Return to the Cloudy Nights Telescope Reviews home page


Astrophotography and Sketching >> CCD Imaging & Processing

Pages: 1
dawziecat
Carpal Tunnel
*****

Reged: 10/20/10

Loc: Rural Nova Scotia
Need AnotherTube for AT8 to Reach Focus:Source?
      #5629647 - 01/18/13 10:36 AM Attachment (19 downloads)

I have only a single 1" and a single 2" tube for my AT8RC.
Seems I need more extension to reach focus with the ST8300M and FW8.
I see Astronomics are out of stock. I don't want to wait an interminable period of time for a tube. Any other sources for these?
Pic attached showing my FT at max extension. I'm still short.


Post Extras: Print Post   Remind Me!   Notify Moderator  
Dan Crowson
professor emeritus
*****

Reged: 10/08/10

Loc: O'Fallon, MO
Re: Need AnotherTube for AT8 to Reach Focus:Source? new [Re: dawziecat]
      #5629696 - 01/18/13 11:01 AM

Terry,

one option would be to buy a 2" extension tube to put between the SBIG and the focuser. Here's an example - Agena 2" Extension . Another option would be to look for the AT2FF flattener which would add some distance. If you ever thought about adding a focuser, the Moonline 2.5" also adds to the back-focus, too.

The problem you're going to have is that the Astro-Tech extenders are required with these scopes and even people with extras (I have an AT6RC and AT8RC) are reluctant to get rid of them.

Dan


Post Extras: Print Post   Remind Me!   Notify Moderator  
jmasin
Carpal Tunnel


Reged: 12/22/08

Loc: Murphy, TX (DFW)
Re: Need AnotherTube for AT8 to Reach Focus:Source? new [Re: Dan Crowson]
      #5629998 - 01/18/13 01:58 PM

I'd do what Dan says. Just get a 2" t-thread between the cam/focuser.

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

Reged: 10/20/10

Loc: Rural Nova Scotia
Re: Need AnotherTube for AT8 to Reach Focus:Source? new [Re: jmasin]
      #5630134 - 01/18/13 03:40 PM

Thanks, Dan and Jon. I ordered the Agena 2" extension. I hope it will be enough.

Post Extras: Print Post   Remind Me!   Notify Moderator  
pfile
Post Laureate


Reged: 06/14/09

Re: Need AnotherTube for AT8 to Reach Focus:Source? new [Re: dawziecat]
      #5630502 - 01/18/13 07:54 PM

that's actually kind of weird, i don't think i've ever not been able to reach focus on an AT10RC and an AT6RC. the 2 stock rings have always been enough. and right now i think i have only the thinnest ring installed, but that's with AO-8+STT-FW8+STT-8300M.


i wonder if this means your (or my) primary mirror position is wrong relative to the secondary?


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

Reged: 10/20/10

Loc: Rural Nova Scotia
Re: Need AnotherTube for AT8 to Reach Focus:Source? new [Re: pfile]
      #5630757 - 01/18/13 10:53 PM

Quote:

i wonder if this means your (or my) primary mirror position is wrong relative to the secondary?





I hope not!!!

According to this link the focal plane of the AT8RC is located 255 mm behind the back plane of the rear plate.

The front of my FW8 as pictured is about 65mm short of that.
The camera sensor is further back still.
In reading this thread bear in mind I have not achieved focus but have only tried in daylight and with an object some 500 to 700 feet away (more or less). Perhaps I am shooting myself in the foot here?


Post Extras: Print Post   Remind Me!   Notify Moderator  
jmasin
Carpal Tunnel


Reged: 12/22/08

Loc: Murphy, TX (DFW)
Re: Need AnotherTube for AT8 to Reach Focus:Source? new [Re: dawziecat]
      #5630774 - 01/18/13 11:02 PM

This is what it takes me to reach focus with my AT10...

The MMOAG takes up alot of backfocus

http://www.jemastrophoto.com/wp-content/uploads/2011/09/CS_Image_Train.jpg

Image train with measurements here: http://www.jemastrophoto.com/wp-content/uploads/2011/10/AT10RCF_Image_Train.pdf
Again, that's an AT10

Edited by jmasin (01/18/13 11:03 PM)


Post Extras: Print Post   Remind Me!   Notify Moderator  
pfile
Post Laureate


Reged: 06/14/09

Re: Need AnotherTube for AT8 to Reach Focus:Source? new [Re: jmasin]
      #5631527 - 01/19/13 12:58 PM

oh - i'm not sure 500-700 feet is really far enough away. can you see something a few miles away?

like jon, i have the 1" spacer, a moonlite focuser, an SBIG AO-8, FW8-STT and STT-8300. focus is reached maybe 2/3 the way thru the focuser travel.


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

Reged: 10/20/10

Loc: Rural Nova Scotia
Re: Need AnotherTube for AT8 to Reach Focus:Source? new [Re: pfile]
      #5632313 - 01/19/13 10:09 PM

Quote:

oh - i'm not sure 500-700 feet is really far enough away. can you see something a few miles away?




In a word, "no!"
I just will have to try on a star at night. (What an idea that is, eh? )

Trouble is, I am OOF, and don't really know where the thing is pointing. Until I can get a star in the FOV and a finder aligned, I don't know where the thing is pointing. The star has to be close enough to focus to at least be visible. Surely everybody is faced with this with a new system?


Post Extras: Print Post   Remind Me!   Notify Moderator  
JoseBorrero
Post Laureate
*****

Reged: 09/04/09

Loc: Puerto Rico Island
Re: Need AnotherTube for AT8 to Reach Focus:Source? new [Re: dawziecat]
      #5632464 - 01/19/13 11:53 PM

I think the mallicam RC version has more backfocus, had you researched that?

Post Extras: Print Post   Remind Me!   Notify Moderator  
kfir Simon
Vendor-PowerNewt


Reged: 09/21/10

Re: Need AnotherTube for AT8 to Reach Focus:Source? new [Re: JoseBorrero]
      #5636230 - 01/22/13 04:49 AM

I bought a 2" extender from here:
http://www.teleskop-express.de/shop/product_info.php/info/p2773_GSO-50mm-exte...

Cheers

Kfir


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

Reged: 10/20/10

Loc: Rural Nova Scotia
Re: Need AnotherTube for AT8 to Reach Focus:Source? new [Re: kfir Simon]
      #5640224 - 01/24/13 09:08 AM

Hi Kfir:

Looks like a nice spacer but I only tried once to order anything to NA from Europe and it was not a success. The vendor had no interest it seems.
Sort of soured me on the experience.

I focused the AT8RC last night, using the 2" Agena extender.
Focus occurs with the SBIG FW8 face plate 227mm back from the rear of the AT8RC back plate. This was with the Astrodon 3mm Ha.


Post Extras: Print Post   Remind Me!   Notify Moderator  
jmasin
Carpal Tunnel


Reged: 12/22/08

Loc: Murphy, TX (DFW)
Re: Need AnotherTube for AT8 to Reach Focus:Source? new [Re: dawziecat]
      #5640246 - 01/24/13 09:23 AM

Quote:

I focused the AT8RC last night, using the 2" Agena extender.
Focus occurs with the SBIG FW8 face plate 227mm back from the rear of the AT8RC back plate. This was with the Astrodon 3mm Ha.




Good!

That sounds about right... glad you got it!


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


Extra information
11 registered and 14 anonymous users are browsing this forum.

Moderator:  Oldfield, droid, Scott in NC, bilgebay, WOBentley 

Print Thread

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


Thread views: 579

Jump to

CN Forums Home




Cloudy Nights Sponsor: Astronomics