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rwiederrich
Goldfinger
*****

Reged: 11/17/05

Loc: Always Dark skies of Belfair W...
Re: Pacific NW Mt St Helens EternaThread Pt 6 new [Re: rainycityastro]
      #5504485 - 11/04/12 08:10 PM

Quote:

I had the opportunity to talk with Roland several times during the conference. His opinion was that a 7-8" APO would have tighter stars, larger field and higher real resolution than practically any other instrument including those beauties seen here when you take into consideration actual seeing in most places in the US.

The only problem is that 7-8" refractors are becoming increasingly harder to get and when one becomes available, they are as expensive as a very nice car.




I agree with Roland. I have never seen images in any larger Cass that compared to my 6"f/15...or not in my 10"f/15. Once the central obstruction is eliminated from the equasion and the cool down issues are calculated..the refractor comes out the winner in my view. Those other scopes are nice..but I made my scopes for far less money and got the most aperature. It just takes ingenuity and work.


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rainycityastro
professor emeritus
*****

Reged: 03/29/10

Loc: Seattle, WA
Re: Pacific NW Mt St Helens EternaThread Pt 6 new [Re: bluedandelion]
      #5504526 - 11/04/12 08:42 PM

Quote:

About aperture: I have to disagree with Roland somewhat.
You can do great lunar and planetary work where seeing is of paramount importance with the most compromised design of all (the SCT) by using a webcam and the trickery of lucky imaging. People have done great w0rk with C9.25, C11 and C14.
Ajay




Roland was specifically calling out imaging I think. I doubt he is as much of a visual astronomer these days as an imager. Since the conference was 100% deep sky, I am sure he wasn't talking about planetary or lunar imaging.


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rainycityastro
professor emeritus
*****

Reged: 03/29/10

Loc: Seattle, WA
Re: Pacific NW Mt St Helens EternaThread Pt 6 new [Re: bluedandelion]
      #5504531 - 11/04/12 08:44 PM

Quote:

Thank you Ram. If you have some time we should meet during the Christmas break and compare notes. I am sure you learned some cool tricks at the imaging conference.

Ajay




Would love to. There might be a day or two of clear skies/imaging possible before then. We might be able to meet then.


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rwiederrich
Goldfinger
*****

Reged: 11/17/05

Loc: Always Dark skies of Belfair W...
Re: Pacific NW Mt St Helens EternaThread Pt 6 new [Re: Stacy]
      #5504692 - 11/04/12 10:18 PM

Quote:

Quote:

Indeed...but with a 10~12" central obstruction..making it about a 13ish scope...in reality. What a trade off, for fast ratio and large aperture.




Sorry, but the light grasp of that instrument would be far more than a 13" scope of any kind. Let's be realistic here...




I'm sorry. 14" then.


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Stacy
Star Partyer
*****

Reged: 09/15/02

Loc: Seattle, WA
Re: Pacific NW Mt St Helens EternaThread Pt 6 new [Re: rainycityastro]
      #5504719 - 11/04/12 10:33 PM

If you read This , you will understand why an SCT performs EXACTLY the same as a refractor of equal diameter on high contrast targets. On low contrast targets, the SCT or Newt performs the same as a refractor of EQUIVALENT diameter (ie, the diameter of the objective minus the CO expressed as a percent). So a 12" SCT with a 25% CO performs visually equal to (and many times will out-perform) a 9" refractor on low contrast targets.

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Stacy
Star Partyer
*****

Reged: 09/15/02

Loc: Seattle, WA
Re: Pacific NW Mt St Helens EternaThread Pt 6 new [Re: rwiederrich]
      #5504757 - 11/04/12 11:10 PM

Quote:

Quote:

Quote:

Indeed...but with a 10~12" central obstruction..making it about a 13ish scope...in reality. What a trade off, for fast ratio and large aperture.




Sorry, but the light grasp of that instrument would be far more than a 13" scope of any kind. Let's be realistic here...




I'm sorry. 14" then.




Well, I guess the attraction is that it would perform like an UNOBSTRUCTED 13 or 14". But alas, some scopes only an imager could love!

Could just grind down that secondary and make a nice little scope.


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rainycityastro
professor emeritus
*****

Reged: 03/29/10

Loc: Seattle, WA
Re: Pacific NW Mt St Helens EternaThread Pt 6 [Re: Stacy]
      #5504876 - 11/05/12 02:33 AM

Stacy, thanks for the link. Quite helpful.
Visual is kind of like lucky imaging. i.e. Objects go in and out based on instantaneous seeing. Imaging on the other hand is limited by the average seeing of that sub.
Since most of us are not lucky enough to have an observatory on top of a mountain in a desert, our seeing is typically limited to 2 arc secs in most places. WA state is typically worse than this most of the year other than summer.
A scope of approximately 5.5 inches is sufficient to sample at 1 arc sec (assuming 1 arc sec is the Nyquist sampling rate of a 2 arc sec seeing). Anything larger is simply going to be brighter but is not going to resolve any better. Given that cameras can continue to integrate light unlike the human eye, this is not really a problem.

