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Messages - Donnell Keown

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Light Pollution Topics / Re: "Transform your house from dark to dazzling!"
« on: February 09, 2018, 03:53:12 AM »
I love the alternate reality in all of these commercials where people consistently fail to perform common tasks like Christmas decorations, opening cans, mowing a lawn, wrapping a hose up (etc).

And camera tricks, where you have one of those LED tape up lightbulbs and it somehow lights a spot around a corner where no light would ever get to from the device and as bright as a 100w bulb.

You probably have nothing to worry about from the "laser light show" with all the exaggeration from the commercials. Nothing that a well placed towel rack (with towels) couldn't solve at least.

Reflectors Telescopes Forum / Re: Simple secondary dew prevention for Dob
« on: February 09, 2018, 01:42:49 AM »
So I'm starting to add this up if I need more than passive dew protection:

Portable dryer, $15, and/or:
Heat strip around $30-50, connects to:
Dew controller $105, connects to:
portable battery $?, connects to:
portable battery charger (if not included with portable battery) $?

So maybe another $200-250 by the time I'm done, unless I'm missing something.

Yes. The dew shields for the Dob and the finder scope. But you can make them yourself.


Star testsStar testsStar tests

Beginners Forum / Re: Hotech Collminator worth the $$$?
« on: February 08, 2018, 10:41:48 PM »
My point is that you spend all that money, go through all that grief and still end up not satisfied.

I spent $85 on a laser that I never used because I tricked myself into thinking I needed one (and yes, at night is supposed to be a good point), but in the end, I always set up well before dark and the laser never worked worth beans to begin with due to...ready for it...focuser slop.

Not the right tool. Time to buy another one or go through a bunch of grief to fix it so it'll work.

Instead, I look at that little plastic cap I've been using for decades that has worked RELIABLY all this time and weighed the options.

It goes back to what do I really need?

For you tweakers, keep on spending. However, for those of you that aren't and have a budget...well...consider simplicity.

I've passed through Marathona few times on my way to elsewhere. Most times, on one end of town or the other, is a photo radar speed trap. When the speed limit drops to 35, they mean 35. 36 MPH will get you a ticket!!!!!!!!!!!! I live in Arizona, we don't have front license plates, so, I've not gotten an invitation to court! But, I have had my picture taken!

Other than the above, a great place with dark skies!

Thanks for the info, do you guys know what the hole diameter in the back of an Edge 8 is? I've read 42mm, but not 100% sure.

FS = 0.5*D*L/X +L/FN (for 100% vignetting) or -L/FN (for 0% vignetting)

I did 0.5 x 42mm x (183mm/1.5) = 2562?? - 18.3 (183mm/10) = 2543.7??

FS = field stop with calculated illumination.
D = 38mm aperture in back of scope
L = 125mm (Ernest's estimate, but sounds about right)
X = 305mm (Ernest's estimate)
FN = 10

UseFS = 0.5*D*L/X (for 50%) +L/FN (for 100% vignetting) or -L/FN (for 0% vignetting)
and you get 7.8mm + 12.5 = 20.3mm for 100% vignetting
and you get 7.8mm - 12.5 = -4.7mm for 0% vignetting
The formula simply doesn't work

Here is a table with values of x = 1.5, 1.0, 0.8, 0.7, 0.6 and 0.5 times A
(You KNOW it isn't less than 1.0A)
D.... L..... X.... L/FN.....................  100% Vig..................0%Vig
38 125 304.5 12.5  7.799671593 20.29967159 -4.700328407
38 125 203  12.5  11.69950739 24.19950739 -0.800492611
38 125 162.4 12.5  14.62438424 27.12438424 2.124384236
38 125 142.1 12.5  16.71358198 29.21358198 4.213581985
38 125 121.8 12.5  19.49917898 31.99917898 6.999178982
38 125 101.5 12.5  23.39901478 35.89901478 10.89901478
I can tell you for a fact that illumination is not zero at a field stop of 46mm so either the formula doesn't work, or
the opening in the back of the scope is >38mm (and it isn't on the 8") or L is <125mm, or X does not = 1.5A
I think the formula is off.

I too, have one of these.

It was originally sold Mar 2, 1982 so it is very early. I acquired it from a Craigslist ad in 2014 for just $100. These do come up from time to time in various places like craigslist, ebay, astromart, cloudy nights and at least on the latter two sites, you can post a Wanted ad. Truthfully, I would suggest that you use the SEARCH ALL OF CRAIGSLIST sites and actively search for one that way. You might be amazed.

I would file a claim and send it back or negotiate a much lower price.

I believe that the Schmidt corrector of the Comet Catcher has about half the correction on each side of the corrector plate which would make the corrector too thin to support the secondary without flexure of the corrector or even damage to the corrector if the OTA is bumped. This half-and-half approach maximizes coma correction and minimizes the mass of the corrector. The thinner corrector is likely the reason for Celestron's choice to have the secondary mounted on the unique "sled and stalk" focuser.

