Mirror storage whilst flocking OTA

[Doc]

Well done Rob.

 

I have only ever flocked truss tube dobs and they are a breeze to do.

 

At least the hardest job is out the way.

[Daz Type-R]

As Mick said, nicely done.

 

When we did mine, we made the job easier by spraying the inside of the OTA with a drop of washing up liquid mixed with water, while the OTA was damp, the glue would not stick so that meant we could slap it on and then move it into place, once the liquid dried, the glue bonded to the OTA.  Made flocking my 8" solid tube newt loads easier.

[+Bino-viewer]

8 hours ago, Tweedledee said:

Nice job and we'll done. 

 

It certainly is a long tube to reach into.

 

When storing the scope after observing I use one of these over the mirror end to prevent dust and spiders etc from getting in. I also chuck in a big bag of dessicant...

http://www.teleskop-express.de/shop/product_info.php/info/p5106_Astrozap-Dust-Cover-for-10--Newtonian-and-Dobsonian-Telescopes.html

Thankyou Pete.

 

I use the same Astrozap covers as those !!

The plastic OO covers were unfit for purpose.

 

I'm not sure that they are worth €25 each though......

[catman161]

Very nicely done indeed. You'll be amazed at the difference in contrast when you view through it once it is all flocked. I was a bit skeptical when I did my 200P but I actually noticed a difference.

[BAZ]

Well done Rob, it's one of those things which either goes right, or as you found it can get really annoying really fast. As Daz said, Perkil8r advised spraying water with just one drop of washing up liquid, it makes a huge difference. 

You will definitely notice a improvement in contrast, it sure helps with the faint fuzzies.

[+Bino-viewer]

Thankyou all.

 

I'll be  quite confident in doing the rest of the tube now. Hovever, i am glad its a 10" tube.

OO sell (custom order) a 6" F/11 and an 8" F/8. I think flocking a long FL 6" tube would be next to impossible.

 

I'm holding off finishing the other half of the tube till i've done more research into active mirror cooling.

My mirror cell has a factory fitted fan in it, but it looks a bit feeble, so i'm planning upgrading it.

I'm aware of vibration issues btw, so i need to source a suitable fan.

And does it suck air in from the top of the tube downwards, or should it draw it in from below the primary, upwards ??  Or both ?

Some excellent examples of fan mods here, including those done by our very own Steven & Andy.

 

http://stargazerslounge.com/topic/215598-newtonian-reflector-cooling-fan/

 

https://www.eastmidlandsstargazers.org.uk/topic/10576-250p-cooling-thruster-mod/

 

https://www.eastmidlandsstargazers.org.uk/topic/9817-cooling-fan-mod/ 

 

Perhaps more importantly, (for me) is the boundary layer issue above the primary.

I want to fit a pair of fans to blow cool air laterally over the mirror.

And i'm not entirely sure of the best way to do this. I'm looking into it in detail.

 

Once this is done, i finish the flocking, clean the primary, wire everything up, then i'm done.

My Dob Planet Disrupter will be ready. 

Btw, check out my new mount (Latest Purchases)

 

 

[Daz Type-R]

Here is mine Rob.....

 

 

You suck the air from the bottom of your OTA (primary mirror end) and it goes up and over your primary and then disperses up the tube.

 

Ive done just about every mod you can think of to my dob, if you want to have a look or need some help, just give us a shout.

 

Also, what do you mean, boundary layer issue, what issue?

 

It's the layer of air that sits over your primary that stops it from dewing up.

Edited December 3, 2015 by Daz Type-R

[Tweedledee]

1 hour ago, Bino-viewer said:

Thankyou all.

 

I'll be  quite confident in doing the rest of the tube now. Hovever, i am glad its a 10" tube.

OO sell (custom order) a 6" F/11 and an 8" F/8. I think flocking a long FL 6" tube would be next to impossible.

 

I'm holding off finishing the other half of the tube till i've done more research into active mirror cooling.

