Star Alignment Issues with GSO 8RC

[mcmalloy]

Hello there!

A few weeks ago I decided to purchase the 200mm GSO RC. It has been fairly cloudy, enough that I have only had the chance to be out with the scope twice since I have gotten it.

However I have had major issues doing the 3 star alignment with my AZ EQ6 GT mount, while using the 8RC. This is the way that I have normally aligned:

I attach my 700D camera to the OTA and control it through Backyard EOS. When I have entered the Time and Date details, and doing a polar alignment through the polar scope, I choose the 3 star alignment method. At this point my Camera is set to Liveview Mode at 12800ISO on Bulb settings. The mount then continues to slew to a given bright star, such as Capella, Arcterus etc. Normally I would see the star inside the FoV of my Camera, and then slew the star towards the center of the image crosshair. However this is where my problem comes:

There are absolutely no signs of a bright star inside of my FoV. I am aware that the 8RC has a moderately high Focal Length, however I still cannot figure out why I cannot see any bright star in my fov. I tried slewing the mount gently in a few different directions, making sure that the chosen star had not slipped outside of the cameras FoV. Nothing. I am afraid that it is because the 8RC has a focal ratio of 8, meaning that stars dont appear bright enough in the liveview function. However I have seen and read other places that people have been able to use the liveview function with their cameras on the very same telescope that I now own. 

Another thing to notice : I have made sure that the telescope itself is collimated (which it is). The telescope is at least collimated enough to reach a pretty decent focus, so the collimation is definitely not a factor in all of this. If someone could give me a little insight into their methods of aligning with this type of telescope, and what I might be doing wrong - Then I would appreciate to hear what you have to say! 

 

Clear Skies, Mark Malloy

[Oddsocks]

I had the Altair version of this scope a few years ago and I remember the focal position when using an eyepiece was very different to that when using a camera. The Altair version was supplied with a set of three large backfocus spacing rings that screw on the rear of the scope between the visual back rear thread and the focuser, I can't be sure but I think it needed one spacer for visual with a diagonal and Televue Radian eyepiece and three spacers with the camera fitted and no diagonal.

The focuser did not have enough range to bring a star into focus if the spacer rings were not fitted.

You can confirm if this is your problem next time you are out by pointing the scope at the moon or bright star and look through the DSLR reflex viewfinder, if the spacing is wrong you will barely see anything but an image might slowly begin to appear at the very ends of the focuser travel, if this is the case add or remove a spacer ring as appropriate and try focussing again. once the spacing and focus is correct then live view should be able to pick up the stars easily enough.

I always did my alignment by eye using a Telrad and found it accurate enough to put the target somewhere in the field of view of a Starlight SXH9M which is quite a small chip compared to a DSLR so you should not have any problems once the spacing/focussing is sorted.

[Daniel-K]

Are you using the extensions that should come with the scope? 

 

For me I need  all 3 to get focus on my RC6

[mcmalloy]

Sorry I forgot to mention that yes, I can bring my telescope in focus with my camera. I know this because I could take a short exposure of like 3-5 seconds, and i will se stars in focus. I have the spacers needed to achieve focus, so that is not the issue..

[Daniel-K]

3 hours ago, mcmalloy said:

Sorry I forgot to mention that yes, I can bring my telescope in focus with my camera. I know this because I could take a short exposure of like 3-5 seconds, and i will se stars in focus. I have the spacers needed to achieve focus, so that is not the issue..

Then it sounds like you just need to align your finder propperly.

I assume you know how to.