Primary mirror plate - can you buy these ?

[Rigel-7]

On my Explorer 150p there is no plate behind the primary. Seems that it leaves it a bit exposed. Can you buy a plate or cap it? I have also read if you add a small fan to draw air through the tube the image can be improved - is this worth doing ?

[Bizibilder]

They used to put a plate on scopes but no longer do (as far as I'm aware). You are probably better off without one as it will allow air to move around the main mirror and will help significantly with cooling the mirror when you take the scope outside. Overall probably more advantageous to not have the plate.

You can put a fan on the end of your scope to force air over the mirror but it is debatable as to whether it really does give an advantage.

[John]

I doubt you can buy them but I guess you could make one with thin plywood and attach a fan to it for cooling / air circulation though it's not really necessary with a 6" scope in my opinion. Folks who do have the plate behind the primary often remove it and leave it off to speed up scope cooling so thats not really essential either. The dobsonian versions of the scopes don't come with one.

Edit: Bizbilder got there 1st !.

[assasincz]

It might be sensible to use one for when you store away your scope for a longer period of time to prevent dust from getting into it, but other than that, it seems counterproductive to me and I agree with the above stated.

[Rigel-7]

I have to say I was sceptical about the fan. I would like to cap then end of the scope to protect it against little hands... Alternative is buying a road trunk for storage.

[umadog]

The fan makes a vast amount of difference. People have plotted cooling curves with and without a fan. The fan more or less halves the cooling time. Some DIY guys are boarding up the back of the scope and placing a fan in the rear cover. The fan blows air and the logic is that the cover ensures all the air coming into the scope makes it around the sides of the mirror. Adding a baffle in front of the mirror allows this arrangement to scrub the boundary layer:

Telescope Reviews: Real life experiment with fan configurations...

Then again, there are also reports of scopes working superbly well with the mirror actually hanging out of the back of the tube. There is more than one way to solve the same problem.

I wouldn't worry about covering the back for safety, though. The back of the mirror is quite tough: it's the front you're worried about.