Focussing a Starlight Express SXV H9-C


#1

Please forgive me (and point me in the right direction if this is not the correct topic for this forum, I am very new to this and dont want to offend :slight_smile:

Until now have been using a DSLR Canon 1100D together with my Sky-Watcher Explorer 250 to take some adequate images using Backyard EOS. I have an EQ6 mount connected to a laptop using an EQMOD cable and guide using a QHY5II camera connected to a EGZ-60 scope. I have sporadic success with astro tortilla and reasonable success with PHD2 and until now everything has been working well (as well as anything astro works that is lol).

Anyway, a friend has recently given me a Startlight Express SXV H9-C which has its own seperate guider and told me to replace my my DSLR to start taking better pictures, he has recommended using SGP.

I have removed the DSLR and fitted the SXV H9C (I decided not to use its autoguider camera as the cable isn’t long enough to reach to my EGZ-60 and to be honest I am happy enough with the guiding setup I have.

I have managed to add all of my equipment to SGP (scope, mount and cameras) and I have found the focus section of SGP and this is where I’m having problems :frowning: I cant bloody focus the thing - talk about having all the gear and no idea, I feel so stupid!

I have the SXV H9C attached to the view finder, I wind it all the way out, start the frame and focus and slowly (over several minutes) wind in the focusser until it is wound all the way in, I never see anything (not even a smudge on the screen). I am pretty sure that I have everything setup because if I shine a light into the end of the camera I get a white screen so the camera must be reacting to light right?) I have also added an extender (maybe I’m not wound out enough? However doing the same thing I get nothing on the screen, its really frustrating, especially when I know I can reattach my DSLR and start imaging in minutes.

Can anyone offer any suggestions as to what I am doing wrong or perhaps how I can start to fault find where the problem lies?

Many thanks

Richard


#2

Richard,
Chill out, lots of people on here who will help you get this sorted out im sure.

I have absolutely no experience with Starlight camera’s but judging by your pic you will likely need
an extension tube screwed to the front of your camera to enable you to get focus. My camera has a
38mm extension tube screwed between a coma corrector and camera.

Don’t go buying tubes yet though, wait til someone here confirms this, could be completely wrong when
it comes to Starlight camera’s. Alternatively, any of the major astronomy stores will sort you out if no
good info comes from here.

Good Luck
Paul


#3

I’m pretty sure this is just a spacing issue. With your DSLR, the backfocus is probably 55mm. That means that from the front of the camera where a lens would attach to the actual CCD sensor the light travels 55mm. Your SXV H9 however only has 17.5mm from the front of the camera to the CCD sensor, a difference of -37.5mm.

It sounds like your focuser is not able to make up the for the difference. So you need to ADD 37.5mm in order to focus the SXV at the same spot as you would focus the DSLR. It wouldn’t have to be exactly 37.5mm, but it does need to be enough to allow your focuser to travel out far enough for the camera to reach focus.

I hope others will confirm this because I do not image with a DSLR or Newt.


#4

What Joel says seems perfectly reasonable to me. The camera needs an extension of something like 37mm to focus with the same focus position as a DSLR with a T ring.

Rings are easily available and I would get several, maybe something like 5mm, 10mm 15mm and 30mm. They often come in sets. You can never have too many.

One way to sort out focus is to start in daylight focussing on a distant terrestrial object. You should be able to see something and that will help. This depends on your camera being able to take really short exposures but I think the camera you have will do that.
The trouble with stars is that if you are a long way out it’s difficult to see anything because the star disks are so big that they are very dim.

Chris


#5

Perfect thanks guys, I’ll go shopping!

Richard


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