Happy but baffled... ETA Carina

EzyStyles (Eric) · #1 27-09-2006, 02:27 PM

hi guys...
im so confused right now. Last night i spent from 4pm - 2 am and only captured 1 single object before the clouds came in. The Baader MPCC came in the mail yesterday and it works 'i think' perfect for my F/4 scope can also screw 2" eyepeices in.

The problem, i have attached 2 crop images of Lagoon single frame. The first one as you can see from the bright star diff spike, it is in focus but the stars are elongated. The second pic the stars are nicely rounded but the diff spike from the bright star isnt in focus?? I only noticed this after using the MPCC. I also tried Merlin's Lumicon Coma Corrector same problem. I have played around the collimation last night it didn't help. Its not guiding/tracking as I was monitoring the autoguiding the entire image.

Later in the night, i imaged ETA the stars look more rounder with focused diff spikes?? maybe due to the object closer to the SCP?

I really don't know.. Im beginning to dislike F/4 scopes.

Oh the Baader MPCC works magic! Compared to my previous ETA shot without it, There is hardly any coma at all.

Lee · #2 27-09-2006, 02:32 PM

Eta Carina! - don't you sleep Eric!

I'm going to stick with my f/6, sorry I can't help you out.....

EzyStyles (Eric) · #3 27-09-2006, 06:24 PM

i did at 2:30am

want to swap scope lee?

Lee · #4 27-09-2006, 10:27 PM

I'll swap you for mine after I cut it in two hehe

2020BC (Bill Christie) · #5 27-09-2006, 10:48 PM

Eric,

I have the same problem in my SN-8 if I use the MPCC and the scope is not well collimated.

When it is well collimated the MPCC gives nice round stars right across the field of view.

If it's not well collimated then I see the shapes you are seeing in image #1 and judging focus is more difficult.

EzyStyles (Eric) · #6 27-09-2006, 11:10 PM

cheers bill. so you definitely think it is the collimation? im having a real hard time seeing weather my collimation is correct or not. I'll triple check it maybe im just doing it wrong

back to newbie questions again...

2020BC (Bill Christie) · #7 28-09-2006, 08:07 AM

Good luck, Eric. I find collimating my Schmidt Newtonian to be a right royal pain. I keep reading how easy it is - and then there's the reality.

I can't say for sure if you've got collimation problems. The example images you posted look like what I see through the MPCC when my scope needs collimation. When I'm collimated the wierd shape of the stars disappears and I get round stars right across the field of view.

BTW I can now get good, repeatable, and easy collimation of the primary mirror by using a device called a Barlowed laser. Sounds complex but it's just an ordinary barlow with a paper disc stuck to the end. A hole is made in the centre so laser light can come through. If you have a centre-spot on your primary mirror this barlowed laser creates a shadow of the centre-spot on the paper disc. This shadow is unaffected by focuser slop or the laser being incorrectly seated in the focuser. The efect is to give a more accurate collimation of the primary.

The LXD-75's secondary, for me is a nightmare at the moment. When I touch the secondary screws the whole secondary mirror will spin !

It's very difficult to precisely collimate a secondary that's doing that!

tornado33 · #8 28-09-2006, 08:40 AM

Hi folks.
My 6 inch f3.6 SN is very touchy re collimation. Its primamry is fixed, and so then only means of adjustment is in the secondary. It has a metal pin in the holder to stop it spinning when I adjust the screws. Ive found a standard laser collimator isnt too bad, just adjust till laser lands on centre spot on primary. However I stil get an odd effect, stars in the top left of the field tend to be out of focus but elsewhere not too bad. This effect is far worse without the MPCC. Another odd phenomenon, when I collimate using star testing, if I use an eyepiece (4.7mm Nagler) the star will look good with even diffraction rings, but if I use my 2,8x Barlow star looks uneven, if I then adjust so it looks good, it then is out when looking without the barlow.

I once used a mates hi tech grid laser collimator that projects a grid, allowing one to check for everything even for an out or parrallel focuser, but on my SN I got all these wierd reflections I couldnt interpret at all. So it seems that SN's at least can be an odd thing to collimate.

For a normal Newtonian I just recoment adjusting the secondary and primarywith a laser collimator, if really fussy can tweak primary with star testing, rack focuser out past focus till u get the donut, adjust primary till "hole" is dead centre, using a medium to high power eyepiece.
Scott

EzyStyles (Eric) · #9 28-09-2006, 11:41 AM

thanks guys. i really think they should make newt with fixed mirrors all lined up for you. will definitely makes things easier.