First Nebula Image with OSC camera

[Mr Green]

I've definitely had an issue with egg shaped stars since starting out but I felt as though these images were my best so far. 

I'll maybe order a set of spacers and add a mm or two to the image train and see if that sorts the issue with the stars.

This is the first time DSS has refused to stack for me.... very odd.

[WolfieGlos]

Is it just the corners, or all across the image?

If it's across the image, then that suggests poor tracking, possibly it's out of balance in DEC or RA. It could even be wind affected.

If it's just the corners, I always suffered with eggys stars in the corner of the frame using my 72ED, I did manage to minimize it but not wholly remove the issue. But I never had any issues stacking the images - I did use Siril though. Do you want to share some of your subs for people to analyse? 

Edited November 29, 2023 by WolfieGlos

[Mr Green]

3 hours ago, WolfieGlos said:

Is it just the corners, or all across the image?

If it's across the image, then that suggests poor tracking, possibly it's out of balance in DEC or RA. It could even be wind affected.

If it's just the corners, I always suffered with eggys stars in the corner of the frame using my 72ED, I did manage to minimize it but not wholly remove the issue. But I never had any issues stacking the images - I did use Siril though. Do you want to share some of your subs for people to analyse? 

With regards to the stars, I'd say its mainly in the corners and this can be seen in the heart nebula picture posted on this thread.

I don't think it could have been tracking issues as I had less than 1 arc minute of error in both dec & ra.

I'll attach a few of the subs when I can get in front of my computer. Might not be tonight though. Clear skies tonight hopefully.

[Mr Green]

Frames 1, 13 & 15 are the worst scoring frames and number 11 is the highest scoring frame.

Star detection is between 3 & 9 according to DSS.

Light_IC1396_300.0s_Bin1_20231127-202935_0001.fit Light_IC1396_300.0s_Bin1_20231127-214046_0013.fit Light_IC1396_300.0s_Bin1_20231127-215119_0015.fit Light_IC1396_300.0s_Bin1_20231127-212220_0011.fit

[WolfieGlos]

5 hours ago, Mr Green said:

Frames 1, 13 & 15 are the worst scoring frames and number 11 is the highest scoring frame.

Star detection is between 3 & 9 according to DSS.

Light_IC1396_300.0s_Bin1_20231127-202935_0001.fit 49.78 MB · 3 downloads Light_IC1396_300.0s_Bin1_20231127-214046_0013.fit 49.78 MB · 1 download Light_IC1396_300.0s_Bin1_20231127-215119_0015.fit 49.78 MB · 1 download Light_IC1396_300.0s_Bin1_20231127-212220_0011.fit 49.78 MB · 1 download

I'm sorry to say, but all of those frames appear to be out of focus. That's why DSS can't detect any stars or stack the frames.

Do you have a bahtinov mask, or an electronic focuser? If not, I'd suggest getting either before trying to alter backfocus or tilt issues. The right-side stars - see the aberration view underneath - would suggest that your backfocus needs to be reduced, but the left-side looks much better. That, to me, suggests tilt.

 

 

Edited November 29, 2023 by WolfieGlos

[Mr Green]

I do indeed have a Bahtinov mask and use it as part of my setup routine so that's incredibly odd but at least I now know why I had such an issue and so thanks so much for checking.

Tilt is a new one for me so will have a read up as to what that is.

I'm currently taking subs on the Iris nebula and tomorrow is supposed to be a clear night as well.

Hopefully the images I get tonight and tomorrow will be better although the mentioned tilt might still be an issue that needs addressing.

Thanks again, really appreciate the help.

[Elp]

Are you using the focus routine in the asiair app? Since I used this from my first air I've never really had a focus issue at all, better to have the quantified FWHM number feedback from a focus routine than a visual check with a bahtinov (which is incredibly difficult to judge bang on if you don't know what to look for, you also need to do it on a very bright star otherwise the star diffraction pattern will be very small and harder to judge). A short FL refractor or camera lens will give FWHM figures of around 1-1.6 on a medium bright star during decent seeing when focusing, you'll know when you're in a good range as tiny stars will appear. When you're near focus, the adjustments with the focuser are incredibly minute even with the fine focus knob, with a camera lens the adjustments are imperceptible, that's how careful you have to be. If you're using a narrowband filter you have to set the exposure length on the focus routine to at least 1-2 seconds. You can't focus without the filter than put it in after (I doubt you're doing this) and carry on with the same focus position as it shifts the focal plane in relation to the sensor.

