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Hello fellow Astrophotographers. So I was trying to image the Heart and Soul nebulae last night (under Bortle 3 Skies and very good weather conditions). I was trying to guide with PHD2 and imaging with APT. Also I always use automatic dither in RA axis and manually in Declination. However, there was an issue with Guiding. PHD2 was trying to give really big corrections for some reason and the result was severe star trails in my images and PHD2 was giving me a message that it couldn't give sufficient corrections. I couldn't figure out what was wrong. I tried Different settings for guiding, I used a dark library for my guide camera to minimize the noise, I tried pointing the guide scope in a slightly different angle and still the problem was persistent. So I was wondering maybe that particular area of the sky doesn't have bright enough stars to properly guide? Maybe I should use a guide scope with different focal length? Does anyone have any idea why this is happening? I apologize for the long text and thank you in advance for your comment. I use the following equipment: Imaging camera:Canon 250D Lens: Samyang 135mm Star Tracker:SkyWatcher Star Adventure 2i Guide Camera:ZWO ASI 120MC-S Guide Scope:ZWO 30F4 Miniscope |
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Hi, did you recalibrate after you moved the guide scope in relation to the main scope? That is required or else PHD2 will act very erratic usually. When I have had PHD2 act up, I like to go back to basics. Reset stock parameters, recalibrate within 20 degrees of the celestial equator, then run guiding assistant and apply recommended changes and advice. This is a good guide if you haven’t seen it yet. Good luck with your troubleshooting. |
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I assume that you have had good success with this guiding setup previously. I agree with apennine104. Any time that PhD2 has acted irrationally for me in the past (not often at all), I start from scratch with a new profile and default settings. Create a new dark library, calibrate PHD2 near the meridian/celestial equator, and definitely run the Guiding Assist. Note: I have had PHd2 act wonky at the start of a session and a pc restart corrected the issue. Good luck! Jim |
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| Let phd2 do a fresh calibration! This solves most of the problems. If you don't succeed with that, run the guiding assistant! Best of luck! |
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What mount are you using ? This may be an issue. I had frequent problems with my iOptron mount with encoders. Phd2 is a good software but it is what I call an "engineer's software", with so many settings that the simple amateur wastes entire nights fighting with it. With such a short focale, you should ba able to image without guiding. Anyway, I solved years of guiding issues when I started using ASIAIR. This cheap micro computer does all the job, and it starts guiding in a few seconds, for hours, meridian flip included ! Philippe |
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A few thoughts. Guiding with a color camera is not optimum. I didn't do the math for your guiding fl, but double check it. The fundamentals others have stated related to calibration at the south celestial equator and the value of running the guide assistant for a worm cycle are table stakes. Don't proceed until you've been successful in calibration. If your polar alignment is off, it'll show. If your fl is wrong, it'll show. Follow it's recommendations! Best to run again after making corrections until you get a solid calibration. cheers! |
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Hi all, For all it is worth, here is my opinion on it: Guiding accuracy comes down to math. If we look at a short focal length scope, the dither does impacts the guiding quite a bit. Here is an example: I have a small imaging refractor with 480mm focal length. Imaging camera is a ZWO ASI1600mm with 3.8 micron pixel size. If I calculate the resolution for this setup, I get 1.63 arcsecond per pixel for the imaging train (go to Atronomytools.net for the guidescope calculator). So, to generate a dither of 5 pixel, then my displacement is 5 pixels x 1.63 "/px = 8.15 arcseconds. If my aim is to autoguide at less than 1 arcsecond, then the guide camera just got a big jolt in one direction or another of over 8 arcseconds. PHD will then will try to automatically compensate for it. That is why we are seeing huge spikes in tracking. PHD is simply doing what it is supposed to be doing. For a longer focal length imaging scope, it is not impacted as much by the dither. For example, I have a Ritchey-Chretien at 1645 mm focal length. With the same camera as above, I get 0.48 "/px for this combination. A 5 pixel dither, in this case, will generate a deviation of 5 pixels x 0.48 "/px = 2.4 Arcsecond. When guiding at less than 2 arcsecond, the 2.4 arcsecond displacement is not major impact. I image under a Bortle 9 sky. My seeing is normally not all that great. Therefore, a 2 arcsecond guiding is normally good for my setup. I have however improved my guiding to under 1 arcsecond by doing the following: 1) do a good polar alignment of the mount. It is surprising how much impact the polar alignment has on good guiding. 2) limit the dither to 1-2 pixels at shorter focal length of the imaging scope. Limit the dither to 3-5 pixels for longer focal length. 3) ensure that your setup is well balanced and the backlash is properly adjusted. 4) properly adjust the guiding pulses in PDH. I typically use 1 to 1.5 seconds at shorter focal length and 2-3 seconds pulses at longer focal length imaging scopes. The longer pulses smooth out the guiding. There is a chance, however that you will get drifting if you use too long of a guide pulse. PHD instructions recommend pulses from 1 to 4 seconds maximum. 5) make sure that the guide scope is properly matched to the imaging scope. I try to keep mine under 1:5 guiding ratio. Again, go to Astronomytools.net. They have a guidescope calculator that will give you the guidescope ratio, imaging resolution (arcsec / pixel), based on the focal length of your 2 scopes and the pixel size of both the imaging camera and the guide camera. Don't overthink it and have fun ! François |
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I've had those symptoms before. It was caused by forgetting to tighten the mount clutches (which some mounts don't have). When a mysterious problem pops up on a system that worked well before, it's typically hardware, not software. |
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Ensure you are not trying to use a hot pixel for guding. Paul |
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| How do you manually dither in dec? How do you tell phd2 that you’ve manually dithered in dec? |
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| I have had this issue till I did a hyI have had this issue till I did a hy[ertune on my EQ6-R Pro. Problem is the settle time. I dither 5 to 10px, before the hypertune I was also getting star trails. After the tune my mount can settle within 6 to 10 seonds. |
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| Had this message together with an large peak in guiding every 6 minutes. In my case the belt of my eq6r was damaged. |
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How do you manually dither in dec? How do you tell phd2 that you’ve manually dithered in dec? Well i auto dither in RA every single frame. After 3-4 frames i pause the program in APT and then stop the guiding, i move the dec manually and start guiding again. This takes about 10 seconds. So far this has always worked perfectly and didn’t give me any strange guiding behaviour. The downside is that i have to be constantly monitoring the sequence. |
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Hi, did you recalibrate after you moved the guide scope in relation to the main scope? That is required or else PHD2 will act very erratic usually. This was very helpful thanks |
