Focusing the Altair 50mm Guide Scope and GPCAM

[mountainmadman]

Good evening members of the SGL collective,

This is one of those questions that could be put into several different topics, but seeing as it's a beginner question with this particular bit of kit, I though I'd start here...

I've recently invested in one of these:  https://www.altairastro.com/Altair-GPCAM-50mm-Guide-Scope-Camera-Kit.html to add guiding to my set up.  Because of the weather, I've only managed to get it outside once, but that was enough to raise a question.

Incase you can't visit the link, it's a Altair 50mm Guide Scope Package with GPCAM Mono.  With the package came with a short extender for the camera along with the associated cables for connectivity etc.  Actually, the description of the kit contents on the website is spot on.  However, what I can't find information on is the process for focusing the kit.  On the only time I had this out under the stars, the only way I could achieve any sort of focus is partially pulling out the camera from guide scope.  It just seemed like that there wasn't enough back focus on the guide scope by quite some margin.  Eventually, I did get some sort of focus, although definitely by luck.  It was sufficient to get the SharpCap software working though.

So, what I was wondering is if there were any other SGL members who own this guide kit, and, if they have any words of wisdom to impart about its correct setup please?

Thanks for your time everyone,

Clear Skies,

Tony

 

[Starlight 1]

I have the 60mm with this camera , for me to work it out I put the filter on then the Nosepiece/Barrel (do not use the red filter)them put the camera out to the point were you can just see the Nosepiece/Barrel and  focus  all the way out as well , that give you about 20mm back. and it do hold ok . you be about 1 mm in or out .

Edited January 31, 2017 by Starlight 1

[mountainmadman]

38 minutes ago, Starlight 1 said:

I have the 60mm with this camera , for me to work it out I put the filter on then the Nosepiece/Barrel (do not use the red filter)them put the camera out to the point were you can just see the Nosepiece/Barrel and  focus  all the way out as well , that give you about 20mm back. and it do hold ok . you be about 1 mm in or out .

Thanks for your reply Starlight 1.

I'll need to go and get the camera and the kit and have a closer look.  I don't recall seeing a red filter in the box, so I'll double check that.  Unfortunately, there's no sign of anything remotely approaching a clear sky foreseeable for the next week or so.  I'll give it a try when weather allows.

Thanks once again for your time,

Tony

 

[tomato]

Hello Tony,

I have the same set up as Starlight 1 and pretty much use the same method. If you wind the helical focuser nearly all the way out and centre on a bright star (if the clouds ever go away☹️), then you can gently slide the camera in and out to find the point of focus. 

Make a note of the ideal length of the camera barrel proud of scope tube for future set ups.

Clear Skies

 

Steve

[mountainmadman]

5 minutes ago, tomato said:

Hello Tony,

I have the same set up as Starlight 1 and pretty much use the same method. If you wind the helical focuser nearly all the way out and centre on a bright star (if the clouds ever go away☹️), then you can gently slide the camera in and out to find the point of focus. 

Make a note of the ideal length of the camera barrel proud of scope tube for future set ups.

Clear Skies

 

Steve

Thanks for your reply Steve,

It sounds like one of those tasks that when you get it sorted, it should be easily repeatable.  I keep a little roll of masking tape in the box of tricks, so I'll tear a piece off when I get optimum focus and stick it to the side of the camera to mark it for next time.

All the best,

Tony

[rigradio]

Rough focusing:
- focus in day time on a distant object...or
- focus on the moon
it's much easier  ....you want the star slightly defocused anyway

Ketut

 

Edited February 1, 2017 by rigradio

[mountainmadman]

12 hours ago, rigradio said:

Rough focusing:
- focus in day time on a distant object...or
- focus on the moon
it's much easier  ....you want the star slightly defocused anyway

Ketut

 

Hi Ketut,

thanks for your reply.  It just so happens that the time I was trying this guide scope package out for the first time, it was new moon, so I couldn't use that as a focusing target.  But it's a very valid point and one that I shall remember.

Day time, I don't have anything far enough away in line of site that I can practise on.  Nevertheless, another very valid suggestion.

I have a question though, why would I want the start to be slightly defocussed in the guide scope image anyway?  I have assumed that a sharp focus is best to make it easier for software such as PHP2 to detect the movement of the start in the field of view.  I expect I've misunderstood how that would work.  Again though, if that is the suggested way of focussing your guide scope and camera, then that's what I will do next time.
Thanks once again for your reply,

Tony

[tomato]

Yes, a piece of tape on the barrel, should do the trick!?

PHD can work better on a slightly out of focus star, I think it allows the software to read the brightness trend across the pixels more reliably. In practice if I see a lot of faint stars come into view on the guide camera as I move the focuser, I generally leave it at that.

[rigradio]

9 hours ago, mountainmadman said:

Hi Ketut,

thanks for your reply.  It just so happens that the time I was trying this guide scope package out for the first time, it was new moon, so I couldn't use that as a focusing target.  But it's a very valid point and one that I shall remember.

Day time, I don't have anything far enough away in line of site that I can practise on.  Nevertheless, another very valid suggestion.

I have a question though, why would I want the start to be slightly defocussed in the guide scope image anyway?  I have assumed that a sharp focus is best to make it easier for software such as PHP2 to detect the movement of the start in the field of view.  I expect I've misunderstood how that would work.  Again though, if that is the suggested way of focussing your guide scope and camera, then that's what I will do next time.
Thanks once again for your reply,

Tony

Hi Tony,

Quoted from another thread:
"The next tip is that it might help defocus the guide scope slightly. If you are having problems with saturated stars, or you are exceeding the 4x pixel scale rule, this may help. Defocusing will spread the light of the star over more camera pixels which can prevent saturation, and also makes it easier for PHD to detect the centroid of the guide star more accurately. Don't go mad with defocusing or PHD won't be able to lock onto the star and you may start getting ‘Star Lost’ errors if your SN figure drops too much due to de-focusing.

In all cases your guide star still needs to have a brighter central peak and not turn into a hollow doughnut, but a bit of defocus on the guide scope may help where you have SN to spare. You can use the ‘Star Profile’ option on the ‘Tools’ menu to check the profile of your guide star once selected. It should have a peak in the middle like a mountain. If it is flat on top you have a saturated star, and if there is a dip you need to focus more."

Source -> PHD Guidng Basic & Troubleshooting

Ketut

[woldsweather]

I'm glad its not just me who cant focus this guidescope. I spent 5 hours 2 nights ago trying to focus and find stars in Sharpcap. I'm on the verge of selling it and trying to find a guidescope WITH a focusser.