Help with recently acquired Skywatcher 190MN for imaging

[CraigD1986]

HI All.

I've just borrowed a Skywatcher 190MN from my local astronomy club and have had one night of imaging with it so far. I'm coming from imaging with a Skywatcher 72ED so this is a new challenge for me. The scope is for sale so I don't mind investing it accessories as I'll probably buy it if I get along with it. Here is my current setup:

Skywatcher 190MN, EQ6-R Pro, ASI533MC Pro, ASIAir Plus, EAF, ZWO 120MM guide scope and 120MM mini guide camera, Astronomic L3 UV/IR filter.

I'm looking to image galaxies at the moment so started with M101. Here are my observations and challenges so far and I'd really appreciate some advice:

1) Collisions: As this is such a big scope, I quickly found that I can't get much imaging time in without the scope hitting my tripod legs. Would this solve my problem:

https://www.firstlightoptics.com/sky-watcher-mount-accessories/skywatcher-eq6-extension-tube.html

I thought about setting my plan to image multiple targets based on when the scope was going to hit the mount but I can't figure out a way to work out when this will be a problem with target 2, etc. As it's a borrowed scope, I don't really want to risk damage with a collision.

2) Guiding: I'm currently using my 120mm guide scope. Is this too short for the 1000mm focal length of the 190MN? Other options are to get an off-axis guider, use my 72ED as a guide scope in a piggyback arrangement (Although I'm worried about adding even more weight as I think I'm really pushing it with the mount as it is) or I have a Celestron Travel 70 scope that is very light and about 400mm focal length.

3) Dew/Frost. I got about 12 images in last night before the signal started gradually fading. The stars were still visible but the galaxy signal faded to practically nothing. I'm guessing this is a dew problem as the front element was completely frosted over by morning. I have these for my guide scope and 72ED. Would a larger version fix the problem on the 190MN:

https://www.firstlightoptics.com/dew-prevention/lynx-astro-30cm-dew-heater-strap-for-3-telescopes.html

Thanks in advance! On first impressions, this scope looks like an absolute beast so I'm keen to get going with it.

[almcl]

I have had a SW 190 MN for 3 1/2 years now, so here's my experience.

I fitted the extension tube you linked to and it definitely helps avoid collisions with the tripod legs although not sure it completely eliminates them.   

I had been using an OAG before with my 200P, and with any large(ish) reflector, I now wouldn't guide any other way.  I am using the ASI OAG with an ASI 120 MM and never lack a large choice of guide stars.  Routinely we get ~0.6 " oscillation in PHD2's guide stats and on nights of exceptional stability, periods below 0.5" 

I found an Astrozap dew shield (there's one specifically for the 190 MN) to be absolutely essential: that huge chunk of glass at the front is a real dew magnet otherwise.  It also helps to keep stray light out.

I found the standard focusser to be too wobbly for my ASI 2600 and, on advice from FLO, fitted a Moonlight. Sadly I don't think these are available at the moment. 

One advantage I haven't seen much mentioned of the 190 MN over its similarly tubed brother the 200P, is that the baffles keep the tube much more rigid.  As a result it hardly ever needs collimating (after the first go on delivery) whereas my 200P needed doing every time it was lifted out of its box.

All in all, I think it's a great scope although it is markedly heavier than the equivalent straight Newtonian and lifting it up high on to the AZEQ6 plus extension, is a liitle bit of weight lifting challenge!

 

Edited March 15, 2023 by almcl

[CraigD1986]

Thanks for your response.

I think I defiantly need to purchase these:

https://www.firstlightoptics.com/sky-watcher-mount-accessories/skywatcher-eq6-extension-tube.html

https://www.firstlightoptics.com/lynx-astro-heated-dew-shields/lynx-astro-heated-flexible-dew-shield-for-8-telescopes.html

On my first outing, I was getting guiding at about 0.8 so I don't think that's an issue. I looked today though and there was a lot of play between my camera and focus tube so I suspect that might have been causing the minor issues I had. FLO are recommending that the 120mm guide scope is okay for now so I'm happy with that. I've read a little about the ZWO OAG and it sounds like it might cause initial frustrations so it's not a priority at the moment.

[Clarkey]

18 hours ago, CraigD1986 said:

Celestron Travel 70 scope that is very light and about 400mm focal length

I have the SW equivalent of this, and it is not a good guidescope. There is a lot of play in the focuser. I use an ST80 for guiding my RC8 and 115mm refractor which is much better. I have flipped between OAG's and guidescopes at longer focal lengths and come to the conclusion that I prefer the scope option. Firstly, even with an ASI290 I have sometimes struggled for guide stars - some areas of sky seem pretty devoid of them. Secondly, every time you have to turn the camera for better framing you need to re-calibrate PHD2.

Have you considered using a standard 9x50 finder as a guidescope using the adaptor? Gives a longer FL and guides well:

Astro Essentials Sky-Watcher 9x50 Finder to C Adapter | First Light Optics

 

[CraigD1986]

That might be a good option. The scope came with an Altair finder scope of some description. it's a little white thing, possibly this (Although not with the red):

https://www.altairastro.com/altair-10x60mm-raci-finder-scope-90-deg-erect-image-prism-variable-illuminator-eyepiece-2504-p.asp

 

[MartinB]

I have had an MN190 for many years.  It is a truly fabulous scope!  I have stuck with the original focuser since it works fine and I have had no problems with play/flex/slipping and I can achieve precise focus easily.  It sits under a dome so dew has never been an issue.  The extension tube sounds like it should do the job but I can't say for certain because my mount is on a pier.  I use an OAG  but the mini guide scope should be ok, the guide star uses the point spread function of the star to achieve focus so it should still be very accurate.  

I have found that I do need to collimate from time to time despite the fact that it is never moved off it's mount.

[CraigD1986]

Thanks for your input Martin, that's really helpful.