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Quote:Also if I do an all star align. In what part of the sky should I choose a star from to get the best results?
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Quote:Why not just use AllStar? Easier, faster.
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Quote:Quote:Why not just use AllStar? Easier, faster.So far I haven't been able to get the Allstar align to work. Every time I have done it I have had to make massive adjustments in the Polar alignment to get the star centered even though I had done a very precise polar alignment with the finder scope.It seemed like I was doing fairly well with the Polar finder alone and it would always be off after I did the all star so I just gave up on it.
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Quote:The rationale, I assume, behind using a star near the celestial equator is that it is there that the effects of mis-polar alignment are greatest. That is the reason you do drift alignment with stars on the celestial equator, at any rate.
Quote:While we all have our methods, I'm still not clear how a 2+4 alignment, then an ASPA is faster than sighting Polaris through a polar scope and offsetting for the pole. Takes less than a minute. I suppose my bias here is that I rarely used the GOTO function so am not doing any alignment at all.
Dave JessieOutreach Events
Quote:Quote:While we all have our methods, I'm still not clear how a 2+4 alignment, then an ASPA is faster than sighting Polaris through a polar scope and offsetting for the pole. Takes less than a minute. I suppose my bias here is that I rarely used the GOTO function so am not doing any alignment at all.
The situation is that very very few polar alignment scopes are aligned properly, and even if they are, are not oriented to the sky properly. As I responded to another of your posts, ASPA REQUIRES a 2+4 alignment FIRST to build an accurate model of the sky - including corrections for cone error. If that isn't done, the ASPA will not work because it can't hope to function as designed. "Garbage in - garbage out" as we used to say in the software development environment I used to occupy. If you don't want to do the alignments, then, by all means, DON'T USE THE ASPA since it will not work properly. Those of us that do the 2+4 alignments followed by the ASPA are universally thrilled by the process since it results in a much closer-to-perfect polar alignment than the polar scope can.
I know that the manual recommends a star near the equator - but I think people will have more accuracy with a star down low and on the meridian - but not too low - maybe 20 degrees above the horizon. The reason is that the polar alignment adjustments are in alt/az directions and have no concept of the equator. This becomes more important the closer you get to the Earth's equator.
Imagine doing ASPA on the Earth's equator - and polar aligning with a star on the celestial equator. It would be at the zenith - and the azimuth adjustments of the eq. mount would not have any effect. It would fail badly.
Although that is an extreme case of a user on the equator - the problem is always there and gets worse as you approach the Earth's equator.
For people in the extreme north or south latitudes the celestial equator should work ok because it is lower in the sky - but there is nothing magical about it. ASPA relies on a star that is sensitive to polar tilt adjustments of the mount - and azimuth adjustments of the mount - and the part of the sky where those adjustments are most precise is down low toward the horizon, for azimuth sensitivity, and near the meridian - for polar tilt sensitivity.
If a user has trouble with ASPA - I recommend trying a star down low, and near the meridian. Make sure the all-sky accuracy is pretty good with a fresh 2+4 alignment - and follow the directions. When making adjustments to center the star by adjusting the mount - don't iterate a bunch of times. Just make a motion in azimuth, then a motion in polar tilt - and lock it down even if it isn't perfect.
Quote:The rationale, I assume, behind using a star near the celestial equator is that it is there that the effects of mis-polar alignment are greatest.
Quote:Or use a star near the horizon on the equator.
Quote: The intersection of the meridian and celestial equator is best, by far, to maximize accuracy in both altitude and azimuth.
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Quote: Quote: The intersection of the meridian and celestial equator is best, by far, to maximize accuracy in both altitude and azimuth.
You could use a land reference to polar align also. Just polar align well, then aim at some fixed object and turn off the mount. When you set it up again, just orient it so the mount is pointing at that object and adjust in alt/az so it is centered.
Since you are moving the mount in alt/az to do this, the best object would be one on the horizon and meridian. Nothing to do with the equator at all.
The same applies to a star. The mount knows where the star should be at all times - and the speed of the star across the sky isn't relevant since its position is always known accurately.
The sensitivity of the az motion just goes as the cosine of the altitude above the horizon. You have no motion at all at the zenith, and maximum motion - and sensitivity - near the horizon.
To avoid refraction and flexure - go up a bit - maybe 20 degrees.
I use ASPA for imaging at around 40N and higher, and I always use a star down low. With cge and cge-pro. Example images are on the MetaGuide site - typically 15m guided with no field rotation.
Again- in many cases the equator/meridian would work ok. But when people say they have poor accuracy with ASPA, I recommend 2+4 and a star lower down - at least to try. No matter what you do want a star near the meridian - for the same reason you want a star near the horizon.
Quote:My subs are all 30 min ...
Quote:Quote:My subs are all 30 min ... Without guiding?
Quote:“For best results choose a bright alignment star that is near the Meridian, preferably close to the celestial equator. Try to avoid stars that are close to the west/east horizon or directly overhead because they can be more difficult to center using the mount's altitude and azimuth controls. Also stars too near the celestial pole are less accurate than those further away.” Is the intersection of the Meridian and the Celestial Equator directly overhead?
Quote:Please stop trying to confuse people.
Quote:The closer you get with that initial rough or what I called "visual" polar alignment (orienting the tripod and mount and sighting up the bore hole) the less movement of the alt and az controls you'll need to do when performing the ASPA. That means less wear and tear on those adjustment bolts and a faster ASPA procedure.
Quote:You guys sure got me confused, it's like reading one of those Newtonian collimation post.