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Optimizing an SCT, simple steps

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#1 Mike B

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Posted 07 July 2005 - 04:41 PM

Several threads on another CN forums have me thinking :scared:... what are some simple steps we SCT users can take to optimize our scopes for happy viewing? I'm thinkin' here more of optics & thermal issues, not eyepieces & user-specific hardware, and definitely not invasive & advanced procedures like dismantling & flocking the OTA ;). I'm hoping this will assist some newer SCT users up the learning curve to more fully enjoying their scope! For the record, i'm using an older 10" f10 LX-50 on a std. wedge.

I'll start with my own points/ideas, with others hopefully adding their experiences & wisdom derived therefrom:
a) Vibration-supression pads. Yeah, they really do help steady the image ;), especially on a heavier rig where its own weight may be a problem in this regard.
b) A "Cat-Cooler" to "air-out" the OTA interior, helping all the interior materials to achieve ambient temperatures more quickly than if simply left to sit sealed-up.
c) Setting up on grass or other non-radiating surface... importance diminishes in milder climates and/or later into night as everything gradually reaches thermal equilibrium. I've even hosed down the patio prior to set-up to help speed it's cooldown. Not recommended for optics ;)
d) Collimation!
e) Location. Location. Location. I was amazed, yet again, on how much nicer the images of Jupiter were when set-up in a rural setting, viewing over open pastures- instead of in town, viewing over rooftops, plastered buildings & asphalt roads. Yes, this like other points above is pertinant to any scope- but larger scopes like SCTs i suspect even moreso.

Now a question. My flex dewshield is determined to end it's usefull life, ductape notwithstanding. I was going to look at some "reflectix" to try making my own... but memory flashed upon the topic of "boundary layers" for Newts. Is a large, deep, dewshield preventing an SCT's corrector from clearing a boundry layer? :question: Would judicious use of a "dew-zapper" be a better solution for both preventing dew and any boundary layer(s) of air? Or is that piece of glass too small/thin/thermally insignificant to be an issue?

How say ye? I'll bet CN has, collectively, thousands of hours using SCT's... please help us get better at using our scopes! Even if it means stumbling around in pastures ;) mike b

#2 pstarr

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Posted 07 July 2005 - 06:08 PM

On the dew shield question. The corrector cools long before the primary. That's one of the reasons we need it, to prevent dew on the cool glass. Also, stray light hurts contrast. That why some people flock their scopes. The dew shield prevents stray light from entering the tube. I had an interesting experience last night with my dew heater system. Its been quite warm here so I haven't had to use much heat. Last night I turned the setting up two notches because it was cooler. Shortly after doing so I noticed an almost perfect star test. In my case the conditions and heat were just right to optically affect the scope for the better. I have heard others say some heat helps the image in their scopes. I plan on doing some more experimenting with the heat settings in the future. I also use a Lymax cooler. It really helps the cool down time.
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#3 Mitrovarr

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Posted 07 July 2005 - 07:05 PM

Seriously, everyone needs a tube cooler. Without one, you are stuck with a cooling tube your first 1-3 hours of viewing, with effectively terrible seeing no matter how good the atmospherics actually are. With one, you just turn it on and put the scope out on your balcony or in your yard, wait half an hour, and then go out and set up with your views immediately good and soon progressing to as good as is possible on that night. They are particularly important for flocked scopes, which are effectively insulated.

It's not terribly hard to make a tube cooler if the price of the commercial ones bothers you (it seems awful high for a computer fan, a filter, and a little piping.) The important part is to get a decent air filter to keep from dusting up the inside of your SCT.

#4 Psa19one

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Posted 07 July 2005 - 07:30 PM

Is there a website detailing the materials, etc., needed to make your own cooling tube??

Say, I've also seen those who've drilled some holes in the back of their SCT OTA (after removing the guts, of course!) and attaching a fan to the back. What do you all think of this idea? Good one? Bad one?

#5 Guest_**DONOTDELETE**_*

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Posted 07 July 2005 - 07:42 PM

Get rid of standard 1.25" diagonal and upgrade to 2" dielectric (in my case, upgraded to Stellarvue).

Upgrade focuser

Note: Upgrades mean nothing if temperature inside tube is 100 degrees! LOL

Gary

#6 Psa19one

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Posted 07 July 2005 - 07:42 PM

I just found the answer to my own questions! :)

Here's a site detailing how to make your own SCT cooling tube: http://www.starcrwzr.com/cooler.htm and another one: http://members.tripo...cope_cooler.htm

#7 Psa19one

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Posted 07 July 2005 - 07:46 PM

And here's a site dealing with adding a cooling fan to the back of the OTA...

http://easyweb.easyn...lx_misc.htm#lcf

#8 Guest_**DONOTDELETE**_*

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Posted 07 July 2005 - 07:48 PM

Now I wonder how much time all that running around to buy the hardware, and all that time spent assembling it COST in a dollar/time ratio. Looks like he made it alright, for a cost of about $1,500 in time! LOL

(excluding gas/amoritized insurance rates/wear and tear on car and tools, possible risk of fatal injury should Dremel tool happen to drill thru eyeball, etc etc)

#9 Psa19one

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Posted 07 July 2005 - 07:53 PM

Well, the *cost* in just materials is most definitely cheaper, and if you like making stuff like that, then a 30 minute trip to the hardware store and radio shack is probably more enjoyable than burdensome. I will probably do one of these projects rather than buy the Lomax cooler since I'd rather spend a few bucks and little time and save my bigger expenditures on accessories I *can't* make. ;) That will mak my wife happier too!

