Collimating a Celestron Nexstar 6se/8se using a Star

[@derrickdzurko2068]

Thank you!

[@ronmac1832]

Useful- thanks!

[@freddyking8742]

If you could help me, I have a SCT and it seems to be collimated but the stars are like yours, not pinpoint and wobbles, is this normal for SCT? I have a Dob as well and it is pinpoint and the stars do not wobble. Looking at stars with SCT seems to be disappointing, moon looks good, terrestrial viewing is great, I can see ants on pole 30-40m away (clearer than the dob), stars just look crap. Do I have a dud?

[@jamesw5713]

Going to do this on my 6SE tonight for the first time. Fingers crossed 🤞

[@jedislayer0719]

I have a question about 130SLT astrophotography. I’ve been following your method for a while and took some amazing pictures, but I noticed that over time, field rotation and imperfect tracking slowly cause the object in frame to drift. Out of curiosity, how much more of an issue is this with a barlow lens? I figured that since it is zoomed in more I would have to correct more often, but I just wanted to ask how frequently I will need to do this.

[@kylemccaslin]

You are correct that adding a barlow forces you to do corrections more frequently. Theres not going to be a perfect rule one how often, but generally speaking, it'd expect it to be similar to the barlow multiple. E.g. if you use a 2x barlow, then you will have to halve your exposure time per image and double your current adjustment rate (atleast for the drifting FOV). You also have to expose for x^2 = 4 times as long to get the same signal to noise. You do get increased resolution, but its not worth it since it makes your sessions both more tedious and 4x as long for the same S/N.

[@edwigesdemello7441]

Hello, thanks for the video. What software is on the computer?

[@kylemccaslin]

SharpCap

[@georgewashington7444]

Insulating your tube/dew shield with reflectix (like shiny bubble wrap) allows instant use of your sct with steady images. Also, most scts are shipped with corrector plate tightened far to tight causing it to warp and a stress point to break these screws should be backed off slightly @ 1/5-1/4 turn. This will improve image noticeably.

[@kylemccaslin]

Yeah, a dew shield would be a nice accessory. I've been in a few situations where having one would've been fairly significant, but don't think they are terribly important most of the time. And great input, did not know that.

[@markm75]

I've wondered if reflectix is of any benefit when the telescope is in a dome. For awhile i had it on my scope, but i wasnt sure in the dome scenario it benefited.

[@Rubik3x]

Thanks for the tutorial. I'm having trouble seeing what is wrong with the "doughnut". What do you mean by the "shorter area"?

[@kylemccaslin]

It's that the donut should be perfectly symmetric. The dark circle should be perfectly in the center, not closer to one side.

[@Rubik3x]

@@kylemccaslin Ahh. Got it. Thanks.

[@joshuaparsons4912]

Dang, where was this video last week for my 4se!

[@michael9061]

Great videos. Ive been looking at a $500 130 slt or $1500 6se. What do you think? Is the 6se worth the extra money? Is it good for dso?

[@georgewashington7444]

Get a 8” cheapy dob, best first telescope to purchase. No go-to stuff. Learn the sky using a Orion deep-map 600.

[@kylemccaslin]

Really depends on what you want to do. I've found the 6se very convenient since I like doing time-lapses of the planets. The size of the aperture and quality of the optics are pretty good in my book. But, for DSOs without a Focal Reducer, I find it very much lacking. Also quite expensive new. The 130slt helped me first get into Deep Space, but do bear in mind that I modded the scope and drove an hour to darker skies to shoot. That's not always an option for everyone. If you don't mind tracking things yourself, an 8" dob can be a good option as george suggests. It'd be really hard doing the timelapses, but the larger aperture has the potential to provide you with better individual stills. But a really nice thing to try (if you have a DSLR of some sort) is just going out a little ways away from the city lights and trying your hand at some wide-field Milky Way shots. That's the easiest way most people start with DSOs since wide-field is just so accessible. And as always, give the used market a look. There can be some ridiculously good deals there. If your in a big city, it almost doesn't make sense to get something brand-new.

[@michael9061]

@kylemccaslin thanks for your reply. I ended up getting a 130slt for $375 AUD. Going to do your mods and get a $200 dslr and try to emulate your shots

[@michael9061]

@@georgewashington7444 8"dob does seem like good value. I picked up a 130slt for fairly cheap. See how it goes.

[@exif6839]

I have tried this with my EHD800. It is very difficult to collimate due to no exact measurements of the symmentry of the diffratciton rings and also the influence of the heat by targeting the adjustment screws. So for my opinion it is not the best solution to operate the collimation with such a star at all. additonally negative effects due to bad seeing. Im changed over to a collimation system with camera. but here we have also a lot of problems to do this in a perfect way because the camere only sees a very small round picture in the middle and mots of the camera resolution is lost. all together this collimation is a game with unknown end. For the best results an optical bench with plan parallel mirror and a laser system is necessary.

[@kylemccaslin]

Very fair point. The method I use is absolutely very qualitative and somewhat dependent on the seeing. I think it gets you 80 - 90% of the way there though without additional hardware. Certainly agree that a numerical camera-bazed measurement would be better, and a true optical calibration test bench with a controlled light source would be the absolute best. Thank you for the comment!

[@krishnamurthym595]

great video. a newbie question if you don't mind. so you attached a camera in place of the eyepiece and connected it your laptop with a USB? I don't understand how your display is showing you the primary mirror.

[@kylemccaslin]

Well, to be clear it's showing me a super out of focus image of a star. It simply looks like a donut because that is what the telescope looks like from the front - a large circle (the primary mirror) with an obstruction in the center (the secondary mirror). So you're sort of correct in saying that it is the primary mirror?

[@4ThoseAbout2RaxxWeSaluteU]

Does tightening the screw make the rim thicker or thinner? If Does it move the black to the center or away from the center?

[@kylemccaslin]

@@4ThoseAbout2RaxxWeSaluteU it changes the angle at which the secondary mirror reflects the light, changing the light path. The result is that it moves the central black circle towards or away from the center of the image.