My mirror cell has a factory fitted fan in it, but it looks a bit feeble, so i'm planning upgrading it.

I'm aware of vibration issues btw, so i need to source a suitable fan.

And does it suck air in from the top of the tube downwards, or should it draw it in from below the primary, upwards ??  Or both ?

Some excellent examples of fan mods here, including those done by our very own Steven & Andy.

 

http://stargazerslounge.com/topic/215598-newtonian-reflector-cooling-fan/

 

https://www.eastmidlandsstargazers.org.uk/topic/10576-250p-cooling-thruster-mod/

 

https://www.eastmidlandsstargazers.org.uk/topic/9817-cooling-fan-mod/ 

 

Perhaps more importantly, (for me) is the boundary layer issue above the primary.

I want to fit a pair of fans to blow cool air laterally over the mirror.

And i'm not entirely sure of the best way to do this. I'm looking into it in detail.

 

Once this is done, i finish the flocking, clean the primary, wire everything up, then i'm done.

My Dob Planet Disrupter will be ready. 

Btw, check out my new mount (Latest Purchases)

 

 

I did some research and found these fans to be about the best...

http://www.quietpc.com/afdp-8025b

These are as near silent and vibration free as you are going to get and are dust and damp proof. On discussing the issue with the manufacturers, they said they had actually run the fans successfully for a substantial length of time under water with no problems.

 

Here is some useful info about cooling and disrupting the boundary layer. Don't miss out on the second page...

http://www.garyseronik.com/?q=node/55

 

I remember Philjay advising me that although some people do it differently, he prefers to have the air blowing onto the back of the mirror, rather than sucking crap down onto the mirror surface, so I did it Phils way

 

Hope this helps.

Edited December 3, 2015 by Tweedledee

[catman161]

If you want an easy solution like Daz's Rob just give Dion from astronomy shed a PM. Let him know your primary mirror size and model of scope and he will make you one just like Daz had. I got mine (identical to Daz's-I can't remember but actually it may even be mine that I sold to Daz!) from Dion. He has the plastic laser cut and the fans are whisper quiet and speed adjustable. Great build quality. He's a top bloke Dion and will sort you out [emoji4]

[+Bino-viewer]

Great looking bit of work there Darren. Thanks for your offer of assistance.

 

I'm not experienced enough with Newtonians yet, but have read alot into Thermal management, and have friends in our society who are way more clued up than me.

A couple of points.

 

Not all fans on Newtonians work like this.

Mine DOES NOT. It works the other way. I have tested it and confirmed it.

Even though my fan is mounted on the mirror cell below the primary, it draws air DOWN the tube from above.

If the fan works the other way, like yours you are only cooling the rear of the mirror.

You then have a small pocket of warmer air that sits directly above the primary, which will degrade the scopes performance, particularly high power work.

So to shift this boundary layer, laterally blown air across the face of the primary is recommended.

 

I'm reading alot in to this, maybe too much, but i really want to get the best out of this scope.

Here are some detailed reports by experts. Gary Seroniks paper is especially interesting, and very indepth.

 

One thing of note though, is this problem is more of an issue with larger mirrors that are 2 inches (or more) thickness.

My primary is i think 26mm deep. So getting thermal equilibrium is easier and quicker.

 

 

http://www.deepskywatch.com/Articles/rear-fan-newtonian.html

 

http://www.garyseronik.com/?q=node/55

 

http://www.garyseronik.com/?q=node/69

 

[+Bino-viewer]

Thankyou Pete for the fan link.

The one advertised may be too deep at 25mm.

I wonder if they do a lower profile one ?

 

I have read and book marked Gary Seroniks paper already. Very interesting isn't it ?

 

You make a good point about drawing dirt / dust down the tube and on to the primary.

But OO do it this way. Which way is best ? Who knows ?

 

 

 

Felix : thats a good idea. 

I am a member of Dions AS forum. I will drop him an email.

