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Topics - Adam Washington

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ATM, Optics and DIY Forum / Outer zones too high?
« on: January 03, 2018, 08:42:06 AM »
I'm having a senior moment....figuring/testing my 12" mirror, I'm thinking my outer zones are too high, IE they need to be worked down?

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Reflectors Telescopes Forum / New coma corrector, now illumination problems
« on: December 30, 2017, 06:53:48 PM »
Unfortunately, I always have a hard time trying to explain myself in a few words so be prepared for a lenghty description of a problem with my Newtonian telescope (if it is a problem).

I have a german made 12 inch ONTC F4 Reflector with a 100mm secondary mirror and a 3 inch JMI focuser and I used to have an ASA Wynne 0.95x 3 inch coma corrector. When I first used the telescope with my ATIK 11000I immediately noticed a huge amount of vignetting. I contacted the seller of the telescope and he said it's a common problem with fast newts and the 0.95x Wynne that can be solved by a newly developed "TS N-AGK corrector". Important detail: instead of 0.95x, this corrector is a 1.14x.

They were kind enough to let me swap the ASA corrector for this new TS corrector with no additional costs, I only had to pay for the M68 > M64 adapter + extensions that goes between the Atik + Filterwheel and the new TS Corrector, so I was very happy. It was after all a few years ago that I bought this scope but haven't used it much because of problems with my mount that are now finally solved.

The ONTC12 comes with a couple of drilled holes which you can use to change the position of the primary mirror, very handy. The seller suggested I kept the mirror in the same position as before, he said: in the last hole closest to the end of the tube. I used to have the primary mirror in the hole closest to the focuser, I suppose he also means that position.
I've put the new system to the test one clear evening and immediately noticed I have to rack the focuser all the way out and then pull the camera + corrector almost all the way out too to reach focus. The corrector + M68 adapter pieces are very long so I now have a camera sticking out of the telescope tube a very long way. It looks a bit weird and I'm afraid it will also put some stress on the focuser. But maybe this is the way it should be. On a positive side there was much less vignetting but I noticed last week that my fully illuminated circle is no longer exactly centered in the field of view. If I now take a picture of my light panel, the brightest part of the circle is hanging somewhat "down" on the picture. When I made this picture, I had played around with the focuser before so I believe I was out of focus, and I'm not sure how to find the focus position again in daylight but should the illuminated circle always be in the middle regardless of your focus? That's actually my prime question. If so, somethings wrong with my scope because the FIC only moves up when I pull out the camera to reach focus.

I further tested some things, I put the primary mirror all the way back (away from the focuser) and if I take (out of focus, I'm sure) pictures of the light panel, the illumination still "hangs in the bottom" of the field of view. I tweaked collimation with a chesire, I've checked as good as I could the rotation of the secondary mirror, I've checked if the secondary is centered under the focuser, but whenever I collimate the best I can, the light stays hanging down in the bottom. Turning the camera in a different angle doesn't change this. In fact, the only thing that brings the illuminated circle "upwards" toward the center of the FOV is when I rack the focuser out completely and pull the camera + corrector all the way back in the focuser.
Does this mean I have to change something to my telescope to make things better? Or should I just put the primary mirror back in the hole closest to the focuser, wait for a clear night to focus on a star again and see if the illuminated circle is close enough to the center when I'm in focus and leave the camera and corrector sticking out a long way and be happy with it?

Is there anything I can do to get the camera + corrector closer in the focuser to reach focus and at the same time get the fully illuminated circle in the center FOV? I suppose I could drill new holes so the primary can be moved more upwards towards the focuser but that would also mean I would have to get a bit bigger secondary (110mm?) or will moving the mirror up only mess things up more? I've tried so many things now, I just can't think clearly anymore

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Eyepieces Questions & Recommendations / 12mm (or thereabouts) for XT6
« on: December 30, 2017, 02:26:28 AM »
Hello all,

After 14 months of observing, now mostly on an XT6, I have started upgrading my eyepieces and want some advice.

I've got the stock Plossls but don't use them, preferring a one-model-ago Meade 8-24 zoom for its convenience and as a tool for learning about exit pupil and other factors involved in observing. I also have a 7mm X-Cel LX but find the images much dimmer with that one (I don't do much planetary observing).  I find for the open clusters and star fields that are my main diet, something around 12-13mm often seems right.

