help! Help! Facing Problems with processing of M31 - Andromeda Galaxy images on DSS.

[AdityaR]

Equipment:

Telescope - Celestron Nexstar 8SE with f/6.3 SCT Focal Reducer on an Alt-Az Mount

Alignment - Standard Three Star Align

Camera - Canon EOS 600D/ T3i (used a Canon T-Ring and T-Adapter to mount it to the OTA.)

Software Used to Capture - APT

LIght Frames - 10s x 60 decent frames at ISO800

Dark Frames - 10s x 60 decent frames at ISO800  (The Dark Frames were taken after dismounting the camera from the OTA and covering the camera sensor with its Black Cover.)

Problem: *This is my first time taking a Deep Sky Image So Correct Me If You Can In Anyway, Thanks!*

So, I recently took around 60 light/ 60 dark frames of Andromeda Galaxy (Bortle Scale of my area is usually 5). But when I tried to process(stack) the images the next morning with DeepSkyStacker - It wasn't able to detect the Stars in the images(I set the threshold to 2% but then it started detecting noise too.). However, I somehow solved that and got the star count to 50 at 20% threshold but when I proceeded to stack the images it gave me warning sayin "Only three out 60 frames would be stacked". Me being a dumb brain proceeded with this anyways, and the resulting image was NOT aligned and was with an Exposure of only 30s, and now The star count problem has also come back. Moreover, when I tried the same process with Sequater (WHICH I THINK I READ SOMEWHERE IS NOT SUITED FOR DSO's) gave a decent aligned result but not much data for processing. I can't seem to get around these problems with DSS, So any help would be appreciated. Please!

for those who might say the 8se is not suited for DSO imaging, refer to here - https://www.cloudynights.com/topic/826723-nexstar-8se-imaging/

Here are the images if you might want to take a look - https://drive.google.com/drive/folders/1VTqSG77R2kvuEKq1cQvcXFhS72FHF6rW?usp=drive_link

I have also attached some light and dark frames and the image I got from Sequater and SIRIL.

 

Pardon my english (am not a native speaker)!

IMG_6470.CR2 IMG_6492.CR2 IMG_6493.CR2 IMG_6494.CR2 Andromeda-Proccessed.tif

[powerlord]

forget about darks - don't need em. flats and bias would have been better. I imagine your darks are screwing up your lights.

I use APP not DSS, but I've seen this issue before especially with DSLRs - where the reference frames once calibrated into the lights, screw them all up.

In APP, all but 5 frames integrated, but the subs are all over the place - it doesn't seem to have been tracking much or at all tbh. I mean I know its az, but I'd still expect M31 to stay in the middle ?

The integrated result was just a blur though so it was a false positive. But just have a look at the subs and you can see they are very streaky and moving about everywhere really.

I'd suggest trying again and this time:

1. take flats

2. take bias.

3. don't bother with darks.

4. try to make sure your tracking is keeping target centred, and if you are getting star trails, reduce the exposure until you don't, and take more subs. you can't really shoot a target off centre with az, as it's going to be rotating, so will just end up off the frame - so make sure your target is dead centre.

stu

[AdityaR]

2 hours ago, powerlord said:

forget about darks - don't need em. flats and bias would have been better. I imagine your darks are screwing up your lights.

I use APP not DSS, but I've seen this issue before especially with DSLRs - where the reference frames once calibrated into the lights, screw them all up.

In APP, all but 5 frames integrated, but the subs are all over the place - it doesn't seem to have been tracking much or at all tbh. I mean I know its az, but I'd still expect M31 to stay in the middle ?

The integrated result was just a blur though so it was a false positive. But just have a look at the subs and you can see they are very streaky and moving about everywhere really.

I'd suggest trying again and this time:

1. take flats

2. take bias.

3. don't bother with darks.

4. try to make sure your tracking is keeping target centred, and if you are getting star trails, reduce the exposure until you don't, and take more subs. you can't really shoot a target off centre with az, as it's going to be rotating, so will just end up off the frame - so make sure your target is dead centre.

stu

So basically the current lights can't do me any good? that about right? - then I should probably pass it as a learning experience and just try again, lol. Tbh, I was questioning the tracking of the scope too - and you confirmed it. Next time would double check the tracking. I wont get a chance this week but I will try again and surely post the results here. Thanks! 

[Elp]

I haven't looked at your images but experience tell me to take a look at each one of your light frames, I suspect if DSS has stated that message the majority have blurred or streaked stars so there's slim to no chance of those frames registering. Also if using DSS check for one good image with good stars, right click and make it the reference image which DSS will use to check all the other images against and align to.