If you have any interest in imaging you will needCelestron Comet Catcher T-Adapter, #93634 otherwise it is highly likely that you won't be able to reach focus using the standard 1.25" focuser and a 1.25" camera adapter. Not that there is a compelling need to do so, you could acquire a T-Thread to 2" adapter and with the Camera Adapter, you could use 2" barrel eyepieces. A 19mm (1.25") Panoptic is such a wonderful eyepiece for this scope yielding a 2.5 degree field of view!

The Parallax Rings (160mm) work perfectly on my Comet Catcher although they are a bit heavier than the original Celestron Comet Catcher rings that came with Comet Catcher Packages that included a mount. Finding a set of Celestron Comet Catcher rings separate from a Comet Catcher OTA is unlikely as they are usually sold together. I toyed with using Losmandy DVR160 rings but I would have had to remove the corrector and remove the 1/4x20 tripod mount to place the rear ring. I put the project off and then I came across a used set of Parallax rings so I still have the DVR160 rings, new and unused and just haven't gotten around to listing and selling them.

If you need a pdf of the Comet Catcher manual which includes instructions for collimation, I can help with that. Collimation of this OTA can be a bit tricky because it is so fast.

[Edited for Grammar and Spelling]

Beginners Forum / Re: $20K+ refractors?
« on: February 03, 2018, 05:01:15 AM »

Or the color correction may be better... One thing for sure.. The focuser is certainly better on the A-P..

At the top of the heap, there are four main players, Astro-Physics, TEC, Takahashi and TeleVue though TeleVue does not make large scopes and plays a somewhat different game.

Both A-P and TEC do everything in house, the design, the mechanical and optical fabrication, the assembly and testing. Takahashi and TeleVue do the design, the assembly, the testing in house but go outside for the optics, someone else does the optics, both in Japan. The A-P and Tec model give them more control over the final product...

'nuff said.


Mounts Questions & Expirience / Re: Classic Meade LDX-600 Mount problems
« on: February 02, 2018, 10:20:32 PM »
Now you have your visual mount!
Clear Skies!

Give yourself permission to go on furlough, so to speak. Do NOT start selling off your gear. Store it carefully under dust covers. Explore other areas of astronomy or completely different interests. Come back when you feel differently. Good luck.

Totally agree...

Beginners Forum / Re: Which would you pick?
« on: February 02, 2018, 08:12:32 PM »
I went through this very thing a year and a half ago. I got a Dob 8" The wow factor was there at first. Then I wanted too know what I was looking at. Wow turned into frustration. The key is, I wanted to know what I was looking at. If it just the wow factor go with the Dob. It's east it is a good beginners telescope. But if he really wants to know what the name of that first cluster. Then the goto may be a better way to start. I still have my 8" Dob. I've added a 12" push too and a Celestron 6se. But at the very beginning the 8" dob was a wonderful way to get me excited. But then again I'm 67 retired and not a teenage boy.

Reflectors Telescopes Forum / Re: What scope is this Meade?
« on: February 02, 2018, 06:26:06 PM »
Robert,As long as you're good with tools build yourself a Dobsonian mount and incorporate a degree circle. There is more info in the Equipment Forum. With the circle and a digital level you will make your Dob a push-to for finding objects on an astronomy app like Sky Safari for your phone or tablet. Also, get a Telrad zero power finder; you won't regret it.

Eyepieces Questions & Recommendations / Re: APM coma-correcting barlow
« on: January 31, 2018, 09:52:38 AM »
Doesn't sound kosher to me. Introducing coma correction in optical systems that do not need coma correction? And it does not play right with the Leica Zoom. Two strikes in my book. Actually, with the Leica Zoom, that would be a continuum of strikes.


Beginners Forum / Re: Alignment Frustration: Celestron 6SE
« on: January 31, 2018, 09:11:46 AM »
too many think its batteries i had the nexstar8 when it first came out and had that for like 8 to 10 yrs and later the 8se and the 6se i only use rechargable battiers and never used used ant kinda power tank and my battiers never died once, it even lasted the whole weekend.

General Astronomy & Observing / Re: Do you feel this is going too far?
« on: January 31, 2018, 06:19:51 AM »
Has anyone considered, intentional or not,
that this is space weaponization research?
Testing satellites that release many projectiles at a specific time in a specific direction,
and calling it advertisement/entertainment could provide great cover for nefarious purposes.....

It is typically the other way around, and that some already weaponized concept is finally thought of by the commercial world. No doubt that stuff like this is already in the inventory, except it probably would not leave any burn up trails as that would be advertising that it has been deployed. So probably much more sneaky than what this proposal is doing.

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