bhuloka
super member
Reged: 03/06/12
Loc: Maryland, USA
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Re: Let's talk about the Hubble Optics UL16
[Re: Gastrol]
#5350824 - 08/03/12 08:36 PM
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Yes, I checked all of that pretty thoroughly. I'll give it a few more days of testing before I conclude that it's defective. Only if I'm absolutely certain i I haven't missed anything, that it won't work, then I'll ask Tong to send me a new one right away.
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WhoGoesThere
member
Reged: 07/26/12
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Re: Let's talk about the Hubble Optics UL16
[Re: Gastrol]
#5352184 - 08/04/12 07:36 PM
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Hmmm I wonder if this scope would like the Explore Scientific 9mm 120° 2" eyepiece? 203x with a .6 FOV! The entire moon at 200x!
Edited by WhoGoesThere (08/04/12 07:37 PM)
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bhuloka
super member
Reged: 03/06/12
Loc: Maryland, USA
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Re: Let's talk about the Hubble Optics UL16
[Re: WhoGoesThere]
#5352615 - 08/05/12 03:55 AM
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Finally had a clear night! Tested a few views: Split epsilon Lyrae at 61x (barely, but I think that's pretty good for such low power, as seeing was only average). It was more clear at 100x. Star test (Polaris at 38 degrees) showed collimation just a tiny bit off after a few hours. However, the barlowed laser did seem to move a bit too much when going from low to high altitude. M13 resolved cleanly and pretty deeply. M57 also good. Wandered through star fields of Milky way in Cygnus. Sharp pinpoint stars in center half of view (30mm ES 82 degree eyepiece), but noticeable coma in outer half of view. A paracorr is in the future for this scope...
Movements are now much better, as I replaced the too-small 5/8" rubber stoppers, with slightly larger 3/4" stoppers. This slowed the lazy Susan azimuth bearing down, so the scope now stays where I point it. Tracking and moving around the zenith was easy.
Wind is the enemy of this scope, as a slight breeze sets the spider vibrating. The spider is the weak point of this scope, stability-wise and collimation-wise, I think. I didn't use the shroud tonight. That would have caught the wind and required still a bit more friction on the azimuth bearing to keep the scope from blowing around. The focuser is still a mess. I had to push and pull the drawtube while turning the knob. I may upgrade to a Moonlight focuser. Balance of the scope is quite good, using 2 or 3 Bogen super clamps as counterweights. Finally, this scope is beginning to settle in and perform well. It has been frustrating getting the movements to a useable status, and especially having the focuser fail, but tonight everything other than the focuser seemed to work, at least. The next step is to set this scope up next to my Edge 8" and do some comparisons. I believe the Edge will win in some respects.
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WhoGoesThere
member
Reged: 07/26/12
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Re: Let's talk about the Hubble Optics UL16
[Re: bhuloka]
#5363450 - 08/11/12 02:51 PM
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Thanks for the insight. I look forward to getting mine.
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TechPan6415
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Reged: 07/29/12
Loc: Aspen, Co
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Re: Let's talk about the Hubble Optics UL16
[Re: WhoGoesThere]
#5392964 - 08/29/12 10:18 AM
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I got my 16" Hubble Optics mirror yesterday, I suspect the structure is not far behind. The F ratio is actually 4.43 since it is 70.94" focal length, test numbers on the certificate are Strehl 0.987, 1/13.4 PV. 1/56.4 RMS.
It looks good but the center spot is off by 1/8th. I will be using a laser collimator to align it, how will this affect it and can I just mark the actual center on the white ring which is where it is? I am hoping to not have to move it because in searching for over an hour, it seems the only way to do that is to use acetone which might spread the adhesive on a brand new and very clean mirror.
bhuloka, any updates?
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WhoGoesThere
member
Reged: 07/26/12
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Re: Let's talk about the Hubble Optics UL16
[Re: TechPan6415]
#5393131 - 08/29/12 12:47 PM
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I'm sure someone on here has a good idea on how to help. As I told you in a PM I had a change of heart and canceled my order and decided to go in a different direction but I did not do that because of the scope itself. I'm sure it would have been fantastic!
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Mirzam
Post Laureate
Reged: 04/01/08
Loc: Lovettsville, VA
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Re: Let's talk about the Hubble Optics UL16
[Re: TechPan6415]
#5393250 - 08/29/12 01:37 PM
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Did you use a template to find the center spot error? I use the Catseye template and would definitely be concerned about 1/8" positional error. My spot placement accuracy with the template is about 1/32" or a bit less.
I see no reason why you cannot simply mark the proper spot position with a small catseye triangle right on top of the old spot. This avoids the possibility of an acetone smear mess, which I've already experienced myself.
JimC
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Mike B
Starstruck
Reged: 04/06/05
Loc: shake, rattle, & roll, CA
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Re: Let's talk about the Hubble Optics UL16
[Re: Mirzam]
#5393427 - 08/29/12 03:12 PM
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Quote:
I see no reason why you cannot simply mark the proper spot position with a small catseye triangle right on top of the old spot. This avoids the possibility of an acetone smear mess, which I've already experienced myself.
True, but you have a 2-1/2" (or so?) circle to play within that will never see the light of stars... only the laser.
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sixela
Postmaster
Reged: 12/23/04
Loc: Boechout, Belgium
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Re: Let's talk about the Hubble Optics UL16
[Re: Mike B]
#5393452 - 08/29/12 03:23 PM
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You don't want glue residue in that circle if you ever plan to use an autocollimator...
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TechPan6415
member
Reged: 07/29/12
Loc: Aspen, Co
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Re: Let's talk about the Hubble Optics UL16
[Re: sixela]
#5393510 - 08/29/12 03:53 PM
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I simply measured it from the outside edge of the mirror. I have and will be using a 2" & 1.25" Hotech crosshair type of collimator.
I can't see how the laser hitting the white of the center sticker is going to allow me to actually collimate...
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bhuloka
super member
Reged: 03/06/12
Loc: Maryland, USA
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Re: Let's talk about the Hubble Optics UL16
[Re: TechPan6415]
#5394585 - 08/30/12 09:41 AM
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I have not checked the accuracy of the center spot placement on my UL16. But I will now. However, when viewing, it does seem that the sweet spot for sharpness is centered in the eyepiece fairly well. Collimation is with Glatter laser and TuBlug.
Since my last post, I've only had the scope out once, a good night at Sky Meadows state park, VA (Yellow zone). I set up the 16 and my Edge 8" side-by-side. The 8" gave a much cleaner image on star splits (Epsilon Lyrae). Seeing was not good, and I believe the 16" was more affected by the poor seeing than the 8". The 8" also yielded a blacker sky, and thus better contrast. But of course, overall brightness was much better in the 16". M13 was much more resolved. The Lagoon nebula was brilliant. But I am still waiting for a night of good seeing and transparency to really check out the optics. If what I've seen so far is the sharpest the UL16 can get, then I am not satisfied at all.
A friend with a nice Webster 18" has told me he notices the same limitations in mediocre seeing; stars puff up into fuzzy balls, but when he applies an aperture mask to the scope, reducing it to 8", they snap into tight little airy discs. Only in good seeing will the 16" appear sharper.
I don't expect to have any good chance around here at least until mid-September, 2-3 weeks from now. (One giant, 4-month-long cloud has been hovering over the East coast.)
So the Jury is still out on the optics.
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bhuloka
super member
Reged: 03/06/12
Loc: Maryland, USA
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Re: Let's talk about the Hubble Optics UL16
[Re: bhuloka]
#5394621 - 08/30/12 10:11 AM
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Mechanically, I'm still working on it. Balance is great.
Stability, once I've got an object in view, is good now.
The scope settles OK after movement, and stays put.
But movements are pretty jerky in several spots, and so high-magnification tracking does not seem doable, for 2 reasons: 1.)Azimuth motion has a sticky spot (lazy susan bearing seems to not be perfectly round, and presses harder against the rubber bumper at the tight spot in its rotation); 2.) There is a bump in the altitude motion when the folding bearing joint slides over its support. It is very difficult to get this joint aligned smoothly during setup. Some machining may be necessary for both of these problems.
I found the problem with my focuser. I took it apart, and examined the 4 steel rollers upon which the drawtube moves.
