Aramcheck

Couldn't get the 32bit TIFF to open in PI, so here's a quickish process of the 16bit version.
Cheers
Ivor
 

Hi Bill,
Here's a couple of stretched jpgs from the tif file, which may make it easier for folks to comment. (Saves having to download & modify the tiff).

I'm not an expert, but it looks to me that you have some coma issues, with the the distortion of the stars at the edges / corners of the image pointing towards the centre. Also - as there is some trailing at the centre, you probably should check the individual light frames, as some may have defcets due to movement of the scope during the exposure. This can be caused by gusts of wind, snagging cables, or mount issues.

Also - the flats don't seem to have worked. There's vignetting around the edge, which the flats should have compensated for and a dust bunny is visible to the right (& up a bit) of 52 Cyg.

It might also help to know what equipment you have used.
Cheers
Ivor
PS: You can also try stacking in Pixinsight.

Thanks everybody - that's been a great help! Much appreciated.

As per @happy-kat's suggestion I've loosened the bolt a bit, so the Alt-axis moves a bit more freely, but I'll be getting an AZ5 with Steel tripod ASAP.

Cheers
Ivor

Last Christmas we bought a SW Startravel 102, hoping to use it as a grab & go. I have however, found the mount to be rather disappointing, with the Alt-axis in particular being too stiff to position accurately (unless using the slow-mo control). I'm therefore thinking of upgrading to either the AZ4 or AZ5, but not sure which would be best option.

The AZ4 doesn't look like it has any slow-mo controls, so how easy is it to locate & keep targets in the FOV?

On the plus side, the AZ4 has a steel tripod, but for £30 more, the AZ5 has slow-mo controls... however, it comes with a lightweight aluminum tripod, which on the one hand would be good for moving around, but probably not so good if I wanted to mount our SW 130dps?

Any advice from users of either mount would be much appreciated!

Cheers
Ivor

I use an A3 LED panel with a couple of sheets of white perspex to help disperse the light & a plywood frame to hold everything together.

As others suggest make sure you pick one which can be dimmed.

Cheers
Ivor

8 hours ago, Erling G-P said:

Hi Ivor, what are you using to get the annotations?

Three scripts in Pixinsight:- ImageSolver + CopyCoordinates + AnnotateImage

Cheers
Ivor

PS:- Couldn't resist... PGC281352  works out at about 10 billion light years away!

Thanks @alacant! I've been hoping to have a look at NGC7293 since spotting it in a German TV show with The Byrds miming "Eight Miles High".

Here's a rather quick process & an annotated version - lot's of faint galaxies, which I look forward to looking up on Simbad.

Cheers
Ivor

2 hours ago, rnobleeddy said:

For this analysis, were the lights dithered, and how many darks went in to the master dark?

Yes I dithered between subs & there were 50 darks used in the master darks. I don't think temperature is that significant with a DLSR? (I vaguely remember somebody doing a comparison with darks taken in a fridge (with camera in a poly bag) & room temp.)

I re-use the Master Dark & Superbias & just take Lights & Flats on  the night. Usually 30 Flats & as many Lights as I can manage.

Cheers
Ivor

Last week I mentioned in a reply that I'd previously tried stacking a set of images from my Canon 600d with & without Darks, and that with Darks the noise level was reduced by 50%. I've now tried to quantify things a bit better & have found that I'm now only getting about a 7% improvement in noise levels when using Dark frames.  I'm not sure why there is such a discrepancy, unless I did something wrong with my early comparison, but that would have back before I'd started guiding /dithering & using longer subs.

To quantify the effect of Darks with my Canon 600D (astromodified), I processed 21 x 180 sec Lights in PixInsight with:-
a) No Master Dark
b) a 97 sec Master Dark
c) a 180 sec Master Dark
(All with a SuperBias and Master Flat).

I first weighted the 21 x Lights using PixInsight's SubFrameSelector process, & then applied ImageCalibration, CosmeticCorrection (with Auto Detect set to 5 for Hot & Cold pixels), Debayer & Alignment, before Integrating, cropping & applying DBE. Only the ImageCalibration was applied differently, with the different Dark options.

I then cloned 9 background previews & combined them with the Preview Aggregator script, and ran the Statistics process on each of the results.

With the 180sec Master Dark applied, the Mean & Median noise levels came out at 93% compared to the No Dark, with a similar reduction in the (averaged RGB) Max value, and a 2-3% improvement in the std/avg deviations. The 97 sec option had minimal effect.

Cheers
Ivor

On 26/09/2020 at 07:10, 04Stefan07 said:

I used Dynamic Background Extractor but that made my image look worse.

It might be worth posting a TIF of the unstretched image.

DBE does a good job of removing background gradients, but does require some thought as to where you place the samples. You also have to consider whether the background is additive (as in the case of light pollution) or multiplicative (as in the case of vignetting). If the image suffers from light pollution, then the modelled background should be subtracted from the image, and any vignetting effects require division.

The background gradients are usually at a large scale, so fewer sample points may be needed, but you'll need to compare the generated background with your image, to check that any nebulous areas are not being affected too. (I usually start with 7 samples per row & a min. Default Sample radius of 20)

Some images also benefit from using either the Axial or Horizontal/Vertical/Diagonal symmetry options.

I usually increase the Tolerance up to 1.5 & then, with Zoom set to 1:1, enable tracking of the current sample & reposition samples so that none of them overlap any stars or nebulosity.

Cheers
Ivor

9 hours ago, gaz81 said:

I just finished doing the set up in APT... such a good tutorial.

Thank you!

Also did the extra bit that been added to APT since (ASTAP)

Tested some older images, solved in a few seconds... just need a clear night to try it while APT is actually hooked up to my AZ GTI (EQ).  APT can already talk to it, so should be good there. 

