Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_celestial_motion.thumb.jpg.a9e9349c45f96ed7928eb32f1baf76ed.jpg

ZOG

Barlowed Laser Collimation Method

Recommended Posts

Hi Jason im not sure, i could give it a try, bear with us for a bit and ill see if i can get some photos. wish i knew if the laser was collimated at least that would be a starting point. my collimation is likely not terrible as the planetary images i consistently get are reasonable. but its a good set of optics, one of the best ive imaged with, and i do belive if something is slightly off, even sharper results might come hence the discussion, thanks for the interest

Neil

uk 34 degrees

http://farm6.static.flickr.com/5045/5296187688_72ce6a6838_o.png

Edited by neil phillips

Share this post


Link to post
Share on other sites

Neil, that is an impressive photo. If I were you, I would not worry too much about perfecting collimation any further.

But if you want to perfect it further, I will try to help.

Jason

Edited by Jason D

Share this post


Link to post
Share on other sites

Cheers Jason its always worth trying squeezing every last ounce out of the system, has to be a planetary images eternal goals, clearly the errors im getting as mentiond early on, can not be day and night errors, but that doesnt mean even better results cant be had, i think im at about 85% collimation tolerance i want 95%. And your knowledge will most likely help me a lot.

so thanks for the offer, ill try to get some photos, never tried that before not sure if i have batteries, not sure if ill need to use the flash. doing it in sunlght or a lamp refecting down the tube might be ideas to get a good photo, i assume i just put the the lens over the focusser and snap away. but there is a slight error between the laser and visual, im just not sure at present what that error is, if i can get photos of my new visual collimation, ( i redid it yesterday ) ill post pics of the secondary, and the laser position in relation to the secondary photos, so you can get a idea of both positions, with everything looking close, the laser is on the primary sticker not in the centre, as soon as the laser is centred, the dark shadow around the primary, inside the secondary is no longer centred rather like your animation but to a slightly lesser degree.

Cheers

Edited by neil phillips

Share this post


Link to post
Share on other sites

Hi again Jason ok ive tried to get some shots just holding a camera over the focuser, not too sure if not centering the camera over the focuser precisely affects the image appearance or not, Not sure how much you can tell from these, the laser as mentioned is right on the sticker of the primary not the centre, with the alignement you see here, i managed to get one shot of the laser but its a refelection about where my hand is that actually shows you where the laser is, i couldnt get a actual shot showing the position of the laser, but the relection about where my hand is, shows roughly where the laser actually is, the primary sticker in these shots seems to move about a bit, not sure if thats the camera position error, ive moved the scope a couple of times i forgot to check the primarys collimation here, so it may have moved a touch, but not likely a lot. i could centre the laser and do them again to see the effect and post them here, but as mentioned, visually when i have the primary looking even inside the secondary, the laser is as of the photo, if i centre it, the shadow around the primary inside the secondary, no longer looks even, now leaning more to the right and often up a bit, it just doesnt visually look centred anymore ? my laser hasnt been checked for collimation, and i have never adjusted the spider as yet, i tried to measure it the other day, but it was too difficult, all i had was a tape measure

5497453054_a21dafe807_o.png

http://farm6.static.flickr.com/5091/5496854235_c596236b59_o.png

http://farm6.static.flickr.com/5177/5496848419_0d52773aa1_o.png

http://farm6.static.flickr.com/5253/5496839345_5a2f69598d_o.png

http://farm6.static.flickr.com/5019/5496567753_fd58a4b503_o.png

laser

http://farm6.static.flickr.com/5052/5496844275_1ab2912b27_o.png

Edited by neil phillips

Share this post


Link to post
Share on other sites

What you have is a tilt/rotate error. This happens when the focuser is not well-aligned with the spider vanes.

Note how the spider vanes axis in red is noticeably away from the focuser center. That is why you have to tilt/rotate the secondary mirror. Note how the secondary major axis is tilted. Also notice how the secondary shadow is elliptical.

Yellow, red, blue arrows need to line up. When the focuser is squared and the spider vanes are centered, things should line up nicely. If you do not want to touch the focuser then try to move the spider vanes center lower by loosening the two top spider vanes thumb knobs and tightening the two bottom ones.