I recently got an ES 68º 24mm which I really like--way improved FOV, contrast, and color, as well as adequate eye relief (I wear my glasses while observing and will probably continue doing so). SO, to the question: What eyepiece might give a similar experience in the 12-13mm range?

I've used Don's eyepiece guide (thank you SO much!), and read about the various model lines and options between 60º and 70º (didn't consider 82º and up--not sure of the added value in a 1.25"), but in the various threads I find it difficult to disentangle focal length/eye relief/FOV/EOFB as interacting factors. I'd rather not go as expensive as a Nagler T4 but am certainly on the lookout for a used one.

Maybe I just need to use the 24mm I have and swap a 2x Barlow in and out, but thought I'd ask about standalone options.

Thanks--

Ric

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ATM, Optics and DIY Forum / Thin 18" Mirror Blank
« on: December 29, 2017, 11:44:55 PM »
Recently got an 18" glass mirror blank, 3/4" thick. It came with a bunch of other astro stuff, was in a Coulter box and "Crown" was hand written on the box. Seems doubtful this is a Coulter product, probably just a handy box at the time. Newspaper that is was packed with is dated 1978.Perhaps the 'crown' refers to the glass type? Little to nearly no green cast to it. Surface on both sides is pebble like, appears to have been cast in, if it hadn't had been with the other astro stuff and had been a bit thinner I would have guessed it was a top for a small porch table.

Seems rather thin to be an 18"+ mirror, is this common? And is the pebble finish common to mirror blanks?

Thanks

Tom DuncanAttached Thumbnails




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Reflectors Telescopes Forum / Dobsonian primary mirror cleaning
« on: December 29, 2017, 01:31:54 PM »
While collimating my Z12 dob yesterday, I noticed what appeared to be a build up ofdust/dirt/grime/organics on my primary mirrorcaught in the stray light of my laser and red LED headlamp. Thereis not like a ton of stuff on it but enough to notice it in the light. At what point would you remove and clean the primary?

I know there are basically 2 schools of thought on this. One being DONT EVER CLEAN IT, and the other being that its required every couple years or so especially with dobs being that their optics are exposed to the elements.

I found this video on youtube, https://www.youtube....h?v=8rZP7mTEutE ,and these guys seem to know what they're doing and the results looked good but just figured I'd run this by the forum and get some opinions and experience that's superior to my own.

Thanks again...

Alan

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Mounts Questions & Expirience / 10 Micron mount playing up!
« on: December 27, 2017, 02:32:35 PM »
Calling all 10Micron owners. Has anyone experienced the following issue and is there a way to stop it happening?

Tonight I turned on the mount and slewed to Arcturus to focus the scope. I noticed that Arcturus started off centered in the FOV but drifted at a constant rate in RA to the East. I checked that the mount was in Sidereal mode - it was. Then I noticed the hand controller was permanently displaying "<- A" on the bottom line (the newer multiline hand pad).

Reading the manual this symbol combination says that the autoguider port is slewing the mount - which in my case is odd as I don't have an autoguider camera connected! The port socket is empty.

Further more I checked the hand pad to see what the guider rate was - x0.5 sidereal. Indeed I could cancel the drift by setting a suitable counter slew rate and commanding the mount via the hand pad to slew in the reverse direction (West). Then the hand pad showed a constant RA position.What am I dealing with here? Anyone experience this issue before? The mount is just over a 1 year old and has performed flawlessly until tonight. Is this a firmware glitch that can be reset? Or is this likely a hardware fault with the autoguider port? I guess I might have to log this via the 10Micron support channel - I give it a few days to see if anyone has any suggestions first.

Thanks, Tony.

PS - this is a dup of the post I did on the 10Microm forum - but that place is normally glacial regarding responses - so also trying my luck here too

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ATM, Optics and DIY Forum / An easy to build 8 inch tracking ball scope
« on: December 27, 2017, 10:16:19 AM »
Back in the mid-90's I was looking for a simple, novel way of driving a ball scope. The purpose was to eventually incorporate this drive to a 20 inch ball scope I had started making, which I would eventually finish, twenty years later. You can see construction details of the 20 inch on my website (see my signature) and in thisCN thread.

