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Best daytime collimation target

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#1 grif 678

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Posted 21 August 2019 - 08:00 PM

I want to tweak my newly acquired small SCT. I have read that a trailer hitch ball, or a silver round Christmas ornament were good. Any better ideas.



#2 RazvanUnderStars

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Posted 21 August 2019 - 08:14 PM

Whatever it is, it has to be quite far, see https://guysmathastr...n-star-testing/.



#3 markb

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Posted 21 August 2019 - 08:51 PM

Christmas ornaments can give double images as they are silvered inside, not good. Been there, did that.

I picked up a chrome 3/4 ball bearing as a target, but the sharper curves of a 1/4"-1/2" bearing would give a better point reflection of the Sun. Smaller can be better, particularly if you are working at minimjm distances. Nonetheless, it works well in full Sun. I keep forgetting to sneak glue one on a nearby Sun illuminated sign or plle. Easily bought on Amazon, don't bother looking locally for these tough to find bearings.

But my usual target is the very affordable and well made Hubble Optics 5 star Artifical Star (flashlight body with 5 laser drilled holes of different diameters). $20 IIRC.

There are formulas for calculating minimum distances, and the warnings about doubling those minimums for maks and possibly SCTs should be followed, otherwise false indications of spherical aberrations will show up. Daytime Rochi tests are easily done.

Collimation is easily done with these artificial star targets.

Note, however, that even small breezes or heat driven air movement can impact daytime targets! I had noticed this outdoors, even over grass, but the real shock was seeing diffraction rings break up indoors, just from a person walking by the optical path, creating a breeze.

#4 Defenderslideguitar

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Posted 21 August 2019 - 09:08 PM

I read where someone was using the small piece of metal on a telephone pole that was quite a distance away but was sunlit 

 

I took a small brdige plate off a fender stratocaster guitar   and  it to the telephone pole 500 feet away      it was a good idea     but    the sun only hit it for a small window of time that was not helpful

 

a small flashlight  at the right height and distance would work I guess


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#5 vtornado

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Posted 21 August 2019 - 09:23 PM

You can make an artificial star.

 

You need the smallest sewing needle you can find, and aluminum foil.

Put a piece of cardboard behind the foil, and poke the needle through as gently as possible.

DO NOT drive the needle until the body is though the foil just the smallest part of the point you can manage.

Place this in front of a flashilight.  You will have to have the telescope about 50 ft away.  I assume farther would be better.

This will not be a perfect collimation, but it will be close.  You will have to fine tune with a star.

If you don't have a guided mount, the North star is best,  because it does not move much.

 

===============

P.S.

 

as others have mentioned, this is a gross adjustment.   If you jar your SCT you may have to do this.

Also I replaced the phillips screws with hex cap nuts, and had to recollimate from scratch.

This saved me from monkeying with the scope in the dark at night, taking up precious observing time.


Edited by vtornado, 22 August 2019 - 12:35 PM.

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#6 cytan299

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Posted 22 August 2019 - 06:04 AM

If it is just a tweak, I'd suggest skipping indoor collimation and using Polaris. IMO, even if you do it with an artificial star indoors or outdoors, you still have to finish collimation with a real star.

 

A quick check to see to see if you're close to being collimated *without* using an artificial star is with this method:

 

http://www.mira.org/...ures/collim.htm

 

cytan


Edited by cytan299, 22 August 2019 - 06:09 AM.

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#7 WadeH237

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Posted 22 August 2019 - 07:20 AM

If it is just a tweak, I'd suggest skipping indoor collimation and using Polaris.

This.  Totally this.



#8 luxo II

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Posted 24 August 2019 - 09:14 AM

Use a bright star, as above, on a night with good seeing. If the seeing is poor don’t bother.

Daylight targets are fraught with turbulence due to thermals which will defeat any precise collimation.

If you have a huge cool underground space with a long light path (apartment block) then it is possible to use an artificial star.

Edited by luxo II, 24 August 2019 - 09:18 AM.



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