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Hello, I just got a Evostar 72ED (420mm) which I'm using on a Star Adventurer Pro Kit (no guiding) + Sony A7III. Looking into my light frames I noticed that while 60% of my subs are great (which means I got a pretty good PA), I get a significant amount with signs of star trails. At the moment I go for 1 minute subs. Is it possible that this is just due to the SA not balanced properly? At the moment I can't get a decent balance on the Dec axis due to the dovetail being too short. I'm also having problem balancing on the RA axis, not sure why but when I reach a balance in a position, if I move it 45 degrees on either side, it's not balanced anymore. Any tips welcome if anybody has a similar set up! I'm also planning to try a 3 or 5 minutes trial with my 200mm lens just to double check if is not an internal problem of the motor. |
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Yeah it sounds like balancing to me. The SA is struggling under the unbalanced weight. And you need to balance DEC too, this is what breaks the symmetry since it results in non-zero forces on the RA axis with changing angle. I would not exclude PA error despite your 60% good subs nor motor issue (although SAs are hard little beasties). Could also be your tripod or the shoe wiggling under the wind (make sure there is no play). But you definitely must balance the gear, no two ways about it. Cheers, D. |
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| Thanks for the reply! I will try to get the balance on point then and see if I manage to get longer subs! |
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It could be a balancing issue. I had two of those trackers and both had the same assembly issues preventing tracking properly: Worm bearings to tight Worm housing tilting mechanism way to tight. Youm might check on those points if you are up to it. Best regards, Stephan |
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This is most likely the periodic error of our Star Adventurer. All mounts have a periodic inacuracy in their tracking due to gear inacuracies; cheaper one have a larger error than the more expensive ones. The Star Adventurer, for example, has an error of 20-40" across a 10min period. The error is distrinuted unevenly across the period, which is why 60% of your subs are okay and only 40% are affected. The periodic error can be fixed with autoguiding. |
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Thanks for all the replies and suggestions! I will try to first get balancing right and autoguiding is the next step up. Probably next month or so. Looking into the ZWO Asi120mm and mini guide scope, I have already a Raspberry Pi with Astroberry installed on it. Looking into this video I see that it's hard to get more than 30s subs with longer focal lengths even with balancing and focal length. |
