Why is it I can focus on a star with the eyepiece but not through my dslr

[DavidBrmley]

Hi, I am new to astroimaging.  I have a celestron nextetar 130slt, canon 250D dslr and celestron tiring and adaptor.  I focus on a star starting with those lowest magnification lense (25mm), then 9 mm Centre the star in both. Then switch the camera in to the eye piece mount. Some times i can focus on the star but some times it does not appear on the camera screen or view finder. I know that the star moves from the centre of the imaging field.  So I have to re-centre.  Is it a problem with the colimation?

 

david

[Cornelius Varley]

5 minutes ago, DavidBrmley said:

Hi, I am new to astroimaging.  I have a celestron nextetar 130slt, canon 250D dslr and celestron tiring and adaptor.  I focus on a star starting with those lowest magnification lense (25mm), then 9 mm Centre the star in both. Then switch the camera in to the eye piece mount. Some times i can focus on the star but some times it does not appear on the camera screen or view finder. I know that the star moves from the centre of the imaging field.  So I have to re-centre.  Is it a problem with the colimation?

 

david

Hello and welcome to SGL. Not being able to achieve focus with a DSLR on a Newtonian is a common problem, the telescope wasn't designed for it. There are some remedies though. Firstly, check that you have no extra extension tubes fitted between the camera and focuser. You said that you were using a t-ring on the camera and a Celestron adapter, if your telescope accepts both 2" and 1.25" eyepieces it should be possible to remove the adapter and the eyepiece holder (this should unscrew into two pieces) and screw the t-ring on to the bottom half of the holder. This video should explain the procedure

 

 

[Knight of Clear Skies]

26 minutes ago, DavidBrmley said:

Some times i can focus on the star but some times it does not appear on the camera screen or view finder.

It's difficult to say what the problem is here. If you're getting good focus sometimes it means your telescope can reach focus with a camera (not all can, the sensor is further back than an eyepiece - not all focusers are designed to work with cameras). have you tried focussing the camera on a distant object during daytime to confirm there are no problems?

It could be that the star is moving out of the field of view when you switch over, or it could be an exposure setting issue on the camera. Have you tried increasing the ISO level to the highest level when focussing? Also, you could try taking an exposure of a few seconds to confirm whether the star is within the field of view.

[DavidBrmley]

Thank you all I will try you suggestions.