I presented the first world prototype ever made of a ball scope driven by this novel roller drive, a 6 inch f/3.7 Newtonian, at the 1995 Stellafane convention. Not only could it track the stars, just like a Poncet platform, but it could also have the potential of doing astrophotography since it would also incorporate a dual axis. Unlike the Poncet and other tracking platforms, it is ajustable for any latitude from about 10 to 60 deg (northern or southern hemisphere), and it doesn't need to be reset every hour or so, like all those other platforms have to. In addition to introducing it at the 1995 Stellafane meeting, the 6 inch was also briefly described in a January 1996 issue of Sky and Telescope magazine article entitled "The ten top telescope ideas of the year".

Here is what the fibreglass ball mounted 6 inch telescope looks like:
The ball scope tracking mount didn't catch on and, as far as I know, no other ATMs built one after I described it. About 10 years later it was "rediscovered" by, now, S&T Telescope Making Telescope Workshop editor Jerry Oltion who described his ball scopes in a few articles between 2005 and today.

Many comments I got after describing my 20 inch ball scope, including after publication of the article in this year's March issue of S&T, told me that this is a very nice concept but so complex to build, particularly the hemisphere, that it scared people away.

So, in the fall of last year I decided to pool all the knowledge I had acquired over the past two decades making tracking ball scopes and design an instrument that would be so simple to make, practically anyone could do it with very simple hand tools, in only one or two weekends and for a cost of about $300, excluding optics.

The resulting telescope is an 8 inch f/5 newtonian mounted in a 12 inch diameter aluminium hemisphere.
The telescope OTA weighs exactly 17 pounds (including eyepiece and finder). And, of course, being a ball scope, the OTA does not need anything else to operate. A shallow hole in the ground makes a great base! However, in my version, it rests upon a plywood base which holds the tracking platform, which weighs about 5 pounds. The OTA comes apart in less than a minute and will eventually store in a one cubic foot box that will cover the entire telescope for storage. The soon-to-be-built box will also double as an adjustable tripod base that levels the tracking platform and brings the eyepiece to a confortable height. More on this later as I finish making it.

The equatorial platform incorporates a single, 5v geared stepper motor which beautifully drives the scope in a very consistent way, half-stepping every 0.88 seconds (both the 6 and 20 inch use two synchronous motors). I have not included the dual axis function in this telescope because I doubt it would be used for astrophotography, but that feature can easily be added later if wanted.

In the coming weeks I will describe how you can make this telescope using commercial off-the-shelf (COTS) parts and where to get those parts. My version is entirely machined but all the machined parts can be made with alternate materials, including wood. The OTA can be made first and used on the ground, sitting the hemisphere on nothing more than a small plastic cover you can find in your kitchen shelves. However, I highly recommend you build the drive platform which can be made for about $30 and which will provide continuous tracking for your telescope, from almost anywhere you live or travel in the world.

And, of course, this being a ball scope, the eyepiece position is always in the most confortable position and, unlike a dobsonian, there is no gimble lock ("Dobson's hole") when observing near the zenith. I'm looking forward to sharing with you some of the new innovations I had to come up with to make this scope work, especially the very clever, and simple, primary mirror collimation system which is at the heart of the success of this project.

So please stay tuned as I write up the details and provide photos and sketches. As I did with the 20 inch, I will then incorporate the material I write here to my website so that it can easily be found at a later date, once this thread as migrated deep down in the archives of CN and becomes harder to locate.

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Hello all,

I am hoping that I would have the ability to receive some guidance in my next telescope purchase.  I currently have a 80mm goscope which is great when your revealing some planetary bodies for your 4.5 year-old.  I am looking at getting another telescope though because the goscope is quite restricted.

*** Sorry it published if I didn't want it too***

First things first what's my budget.  I am looking at an 'all-in' cost of 1000$.  Decent optics, mount and eye pieces.

Second, I do not own a lot of time to allow a telescope 'cool' to ambient temperature with a household of 3 below 6.

Third, smaller and more mobile is an asset.

Fourth, time line for purchase is 3-6 months.

Thus, from my limited expertise and exploring, I believe a refractor or cassegrain will be most suitable.  I'd like to see at least 10 messier objects and a few fantastic views of the planets.  I am not anticipating a 'superb' scope but something that will last.  Something that is used or available is preferred!

The problem is light pollution....  It is really bad where I live... I can not make out Ursa Minor...

Thoughts, questions?

Thanks for your attention.

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