Star Perfection - Calling Newtonian Experts

[cjr]

Hey all,


Doing some star tests tonight, I have been working on getting nicer stars at the moment so far i have triple checked collimation, checked for pinched optics, cut down the focuser, made up and printed a clip cover and made an apeture mask to cover the spider vane bolts.


I'm pretty sure by the looks of my diffraction spikes the spiders might not be in line properly even though i put a set of calipers on them to make sure they were equal length i look like i have goofed it some where.


Attached is a copy of a star test on canopus. I'm pretty happy with it other than fixing the spikes misalignment. One thing that I'm not happy about is the dark area around the diffraction spikes. I'm not sure if this is just something to expect with a newt or if i can get a more even spread of light all the way around.


I have cut down and blackened the focuser to stop it impeding in the light path but its still probably 20mm into the light path at the moment, I'm wondering if this might be the cause.


I might also be chasing something that's not possible.


Any opinions would be welcome so i can butcher my scope further :rofl:

[Saturnine]

Hi Cody

The diffraction spikes look fine, like they should. Don't start getting OCD about every little perceived flaw. If your spider vanes were slightly not at 90 deg. to each other then you would get a twin spikes , might not look the prettiest in images but your scope wont self destruct and it will only be on bright stars. Also, I don't see any dark areas around the spikes so can't help you there.
In what way do you think that the diffraction spikes are misaligned and the focuser drawtube intruding into the tube by 10 or 20mm is not going to have any noticeable effects with visual observing or photography, that I'm aware of.

[RyanJones]

Hi Cody,

Like you, I’ve been butchering my scope recently to chase that extra few percent. I live in a Bortle 8 area ( although I think even that is conservative) so most of my work has been to limit stray light and gain better contrast. To me your spikes look good. The focuser tube will cause vignetting more than affect the spikes in the center of you field. If you’re interested in the affects of your light path you can put the details of your OTA into “ Newt for the web “ ( google search it ) and it will show you the ray trace of your OTA and any obstructions.

Cheers

Ryan

[Startrek]

Cody
Star diffraction spikes look good to me
Like Jeff said don’t be fussy about the spikes being like single swords or needles
You can spend hours using geometry trying to get the spider vanes perfect, the answer is they aren’t perfect, and the bigger the aperture the harder it is
Yours look fine
One advantage about a newtonian is that I use my spikes to fine focus before imaging ( never used a Bahtinov mask )
I use APT with my 2600MC set to live view bin 4x4
Then pick a single star around mag 2.0 to 3.0 in the region of the imaging target at least 50 deg in Altitude, centre the Star then take 15sec exposures.Switch on zoom and adjust histogram to get a good close up of the Star and its diffraction spikes. Adjust fine focus in and out with my JMI focuser until it’s a tight and sharp as possible ( usually takes up to 5 or 6 exposures until I’m happy) then I’m done. Never lets me down always tight focus. Did the same for my old Canon 600D on BYEOS and worked great.
One caveat with the way I focus, you must ensure you pick a single star ( not a double star) as it can throw you off with focus

Keep up those great images

Cheers
Martin

[xelasnave]

Hi Cody..if you want a project...consider a baffled dew tube..look at Hubble the tube in effect goes well past the secondary and is baffled...also consider baffling the current tube...I don't have comparisons of before and after but by the eye I believe contrast is improved...I contend that although the inside of a tube is already black the less light that falls on it the better hence baffling and an extended baffled "dewtube" means less stray light.
Your star looks good to me...
Alex

[RyanJones]

Here’s a before and after of what you’re saying Alex. Just look at the difference in reflection off the side of the tube.

[multiweb]

That's something that shows on any scope that has spider vanes. The different colors cause a rainbow so they don't appear in the same areas. If you separate the colors and have a look at the individual channels you'll understand. Your field looks good and your stars as good as it gets IMHO.

[ChrisV]

+1. Star looks brilliant to me
Ryan - did you do that baffling? Instructions please ...

[xelasnave]

Well done..now think if you had a two foot dew tube ..think of the stray light firstly that never reaches into the tube that is simply shielded by the dew tube..then think of the light that remains and how for want of baffling it bounces around that two foot few tube..do some drawings showing light paths and you will really want a baffled dew tube I bet.
Alex

[RyanJones]

Chris - I’ve PMd you

Alex - You're 100% right. I do currently have an excess weight issue that I’ve spend a rediculous amount of hours making work ( to great success ) on my mount. Despite the obvious gains by adding a tube extension in front, at this stage I’m reluctant to add the weight of it. For anyone else without these issues though it would be well worth doing.

[cjr]

Hi guys,

Sorry i went MIA for a couple of days there.

Thanks for all the great replies.

I think you are all correct in the sense of not worrying too much about the perfection and where i got was good enough.

I think on a high res image the flaws become more present i can see that there is split diffraction spikes and the darkness around them which i can't control as i imagine that's an exact side effect of the light dispersing around that point.

I think like most of us i am being a little OCD in trying to get anything better out of the image which can be a good and a bad thing.

That tool looks excellent too Ryan ill have to check it out.

xelasnave - i am actually looking at printing some baffles for the tube in the near future just waiting on some matte PLA so i can reprint my current stuff and have a go at the baffles. I agree from all i have seen baffling and flocking increases contrast considerably. Those images are really good for reference too Ryan.

Although i still love imaging with the 130P i have fixed all my diffraction spike issues over the last couple of days and purchased myself a neat little refractor :lol:

Shall hopefully have some images of that in the near future.

Cheers