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I would like to share some tips for 190MN after using it for 3 years. Who this scope is intended for: Overall this is an amazing piece of equipment which, in my opinion, targets whoever is looking for cost/benefit in big aperture without diffraction spikes in the 1000mm range. This is a heavy and expensive scope (compared to a regular newtonian), if you like or don't mind diffraction spikes just do yourself a favor and buy a regular newtonian. You can buy a bigger and faster newtonian spending less money. Now if you hate diffraction spikes this scope is an amazing option. Biggest issue: Like most equipment in this hobby there are some details that can be improved, in this case is the focuser. 1- Collimation Whatever you do: do not change Secondary height or Focuser alignment. * "Official guide": You can search for the old manual ("Orion® Premium 190mm f/5.3 Maksutov-Newtonian Astrograph") and follow the instructions. * What I do: I use a "HoTech 2" & 1.25" SCA Laser Collimator - Crosshair", that is enough. After collimating, if the secondary does not look "round" when looking at the front of the telescope then you need to fix its rotation (and collimate again) 2- Focuser Most problems of this scope are caused by the original focuser which will cause tilt in your rig. Having that said, it is possible to use it. If you are going to use the original focuser: * Your scope orientation needs to be in a way that the focuser points to the floor (so it is not affected by lateral gravity too much). * Do not extend the focuser, you need to add spacers to your camera rig and use the focuser in a way that it moves as little as possible (to avoid tilt). * Use an adapter like "HoTech 2" SCA T-Adapter" to make sure your camera is centered in the focuser. Do not use the original focuser clamp, it will cause tilt. * Using an electronic focuser as ZWO EAF helps to achieve focus without messing with the focuser too much but keep in mind that the original focuser (and the ZWO EAF) has some backslash, you will have to calculate it. If you are changing the original focuser: * The easiest way is to use a new focuser that will connect to the original focuser plate (so you don't mess with the collimation). If you need to change the plate, I suggest fully collimate the scope with a laser, change the focuser and achieve collimation by just repositioning (sliding) the focuser plate. * In my case, after 2 years of using the original focuser with ZWO EAF I replaced it with a Essato 2". I built a custom adapter to attach it to the original focuser plate (3D printed a test prototype then custom ordered an aluminum 6061 version). I had fun and success with the original focuser but changing it was a huge improvement to the telescope. 3- Dew I use a heated Dew Shield in the front (mandatory) + a dew heater strip in the back (primary). 4- Cooling I 3D printed an adapter and attached a static pressure optimized fan with a dust filter on the back of the scope. I only use it before imaging for 30 to 40 minutes and keep it off for the whole night, it is enough in my case. 5- Vignetting vs rotators Biggest sensor you can use is an APS-C and you will have some vignetting. The vignetting is not uniform so if you use a rotator you will need to take flats for all rotations you plan using during the night. hope that helps |
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Great post and thanks for sharing. I was recently hovering over the ‘buy’ button on an MN190 but the little angel on my shoulder spoke louder than the little devil on the other shoulder and I bought a 200PDS instead (don’t mind diff spikes)
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Great post, to which I can only add: I collimate my MN190 with just a cheshire and a barlowed laser collimator. I use the barlow that comes with SkyWatcher telescopes. I also replaced the stock focuser with an Omegon Steeltrail crayford focuser, just to get rid of the built in extension tube of the stock focuser. The Omegon focuser is a drop in replacement for the stock focuser that I used for several years, and of which I had wedged the extension tube to fix it in place. But I was never happy with that solution. The Omegon, in combination with a Pegasus Astro Focus Cube, works great. When combining a dew heater with a dew shield, don't use too much power for heating the corrector plate, or you will get deformed stars. This is due to heat plumes above the corrector. It took me a while to figure this out. All this may give the impression that the MN190 is a tricky scope, best to be avoided. But the truth is that it is an amazing piece of kit, with a performance comparable to APO refractors that are much, much more expensive. But unlike standard Newtonians, there isn't as much information available online regarding collimation and general care. If you run into issues, you may have to figure things out yourself, which gives a steeper learning curve. Once set up properly, the scope is a marvel to work with. cs, Wim |
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You’re not wrong, these scopes are much underrated imho for imaging.
