RE: Re ATM !0 in Dob Finished

["Arjan te Marvelde (EMN)" <Arjan.te.Marvelde@emn.ericsson.se>]

If the focal length is 58", which is also the imageplane distance for objects at 
infinity, then an object at 50 yards will give an image at almost 60". So, unless you 
have a very large focuser range, it will likely not reach the image of the chimney
.

Use formula 1/f = 1/o + 1/i, where f is the focal length, o the object to primary 
distance, i the primary to image distance. Substitute the maximum i you can reach, and 
the 58", and the result can be reworked to give you the minimum object distance.

Of course you can also extend the drawtube in some way...

/Arjan

: -----Original Message-----
: From: Peter Jones [mailto:pmjco@email.msn.com]
: Sent: Monday, September 04, 2000 14:01
: To: ATM Mailing List
: Subject: Re ATM !0 in Dob Finished
: 
: 
: 
: Hi Everybody,
: 
: I have just completed my 10 in Dob and everything seems to 
: have worked out
: according to plan as far as I can tell. I am thrilled with 
: the prospect of
: using it but so far have been frustrated by variable cloud 
: cover with stars
: peeping in and out of the clouds. I was also trying to 
: observe in a heavily
: light polluted area with nearby street lights etc. The few 
: glimpses I did
: get showed a few stars as pin points so I guess the optics 
: are not too far
: out. I will have to wait to carry out a proper evaluation 
: when the seeing
: conditions are better. The only small problem I have is that 
: the scope isn't
: quite balanced properly. It is just a tiny bit mirror end 
: heavy so I may
: have to add a small counterweight or try Tom's spring 
: counterweight method.
: 
: I would like to take advantage of this opportunity to say a 
: *very* large
: thank you to everyone on this list who has advised me, giving 
: freely of
: their time and experience to keep me on the right track. 
: Whatever questions
: I have asked have always been answered in a friendly and 
: encouraging manner
: and this saves the beginner lots of time, frustration and 
: money. So THANK
: YOU to everyone and of course to Mel for running the list.
: 
: One question I would like to ask is, What is the closest 
: distance the scope
: should focus on when the scope is correctly collimated? I 
: tried to focus on
: a nearby chimney  (fifty yards or so) to try and align the 
: finder with the
: scope but couldn't get anything in focus. My scope is a 10 in f/5.8
: 
: 
: -Peter Jones, Ipswich, UK
: 
: 
: 
: