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Dumb question about Hubble artificial star...

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#1 jrbarnett

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Posted 10 January 2013 - 11:04 AM

I've used the artificial star at dusk to collimate my C5 OTA.

I don't know why I waited until dusk, but it seemed right. I didn't even try prior to twilight.

My (dumb) question is this - can you use the Hubble to collimate in full sun? I couldn't find anything to say that you couldn't, but...

Thanks!

- Jim

#2 jimarshall

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Posted 10 January 2013 - 11:46 AM

I seem to remember someone collimating under shade trees during daylight hours a couple of years back. I think it was in the vendors forum.

edit: here's the link http://tinyurl.com/a646jzk

#3 Midnight Dan

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Posted 10 January 2013 - 01:27 PM

You just want some decent contrast between the point of light and the background. So if you can put in a shady spot it would help. But you should be able to do it in the daytime.

-Dan

#4 astro_baby

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Posted 10 January 2013 - 01:36 PM

I have read that you can so long as the unit is in shade to give the star some contrast.

#5 DwainM

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Posted 10 January 2013 - 02:21 PM

Jim

I used mine in the daytime at 200 feet from my scope. I had the scope in the garage and the HO across the street in the shade of a neighbor's house with a dark fence in the background.
Worked great.

Dwain

#6 Jon Isaacs

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Posted 10 January 2013 - 04:04 PM

I've used the artificial star at dusk to collimate my C5 OTA.

I don't know why I waited until dusk, but it seemed right. I didn't even try prior to twilight.

My (dumb) question is this - can you use the Hubble to collimate in full sun? I couldn't find anything to say that you couldn't, but...

Thanks!

- Jim


Jim:

I use mine during the day without a problem, mostly to look a CA in achromats. I do prefer the star test with a real star... Build-wise, let's just say you can tell right off that Howie Glatter did NOT make it..

Jon

#7 Gene7

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Posted 10 January 2013 - 04:47 PM

Artificial Star

I like to use an artificial star for several reasons, such as to have reliable and repeatable viewing, adjustable brightness, comfortable viewing, and not have to chase it all over the sky. Reliable viewing is best achieved without the upper atmosphere disturbance and over tree shaded lawn after dark when there is no wind. Of course I want the hole diameter to distance to be over 1 million, so I want the measurement of the system to be known.

A reliable system is made by drilling a small hole in thin phenolic or shim brass. Mic a sewing needle and grind a chistle point on the end. Create a virtual image as reflected in a polished stainless ball. Focal length is D/4. A 3/16 inch diameter ball makes a nice system. Back up hole with a slightly larger high powered LED junction on a high powered heat dissipating star. You may only need to run at a fraction of its capacity. Use Ultra White. Lithium recharge-ables at 4 volts are great with a dimeable pot and bias resister. Mount all in a blackened box with switch, pot, and exit hole. Gene

#8 Scott in NC

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Posted 10 January 2013 - 05:01 PM

Build-wise, let's just say you can tell right off that Howie Glatter did NOT make it..


Yep. Fortunately it didn't cost $200, as the HG version probably would have! ;)

#9 beatlejuice

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Posted 10 January 2013 - 06:50 PM

Yep. Fortunately it didn't cost $200, as the HG version probably would have!



If it did, maybe it could be designed so as not to need 200ft of real estate to use it. BTW I love my Glatter stuff.

Eric

#10 Jon Isaacs

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Posted 10 January 2013 - 07:19 PM

Build-wise, let's just say you can tell right off that Howie Glatter did NOT make it..


Yep. Fortunately it didn't cost $200, as the HG version probably would have! ;)


Cute... On the other hand, if Howie had made it, I would probably use it instead of a star...

Howie's stuff costs money but it's well made and in the long run is the least expensive because it's life time stuff. People balk at a $200 collimator but spend $500 on an eyepiece that won't be worth a darn if the scope isn't collimated.

Jon

#11 Scott in NC

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Posted 10 January 2013 - 07:56 PM

Howie's stuff costs money but it's well made and in the long run is the least expensive because it's life time stuff. People balk at a $200 collimator but spend $500 on an eyepiece that won't be worth a darn if the scope isn't collimated.

