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To follow up on the thread of evaluating when a mirror should be recited, I would like to hear how others store their telescopes during storage to protect the mirror and its coatings. I keep my 15” sores in my garage where the temperature ranges between 55 - 80 degrees F (if kept in an unseated shed, it is recommended to have a low Watt light in the mirror box - something that is not possible to do when away observing). In addition to keeping the mirror box cover on, I lay a piece of muslen ( 100% cotton ) on the mirror. I know of one individual who lays a chamois on the mirror to protect it and absorb Amy moisture. Once a year I will clean the mirror as recommended by Dave K. I have had my scope for about 8 years and the mirror spear to be good condition. -- Mike B

Hello! I made a 3d model for a bracket to attach Nexus DSC Pro to the truss of my 18" UC. I thought some of you may find it useful. https://www.thingiverse.com/thing:4979182 Cheers Nikhil

We are looking in to purchasing everything for our Obsession 18 Classic from Astro Devices including the Nexus DSC Pro. The Encoders offered are the 10k or 40k step encoders, with only a Approx. 12% price difference. Instant thought was buy the 40K, for better resolution. Second thought is using the 40K encoders during calibration make the chance of a successful calibration more difficult and less likely. If the Nexus DSC Pro uses a percentages error to determine a successful calibration this is a moot point. If the Nexus DSC Pro use a fixed number of points to determine a successful calibration, then going for the 10K would make our lives easier, and still give satisfactory pointing. Or is using the 40K encoders just an unnecessary upgrade?

Our club was recently donated an Obsession 18" classic. We are trying to decided which Digital Setting Circles system to acquire. Does anybody have the pro’s and con's of each system? Are we missing a third contender? Bob

I bought my Obsession 18” UC several years ago after the owner had contracted a serious medical condition while he was waiting to receive the scope from Obsession. He sold me the scope and had never even been able to look through it. It was essentially brand new. I previously owned briefly another brand of “compact” Dobsonian with a 20” mirror. The optics were excellent on the 20” but the packaging (mount) was worse than a dime store refractor’s tripod. That is another very long story, but suffice it to say I returned the 20” and about a week later acquired the 18” UC. At this point in my Dobsonian stable I have the new to me 20” Obsession Classic, an 18” Obsession UC, an Orion 12” truss tube goto (which I believe, and many others have conceded to as well, that it has the best 12” mirror they have ever looked through), a 10” Orion Intelliscope, and a fun little 6” Dob. I have observed with many different dobs at many star parties, one of my observing buddies includes a very accomplished ATM fellow who has recently won the highest ATM award for Newtonian (Dob style) reflectors at Stellafane – something he has accomplished more than once. I have learned from some very seasoned and experienced observers, and I have looked through some amazing scopes and some not so amazing scopes. And I will stand by my statement that my Obsession 18” UC Ostahowski mirror is not even very good, I dare say that my 10” Intelliscope has a better view. The dismal performance of the UC’s optics coupled with its inability of the UC design to remain collimated through a heavy night of observing and/or public outreach led me down the path to a Classic Obsession. I tried to buy a NEW one from Dave, but they have abandoned the 20” Classic design in favor of the UC design. v/r Chuck Jagow Member – Dark Skies of The Wet Mountain Valley Member - Back Bay Amateur Astronomers Member – San Diego Astronomy Association Member – Colorado Springs Astronomy Association Future Verde Mont Observatory Gone... Rott'n Paws Observatory From: <[email protected]> on behalf of Jeff Martin <jeff@...> Reply-To: <[email protected]> Date: Tuesday, July 20, 2021 at 7:30 AM To: <[email protected]> Subject: Re: [ObsessionUsers] HELP! 20" Obsession Classic F5 The only way your Ostahowski mirror is exponentially worse is if you have it mounted upside down. The diagonal is flat, so there isn’t a multiplying/fudging factor. As you move a secondary closer to a primary the light cone it intercepts gets bigger. That’s why you have “planet killer” Newtonians: with really slow focal ratios you can mount a small secondary and get better contrast. ?” won’t move you to another secondary size. If it were me, I’d cut ?” off, try the eyepieces and paracorr. Then I’d make another round cutting, if necessary. Only because I’ve overcut more than once. -jeff From: [email protected] [mailto:[email protected]] On Behalf Of charles jagow Sent: Tuesday, July 20, 2021 6:20 AM To: [email protected] Subject: Re: [ObsessionUsers] HELP! 20" Obsession Classic F5 Thank you for your help. The previous owner contacted me after I had put the scope to bed last night. He had the same problem, but he said he moved the mirror up via the collimation bolts such that his eyepieces (ETHOS) would come to focus. I moved the mirror up with the collimation bolts to the point I could only see three threads of travel left on each. I then re-collimated first with the Howie Glatter and then dialed it in with a visual Cat's Eye tool set. This allowed my Nagler 17mm to pass through focus, allowing me to focus that eyepiece. The seeing and transparency was horrible last night, but the view of Jupiter was very well defined with the Nagler 17. Stars are well formed, a little comet shaped much closer to the edge. The mirror combination is exponentially better than the Ostahowski mirror in my UC 18. I was able to bring a few of the other eyepieces to focus, mostly those above 17mm. The range of 7-12mm were not able to pass through focus inward, some were close but no banana. NONE of the eye

I just acquired a 2007 classic Obsession 20" F5. The scope looks to be in excellent shape. I assembled the scope being careful to place the strut poles in the blocks according to the previous owners labels on the blocks and poles. Attached the Upper Cage Assembly and collimated the mirrors with my HG laser and then also eyeballed it with the cats eye tools. I just rolled the scope out to look at the moon. I am unable to bring ANY of my eyepieces to focus on the moon. 17mm Nagler, 35mm Orion Deep View, 42mm Deep view, 40 mm Meade Plossl, and many others, tried everything in my case. The focuser is racked all the way in, not enough inward travel. I double checked to ensure the poles are fully seated in the blocks on the mirror box, and that the Upper Cage Assembly is properly seated on the poles and secured. I have an Obsession 18 UC, but this is my first experience with an Obsession Classic. What am I doing wrong?? I have had many DOBs but this is my first really big classic style. v/r Chuck J.

All, So I pulled out my jig saw and crudely cut out my Bahtinov mask for my UC18 from from 1/8" plywood left over from a furniture project (since I still don't have compelling reasons to purchase a CNC machine yet). It is shaped like an 18" doughnut with 3 notches on the center hole so it just fits on the UC18 OTA around the top of the secondary mirror. It works great, but I don't fully understand the physics of why it works. It makes a pair of opposing crows feet looking diffraction spikes on a bright star. The center diffraction spike moves with the focuser and when centered you get perfect focus (on a bright star). It just takes a second or two to focus and then just lift the mask off the scope and your good to go to your DSO. I have several filters and each one requires re-focus a bit when I change. This was a fun project that I recommend for anyone wanting a simple DIY project or is like me and needs help to get best focus. Richard

I've had 4 scopes with AN/SC (3 Obsessions) and never had this happen before. GoTos are spot on, but then the image drifts up in the EP fairly rapidly, almost as if it is not tracking on that axis. But the AN reads how much off it is and GoTo puts the image right back in the FoV. Not a big problem when just sight seeing, but I like to sketch and having to keep adjusting the aim to center the image while drawing is a pain. Plus it will be a problem once the pandemic panic is over and I can start outreach star parties again. Any suggestions on what is wrong - and how to correct it will be much appreciated.

Anyone using Baader Morpheus EP's with a big-fast DOB? Been thinking about going to very wide Afov's with my Obsession 15" Classic. I do have the 31 & 22 Nags and love them, but I have a collection of 60 degree Radians that I'm using for higher power and would like to upgrade. I need/want long eye relief, so the higher power 1.25" ES's 82s and Nag's don't look like good options. Donald

Hi all, i am new to the group and want to make mosaics and wondered in anyone in the group has automated their astrophoto work flow with their ServoCat? Richard UC18 DS287m

