Why such a big difference in focal length?

Razsky · Post by **Razsky** » Mon Mar 24, 2008 9:28 pm

Thanks for the replies.

Well, i have nvr really seen a dob base before. Will it be stable on a uneven ground? Lets say, a grass field? Would it be difficult to observe as its height is fixed right?

And if i were to get one with such a long focal length, won'ti face the same problem as with the Celestron Firstscope? Dimmer image?

I have read quite some reviews on Starblast. Rated quite well.

And judging by all the comments i received, I think i need to do some more homework!

Thanks.
Razsky

Post by **acc** » Tue Mar 25, 2008 12:31 pm

Hi Razsky
The dob base will have no problems coping with glassy or uneven ground.

For a given aperture and magnification, the f ratio of the scope has no bearing on the perceived brightness of the image.

happy shopping!
cc

rlow · Post by **rlow** » Tue Mar 25, 2008 8:00 pm

Well, i have nvr really seen a dob base before. Will it be stable on a uneven ground? Lets say, a grass field? Would it be difficult to observe as its height is fixed right?

1. Dob base with 3 feet can stabilise on uneven ground, but if the base end up tilted, it may cause unnecessary azimuth movement. You still have to adjust it around the ground to set the base to be level first.

2. Eyepiece height varies depending whether you observe towards the zenith or towards the horizon. Also, small dobs like the StarBlast need to be raised on a tripod or stand so that you can observe sitting down, otherwise you will be squatting down to observe.