Seeking help with blurry views on my new 8-inch dobs

[plkwo]

Hi everyone,

I recently bought the Sky Watcher 8-inch Dobsonian to dive into this fascinating hobby. After assembling it, I added the Baader Mark IV eyepiece along with the included Barlow lens (see attachments) and started testing by observing distant trees.

However, I noticed that the views through the eyepiece are somewhat blurry. While I can see some details of the trees, the clarity and colors are not as sharp as I expected. Interestingly, when I close one eye slightly and position it towards the bottom edge of the eyepiece, the image becomes clearer. I even managed to capture this effect with my camera, as shown in the attachments.

I also tested the preset 10mm and 25mm eyepieces and encountered the same issue. Despite collimating the telescope (see attachments) and tweaking the focuser, the problem persists.

Is it normal to get a slightly blurry image, or am I missing something? Any advice would be greatly appreciated.

Edited August 14 by plkwo

[Bruce Leeroy]

I'd recommend removing the barlow, I think your getting what are called blackouts. If your head is not quite square to the eyepiece (off axis) like in your photo they appear and is fairly normal the barlow is probably exasperating the problem.

Edited August 14 by Bruce Leeroy

[Astronomist]

It is possible that your laser collimator is in fact out of collimation, meaning the scope you collimated with it would be out of collimation as well. It's quite easy to check the collimation of the laser, you just tighten the focuser screws until the collimator can't wobble but loose enough that it can rotate, and then rotate it in the focuser. If the laser spot on the primary remains stationary as you rotate the laser, the laser is correctly aligned. If the spot moves then the laser needs to be recollimated. 

 

Edited August 14 by Astronomist

[plkwo]

Thank you, @Bruce Leeroy @Astronomist

 

Indeed, when I rotate the collimator, the laser spot moves around wildly. It appears that the laser is only aligned correctly when the collimator is in a specific position in the focuser.

[Kon]

The blurry view of the tree could be because they are too close to achieve focus (I have never managed to get trees in focus with either my 8" or 12"). How do the stars look with a low poer eyepiece without barlow? Do a star test with a high power eyepiece to check collimation and get a cheshire:

https://www.firstlightoptics.com/other-collimation-tools/stellalyra-premium-cheshire-collimating-eyepiece.html

 

 

[Astronomist]

42 minutes ago, plkwo said:

Indeed, when I rotate the collimator, the laser spot moves around wildly. It appears that the laser is only aligned correctly when the collimator is in a specific position in the focuser.

Thats probably what the problem is then, I'd do some googling as there are many easy to follow tutorials online on how to recollimate a laser collimator.

+1 on the cheshire Kon linked, thats the one I use and it's very high quality.

[plkwo]

Thank you, @Kon @Astronomist

I managed to recalibrate the laser collimator so that rotating it keeps the laser point steady on the wall. However, when I place it inside the focuser, the laser point still fluctuates, indicating an issue with the fixation.

If fixation were the root of the problem, rotating the eyepiece should produce different results, but the image remains the same regardless of the eyepiece's orientation. This leads me to believe it might just be a characteristic of Dobsonian telescopes in daylight settings and I have test it on stars tonight for further confirmation.

[Kon]

18 minutes ago, plkwo said:

Thank you, @Kon @Astronomist

I managed to recalibrate the laser collimator so that rotating it keeps the laser point steady on the wall. However, when I place it inside the focuser, the laser point still fluctuates, indicating an issue with the fixation.

If fixation were the root of the problem, rotating the eyepiece should produce different results, but the image remains the same regardless of the eyepiece's orientation. This leads me to believe it might just be a characteristic of Dobsonian telescopes in daylight settings and I have test it on stars tonight for further confirmation.

I think you are misunderstanding how/what collimation works/is. If your mirrors are not aligned, just rotating the eyepiece is not going to find the sweet spot as you will be way off along the rotation within the focuser. So nothing to do with daylight etc.  The focuser in the 8" (I have the same one) has some play. Using a cheshire you can tighten the screws evenly and then it will get you almost to perfect collimation followed by a star test. I use this method to collimate my Dob:

https://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

 

[Elp]

I'd also remove the Barlow when checking visually. The view is not sharp at all so optical alignment is the issue. When checking the collimation initially via a star test I believe the star you're checking should be in the centre of the eyepiece fov, and also defocussed ever so slightly so you can see the airy disks and you need to check both sides of focus to make sure collimation is accurate.

