DSLR Unable to focus

[EagleStr1ke (Joel)]

Last night was my first attempt at astrophotography, and it did not work I am using a 10" skywatcher goto dob with a 1200mm focal length, and a Nikon D7000. The problem is, once I mounted the camera on the adapter and put it in, I could not get it to focus. I kept turning the focuser all the way until it couldn't go in any further (ie closer). Does this mean I need a focal reducer or focal extender (barlow)?

I hope I don't have to use a barlow, as I was trying to image the eta carinae nebula and it just fillled the frame perfectly, if I use a barlow I'll miss half the image.

Thanks

[leon]

Joe, you will have to extend it just that little bit, 25mm to 50mm should do it nicely, depending on how far out of focus it really was.

Leon

[EagleStr1ke (Joel)]

Ok thanks so hopefully a 2X barlow should do the trick. It wasn't too far out of focus so it should be alright.

[RobF (Rob)]

Hi Joel,

You have a few options to get more "Backfocus":
- longer main mirror bolts (to move it up the tube)
- different focus
- new 2" adaptor

Many of us have struggled with solutions over the years. Whichever way you go its worth persevering - you'll be gobsmacked when you get it going
By the way, an MPCC is a good investment if you do start taking a lot of pics. Many of these threads talk about them too. Hope you get some ideas:


http://www.iceinspace.com.au/forum/s...atcher+adapter

http://www.iceinspace.com.au/forum/s...atcher+adapter

http://www.iceinspace.com.au/forum/s...le+reach+focus

http://www.iceinspace.com.au/forum/s...ighlight=focus

http://www.iceinspace.com.au/forum/s...ad.php?t=33290

http://www.iceinspace.com.au/forum/s...ighlight=focus

[Jon (Jonathan)]

So Joel, a focal reducer and/or a Barlow is NOT what you need. These are lenses which optically modify the focal ratio.

You need something much simpler. You need to get the sensor of your camera closer to or further away from the primary mirror. Further away is easy; you need an extension tube to put the camera further back. If the problem is that you AR not close enough to the primary, then you'll have to move the primary mirror up the tube a little. There are plenty of threads on IIS describing how to do that.

[Marios (Marios)]

You should be able to attach the DSLR with a T thread directly to the focuser just unscrew the 1 1/4 inch eyepiece.

[Lee]

With a newtonian, you almost certainly need to get the image sensor closer to the primary mirror....
Two main options - get a low profile focuser, or move the main mirror up the tube - this is generally done by installing longer collimation bolts, or more drastically by cutting the bottom off the tube and then reinstalling the primary mirror....

[EagleStr1ke (Joel)]

Thanks for all the replies yes I've worked out how to get the camera closer now and it's all working

[rustigsmed (Russell)]

Originally Posted by EagleStr1ke

Thanks for all the replies yes I've worked out how to get the camera closer now and it's all working

look forward to seeing your pics
you can get some good results out of a goto dob and should be easily be able to photograph the eta carina neb.
feel free to check out my flickr page to see what you can do, esp deep space-wise
http://www.flickr.com/photos/80336656@N07/

cheers

rusty