On occasional nights we might be lucky to get 1.5 arc sec seeing and a 7-8" refractor will provide everything there is to be seen.

Potentially small obstruction reflectors (like maks that are sufficiently cooled down) can perform just as well. But most reflector designs have large spot sizes or large diffraction rings as you go further off axis.

Of course all this assumes that the scope doesn't have aberrations and is adding next to nothing to perturb the wave front any further beyond the seeing. This is not a valid assumption with many mass market instruments.

Quote:

If you read , you will understand why an SCT performs EXACTLY the same as a refractor of equal diameter on high contrast targets. On low contrast targets, the SCT or Newt performs the same as a refractor of EQUIVALENT diameter (ie, the diameter of the objective minus the CO expressed as a percent). So a 12" SCT with a 25% CO performs visually equal to (and many times will out-perform) a 9" refractor on low contrast targets.




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Sean Puett
Carpal Tunnel
*****

Reged: 09/06/10

Loc: always cloudy, washington
Re: Pacific NW Mt St Helens EternaThread Pt 6 [Re: Sky Captain]
      #5505154 - 11/05/12 09:46 AM

Quote:

Quote:

Luckily i don't really need anything right now.



Now I've heard everything.




I forgot I typed that. I was looking at a local stellarvue 90mm bv triplet with flourite objective. I just decided not to get it but, if I hadn't sold my binoviewer and pairs of eyepieces, I would have one unhappy wife.
It is still on AM and the guy is in Seattle. Someone could get a good deal.

How is everyone dealing with all the clear wonderful nights we have been having? I am now thinking that rereading the "song of ice and fire" series may be in the cards. I was so hooked on the world he created in that series that i read them very quickly so I think reading them again may be fun.


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Sean Puett
Carpal Tunnel
*****

Reged: 09/06/10

Loc: always cloudy, washington
Re: Pacific NW Mt St Helens EternaThread Pt 6 [Re: rwiederrich]
      #5505232 - 11/05/12 10:50 AM

Quote:

Quote:

Thanks for the photo's Ram!!!
That 24" is amazing!




Indeed...but with a 10~12" central obstruction..making it about a 13ish scope...in reality. What a trade off, for fast ratio and large aperture.




It doesn't quite work like that. You still get the resolution of a 24" but, you lose the surface area of the CO in brightness. There have been quite a few comparisons done between these large super fast reflectors and slower scope of the same aperture and the fast ones always surprise the skeptics. I want to point one of these fast scope at a low contrast planet like Jupiter and Saturn to see how much contrast is lost. They are excellent for galaxies and globs, nebulas, and milky way scanning. And they are CA free.

I thought everyone who bought one of the super fast reflectors must be ignoring huge issues or not reporting them until I looked through Bill's 22" f3.3 or f3.6 scope and his stars looked as nice as the refractory I Had at the time minus the CA. I think his secondary is 7". I hope he comes back around some day and comes to a party at your house so you can check it out. Paracorrs handle all the coma and if his collection is good, stars look great in it. There are extra though. So many tiny stars ahhh...telescope envy.


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Spaced
Post Laureate
*****

Reged: 03/01/05

Loc: Tacoma, Washington, USA
Re: Pacific NW Mt St Helens EternaThread Pt 6 [Re: Sean Puett]
      #5505254 - 11/05/12 11:04 AM

Quote:

I am now thinking that rereading the "song of ice and fire" series may be in the cards. I was so hooked on the world he created in that series that i read them very quickly so I think reading them again may be fun.




Sean, I read that series earlier this year -- actually just finished about a month ago. Amazing stuff. Bring on the next!

And if you aren't daunted by multi-volume stories of epic length, I've been "reading" (recorded books) and recommend "The Dark Tower" series by Stephen King. It's superb.

The weather-guesser is saying we may be able to see something other than clouds Friday.

. . . and speaking of clouds, Saturday Anne & I saw the movie "Cloud Atlas." They did a terrific job making a movie out of a very complex story. (Sean, that's a book you'd really enjoy.) I disagree with the critics on this one. Go see it!


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SteveG
Post Laureate
*****

Reged: 09/27/06

Loc: Seattle, WA
Re: Pacific NW Mt St Helens EternaThread Pt 6 [Re: Spaced]
      #5507101 - 11/06/12 03:43 PM

After quite a long break due to weather & schedule, I finally got out last night to catch some photons. I looked at Jupiter after it cleared some trees off my back deck where seeing is usually much better. Because I'm on a narrow deck, I use my 100 ED for it's light-weight and easy portability. This cheap little scope never ceases to amaze me. Jupiter stood out with very crisp detail, many bands showing including the polar bands. The SEB looks quite different this year. I was experimenting with Brandons & plossls through my Celestron prism diagonal. All views were CA free, and crystal sharp when seeing permitted. Unfortunately I was viewing through thin clouds that were passing by, and it got so bad I had to pack it in after an hour (it was late). Of course as soon as I got everything inside it cleared up!

