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Issues with guiding

astrophotography CMOS imaging
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#1 avodcap7



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Posted 04 July 2020 - 07:38 PM



I just got my guiding package and got a chance to try it out tonight. The package is this: https://www.astrosho...g-set60/p,52859

I used PHD2 with the ST-4, because I cannot connect my hand controller to the PC yet.


I had a few problems with the package tonight:

  • The focusing - I found Arcturus and tried to focus on it with 1 second loop, and it seems to focus fine, but when in focus, the star has a big, dimmer circle around it.
  • The camera, when in focus, detected only 3 or 4 stars with a 3 second loop. Even then PHD2 lost the star a few times. Also, there is a weird issue: the looped image sometimes gets very bright (star lost), sometimes it's barely visible (star lost). I set a constant loop of 3 seconds.
  • When guiding, my total error was around 2", which I expected because my guide scope is in a position a bit of centre, so that creates problems.

So, my question is: what settings can I change to see more stars in the loop, fix the weird brightness change issue and finally, the focusing issue.

PS: How do I connect my hand controller to the PC without using an EQDIR cable?


Thanks to anyone that answers,



#2 scopewizard


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Posted 04 July 2020 - 07:47 PM

The glow around bright stars is more than likely because your sensor is a color one and you do not have an IR cut filter installed.

It is not critical as you will track on fainter star.

For more stars set the gamma brightness higher (slider beside the brain) with loop at 1.5 second.

#3 mborland


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Posted 04 July 2020 - 08:41 PM

It's best not to have any really bright stars in the frame when you set up guiding. It makes it harder to see the stars that you want to use. You can get your focus roughly right with a really bright star, but you need to use a dimmer star to fine-tune the focus, calibrate, and run Guiding Assistant.



#4 rgsalinger


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Posted 04 July 2020 - 09:00 PM

The link the OP put in his post says that the camera in question is a mono camera. It's the same Aptima chip that has been around almost forever and it quite useable. mborland has the right idea. Let me amplify that a bit. 


First, if there are halos, etc the most likely cause is the optics of the inexpensive guide scope when looking at an extremely bright star. It's called diffraction and it's just too bad :)


The speed of the loop is not likely the issue either. If a star is brightening and dimming  a great deal, then there is most likely some haze around that's hard to see. Note that the Aptima chip is an 8 bit chip. So it's really easy to overexpose because you have only 8 stops to play with in the first place. So,  even a smallish change in real brightness will give rise to a large change in apparent brightness when looking at a bright star. In sum, then probably the last thing that you want to do is to try to focus on Arcturus. It's so bright that it will be very hard to determine the correct focal point for the camera regardless of the halos. 


It's a much better idea, now that the Milky Way is up, to point anywhere even near there and focus the scope until you can see a lot of stars. Set the gain way up --- maybe around 90 or so and near the milky way you should see a lot of stars. You can play with the gamma but if you just set the gain correctly it should be unnecessary. (I can't remember the last time I had to do that.)


Once you have focus you should run the guiding assistant before doing anything else. That will give you a reasonable starting point. Don't try to calibrate right out of the box. Since you are using the ST4 cable you're going to have to re-calibrate the guiding system every time you move the camera. 


Please give the documentation a good read as well. There's a reason why they wrote it and most questions can be answered in minutes if you familiarize yourself with it. 



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