#10 Guest_**DONOTDELETE**_*

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Posted 07 July 2005 - 08:16 PM

I understand that perfectly....its just that if I tried to make something...i WOULD be the guy in the Emergency Room for a Dremel Tool Extraction in conjunction with the now necessary bi-frontal stereotaxic radiofrequency cingulotomy. In MY desire to save $100, I would end up permanently brain-damaged (all those piano lessons out the door) and semi-ambulatory by electro-mechanical assistance for the rest of my life. (the thought saddens me deeply) sniff!

Gary

#11 Guest_**DONOTDELETE**_*

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Posted 08 July 2005 - 12:18 AM

Seriously, everyone needs a tube cooler. Without one, you are stuck with a cooling tube your first 1-3 hours of viewing, with effectively terrible seeing no matter how good the atmospherics actually are. With one, you just turn it on and put the scope out on your balcony or in your yard, wait half an hour, and then go out and set up with your views immediately good and soon progressing to as good as is possible on that night. They are particularly important for flocked scopes, which are effectively insulated.

It's not terribly hard to make a tube cooler if the price of the commercial ones bothers you (it seems awful high for a computer fan, a filter, and a little piping.) The important part is to get a decent air filter to keep from dusting up the inside of your SCT.


Ok those of you with SCT coolers, you obviously believe they work well as they are deemed "necessary." My fear is dust inside the OTA. Any input as to whether they REALLY DO keep dust out of the OTA? I don't want to use one at all if it's going to compromise in that area even a LITTLE.

#12 Mitrovarr

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Posted 08 July 2005 - 02:05 AM

Now I wonder how much time all that running around to buy the hardware, and all that time spent assembling it COST in a dollar/time ratio. Looks like he made it alright, for a cost of about $1,500 in time! LOL

(excluding gas/amoritized insurance rates/wear and tear on car and tools, possible risk of fatal injury should Dremel tool happen to drill thru eyeball, etc etc)


I don't know about that guy, but mine took me about two hours. Just slap a couple of pieces of PVC together, stuff a filter in somewhere, and tape a computer fan to the back. Looks like junk, works just fine. Net cost, about 20 dollars and an extra fan from a dead power supply. As a college student, my time wasn't exactly worth $75 an hour, so building it was a vastly better idea. Besides, I can't stand the idea of blowing $140 on a little piping, a computer fan, and a $2.95 filter. Those things should be WAY cheaper.

If you're really worried about dust, you could just buy a lymax replacement filter and use that inside your own homemade unit. That way, yours should eliminate dust as well as it does. Reports indicate that yes, even the Lymax unit will dust your tube, but not quickly or badly. You still might not want to use one if you permanently and completely reject the idea of opening your tube.

If you make one, remember to run it outside your scope for a couple hours to blow the dust out, and don't forget that you can shine a flashlight across the opening to see if any dust is passing through.

#13 pstarr

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Posted 08 July 2005 - 06:08 AM

I have been using my cooler (Lymax) for about 9 months. since May, I've gone out every clear night. I have not noticed any dust inside my tube. I run it for about a half hour before observing. I do run it for about 30 seconds before putting it in the scope and I wipe the tube with my hand to remove any dust. I can't imagine using my scope without it. It works that well.
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#14 Guest_**DONOTDELETE**_*

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Posted 08 July 2005 - 11:09 AM

I just put my scope outside 2 hours before I view (easier to set up in daylight anyway.. ). Any other benefits from a cooling system that wouldn't get absorbed by this?


#15 pstarr

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Posted 08 July 2005 - 12:21 PM

The temp. really dosen't start to drop until the sun sets. Are you saying, if you put your scope out at 9:00, you don't start observing until 11?. My scope is in a roll off roof observatory. Although well ventilated, on a sunny day it gets 8 to 10 deg. above the air temp. I roll the roof off as soon as the sun is off the building. I like to look at Jupiter as soon as I can find it. Thats before the sun sets, I can usually find it around 8:30. The air is very steady at this time of the day and I get some really good views. With the cooler, I can get views with little or no air currents in 15 min. to a half hour after running it. If the scope can't keep up with the falling temps after dark. I put it in for another 5 min. and I'm good to go again. If you ever use one you will wonder how you got along with out it. It saves a lot of time that you could use looking instead of waiting.
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Paul
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#16 Mike B

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Posted 08 July 2005 - 12:25 PM

Hey all-

My home-built solution to the "Cat-Cooler" was inspired purely of ignorance... had never even heard of the "Lymax" version. Feeling particularly clever, i was all set to patent the dumb thing- when a random swerve to their website elicited a "duh" from the clever inventor. :lol: :lol:

