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Hi Franz, I got nearly the same equipment as you and I am already wondering how you achieve good 60sec frames with an unguided Redcat!  Earlier I used a 135mm Samyang on my SA and it was pretty easy to reach 2min frames. The Redcat is a totally different story. It is heavy and exceeds the limit of the SA. Even the tiniest things will disturb your tracking: I ruined half a night because a cable was hanging down on the ground from the camera. So even a good cable management can lead to less trouble.When switching to the Redcat I started to use guiding in every session. The balancing becomes a problem, because the counterweight is not big enough anymore. I use a spare tripod head that I mound on the unused screw of the L-Holder. Always remember that you should not be in perfect balance. The side that moves up should be a little bit heavier, maybe 100gr or so. When setting up the guiding I do a very precise drift correction. So I look at the two guiding curves for several minutes and if something drifts away, I correct the polar alignment and try again. With guiding it is no problem for me to reach 3min subs. I use the classig way with laptop, but there are many solutions with battery-powered Raspberry Pi and Smartphone control, if you a maker. ;) |
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Hey Björn, thanks for the insight, but does the spacecat really exceed the SA limit? consulting the raw numbers my setup should not reach the 5kg payload-limit. i find balancing still quite easy to do, although i didnt know before that it should be slightly east-heavy. luckily i got a spare counterweight i ordered seperatly, not knowing that my SA package has one included. anyway its true that the spacecat is at the edge of what the SA can take, especially regarding focal length. |
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Franz Ferdinand: Well, usually one would say photographic capacity is maximum 50% of the stated 5kg. That would mean 2,5kg for the star adventurer. I think I have tortured the poor thing more than most people, with a 72/430 Apo, flattener and Nikon D5300, amounting to roughly 3 kg! I used a neat trick though, detailed earlier in this thread I believe: Since you only guide in RA, you can put your guidescope on the counterweight side, for example with a ballhead. If you point it in roughly the same direction as your imaging scope, guiding will be just as good, as long as every screw is tight on the mount and its base. |
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Hello Everyone, Thanks for all the advice I've read here... I'm afraid I'm currently limited to 60-90sec subs with my SA and RedCat. I have a rejection rate of about 12% at that point. It goes up rather drastically thereafter. I haven't tried guiding yet, perhaps that will be my next step. Dovetailing on Marc's comment, I'd refer everybody to this video from Philippe Leca, who really seems to know how to load up a SA! YouTube link: https://www.youtube.com/watch?v=tEfw2tD94Hg&list=PLSMtlsWfo9_0r1N85Sa3NNYUOPPZl5He5&index=11 |
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Hey Daniel, I had almost exactly the same numbers you are reporting. The autoguiding with the mgen2 drastically improved on that matter. I followed the recommendations fromKarol at star-watcher.ch. really happy now! Franz |
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Franz Ferdinand: Like you, I really don't want to get into using a PC in the field (besides, I'm a Mac user and we have fewer options anyway), so I'm going to explore this option. Vielen Dank! |
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Skywatcher was kind and replaced my SA1 unit with an SA2i. Results were certainly better, at 100mm 60sec unguided I can almost keep 100% subs. At 200mm 30 sec I can keep 30%. With a guider at 200mm I can do 120sec with almost zero. I confirmed with Alan Dyer and read other reviews that indicate typical periodic error is on the order of 50-70 arcseconds. Stop expecting Porsche performance - a few people get lucky with theirs. Here is PHD output in NON-guided mode revealing the drift, but note how each cycle is different. Two nights earlier I had 100 arc-seconds peak to peak. Alan also recommended running the mount for 2 days straight to smooth things out - it worked! Out of the box, my unit had a 30-arcsecond spike that neither PPEC nor aggressive guiding could catch, now it is at 6-arcseconds when guided. For those of you NOT guiding, notice how many 10 arcsecond shifts there are. |
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| Anyone have good PHD guide settings for their SA? I can't seem to get less than +/-3 arcseconds. Yes majority is +/- 2, but lots of brief excursions to +/-3. I've tried for the guidecam exposures of 1.0 seconds, 1.5, 2.0, but the corrections can't react fast enough if I am at 2.0 seconds. 1.5 seconds seems to be best for my setup. |
