Where Has My Target Gone ???

[Vortex]

Hi All,

A question about alignment on astro targets ...

I always set up in the following way :-

1) Align Tripod and Mount pointing North.

2) Polar align using Polemaster.

3) Calibrate scope using Celestron Star Sense

4) GOTO target (in this case VEGA) - VEGA is slightly to one side in my 25mm eyepiece.

5) Calibrate STARSENSE using VEGA - swap to a 15mm eyepiece and centre VEGA.

6) Perform a STARSENSE AUTO alignment once again.

 

After these steps, whichever target I choose, it ALWAYS appears smack in the centre of my eyepiece .... HOWEVER ....

when I switch the eyepiece out and replace with my ALTAIR GP-CAM 290C - the target is not in the FOV, I have to go hunting for it.

 

If at this point, I pop my 15mm or 25mm eyepiece back in, the target is dead centre again!

 

Is this just because of the FOV of the CMOS camera ?

 

What would be the best way to ensure that I don't have to keep hunting around ?

 

Many thanks!

 

Regards

 

V

[Neil H]

Hi I use a cross hair eyepiece to do set up you then know your 100% right , if jump down to a low mm eyepiece  it's normally in the field view but not centre so I would say it's is just the fov of the camera but may be worth trying a cross hair eyepiece

[Cornelius Varley]

Your camera will probably (most definitely) have a much smaller field of view than the eyepiece. If you use an eyepiece with a shorter focal length to centre the target then you might get better results.

[Vortex]

Thank you Neil H and Cornelius Valley.

Yes, I suspected FOV, so I think when calibrating the Starsense, I will use gradually shorter focal length eyepieces until I have the target centred with the lowest I have ( a 5mm I think).  That will maybe do the trick.

Best Regards

V

 

[Cosmic Geoff]

The field of view of the CMOS camera will be very small. If you accurately centre the view in an eyepiece it should be easy to pick it up with the camera, but only if the camera is in focus. If the camera is not in focus (which is highly likely) even a bright object will be invisible.  Getting this right is something of an art...  To bring the camera into focus with a Newtonian you may have to move the camera/focuser inwards from the eyepiece focus by a quarter of an inch or more (There is no guarantee that this is even possible)...

I found two finding devices very helpful - a RACI 9x50 finder accurately aligned (for bright objects) and a "flip mirror" for faint objects. Unfortunately the latter won't work with a Newtonian.

[Neil H]

The crosshair eyepiece is normally 12mm so it's narrow FOV , so for the cheap price may be worth trying one it will make things faster and easier

https://www.amazon.co.uk/Seben-Illuminated-Eyepiece-Crosshair-Telescope/dp/B00I4RHUTU/ref=sr_1_5?dchild=1&keywords=reticle+eyepiece&qid=1590953503&sr=8-5

Cheap one 

https://www.amazon.co.uk/Explopur-Illuminated-Eyepiece-Planetary-Telescope/dp/B07VG5V298/ref=sr_1_10?dchild=1&keywords=reticle+eyepiece&qid=1590953503&sr=8-10