With a DSLR it's also good practice to use an intervalometer and input a slight delay between shutter actuations so you don't get shutter shadow (the sensor can see the shutter as it hasn't moved out of the way quick enough before the next capture), but I doubt this is your issue.

The scope is fine for AP but even at F6.3 reduced it's imaging at around 1280mm focal length, you need super accurate equatorial guiding (likely via an off axis guider too, I've got a C6 so know about imaging with such a setup even autoguided and equatorial) at such a focal length otherwise any error, even a slight breeze may ruin the sub. When I last did Andromeda on an alt az I was imaging at 370mm focal length and could only do 9 second exposures, you're imaging at nearly triple that focal length on an alt az which will be correcting in both X and Y axis constantly, so not really suited. You'd ideally need an equatorial mount. Try shortening your sub lengths significantly, you'll be able to tell from the shape of your stars when taking trial images.

Edited September 27, 2023 by Elp

[The Lazy Astronomer]

I downloaded your whole light frame dataset and fiddled with StarAlignment in Pixinsight for a short while. It mostly kept trying to align on the hot pixels, but eventually found settings to get some to align (34/60). This was the result after a basic stack with no rejection algorithms:

The galaxy cores are clearly there, and there are hints of the dust lanes in m31, but you can also see all the multicoloured streaks of hot pixels - these are what DSS would have been mistaking for stars and trying to align on.
You can also see how the frames are slowly rotating throughout the course of the session, because an alt-az mount cannot properly follow the motion of the stars.

Tracking has been mentioned above, and just to confirm that, the stars in a single sub are all elongated:

Unfortunately, I would say this data is not salvageable, but as you say, you can chalk it up as a learning experience.

A piece of advice though: trying to do DSO imaging at 1.3 metres of focal length on a non-premium mount, without guiding, is likely to be a recipe for disappointment.

[AdityaR]

5 hours ago, The Lazy Astronomer said:

I downloaded your whole light frame dataset and fiddled with StarAlignment in Pixinsight for a short while. It mostly kept trying to align on the hot pixels, but eventually found settings to get some to align (34/60). This was the result after a basic stack with no rejection algorithms:

The galaxy cores are clearly there, and there are hints of the dust lanes in m31, but you can also see all the multicoloured streaks of hot pixels - these are what DSS would have been mistaking for stars and trying to align on.
You can also see how the frames are slowly rotating throughout the course of the session, because an alt-az mount cannot properly follow the motion of the stars.

Tracking has been mentioned above, and just to confirm that, the stars in a single sub are all elongated:

Unfortunately, I would say this data is not salvageable, but as you say, you can chalk it up as a learning experience.

A piece of advice though: trying to do DSO imaging at 1.3 metres of focal length on a non-premium mount, without guiding, is likely to be a recipe for disappointment.

Yo thanks for doing that, I was not expecting someone to actually fiddle and experiment with the data and here you are! Well as you said it a learning experience and but I would be sticking to this trial and error for a while tho(I blew my budget lol). However, I am persistent so I would be trying again until I get a showable result!

Thanks again!

[AdityaR]

11 hours ago, Elp said:

I haven't looked at your images but experience tell me to take a look at each one of your light frames, I suspect if DSS has stated that message the majority have blurred or streaked stars so there's slim to no chance of those frames registering. Also if using DSS check for one good image with good stars, right click and make it the reference image which DSS will use to check all the other images against and align to.

With a DSLR it's also good practice to use an intervalometer and input a slight delay between shutter actuations so you don't get shutter shadow (the sensor can see the shutter as it hasn't moved out of the way quick enough before the next capture), but I doubt this is your issue.

The scope is fine for AP but even at F6.3 reduced it's imaging at around 1280mm focal length, you need super accurate equatorial guiding (likely via an off axis guider too, I've got a C6 so know about imaging with such a setup even autoguided and equatorial) at such a focal length otherwise any error, even a slight breeze may ruin the sub. When I last did Andromeda on an alt az I was imaging at 370mm focal length and could only do 9 second exposures, you're imaging at nearly triple that focal length on an alt az which will be correcting in both X and Y axis constantly, so not really suited. You'd ideally need an equatorial mount. Try shortening your sub lengths significantly, you'll be able to tell from the shape of your stars when taking trial images.

Here in india the equatorial mounts costs more than the full setup itself and as mentioned I have blown my budget out. However in half a year or so I would be getting the wedge  which I think would help - and I would try again on this setup until I get a result (sorry, I am persistent) 

But thanks!

