One failing of a Dob

[JimmyH155]

Before being accused of heresy for saying anything bad about the Dob that most of us seem to own - due to the great bang for buck and aperture, I have come across a definite limitation of the Dob, that I cannot remember anybody commenting on:rolleyes:
It is this.... The other night, the seeing was appalling, and I thought I would just have a peek at Venus with my Lightbridge 12" to check the collimation. It was shining nice and bright in the West just after sunset. I live in a north of Bris suburb, in a crummy standard residential block - all 26 perches of it. There are trees and hedges around, and although the storm in November cleaned up 3 of my huge trees, to look to the west, I have to look over the chook pen and the neighbour's hedge which is about 2 metres high
Venus was about 45 degrees up from the horizontal.
Here's the problem:shrug: Being a Dob, the axis about which it turns (up and down on the trunnions) is very close to the ground and therefore, when I pointed it towards Venus, the 45 degree angle ended up half way up the hedge:lol: No good. So I had to put it away and get out my 120 mm refractor on the tripod. The tripod of course has its axis about 1500 mm above the ground, and when I pointed it to Venus, the light path easily cleared the hedge:D

So Newbies who live in "restricted" properties, remember that with a Dob (without putting it on a table, where it would be too high to look through), you may not be able to see much from the horizon up to about 45 degrees, if you have hedges, fences etc close by.
This, to my mind, is a big plus for getting a telescope on a tripod mount;);):thumbsup:
Fortunately though Good 'ol Orion is nice and high at the moment, and through the LB 12" it is FANTASTIC:D:D

[gary]

Hi Jimmy,

Thanks for the post. :lol:

Sounds to me you don't need a tripod. You need a hedge trimmer! :lol:

Best Regards

Gary

[dannat]

hedge trimmer, how about some good quality binos - 2nd best optical dvice around... you can think of the first

[erick]

I agree, this has happened to me several times. I live with it in return for the benefits.

[Davekyn]

Also agrees...but prefers the hedge trimmer over the tripod as well:)

[astro_nutt]

Hi Jimmy..
I had the same problem when viewing from my backyard...so I built a concrete pier to raise the scope's mount about 40cm off the ground..plus I made an observing chair to suit...so I can see a bit more over the fence..in comfort too!
Cheers!

[JimmyH155]

Thanks guys for the advice about the hedge trimmer - only one snag though - behind the hedge is this enormous ugly colourbond shed. What do I do about that???:shrug::lol::lol::lol:

[gary]

Grab a copy of this catalog from this astronomical solutions supplier -

http://www.cat.com/cmms/images/C453359.pdf

[JimmyH155]

WOW!!:) That Cat 973C would do the trick! Can I hire one:D?

[Spanrz]

Hey, if you need a 973, you've come to the right place.
Talk to me for all your CAT needs (plug).:thumbsup:

I fix em for a living.:thumbsup: Can even give you an excavator that will pick up the weeds too. (CAT 5230 - 230ton machine)

[garyp]

wow :eyepop:that CAT 5230 will do me:thumbsup:



Spanrz, Sometimes where I work I get to drive a CAT Challenger 45 (on cropping farm) Do you know that machine?

Jimmy, good point about the Dobs limitations.

Cheers

Gary:)