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Anyone have good PHD guide settings for their SA? I can't seem to get less than +/-3 arcseconds. Yes majority is +/- 2, but lots of brief excursions to +/-3. I've tried for the guidecam exposures of 1.0 seconds, 1.5, 2.0, but the corrections can't react fast enough if I am at 2.0 seconds. 1.5 seconds seems to be best for my setup. Hello, All my PHD2 settings are default and 1.5 sec exp is best for me too (ASI120MC-S). Please try PHD2 Dev3 which now sports multi-star guiding. Accurate polar aligment and calm wind are critical for staying below 3". There will always be excursions but with, say, a 135mm lens this has no great impact. However hard you try, 100% yield is a rare case. Cheers Robert |
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Thx Robert. I'll get Dev3 loaded. In principle multi-star will suppress seeing wobbles because they will be different for each star and either averaged or ignored but the common shift due to mount excursion should be trapped. Looking forward to it, because the drift-limiting exposure for many of my runs (and 2 different SA units) are at 0.4 sec. Al. |
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Holy smokes, the latest PHD version with multi-star guiding nearly halves the errors !!! Here is a before and after on the same vertical scale, and close to the same horizontal one. I can now set my exposure to 0.5 sec in order to further mitigate the spike. Undoubtedly the longer exposure times I'm running (4 mins), help because any excursions leave only the faintest trace. For the record, I am at hysteresis 0.1 and aggressiveness at 0.85. Problem solved!  |
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Bonjour Thibault, in my experience (THREE SAs) your performance is way better than what I had. Yours is not problem but something to be content about, the best you can hope for with the Star Adventurer. My SA at 200mm is limited to 45 sec subs. Any more and my rejects are too high. The limitation is precision in the gears causing periodic error. Perfect balance (slightly east heavy) and perfect polar alignment cannot fix gear inaccuracy. Al. |
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| @Thibault I guided my SA for two years and it easily tripled my usable exposure time. Another big advantage is that you can perform drift alignment in PHD2, so you can fine tine your polar alignment. If you cannot get in balance, you should get another counterweight. However, you are at the limit of the mount already, so don't expect wonders. |
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| @Björn Hoffmann is right. With a guider, I can now do 4 minute subs at 200mm! I also polar align in under 5 minutes using PHD drift align. As you can see from my PHD guide output above, the best I am getting is a 3 arcsecond "channel" or +/-1.5 arcseconds. Calculate or measure your setup, how many arcseconds your field is divided by the width of your image in pixels. So a 360mm is about 5.7 degrees, or 20,520 arcseconds, and your camera is say 6000 pixels in the horizontal, gives you 3.4 arcseconds per pixel. This means, for my SA, all the error is (just) contained in one pixel. Bigger mounts still require guiding. My friend's EQ6-R is +/-4 arcseconds with no guiding. Total 8 arcsecond shift in 10 minutes. So you could likely do 2 minute subs with no guiding and get only 20% rejects. Bigger mount also gives you GoTo. But they are heavier, take up more place. An autoguider cam and scope you should be able to find second hand for $100. Then remember you need a laptop and cables, another dew heater. A happy solution could be: shorten your exposure to 30s, keep 85 or 90%, and no complications. |
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| Unless you are a mechanic at heart, do not dismantle equipment. It is possible to re-engineer the mount replacing this and that, a UK company does this for 100 GBP or so, but then you ask yourself: Spend money on 1) better equipment to start AND you get goto or 2) pay someone to improve the mount, or 3) do it yourself, or 4) leave it alone and shorten exposure to get more keepers. Because I am not a mechanic, I would go with 1) or 4) |
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I have created a "Star Adventurer drift align with PHD in 5 minutes" tutorial in case anyone comes to this thread looking for a bit of extra detail: https://edmontonrasc.com/wp/wp-content/uploads/2021/05/PHDDriftAlign.pdf |
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| Hi all, I’ve managed 600s at 545mm guided on my SA 2i pro. Generally my sky conditions don’t allow >300s. I expect I could do 1200s with wide angle camera lens. I autoguide with small 120mm 30mm guidescope and tiny GPCAM 130m. Good PA and balance are essential. I’m trying to develop guiding in DEC too, using a stepper motor and Waveshare HAT on my RPi4. Happy to share ideas. |
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| Hi all, I’m getting 0.8-1”/px guiding using PHD2 via Stellarmate OS on RPi4. Short 1s exposures work best. Currently switched to internal EKOS SEP guider and getting similar, and going to try GPA (PEC) guiding with longer exposures. I’ll post results in due course. |