So in effect now....

1. Polar align

2. GoTo a target via the APT object list

3. Take an image

4. Plate solve

5. Sync those coordinates back to the mount? 

6. GoTo again and repeat the sync

7. Then... image away

 

Does that about cover the process?

Pretty much - except, worth checking out the focusing with a Bahtinov mask & using APT's 'Bahtinov Aid' under the 'Tools' menu.

So:-

1. Polar Align
2. Rough focus, then GoTo bright named star
3. Take short 10-15 sec exposure
4. Click 'PointCraft', select bright named star; Plate Solve; Sync co-ordinates; then pick named object in the 'Center FOV at position' & click "GoTo++". APT will then precisely centre the target in the centre of FOV, through a series of exposures & mount corrections.
5. Switch to LiveView & fit Bahtinov Mask + use Bahtinov Aid to refine focus.
6. Select Target from list (or custom list) + GoTo
7. Repeat 'PointCraft' to position target in centre of FOV using GoTo++.
8. Start guiding / imaging plan.

Cheers
Ivor
 

50 minutes ago, ollypenrice said:

But did you compare this with subtracting a master bias instead of a dark?

Olly

In Pixinsight's ImageCalibration process, when calibrating the Lights I use a SuperBias file as a Master Bias (Calibrate unchecked) and a Master Dark (with both Calibrate & Optimise checked), so the comparison had the SuperBias included in both integrations. One caveat is that my Master Dark is taken from a set of 97 sec exposures, whereas I now take 180 sec lights.

I'll run some tests when I get back from holiday, to try to quantify the experiment.

Cheers
Ivor

1 hour ago, Rustang said:

So to clarify on your test, you stacked a dithered set of images with and with out Darks and the noise appeared to be less when you still added Darks? 

Correct, but I'll have another look at this at the weekend when we get back from our hol's. (No access to unstacked data at the moment).

Cheers
Ivor

On @alacant's suggestion of stacking without Darks, you can of course try this & compare the noise levels on a background area. I tried it once & found that with Darks included in the process, my background noise with my astromodified 600d appeared to be about half that compared with the same set of Lights stacked with only Master Bias & Master Flats.

BTW I also have the problem with Dithering timing out on occasions.

Cheers
Ivor

From last Thursday night. Only processed 24 of 48 3xmin subs, as I suspect high cloud was impairing the view. SW200dps + EQ6, Canon 600d & IDAS D2 LP filter. Bortle 6 skies.
Still on the learning curve with Deconvolution, but it has genrally made a big improvement on reducing star bloating.

There's an interesting faint blob near to the star TYC4233-886-1 in the bottom right corner. From Aladin, I think it may be "IRAS 20332+6035", which Simbad identifies as a "Far-Infra Red source".

Cheers
Ivor

Thanks folks - much appreciatted. I've opted to extract Lum from the OSC, apply Decon to that & then LRGBCombination.

Cheers
Ivor

Any ideas how to prevent this ringing effect I'm getting on a few stars when using Deconvolution in Pixinsight? Having read Jon Rista's webage, I've used Wavelet Regularization to prevent Deconvolution from affecting the background & am otherwise happy with the Decon... results.

Many thanks
Ivor

Hi Capt. Slog,

Welcome to the SGL! I found Astro-Baby's guide to collimation to be very useful:- http://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

Cheers
Ivor

You say the problem also existed using EQMod. Have you tried using Astro Photography Tool to platesolve an image & sync the mount? On my SW AZ EQ6 GT I found that after a 1-2 star align, slewing to a target was usually off by some margin (but nowhere near 10-20 deg). (I've subsequently ditched the handset & star align & just rely on APT & platesolving, unless needed for visual use.)

Platesolving an image, would at least quantify the scale of the error & whether it lies in RA/Dec. It'd be interesting to see if the error is consistent for different slews to the same target or random...

BTW - After selecting a target, my mount will slew to the object & then make a small slow speed adjustment. I normally do a rough focus, slew to a bright star and then platesolve with APT & do a fine focus. The mount position is then synced to APT & I find after slewing to a target, the object is usually within the camera's field of view & requires only minor adjustments.

I presume there are no leads causing any drag or snagging issues?

Cheers
Ivor

https://twitter.com/i/web/status/1311680927639244805

"Thank you to all those who took the time to respond to our consultation.
We have received over 150 submissions, giving us so many great ideas about how we can start recommending viable policy solutions to deal with the growing issue of light pollution. Watch this space!"

Cheers,
Ivor

I recently posted an image of NGC6888 the crescent nebula, and have been having a play around with Deconvolution in Pixinsight to try to improve on the result.

It's a bit fiddly but worth doing methinks. Is the process best applied to the whole image, or masked? As I understand it the process of measuring the typical star shape allows for a correction to be applied, to help reduce the effects of the atmosphere. If so I presume it's best applied to the image as a whole?

Here's a comparison close-up with & without Deconvolution, and the v2 image with it applied.

Cheers
Ivor

I also had the same problem, but it turned out I'd loosened off the clutch too much & ended up locking it in the "open" position.  See: https://stargazerslounge.com/topic/345629-eq6-ra-clutch-problem/

Cheers
Ivor

I had a quick play with the TIFF. Looks to me that you had movement of the mount on one image in the stack, resulting in the star trail.

Cheers
Ivor

If you post the stacked TIFF (or a link to it, if saved to googledrive or dropbox), I'm sure some folks will have a quick play with it.

From your description it sounds to me that you've caught the central part of M31, which is much brighter than the outer edges. Have you stretched the image to convert if from linear to non-linear?

M31 is also a big target, so worth checking that it will fit in your camera/scope's field of view. I like to use the free Stellarium program to do this, when planning a night's session, but there are other tool's out there too.

Cheers
Ivor