 

I can't recall seeing any of his video's that relate to fan modifications ?

I will have a look.....

Edited December 3, 2015 by Bino-viewer

[catman161]

Thankyou Pete for the fan link.

The one advertised may be too deep at 25mm.

I wonder if they do a lower profile one ?

 

I have read and book marked Gary Seroniks paper already. Very interesting isn't it ?

 

You make a good point about drawing dirt / dust down the tube and on to the primary.

But OO do it this way. Which way is best ? Who knows ?

 

 

 

Felix : thats a good idea. 

I am a member of Dions AS forum. I will drop him an email.

 

I can't recall seeing any of his video's that relate to fan modifications ?

I will have a look.....

Hey rob here's Dion's video detail g the mirror cooler

[+Bino-viewer]

Cheers for that Felix.

I shall make a cuppa and hear what Dion has to say on the matter.

 

Btw, i hope i haven't gone too much off topic.

Apologies to Poddy (the OP) if i've hijacked the thread a bit.

[Daz Type-R]

Rob, you may be reading too much into it.  While my fan does indeed cool the back of the mirror, the mirror is not a tight fit into the tube, there are gaps all around the side, thus allowing cool air to circulate around the primary and up into the tube.  That is the reason my fan system is sealed, if it's not sealed, all the air just blows off the back of the primary and what's the point of that?

 

As mentioned above, you do not want to be pulling cool air down the OTA, your just going to pull dust ETC directly onto the primary.

 

Ive been running my fan system for approx 18 months now and have noticed no visable degradation in view between fan on and fan off, it's used purely to keep dew of the primary.

[+Bino-viewer]

I hadn't factored dew on the primary as being a problem.

 

Maybe on a truss type scope its more of an issue. 

How do you see the 3 deg C rule in Gary Seroniks paper ?

 

Do you use a thermometer to keep track of the primarys temperature ?

As long as the temperature of the primary keeps above ambient how can it dew up ?

I would have thought further cooling (after the mirror has reached thermal equilibrium) would exacerbate dewing issues ?

 

You are probably right : maybe i am reading too much into it.

I'm not 100% convinced though about which direction the fan needs to blow.

Why do OO fans draw air down the tube from above rather than the opposite way ?

 

The only sure way is to test every variable out in the field. 

I will be contacting Dion to see if he can supply a fan system to work with my scope.

But i'm still planning on fitting a side mounted fan (at primary height) to shift this boundary air.

Certain telescope makers have them fitted as standard.

Teeter (US) for example. (scroll down a bit)

 

http://www.teeterstelescopes.com/#!components/c1ljq

 

[Daz Type-R]

All I know is, my primary has dewed up on 4 occasions now and not one of those occasions has been while the fan is fitted and on.

 

I'm talking about out in the field proof, not theory. I have also never used a thermometer on a telescope and I'm never going too.

 

With visual observing, these things really don't matter, does collimation have to be 100% accurate to a fraction of a MM, no not really, does the temp of the internals really have to matter, I don't think so, what I find does matter is dark skies, good seeing, semi decent eps and dew protection (in my case, lots of it).  

 

Plenty of times at Belper and star parties I've been observing long after people have packed up with dew issues.

 

I guess the point I'm trying to make is, use it first, you may find you need none of this, I started out with a bog standard scope and standard eps and modded as I went, fixing each issue as it cropped up, with dew protection being the first thing I sorted.  The fan has been the last thing I fitted after the primary kept dewing up.  I can also turn my fan off, so if your still worried about boundary layers, whack it on to cool it down then turn it off to observ, if it starts to dew up, turn it on.

 

Me personally I whack it on full while setting up and turn it down to low while observing and leave it on all night.

 

Hope this helps.

[Tweedledee]

I know you are wanting to get top class planetary performance from your newt, so I would also be thinking of using some air blowing across the mirror surface. 

 

Whatever you do with moving air has to help with both cooling and quickly getting great rid of image degrading tube currents and boundary layers.

