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Anyone managed to split Porrima?


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I set out to split Porrima tonight -- it didn't work! However, the idea of distances is finally getting through to me. I was unable to split Izar previously (a 3" separation), so why would I think I could split Porrima (a 2.5" separation)? At least with Izar I could see somewhat of a shifting blob and could more or less tell that it was a double..but with Porrima I couldn't really tell anything. 

Anyone managed to split Porrima? How'd you do it? Does a dark site make a big difference in splitting doubles? I was trying this from a light polluted back yard close to the city core. Stars were dull and twinkling with naked eye.

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It's not one I remember trying, but looking at the info on it, it should be fairly straightforward as they are reasonably bright and equal magnitude.  If the seeing was poor then that may explain your lack of success so give it a go on another night.

Have you been able to split the Double Double in Lyra? That is similar, if a little tighter and dimmer stars but is a very good test of scope and conditions. In a refractor I can split this down at x55 or so on a very good night, but to be comfortable you probably need over x100.

Sorry, I can't see what scope you are using. If it's a newt or an sct/Mak then usual comments of cooling and collimation apply. I just find a good frac will split tight doubles far easier than most reflectors

EDIT Have you tried Castor in Gemini? Getting lower now but at 5.1" separation and brighter stars it's an easier split to get going on.

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Porrima is a very pretty double and although close, should readily be split even with small scopes. My ED80 splits it on a good night to give an effect like the headlights of a car coming towards you, two whitish close, similar brightness disks. It's easier of course with my larger scopes, but needs a good night and decent collimation if you're using a reflector.

The XT8 (if you are using that) should split it easily, but as Stu says, try Epsilon Lyrae first - if you can't split that then Porrima will probably not be split.

Chris

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PS you might find a sub aperture mask will help with doubles even with your 8" newt. It will dim the view but will certainly tighten up star shapes. You'd probably get away with a 70mm hole which would give a 70mm f17 dobfractor.

 

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9 hours ago, Stu said:

It's not one I remember trying, but looking at the info on it, it should be fairly straightforward as they are reasonably bright and equal magnitude.  If the seeing was poor then that may explain your lack of success so give it a go on another night.

Have you been able to split the Double Double in Lyra? That is similar, if a little tighter and dimmer stars but is a very good test of scope and conditions. In a refractor I can split this down at x55 or so on a very good night, but to be comfortable you probably need over x100.

Sorry, I can't see what scope you are using. If it's a newt or an sct/Mak then usual comments of cooling and collimation apply. I just find a good frac will split tight doubles far easier than most reflectors

EDIT Have you tried Castor in Gemini? Getting lower now but at 5.1" separation and brighter stars it's an easier split to get going on.

I'm using my 8" dob. I'm pretty sure it was well collimated (laser plus did the de-focus thing and the secondary was right in the middle of the blurry star). I think it could have been a bad night...the stars looked pretty fuzzy with naked eye.

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As long as you sure the collimation is good, then it is likely the seeing conditions were poor.  I have split the Double Double at 88x using a 60mm scope on a good seeing night so none of the doubles listed should be a challenge for your 200mm scope.  But as eluded to in this thread, seeing conditions play a big role in ones ability to split a double star.

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I was out tonight checking out M5 for the first time (wonderful views) and happened across a chance double. I found 5 Serpentis and immediately saw the double...was quite rewarding given my recent failures with other doubles!

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30 minutes ago, Mr Spock said:

It will be seeing conditions. On a reasonable night my C9.25 will split 0.7" doubles with room to spare.

What sort of magnification do you need for this Michael? I'm playing around with a C9.25 at the moment so will give some doubles a go, never had much luck with them through SCTs before.

By the way, you were right about image shift, I find it much more acceptable in the 9.25 vs the 8 for some strange reason, the 9 seems better engineered in this respect.

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