Focuser Upgrade for the MN190 - Forums

Topic starter

Jul 24, 2023 · Edited: Aug 29, 2023

For the last year I have been looking for an upgrade to the sub par standard focuser that comes with the MN190.
The only options I could find were the Feather touch and MoonLite which were out of my price range.
By chance I came across the Skyoptikst Optical Technology CO., LTD unit on Bay. $310 US
https://www.ebay.com/itm/144959646948
This is a really well made focuser, very smooth operation and no movement side to side, the original focuser had a fair amount of play and large gaps between the inner and outer tubes.

I ordered the 60mm stroke version with 56mm thread, Options for a 2 inch adaptor and 48mm thread adaptor for astrophotography are optional extras.
Centre of image is the adaptor that attaches the focuser to the existing Skywatcher mounting plate, this comes standard with the purchase.

ZWO focuser attaches easily using standard brackets.

Removal of the old focuser is very easy with the loosening of the 4 grub screws, 2 on each side of the mounting plate.

New focuser installed, zero backlash and a huge upgrade over the original unit.

Addition of the 56mm to 48mm rotator adaptor in place of the 2 inch eyepiece unit.

Right hand of image shows the 56mm to 48mm thread adaptor, on the left is the rotator with 48mm thread.

I hope someone else finds this information helpful.
CS
Greg

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Wim van Berlo

Oct 27, 2023

Thanks for the info. I upgraded to an Omegon 2" Steeltrail Crayford focuser. It too fits in the stock base plate. It seems that any 78 mm diameter focuser does. The only issue I had was that the focuser's knobs go a little below the focuser's body. I had to make a 1 mm ring out of gasket material. It sits between the base plate and the focuser.

Wim

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DeltaSolo

Nov 16, 2023

Hi Greg,

Very helpful and I've found it just in time for my new MN190.
Could you please confirm that you ordered 60mm stroke version?
It looks like you have the focuser+56_to48_adapter+48_rotator+filter wheel.
So, measuring from the SW baseplate - what is an approx distance to the camera sensor?
I am getting smth around 130mm on mine (with the original focuser, just got the scope, and it's cloudy as it should be

, so testing on a target at ~300m).
Is this close to what you see?

Alex

gregengland

Topic starter

Nov 16, 2023

Hi Alex, welcome to the 190MN club.
I am getting around 132mm from Skywatcher base plate to the 2600mc sensor.
And yes I ordered the 60mm stroke version.

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gregengland

Topic starter

Nov 16, 2023

Hi Alex, the Omegon 2" Steeltrail Crayford focuser is another option.
CS
Greg.

DeltaSolo

Nov 16, 2023

Hi Greg, how do you find the M48 CAA? Is it stable - like tilt / shift?
How easy is your collimation done?
I see you have the scope wrapped with smth like Reflectix. Is it for temperature stability?

I am currently imaging with refractors and usually don't have any temp related issues, although the dew is a major one. I expect MN190 to be a major dew-loving device. I am going to put dew strips on both sides - the mirror and the corrector.

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Wim van Berlo

Nov 16, 2023

Hi Greg, how do you find the M48 CAA? Is it stable - like tilt / shift?
How easy is your collimation done?
I see you have the scope wrapped with smth like Reflectix. Is it for temperature stability?

I am currently imaging with refractors and usually don't have any temp related issues, although the dew is a major one. I expect MN190 to be a major dew-loving device. I am going to put dew strips on both sides - the mirror and the corrector.

