[RCC] First light - Pelican Nebula

Min Xie:
Wonderful first light! The only thing I noticed is that there might be some tilting in the optical train. The stars to the top left corner for example.

Thank you @Min Xie!

I think I see it - actually all four corners look like the stars are less “pointy”. Am I looking at the right thing?

Is this something that can be fixed in processing? Or is it in the raw data?

This is really good!

The 4 corners look a lot like what you see when a field flattener isn't at the right distance. (I'm dealing with that on my ZS61 now.)

I guess with a triplet you wouldn't need a flattener but advice to check backspacing is reasonable. 

Increase it a bit?

Great! That's exactly it!

I'm working on mine next clear night. pity to lose my flats library though.

I wish my 1st light looked this good Sid! Wonderful 1st image.
The only thing I see is exactly what was mentioned above about the either tilt or possibly the distance of your ff to your sensor not quite spot on. 
Looking at it I’d say a touch of both. @Min Xie hit it as well as the others.

FWIW, I took an image using close to the same setup. L-enhance, 294mc pro, CGE Pro, and most of the same software.  https://www.astrobin.com/ab5w4q/

Congrats on a wonderful 1st image!

Dale

That's a great 1st light, 1st photo.

Distance to chip only matters if you are using a Field Flattener or a Reducer/Flattener.  You do not list a flattener in your equipment list.  Are you using a flattener?  If not,   distance is a mutt point.  Without a flattener, the correct distance is focus.  If you are at best focus, then you are at the correct distance.

All optical designs  will display coma to some degree. All refractor triplet designs will have coma.  As the stars (points of light) move away from the center of focus they become distorted.  Consequently the elongated stars.  Even my Astro Physics AP130GTX has coma.  The larger the imaging chip, the more noticeable this is due to being further from the center.  Coma is eliminated by more complex optical design such as 4 to 5 element design refractor.  My Tak FSQ106ED and AT65EDQ ore quad flat field designs and do not suffer from coma.

If the stars are equally distorted (oval stars look the same ) in each corner, your imaging train/chip is orthogonal with the optical light cone.  If one corner is worst, then you are not.  Bad tilt in the imaging train can result in oddly shaped stars in the corners.  The streaked stars should point towards the center.  Badly tilted imaging trains can result in stars being perpendicular to the center.

All this can be caused by incorrect distance from a flattener to chip.  IF  YOU ARE USING ONE. 

A few notes about CCDInspector.  It is expensive.  $180 US.  It is finicky and needs a really good star base to work well.  Best near the Milky Way.  It can vary a great deal base on seeing and star base night to night.  You will need some way to alter the angle of you Camera or imaging train.  Some camera have a built-in tilt plat on the front of the camera.  Most do not, and a tilt adapter has to be added.  I have just spent 4 nights getting my Starlight Xpress Trius 694 orthogonal.
Every time I remove and and replace the camera the CCCDInspector grafts were drastically different.  Even though I use all threaded connections.  As I stated, CCDInspector is very sensitive and the nights star field can change everything.  During the same night on the same field (averaging 3 subs each) I got 7% to 1% tilt readouts.  You will be out several nights and end the end, you get best guess results.  However, I do not regret buying CCDInspector.  It has helped me analyze my cameras' tilt over the years.  It will also analyze field curvature and collimation.

I get best results adjusting camera/chip tilt with a home-made jig.  It has a laser pointer that reflects a beam off the chip to a flat plane, as I rotate the camera.  I adjust until the laser light point wobble on a flat plan is to  the minimum. 

OR, you just adjust in the field by looking at the stars in the corner.  Be ready for a few hours in the dark with small hex wrench.  Wrap some white tap around the hex wrench.  You will drop it.

Lynn K.

Bob Lockwood:

Paul Macklin:
This is really good!

The 4 corners look a lot like what you see when a field flattener isn't at the right distance. (I'm dealing with that on my ZS61 now.)

I guess with a triplet you wouldn't need a flattener but advice to check backspacing is reasonable. 

Increase it a bit?

The ASl533 chip is way to big for that scope and not be flattened, but you don’t state your using one in your equipment list, is this correct? If you are not using a flattener, you need one. A back-focus distance will then need to be met. A far as not needing a flattener because it’s a triplet is not so, ED, APO, doesn’t matter, if the chip is bigger then the usable image-circle of the scope, it will need a flattener. Other then that, I think it’s a great first-light, well done.

Just added a flattener into the mix, so of course it’s been cloudy every night since then. I’m excited to try it out, because my recent strategy has just been cropping the image down significantly.