Just Another Noob

[Comet]

Hello I've been looking at this site for a while now. I feel making this account has been long overdue. Its been over almost 3 years since ive purchased my telescope and only taken it out a handful of times. For the past 3 years ive been saving almost every gift in the form of money for astronomy related purposes. Anyhow i think ive got a decent kit with some potential.
- 8'' skywatcher dob
- Baader hyperion 13mm, 21mm
- Big fat bintel 2x 2'' barlow
- telrad
- bintel 15mm, 30mm superview
- bintel right angled finder

So here are the questions
-i live in suburban melbourne. the highest mag ive used is 7.5mm. How far do you reckon i can push it? and if so what other eyepieces match well with the scope
- I've given up on my planisphere. I genuinely have no idea how to use it. stellarium is suffice. i could really use a goto. not sure whether its better to buy a new scope or goto/argo navis on its own.
- when you look through a finder are the images of stars ment to be crisp? mines quite blurry.
- the other night when i had my 13mm hyperion with the 2x ed barlow i became a little scared my poor focuser was under too much pressure and the scope began to lean. the tension handles couldnt keep the scope still. Any tips?

Thats all for now. im sure there'll be much more coming. Many Thanks

[Renato1 (Renato)]

The highest useful power I've ever gotten in suburban Melbourne from an 8" is 400X a few times, 300X fairly frequently, 200X most of the time. For the very high power, the atmosphere has to be good, and it should be at the time of year when you neighbours aren't running airconditioners or heaters, which will tend to stuff up the seeing.

Basically, if your image is sharp at 200X, bump it up and see if the image is improved. If it is, bump it up again. When it looks like mush, lower the power.

Using a planisphere. Look at your watch and find the time. On the planisphere, set that time against today's date. Go outside with a low power torch. Face South. Hold the planisphere over your head, with the south part of the planisphere pointing south. As you look at it with your torch, starting off with the Southern Cross, you can match up all the over head stars. Face north and do the same thing.

After a while, you stop putting the planisphere over your head, because you don't need to.

Finders are meant to be crisp. On most of them, you unscrew the front collar a bit, then rotate the objective element back or forth until you get the image sharp, then screw the front collar back in again to lock that focus position into place.

I don't know enough about your dob to offer any comment on your last point. But you do have a set up, that should keep you happy for years.

Hope this helps,
Renato

[Allan_L (Allan)]

Renato has covered off on most of your points quite well.
Indeed the skywatcher view finder is focused in the way he described (loosen top dew shield bit, then rotate the next ring to focus, then retighten dew shield part.

I had a 10" skywatcher dob so I know what you mean about heavy eyepieces.

You need to add weight to the bottom end of your scope.
I used to tie some ankle weights to the bottom end, probably about 2kg should do it.

Now I use a more sophisticated method, bar magnets.
Just be careful not to obstruct the free swing of the tube in the mount.

Easier than a planisphere or star atlas is a smart phone app.
For my Android I use Google sky. (Free)
It helps identify where you are looking and what you are looking at.

Another tip, always try to have the mount level to stop it moving "downhill".

[Comet]

Alright thanks guys. this means im in the market for a 5mm eyepiece. is it worth buying the 10mm, then just barlowing it. or would a 5mm be better? im thinking of another hyperion

[Renato1 (Renato)]

I once read Al Nagler's guide to selecting eyepiece focal length. His recommendation was to get eyepieces that delivered 4mm and 2mm exit pupils for low to moderate power, and 0.5 to 1mm (in a lower focal ratio telescope 0.5 to 0.7 is probably better) exit pupils for high power. And I've pretty much always found that very good advice. The lower power 6 and 5mm exit pupils I have used, but usually with a nebula filter.

So, just multiply your telescope's focal ratio by each exit pupil figure, to get his recommended eyepiece focal lengths - which you can achieve either with individual eyepieces or by Barlowing.
Regards,
Renato