So I've got multiple telescopes (don't we all?) including an 18" classic. LOVE my Obsession. However, I've also got a couple of nice Mallincam video cameras, and I know that there isn't enough inward range on the focuser to bring them to focus. The focal distance is the same as most other astro cameras (and DSLR cameras). I'm thinking about getting another set of poles cut to length so I can swap them out when I want to use the camears - after all, 18" at F4.5 would be very nice, as opposed to 8" at F10. So, here's the question for anybody who has done this before - how long do the poles need to be? I have read posts in the past (not necessarily here, but possibly) about trimming the existing poles down to work with a camera, but my memory suggests that it was a multiple step process to get the length correct. But if there's someone who HAS poles of the proper length, you could save me a good bit of time and pain! Thanks! Mark

Thought I would post this here in addition to the ServoCAT forum. Unfortunately, there are ObsessionUsers archives to search through on this topic. I have been working on trying to get PHD2 talking to my SC Gen3 mount running with Argo Navis on an Obsession 18" Dob (alt-az). I wanted to try some short-exposure astrophotography with a DSLR, and wanted to have more precise guiding. I am not asking "is this a good idea?", I know this is not an ideal way of doing astrophotography, and I am aware of the problems of doing astrophotography with an alt-az scope. I want to try it anyway. My inspiration is someone using a Panther alt-az mount which can be controlled with PHD2 via a Meade LX200 ASCOM driver. Dave K's website shows pictures from Obsession owners doing deep sky imaging with SC without derotators or a platform: Johannes Brachtendorf from Germany and Todd Kozikowski from New Boston, but other details of their imaging procedure are not listed. I have installed ASCOM on my PC and the ServoCAT ASCOM driver. I can use this to control the scope via Stellarium (through "device hub") and Cartes du Ciel (through the servoCAT driver), it's quite neat. When I try to connect PHD2 to the SC unit, I get the error "Mount does not support the required pulse guide interface", then the connection fails. I can connect my camera and a Telescope simulator mount. I tried both the ServoCAT driver and Device Hub (where I set up ServoCAT when connecting to Stellarium), both return this error. I tried setting my COM Port which was connected to the SC unit to 9600 baud but that did not seem to make a difference. I reviewed the driver information here and did not find much help. I assume others have had success connecting, what am I doing wrong? I tried attaching a ST4 cable to the ST4 cable interface on the SC unit, but when I try to use the motion control on PHD2 the SC unit does not seem to respond - with I am in MODE ENCODER in the Argo Navis the encoder positions do not change when I press the directional keys in PHD2. Using the ST4 cable with my ZWO ASI camera and Firecapture, autoguiding on the planet works great, so I know the ST4 port and cable work. I would not mind using a ST4 cable for autoguiding, although it seems most users prefer ASCOM control, as it provides the program with information about to where the telescope is pointing. Anyone out there with PHD2-to-SC communication success that they can share? Thanks Greg

For those of you with SC/AN on your Obsession scopes, I have been working on how to control the scope with Stellarium or Cartes du Ciel planetarium programs (both free) running on a PC using either a wired USB connection to the SC Gen3 unit, or Skysafari6 planetarium program (paid app) running on a tablet or smart phone by wireless connection to the SC unit via the SkyFi3 wifi device. This setup is not completely intuitive, so I thought I would share step-by-step instructions. The PDF documents are in the "Files" section of this group. Use the instructions on "Faux alignment of telescope" in my SC/AN guide ("OBSESSION REFERENCE GUIDE 1.0 2020 07 02 Groups.pdf") to set up and test this indoors when the sky is cloudy and not waste observing time. It is really a lot of fun if you have not done this before, and would make it more accessible for visitors at star parties as people can see on the planetarium exactly where your scope is pointing. Let me know if you find any errors or have questions. Greg

A past member's family just donated a 18" classic to our club. I have some experience on truss tube dobs, but some things on this scope gives me pause. 1. The primary mirror just loosely sits in box, has side to side movement, about 1/4 inch. 2. There are 3 fingers, rubber sleeved, on the front of the primary mirror, one is firmly contacting mirror, the other two just spin around in front of the mirror. We were able to get the scope close to collimated, views were great! But with these problems, i know that it is just a temporary collimation. Is there a manual, that shows the correct procedures for correcting this problems. Any help is greatly appreciated. Bob