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Topics - pafunsirep

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Well, I have almost narrowed this choice down to these 2 telescopes (the one that comes with the AVX and the OMNI XLT 150).

If you only look at the OTA, I have hard time deciding which way to go:

The AVX telescope has a smaller secondary mirror, 1.25" focuser, and interesting hex-screws in the back for collimation.
The OMNI XLT has a larger secondary mirror, 2" focuser, traditional colliation screws and XLT coatings.

Why should I pick one over the other for primarily visual - only looking at the OTA?

ATM, Optics and DIY Forum / Help from the glass Guru's
« on: December 30, 2017, 01:02:56 PM »
Many years ago (maybe 18 or so) I was surfing ebay and came across a package of lens blanks. In my astronomical youth and enthusiasm I purchased them thinking that I would be able to make a refractor - or several - from them. (I have zero experience pushing glass - Ah Youth!) Of course they hit the shelf and were promptly buried under the tons of other projects that came up. I was giving my office a good "mucking out" between the holidays and the box came to light. I am wondering if anything can be done with them. They are 5.06" in diameter and 1.1" thick polished to be clear on both sides. The blanks have some etched numbers on the surface and a grease pencil number that corresponds with the number etched in the surface. The numbers are as follows:

"KZFS4 100127/74"

The last two digits change to correspond with the blank.I am assuming that these are some kind of flint. Can these be used as an element in a doublet or triplet refractor objective?

It would be nice to know if these are useful in any way. I can always let them rest in the box for another 20 years or so but heck - a 5" f15 refractor would be pretty nice to have. Any advise??

Best Regards

Clay Kessler

Hi everyone,

I've been looking around the internet trying to find an answer to a question I have regarding GOTO equatorial mounts. I own an iOptron SmartEQ Pro with a small, light refractor typically mounted on it. This mount comes with two alignment procedures, a "one star align" and a "multi-star align". The former only uses one star to align the mount, while the latter can use many stars. I believe, in doing my research prior to making my purchase, that many GOTO mounts feature similar routines.

What I would like to know is this: how does the use of one star and multi-star alignment impact GOTO pointing (the ability to accurately slew to and point at a target in the sky) and tracking performance (the ability to keep the target centered in the eye piece)? Or, put another way, how does using more stars impact GOTO and tracking performance? Assume a "normal" amount of polar alignment error for a beginner. My instinct is that the more stars added to the mount's internal pointing model, the more accurate the GOTOs will be. I have no intuition yet on how it would impact tracking, though.

This leads to a few more follow up questions:
What is the purpose of a one star alignment if two (or more) star alignment is naturally better (assuming it is)?
Does the quality of the internal pointing model impact the tracking performance (the ability to stay centered on a target) on a GEM?
Can a high quality pointing model (with, say, six well-centered stars) compensate for less than stellar polar alignment or collimation of the scope and the mount's polar axis? Either w.r.t. GOTO accuracy or tracking performance?

Mounts Questions & Expirience / What mount for 9.25" SCT - AP
« on: December 27, 2017, 11:06:28 AM »
I want to eventually get back into imaging when I have the time but when I do I want to start out right and get a good "forever" mount. I currently have a 9.25" EdgeHD and plan on using that for imaging, both at F10 and F/6.3, and dont plan on upgrading in size unless I some how acquire a boat load of money. So for the next several years I plan on slowly saving up to buy a high quality mount. My initial thought was to buy a used AP900. Great mount that would allow me to achieve at least 20min subs at F/10 probably longer once my skills improve. But even used its pretty expensive for me at $5000 and up. Not that I'm not willing to spend that kind of money of such a great mount I'm wondering if its a bit over kill for what I need. I know it would "future proof" me but the sake of this thread lets say I will never get a scope bigger than the 9.25"EdgeHD.

So My question is: Is there another good quality mount that would allow 20min + subs for imaging with my scope and not have to struggle to do so thats not $5000? Now I know in a couple years who knows what prices are going to be and what new mounts there are going to be so lets just assume the status-quo stays the same. I'm very open to suggestions and don't mind having to do a little DIY to get a mount up to par but I dont want to have to rebuild the thing either.
Note: The mount will be on a pier in an obsy.

Beginners Forum / Please help: 102mm APO or 152mm ACHRO ?
« on: December 25, 2017, 09:48:03 AM »
Hi All,

Your experienced guidance as I get ready to make a purchase would be >greatly appreciated

Its been 40 years because I had a telescope for a teenager.  With children grown and out of the house, I am finally in a positionto get a nice telescope and rekindle my passion for astronomy.  I am very enthusiastic and have been studying the Cloudy Night forums almost daily to the last monthto help get educated.

My budget allows for somewhere in the $1300 +/- range (including mount) and from all my reading, I seem to ardently gravitate towards refractors (fairly depended on that).  I've got zero interest in astrophotography and do not need a computerized mount.  I would like to learn the art of hunting/tracking objects manually with an equatorial mount.  I am interested in all sorts of items from Sun, Moon, Planets, to DSO's.  I've got a deck to observe from with some light pollution (not terrible) and can get to really dark skies in the Rocky Mountains in roughly 45 minutes.

In terms of brands, it appears Explore Scientific and SkyWatcherget good reviews for mid-priced well made stoves.  I am also completely open to other brands and welcome all suggestions. $1300 in disposable income is a rare opportunity for me and I don't hope to purchase another scope anytime soon, if ever, so this is a major decision and I truly want to generate a great choice !

In particular, I am leaning towards a 102mm APO or a 152mm ACHRO but am unsure which direction is more smarter.  Larger aperture or better optics?  The below Cloudy Nights link compares a 6" APO and 6" ACHRO at a celebrity party and appears to imply that the ACHRO is almost (not quite) as sharp as the APO except for small CA that can mostly be corrected with filters.  I cannot afford a 6" APO however its great article comparing APO's and ACHRO's which is my principal concern.  The report states that at lower powersthey were essentially identical in performance.  Because I have no experience and have read elsewhere that CA could be fairly important in ACHRO's I am unsure which way to go.  Please visit links below to a review and a few possible scopes I am thinking about.  All suggestions and feedback is most welcome.  Thank you

Your help and advice is >greatly appreciated !!!




My son is performing his10th grade science fair project on light pollution.  On an extremely transparent (and moonless, of course) night we took five readings on each of two iPhone 4s mobiles at nine locations from downtown Washington DC to the foothills of the Blue Ridge mountains.  Readings ranged from 16 downtown to about 18.8 in the west, and variability was quite low, rarely over 0.1.  So the data looked excellent.

Now I found a map, with all DSM and SQM data gathered by numerous users, which provides radically different results from what we gathered.  This map shows readings about 1.5 units lower than ours across the area we surveyed.  Oddly, the estimated naked eye limiting magnitude that communicates those readings matches with the NELM which was reported by the DSM app on our phones (and matches exactly what we see with our eyes, too).  It's only the DSM/SQM readings which change.

Any idea what this means?  The writers of the DSM app say it should work fine with anything newer than an iPhone 4 (seemingly the older phones utilized a very different camera), and we have identical results on two cameras.  The only additional thing I can come up with is that somebody has altered the definition of the numerical reading documented by the DSM app.  That seems wildly unlikely, however.


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