Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

May buy a 18" Obsession

  • Please log in to reply
183 replies to this topic

#176 Vic Menard

Vic Menard

    Cosmos

  • *****
  • Posts: 7,926
  • Joined: 21 Jul 2004
  • Loc: Bradenton, FL

Posted 22 February 2021 - 02:33 PM

...Just took a lot of playing around to get things right. The owner before me never used the sling and just let the mirror sit on the bump stops.  

A Glatter cable sling would be another big improvement.


  • RobTeeter likes this

#177 CHASLX200

CHASLX200

    ISS

  • *****
  • topic starter
  • Posts: 21,710
  • Joined: 29 Sep 2007
  • Loc: Tampa area Florida

Posted 22 February 2021 - 02:34 PM

    blush.gif    That must be a crime of some sort!

Not sure what the image could have looked like other than what pinched optics will show. Maybe one nite i will give it a shot for kicks.  I also notice the mirror will flop to one side or the other when i move it out about 10mm's. I just center it and do my touch up collimation before dark  What is so nice it that i just roll the whole scope out in one lick and let it cool and no lifting or making many trips to set up.  18" gives me a bright image of a planet at high powers that much smaller scopes can't touch.  Would have gone with a 20" F/5 if one ever popped up local. But i don't think a 20" will fit thru my door.

 

There is a nice 20" Obsession for sale south of me with GO-TO and all that stuff.  For the money you can't beat these used Dobs vs what they cost new these days.


  • 25585 likes this

#178 Vic Menard

Vic Menard

    Cosmos

  • *****
  • Posts: 7,926
  • Joined: 21 Jul 2004
  • Loc: Bradenton, FL

Posted 22 February 2021 - 04:04 PM

You can always add Go-To to your 18-incher. If you're not handy with tools you could probably get Mike Zammit to help/install it for you. I don't think you'll see much difference between a 20 and an 18. I keep revisiting the idea of moving to an 18 if I get to the point where my 22 is too big for my vehicle (or my back). I'd probably stay f/4, although f/3.6 would be one less step up a comfortably short 2- or 3-step step stool with a handrest, and f/3.6 still performs very well with a Paracorr 2.

 

(To me, Go-To/tracking is just as important as a Paracorr 2. I've often considered a tracking 22 to be every bit as powerful as a non-tracking 24. I suspect a tracking 18 may seem even bigger than a non-tracking 20.)

 

That's my penny.gif penny.gif


Edited by Vic Menard, 22 February 2021 - 04:05 PM.

  • turtle86 likes this

#179 CHASLX200

CHASLX200

    ISS

  • *****
  • topic starter
  • Posts: 21,710
  • Joined: 29 Sep 2007
  • Loc: Tampa area Florida

Posted 22 February 2021 - 05:33 PM

You can always add Go-To to your 18-incher. If you're not handy with tools you could probably get Mike Zammit to help/install it for you. I don't think you'll see much difference between a 20 and an 18. I keep revisiting the idea of moving to an 18 if I get to the point where my 22 is too big for my vehicle (or my back). I'd probably stay f/4, although f/3.6 would be one less step up a comfortably short 2- or 3-step step stool with a handrest, and f/3.6 still performs very well with a Paracorr 2.

 

(To me, Go-To/tracking is just as important as a Paracorr 2. I've often considered a tracking 22 to be every bit as powerful as a non-tracking 24. I suspect a tracking 18 may seem even bigger than a non-tracking 20.)

 

That's my penny.gif penny.gif

I wished i could have bought your 22" F/6 back in the day. I would love a F/6 18".



#180 CHASLX200

CHASLX200

    ISS

  • *****
  • topic starter
  • Posts: 21,710
  • Joined: 29 Sep 2007
  • Loc: Tampa area Florida

Posted 22 February 2021 - 05:34 PM

A Glatter cable sling would be another big improvement.

I hear they are good.  That is the cable sling i guess.
 


  • RobTeeter likes this

#181 Bonco2

Bonco2

    Viking 1

  • *****
  • Posts: 598
  • Joined: 01 Jun 2013

Posted 23 February 2021 - 03:49 PM

I wished i could have bought your 22" F/6 back in the day. I would love a F/6 18".

Chas,

Once you get everything tweeked. I suggest you mask the 18 inch to  17 or 16 inch and compare the views. This will get you  to around f/5. Light loss for sure but you might improve sharpness. Virtually no cost to give it a try. I'd love to own a quality 16 inch f/5 for planetary use.  Remove the mask and you'll be back to 18 inch for deep sky views 

Bill


  • 25585 likes this

#182 CHASLX200

CHASLX200

    ISS

  • *****
  • topic starter
  • Posts: 21,710
  • Joined: 29 Sep 2007
  • Loc: Tampa area Florida

Posted 23 February 2021 - 07:16 PM

Chas,

Once you get everything tweeked. I suggest you mask the 18 inch to  17 or 16 inch and compare the views. This will get you  to around f/5. Light loss for sure but you might improve sharpness. Virtually no cost to give it a try. I'd love to own a quality 16 inch f/5 for planetary use.  Remove the mask and you'll be back to 18 inch for deep sky views 

Bill

Once Jupiter is up i will push the mirror to the limit.  So far it seems good, but i want Zambuto good. So it may take a trip to Mike Lockwood for a little touch up work.  Hate to see what shipping will cost for that heavy mirror plus i would be scared to death shipping it.



#183 25585

25585

    Voyager 1

  • *****
  • Posts: 11,944
  • Joined: 29 Aug 2017
  • Loc: In a valley, in the UK. Dark end of the street.

Posted 23 February 2021 - 08:05 PM

An equatorial platform could be worth a try?



#184 CHASLX200

CHASLX200

    ISS

  • *****
  • topic starter
  • Posts: 21,710
  • Joined: 29 Sep 2007
  • Loc: Tampa area Florida

Posted 23 February 2021 - 08:18 PM

An equatorial platform could be worth a try?

I don't see how. No way to roll it out that i know of.  This is why i got a 18" so i can roll the whole scope out in one lick. I am lazy and no lifting is in my plans.  They also cause problem with slings as the mirror will want to move around.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics