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Home > Forums > ASTRONOMY EQUIPMENT > Reflectors > Message #832570

Re: 36-INCH TELESCOPE

Posted by Thomas Dey on 2/6/2017 5:55 AM in response to Re: 36-INCH TELESCOPE   (357 hits)
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~had to delete and re-post this because the "replace image" feature doesn't function~ Looks OK now. Tom

I found my ancient picture of the interferometry fringes that I did on the 6.25 folding flat! I configured it at the (proper!) 90-deg fold in an otherwise perfect cavity comprising a 6-inch Zygo Mark IV Fizeau and (superb) AC flat. Thus configured, one is justified in ignoring the power and scrutinizing what remains... in this case, 0.3 wave peak-valley pureish astig, scaled to green, single-pass, as it will be in use. Now that astig will impress many as marginal... but NOT! -->> What you see here is doubly-sensitized because it is double pass, so think twice as good. Mentally "filter out" the quadratic power that you see in the fringes, because one focuses that out in-use. Most all vendors show Ronchi, which is typ 10x further desensitized (i.e. 10% sheared wavefront, NOT direct wavefront) A perfect 36-inch scope theoretically would resolve ~0.1 arc-sec; not needed because atmosphere will NEVER allow that. So, for those reasons alone, this folding flat "diagonal" will not noticeably degrade performance from perfection = keep, use, enjoy! General comment: When building instruments, it is important to know what to allow and what to not, so one's $ and energy can address what matters. Tom


29-inch Dob in a dome
36-inch upgrade soon
LUNT 80/80 solar scope
FLI 6803 cam
APM 100mm APO Binos
JMI RB-16 Night Vision Binos
Zeiss 20x60 IS binos

Photo Attached (285KB) - Click to view

Thread:

Subject Posted By Date/Time Hits 
36-INCH TELESCOPE Thomas Dey 2/2/2017 4:43 AM 473
Re: 36-INCH TELESCOPE Thomas Dey 2/2/2017 4:44 AM 330
Re: 36-INCH TELESCOPE Thomas Dey 2/2/2017 4:45 AM 313
Re: 36-INCH TELESCOPE Thomas Dey 2/2/2017 4:46 AM 343
Re: 36-INCH TELESCOPE Greg Shaffer 2/2/2017 5:38 AM 322
Re: 36-INCH TELESCOPE Thomas Dey 2/2/2017 6:30 AM 251
Re: 36-INCH TELESCOPE Rod Kaufman 2/2/2017 6:09 PM 253
Re: 36-INCH TELESCOPE Thomas Dey 2/2/2017 9:11 PM 287
Re: 36-INCH TELESCOPE Walter Hamler 2/3/2017 9:30 AM 239
Re: 36-INCH TELESCOPE Thomas Dey 2/3/2017 10:31 AM 325
Re: 36-INCH TELESCOPE Thomas Dey 2/3/2017 10:32 AM 266
Re: 36-INCH TELESCOPE Thomas Dey 2/3/2017 10:32 AM 288
Re: 36-INCH TELESCOPE Rod Kaufman 2/4/2017 9:06 AM 266
Re: 36-INCH TELESCOPE Thomas Dey 2/4/2017 4:53 PM 291
Re: 36-INCH TELESCOPE Thomas Dey 2/6/2017 5:55 AM 357
Re: 36-INCH TELESCOPE Greg Kim 8/20/2017 11:01 PM 164
Re: 36-INCH TELESCOPE Thomas Dey 8/22/2017 11:12 PM 135
Re: 36-INCH TELESCOPE Greg Kim 8/25/2017 170
Re: 36-INCH TELESCOPE Thomas Dey 12/1/2017 5:14 PM 83
Re: 36-INCH TELESCOPE Thomas Dey 12/1/2017 5:15 PM 73
Re: 36-INCH TELESCOPE Thomas Dey 12/1/2017 5:18 PM 68
Re: 36-INCH TELESCOPE Thomas Dey 12/1/2017 5:19 PM 89

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