Telescope Types - THE BIG DEBATE

[great_bear]

The key is that the pressure point/'lever' is at the end of a long tube, generally well away from the balance point.

Ah OK - like the way my AZ4 works a lot better with my F8 150 newt than when it's got the stubby Mak 180 on it I guess

[Moonshane]

yep - I agree it seems better to have more weight and length either side of the balance point. the mount will be more slick that way based on my short experience with the Giro.

[great_bear]

So if i was to geet a 10" dob what number would this fit into.

It easily encompasses the whole range although - as John points out - for practical purposes the upper limit is in the middle of band 3 because - at a magnification of 250x - the atmosphere of the sky tends to limit further magnification. This is mentioned in a more detailed description of power ranges by David Knisely: "This power range is sometimes compromised in apertures larger than 5 inches by seeing effects (ie: disturbances in the Earth's atmosphere which can blur fine detail)."

That's not really a problem, since (at 250x) that's already plenty of magnification for planetary and double-star observing anyway. Once in a while you'll get lucky (usually around 2 in the morning, I find) when the air is very still, and you may be able to use even more. Earlier this year when observing Saturn, there was a night when 360x was the best magnification for me - even though that's right at the top end of what's possible with a Mak 180. Normally in my scope, 360x is a complete mess - but not that night though.

Note that David's ranges are slightly different to mine; such figures are rough, and mine are easier to remember

Some people prefer to think of power ranges in terms of exit-pupil (the width of the beams of light leaving the eyepiece), in which case of my earlier list would be:

1. 6-3 mm - for open clusters and general sky-sweeping
   
2. 3-1.5 mm - for galaxies, nebulae and globular clusters
   
3. 1.5-0.75 mm* - for lunar and planetary observing
   
4. 0.75-0.38 mm - for double stars
   

* note that this figure (0.75) corresponds to the paragraph "Take your focal ratio, and multiply it by 3/4..." in The Warthog's seminal post Eyepieces - the very least you need.