The mirror doesn't need a dew heater, I've never used one on mine. The corrector needs a dew heater and dew shield. The scope is closed with a large volume and a lot of mass. It needs a fair amount of time to reach ambient temperature. You can install a computer fan to cool the tube faster.
If you need to collimate the MN190, never ever adjust the middle screw of the secondary. The secondary distance down the tube is factory set. Only use the three tilt screws for secondary adjustment.

cs,

Wim

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gregengland

Topic starter

Nov 17, 2023 · Edited: Nov 17, 2023

Hi Alex, I find both the M48 CAA and 2 inch adaptor both to be very stable, have not noticed any tilt using either.
Having the 3 screws on the 2 inch adaptor as opposed to the one screw on the original focuser gives a sturdy hold.
I find collimation easy and quick once initially done.
Mine was way out when purchased and the flats showed a dark gradient to one side.
Even with this shadow the stars were round and when out of focus showed even donuts.
My secondary mirror needed to go pack a few mm.
Some users state you should never touch this or other settings but I have had the whole thing apart down to an empty tube.
It did cause me some pain getting collimation back again and took a few tries using the O-Cal collimator and Laser collimator.
Now it is just a matter of a quick tweak with the Laser collimator before each use.
If it is not too bad on yours I would leave the secondary set as is.

This is what my flats look like now, way better the when I first got the scope. (2600mc sensor)

The main mirror is held in a very flimsy annulus with push pull screws and only 2 O-rings for compression (not springs) on each of the pull screws.
You need to be very careful when tightening the pull screw as it will push against the main mirror and push it up towards the retaining clips, this will cause triangular stars.
There is no stop in the mirror holder to prevent this and the mirror only sits up 1-2mm on thin cork type material above the annulus.
I replaced my collimation screws for the secondary and main with Bobs Knobs.
If doing this be careful as the O-rings can move when you take the pull screw out.
The secondary mirror has the three collimation screws and 2 others.
The centre one adjusts the forward/ back distance (undo this too far and as Wim said the secondary will fall off.
And the other screw stops the secondary from rotating.
I wrapped the telescope in foil bubble wrap to try and stabilise the thermal properties, no idea if this helped but I like to think it did

For dew I have a dew shield with dew heater band built in (8 inch Astrozap model)
I have had the main mirror fog after an all night session in very frosty conditions (this was before the bubble wrap)
If it is going to be really cold I do put a dew heater band around the main mirror (outside end of tube)
Hope this helps.
CS
Greg

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Wim van Berlo

Nov 17, 2023

"And the other screw stops the secondary from rotating."

Unfortunately, the entire secondary assembly can still rotate in the corrector. I've had this happen.
As I wrote before, I've never had problems with dew or frost on the primary mirror. My scope is permanently installed in an observatory near the East coast of Sweden, just North of Stockholm. Temperatures can occasionally reach -20C, but most of the time stay between -15C and +10C for most of the imaging season (end of August till beginning of May). Humidity earlier this autumn reached 97%, though.

DeltaSolo

Nov 17, 2023

Hi Wim and Greg,

Thanks for your comments, really helpful!
I am going to order this focuser and right now texting with the seller. He is saying that 60mm version will protrude down inside the tube.
I doubt it - you, Greg, have it and it works for you.
It's obvious that when fully compacted the focuser tube will be inside the scope, my guess is ~ 20mm. But we use it extended usually.

My optical chain is (from the front of the camera)

filter drawer -21mm
48CAA - ~10mm
M56 to M48 ring - ~1mm
focuser tube extended - ?? mm
focuser body - 40 mm
adapter to SW base plate - ~10mm
SW base plate - ~ 8mm

total ~ 90mm + ?? tube extended

In my case (measured today focusing on the tree at ~350m, no stars - 100% clouds) with native focuser the distance from the tube to camera front is ~120mm.
This gives ~ 30mm for the focuser tube.

The question is - with the focuser extended to ~20-30mm mark will it be still protruded inside the scope tube?

Alex

Wim van Berlo

Nov 17, 2023

The focuser tube may protrude inside the tube, but the tube isn't the aperture stop of the scope, the meniscus is. Inside the tube you also have the baffles. This means that you'll have some margin in your calculations.

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Glenn Orzepowski

Jan 13, 2024 · Edited: Jan 13, 2024

Hi. I have a MN190 and I’m thinking about upgrading to the Skyoptikst 60mm to M56 thread focuser (plus M56 or M48 adapter) to use with my 2600MC. But I have a question… what adapter do you use with the Skyoptikst focuser if you want to shoot with a 1.25” planetary camera or use a 1.25” eyepiece with this focuser?

Thanks!

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