Collimation and eyepiece question

[Sven Buttler]

Hi there,

so I shelved my plans to get into astrophotography anytime soon, and went with a Sykwatcher Dobson, 8" instead.

The first night was pretty frustrating as I couldn't get Jupiter into view at all, even with the low power 20mm eyepiece

that came with it. I also found navigating the sky with a Newton to be quite a challenge, because with the upside down

/inverted view it's difficult to get something to center because moving the tube is somewhat disconnected from the view

but I assume thats something you get used to eventually. So that night I pointed the scope at the moon and boy I didn't

expect it to be that bright. It took 10 minutes for me to regain vision I will probably have to get some sort of lunar

filter.

Next up was collimation. I ordered a Cheshire (?) collimation eyepiece with the scope. I dreaded collimation and

rightfully so, after spending 2-3 hours I was so frustrated I left it as it was, which wasn't too bad I guess because

that night I finally managed to get Jupiter in view with both the 20 and 10mm. I live in a bad spot in terms of light

pollution but every now and then I could make out two small, brownish bands on the plant, so I was quite pleased.

Maybe I'm just a bit overly OCD to the mirrors aligned perfectly? Also the 2" to 1.25" adapter and the eyepiece

itself are somewhat lose which makes collimation difficult. Is this normal? I tried to fixiate them with the

screws but it didn't help much I could still very much move the adapter and eyepiece even with the screws

fastened. Is this considered normal?

The next thing on my shopping is a better, high powered eyepiece. I've heard a lot of good things about the Televue

Naglers but the Baaders don't seem to be shabby either. I don't spending a bit more the eyepiece, as it will probably

last me a while even if I consider replacing the scope at some point. Any suggestions? I thought 5mm would probably

give me a bit more magnification. Also would you recommend getting a barlow lens?

Best regards,

Sven

[NGC 1502]

Hi Sven. Good call 8" Dob. Such a scope could be a lifetime friend, with no real need to upgrade, if observing is your main interest.

First, have you aligned the finder with the scope ? If not, even bright objects like Jupiter will be a challenge to locate.

Second, before you collimate, do you actually need to ? At medium to high power, view a slightly defocused bright star, keep it centred

in the field of view, are the rings in the expanded view of the star concentric or lop sided ? Should be concentric if collimation is ok. There's a lot more to be said about collimation, but that's a basic check.

I'd have a few sessions with what you have before considering new eyepieces. The 5mm you mention will give 240x with your scope,that's high whatever the specifications may say, needs very good conditions to be worthwhile, and manual tracking is more difficult at high mag.

And yes, it definitely does get easier with practice.

Good luck, Ed.

[Charic]

I like all the EPs in my signature. The 32mm is suitable for my eyes ( choose an eyepiece that produces an exit pupil no greater than your own dilated pupils )

The 6mm in my collection gives me an exit pupil size of 1mm and a power of 200x. As you go less than 6mm on your scope, the image will appear darker as the size of the exit pupil gets smaller. Going below 6mm also requires perfect conditions for viewing, except for the Moon. I would try something between 6 - 12mm for your next EP.

Dont assume you just need high powered EPs. Although the actual image size decreases with longer focal lengths, often more detail is gleaned from the longer focal lengths.

As for the Moons brightness, dont discard the fact that you can wear Sunglasses, you can also leave the dust cap on the end of the telescope, and just remove the smaller 2" cap ( one is removeable, the other is fixed. The cap you remove sits on the one that is fixed? )

Folk will advise against this as it reduces aperture, contrast and effects the focal ratio, but try it on the Moon, you'll find its not so bright.

[RichM63]

I won't advise against it Charic as all it does is to limit the collimated light going in, rather than changing FL in a reflector, thus dimmer but all other aspects of the optical train remain the same.

I agree, 6mm, for me is sensible, and I am with no LP.

Collimating a factory SW telescope should be done AFTER using it, but it is not something to be worried about. Loads of tutorials/vids, etc to work through.

[Charic]

I won't advise against it Charic as all it does is to limit the collimated light going in, rather than changing FL in a reflector, thus dimmer but all other aspects of the optical train remain the same.

I agree, 6mm, for me is sensible, and I am with no LP.

Collimating a factory SW telescope should be done AFTER using it, but it is not something to be worried about. Loads of tutorials/vids, etc to work through.

If I limit my 200 down to 50 by using the smaller aperture, my scope becomes an f/24, do you not agree!

[Qualia]

The first night was pretty frustrating as I couldn't get Jupiter into view at all, even with the low power 20mm eyepiece

that came with it...I also found navigating the sky with a Newton to be quite a challenge

Hiya Sven,

The best way to align up planets or stars etc, is to get yourself a RACI Viewfinder this. It makes finding planets easier and will deliver stars right down to about 8 magnitude, even if you're in an light polluted (LP) area, meaning you’ll be able to see every star plotted on your sky atlas and when you move amongst those stars, your left is left and your up is up.  As the evening wears on and brain fatigue sets in, this correct-image feature is a huge aid when it comes to moving amongst the stars and following your star map.

You might also want to check out something like a Telrad or Rigel red-dot finder. These can’t deliver more stars than your eyes alone can see, so if you're in an LP area, you're relatively limited. But, they really do speed up your finding, really do help judge where your scope is pointing but I feel it must be used in conjunction with the finder-scope. Whether in decent dark skies or light soaked LP areas, you position the bull’s eye or the other two rings in the proper place against the stars and you’re done. If you're out a little you can work out where you are by either looking through your viewfinder or the three ringed circles of the red-dot finder giving you varying degrees of the sky you're looking at.

Hopefully with these two additions, navigating with the Newt will be easier. You'll find that the eyepiece image isn't so much inverted as just upside down making Newts a little easier to use that fracs. Watch where the planet or star drifts in the eyepiece and this is west. If you gently nudge in that direction while viewing, you should be able to follow a star or planet with relative ease.