[Tiny Clanger]

2 hours ago, plkwo said:

Thank you, @Bruce Leeroy @Astronomist

 

Indeed, when I rotate the collimator, the laser spot moves around wildly. It appears that the laser is only aligned correctly when the collimator is in a specific position in the focuser.

 

1 hour ago, plkwo said:

Thank you, @Kon @Astronomist

I managed to recalibrate the laser collimator so that rotating it keeps the laser point steady on the wall. However, when I place it inside the focuser, the laser point still fluctuates, indicating an issue with the fixation.

If fixation were the root of the problem, rotating the eyepiece should produce different results, but the image remains the same regardless of the eyepiece's orientation. This leads me to believe it might just be a characteristic of Dobsonian telescopes in daylight settings and I have test it on stars tonight for further confirmation.

I've the similar 250 dob. and found the focuser tube has some 'slop' as you touch the thing, or rack the focus in or out, plus the screws which hold the eyepiece or laser in place push the laser out of line. Trying to collimate with a laser is therefore an exercise in frustration. I found the best way for me with a laser was to use the barlowed laser method, which is not affected at all by focuser slop:

https://www.tomhole.com/wp-content/uploads/2020/12/blaser.pdf

Or just forget the laser completely and use a cap and cheshire as clearly explained by Gary Seronic here: https://garyseronik.com/a-beginners-guide-to-collimation/

and

https://garyseronik.com/collimation-tools-what-you-need-what-you-dont/

Don't worry about eyepiece results seeming different to the laser, they have different jobs to do.

Your dob isn't ideally suited for looking at trees , they are too close (plus the primary mirrors of Newtonians are held loosely in their clips to allow for expansion in the glass and avoid distortions that happen when the glass is squeezed, so there is a slight possibility there could be a little shift in position when it is tilted down to horizontal)

I'd not stress over the views until you've had it pointed at stars. At which point. Mr, S comes to the rescue with more help : https://garyseronik.com/no-tools-telescope-collimation/

Heather

 

 

 

[davidc135]

Isn't your scope just badly out of collimation?  David

[Alan64]

I was wondering same.  The OP might provide a clear and concise collimation scene of their Newtonian, albeit on a Parsons-Dobson base, like this of my 150mm f/5 upon its arrival in 2012...

It had come with a one-arm base that I had discarded in favour of a tripod-type alt-azimuth mount.  It's historic to me, now, and perhaps never to be used again.

[Alan64]

Here's a mock-up I made of a 6" or 8" f/6, and how its scene should appear...

...and through a collimation-cap...

I illuminate the interiors of my Newtonians with a small lamp, and the light diffused by gift-tissue and a rubber band, then I snap a shot of the scene with my camera, not that of a mobile phone...

[impactcrator !!]

HI and welcome to stargazing,

Starting up is always very frustrating. I will make a few comments and the Dob mob will correct me if I am wrong. I have a celestron nexstar 127 slt Maksutov-Cassegrain so no collimation is needed. It sees the leaves on a tree across the valley. That said, who really cares! You can get good binoculars to do that. The dob is the go-to to see distant objects like galaxies but is less useful for the planets. 

Firstly, get rid of the Barlow (as has been already said) as that magnifies things by a factor like 2 making things harder to focus on. I tried one once and did not like it. Secondly, switch the Baader 1V to 24. It clicks in place. I use one.  This gives you a wide field of view and less magnification making it much easier to focus. Finally, look at the Moon as your first object as it is hard to miss and see if you can get used to your machine. Otherwise, find a star and make it look like a single point of light. In other words, baby steps. Soon you will have it!

Happy Gazing and Clear skies.

[bosun21]

3 hours ago, impactcrator !! said:

The dob is the go-to to see distant objects like galaxies but is less useful for the planets. 

I beg to differ. Dobsonians are a good choice for planets especially the full size 8" and upwards.

[Cosmic Geoff]

3 hours ago, impactcrator !! said:

The dob is the go-to to see distant objects like galaxies but is less useful for the planets. 

I don't agree. A Dob (or Newtonian)  is as good for planets as anything else, with its simple but effective optics.  And I don't agree that it is the 'go-to' for deep space. Other designs will perform equally well.

 

3 hours ago, impactcrator !! said:

Firstly, get rid of the Barlow (as has been already said) as that magnifies things by a factor like 2 making things harder to focus on.

The Barlow might cause a total newbie difficulties in focusing.  Otherwise, it is a very useful device for helping to reach higher magnifications with a f6 telescope.