Return to the Cloudy Nights Telescope Reviews home pageAstronomics discounts for Cloudy Nights members
· Get a Cloudy Nights T-Shirt · Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

Astrophotography and Sketching >> Beginning and Intermediate Imaging

Pages: 1
star chaser
member


Reged: 02/10/13

Primary focus new
      #5686124 - 02/17/13 10:45 PM

My 10" 1200mm f/4.7 Dob primary focus is flush with the optical tube so I am unable to attach my camera to the focus tube for primary photography.How far back will a barlow or coma corrector bring my primary focal plane so I can start using the telescope for primary photography?

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jeff2011
Carpal Tunnel
*****

Reged: 01/01/13

Loc: Sugar Land, TX
Re: Primary focus new [Re: star chaser]
      #5686150 - 02/17/13 11:02 PM

That is a common problem with Dobs. Using a Barlow is a form of eyepiece projection. Just about any Barlow will work, but it shrinks the FOV considerably. With barlows you don't have to worry too much about a specific length behind the Barlow, however the further back the greater the magnification. That is not true with coma correctors as you need to get the correct distance as specified by the manufacturer. I was able to achieve true prime focus or more correctly Newtonian focus by moving my primary mirror up about 1.5 inches. This was done by simply replacing the collimation bolts. I replaced the 1in bolts with 2 in. After doing this I had to get a tube extender to use my eyepieces and had to do a serious collimation.

Edited by Jeff2011 (02/17/13 11:05 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
star chaser
member


Reged: 02/10/13

Re: Primary focus [Re: Jeff2011]
      #5686160 - 02/17/13 11:07 PM

thanks. I am trying to avoid changing the position of my primary mirror but maybe that is the best option.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Jeff2011
Carpal Tunnel
*****

Reged: 01/01/13

Loc: Sugar Land, TX
Re: Primary focus new [Re: star chaser]
      #5686292 - 02/18/13 12:38 AM

You can also try replacing the focuser with a low profile. I think the combination of a low profile focuser and coma corrector might get it for you. Moving the mirror is less expensive however.

Post Extras: Print Post   Remind Me!   Notify Moderator  
star chaser
member


Reged: 02/10/13

Re: Primary focus new [Re: Jeff2011]
      #5686707 - 02/18/13 09:59 AM

Thanks again I will start doing my home work.

Post Extras: Print Post   Remind Me!   Notify Moderator  
Pages: 1


Extra information
2 registered and 20 anonymous users are browsing this forum.

Moderator:  Knuklhdastrnmr, WOBentley, rflinn68 

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled


Thread views: 279

Jump to

CN Forums Home


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics