Getting the best performance from my AM5
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w7ay Because the current PHD2 uses SNR as the weight of the stars, you end up with the equivalent of 3 or 4 stars versus 12 stars. I had gathered some images the other night to help me study what the proper weights to use is.
Is there a way to get phd2 to lock onto more than 5-6 stars? What is the better weight to use? Or is it a phd2 limitation? I have noticed many times that it will only select those 5-6 stars when there are plenty more around (saw that often when using a worm drive mount with 3 sec long exposures). Changing the weighting didn't seem to make a difference. If it's a limitation imposed by Phd2, what is the advantage of going to a bigger sensor (178MM) over something smaller and cheaper?
tempus Is there a way to get phd2 to lock onto more than 5-6 stars?
Large aperture guide scope, larger FOV camera, low read noise cameras (since the frame rates are so fast).
I have zero problem consistently hitting the 12-star liimit on the ASIAIR by using a 55mm APO refractor with 200 or 250 mm folcal length, and an ASI178MM guide camera. Even with a 0.5 second guide exposure.
Chen
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tempus it will only select those 5-6 stars when there are plenty more around
Adjust the guide camera gain. You probably have it set too high. Autoguiding cannot, and does not, choose saturated stars. There is no way to estimate the centroid of a saturated star.
Please read the PHD2 manuals.
Chen
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tempus What is the better weight to use?
You will have to write your own autoguide program to apply different weights. PHD2 always uses SNR of a star as its weight.
https://en.wikipedia.org/wiki/Weight_function
Chen
w7ay Notice that an aluminum plate holds the EAF low (with strain wave gears, you want the moment arm of the payload the declination axis to be as short as possible, since the bearing is the limiting factor).
I saw your comment (top) hence my question ;-).
I didn't see any other comment on that topic. We have all been told the strain wave mounts have lots of power. Why is the stacking on top bad for this type of mount? Does it have more of a negative effect than with a worm drive mount?
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tempus Why is the stacking on top bad for this type of mount?
Because of the load on your declination bearing?
Notice that ZWO copied the RST-135 design, which on purpose, has a very, very short declination axis (see that 36mm number?):
It defeats the purpose if you then hang payloads far away from the RA axis. RainbowAstro's parent company is RainbowRobotics, and they have been building robot arms forever. They know their mechanical enginnering.
Does it have more of a negative effect than with a worm drive mount?
Because a traditional German mount has a counterweight?
In that case, the total payload is what matters. Without a counterweight, the moment arm matters.
Take a dumbbell. Remove the weights on one side. Now try to lift the rest with your hand near the remaining weight while keeping the shaft horizontal. Then try to lift it from the empty end of the shaft. With enough weight, your wrist breaks -- same as the declination axis. If you place the removed weight back in, and try to lift the dumbbell from the center (balanced), all is good again, but it is now the total weight that will break your wrist.
Chen
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w7ay it is interesting that these mounts are marketed as not requiring any counterweights as a standard and more for reducing tipover when scopes exceed a certain weight. Do you think a light guide scope on a 16lb scope would add much more arm moment to the total? Also, do you think that zwo usb suppied cables might contribute to some mount or guiding issues like some of their power cables seem to affect camera images sometimes. They are not great quality.
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Kevin_A Also, do you think that zwo usb suppied cables might contribute to some mount or guiding issues like some of their power cables seem to affect camera images sometimes.
Whenever I open a ZWO box, the first thing I do is to trash any cable that comes with it. I don't even bother to test use them.
I kept a couple to charge my Logitech mouse.
Did you see this post?
https://bbs.astronomy-imaging-camera.com/d/16270-asiair-power-cables
They are depending on the ignorance of their users (perhaps that is why they seldom publish technical specs) and try to save a few pennies. In the meantime, let the customers waste hours worth of time. Using a thick sleeve to mask a 21 AWG wire is at best dishonest.
The worst is that there are people who would power their cameras from the ASIAIR PWM power outlets. Don't people realize that 16 bits at 3.3 volts is just 50 µv ?! A camera should be powered from the cleanest supply possible. I want my images to be clean.
I should put an oscilloscope and a spectrum analyzer (yes, I have both) on one of the ASIAIR power outlets. I'll bet it has millivolts of noise. I haven't done it so far because like their cables, I never, ever use the ASIAIR power outlets.
Actually, I should buy one of ZWO's power bricks to measure the noise. It probably is cheap enough, although the tree huggers in Oregon won't like me adding to the landfill after testing it.
Chen
Kevin_A Do you think a light guide scope on a 16lb scope would add much more arm moment to the total?
Just 2 lb that is a foot away from the RA axis is as bad as 10 lb that is 2.4 inches away from the RA axis.
If you have a heavy OTA, it needs to be as close as possible from the declination plate. Use minimal risers. And avoid a guide scope on top of the OTA.
BTW, I think I have found a way to mount the FRA300 closer to the dovetail plate. ZWO sells some cheap camera rings that are 86mm. With a layer and a half of 1 mm cork sheet appled to the ring, it grips the FRA300 tube rather well. Two of the rings would make a secure mount, and much lighter than the silly red tower that came with the FRA300.
I will be trying that mounting once I get the Gerd 54mm tilt plate to correct my FRA300 tilt error. The ZWO tilter, although in stock, is not worth using.
Chen
w7ay for some reason my heavier 115mm triplet guides better than my lighter Askar! Maybe the arm moment is being offset by the mass dampening the effects of wind, vibration etc.
i do agree that all mounts prefer to have weight nearer the axis to reduce arm moment but I havent run into it with my lightweight setups. I can see that with a c8 or bigger.