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My primary scope is a 190MN, which I use with a 533MC Pro and the scope is truly astonishing. A few things I can add: 1) The stock focuser is absolutely useless - Change it asap. I installed a Baader steel track diamond NT, which isn't a direct replacement for the mounting plate. This resulted in me having to drill the tube to fit the new plate but it was well worth it. The Baader focuser is absolutely rock solid with very little backlash. During this process, I had to remove the corrector plate so I could remove the mess from drilling the tube. This resulted in a full re-collimation. I used an OCAL for this. The whole process was very frustrating and there was a lot to learn but I got these eventually and the scope I'm glad I did it. 2) Dew: I just use a heated dew shield - nothing for the primary. I've had a couple of problems in winter with the primary mirror filling with dew but haven't yet found a solution. @pessorrusso you mention that you use a dew band on the back. It this just wrapped around the exterior of the tube or the primary mirror itself? 3) My scope is mounted on a pier in an observatory and I use an EQ6-R Pro. Before I built my obey, I was having to carry out the setup in three stages (50kg in total) so having the scope permanently mounted is a big advantage. Although the scope is big and heavy, I honestly can't understand why more people don't use them. The focuser upgrade isn't that big of a deal and the scope holds it's collimation very well. It's a fantastic scope. I used my 190MN for most of the images here: https://app.astrobin.com/u/craigdixon1986#gallery |
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Great post as I love my MN-190 for imaging. 190 mm aperture, 1000mm FL and F5.3. What's not to like? See my set-up https://www.astrobin.com/n2ht7t/ The cost is much less than a big APO. Compared to a Newtonian it has no spikes and the corrector plate keeps the dust pollen etc. out. No field flattener needed. I have the scope wrapped in reflectix insulation to help with temperature currents during cool down. At the least the reflectix protects the telescope. It holds its collimation really well. My scope is placed on a dolly and for every session it is being bounced around when moving it from the garage to my yard. The collimation never changes and now I check it only every 6 months. The stock focuser is frustrating for imaging and I changed it for a Moonlite automatic focuser which is a drop in replacement with the correct adapter. https://focuser.com/motorfocus.php The big negative is the weight and size. It needs a strong mount and does not do well in windy conditions. I use an Iopton GEM70. A good article was posted on Cloudy nights on how to collimate a Maksutov-Newtonian. https://www.cloudynights.com/articles/cat/articles/collimating-a-maksutov-newtonian-with-a-howie-glatter-laser-collimator-r3377 Greetings Maarten |
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Craig Dixon: Yes, just use a heated dew band around the exterior. No need to overthink, during cold nights you will notice that no dew will be formed around that region. |
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I recently installed a 70mm 12v fan on the back of the scope behind the primary mirror to pull air out of the tube in the hope that this would help with dew. However, even though the fan felt super stable, as soon as I turned it on, I was getting eggy stars. I expected that if the fan were shaking the scope, I'd see bloated stars or something similar to what you get on a windy night. These stars looks were elongated as though the tracking was off but the problem stopped as soon as I turned the fan off. I've therefore concluded that installing a fan on the back of the scope is a bad idea. I'm planning on purchasing this but I'm worried about creating thermal currents inside the tube that will create the effect of bad seeing: https://www.firstlightoptics.com/lynx-astro-dew-straps/lynx-astro-80cm-dew-heater-strap-for-8-telescopes.html I already use this on the front: https://www.firstlightoptics.com/dew-prevention/lynx-astro-heated-flexible-dew-shield-for-8-telescopes.html For those of you that run a heater at the front and back, at what power do you run the heaters? |
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Craig Dixon: *I have the former attached to front of my Mak-Newt, half power all the times. No thermal effects whatsoever. I can't see any good reason to strap one on the back (besides the obvious risks of creating a thermal plume) and in several years of imaging with it in the inclement UK weather I have yet to witness even the smallest hint of dew forming on the primary, which would be unheard of in any of the closed tube scopes that I have possessed over the years. |
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I'm afraid that I'm definitely getting a bit of dew on the primary mirror
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I hope sometime in the future, I will have a roll off roof observatory and a fixed pier for this scope! Right now, sticking to < 4" refractors till I hone my skill. Plan to try the Apertura Carbonstar 6" at some point. Maybe a 8-10" carbon fiber tube RC. That's my wish list! |
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Craig Dixon: Try with a pack of dessicant silica pearls taped to the inside of the primary mirror back cover. That should remove any moisture trapped inside the tube. Apart from a filter in the corrector ring, the MN190 is a closed system, and there shouldn't be any dew inside the tube. You must have very high humidity at your observing site. Like Andrea, I also have a dew strap only near the corrector. This is attached to the heater output of a pegasus astro power box advance. I use the autodew function of this device, limiting the power to 40%. |
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