processing with shorter subs

Jonathan Anderson

I am running some experiments that I KNOW people are going to balk at . . . but I'm just testing out different stuff.

I live on 3rd floor and have a balcony that faces east--I cannot
polar align bc Polaris is out of view completely, so I find a star,
plate solve/sync to mount and use tracking...then pause autorun every
20-30min and plate solve and sync again. . . Yes, I know that balconies
shake a little, but I am just testing this out to see what can be done,
if anything, if I don't feel like packing up gear and driving an hour
out of town.

What I've been trying is shooting short exposures (15sec, 0 gain, 0c)
(asiair plus 256gb, AM5, redcat 71 wifd, asi2600mc pro, L-pro, L-enhance, or L-extreme filter
bc I'm on outskirts of austin tx).

My stars actually look pretty dang good...nice and round. BXT cleans
up the normal issues. Trouble is, I think I need to process a bit
differently because of the noise trade off. I have gotten about 500 subs
of: ic434, m1, and m45 (500 of each . . . prob getting another 500 of m1 tonight).

I tried setting gain at 100, but I
got star trails--stubby, but trails nonetheless. I am thinking that BXT
may fix them, but I want to see if I can pull good results from what I
have.

Any suggestions for how to tweak Pixinsight processing for shorter subs?

Thx!

Jon

BlockHead

You can polar align... let me start there. If you can see south and either east or west, you use the drift method. It only takes a few minutes once you know how to do it efficiently.

If you take pictures at a gain of 100 and you see star trails then you are always getting trails... no matter the gain setting. So I really think you are looking for a software solution to a hardware (acquisition) problem.

Yes, BXT will certainly clean things up... but better images with better input. 

The issue isn't vibration...it is the mis-polar alignment that might be your real issue.

-the Blockhead

Jonathan Anderson

Thanks Adam,

I did discover the All Sky Align method, but since I am on my balcony, there is the roof overhang, then my tripod pulls my scope in another foot or so, so the 3rd plate solve position is pointed at the roof, even if I am starting near the horizon.

I guess turning down the gain to zero just gives the appearance of the trails being smaller, or not there. . . when I zoom into the images that are captured on my iphone, the stars look nice and round, but I know there is more data there than what I can see.

I certainly wish I could use the all sky method (just looked up drift align and see that these are the same thing)

Interesting experiment no matter what!

Jon

Jonathan Anderson

Here's a screenshot of my Master Light (after wbpp and auto stretch) of ic434 using 15sec subs, 0g, 0c settings with tracking only where I goto a star, plate solve/sync to mount.

Mainly putting this for a view of the stars.

BlockHead

Looks pretty good.

Drift align requires you to point the telescope on the meridian (due south) around around 0 degrees in declination (the celestial equator). I KNOW you can see this... this is where the horsehead nebula is.

The south point will correct the polar alignment in the azimuthal direction...which is the one you need. It is likely you have the declination error set since your latitude value doesn't change as long as your mount is level.

You can use the drift align method. I do not know what you looked up.

-the Blockhead

Jonathan Anderson

Oh, I was talking using the asiair All Sky Polar Align feature, which sounds very similar to drift aligning (apologies--I sort of jumped back to that when I mentioned looking it up,  but didnt' reference back to it). It automatically tilts by 20 degrees three times from the star that you start with. . . trouble is, that 3rd point has me pointing at the roof. Drift aligning may let me control things better.

I'm going to try the gain at 100 again tomorrow night to see if the thin tik tacs were just a single frame from a gust of wind or something (or, now that I think about it, if my downstairs neighbors opened and clsoed their patio door, it would def shake my balcony enough). So far, I have had round stars. 

Jonathan Anderson

I did manage to use the All Sky Polar Align when a star that was bright enough was close to the horizon. It worked fine, even without going to south meridian at zero dec.

Here's the question though. I was not able to use this feature earlier bc none of the stars that I could find on Sky Safari were actually in the asiair library.

So, would manually drift aligning (without using All Sky Polar Align) involve just eyeballing the drift (I'd use the cross hair in the asiair)? Or is there a specific way that is easier if using the asiair? When I search for drift aligning on the asiair, I just get results for using All Sky Polar Align (which for me, only works a bit later than I'd like to start).

Now, none of this is terribly pressing since I'm just trying to learn the ins and outs at a little deeper level of my equipment . . . I'm typically not collecting data on my balcony for short exposures. . . and it sounds like I may not even need short exposures since balcony shaking may not be an issue anyway since I'm not getting misshapen stars at 15 sec.

BlockHead

COncerning your last statement..correct. I think the issue is polar alignment...not vibration. 

I think you are making this too hard. You do not need any special software!

Just point your telescope on the meridian near due south on the celestial equator. Take pictures of stars... say 5 second exposures... continuously. Watch if the stars drift UP or DOWN in the field. (do have your camera aligned N/S before you begin). Now turn your mount in azimuth a little bit. If drift gets worse (or you can't tell a change)- rotate your mount in azimuth until you do not see drift in a reasonable period of time (maybe 2-3 minutes). 

Then, if you can, point towards the East or West horizon. Watch the drift again. This time you adjust the elevation of your mount to minimize the drift.

That is really all there is to it. There are plenty of instructions on line describing this method. Again, once you understand this..you can do it quickly with precision that is equal to or better than what you are doing currently.

-the Blockhead

P.S. One such description https://www.explorescientific.com/pages/drift-method-polar-alignment

Jonathan Anderson

Thanks! I found that ES site too. This'll be a great skill to learn! I got some comet images, but not from the top of the hill where I live that has an amazing view of the western sky with foothills in the distance, but Polaris was blocked, and I had forgotten about the asiair experimental feature of All Sky Polar align! Even that would've worked on that hill!

Ah well, there will be other comets. I'll start practicing drift alignment tonite. Thanks again for all the help!

J

Jonathan Anderson

You were correct: Wasn't the shaking of the patio . . . I was using my iphone compass and pushing the side of the phone (under the buttons so they weren't skewing) on the side of the am5 to get it pointed north not realizing that the metal etc in the mount WAS throwing off my read of north. For some reason it hadn't done that on other nights...no idea what the difference is. I found a different way to get a pretty accurate read of north.

Didn't do the drift aligning tonight since I wanted to test longer exposures on m1, this time guided. Guiding was great: about 0.4. At 30sec exposures my stars were nice and round (I have a little tilt on the 2600 to contend with, but BXT is making me lazy).  At 60 seconds, still nice and round. So, I got about 2 hours of Crab till my roof crept into view. Now I'm going to shoot ic434 and compare things . . . those shorter 15sec subs for horsehead will help give me a tamed Alnitek . . . now I go find Adam's video on combining data for stuff like that! I have some mixed subs for m42 to tame the core as well, just have not gotten around to figuring out how to insert just the core . . . now will be as good a time as any!