10" Skywatcher Dob "enhancements"?

[bmitchell82 (Brendan)]

Hello all,

recently after all pros and cons where weighed up i have put a deposit down for a 10" skywatcher dob. I have been looking though the forums and seen alot of DIY projects. As i am a compulsive tinker'er what are good value for money enhancements to this already decent kind of scope?

Somethat i will be looking at are

Illuminated sight scope (mikes thred)
base enhancement (milkbottle washers thanks mike again !)

I have seen people talking about internal baffling either behind the secondary or all the way up the tube, will this make alot of difference for visual astro?

Also for a person that is new to the game, ambient temperature and thermal equillibrium of the mirror is there a resonably sure fire way of knowing when your about ready to go other than saying yeah its been a hour shell be right?

Any other ideas?

Brendan

[Starkler (Geoff)]

The most worthwhile improvements include

• A lightweight stool or chair to enable a comfortable viewing position at all altitudes.
• Contrast enhancements - Flocking the upper inside of the OTA opposite the focuser. Flocking the lower tube portion thats visible from the focuser. Front ota extension.
• Movements - milk bottle washers around centre bolt, pimply laminate on underside of rocker box waxed with turtle wax paste car polish.
• Right angle finderscope to save your neck, coupled with a Rigel or Telrad finder.
• Balancing - Large speaker magnets covered with cloth or felt to prevent scratching
• A mirror cooling fan
• The biggie! - An argonavis

Threads already exist on all of the above. A bit of time using the search function will throw up a lot of useful info on these.

[Blue Skies (Jacquie)]

Originally Posted by bmitchell82

I have seen people talking about internal baffling either behind the secondary or all the way up the tube, will this make alot of difference for visual astro?

Baffling has it's good and bad points.

On the down side it can trap heat in the tube, or push hot tube currents down into the light path as it rises up the tube. I suppose some people would say if you install a fan that blows across the mirror face to get rid of the heat that way you would reduce this problem.

You probably wont need any baffle low down near the mirror since the back of the skywatcher is enclosed, so you don't have to stop light coming from behind the mirror.

However it might pay to investigate a few baffles up near the secondary and focuser. There is not much at the front of the scope and it's easy to see how light could enter the focuser from the side at the front. A half-shield just extending from the front may solve this problem too. Newt is a good well-known program that computes baffle locations for you if you're interested. But I really don't think you'll need them all the way up the tube. A bit of judicious flocking would probably be better.

[Starkler (Geoff)]

I cant see any point of baffles in a netwonian OTA.

Baffles work where they are between your eye and the light source that you want to block out. In the case of baffles in the main newt OTA, you are viewing the illuminated side of the baffle. The only baffles that makes sense are inside the focuser, or behind the primary mirror to stop light from being seen from the back.

[bmitchell82 (Brendan)]

so in other words, baffling wont give any noticeable proformance enhancement, so don't go to the effort of doing it ... So far i think the next thing that ill be saving for is some really nice eye peices followed by the almighty argo navis ? I will be trying to give a telerad a go to see if it works for me what do you guys suggest on that? because you can pick them up for about 3o bucks on ebay nowdays.

[JethroB76 (Jeff)]

An extension to the upper end of the OTA will help with cutting out unwanted light/reflections and also prevent dew on the secondary...the telrad is a very good option but find I need a regular 8x50 finder too

[tnott]

Originally Posted by Starkler

I cant see any point of baffles in a netwonian OTA.

Baffles work where they are between your eye and the light source that you want to block out. In the case of baffles in the main newt OTA, you are viewing the illuminated side of the baffle. The only baffles that makes sense are inside the focuser, or behind the primary mirror to stop light from being seen from the back.

Yep. It is not a refractor. The focuser baffle can be in front of the focuser too if there is enough clearance. It also means that a baffle placed behind the secondary to block light sneaking in over the top of the OTA can be smaller. Flocking anything you can see though the focuser (mainly on the top end) also helps a bit.

Adding an extension tube around all the way the OTA is something people do sometimes if there is lots of excessive stray light as well.

[Paddy (Patrick)]

I found arranging airflow across the face of the primary (using Scott Tannehill's method http://www.iceinspace.com.au/index.p...63,400,0,0,1,0 ) has significantly improved my 12" GSO dobs performance. Would highly recommend such a modification!

[rmcpb (Rob)]

Take Starkler's advice and add another ---------------- Telrad

[bmitchell82 (Brendan)]

Originally Posted by Paddy

I found arranging airflow across the face of the primary (using Scott Tannehill's method http://www.iceinspace.com.au/index.p...63,400,0,0,1,0 ) has significantly improved my 12" GSO dobs performance. Would highly recommend such a modification!

that would be about right but the sw 10" using pyrex has a extremely low CoE so as soon as the scope has come to equillibrium with ambient temps then all i could see it doing is creating air currents that could distort the light path? am i correct or still would this be a good idea to direct a air flow accross the mirror?

[tnott]

Air flow across the front of the mirror to break up the boundary layer only improves the image when the mirror is still cooling down.

But, having one fan in front of the mirror as well as the one behind can speed up the cooling process. More important if your mirror is thicker than 1.5 inches.

The slight warping of the figure of the mirror as it cools down is more important in the process of figuring. In the field the effect is much less important than the heat waves coming off the mirror.

A small fan on the back of the average 10 inch should be plenty.

[GrahamL]

telrad ,fan a sealed rechargable to run it and I'd wait an see what you think .. these scopes generally work well straight out the box

one little thing I did was stick a little bit of foam down inside the rocker box so when the ota swings to vertical it goes
"bump "into the foam rather than "clunk" into the rocker box .