Posts Made By: joseph cannavo

Curious to hear comments on minimal focuser draw tube length for visual use: 1.5", 2.0", 2.5". My object here is in optimizing for visual use only (small secondary) and avoiding drawtube entering light path.
Clearly, the potential use of barlows, binoviewers bear on this. That having ben said break it down... with/without binviewers etc.
Joe

Curious to hear comments. What would most consider to be the minimal focuser draw tube length for visual use(1.5", 2.0" or 2.5") that would accomodate most eyepieces. Curious to hear answeres covering both 1)with and 2)without inclusion of barlow/binoviewer My object here is in optimizing a design built around a small secondary, and avoiding having the drawtube entering light path with shorter FL eyepieces. Thoughts?
Joe

Has any one seen the this add
http://www.astromart.com/classifieds/details.asp?classified_id=413963
Wow!
PS I'm not advertising for TEC, I just had to ask if I'm the only one blown away by that price. A Televue 127 - for ex - is significantly more.
Joe

I know this is the wrong forum for this, but people simply have to see this. Possibly - IMHO - the finest amateur planetary image obtained yet.
Enjoy!
http://www.astromart.com/forums/viewpost.asp?forum_post_id=427203&poll_id=&news_id=&page=
Joe

I have a speculative question for this group based on some of what I have gleaned in peering over your collective shoulders. First, it seems that most of the cutting edge images here are being done with scopes in the 10-18" range. Second, these images often appear to be diffraction limited.
Would it be safe to say then that if the imaging techniques of the best amoung you were utilized with scopes in the 20" and up range that the resolution achieved would be proportional to the increase in aperture. (Of course this assumes 1st rate optics) Or, is it the case that some other limitation would impose a diminishing return.
It just seems to me that you-all are effectively "parting the atmospheric sea" and peering through the diffraction limit of the optical system. Its exciting to think what could be achieved with say a 30" Kennedy (the zambuto of larger optics)mirror. Thoughts?
Joe
Check this mirror out
http://www.webstertelescopes.com/cellular_mirror.htm

As I slowly piece together the dob structure for my 16" Royce conical, I have been playing around with spider designs, which has raised for me an interesting question.
It has been reported that wire spiders seem to yield less diffraction/scattering than conventional straight veined spiders of equal thicknes. It has been furthermore argued that this is largely due to the veins cooling to sub-atmospheric temp, and thus introducing an optically active boundry layer of cooler air.
But another thought occurs to me. Is it also possible that conventional veins - painted flat black - nonetheless reflect a significant amount of light at very low angles of incidence, therby increasing light scatter. (Recall that reflectance rapidly increases as angle of incidence decreases)
To check this out I took one of my protostar spiders and viewed a light source, holding the spider in proper position in fron of my eye. Despite the flat back finish, at this low angle of incidence, a surprisingly bright line of reflected light emerged along the vein.
I am wondering then: 1)Is the absence of such reflection in a wire spider (With far less surface area to refect such incident light) part of their advantage?
2) Are there better ways of blackeneing spider veins, without significantly increasing their thickness.
With regard to this last question, I have tried roughening the surface of a vein with sandpaper and then repainting. No good, with light source at low angles of incidence - as occurs in lunar, planetary mode - no improvement.
Thoughts?
Joe

Its been a while, and I'm always curious to hear the answeres. What would be part of a top ten list of deep sky showpieces - excluding globular clusters - for a mod to large dob under dark skies.
Joe

As epilog to the thread on micro-roughness:
A link to a website showing how optical smoothness is quantified - above and beyond surface rms - for truly large glass.
http://www.noao.edu/wiyn/wiynfacts.html
Joe
PS: Talks about aperture fever...

Since I'm not yet imaging, I cant possibly say that I would like to try to do this .. oh well... but:
It seems that here are now enough high resolution lunar shots (Wes and others) to creat a high resolution sunrise/sunset time lapse over lunar terrain. Has anyone tried this yet?
Joe

I am driving cross country last two weeks in july and will be bringing my completed - hopefully! - Dob (16" Royce conical). I am planning to visit the Grand Canyon and hope to take advantage of its spectacular skies. Since the Grand Canyon Star Party is over, I am wondering if anyone knows about the avaiability of observing sites.
Joe