Getting the best performance from my AM5: Page 10

Getting the best performance from my AM5

Kevin_A

w7ay yes, i have seen the video and that was the initial reason I have been using 3 minute subs exclusively. On my fast f2.8 glass I was getting impressive results at 3 minutes without too much clipping in my bortle 4 sky so I thought that maybe my bigger f5.6 scope might be able to handle 5 minute subs, thus reducing the number of subs a bit. I have read that you also have tested gain 0 vs gain 100 and you use gain 100, and I have used gain 100 exclusively as well so far… did you find any advantage of gain 0 having better star colours due to the bigger well depth and less clipping? There has also been discussion that using darks and bias just adds more noise in the stack and are not needed on these sensors as hot n cold pixels can be dithered out and removed when stacking. Just curious as to your preferences. I won’t ask much more as I don’t want to go off topic on this thread! Bad me! Haha

w7ay

Kevin_A I have used gain 100 exclusively as well so far… did you find any advantage of gain 0 having better star colours due to the bigger well depth and less clipping?

Yep, I also seldom use gain 0 with the ASI2600. The one f-stop extra dynamic range is not worth it; I just reduce exposure time if some core of a galaxy is clipping. The read noise is so low that we can simply use short exposures, and make up the dynamic range by stacking.

By the way, here is some subjective examples of exposure times:

First, 17x180 second exposure, FSQ85 with 0.73x reducer, so 85mm aperture at 327mm focal length (f/3.9). With the Radian Quad band filter:

http://www.w7ay.net/site/Images/NGC7000-0.5R-AP-scaledx2.png

Next, 33x300 second exposures, FRA300 (f/5) with the cheaper Optolong L-Ultimate filter:

http://www.w7ay.net/site/Images/NGC7000-FR300-Lult.png

There is a left-right tilt on my FRA300 that you can see in this image -- I am waiting for a long backordered Gerd Neumann 54mm tlter to fix it. (Askar has as much QC problems as ZWO does.) There is also chomatic aberration (for some reason, quite typical of Askar OTAs that appears in their own published spot diagrams) if you look at the stars at the bottom right corner. Quite disappointing for a slow f/5 scope. This is why my ASI6200 is pretty much left permanently on the Sigma 135/f1.8 ART stopped down to f/3.9. I am too old and feeble to handle an FSQ-106.

Your FRA300 might be better.

Chen

Kevin_A

w7ay they are both beautiful images. To my eyes i cannot see any tilt and the small stars are fabulously tiny. I am not one for star removal but I love those pin point stars… wow! My Askar needed me to take apart the focusser as it was so tight my eaf would not do a fine focus routine accurately. My 2600 is on my Tamron 15-30 f2.8 run wide open right now as I plan on shooting the milkyway core at 30mm soon. I really enjoy your posts and the proof is definitely backed up in your astro photos. Wow! Cheers!
The coke bottle guide scope works well enough on this rig! Haha

tempus

w7ay

When using phd2 with low max duration values with either 0.5-1 sec exposure interval, what minimum move values would be better for the AM5? I tend to keep it low (10-15) but I might be wrong.

What about Hysteris values? Those mounts are so unpredictable from a minute to another that I can't see the usefulness of a high hysteris value.

w7ay

Kevin_A My 2600 is on my Tamron 15-30 f2.8 run wide open right now as I plan on shooting the milkyway core at 30mm soon

Great minds think alike :-).

If you want sharp stars, though, use step down rings to stop it down a couple of f-stops. This is my f/2.9 stop for the Sigma. I have a few sizes; when I need less FOV, I just open it up a bit more :-).

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). The plate also has the rack handle that I use on most of my OTA.

The plate rests on a Losmany dovetail, and this subassembly just mounts on my dual saddle plate.

The EOS to M54 adapter is Starizona's.

I love those pin point stars…

Yeah, I never could understand why the whipper snappers go out of their way to remove stars. Perhaps their stars are too bloated? Or is it just a social media fad?

Chen

Kevin_A

w7ay good idea, unfortunately te Tamron has a fixed lens hood but is sharp wideopen.
When I look up… i want to see stars…. So why would anyone remove that part of such importance…. Pity.
I may look at using step down rings on my Rokinon setup to get better results.

tempus

w7ay (with strain wave gears, you want the moment arm of the payload the declination axis to be as short as possible,

Is this why you run your guide scopes off to the side?

tempus

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?

w7ay

Kevin_A

Here is a Heart and Soul using a different Askar -- the ACL200 from Autumn 2020:

http://www.w7ay.net/site/Images/HeartAndSoul-ACL200.png

Not impressed by the OTA (I can see why some people don't like Askars), so I pretty much use the Sigma or the FRA-300 when I need the wider FOV.

If you like tight stars, this is my favorite (monochrome camera does not hurt, and on the Takahashi of course). Not many sub frames -- I should have taken more. Look at the stars shining through the Lagoon itself.

http://www.w7ay.net/site/Images/Lagoon.png

Chen

Kevin_A

w7ay i am not convinced on the Askars either. Mono pic….very nice indeed!
Have a great long weekend Chen!

w7ay

tempus When using phd2 with low max duration values with either 0.5-1 sec exposure interval, what minimum move values would be better for the AM5?

If you can control it, try setting a value that moves as a fraction (perhaps less than 1/5) of the slope of the periodic error curve of your mount, divided by the exposure rate (FPS). You do not want to delay the response since the ZWO mount has a slope that is large.

The above give you units of arcseconds. You then use the plate scale of your guide camera and convert that to units of pixels, which is what PHD2 uses.

What about Hysteris values?

Set it to zero. Why add any backlash when there should be none to start with.

Speaking of backlash, I keep reading from ZWO that declination backlash is not a problem as long as polar alignment is perfect. That is also false. When tracking at Lunar and Solar rates, both axes should be tracking. If the ZWO mount does not move the declination when using Lunar or Solar rates, then there is a big flaw in the mount.

Chen

johncdavis200

w7ay Hello Chen - Reading this post on how to calculate the min-move settings for the AM5:
https://bbs.astronomy-imaging-camera.com/d/15989-getting-the-best-performance-from-my-am5/186

I'm curious - I typically run the PHD2 Guiding Assistant for 3 or 4 minutes after calibrating PHD2 - and I let it suggest the min-move settings for my current mount (AP Mach-1 not the AM5), and I use those because they are from data gathered at the time I'm imaging. Curious if the Guiding Assistant will give good values for the AM5 (assuming they do for my Mach-1, which appears to be the case).

Thanks,
JD

w7ay

tempus Is this why you run your guide scopes off to the side?

Of course not. From infinity, the two scopes are virtually at the same location.

The side by side saddle allow me to easily experiment and configure different guide scenarios, including daytime guiders like the Hinode.

Chen

w7ay

tempus Is this why you run your guide scopes off to the side?

Reread my post above too about why you need to keep the moment arm of the declination axis small. When you stack a guide scope on top of an existing OTA, that extra moment arm is going to hurt.

Chen

tempus

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?

w7ay

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

w7ay

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

w7ay

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

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

Kevin_A

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.

w7ay

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

w7ay

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

Kevin_A

w7ay is there any manufacturer brand that makes good usb cables or power cables?

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