First collimation / comparing 8 SE to 127 SLT

[Jeff-Colorado]

I just bought a used Celestron 8 SE (got a great deal) and when I first looked at Saturn with it, it was blurry and there was even a double image. That's probably why the previous owners were able to part with the scope.

I tried daytime collimation following this procedure:
http://www.mira.org/ascc/pages/lectures/collim.htm

But it did not work for me. Tonight I looked at Saturn again and it was still blurry (perhaps slightly better than before). So pointed at Antares, switched to my high power 7mm lens (286x power), brought it out of focus, and noticed the concentric rings were not circular (tell tale sign, of course, of poor collimation). I used my little screw driver to tweak the 3 screws in the center obstruction, and after a little trial and error, my rings were circular. It really wasn't very difficult at all and probably took me about 15 minutes.

Many of you know more than I do about collimation, but in case someone is interested in trying this for the first time on their scope, I have some advice:

-- turn on tracking so your target star stays centered in the field of view
-- make tiny adjustments and then check your progress
-- make adjustments symmetrically (i.e., if you are adjusting in the up-down axis and loosen the bottom screw, then tighten the top screw slightly too)
-- use your red flashlight and move slowly and deliberately (you don't want to accidentally poke your screw driver somewhere it shouldn't go)
-- the seeing does't have to be perfect (it wasn't for me tonight)

Once I finished collimating my 8 SE, I set up my 127 SLT (which I am trying to sell) and pointed both scopes at Saturn. The collimation worked and the 8 SE was in sharp focus! The 127 SLT does amazingly well at showing Saturn despite its 5" aperture, but the view in the 8SE was clearly superior. I could see more detail in the cloud belts, could see 4 moons instead of just 2, and also make out the border between the B and C rings.

Vibrations in the 8 SE, caused for example by adjusting the focus knob, are still suboptimal but clearly better dampened than they are in the 127 SLT.

As for portability, I can carry the 127 SLT back into my house with one hand. You can't beat that in portability! While it does take me two hands to move the 8 SE, it's not heavy. There's no need to separate the mount from the optical tube. I plan just carry the whole thing in and out of the house when I want to observe. 

So my three takeaways tonight are that collimation isn't difficult, the 127 SLT is a very nice scope for the money, and lastly that I will enjoy the even better 8 SE immensely.

[Stu]

Sounds like a successful evening Jeff. I have collimating a couple of SCTs now and agree it's not difficult. With one of them, I had taken it apart so it was badly out. I used the technique of putting the OTA horizontal and standing a few metres away so I could see all the reflections down the tube. By adjusting the collimation I got these all concentric and that then put me in a position to do the star test technique you have referred to to get it much more accurate.

Two things I would add. Firstly don't forget to re-centre the star after each adjustment, the circles are only concentric right on axis. Secondly, if work at smaller and smaller amounts of defocusing as you refine the collimation, it is easier to see very small errors and correct them out. SCTs are very sensitive to miscollimation so it is well worth spending time getting it as accurate as possible.

Enjoy your new scope, I had an 8" and really enjoyed it, a very good compromise of aperture vs portability.

Stu

[laudropb]

Well done. A success is always nice to hear. I have not had to collimated my Mak yet but it's nice to hear it can be done.

[LukeSkywatcher]

Glad you're enjoying the 8se. Ive never collimated mine since i bought it. No need. Glad to know it can be done without taking the OTA apart.

[Jeff-Colorado]

Just one more update on my 8 SE just in case someone has a similar problem one day. I was using EBL 2800mAh rechargeable batteries with my Celestron 127 SLT, and they worked great. With the 8 SE, a heavier scope which puts more demand on batteries, I tried the same batteries and the Goto feature went haywire. I did skyalign with 3 stars, 2 named stars, etc., but when I would try to goto one of my alignment stars, the scope would go to a random place in the sky, sometimes 90 degrees from the target.

I was thinking something was seriously wrong with the 8 SE, until I tried it on AC power and it worked perfectly. I've read that some other people have had similar experiences using the 8 AA batteries. So I've ordered the Power Tank and hopefully it will fix my battery problem.

[Padraig]

Great to hear what can be achieved with an 8se. Thinking of purchasing one of these, when doing a search of the web, it's hard to find out its capabilities. As a beginner, it's a mine field. For portability and power/size , the 8se seems to be up there. Price is a bit on the heavy side for a beginner but  do the job for years. ( I hope  )

enjoy !

is it possible to see nebulae' s clearly on a 8se

[Davesellars]

16 hours ago, Explor said:

is it possible to see nebulae' s clearly on a 8se

Yes.  I've had some really great views of bright emission nebulae as well as reflection nebulae such as M78.  For emission nebulae a UHC and / or OIII filter will give you a much better view (in general).

[cloudsweeper]

The 8SE is a great 'scope.  I too had a 127 Mak - very portable, but I wanted more aperture.  The 8SE can be carried all assembled, but I always take the OTA off for ease (and in case I trip).  It's dead easy to take on and off.

As for collimation, I made a star simulator from a piece of thick black plastic with a tiny hole drilled in it.  I filled the hole with white filler and suspended the thing way down the garden.  Minor adjustments were made using http://asterism.org/tutorials/tut14-1.htm - and a good screwdriver (no fancy knobs necessary).  It was quick and easy, and I doubt it will need further adjustment for some time.

Doug.

 

[Padraig]

1 hour ago, Davesellars said:

Yes.  I've had some really great views of bright emission nebulae as well as reflection nebulae such as M78.  For emission nebulae a UHC and / or OIII filter will give you a much better view (in general).

Thanks for that, 

as a beginner , you hope you're making the right choice of telescope. 

My next port of call, is to contact the local astronomy club to get some hands-on. 

Thanks again

[Padraig]

On 19 August 2016 at 12:54, cloudsweeper said:

The 8SE is a great 'scope.  I too had a 127 Mak - very portable, but I wanted more aperture.  The 8SE can be carried all assembled, but I always take the OTA off for ease (and in case I trip).  It's dead easy to take on and off.

As for collimation, I made a star simulator from a piece of thick black plastic with a tiny hole drilled in it.  I filled the hole with white filler and suspended the thing way down the garden.  Minor adjustments were made using http://asterism.org/tutorials/tut14-1.htm - and a good screwdriver (no fancy knobs necessary).  It was quick and easy, and I doubt it will need further adjustment for some time.

Doug.

 

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