[powerlord]

There's always the moon ? Otherwise, better alignment, max out that iso and much shorter exposures. Biases to get rid of hot pixels, flats to help with detail. Bahtinov to ace focus. And post your results. 👍

[Oddsocks]

5 hours ago, AdityaR said:

Here in india the equatorial mounts costs more than the full setup itself and as mentioned I have blown my budget out. However in half a year or so I would be getting the wedge  which I think would help - and I would try again on this setup until I get a result (sorry, I am persistent) 

But thanks!

I also looked at all your light frames and as the previous respondents have noted, most of the frames are unusable, I only found eighteen that were even close to being usable for integration.

Of the best frames, the stars in nearly all those frames were slightly out-of-focus with a clear central black disk and outer bright ring, also, there was some hint of mis-collimation of the telescope.

Of the full set of lights, approximately half appeared to have a low SNR, possibly taken under deteriorating sky conditions, hazy thin cloud perhaps, or the target becoming closer to the horizon?

Some practical suggestions.....

As you have a heavy camera attached to the back of the Alt/Az mounted telescope try to add sufficient counterweight to the front of the OTA so that the tube is balanced, that will help reduce tracking errors. You should find it possible to make your own counterbalance weights from scrap material for virtually no cost.

While imaging, resist the urge to walk around close to the tripod. The standard Celestron tripod with the 8SE is a rather flimsy affair and will react to footfall close to the tripod unless on solid concrete or hard ground. If you can keep the telescopic legs of the tripod unextended, or as short as possible, and set up with the telescope as close to the ground as you can get then that will help with stability, and, if you can add some sandbags above the spreader plate for the tripod legs that will help dampen down any tripod vibration.

If you haven't already a Bahtinov mask in your toolset to aid focusing you can make one for virtually nothing, details >Here<

Finally, review the collimation of the telescope and make sure the telescope is collimated at the same OTA angle that will be used for the target, or at least, point the telescope to the zenith for the collimation adjustment so that any mirror flop that pushes the collimation out of adjustment with changing OTA angle will be roughly the same either side of the meridian.

William.

 

[AdityaR]

3 hours ago, Oddsocks said:

I also looked at all your light frames and as the previous respondents have noted, most of the frames are unusable, I only found eighteen that were even close to being usable for integration.

Of the best frames, the stars in nearly all those frames were slightly out-of-focus with a clear central black disk and outer bright ring, also, there was some hint of mis-collimation of the telescope.

Of the full set of lights, approximately half appeared to have a low SNR, possibly taken under deteriorating sky conditions, hazy thin cloud perhaps, or the target becoming closer to the horizon?

Some practical suggestions.....

As you have a heavy camera attached to the back of the Alt/Az mounted telescope try to add sufficient counterweight to the front of the OTA so that the tube is balanced, that will help reduce tracking errors. You should find it possible to make your own counterbalance weights from scrap material for virtually no cost.

While imaging, resist the urge to walk around close to the tripod. The standard Celestron tripod with the 8SE is a rather flimsy affair and will react to footfall close to the tripod unless on solid concrete or hard ground. If you can keep the telescopic legs of the tripod unextended, or as short as possible, and set up with the telescope as close to the ground as you can get then that will help with stability, and, if you can add some sandbags above the spreader plate for the tripod legs that will help dampen down any tripod vibration.

If you haven't already a Bahtinov mask in your toolset to aid focusing you can make one for virtually nothing, details >Here<

Finally, review the collimation of the telescope and make sure the telescope is collimated at the same OTA angle that will be used for the target, or at least, point the telescope to the zenith for the collimation adjustment so that any mirror flop that pushes the collimation out of adjustment with changing OTA angle will be roughly the same either side of the meridian.

William.

 

Wow! never thought the collimation of the telescope would come into play, would see if I can do somethin' also I just made a batinov mask today, lol. Anyways these are some very helpful tips you gave me - would try them. Thanks William!

[AdityaR]

Hey anyways could somebody please tell me out of my light frames which are the best ones, I would use those frames as a target quality for my next time yk. Basically it would help me set a standard for me achieve.

[Elp]

Just open them in DSS and after registration it'll provide a score for each one, by hovering with your mouse cursor over a star you'll immediately see if the tracking was good or not if the star is round or not.

[AdityaR]

13 hours ago, Elp said:

Just open them in DSS and after registration it'll provide a score for each one, by hovering with your mouse cursor over a star you'll immediately see if the tracking was good or not if the star is round or not.

okk!