Kevin_A is there any manufacturer brand that makes good usb cables or power cables?
You can try ones at Mouser.com (Mouser is a Texas electronics distributor -- I get my SMD parts from them -- and is owned by Warren Buffet's Berkshire Hathaway).
However, most of the shorter Amazon ones are fine (it is only when you get to the 2 meter lengths that you start seeing failures with cables). They work with any devices you throw at them (never had one fail even with fast disk drives) -- except ZWO USB devices.
The problem is not the cables, the problem is ZWO's USB hardware, which is designed with no margins whatsoever, and on top of that, do not use micro-stripline techniques to route the differential data (just open up one of their cameras or the ASIAIR to look at he PC board layout). No electrical engineer would do that -- which is why your phones and drives would work with the Amazon cables but the ZWO devices do not.
Higher quality cables tend to be constructed tighter to the "perfect" USB specs (especially important for USB 3.1 is the use of proper differential impedance to reduce cable reflections).
It is absolutely disingenuous for ZWO to blame it on cables, when it is their USB interface that is the culprit. Have you seen a Samsung T5 SSD fail (I at least a dozen of T5 and T7 that I use everywhere, including an ASIAIR) because of cables?
Chen
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Kevin_A for some reason my heavier 115mm triplet guides better than my lighter Askar!
As I have often mentioned -- you do want a small imbalance, since, like the worm gears, even the teeth of the strain wave gears are better meshed. You just don't want an imbalance that stresses the drive train.
With stepper motors, you will likely find a difference between when the motor is "pulling" against gravity, or if it is bucking gravity -- i.e., on different pier sides.
Just watch the mount tracking the next time you have it set up, and then switch pier side and watch how it is tracking again.
The RST-135 uses servo motors and suffer less than the ZWO mounts (in addition to having better resolution than steppers).
Often, people just look at the price of a product and buy a copy-cat because the latter is cheaper, without looking deeper into why.
Chen
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tempus Do they have any secondary harmonics or is this an AM5 "feature"?
They potentially have larger periodic errors than the ZWO mounts (RST-135 are spec'ed as +/- 30"), but they have much lower harmonic distortion (check out a Cloudy Nights posting from about two years ago when someone posted the spectrum, and also that NASA paper that I referenced earlier), and also have 430.82 second periods. Even if the harmonic distortion is the same, the slope error of a 288 second mount with +/- 20" p-p is the same as +/- 30" p-p for a 430 second mount.
But as we know, it is the slope of the periodic error that matters for autoguided imaging. For visual work, you can always buy the Renishaw encoder version (RST-135E) that has a periodic error of +/- 2.5".
With a 2 FPS 12-star guiding, and 0.5x sidereal guide rate and good seeing, I see 0.4" p-p RMS error (total for RA + declination). With my new-founded 0.25x sidereal guiding (based on the sawtooth), I see 0.25" p-p total RMS error with halfway decent seeing, using ASIAIR defaults . You probably missed my report here:
https://bbs.astronomy-imaging-camera.com/d/16029-reading-my-pe-graph/34
(and the post just before that one)
My max pulse durations were set to 80ms for 0.5x sidereal guide rate, and 160 ms for 0.25x sidereal guide rate, so you know what kind of PE slope I was targeting. Don't ever, ever use these numbers for your mount, because it will not work if your mount does not have the same periodic error curve as my mount. Read the above posts to see what happens when the max pusle was tweaked too low.
The error is still seeing dependent, that is why I am now doing experiments on the correct weights to use for averaging the centroids. I think I am now limited by the centroid estimation.
It is not just the guiding that matters with a mount. A modern visual mount must also have decent firmware to be able to model itself (which mounts like my EM-11 cannot do because of lack of compute power), albeit it is of less importance if you can do plate solves when imaging. Especially true if you want to track while in Alt-az mode.
Plate solve does not help with daytime Solar work, though. So I have been using a wide FOV "finder" scope (50m f.l. on 290MM mini) to initially find the Sun (or a Sol-Searcher when I am outdoors). I am on the fence about getting an RST-135E for that reason (but reluctant because I already have two RST-135).
I was also looking at the Pegasus Nyx-101 in anticipation of a heavier Mewlon 180 that is in a 3rd-quarter production run, but also took it off my plate because they seem to also have problems, like ZWO does. Neither comany has any experience building traditional mounts before building their first strain wave geared mount. So, I am right now hoping the RST-135 can continue to handle the extra payload.
I am not exactly a spendthrift, but I do care about bang-for-the-buck for my money; and I especially hate companies that use me as a guinea pig to enrich themselves. And make me buy their upgraded product to have a workable instrument, that I should have received in the first place. Copy cats seldom know the "secret sauce" (witness the tantalum capacitor and lithium battery fiascos) and they too have to learn the hard way and make changes to the design. I just don't want them to learn off of my money.
Chen
w7ay m. Try to adjust your guide camera gain so that you get 12 stars, and the stars that get picked have about the same brightness.
I understand that you mean this for ph2 users, don't you? Because for us ASIAR user we can't customise any of it (nor the multistage guiding).
I tried your suggested settings las Friday , and it was "erratic". It was a very windy night (I tried to put de car protecting my Riggs) and sometimes, I got 0,35-0,5 rms, but mostly 0,6-0,8 (not bad, always below 1, I'm happy with that).
Best regards