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Optimizing an SCT, simple steps

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#26 pstarr

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Posted 08 July 2005 - 09:49 PM

I'm out in the woods with the coyotes and an occasional owl. Green stuff all around. Down right spooky sometimes.
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Paul
c-9.25 CF XLT
soon to be zambuto 10" f-6

#27 Guest_**DONOTDELETE**_*

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Posted 08 July 2005 - 10:46 PM

Heh, lookup Area 51 sometime, dark site for South Florida Amateur Astronomers Assoc. It is on the side of an alligator infested canal in the middle of the Florida Everglades.

Talk about wondering what that noise is rattling in the bushes!

#28 Mike B

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Posted 08 July 2005 - 11:21 PM

Paul-
Sounds really nice! I'm envious...
Once had an big ol' owl give me a lookin' over... was then i decided i was glad i'd gone with the 10" SCT... an 8" woulda been too light. :grin: I can see the insurance claim form...
In any event, i'll take owls over gators anyday!!
:cool:mike b

#29 southmike

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Posted 08 July 2005 - 11:52 PM

Mike.
I have tried everything with my building outside of a air conditioner. It is 12'x 12', all wood, no masonry, with white alum. siding exterior. I have a 26 ga. metal roof with ridge vent the whole length. I do have a fan, mounted behind a louver, that I turn on around noon if I'm going out that night. You can see some of the building in the equip. photo section of CN's.
-------------
Paul
C-9.25 CF XLT



Is the building insulated?

#30 pstarr

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Posted 09 July 2005 - 01:26 PM

No, no insulation. I have been thinking about doing the underside of the roof though. The floor is 2x4 treated lumber, like a deck.
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Paul
C-9.25 CF XLT
soon to be zambuto 10" f-6

#31 southmike

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Posted 09 July 2005 - 11:24 PM

Insulation is expensive these days , but it will help stabilize the temp....or at least until you pop the top.
also the types vary a lot. it takes about 2" of Styrofoam to be useful, fiberglass is good but itchy, messy , and adds the need for covering (vapor barrier) but plastic will work. then there is the foil backed foam which has minimal hard r -value but it helps with the radiant transfer value. vents are helpful in the roof, or gable sides (more so in summer). as I said it will help .. but if it is a roll off the temps will equalize once the top is rolled off. so in the winter it might get nippy.

#32 Olivier Biot

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Posted 10 July 2005 - 01:46 PM

Hi Olivier-
Yup- seems we city folks are often runnin' the 'race' of this hobby with a wooden (or concrete) leg. :p How far a trip is the "countryside" for you?
:cool: mike b


Hello Mike,

One of the drawbacks for an astronomer in Belgium is that we have lots of illuminated highways (all in fact). As the area where I live is at the crossroads of Europe, I have to drive for a while in order to find a really dark spot.

The heat issue is also a problem of poor insulation. From infrared measurements it can be deduced that Belgium builds mediterranean-style homes, from the insulation point of view. However, the Mediterranean is still 1000km (625 miles) to the south :grin:

I have been told there is one dark area at about 25km (15 miles) northeast where I live (45 minutes driving). However I have no "power tank" yet so I still need a socket for my transformer at maximum 15 feet away from my scope :)

Cheers!

Olivier

#33 Mike B

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Posted 10 July 2005 - 03:10 PM

Hi Olivier-

Since when has logic & proximity had any bearing on the location of "Mediterranean" homes?:roflmao:Here in California we're practically tripping over them :lol:- or, at least, their Californiaized kin. And i'm partly to blame, being one of a myriad of plethoras of "building designers" designing the things...:getem:

From what i can recall of having seen it, the dark-sky night-time map of Europe had me wondering where y'all manage to find to view DSOs! It's like the Eastern seaboard of the U.S.- marinated in light! In that regard, my proximity is very fortunate, as there are still large tracts of land (ag, preserve, mountains, & rural) as yet undeveloped- between the larger cities- where one can easily drive to. Even my "home" site has mag ~5 skies, and within a 15 minute drive is mag 6+! But it's a never-ending struggle to maintain those dark skies in the wake of the ever-present pressure to develope & utilize cheap, insensitive lighting fixtures. :p In my business, i do what i can to promote intelligent exterior lighting... but i think i'm related to that little Dutch boy...
;) mike b

#34 Jim Easterbrook

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Posted 10 July 2005 - 03:58 PM

USA: 31 people per sq km
Belgium: 339 people per sq km
Whole UK: 243 people per sq km
England & Wales: 389 people per sq km

The consequences are inevitable...

#35 Scott Beith

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Posted 10 July 2005 - 04:09 PM

So far we have:


Vibration Suppression Pads
Cat Cooler
2" Diagonal
Dewshield
Collimation
Location/Surface


What else is useful?

#36 Olivier Biot

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Posted 10 July 2005 - 05:20 PM

There's another (albeit less obvious) option: the CATd esign. Not all CATs use a full-aperture corrector. My scope, a Klevtzov Cassegrain, uses a sub-aperture corrector, hence the OTA is open!

Some purists may object, but to my eyes it has both reflective and refractive elements, which to me is the criterion for a catadioptric telescope.

Cheers!

Olivier

#37 Mike B

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Posted 11 July 2005 - 12:13 PM

"What else is useful?"

Thanks Scott! :lol:

I'm still wondering if & where any "boundary layer" issues may lie with SCTs, & how they might be alleviated. Granted, they're optically not an "optimal" design, but they are so very common!... would be nice to get the most out of them as is practically possible. Is there anything simple we may be overlooking here?

I suppose another thread/direction would be more "invasive" procedures folks have done & the results therefrom:
* dissasembling the OTA & flocking :ooo:
* drilling the back & installing fan(s) :p
* drilling the sides & installing "boundary" fan(s) :confused:
* do away with the tube & use a rigid cage? How nuts is that? :crazy: :roflmao:
Not sure i'm ready, personally, to go to these measures (yet ;)) & risk boogering up my main scope :scared:... but the bold & adventerious amongst us might benefit. or not. :question: How say ye?

SCT regards,
:cool: mike b

#38 Jim Easterbrook

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Posted 11 July 2005 - 01:32 PM

If I were very confident and adventurous, I'd want to consider a system of fans to recirculate air and break up any thermals inside the OTA. There's no dust issue with recirculated air, and such fans can remain on all the time - reportedly making cool-down a non-issue. I've seen pics of such set ups posted to other forums (or fora if you prefer) - they do seem to require some drastic and irreversible metalwork.

#39 southmike

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Posted 11 July 2005 - 02:07 PM

So far we have:


Vibration Suppression Pads
Cat Cooler
2" Diagonal
Dewshield
Collimation
Location/Surface


What else is useful?

light pollution filters can give mixed results.

some things depends on user experience..
if it is a goto cat..... then some knowledge of the sky is needed to set it up properly.

also some models , you can train the drives to help remove backlash..though an improperly trained drive is worse then one that wasn't trained.

Focuser upgrades can be nice but not necessary. there are several ways ranging from add-on microfocusers or even replacing the focuser , to simple bearing kits.

also if astro photo work is in the future you will want a good sturdy wedge, or modify one of the stock ones.

#40 Mike B

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Posted 11 July 2005 - 02:08 PM

Hi Jim-
I've read where a fan blew (or drew) air across the face of a Newt's primary to remove any "boundary layer"- which an air-recirc method might help achieve, but have also read where a tubed Newt worked best with air blown up-the-tube to create a uniform "laminar" section of air for the optics to "look" thru, as opposed to a turbulent/swirling/eddies section of air typically associated with air corralled in a tube with only thermal effects inducing movement. I don't know what the effects would be with swirling recirculated air. "Simple step"?... no. But i'd certainly be curious to see someone's pix/analysis of such a "system".
:cool: mike b

#41 Mike B

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Posted 11 July 2005 - 02:30 PM

southmike,
For a while i used a "Crayford" focuser tailpiece, which was very nice. But when i went to using a binoviewer i was concerned with having so much tail-end hardware that focus would be too far back of "optimum" for the SCT design & might thereby suffer some degree of optical abberations. So i sold off the Crayford & "Petersenized" the std. SCT focusing mechanism (bearing "kit")- the results being largely favorable, yet not really Crayford nice, just better. Honestly have not used a BV and Crayford in tandem, so don't know how well/poor that works in practice... not certain my limited optical savy could divine. Any "experts" know for sure on that? Mike H., where are you :watching: The Crayford is a natural "fix" for the std. SCT focus woes!- thanks for bringing that up! Excellent advice, at least for the mono-eye ;) folks.
:cool: mike b

#42 Guest_**DONOTDELETE**_*

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Posted 11 July 2005 - 02:49 PM

Well...within a week of owning my new 10" Meade, the "cord detect" software detected the electric focuser cord and chewed it to shreds! (i must have misinterpreted the instructions). Personally, I did not like the electric focuser anyway..so a nice upgrade to consider might be the FeatherTouch or JMI focusers.

A mounting plate might be a useful item as well. Lumicon might soon be coming out with one, I am getting the first prototype version this week.....report to follow.

Gary

#43 Starman1

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Posted 11 July 2005 - 05:05 PM


Now, once we're into more invasive procedures, would a side-mounted "cooling" fan that also drew air accross the primary to scrub-off any "boundary layer" be an idea worth considering? Anyone done this, or heard of this being done in an SCT?

Thanks much for all the input!
:cool:mike b


I've seen a C-11 with 12 large square holes cut in the tube, making the scope very open to the passage of air in/around the mirror. The owner claimed thermal issues ceased after 20 minutes. He also pointed out he just blows the accumulated dust off the mirror. "Really no different than a truss dob".
Frankly, the Lymax Cooler is less, uh, frightening.

#44 Starman1

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Posted 11 July 2005 - 05:11 PM

So far we have:


Vibration Suppression Pads
Cat Cooler
2" Diagonal
Dewshield
Collimation
Location/Surface


What else is useful?

Scott,
--focuser upgrade (FeatherTouch/EX Telescopes, etc)
--Right Angle Correct Image finder
--Sliding weight system
--Better eyepiece tray for mount
--larger battery for accessories and scope
--dew zapper cord(s) from many companies
--EZ Telescopes collimation eyepiece
--Piece of carpet for under scope (ever drop an eyepiece?)
--Hi-transmission coatings (order with scope)
If I think of something else, I'll add it.

#45 southmike

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Posted 11 July 2005 - 06:42 PM

some kind of landing pad or similar device can help with setups if it is not being mounted on a wedge. They also add extra eyepiece and controller mounts.

another handy addition is called a springy thingy..
it can be bought or made ...but basically it holds the center bolt up so you can find it.. and allows it to be smashed down when you can't....an over simplification but you get the idea...it works for Meade scopes though i am not sure about celestrons.

also a 2" diagonal wont due much good without 2" eyepieces. If it is a 10 inch or larger Meade ,look for some of the eyeopener kits , a few other make similar devices , as do some of the after market sct mounted focusers. but they open up the field view for some 2" eyepieces.

#46 Mike B

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Posted 11 July 2005 - 06:50 PM

Hi Don-
Yeah- intriguing. And i'd havta agree- frightening! But seems logical... other than holding the corrector & secondary firmly in place (the secondary at ~f2, very firmly!), how is an SCT different than any other basic reflector in regard to using/requiring a "tube"?
:question:

#47 southmike

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Posted 11 July 2005 - 11:04 PM

i would think it also runs the risk of letting stray light and dust in.. not a bigy..one i believe the cure is a black cloth .

#48 Scott Beith

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Posted 12 July 2005 - 06:58 AM

You guys obviously have a lot of experience with these things - I'm impressed.

Don,
That was a good list - thanks Sir.

Nothing stranger than an SRF doing SCT research... :whistle:

#49 matt

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Posted 12 July 2005 - 07:47 AM

I've seen a C-11 with 12 large square holes cut in the tube, making the scope very open to the passage of air in/around the mirror. The owner claimed thermal issues ceased after 20 minutes. He also pointed out he just blows the accumulated dust off the mirror. "Really no different than a truss dob".


I'm really considering doing that. My fear is, wouldn't I risk bending the tube while cutting/drilling the hole?

#50 southmike

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Posted 12 July 2005 - 09:35 AM

he he can you imagine the factories expression if you had to send the ota back in...with it cut up to swiss cheese.
I would love to see a picture of the first guy to un box it. It does some make sense though as basically you are drilling the same kind of holes you would to save weight.
just thyey have the added bonus of air circulation.

However in the end I feel pretty sure i won't be drilling anything blue for a while.


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