See attachments

Jason

post-17988-133877540651_thumb.jpg

post-17988-133877540656_thumb.jpg

post-17988-13387754066_thumb.jpg

Share this post


Link to post
Share on other sites

Hi Jason ok trying to get my head around what your saying here, i thought it looked like what your suggesting too, but when i rotated my head things didnt look quite as bad as when i looked at the pic straight, just to be certain what i have here is as you suggest ive uploaded the pic so its easier to see the spider axis in the centre.

in this rotated view here it doesnt look to me like lowering the spider is going to make a huge amount of different, i could be wrong, plz take a look at the rotated pic and see if you still think that is going to help ? cheers for the feedback its helping.

5499130958_5615afd836_o.png

Edited by neil phillips

Share this post


Link to post
Share on other sites

When I said tilt/rotate error, I was referring to the secondary mirror only. I was not referring to your view from the focuser.

Refer to the photos in my last post. The secondary mirror central bolt axis is not pointing to the focuser axis but rather above it. To compensate for this error, you tilted your secondary mirror clock-wise to bring it the center of the focuser. That is why the blue arrow is pointing down and the secondary mirror shadow looks elliptical.

You need to take proper steps to ensure the secondary mirror central bolt axis is pointing towards the focuser axis. You can either lower the spider vanes structure, or point your focuser up, or take both actions. If you square your focuser and center your spider vanes, then these proper steps will be taken care of.

I do realize the above might sound confusing. Please ask clarifying questions.

Jason

Share this post


Link to post
Share on other sites

Ok i think i understand roughly what your suggesting, correct me if im wrong, the secondary needs to go up and left, which will in that position require the spider to drop somewhat to centre the secondary under the focusser ? if thats what your saying, whats the best to way to achieve that ? do i drop the spider first by a small anount and then centre under the focuser, and see if the error has corrected itself, or do i set the secondary up and left, and then move the spider to centre the secondary under the focusser ? this is certainly something ive never really thought much about, and adds a new element to my understanding of proper precise collimation, it is indeed worth having this disscusion with you, Glad your interested in helping, if i can get this right, clearly the telescope will perform better, i have yet to open the back of the telescope Jason, as its a closed back design, and the thermal issues of closed back designs never ever go away, even after 7 hours cooldown, i know ive tried, but i do have a 9 point Orion cell that is long overdue for me to fit, i need to drill holes, and have been using the scope too much to contemplate a major change, but i can only imagine how this scope will perform, with a new open back 9 point cell with fan,and more precise collimation. I expect things to sharpen up considerably, which is actually quite exciting considering my images rarely suck. The kind of error here, is this the kind of error that will impact on imaging a lot, or just mildly do you know. just out of interest. Ps think ive just realized what you said with you first reply, 2 adjustments of the spider are needed, with the rotated veiw of the picture i just posted here the top screw and left spider screw need adjusting dont they ? plz confirm that is correct, ? yes im still a little confused, but am i getting closer to understanding the problem here, again if you can confirm that i am

Cheers Neil

Edited by neil phillips

Share this post


Link to post
Share on other sites

The impact of the collimation error I see is minimal for visual observation but might be noticeable for imaging -- still it will be subtle. You can leave things as is.

The impact will be in terms of illumination field distribution. Not every point in the FOV at low magnification is at 100% illuminated. A secondary mirror that is not optimally positioned under the focuser means the FOV points with 100% illumination will not be optimally positioned. This has nothing to do with the image sharpness but rather with the image illumination.

See the following two links:

Only the first few pages of the following link

Telescope Reviews: Useful info about secondary mirror alignment

Telescope Reviews: Re: How important is secondary alignment?

Share this post


Link to post
Share on other sites

Ok thanks for that, doesnt sound like its a huge problem then, sharpness is something that obviously is. I have reset it again tonight, once again im trusting the laser, wish i knew the amount of lasers baarder are sending out which are off. But ive centred the laser, and then set the spider so the error i mentioned of the primary not centred inside the secondary is now gone or minimal, looking i think somewhat like here, but now with the laser centrerd. Maybe one day ill try to get my hands on a laser that i know is collimated to cross check my one. Ill read the links so thanks for that. And i might be able to image saturn Monday to see if theres any possible improvement, but seeing varies so much it might take time to really tell. Cheers for all the discussion. The things we do for Astronomy

Share this post


Link to post
Share on other sites
Ok thanks for that, doesnt sound like its a huge problem then,

For planetary imaging it's 100% irrelevant as long as you can still see the entire primary from the middle of the focal plane.

If you change disciplines and hook up a DSLR it's another matter.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.