One of these does not move freely. It is a manufacturing defect, wherein the bearing wheel does not clear its mount, so it seizes up when the bearing assembly is held in place by its mounting screws. Loosening one of these screws allows the tube to move, though extremely roughly. So I've got it at least barely working for now. I will ask Tong to send me a new bearing assembly, and we'll see if that fixes the problem.
I also want to loosen the large nut on the main focus knob bearing (3 steel ball bearings), but it requires some kind of weird spanner to fit into 2 grooves on the nut. Not a normal hex-shaped nut. Has anyone seen this kind of thing before? Where do I get such a spanner?
Still haven't had time for pics of the whole business....
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Mirzam
Post Laureate
Reged: 04/01/08
Loc: Lovettsville, VA
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Re: Let's talk about the Hubble Optics UL16
[Re: bhuloka]
#5394638 - 08/30/12 10:20 AM Attachment (32 downloads)
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You mentioned poor contrast--did you add a light shield opposite the focuser? An annular baffle at the front end of the focuser also helps a great deal.
JimC
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bhuloka
super member
Reged: 03/06/12
Loc: Maryland, USA
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Re: Let's talk about the Hubble Optics UL16
[Re: Mirzam]
#5394694 - 08/30/12 10:46 AM
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Oh, Contrast is fine in the UL16. Very fine, in fact. Yes I did put a light shield opposite the focuser, though I haven't put a baffle ring on the end of the focuser drawtube. (Is that what you mean? How does that help?)
I simply was referring to the fact that the smaller 8" scope is not as bright, so the yellow-zone sky appears more nearly black, while the 16" brightens the background sky glow, along with brightening the target object. So on some subjects, the 8" view may appear more contrasty. But overall detail is still greater in the 16", of course.
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sixela
Postmaster
Reged: 12/23/04
Loc: Boechout, Belgium
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Re: Let's talk about the Hubble Optics UL16
[Re: bhuloka]
#5394707 - 08/30/12 10:51 AM
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If you use the same magnification, yes. But if you use the same exit pupil, the sky will appear just as dark, but objects will be a lot larger.
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bhuloka
super member
Reged: 03/06/12
Loc: Maryland, USA
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Re: Let's talk about the Hubble Optics UL16
[Re: bhuloka]
#5394708 - 08/30/12 10:51 AM
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My issues with the scope currently are mostly about movement smoothness, or lack thereof. (And I've got a bad focuser, but that is probably not an issue for most people, as my focuser problem may be just an odd case.)
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bhuloka
super member
Reged: 03/06/12
Loc: Maryland, USA
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Re: Let's talk about the Hubble Optics UL16
[Re: bhuloka]
#5394712 - 08/30/12 10:54 AM
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Good point about magnification vs exit pupil, sixela.
Yes, I was using matching magnification in my test, so exit pupil sizes were quite different. That affected the sky darkness.
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Mirzam
Post Laureate
Reged: 04/01/08
Loc: Lovettsville, VA
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Re: Let's talk about the Hubble Optics UL16
[Re: bhuloka]
#5394728 - 08/30/12 11:02 AM
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Because the lower end of the focuser is so exposed, stray light can enter from a wide range of angles. The baffle restricts the entry angle to include just the secondary mirror and a bit of space around it. Right now I'm using a 1.25" adapter (flocked) held in place with a set screw that was added to the bottom end of the drawtube. I'll eventually machine a better solution but this works quite well.
JimC
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bhuloka
super member
Reged: 03/06/12
Loc: Maryland, USA
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Re: Let's talk about the Hubble Optics UL16
[Re: Mirzam]
#5394747 - 08/30/12 11:14 AM
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But doesn't this extension of the drawtube get into the light path, partly obstructing the mirror?
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sixela
Postmaster
Reged: 12/23/04
Loc: Boechout, Belgium
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Re: Let's talk about the Hubble Optics UL16
[Re: bhuloka]
#5395149 - 08/30/12 03:47 PM
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Not if you can see the entire secondary from all the points of interest on the focal plane, no. You usually draw an envelope going from the circle of interest on the focal plane (usually the field stop of your widest field eyepiece) to the edge of the secondary, and the focuser baffle may not intrude there. But anything out of there is fair game. The closer it is to the secondary, the wider it becomes and the more effective it is to reduce the size of the light shield behind the secondary.
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