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Messages - postbypopect

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Beginners Forum / Re: Xt10i or xt10g
« on: February 09, 2018, 09:20:57 AM »
IMO there are huge benefits visually at to have both tracking and 'goto'.  Far from 'gee-whiz' type gadgetry it accomplishes it's goals handily. It's not just good for Dob's. Most all my SCt's post late 90's had it and it isn't new, just new to consumer price Dob's.  I greatly prefer it to a Newt on a GEM mount (as for eye placement unless you have rotating rings)  When I do outreach or share the scope with folks, it's great to have the object a good magnification and know that when someone else looks it's still in the best part of the eyepiece.  Sharing with several folks each take their time.  High mag viewing planets at one end or objects like M27 or M81/82 this goes at least double.  It's possible to see a lot and see it well, you can relax and enjoy the view.  I think for beginners it's a fantastic learning tool that rewards it's investment immediately.

Thank you for the confirmation!!

Beginners Forum / Re: Xt10i or xt10g
« on: February 09, 2018, 07:52:14 AM »
Don't underestimate "stiffer" want as smooth a slew as possible when manually using a scope. You want just enough friction to hold the scope in place when you let it go....stiff doesn't really cut it for higher mag viewing....

Beginners Forum / Re: Best 8 inch dobsonian
« on: February 04, 2018, 01:28:10 PM »
Have a look at the Orion XT8 PLUS and the Zhumell 8" Dob.

ATM, Optics and DIY Forum / Re: Cutting Fiberglass Tubes ?
« on: February 04, 2018, 11:27:59 AM »
Yeah, that's kind of after the fact, like when I have to work with ceiling tile.

Great discussion! Let me just add one of my favorite sayings..."the proof is in the pudding." At this point, we've built nearly 50 of our solid tube telescopes in 8", 10" and 11" apertures using mirrors of various thicknesses and substrates (Plate, Pyrex/Supremax and Quartz) and we've tested each one in the field. Only one has come back to us with an astigmatism issue and like Pinbout mentioned above it was because the silicone attachment points were too large. To clarify further, that did not happen with an Aurora Precision cell. It happened with a cell that we designed and built in-house which only had 3 non-flotation contact points. The AP cells have 6 flotation points. We made an immediate adjustment in our design when the astigmatism presented itself. How about since then? Nothing but stunning images at the eyepiece free of astigmatism since moving to the AP cells (from our own testing and field reports from our clients), including that 14" x 0.70" Plate Glass mirror'ed scope. And that's using silicone attachment and no edge support. Were we to see issues with astigmatism we would investigate an edge support system but there simply is no discernible astigmatism at the eyepiece. So why complicate and increase cost when there would be no benefit? We like to K.I.S.S. 

As for silicone adhesion between mirror and cell...that's a discussion that's already been had in a previous thread last year or the year before, and if using RTV Silicone adhesive there are no issues with adhesion on glass and metal due to the characteristics of all three materials.


Beginners Forum / Re: Thinking about a 2" Barlow - your opinion
« on: February 03, 2018, 02:13:51 AM »
Oh, yeah, I completely agree, Ed.

But on the other hand, I don't think we should be recommending really cheap and/or junky scopes or equipment. Especially the type of cheapo refractor that that kid in your story probably had. The story you relate is sort of a one in a hundred for something like that. The other 99 times, a cheap scope like that actually does drive someone out of the hobby, and ends up for sale at one of a thousand garage sales across the country for 20 or 30 bucks each summer, or otherwise just sitting in a corner collecting dust.

Those cheap refractors, under, say, $150, are really badly mounted, and the vibrations make them almost impossible to use easily.  I'm not talking about the optics; the optics are usually pretty decent. But there's just no reason to buy something rickety like that for $150 or $100, when for about $200 or so, you can buy something that is actually good and usable. Not as if that would have made a difference in the story you related, where it was the grandparents who did they buying, not someone asking a question on this forum.

I think we should all continue to - gently - recommend against these cheapo scopes when asked, regardless of the nice story you related. But that doesn't mean that the recommendation for someone looking to spend $150 on a scope should immediately almost triple that and end up with the standard recommendation of an 8-inch dob that costs $400 and more when you factor in the additional eyepieces and such. We're all pretty clever here; and we can try harder to work within the budget limits people set to recommend something that is still reasonably good, still workable, within, or only slightly exceeding their budget.

And by the way, people generally put their actual names in their signatures, just like you've done, so you can call me Jon. 

I think you completely missed my point.

I never suggested that we recommend junk scopes, only that what is junk to one person is a treasure to another. I have read threads telling people they have junk, that they will be so unhappy and will never succeed. Yet the person is quite happy and is enjoying. OK, not I would have suggested you get but if you are enjoying it fine. How can I help you enjoy it more.

The fact that my $10 barlow seems OK to me is a fact. Sorry if that bothers anyone but I think it works fine. Not as good as the $150 TV or the $80 Celestron but it works fine for me, for now. Fact. You can't dispute it.

So, that was the point of the post.

Would I recommend that everyone get one? No, not unless you really want something and don't have the budget for a $100 barlow. Will a $10 throw away tide you over for a while. Maybe.

General Astronomy & Observing / Re: Eclipse traffic horror stories?
« on: February 03, 2018, 01:52:16 AM »
Here's my experience of my trip down to western Kentucky from near Milwaukee WI. I left on my trip at 6:30 A.M. Saturday. I was hoping to beat the rush and had my camping reservation confirmed. The trip down was (mostly) uneventful. I wanted to avoid Chicago traffic so I took I-43 down to Beloit, then I-90/I-39 down through Rockford. A little out of the way but well worth it in my opinion. I-39 south to I-74, cut over to I-57 at Champaign IL and then south all the way to I-24 south of Marion, IL. All pretty well straight forwardexcept stupid IL decided to close I-57 down to one lane just south of Champaign. You know I-57? The route everyone from the Chicago area is going to use to get to the Carbondale area!!! Nobody was there working, just one lane closed! I was delayed a good half hour there at 9:00 A.M. on Saturday but I can only imagine the bottleneck that occurred 24 hours ormore later! I also was very disappointed in the decision of IL to CLOSE 80% of the wayside rest stops. STUPID IL!!! Anyway, from there to my destination east of Paducah it was pretty uneventful and all told took about 9 hours with one stop for gas and food. The trip back was a little faster at about 8 hours. I stayed at the campground until Tuesday around 11:00 A.M. and re-traced my route exactly. Only real traffic problems were caused by the incessant truck after truck after truck etc. Trucks passing other trucks and taking 10 minutes to do so, and so on... However, this is a constant on the interstates and had nothing to do with the eclipse. A little over 500 miles one way. I don't like driving that far any more.

ATM, Optics and DIY Forum / Re: Optics questions about chromatic aberration
« on: February 02, 2018, 11:21:46 PM »
What they used to do before Newton or fancy glass came along was to line up a whole bunch of lenses that had mild magnification to achieve usable power.
It's even funnier than I thought: the etch of Hevelius' telescope is from 1673. The first functional Newtonian is from 1668. Alpollo is using an antedating argument to prove his flawed argumentation. The reason why Hevelius used this telescope was probably because he either didn't know about Newton's Opticks, or simply because a long focal length singlet makes the differences in the angle of incidence smaller and therefore the OPD for different wavelngths smaller therefore the secondary spectrum smaller.

Alpollo: didn't you know that it is the corn that makes the wind? The corn is engaging the milling stones therefore rotating the sails therefore making the air move, creating wind. Here in the NLs we still profit from that.

Beginners Forum / Re: Which telescope to choose?
« on: February 02, 2018, 10:09:24 PM »
So it sounds like, if I were to go with this smaller motorized option, I should go with the 127SLT. It also sounds like I could control this from my laptop and take pictures from there with some sort of camera attached to the eyepiece.

Let me know if I am tracking properly so far.

If your interest is "serious astrophotography" (lets say, anything other than a smartphone camera), you need to know that:

* For larger exposures (better pictures of dim objects), you need a motorized equatorial mount. This rules out alt az mount and dobsonians.
* A good camera (or sensor) costs as much or more as the telescope tube.
* A good sensor for planets is not good for DSOs, and viceversa.
* For astrophotography, the best telescopes are called "Astrographs", they are "fast" (short focal length), have corrector lenses, and more sturdy focusers to hold heavy cameras. Their mounts are equatorial, and motorized.
* You cannot get an astrophotography starting gear with less than $1500
* It takes a lot of time to learn the details on camera settings and image processing. Months to years. This on top of learning telescope use, and the sky.
* The best advice I've read here (from a 20yr astrophotography veteran) is: "just don't"

For casual pictures with a smartphone, most telescopes will do, even a dobsonian.

So, if your interest is serious astrophotography, you need to think about it carefully.

If your interest is observation, with a side of casual moon/Jupiter pictures with a smartphone, then you need to figure out your portability requirements, and then get the scope with the largest aperture that still meets those portability requirements, is within your budget, and features the navigation you want (push to, go to, or manual).

My dream scope for urban watching with occasional road trips is the SkyWatcher Collapsible dobsonian. The 8" model goes for $449

Reflectors Telescopes Forum / Re: Dobsonian "striction" issue
« on: February 02, 2018, 08:18:45 PM »
I dealt for years with my dob AZ motions. I have Teflon pads and a Formica rocker box. I tried everything: if I had nice movements lifting the center with CDs, I would get vibration in the base, but in order to end up with a vibration free base the AZ motions were awful. Soaps never worked for me.

Two years ago, Mr. Dobson gave me the solution: phonograph records. In combination with Teflon pads are great. I think the very low static friction of this combo makes the trick. It´s always helpful to add a soft material ring in the center to lift and decompress the base. I can hand track at 400x with no problem.

Watch at minute 48:30Attached Thumbnails

Beginners Forum / Re: Is there a scope that I can REALLY see the planets?
« on: January 31, 2018, 01:46:08 PM »
Learn how to star test your SCT. As purchased they aren’t always in perfect collimation. Proper collimation is important for them to show fine details on planets, etc.

Beginners Forum / Re: Barlow for Dummies?
« on: January 31, 2018, 05:05:21 AM »
I have added eyepieces in the $60 to $150 range as I have built out and gained experience.  The added eyepieces have all been added to gain wider field of view, lower or higher power.  I don't imagine I will likely go past $150 for an eyepiece. $100 or less is more to my liking. Sure they will not match teh $500 eyepieces but will likely give me 75 to 80% of the performance at 1/4 to 1/10 the price. That is good enough for me for a hobby.

Probably more like 90-95%. Not long ago an acquaintance and I compared my 12mm Astro-Tech Paradigm DualED ($60) with his Type 6 13mm Nagler (he paid $365, but they are currently on sale) in both his telescope (120 mm refractor) and my C-8 EdgeHD. The AFOV with the Nagler was clearly greater in both telescopes, but the resolution, focus, edge clarity, and color were so similar that it was difficult to tell them apart. Of 5 people that viewed several DS objects and the moon through both EPs and scopes, none remarked that the Nagler was significantly superior, with the exception of AFOV. I had the feeling the Nagler owner was somewhat disappointed, but he did mention that he intended to take "a very close look" at the Paradigms.

I suspect I'll catch some flak over this. It's not my intent to start a controversy, rather only report what five of us noted. Seeing was above average that evening, and we all concluded that the Nagler owner's refractor was the superior telescope despite demonstrating lower magnification with the same focal length EPs. But the EPs were very, very close in performance, AFOV notwithstanding. I'm beginning to conclude that AFOV is primarily what more money is buying in EPs.

Evaluating eyepieces is not an easy proposition. Eyepieces like the Dual Paradigms represent very good values, you get a lot of bang for your buck.

When you buy expensive eyepieces like the Naglers, what you are buying is not only the wide field of view but a wide field of view that is free from off-axis astigmatism, even at very fast focal ratios, F/4, even faster. In an F/10 scope, there will be very little if any apparent differences. Even an F/7.5 scope, the differences will relatively small. At F/5, stars towards the edge of the field are sharp, despite the wider field of view. Better coatings, better stray light control, these are things that you pay for.

In a fast high quality refractor like the 4 inch F/5.4 Televue, a difference one would see would be that a close double star in the center of the field would be essentially the same in both eyepieces but as it drifted towards the edge of the field, it will slowly start to be come less well resolved, until at the edge, it will probably be unrecognizable as a double star. With a Nagler, it will still be well resolved as it passes the field stop.

I am not an advocate of spending large sums on eyepieces. There is a lot to know, a lot to learn, years and years. Learning to see the faint objects, the subtle details also involves learning to see the smaller defects and aberrations in eyepieces. There may come a time when you take a look at M22 through that 13mm Type 6 Nagler in a 16 inch F/4.5 fitted with a coma corrector and the view, it's absolute perfection, the stars across the field are all tight and round as there is no difference between the edge stars and the center stars. Back in goes the Paradigm, it's a nice view but just not the same.

One of my favorite quotes:

"It is not usually made clear, that these elements, objective and eyepiece, are by no means comparable in importance. The astronomer's hopes are almost wholly tied to the size and quality of the objectve. The objective of even the smallest telescope, because of its larger dimensions, the severe optical requirements it must meet, and the difficulty of its construction, completely overshadows the eyepiece."

- "How to Make a Telescope," by Jean Texereau, Page 1, Paragraph 2."

Myself, I slowly built a set of eyepieces, it probably took 10 years. At the time, there were no Explore Scientific eyepiece, there were no Ethos's, Delos's, Delites etc. For someone like myself with a 12.5 inch F/4.06, the eyepieces that performed were the Naglers and Panoptics. These days I have a pretty good eye for aberrations, sometimes I am not sure if that is blessing or a curse. It means my eyes can distinguish a tiny planetary nebula at the edge of the field from a star but it also means I see aberrations that are relatively insignificant.

From my point of view, when one is just starting out, this is the time to just enjoy the views, the magic, the magesty of the great universe above, it's there to be seen in most any decent eyepiece.


In the two plus years I have been in the hobby, viewing opportunities from the first year to the second have changed dramatically for the worse here in Texas. El Nino has delivered more clouds and rain than I would ever have expected and my work schedule has delivered fewer days off than I desire. Frustrated? You betcha... but one thing I learned over the years... this too shall pass... better days (nights) are coming... and I will be out there looking again... and I predict that because of this current drought, it will be like when I first started, a new adventure all over again... I can't wait...

No, I ain't selling...


Reflectors Telescopes Forum / Re: Eliminating the spider?
« on: January 30, 2018, 12:56:09 AM »
How would you adjust the secondary for collimation ?
When the secondary is on a spider the adjustment is reasonably straight forward, whereas if on a glass plate it seems somewhat more difficult.

Exactly like a Schmidt-Cassegrain: the window is perforated in the center, there is an internal plate holding the secondary, a plate attached to the window and adjustment screws between the two plates with the screw heads sticking outside in the center of the window.

Sorry guys, I have to lock this thread. We have very strict rules on the discussion of modification (or even fixing) of solar telescopes. Per the TOS ..

CN will not allow posts dealing with the modification of commercial equipment intended for solar astronomy (or images taken with such equipment) or the modification of other potentially harmful devices (e.g. laser pointers). While the results of modifications may seem attractive, the possible adverse consequences are deemed significant. Any posts dealing with these types of modifications, or linking to sites which feature them, may be removed by the moderator.

I know the thread has been up a while so I'll leave it here until the mods have had a chance to discuss it.

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