Jump to content
  • Join the online East Midlands astronomy club today!

    With active forums, two dark sites and a knowledgeable membership, East Midlands Stargazers has something for everyone.

About done now.


Recommended Posts


So most of you have seen my dob by now, but I'm only just really happy with it now it's had most of its mods done. And a few thank yous along the way.

so we have dew protection. 4 port hitecastro dew controller and various dew bands. A resistor on the secondary (ty Baz).

Heated Telrad,

Lazy susan bearing,

Illuminated Setting circle using Daz's as a template and Daz's left over materials (ty Daz, Baz for his workshop and true skills, and rusty for the setting circle).


Wixey angle gauge (ty twiddledee).

Sprung centre bolt, and shed leveling feet (ty Baz).

Fully Flocked, well worth doing (ty Daz and Baz)




Still to come is a raci finder, cooling fan and cowling, replacement alt bearings and a mounted battery.

Can't thank everyone enough and especially Daz and Martyn who have helped me so much to get this scope how I want it.

Edited by tuckstar
Link to comment
Share on other sites

2 inch dew bands on eyepiece and finder, 10" dew band for primary, telrad is heated but it was already modded when I brought it. As for the resistor on the secondary, this is something that Baz did for me. The telrad and resistor go though a junction box and both run off one port.

When I get round to fitting a cooling fan I'm hoping I won't need the primary dew band as in others scopes the fan keeps the dew off as well as cooling.

Link to comment
Share on other sites

Thanks Andy. Had been wondering about the dew band on the primary. I have one that should work for my 8" but wonder how effective it would be.

I am interested in doing similar with a resistor or two for my secondary where I suspect the main issue would be. What resistance is it? May be Baz could let us\me know if it's possible to run directly off a 12v variable output from the dew controller or does it need something else to reduce the output from the battery.

Also size of wire that's suitable and could this effect the diffraction spikes on the vain used to carry the wire?


Edited by Johnnyaardvark
Link to comment
Share on other sites

I'm sure it's a 7 ohm resistor which should be more than enough. The junction box only acts as a splitter as I had run out of ports, and runs straight from controller. Less leads as well.

Not sure what mm wire we used but has made very little difference to profile of the vein.



I'm sure Baz will be able to help you out.

Daz has an 8" and very rarely he gets dew on primary with out anything. Mine was more precautionary due to how bad it was at Kelling. Perhaps if I'd of gone for a fan first might not of bothered with the 10" band.

Edited by tuckstar
Link to comment
Share on other sites

With regards to dew on the primary, it has happened to me 3 times in 3 and a half years, with the last 2 times being at Kelling and EMS 3, so twice in the last 2 months!

I'm going down the fan option at the back of the primary.

Link to comment
Share on other sites

Thanks gents. Would be great if Baz could confirm a few details for me. This did appear in another thread he commented on recently.


Was wondering a little about how well the fan would work and how you go about directing the airflow. The cooling vs the usual heating we do to prevent dew all seemed a little counterintuitive but having read a couple of articles on the web I am pretty much convinced it is something I will do.


I know a few on here have done it already so sound advice already available I am sure but I thought some may be interested in these links.


This looks like a nice mod: http://www.astronomyshed.co.uk/forum/viewtopic.php?f=19&t=21336


And this has some interesting information about different configurations: http://www.deepskywatch.com/Articles/rear-fan-newtonian.html


Peltier cooling the mirror sounds interesting but would not help with dew as the airflow is useful! What makes it move across the mirror to carry away the moisture?


The idea of drawing "dust" up into the OTA is a little bit of a concern. Thoughts?


I think I have a large (old) PC fan from QuietPC.com but will have to check the voltage.





Link to comment
Share on other sites

Guest fondofchips

I added a 120mm fan to the back of my 200P -  http://stargazerslounge.com/gallery/image/24031-200p-fan/


Dew band around the OTA & secondary mirror heater connected here -  http://stargazerslounge.com/gallery/image/24667-dew-control-200p/


I've ordered 2 more dew heaters for the focuser extension tube and the finderscope.


I have got some spots on the mirror all in a small patch which I think is condensation dripping down from the secondary mirror.  I know the mirror was clean when I bought it so the secondary mirror heater is important.




Link to comment
Share on other sites

Peltier cooling the mirror sounds interesting but would not help with dew as the airflow is useful! What makes it move across the mirror to carry away the moisture?

It is my understanding that the airflow stops the moisture from coming down the tube.

Doesn't make sense to try to heat it with a dew band and cool it at the same time with a fan. So once the fan and baffles are in the dew bands gone.


Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.