Dslr focusing

[Brosnan]

Hi guys,

i have a celestron astromaster 130eq and am having great trouble focusing my dslr with it. I have T-adapters etc and a Barlow lens on the way. I am hoping to get some tips on how to focus it without having to buy too many more accessories. For example I am able to find and see the Orion Nebula fairly well with my 20mm eyepiece without the dslr but when it comes to attaching the dslr I cannot get it to focus! 

Thanks guys, hopefully someone has a suggestion. ?

[Cornelius Varley]

Hello and welcome to SGL. The Astromaster, along with many other reflectors, require a barlow lens to get a focussed image in the camera. Without the barlow the point of focus is too close to the telescope to allow the camera to reach the point of focus. Adding a barlow lens moves the point of focus outwards enough to enable the camera to focus.

 

[Brosnan]

Thanks very much! ? Hope this is successful! 

[Nigel G]

Hi there, have you seen these, it might be enough depending on how far out of focus, this will allow 9mm more inward travel.

https://www.firstlightoptics.com/adapters/baader-ultra-short-canon-eos-t-ring.html

Nige.

[Brosnan]

Thanks Nige! Appreciate it???

[mikey2000]

I can't get my DSLR to focus on my 130P unless I use a barlow.  Then, it's a rather magnified view!  Taking pics requires a bit of luck really - it's very hard to avoid star trails at that sort of magnification on my EQ2 mount.

 

The field of view is tiny!   It's really hard to get accurate focus too.  I made a 'bhatinov mask' which helps tremendously.  I cut my own one of card with a craft knife.  Visit http://astrojargon.net/MaskGen.aspx  for a template generator.

 

I often find that I need to look for a brighter star to focus on then re-aim the scope and camera towards the target.  That second part is hard indeed!

 

[RichLD]

I had the same problem and cured it by sawing off a bit off the ota (IIRC it was 30mm or so) at the mirror end, moving the mirror closer to achieve focus. This reduced the focal length of the scope slightly but not by so much that you'd notice in most situations. I can still use the scope for visual by using an extension tube at the eyepiece end.

HTH

Rich

[iapa]

I had a similar issue with my 130 SLT, and solved, initially with a 2x barlow. 

As above, most reflectors have issues when trying to focus with a DSLR as the sensor on a DSLR is generally 55mm from the surface of the t-dapter ( adapters as noted by @Nigel C excepted) which puts the sensor surface a fair bit further out than an eye piece which projects into the focuser.

The Skywatcher P-DS series, as an example, are 'astrographs' and are built, as described by @RichLD, with a shorter tube which brings the focal plane further out from the focuser, allowing focus without a Barlow.

I took the 'purchase' option rather than 'DIY' set about my OTA with a hacksaw - straight lines and my hands do not work together.