Probably a stupid question!

[conura]

Hey all,

I got very interested in astronomy a few years ago using binoculars and just bought my first telescope! I now have a Skywatcher Dobsonian 200p which is great! Jupiter was a little smaller than expected but I could see the detail on it so that's absolutely great! The orion nebulae was also brilliant! It's a shame that here in the UK it's too cold to spend more than an hour up the garden before my feet stop responding!

Anyway, I have a couple of questions! My finder scope is ontop, not really set up in any specific way, just screwed in... (feels odd turning the scope right and the finder scope feels as though it goes left!)...Anyway, it's held in by 3 screws..At the moment, I have to compensate for the amount it's off, for example, it is often 1" right of where the scope is pointed, and 1CM above, is it pretty standard practice to have to learn your finder scope and compensate in this way? I can't really work out how to adjust it with just three screws!

Second, the scope has a cap on it which I take off for viewing, however the actual cap has a smaller cap which I can take off - Can anybody tell me what this is? I've searched the instructions and it says nothing about it!

I think that's about everything for now..My only dislike for the scope is how large it is to move, and how rapidly jupiter and the earth seem to move! It's great actually see the planets and earth do spin, and that I hadn't been lied to all these years! I can see why a more expensive mount will be essential after a while though.

This is the scope in question: Dobsonians - Skywatcher Skyliner 200P Dobsonian

If anyone has some experience with adjusting the finder scope, please do tell!

Con

[Breakintheclouds]

Hi Con,

Welcome to SGL!

My finder scope is ontop, not really set up in any specific way, just screwed in... (feels odd turning the scope right and the finder scope feels as though it goes left!)...Anyway, it's held in by 3 screws..At the moment, I have to compensate for the amount it's off, for example, it is often 1" right of where the scope is pointed, and 1CM above, is it pretty standard practice to have to learn your finder scope and compensate in this way? I can't really work out how to adjust it with just three screws!

The best thing is, during the day, to point your scope at a really distant object like spire, chimney or TV aerial. Get it centred in the telescope's eyepiece, then twiddle those three screws until it's also centred in the finderscope. From then on, the finder and the telescope will 'agree' on what they're pointing at. If the three screws don't make much sense right now, they should do as soon as you try this adjustment whilst looking through the finderscope.

Second, the scope has a cap on it which I take off for viewing, however the actual cap has a smaller cap which I can take off - Can anybody tell me what this is? I've searched the instructions and it says nothing about it!

It's there to give you a smaller aperture to your scope. Sometimes people feel that using the scope with the cap in place and just the smaller hole open gives sharper (and dimmer) views of objects like the Moon and planets, but not everybody seems to agree on this. Try it and see how you get on!

Ian

[Dai150PL]

Best advice is to set the finder during the day. Pick an object several hundred yards away and adjust. It will take a little while until you get the knack. From what I have read thats a great first scope. Any EP will be better than the supplied ones, if you look around the forum you will see the TMB planetary are very popular and without breaking the bank.

[E621Keith]

Hi Con

Welcome to SGL.

Lets start with your finder question. It's not normal to do compensation for finder. In fact the three screws on the finder brackets are there for adjusting its alignment. In day time, your neighbours' TV antenna are good target to get this alignment. In night time, moons and planet make good alignment targets.

As for your second question about the sub-aperture cap. It increases the f-number of your scope and dims the target. For a achromatic refractor, it should reduces the chromatic aberration and increase sharpness of the image. For a Newtonian, I think it should eliminate the artefacts from the secondary and its supports, such as doughnut and diffraction spikes.

clear skies

Keith

[conura]

Thanks very much for all the replies! I will look into some new eyepieces soon! Am I right in thinking the eyepiece literally just magnifies the image that the primary mirror catches?

[pvaz]

Pretty much. You need a few EPs to change magnification. If carefully chosen 3 or 4 will solve 95%+ of all situations.

For a 1200mm focal length scope I favor this 4 EPs focal lengths:

30 to 32mm: To find objects and to observe large DSOs

13 to 15mm: To observe small DSOs

7-10mm: For planets, moon, some globular clusters and planetary nebula

5mm: For the "best" views of planets/moon when seeing conditions allow (not the kind of EP you can use every day, but definitely worth having IMO).

A 30mm and a 10mm with a good barlow will do as well.

[conura]

Thanks again for all the advice - I have one last question!

I'm looking for a decent book for beginners which will teach me the basics of how to find things. I've looked at 'Turn Left at Orion' but it's out of stock nearby! I ideally wanted to pick something up today (I like in the UK) so if anyone can recommend any similar books that'd be fantastic!

Thank you

Con

[Adrian]

feels odd turning the scope right and the finder scope feels as though it goes left!

I've only recently started regularly using my scope and this was annoying to start with - Now I just remember to move the star to the centre of the finder, rather than move the finder to the star.

it's harder to describe than to do

[pvaz]

Well to be honest you really don't need a book.

The book is good, I did use TL@O but you can easily manage without. What is really essential is Stellarium so you can see what constellations will be up in the night sky and in what direction. Then you pick a couple of this charts (2 that contain some of the constellations you know will be visible):

Messier Maps

Print those charts and get out there:

1st) find the constellation naked eye.

2nd) find the closest bright star to the object, still naked eye, and try to imagine lines between that star and some other starts close by.

3rd) take your time imagining those shapes/lines between the starts close to the object.

4th) mimic what you memorized on 3rd against the sky. Now you can use the binos or scope. (With a scope, a telrad finder really makes this step a lot easier)

That's basically what TL@O will teach you to do so I may have just saved you 20£. :)

As an alternative to using stellarium to see what constellations will be up, you can make a home made planisphere using this:

Planisphere

I found a planisphere is the best, and simplest, tool to find and learn the constellations. It's a simple round chart on a sleeve. you align the date wheel with the current time wheel and you get a pretty good representation of the current night sky.

[conura]

that list is great! I will give that a go however have the feeling I will be spending most of my time badly collimating the scope! Thanks again, great link!

[pvaz]

You're welcome.

Just to clarify, TL@O is a great book and can make the process easier. However with all the online resources I wouldn't say it's essential.

[Zakalwe]

"Turn Left" is now available for less than £16 delivered at Amazon.

[The Warthog]

I put a right angle finder with correct view on my Newtonian. Although its view is right side up and correct left to right, it is easier to use than a refractor-type correction with the inverted view of the Newtonian, and helps me avoid neck strain.

I use a red-dot finder to get close to the object and use the optical finder to close right in on the object. Adrian's description of using an inverted finder is probably the best description I have ever seen. If the crick in your neck doesn't bother you, you will have less need for the red-dot, as you will be looking along the axis of the scope when you are using it.

[Chris H]

You'll soon get the hang of tracking objects, wide angle ep's help keep objects in the field of view for longer than with the ones supplied with the scope.

A good book to purchase is Nightwatch: A Practical Guide to Viewing the Universe: Amazon.co.uk: Terence Dickinson: Books

Along with a wealth of astronomy info it has 20 star charts which are excellent and not just for beginners.

A Telrad or Rigel Quikfinder make finding objects a lot easier.