 

I think I am probably quite lucky with the design of my 14" primary mirror. The rear of my mirror is curved with molded ribs and is epoxied into the centre of the mirror cell, holding it firmly without stress. The mirror is about 10mm thick on the edge and thicker towards the middle. It is designed to be very lightweight and have very quick cool down times. My mirror is always kept at maybe 5 degrees above the outdoor temperature. I reckon that my three 4" fans will blow the air up and around the curved mirror back and will cause enough air movement to dispel any boundary layer which will probably only be there for maybe the first 30 minutes of cooling, by which time the mirror temperature will be very near ambient.

 

I can see that if you keep your scope indoors and it has a conventional flat backed thick mirror then This will be more of a problem and blowing air across the mirror surface would be a big advantage.

 

I will be very interested to see what your final solution will be and if it works for you.

Edited December 4, 2015 by Tweedledee

[Brantuk]

Believe it or not - I have watched a mirror for half an hour seeing it clear as the fan blows it cool. It does make a huge difference to the state of the mirror - but how much difference that makes to what you see in the eyepiece I'm more hazy on - mostly cos I did this little exercise during the day to see the effect with my own eyes.

 

What I can say is that Daz and Pete above make perfectly valid points - the theory doesn't always match the reality cos things are varying or changing all the time - and we can't control the weather or atmosphere with any degree of precision and timing.

 

You can use a scope right from the get go once you've set it up for sure. And switching on a fan or dew heater will help it to cope if for some reason it conditions start to change. The human eye doesn't detect changes as precisely or consistently as a giga pixel dslr array. So for visual use it doesn't always need to be collimated to micrometer tolerances nor as clear and shiny as seeing your face in the floor at the Savoy. Near enough is often near enough.

 

Imho you get much more enjoyment actually using it and just tweaking as you go along - and you get more time at the eyepiece too. Hth

 

 

 

 

[BAZ]

I can only side with Daz on the dew issue, since having a fan on the back and a back plate to force air up the tube rather than bouncing off the rear of the mirror, I have had no dew issues on the primary. In fact having the fan on low improves my view, I suspect that the air flow being directed up the OTA stops turbulent air currents forming. This is so apparent on some nights that turning the fan off and watching the view deteriorate, then turning it back on and seeing the view almost snap back is amazing. Using high mag on something like Jupiter gives the most marked effect.

 

When I got my Dob, I went mad and stuck every mod on it that was going. I have since removed most, as they are simply time consuming distractions to actually looking through it. I have setting circles and a Wixey, but most of the time still star hop to stuff, I find it easier and believe it or not, less distracting. I find I focus more on what I am looking at and for.

 

Dew control is the top priority, this is the one thing that really stuffs a good night up. A suitable sized resistor siliconed onto the secondary is pretty much a must. Dew shields help, but even these cannot keep dew off all night. Dew heaters on the finder, eyepiece and Telrad just help stop any dew frustration. The only thing which limits me now is battery capacity, but if I charge it after any use I can get a full night out of it. (17A/Hrs).

[Tweedledee]

As Kim and Martyn say above, you can't predict the variables in the english climate. I'm sure that whatever you do the atmospheric conditions will eventually conspire against you and screw up all your plans, but the more you try, hopefully, the less frequently that will happen. The ideal fan/heater system would really need complex sensors and computer control systems to cope with variable conditions as they change.

 

I remember observing for a couple of hours under a lovely clear sky and suddenly feeling raindrops on my head whilst looking through the eyepiece. Just never saw it coming. 

 

The other option may be to take your scope up a mountain in the Atacama desert with a constant 0.5% humidity and virtually guaranteed predictable climate above the clouds. The fans might be easier to implement though 

 

Like Martyn, I've tried to implement various bells and whistles on my setup, but have now come to the conclusion that keeping it simple is better. All I really want to do is see good views in that eyepiece, and think now that fans and dew control are the only really essential extra gadgetry needed for doing that.