaked and busted. The aesthetic component is extremely important and thankfully being a truth grounded on mankind, allows us to experience a wide variety of optical wonders.

There’s no correct way for enjoying a stargazing session and no correct telescope to enable this; each telescope type brings something to the table of our experiences, revealing something more, something less, something different. At the end of the day, it matters not what telescope type is used. Each in their own manner will present and frame the universe in a slightly different manner which suggests that each type is essential to enjoy and learn from.

I've said this before, but I feel that each telescope inevitably brings us back to ourselves; that we have been a nebula and an open cluster, a red giant and supernova and one day, we will be again. There is no correct telescope separating us from the stars and the DSOs, there is only time...

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  • 1 month later...

I have found my OO 8" f6 scope to be a very good splitter of doubles. 

If you spend a bit of time on collimation and the seeing is steady then it can be quite amazing how well  close and uneven pairs can be resolved.

My other suggestion is to use eyepieces like orthoscopics as these keep the images nice and sharp and the relatively small FOV is irrelevant :)

Cheers

Ian 

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