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rwiederrich
Goldfinger
*****

Reged: 11/17/05

Loc: Always Dark skies of Belfair W...
Re: Pacific NW Mt St Helens EternaThread Pt 6 [Re: SteveG]
      #5507122 - 11/06/12 03:56 PM

Quote:

After quite a long break due to weather & schedule, I finally got out last night to catch some photons. I looked at Jupiter after it cleared some trees off my back deck where seeing is usually much better. Because I'm on a narrow deck, I use my 100 ED for it's light-weight and easy portability. This cheap little scope never ceases to amaze me. Jupiter stood out with very crisp detail, many bands showing including the polar bands. The SEB looks quite different this year. I was experimenting with Brandons & plossls through my Celestron prism diagonal. All views were CA free, and crystal sharp when seeing permitted. Unfortunately I was viewing through thin clouds that were passing by, and it got so bad I had to pack it in after an hour (it was late). Of course as soon as I got everything inside it cleared up!




Yeah..it cleared up here at Gomoc as well last night for some time. I was focusing on the election so I didn't do any viewing.


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Stacy
Star Partyer
*****

Reged: 09/15/02

Loc: Seattle, WA
Re: Pacific NW Mt St Helens EternaThread Pt 6 [Re: SteveG]
      #5507400 - 11/06/12 07:01 PM

Quote:

Of course as soon as I got everything inside it cleared up!



Hmmm... Sounds like Murphy's Law at work here, which can't normally be broken. However, a "mock" pack-up has been known to thwart the phenomenon.


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Spaced
Post Laureate
*****

Reged: 03/01/05

Loc: Tacoma, Washington, USA
Re: Pacific NW Mt St Helens EternaThread Pt 6 [Re: Stacy]
      #5507855 - 11/07/12 02:11 AM



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Spaced
Post Laureate
*****

Reged: 03/01/05

Loc: Tacoma, Washington, USA
Re: Pacific NW Mt St Helens EternaThread Pt 6 [Re: Spaced]
      #5509692 - 11/08/12 10:41 AM

Last night I put together an observing list for this weekend. Inspired by clear skies, no moon and by S & T's finder chart in the Oct. issue I'm going to look for Vesta & Ceres. I'll sketch positions and try to get out both Fri & Sat. for comparisons. And while I'm in the area, Jupiter, M35 & NGC 2158(?), Eskimo planetary, M1, some open clusters in Taurus and a couple of double stars. Also a couple of other things which currently escape my feeble memory.

The good news is I should be able to do this from my driveway (but whether LP allows a view of M1 is a question). The bad news is that things won't be well-placed 'til about midnight. I hope I can work in an evening nap!


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zerro1
Postmaster
*****

Reged: 08/02/09

Loc: Smokey Point , 48.12°N 122.25...
Re: Pacific NW Mt St Helens EternaThread Pt 6 [Re: Spaced]
      #5509781 - 11/08/12 11:26 AM

There is sky beyond those clouds. it's blue! wonder what it will look like after the sun go's down. it's been so long, the memory of what it looked like has faded.

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rwiederrich
Goldfinger
*****

Reged: 11/17/05

Loc: Always Dark skies of Belfair W...
Re: Pacific NW Mt St Helens EternaThread Pt 6 [Re: zerro1]
      #5509837 - 11/08/12 12:02 PM

Last night was totally clear here and Jupiter was amazing. It was calm and cold for sure. Looks to be the same tonight.

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SteveG
Post Laureate
*****

Reged: 09/27/06

Loc: Seattle, WA
Re: Pacific NW Mt St Helens EternaThread Pt 6 [Re: rwiederrich]
      #5510219 - 11/08/12 04:31 PM

Quote:

Last night was totally clear here and Jupiter was amazing. It was calm and cold for sure. Looks to be the same tonight.




Yep - Same at my house. I lugged out my 10" to my back deck, and after 1.5 hrs of cool-down I was rewarded with some very nice views of Jupiter. I've decided I now need an XW10!


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Spaced
Post Laureate
*****

Reged: 03/01/05

Loc: Tacoma, Washington, USA
Re: Pacific NW Mt St Helens EternaThread Pt 6 [Re: SteveG]
      #5510360 - 11/08/12 06:14 PM

Quote:

I've decided I now need an XW10!






One good night, and just look at what happens!


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Stacy
Star Partyer
*****

Reged: 09/15/02

Loc: Seattle, WA
Re: Pacific NW Mt St Helens EternaThread Pt 6 [Re: Spaced]
      #5510953 - 11/09/12 01:45 AM

Got out with my new (to me) older Adlerblick 7x50. Man these things are awesome! Super light weight (about 22oz.) and nice wide view (7*). Got these free with some large binos I got last week (and sold in S&S) They are exactly like these and in like new condition.

Jupiter was sweet as was the double cluster and Pleiades. .... Well, that's pretty much what these are made for. Simply stunning.

Sold the Pentax 7x50's the Nikon 10x50's and the Orion 16x80's and ended up with some nice Steiner 10x40's and these and still came out $100 ahead. Combing Craigslist pays off every once in awhile...


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