All MAK and SCT Owners

[FlashDrive (Poppy)]

This should be helpful in checking collimation ....

https://www.youtube.com/watch?v=vMkURZdJ84Q

Very helpful I reckon

Col...

[mental4astro (Alexander)]

Thanks Flash!

Worth exploring. Without the pressure of beckoning stars at night, this DIY artificial star allows me to tinker during the day. I been wanting to tinker some more with my Cats, weather's been so difficult, and this looks like a neat tool

Alex.

[casstony]

With a long enough distance inside the house I use a hubble artificial star to collimate my 8" Edge SCT. Collimating early in the morning allows magnifications of a few hundred times to be used and being closer to focus gets it more accurate.

[mental4astro (Alexander)]

One thing I have noticed with scopes that experience mirror shift is collimation changes when the focus is adjusted and the primary shifts position. Major pain in the bum.

Geoff White told me of a simple technique that deals with mirror shift when focusing, is to always wind out in the one direction and then adjust focus in the opposite direction. This restores the primary mirror back into the position that had the target centered.

This same technique applies for collimation - you wind out a bit further than you would for the focusing proceedure to get a larger doughnut. You then wind in to reduce the size of the doughnut and this also sets the primary mirror back into its optimal focused position.this way when you focus, the mirror shift both recenters the object and collimation is also at its optimal.

Checking collimation also allows you to check for astigmatism in the optics. Rather than explain everything again, have a read through this following IIS link:

WARNING: Scope assembly practices may be vexing many SCT's and Maks

Alex.

[multiweb (Marc)]

I don't think his star is at 50m away, more like 30m. I'm also not too keen on looking at anything that much defocused. I don't know if it matters for a MAK as I've never had one, but for a newt or cassegrain, especially for a newt you can still have non concentric shadows that far out of focus for a system that's properly collimated. I love artificial stars and they have their place, but you need to add extension tubes at the back so your mirror spacing is as close as it is when focused at infinity and look at diffraction rings rather than secondary shadows. Then you finish with a real star test in any case for the final tweak.

[Outcast (Carlton)]

I watched it; I think he actually said 15 metres; which looking at it sounded about right...

Is 15 metres really far enough away?

How powerful an LED torch do you need..?

I have a single led LED Lenser... If I need to buy a more powerful LED Lenser I might as well by a dedicated artificial star...

[Wavytone]

Mmm .. old news ... by about 6 decades. Using an artificial star is described in one of the ATM volumes (Ingals et al).

Key point is to set it up at least 20 focal lengths from the scope in stable still air, which for larger scopes might be difficult or impossible, however.

While my apartment does have a long basement - more than adequate to use an artificial star to align my mak Newtonian - it isn’t long enough to do the job for my MK91 which requires over 60metres... so for that it has to be a real star.

While star testing in daylight is possible in theory (eg sun glinting off a distant object) having tried it the atmospheric turbulence was so bad as to make this useless.

Even his method for making the pinhole is crude... the article I recall recommended honing a needle point then an arrangement to drop it precisely on tinfoil placed on glass. Virtually any other method results in a ragged miss-shaped hole.

A modern way to make precision pinholes exists - using a laser - however a beam with the required power poses a safety hazard to eyes and skin, and is illegal outside a company with an established laser safety system.