8 replies to this topic

[bldeagle1]

So....I am still learning, both imaging and my ASIAIR+ ....

 

My first time shooting M42 (photo attached), this is a single sub, unprocessed, and clearly overexposed...

 

ES ED-80 FCD-100

EQ6R-PRO

60MM Starfield Guide Scope

ZWO Guide Camera

ZWO EAF

ASIAIR+

Ha Modified Nikon DSLR

Optolong L-Enhance filter

 

Bortle 4 skies, Central Florida

 

Polar Alignment was completed and good

 

I set a 2 target plan (first time trying multiple targets in one session just using the plan mode and heading to bed after the first sub is checked good), the first was M33 as it was high in the sky, the second M42, as it wouldn't clear the large Oak tree on the East side of our tree-line till after 11pm. I slewed to M33, calibrated and started guiding, started the Plan mode on the ASIAIR+...5 min subs at ISO 2000, 30 images. I have it set to auto focus before starting the imaging plan. Checked the first sub, and went to bed. 

 

The subs for M33 look good, pinpoint stars, but the M42 ones...definite trailing.... the overexposure I can see....5 min subs much too long for such a bright target, I will try 2 min next time....

 

The trailing is what I am trying to figure out...Does the guiding not automatically find a new guide star and start guiding when it switches targets?? There isn't a setting for that I can find, so just assumed it did?? When it switched from M33 to M42 it wasn't like I was going from the North to the South, so the calibration I ran before starting should have been OK??

 

Thoughts? TIA

 

 

 

 

Attached Thumbnails

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[Brian Carter]

I am working on processing an M42 right now.  My first night was 180s subs, and the core/Trapezium region was quite over exposed.  Another night I took about 4 hours of 30s subs, these were not over exposed.  I'm making an HDR image of the two.

 

So I would expect that you would need 30-60s subs in order not to overexpose M42 with your gear.  That creates a lot of subs, but I think you'll get better results.

[rj144]

If you want simple and no HDR, just take short subs.  30 seconds is all you need... or even less.

 

Then learn how to stretch precisely.  I use GHS in Siril.  I do a LOT of tiny stretches while protecting the highlights for high dynamic range images like M42.

[klangwolke]

Tracking acquires new stars when you move to a new target. If you didn’t have trailing with the first target then it is could be related to something mechanical with the second target. For instance cord snagged and caused the mount to drag. I know it’s not what you want to do necessarily, but I would set an alarm and go take a look at it after it slews to the second target.

[kathyastro]

The fact that your stars were sharp with an overhead target but trailed with a target just clearing the trees suggests to me a balance issue.  Check that the mount is well-balanced for all three directions: Dec laterally, Dec lengthwise, and RA.

[Brian Carter]

If you want simple and no HDR, just take short subs.  30 seconds is all you need... or even less.

 

Then learn how to stretch precisely.  I use GHS in Siril.  I do a LOT of tiny stretches while protecting the highlights for high dynamic range images like M42.

The problem with 30s subs is the file size.  I did one night of 30s subs and generated several hundred files.  Each of those files is 20mb and would be 50mb if I'd used the ASI2600 camera.  

 

The issue isn't storage space, I have oodles of that.  But stacking all these images can take a long time.  If I set a goal of 12 hours on M42, that's 1440 subs and it will take half a day to stack those.  But if I took just one night of 30s and the rest of the nights at 3m or 5m subs.  I can collect most of the integration in fewer files and just HDR with the 30s stack for the overexposed region.  This cuts my processing time down by hours.

[rj144]

The problem with 30s subs is the file size.  I did one night of 30s subs and generated several hundred files.  Each of those files is 20mb and would be 50mb if I'd used the ASI2600 camera.  

 

The issue isn't storage space, I have oodles of that.  But stacking all these images can take a long time.  If I set a goal of 12 hours on M42, that's 1440 subs and it will take half a day to stack those.  But if I took just one night of 30s and the rest of the nights at 3m or 5m subs.  I can collect most of the integration in fewer files and just HDR with the 30s stack for the overexposed region.  This cuts my processing time down by hours.

True.  I have a pretty fast computer and use Siril.  I stacked 1200 pics last week and it took like 8 minutes. 

[jml79]

The problem with 30s subs is the file size.  I did one night of 30s subs and generated several hundred files.  Each of those files is 20mb and would be 50mb if I'd used the ASI2600 camera.  

 

The issue isn't storage space, I have oodles of that.  But stacking all these images can take a long time.  If I set a goal of 12 hours on M42, that's 1440 subs and it will take half a day to stack those.  But if I took just one night of 30s and the rest of the nights at 3m or 5m subs.  I can collect most of the integration in fewer files and just HDR with the 30s stack for the overexposed region.  This cuts my processing time down by hours.

 

True.  I have a pretty fast computer and use Siril.  I stacked 1200 pics last week and it took like 8 minutes. 

I use a 294M with 94MB subs and tiny wells so for Lum it is always 60s or less to not blow all the stars out. Siril stack tons of frames fast. APP is next fastest. 

[WadeH237]

But if I took just one night of 30s and the rest of the nights at 3m or 5m subs.  I can collect most of the integration in fewer files and just HDR with the 30s stack for the overexposed region.  This cuts my processing time down by hours.

The math is even more favorable than that.

 

By definition, the areas that would be saturated in longer exposures are intrinsically high signal.  Because they are high signal, they'll vastly overwhelm the read noise with even short exposures.  As such, you don't need very many of them.

 

If I were doing M42, I would never spend a whole night on the core.  I would take maybe a 30 minutes of 10 second exposures, and then do normal exposures for the rest of the session.  You are only interested in the very brightest parts of the area for the short exposures.

 

When you process the data, you will want to integrate the short exposures into one master, and the longer exposures into another master.  You would then do a linear stretch to scale up the short exposures to match the signal level of the longer ones.  Finally, when you blend them, you will be taking the low noise areas from the short master, and the higher noise areas from the longer master.