Cat for planets
Posted 17 December 2011 - 11:20 PM
Lol, its not even fair!!
Posted 17 December 2011 - 11:37 PM
I have astig, too, and wear glasses (as of a year ago.) But, maybe you find you don't really need them at the eyepiece. I was afraid to use my 12mm Ortho, but hey...no prob. No glasses needed.
Oh, and I look forward to your first light...and sketch. I am waiting with baited breath (need to brush.) Hell, maybe you'll spend more time in the observing forums, too, and not arguing much over MTF.
Personally, MTF is great and interesting, but I've learned not to worry about it. CATs do fine on planets, IME. In fact, it seems collimation, focus, and cool down (factors we can control) coupled with good seeing (which we cannot control, mostly) allow all scopes (CATs, Newts, and refractors) to perform closer to their theoretical MTF. And the results can be stunning, even with a little residual SA.
Anyway, back on topic. Go CATS!
Posted 18 December 2011 - 12:36 AM
If I could sketch that would be a time I really apprecieated the SCT and Go To.
Posted 18 December 2011 - 09:48 AM
Sorry about the floaters. Also, the virtues of higher magnification are lost if the scope isn't tracking (I find it hard to keep my attention focused on a particular detail when the object moves quickly across the EP FOV). Really smooth optics with first-rate coatings in the 10" to 12" class help too. My eyes aren't getting any better with advancing age, so I don't mind dropping coin on the best optics I can get. When my eyes get worse to the point that the optics don't help at the EP, or with imaging that can be visualized well enough on a computer screen, I'll sell my premium OTAs.
The floaters are merely an inconvenience, but the retinas still function very well. I can see fine detail at more moderate powers, which works out well, because I don't like uberhigh magnification.
I don't need to push the magnification to see detail in the GRS, strings of small barges, over a dozen bands, networks of festoons, white ovals, etc. I can get good results with a binoviewer, Baader M&SG filter, an apodizing mask, a C10NGT on a Dob mount and decent though not exhorbitant eyepieces. Go figure. YMMV. My sketches of the planet's surface always closely match the photos.
Posted 18 December 2011 - 01:58 PM
There are no details to observe on double stars (other than their separation). There are on planets.
This strikes at the heart of the matter.
Angular Resolution is not meaninful in terms of describing visual performance in extended objects.
Theory (and I know that is a dirty word for many people but it is hard to have a meaningful dialog without it) says that an extended image is composed of an infinite number of overlapping DIFFRACTION PATTERNS. Note, theory does not say it is composed of overlapping AIRY DISK.
You must be referring to Huygens’ principle of constructing a wavefront from point sources. The Huygens’ principle shows/explains why angular resolution is a defining factor and contradicts your statement “Angular Resolution is not meaningful in terms of describing visual performance in extended objects” Sorry, Ed. You couldn't be wronger on this one.
Posted 18 December 2011 - 04:14 PM
Ive NEVER seen a ten inch f/4 produce images on par with a like sized refractor visually. Not even close.
You've viewed planets through a 10" refractor? Which observatory was that in? That is getting up to a monstrous size for a telescope. I've looked through an 8" f/15 refractor, and that thing is a behemoth mounted permanently under a dome.
But like I said, it didn't show me anything on the image of Jupiter that I couldn't see in my 8" f/6 reflector. My 10" f/4.8 Newt shows me more. So far I'm not impressed by what a refractor can do for planets versus a stabilized, well-collimated Newt with decent optics.
Posted 20 December 2011 - 08:22 PM
Posted 20 December 2011 - 09:07 PM
I get a "404 not found" error at that link. "We're sorry, the page you requested cannot be found. Try searching for something else."
I suppose with an aperture of 32", the observer would be able to use magnifications well over 300x with good effect, as long as the seeing cooperated. That would be about a 2.7mm exit pupil, which would be very comfortable. And Texereau's ideal planet observing exit pupil of 0.8mm would put you at around 1000x on a 32" aperture, which would be very nice ... during a night of good seeing ... with a thermally stabilized instrument ... that tracks. It is not the high power that I object to so much as the narrow exit pupil and the difficulty of manually tracking at high powers.
If the aperture is large enough to support high power without torturing me with an exit pupil substantially below 0.8mm, and there is tracking, and the seeing is good, and the telescope is thermally stabilzed, then I have no problem with high power. Otherwise, I will make do with more moderate powers and try to use my experience and technique to make up the difference.
Posted 20 December 2011 - 10:06 PM
Posted 21 December 2011 - 08:16 AM
Posted 21 December 2011 - 06:51 PM
Sorry. My iPad automatically transfers the URL to an app.
Search for "mega home made telescope" and select PART SIX.
Posted 21 December 2011 - 08:03 PM
Thanks. Here is a link to the video on YouTube:
Mega home_made telescope PART SIX
Uploaded via my trusty, crusty eight-year-old PC clone running XP.
After watching the video, I realize the ATMer will not have to transport the scope, set it up, or even climb a 10' ladder to look in the eyepiece. Yes, very comfortable indeed. Well done!
Posted 21 December 2011 - 09:13 PM
The Sky & Tel article on the builder/owner of instrument and the scope was pretty interesting, but it was cool to see the owner describe the system in a talk spread across seven videos on YouTube.