Sky-Watcher Skyliner 200P Dob

[dweller25]

Hello,

I have just ordered one of these from FLO - thanks Steve.

I want to mount a fan on the back of the tube for two reasons :-

1. To initially cool the mirror down to ambient temperature.

2. Once cooled to move any tube currents/residual boundary layers.

Has anyone done this ???? - if so it would be great to hear how you did it and how effective it was.

Also could someone with a 200P please supply a photo of the back of the scope with the mirror blanking plate off.

Thanks.

D25

[adamsp123]

I read a big article that clearly showed that the fan is by far the most effective if placed at the side of the tube blowing or drawing air across the mirror. The boundary layer is the one that really wrecks the seeing so "removing" this is most beneficial.

Pizza

[dweller25]

Hello Pizza,

Yes, that makes total sense to me.

This thread is interesting ....

Telescope Reviews: Refractor vs. Reflector ?

Around halfway down page 3 it says side fans are great for cooling down but are then turned off just leaving the rear fans on to remove the tube currents.

Probably both side and rear fans are the best bet - certainly for really big reflectors but I don't want to drill holes in the tube so may have to compromise with just a rear fan.

[John]

I used to own that scope. My Skyliner 200P (also supplied by FLO) was not fitted with a mirror blanking plate - I think it's only the F/5 EQ mounted 8" Skywatcher newtonians that have them (I've owned a couple of those as well). The mirror cell is completely open with the back of the mirror revealed on the Skyliner 200P which helps mirror cooling of course.

To fit a fan at the back of the mirror you will probably need to fashion something to fix the fan onto such as a sort of "spider" arrangement. TBH I never had any problems with mirror cool down or excessive tube currents - 30-60 minutes was enough from taking the scope from my house to my garden.

Great scopes by the way - the focal ratio (F/6) makes collimation easier and minimises the secondary obstruction size so resolution and contrast are excellent.

John

[dweller25]

Hello John, thanks for the response.

My thought was to support a fan using strong elastic hair bands stolen from my wife !!!

Just need to figure out how to anchor the bands to the scope.

Still think the side fans are a good idea too but I don't want to put holes in the tube.

My/our problem is that by the time the scope has cooled it's cloudy !!! so I want to decrease cooling time to the max.

Regards.

[John]

Hello John, thanks for the response.

My/our problem is that by the time the scope has cooled it's cloudy !!! so I want to decrease cooling time to the max.

I know the problem

I was concerned about the same issue but in the end I found that the 8" was useable quite quickly without a fan. Even my current 12" is not too bad in this respect - it has a cooling fan but I don't use it despite keeping the scope in the house. What I do find is that the dob gets used on the nights which look relatively cloudless and my 4" refractor comes out on the more "iffy" nights.

John

[PhillyDee]

I have a Skywatcher 200P which I bought 2nd hand from here and it did indeed come with a rear blanking plate. The lad I bought it from also attatched a fan, which I upgraded for a PC case fan. I find it works a treat and helps the initial cool down time. Basically just a round bit of steel plate painted matte black on one side, hammered black finish on the other and mounts on the rear via 3 small screws. I suppose you could easily make one out of aluminium, just remember to paint it for protection.

[dweller25]

Hello PhillyDee,

Thanks for that.

Any chance of a picture please ???

And do you observe with the fan running ???

[PhillyDee]

Should of mentioned mines the blue reflector . . . . My excuse is im tired as ive just come off nightshift. I have no idea if they are the same. I can still take some pics.

[dweller25]

Hello PhillyDee,

I would really like to see some pictures - thanks.