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Cannot get good focus with OAG and Lodestar x2


kirkster501

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After weeks of bad weather, I had a torrid time last night, a precious clear night blown..... :(  I gave up at 00:30 and went to bed after three hours wasted.  Another guiding issue with the TEC as well but I'll save that for another post.  So could not get either system to work.  So my plan B fell through as well.... 

I have my FSQ85 and G2-8300 with OAG.  Main imaging camera focuses perfectly, no issues there and I get great stars that are pinpoint edge to edge.  But look at the guide stars in the image (taken with iPhone) below.  The stars look rubbish and I don't think that is good enough focus? The calibration ran perfectly but look at the graph afterwards (ignore the first bit).  I don't think there is enough of a centroid for PHD2 to lock onto? What you see below is absolutely the best focus I could get after 60 minutes of fiddling and faffing around.

I know that perfect focus is not necessary for PHD2 (even beneficial).  The weird thing is that I can get inside focus and outside focus. i.e stars get progressively blurrier either side so it's not that I need extensions.  But at the point where it should be in focus, where it "snaps" in (and I get there by tiny movements of the helical focuser) my stars are still not tight enough.  What could be causing this?  I'm starting to think is it something to do with binning?  My guiding graph is dreadful.  From my observatory I do not have a distant enough object visible to be able to focus them both during day time, I am in the middle of an housing estate (quite a dark one fortunately).

I am going to reinstall PHD2, check balance again (not especially easy with the MESU) and polar align to eliminate those.

Would appreciate any thought please guys? Struggling a bit with this one. 

Thanks, Steve

IMG_0539.thumb.jpg.07d99fa96be4155b8775ea19992600cd.jpg

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I can't see how with the Moravian OAG that I can push the prism into the light cone further. I need to play about.

Yes, the moon trick is the nexy thing to try.  How do you guys focus on the moon with the OAG guide cam? PHD2 cannot go low enough in exposure....  Is there another application?

Thanks.

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Hi Steve,

Sorry for your woes, especially on a clear night. PHD or PHD2 does not require sharp stars to guide on, if anything Craig Stark does mention a slightly out of focus star gives better results. If you need to set up your OAG it is better to do this during daylight, on a distant terrestrial object, focusing both the Moravian & the LodestarX2. You say you used the Guiding Assistant in PHD2 as this usually gets you a reasonable starting point. Also, have you checked on the PHD2 & Mesu forums to obtain suitable guiding parameters for your set up. Once fine tuned you will have amazing guiding with the Mesu.

Steve

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Hi. It looks like you're only partly in the light cone and so at the extremities of the fov where star and focus distortions are more evident. To get the best prism position, take a series of flat frames whilst pushing the prism further centre field until it forms a shadow thence outward to optimal where the shadow just disappears.

To get best focus, no need to use your eyes. Use PHD2's star profile; loop on a star and with your god-send helical focuser, twist in small amounts whilst observing for minimum HFD. Allow a little settle time after each twist.

HTH. When it's up, you'll never look back:)

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I use a FSQ85/QSI/Lodestar combo with no real problems, so your setup should work ok.

To get better star shapes (although PHD2 doesn't appear to need them) have you checked that the CCD is aligned to minimise offset of the guide cam from the optical axis?

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On my TEC where I was also having issues, I managed to get a focus on a roof 200 metres away and aligned the main camera (ATIK 460) and the guide cam (ZWO ASI174).  I assume the focus relationship between the two is linear when I go to infinity and not a roof...?

Will do the same with the FSQ and the Lodestar.  However the Lodestar still shows completely washed out white even with tiny exposures, 0.0001sec..... ??   I'll need to try later when it is getting darker and not on a brilliant sunny day.

My balance is fine and I reinstalled PHD2 and did a new darks library.

As I have been discussing with Geof, could also be because the seeing was shi** last night as well.

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I think Alacant could be spot on, Steve as your stars look focused, but just not enough light on the sensor.  I find that with my X2 1 second is a little short, and tend to use 2.5s.  I don't think you will do any testing during the day as it will do what you have found, and just over expose, so you'll unfortunately probably need to do any testing in pretty dark conditions.

Hope you get it sorted as that's an awesome combination.

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I have the same camera and OAG as you.  Is the helical focuser a separate piece of kit, or is it that thing that just screws into the OAG and holds the guidecam ?  I ended up 3D-printing a really thin spacer so I could keep it at optimal distance.

I found that having focus too tight was actually counter-productive since all those edge-of-frame effects made the stars become double or triple lobed.  Just slightly out of focus (outwards) for me brought it back to a nice round blob with a clear centroid.  I use about 3s exposures in phd, which will probably help you.

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