Next up was collimation. I ordered a Cheshire (?) collimation eyepiece with the scope. I dreaded collimation and rightfully so, after spending 2-3 hours I was so frustrated I left it as it was

It's best not to do collimation at night, but to set yourself the task as a day time job. It isn't as difficult as made out to be but I find it helps if you can grasp or visualise what is necessary before working on the scope. The best collimation guide I'm aware of can be found here. Print it out and work with it as you set about collimation. It might also be an idea to read Shane's star-hopping guide as well.

I live in a bad spot in terms of light pollution but every now and then I could make out two small, brownish bands on the plant, so I was quite pleased.

And rightly so. Excellent observation and it doesn't sound like your collimation was so bad either You'll find that light pollution won't affect planetary or lunar viewing, but it is a good idea to shield your eye from stray light.

Also the 2" to 1.25" adapter and the eyepiece itself are somewhat lose which makes collimation difficult. Is this normal? I tried to fixiate them with the screws but it didn't help much I could still very much move the adapter and eyepiece even with the screws fastened. Is this considered normal?

I honestly don't know for I don't own your type of scope. However, in my own truss dob, I don't find the focuser or screws loose, that is, eyepieces sit snug. Check again in the day time and if you do have any more problems, it might be worth taking some photos to show us what is going wrong and how we can help .

The next thing on my shopping is a better, high powered eyepiece.

Personally, I'd hang on for a little bit. Get to know your kit, find yourself about the night sky with a little more ease, get collimation grounded so it is no longer feared but just part and parcel of tuning your scope for the night, before purchasing more astro-gear (other than the aforementioned finders and a star atlas if you don't have one yet).

In general, for something like an 8" Newt, I'd recommend a three eyepiece set up to get started with. A nice wide field 24mm and two nice wide field eyepieces around 14mm and 10mm. If you throw in a decent Barlow, you'll have a working range of 24mm, 14mm, 12mm, 10mm, 7mm and 5mm, or there abouts.

With this set up in place, you'll then be able to work out what you're missing or whether it is worth purchasing dedicated focal length eyepieces. Needless to say, when it comes to buying new eyepieces, it might be worth setting up a thread in the eyepiece section.

Hope this helped a little

[Sven Buttler]

Thanks a lot everybody, really appreaciated. I'll stick to those two eyepieces for the moment, but I'll think I'll get a barlow lense

And rightly so. Excellent observation and it doesn't sound like your collimation was so bad either You'll find that light pollution won't affect planetary or lunar viewing, but it is a good idea to shield your eye from stray light.

Thanks, a lot, Rob, great advise there. In fact I got myself an eyepatch after the first viewing. It sure looks funny but gets the job done

[Sven Buttler]

First, have you aligned the finder with the scope ? If not, even bright objects like Jupiter will be a challenge to locate.

Well, yes but the other way round, sort of. After I had managed to get Jupiter in view, by chance that is, I aligned the finder with the scope. Not sure if there's any other way?

[NGC 1502]

Well, yes but the other way round, sort of. After I had managed to get Jupiter in view, by chance that is, I aligned the finder with the scope. Not sure if there's any other way?

 

Hi again Sven. Sounds to me like you did it the right way by viewing Jupiter in the eyepiece, then aligning the finder.

Regards, Ed.

[Tinker1947]

Finding your way round the night sky isn't that easy, but you can make it a lot easier by adding a Telrad, download the Telrad maps theses have Messier DSO with the Telrad circles printed on them, makes star hopping a breeze, if you don't have it download Stellarium put your location in and turn on the Telrad circles, give it a couple of nights and your wonder what all the fuss  was about, it really is easy with the right equipment, Collimation i use a Laser its easy once you understand why you are turning screws and what they do, find a Collimation thread and read and practice you get the timing down to a minute or 2.....Picture of my Dob notice the Telrad stand-off base makes looking through it comfortable.....I had a set of baader EP's they were nice to view through but did suffer from elongated star right around the very edge of the FOV, my present EP's are listed in my Signature 

The Telrad is the bit with the dew shield, that's piece of cell foam......

[Charic]

The problem with aligning at night, is that your targets  keep moving across the field of view, so its a better choice to align the scope to the finder during daylight. Look at some distant target on your horizon, with your lowest focal length eyepiece. Once  centred and in focus, lock the telescope into position using the tension handle. Next, view through the finder-scope, and using the adjusters, align the finder to the same target. The viewfinder can also be finely tuned into focus, mine was slightly out for my eyes, the adjustment  locking  collar is on the field lens end of the finder scope, loosen the knurled collar, then rotate the end cap to adjust focus, re-lock when satisfied  Both views should now be central. Thats the telescope aligned.  You can correct even  further if you like by going up in magnification. 

Also when viewing through your standard 9x50 finder scope at night , try looking with both eyes open?  try it.....take a prominent Star and aim the scope in the general direction first, simply by rotation and elevation,  then look through the finder, your  brain may get confused, but you should see two separate images, one normal, one magnified.  When aligned,  the two images overlap, your  now on target.

Wearing an eye patch also prevents eye squinting and muscle straining, when using  the eyepiece, as were not used to just looking through one eye for long periods of time.

Tinker1947 reminds us that a Telrad is a good device to use in helping to search the skies above, I agree, this is a good piece of kit, although I need to wear my prescription glasses to enable me to focus on the rings?

here's an image of my Telrad with a clear Dew Shield made from a drinks bottle!

[Stropper]

Interesting thread Sven, thanks for starting it

As a Newbie my self with an 8" Dob I was worried about collimating but I got a laser collimator and after about an hour have found it easy to use