:ubetcha:

I was just poking a little fun, Jon. I believe in buying quality stuff, too (yet I do have a $24.95 Hubble Optics artificial star, lol).

#12 Jon Isaacs

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Posted 11 January 2013 - 09:03 AM


Howie's stuff costs money but it's well made and in the long run is the least expensive because it's life time stuff. People balk at a $200 collimator but spend $500 on an eyepiece that won't be worth a darn if the scope isn't collimated.

:ubetcha:

I was just poking a little fun, Jon. I believe in buying quality stuff, too (yet I do have a $24.95 Hubble Optics artificial star, lol).


Yeah, I know you were just poking fun but I had to take the opportunity to give Howie a plug... not that he needs it anymore... I have had my original Howie Glatter collimator for somewhere around 12 years and back then, laser collimators were not common, Howie was making his stuff but not many people knew about it... So I got into the habit of spreading the word...

I have the Hubble Artificial Star, I was somewhat underwhelmed when I first saw it and it didn't really work for me when I tried to collimate my NP-101 with it.

Jon

#13 turtle86

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Posted 11 January 2013 - 02:21 PM

I've also been able to use mine during the day by having some shade around it for contrast. I'm a little underwhelmed by the build quality too, but the Hubble unit doesn't really require the precision or ruggedness of a Glatter collimator. It does work and the price is reasonable enough. All the same, though, I personally find it easier to collimate on Polaris so my unit doesn't get a lot of use.

#14 jrbarnett

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Posted 11 January 2013 - 05:10 PM

Glatter. Bah. Give me passive collimation tools any day.

It's fun to use a Glatter to collimate then switch to Catseye tools and use the CDP method to see how far off the Blugster left you. :grin:

- Jim

#15 Jon Isaacs

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Posted 11 January 2013 - 11:55 PM

Glatter. Bah. Give me passive collimation tools any day.

It's fun to use a Glatter to collimate then switch to Catseye tools and use the CDP method to see how far off the Blugster left you. :grin:

- Jim


Not using the Blug...

Jon

#16 johnnyha

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Posted 12 January 2013 - 05:42 AM

I tried my Hubble artificial star once, and the amount of thermals coming off the ground between me and the star was ridiculous.

#17 Pinbout

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Posted 12 January 2013 - 08:15 AM

and the amount of thermals coming off the ground between me and the star was ridiculous.



:waytogo:

daytime star test

#18 Eddgie

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Posted 12 January 2013 - 12:18 PM

SCTs can be problematic to collimate during the daytime using an artificial star.

You can of course collimate it, but when the scope is horizontal, the mirror carrier will settle evenly against the baffle at the front and the rear of its length.

When you point the scope upward though, the mirror will take a different orientation. One side of the mirror will be held up (or settle against) the focuser rod threads, while the other side of the mirror carrier will tilt down to rest against the baffle.

The amount of shift away from perfect collimation will depend on the amount of play between the mirror carrier and baffle and on the thickness of the grease film, but in most cases, given a few minutes, the weight of the mirror will cause it to sink though the grease film.

For this reason, if you want the absolute most perfect collimation (which despite popular belief that it must be exact for the scope to perform decently), you should collimate with the scope pointing at the sky.

You should also always approach final focus by using a counter-clockwise motion of the focuser knob. There are several good reasons to always do this, but from a collimation standpoint, approaching using CCW turns "Lifts" the primary mirror into position so that the focuser screw side comes closer to its final rest position every time.

If you focus using back and forth turns (chase focus), the mirror can continue to move slighty after you release the know as the mirror settles against the baffle.

If the mirror is fairly tight on the baffle you might not have and issue, but for people using SCTs with some mirror mirror shift while focusing, collimation should always be done with the scope pointing up and with the final motion of the focuser knob in a CCW direction to test final collimation.

I have not collimated mY C14, C8, or C5 in years. Lots of time people that are having to tweek collimation are having to do it because they are fighting mirror shift.

I you follow this practice, you elminate a lot of fine collimation fussing.

Also, approaching focus using CCW motions is really the best way for viewing as well.

If you overshoot a tiny bit, most people have enough visual accomdation that their eye will automatically bring the center of the field back into best focus. I always make my final approach using CCW motion (Inward on refractors for the same reason).






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