Skylab1 I just got notify 1.6 (7.75)beta is ready to install

Told you to be patient, eh? :-) :-)

What is the build number that you are seeing?

I don't think I got firmware 7.75 pushed to me. For build 3, I had noted down in my log as firmware 7.73 (perhaps by mistake?). Build 4 came out yesterday morning with firmware 7.77, and Build 5 appeared this morning with firmware 7.79.

The build number is usually denoted in parenthesis, after the "1.6". E.g., "1.6(5) 7.79"

The 1.6 is the app version, and the 7.7x is the firmware version. Back in the v1.3 days, the firmware version was an integer, e.g., 775 instead of 7.75.

All the actual multi-star mechanism is in the firmware. The app is just the GUI for it.

With Build 4 (yesterday), the Multistar switch had been removed from the Advanced Feature window (a sub window of the window with the ellipsis icon). I think they must consider the feature to be good enough (when all the remaining multi-star bugs are finally squashed) to be used by the regular folks.

Muti-star selection is now simplified, so that if you tap on a star (either to calibrate or to guide) it will use single star. If you ask it to calibrate or guide without tapping on a star, it will use multiple stars.

When you are testing multi-star, you might get the green circles to vanish one by one, never to return, until over time, you are left with just a single star for guiding.

Don't worry (this is beta!).

They are actively working on this problem, and I wouldn't be surprised if the Build 5 that I got this morning has already fixed it. They know why it is happening, so it is just a matter of finding a best approach.

Build 3 was dropping stars when the star size dropped below 2. With build 4 last night, it is stable down to at least a star size of 1.8.

You may not even have a star size ever go below 2 with your guide system. I use a Borg 55FL (a doublet which Borg advertises as apochromatic, but really between achro and apo) objective and ASI290MM. On top of that, I have a strong UV/IR cut filter to get rid of optical aberrations outside of the visible spectrum. If you have a smaller pixel size or if the optics don't have good MTF, you will not see a star size that small even when focus except when the intensity really drops. If you guide with a ASI174-mini, though, you might see small star sizes too.

Even though recommended by the unwashed crowd who pass information through hearsay, defocusing to get a larger star size is never a good idea because you lose signal to noise ratio. I always keep my guide scope as focused as possible and depend instead on good algorithms to figure out the centroid. An HFD of 2 is plenty good to find centroids since half of the photons are outside a diameter of 2; the centroid computation des not depend on just a 2x2 area. Viewed another way, it satisfies the sampling theorem.

With build 3, I was seeing the multi-star green circles disappear within a minute of staring to guide. With build 4 last night, at one point it took an hour for 12 stars to dwindle down to 8 stars; so much improved already.

The stars that temporarily are unguidable should return, but there is a bug that causes them to not come back. Again, don't worry, they are really actively working on it.

The key is if you can get improved guiding with multi star when there are many stars available. I get between 1.5x to 2.5x smaller total RMS error when I use multi-star. That is a whopping big improvement in the guiding world. But my mount has virtually no backlash. If the total RMS error is mostly caused by the mount, you might not see as big an improvement.

By the way, a 2.5x improvement is the equivalent of using 5.66 stars (2 to the power of 2.5), and if all the errors are caused by centroid estimation.

There are other errors obviously, like pulse latency, pixel quantization, and all the mechanical errors. So, getting a 2.5x is a very big improvement, since as I had described in past postings, multi-star only improves centroid estimation. It does not cure other errors, particularly mechanical problems. It also means that for my particular mount, their choice of 12 stars is actually quite good; I am at the point where something else is a limiting factor after the 5.66 stars. But the extra stars will help when seeing becomes worse.

Being able to get 2.5x improvement just from improving centroid estimation also says that "seeing" is one of the biggest culprit to good guiding, since all that multi-star does is to average out seeing errors.

Right now, you can actually see the RMS error climb as the guide stars disappear. Quite fascinating to watch.

Also, since I think you are one that complained about MinMo, it is now defaulted to 0.1 pixel (I don't know if it is mount specific), so that should be an improvement for you too, if MinMo used to be limiting your guiding before. With the improved MinMo, single star guiding on average for me has improved from perhaps 1.3" RMS to perhaps around 1.0" RMS (need longer term testing to be conclusive). But the RainbowAstro and Avalon mounts (large periodic error slopes, but very little backlash) are known to be finicky with the MinMo parameter. It may not matter as much to mounts with larger backlash.

Remember to feed back any anomaly (the TestFlight app has the link to feedback). Remember that Beta is a two way street. It is not a final product, where you are just the consumer. There is an implicit contract that you use it for testing and feed back test data.

Have fun. IMHO, Multi-star is a pretty big deal. It was for DONUTS and its predecessors, and it is for the current PHD2 beta testers, and I suspect it will also be a big "whoa" moment for ASIAIR users. I am pretty sure the ASIAIR multi-star centroiding part is different from the PHD2 multi-star centroiding part (thus the bugs with disappearing stars, star sizes and so on that don't exist in the PHD2 version of multi-star), but it still depends on PHD2 for the inner workings of autoguiding (thus, the PHD2 log part has not changed).

Chen

Skylab1 I believe we are in the same time zone, it won’t get dark for about 7.5 hours. I looking forward to it.

I haven't had a chance to test build number 5 yet. Tonight perhaps, if things are favorable. Winds were gusting above 10mph, but should die down a bit tonight.

You might not be as high in latitude as me; unless you live near Seattle or Vancouver BC. It does not get dark here in Summer until past 11pm, and I usually get no more than 4 dark hours in summer for DSO imaging. Perfect season for solar imaging, though :-).

Today, the Sun sets at 7:59pm local time, but we won't leave astronomical twilight until 9:49pm. And then re-enter astronomical twilight again at 4:34am. So, only 6-1/2 of useful imaging hours already, and it is just Spring.

Last night, it was dark enough to plate solve for polar alignment at 8:30pm.

Good luck tonight and have fun. The multistar stuff should be quite entertaining :-).

Chen

OK, ZWO announced 1.6 beta with firmware 7.79 on the Facebook page. I can confirm that the firmware of this morning's Build 5 is indeed 7.79 when I run the Raspberry Pi.

If they have also fixed the permanently dropped star, this should be a very solid build with respect to autoguiding.

Even if it is still dropping stars slowly, you should still be able to get a good feel of the multistage capability, and provide feedback on what else is keeping it from working for you.

Chen

Skylab1 so far so good, multi-star guiding appear to be working, no lost of stars yet.

Yeah, loss of stars is quite stable since firmware 7.77.

But it still can happen. You can reduce gain of the guide camera so that the number of green circles is fewer than 12. When the stars are lost, they still do not come back, so that bug still remains -- as of last night, it looks like they have not yet picked the method to fix it. So I didn't expect t yet in this morning's beta release (there is a lag time with Apple too). But it should be a relatively easy to fix since it is an understood mechanism, so I am not concerned.

So, has your total RMS improved?

For my mount, it is pretty consistently better than 2x smaller RMS error than with 1 star case back in v1.5.3. At times, it is 2.5 times better.

Once they eradicate the permanent/progressive star lost case, I am definitely good to go with routine photography without having to worry if my stars get bloated from poor guiding. I am quite happy with the 1.6 release. 1.5.x was a disaster :-).

Oh yeah, the Sync And Goto bug is definitely squashed. Sync and Goto has not failed yet in v1.6 betas. The meridian transit between the pole and Nadir is also fixed. I can see that Autorun identifies that right now, Talitha Australis is due for a Meridian flip in 10.5 hours. That is the 180º Meridian transit -- the star is already west of the Prime meridian right now.

Chen

astrosatch How many stars must be minimum on screen for multistar guiding to kick in? I have OAG and there are not many stars to choose from.

As usual, the answer is "it depends."

ASIAIR will obviously not pick any stars that are saturated (I did confirm this with their folks) since saturated stars are pretty useless for guiding (centroid changes with how much it is saturated as the star scintillates).

When stars are too dim, their signal to noise ratio will also make it not useful, since at some point, the noise is greater than useful contribution of the star centroid. I do not know what ASIAIR is using as the SNR (or whatever criteria for dim stars).

So, there is only a range of stars that are usable. If too many stars are saturated, you are wasting those stars (and the camera gain will just add noise to the dimmer stars). As usual, don't just crank up the gain, as many people do, but to adjust the gain to find the "goldilocks" region where you have the maximum number of guidable stars.

One way you can do it is to start with a log gain. Ask ASIAIR to guide and look at how many stars it chooses. Then go increase the gain by say 3 dB (30 units in the gain slider) and restart guiding again. Keep doing this to see if the number of stars ASIAIR picks increases.

As of the v1.6 Beta 5, ASIAIR autoguides with a maximum of 12 stars.

If the best you can get is say, 4 stars, then your guide system does not have a high enough dynamic range. You may beed a camera with a lower read noise, or a guide scope with a larger objective.

There may be regions of the sky where you might not get 12 stars. While moving the mout by just a little will give again more stars.

Remember that multiple stars just reduces the centroid estimation error. And if probability theory holds, the variance half each time you double the amount of stars; i.e., the RMS changes by 0.707 each time you doule the amount of stars.

The biggest improvement is of course doubling from 1 star to 2 stars, where the RMS of the measurement (not the RMS of the guiding, since that depends on the quality of the mount) drops by 0.707. Adding a third star won;t have as much an effect, unil with 4 stars, you again improve by another factor 0f 0.707.

Similarly, you won't gain the full 0.707 factor until you hit 8 stars, etc. So, 10 stars and 8 stars are probably not very noticeable.

Most of all, more stars does not mean you have better guiding, as I discussed very early in this thread. If the mechanics of your mount may be a limiting factor well before the limitation of accuracy the centroid. The mounts that benefits most from multi-star guiding are mounts that have very small backlash. (The PHD2 log should give some idea of how much backlash is measure during the calibration phase.)

I had already mentioned to ZWO folks some time back that I expect people with OAG not to benefit as much as people with large guide scopes, together guide cameras with a deep well. OAG typically have a 8x8 mm prisom, which limits how much light reaches the sensor. I have myself stayed far, far away from OAG for years now.

Focus as well as you could and you should have the most guidable stars.

I also use a Baader Semi-APO filter on my guide scope (55mm aperture, fluorite doublet) to minimize UV (it starts cutting off at 480nm) and IR (it cuts IR past 1200nm, beyond most IR cut filters). That also maximixes SNR, but also cuts about half of the light, so probably not suitable for OAG either. I use a ASI290MM (not the mini, but the USB3 version). I wish I could use a ASI178MM for better dynamic range, but the frames are too large and the FPS is too slow for guiding (I wish you could select the guide ROI), so I am stuck with the 290. I have a ASI462, but that is a color camera and not useful as a guide camera.

Chen

Skylab1 IR from security cam can cause seeing problem on guide cam

Ha ha, thats funny.

A good IR filter should do better, if that is the case. Plus a loooong metal dew shield.

It does not help that the ZWO mini guide cameras use AR window instead of an IR cut window.

IR goes through cardboard like its not there -- I found out the hard way when IR from the ceiling light was going through a cardboard shield that I built around my mount simulator -- I added a Baader Semi APO filter to the camera, and all the bright areas vanished. I now swear by the Semi APO (or at least the Baader Neodymium filter -- to get rid of any fringes around stars, the Semi-APO cuts more on the UV end than the plain Neodymium, but it ends up cutting down a lot of light, perhaps 3 dB; and my Borg 55FL guide objective may not need such an aggressive UV cut). This will allow me to use a lower camera gain, and better SNR.

I'll bet the ZWO UV/IR filter still leaks a lot of IR and the passband itself may be poor too (the graphs show their windows already leaking around 1200nm). Your LP filter probably blocked IR better than the ZWO and/or pass the visible light with less attenuation (or better coating, so more light passes through). ZWO glass tend in general to have halos too. You can try the black felt tip pen trick on the edge of the glass to see if it improves for you.

In my case, the Baader Semi-APO visibly beats out the cheaper Optolong UV/IR cut filter on star sharpness in the guide window. I will try the Baader Neodymium when I get the chance, to see if that will give me more photons than the Semi-APO.

Chen