I feel like this is going to be a duplicate of this question, Astrophotography - Unable to achieve focus with current setup.

However, the suggestions to go to a straight adapter doesn't apply in my case. I have a Canon Rebel XT, with a 2" 48mm adapter https://www.amazon.com/gp/product/B00T3P5ABC/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1, on my Orion XT10 dob, http://www.telescope.com/Telescopes/Dobsonian-Telescopes/IntelliScope-Dobsonians/Orion-SkyQuest-XT10i-IntelliScope-Dobsonian-Telescope/pc/1/c/12/sc/27/p/102013.uts.

When I attach the adapter to the camera and focus on a planet or star, I can't achieve focus. My focus adjuster on the scope can't get close enough. It's as if the camera is just out of range of the focuser.

I'm not sure what the issue is and would love to hear some suggestions. I'm just a noob getting started and have a lot to learn so I apologize at all the beginner questions here.

  • $\begingroup$ I think that the link you show does actually provide the possible solutions for you, since it deals with the case where you can't get the focuser far enough in. An alternative might be to get a low profile focuser, and replace the one on your dob. $\endgroup$ – Dr Chuck Jun 24 '16 at 5:48
  • $\begingroup$ Surely someone makes a negative lens to fit on these adapters, or within the focuser? $\endgroup$ – Wayfaring Stranger Jun 24 '16 at 13:33
  • $\begingroup$ A barlow lens might move the focus in the correct direction, but would also increase the effective focal length and focal ratio. $\endgroup$ – James Screech Jun 24 '16 at 13:41
  • $\begingroup$ This telescope was probably designed for visual use only, since the mount is not driven. Even if the focus problem is solved, it will only be possible to take short duration exposures, so as to avoid star trails. $\endgroup$ – Dr Chuck Jun 25 '16 at 8:20

This is a common problem with Newtonian type telescopes and DSLRs, the sensor in the camera is too far back to reach focus. As mentioned in the comments a low profile focuser may help or move the main mirror up the tube, I've seen this done on some Skywatcher Newtonians to solve similar problems.

  • $\begingroup$ Do you know if a Barlow Lense would extend the focal length? $\endgroup$ – Joshua Belden Jun 27 '16 at 15:25
  • $\begingroup$ The point of a barlow is to extend the focal length. Most also move the focus point further out as a side effect of this. Its a common trick with people who image with PST solar telescopes, who remove the lens cell from a barlow and screw it into the camera adapter, though this is with 1.25" barlows / adapters. I've never heard of anyone doing it with a 2" barlow as you would need with a DSLR. $\endgroup$ – James Screech Jun 28 '16 at 7:17

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