Mine is PVC pipe & fittings, stuck (not glued) together in an unorthodox, Tim-Tayloresque conglomeration, with the RadioShack CPU fan at the tailpiece- but mine sucks. I mean, it draws air out, not blowing in... the air is drawn in thru perforated holes in a film-cannister sleeve that is fitted & glued over the PVC pipe, the cannister being packed with lens-tissue as a "filter". I was very nervous of blowing even "filtered" air discharging from the tube directly at & in-front-of the secondary mirror; My air swoops (sorry, technical term ;)) up the baffled focuser-tube, slowly swirls inside the OTA, is drawn across the inside face of the corrector, then down the "tube" & out. This all accomplished with the OTA pointed up, so warmer air is theoretically risen upward toward the corrector. Been using it for maybe 18 months- not really seeing much dust. If some accrues, s'pose we'd treat it like a typical Newt with fully exposed optics- clean 'em. While opened up for such, would probably flock the OTA.

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

#17 Guest_**DONOTDELETE**_*

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Posted 08 July 2005 - 12:36 PM

you saying, if you put your scope out at 9:00, you don't start observing until 11?


Pretty much. I'll usually put the scope out around 8ish, and won't start viewing until about 10 - 11.

EDIT - of course, keep in mind I'm talking about a 5" scope.

#18 Mike B

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Posted 08 July 2005 - 12:46 PM

Hi Paul-
I wonder if we viewed our observing environment with an IR device if it would change the way we go about picking our site(s)? Being a professional "building designer", i have become somewhat attuned to issues of "thermal mass", where materials like concrete, plaster, masonry, etc. (especially concrete-type materials on a roof!!) will radiate their stored heat often for hours after sundown! Depends on their mass, therefore thickness, but a 6-8" masonry wall, or a 4" concrete patio (plus sand/dirt below it) that has been in the sun for hours before sundown can emanate heat for some time afterward! I'd hate to think my 3-hour investment in my "Cat-Cooler" would be a total loss ;). Worse yet, could render drilled holes & CPU fans in our OTAs inconsequential?... or a $10,000 Dob with all the techno bells & whistles brought to it's knees (for a few hours, anys how) 'cuz of some low-grade roof-tile job next door.
:pmike b

#19 pstarr

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Posted 08 July 2005 - 01:15 PM

Mike.
I have tried everything with my building outside of a air conditioner. It is 12'x 12', all wood, no masonary, with white alum. siding exterior. I have a 26 ga. metal roof with ridge vent the whole lenth. 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.
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Paul
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#20 Mike B

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Posted 08 July 2005 - 02:08 PM

Paul,
Sounds right-arm... you've done yer homework! ;) Are you near other structures, or out away in a lawned area? Is "lawned" a word? :lol:
:cool:mike b

#21 Olivier Biot

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Posted 08 July 2005 - 03:48 PM

Hi Paul-
I wonder if we viewed our observing environment with an IR device if it would change the way we go about picking our site(s)? Being a professional "building designer", i have become somewhat attuned to issues of "thermal mass", where materials like concrete, plaster, masonry, etc. (especially concrete-type materials on a roof!!) will radiate their stored heat often for hours after sundown! Depends on their mass, therefore thickness, but a 6-8" masonry wall, or a 4" concrete patio (plus sand/dirt below it) that has been in the sun for hours before sundown can emanate heat for some time afterward! I'd hate to think my 3-hour investment in my "Cat-Cooler" would be a total loss ;). Worse yet, could render drilled holes & CPU fans in our OTAs inconsequential?... or a $10,000 Dob with all the techno bells & whistles brought to it's knees (for a few hours, anys how) 'cuz of some low-grade roof-tile job next door.
:pmike b


Yuo're absolutely correct, I can testify :)

When I observe at home, I have no other option than setting up my scope on a concrete patio which gives access to the garage boxes of the apartment where I live. The patio is exposed to the south, hence it accumulates LOTS of heat. On a hot summer day, I can "comfortably" observe the zenit on my knees, and still feel the warmth of the patio.

The roofing on the garage boxes also accumulates LOTS of heat. With Jupiter wandering lower in the skies nowadays, I only get very poor planetary images after a hot day :(

I still have zenit, east and west to look at, though :grin:

One day I'll buy a "power tank" and perform observations on more remote, less light-polluted and definitely "concrete-less" locations.

Cheers!

Olivier

#22 Mike B

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Posted 08 July 2005 - 05:51 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

#23 Joel

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Posted 08 July 2005 - 06:08 PM

I just found the answer to my own questions! :)

Here's a site detailing how to make your own SCT cooling tube: http://www.starcrwzr.com/cooler.htm and another one: http://members.tripo...cope_cooler.htm


This cat cooler project seems pretty simple. I started pricing materials for it today. Only thing I wonder about is the venting. If you look at the Lymax cooler it has vents that cut into the body to exhaust the air to the back. This homemade cooler does not. Maybe some vents could be cut into it?

#24 Joel

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Posted 08 July 2005 - 06:15 PM

Actually looking at the second page, he does an offset that allows a gap in the back to let air escape. The first guy doesn't.

#25 Joel

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Posted 08 July 2005 - 06:17 PM

Here's another cat cooler. :grin:


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