Cooling fan for large Dob

[DRT]

I have recently acquired a 16" dob and have read various threads discussing the need/desire to have a cooling fan fitted to the primary mirror.

I understand why I should probably buy one but I have no idea what to buy and from where.

Can someone please point me in the right direction?

[brantuk]

Use this link Derek to determine your requirements:

http://www.fpi-protostar.com/bgreer/fanselect.htm

I got an almost silent Noctua fan for my dob from here:

http://www.quietpc.com/casefans

Also - I believe Dion on astronomy shed still supplies them ready to fit for a variety of Newtonians.

Hth

[swamp thing]

I don't observe planetzzz zzz zzz! with my Dob so have never bothered fitting one. 

Oh BTW they attract dew to your primary too. Watched a buddies 14" (previously clear) dew in seconds after switching his fan on......

[DRT]

I don't observe planetzzz zzz zzz! with my Dob so have never bothered fitting one. 

Oh BTW they attract dew to your primary too. Watched a buddies 14" (previously clear) dew in seconds after switching his fan on......

Good god! And there was me believing the internets!

OK - I will try without and see how it goes.

Dare I ask about dew heaters for the secondary?

[triton1]

I use a camping mat on my newt never needed a heater yet.

[brantuk]

Kendrick have a variety of secondary dew heaters to fit most types of mirror - I use a split ring one. You can get them through most astro retailers in the UK - but there are other makes available if Kendrick's too dear - their website has loads of useful info on it though so do have a read.

http://www.kendrickastro.com/newtonian.html#Split

[Moonshane]

I use a fan on my dobs and have never had a problem. The key is that you need one a lot smaller than you think. 

The one on my 12" and 16" dobs are about 80-100mm in diameter only and this creates a decent flow of air but not too much. As I understand it, there's a range of appropriate size for a mirror diameter / thickness; too much and you have the problem of the mirror getting a cold spot which can create dewing issues. Anything will do really as long as not too big.

[Bart]

I have a 10" and 16" and don't use it on either. Like Swamp Thing, I have found they attract dew, so never use them

Barry

[John]

My 12" OO dob is fitted with a very small (50mm ?) fan behind the centre of the primary mirror but I've never used it.

[glowjet]

Just for info, there are 25mm PC square frame 12V DC fans, at very reasonable prices on the Bay. maybe two or three of these could be considered, rather than a large one

[avtaram]

My 12" Revelation Dob came fitted with a fan but never felt the need to use it as it is kept in an unheated summer house.

Avtar

[DRT]

Thanks for all the helpful comments. I think I will try it without and only get one if I think the views are not as good as I expect.

[faulksy]

as steve said it was my dob that misted up. everyone elses had gone so i put my fan on to prevent mist and within minutes it was covered in due. i think it might work to cool it quicker but no need realy. steve and calv have got amongst the biggest mirrors on sgl and they never use there fans.

what 16" did you buy ?

[DRT]

what 16" did you buy ?

A second hand (6 months old) Skywatcher Flextube 400P that I am going to pick up today. My longer term plan is to buy something a bit more specialist but want to test how a big light bucket copes with my skies at home before investing four or five grand.

[faulksy]

A second hand (6 months old) Skywatcher Flextube 400P that I am going to pick up today. My longer term plan is to buy something a bit more specialist but want to test how a big light bucket copes with my skies at home before investing four or five grand.

just seen it in your signature , so if you like it whats your plan. a obsession or webster maybe

[DRT]

so if you like it whats your plan. a obsession or webster maybe

Not yet decided but something along those lines. I posted this thread a while back to get suggestions and advice from the Dob Squad - feel free to pile in if you have any words of wisdom

[fondofchips]

Use this link Derek to determine your requirements:

http://www.fpi-protostar.com/bgreer/fanselect.htm

I got an almost silent Noctua fan for my dob from here:

http://www.quietpc.com/casefans

Also - I believe Dion on astronomy shed still supplies them ready to fit for a variety of Newtonians.

Hth

I used a 120mm Noctua low rpm fan (600 - 800 rpm) fan on my 8" Newt and it worked fine, no problems with vibration either, purchased from Quiet PC.  I also fitted a Zalman speed controller so I could run the fan really slow.

Cheers,

Fondofchips.

[Paul73]

If that is the scope off ABS a from couple of weeks ago, it looks like a cracking buy.

Looking forward to the first light.

Paul

[DRT]

If that is the scope off ABS a from couple of weeks ago, it looks like a cracking buy.

Looking forward to the first light.

Paul

Yip, that's the one. I watched it for a couple of weeks and then cracked - the seller (a very nice man named Mark) lives only 20 minutes from me so it proved just too hard to resist

I'm just hoping it will fit in my car this evening!!!

[Paul73]

Yip, that's the one. I watched it for a couple of weeks and then cracked - the seller (a very nice man named Mark) lives only 20 minutes from me so it proved just too hard to resist

I'm just hoping it will fit in my car this evening!!!

20 mins! What else could you do??

Good luck this evening.

Paul

[DRT]

20 mins! What else could you do??

Good luck this evening.

Paul

Thanks.

That's more or less the excuse I used on Mrs T - she didn't look particularly convinced