[Mr Green]

Hey Elp,

Yes I am using the ASIAIR focusing routine along with the Bahtinov mask and I always use Capella as it's the brightest star visible from where I setup. Thank you for trusting that I focus with any filters being used, I assumed from the outset that this would be the correct way to focus.

I've spoken with Alex at FLO and he's asked me to take a series of images rotating the camera to determine if its the sensor that's the issue therefore will be trying to do that later.

Below is a screenshot taken with my phone from ASIair plus which shows that there must be tilt somewhere.

[Elp]

17 minutes ago, Mr Green said:

I always use Capella as it's the brightest star visible from where I setup

This is the mistake. Do not use a bright star because its light intensity will be causing non average star bloat giving you incorrect FWHM for the rest of the star field. When you're active in the focus routine, try and find a medium bright star, get this good, then find a smaller one and fine tune. If the graph is not updating find a star which will, you may have to touch the focus a tiny bit to get the routine to start updating the graph again if you've changed stars. You can then take a stop the routine, go into preview mode and take a 10s image or so, there's a button on the LHS where you can identify/assess the stars and it'll give a FWHM for a few sample stars. Anything with a short FL refractor below 2.5 will be decent from my time imaging, the smaller the figure the better but as mentioned you'll know when you've got good focus as tiny stars will appear in your image previews.

[Mr Green]

I'll try a different star when I next setup. I used Capella as it seemed to be the only star that would show the defraction spike with the Bahtinov mask, especially with the L-extreme filter.

Thought I was making good progress earlier in the week but feeling a bit deflated now haha.

[Elp]

I understand the frustration. The more you setup and process, the more methodological you become with it almost to the point where it's quite therapeutic setting up and starting (if you use the same setup without changing it). Its when issues come up and you have to problem solve it starts becoming a headache, or even getting multiple setups going at the same time, but again experience pays dividends.

[WolfieGlos]

1 hour ago, Elp said:

This is the mistake. Do not use a bright star because its light intensity will be causing non average star bloat giving you incorrect FWHM for the rest of the star field. When you're active in the focus routine, try and find a medium bright star, get this good, then find a smaller one and fine tune. If the graph is not updating find a star which will, you may have to touch the focus a tiny bit to get the routine to start updating the graph again if you've changed stars. You can then take a stop the routine, go into preview mode and take a 10s image or so, there's a button on the LHS where you can identify/assess the stars and it'll give a FWHM for a few sample stars. Anything with a short FL refractor below 2.5 will be decent from my time imaging, the smaller the figure the better but as mentioned you'll know when you've got good focus as tiny stars will appear in your image previews.

That's interesting, I hadn't ever considered that Elp. Although I use NINA with my EAF, I always focus on a bright star (from when I used to use a Bahtinov), and always on Polaris at the Home position.

I then slew to the target and refocus within the first half hour - which I've always put down to temperature differences where the scope has acclimatised - which was going to be my suggestion to Mr Green. Whilst we know temperature does affect focus, I didn't consider the brightness of the star. Thanks, I'll try this myself. Just typical that with tonights clear sky that I'm off out...can't exactly cancel an anniversary meal 😒

 

53 minutes ago, Mr Green said:

I'll try a different star when I next setup. I used Capella as it seemed to be the only star that would show the defraction spike with the Bahtinov mask, especially with the L-extreme filter.

Thought I was making good progress earlier in the week but feeling a bit deflated now haha.

It happens mate, AP is complicated and even now 2 years in, I'm still learning (see above!). We've all shot a whole night out of focus, found trails or cable snags.

[Mr Green]

Hopefully I'll get the tilt issue sorted.

Going to send a couple of images to Alex at Flo to inspect but I am not sure what will come after that.

Think tonight and possibly tomorrow are the last clear nights at least for the next couple of weeks which is frustrating when having issues to address. 

I'm guessing I'll need to purchase more kit and that's not happening until after Xmas.

Enjoy your night out!

Cheers,

Jon

[Elp]

9 hours ago, WolfieGlos said:

temperature

You know, in three years of imaging I've never refocused during an imaging run (unless a camera lens has shifted due to a cable tug with its dew heater).

[alacant]

On 01/12/2023 at 03:01, Elp said:

never refocused during an imaging run

We neither. 

Edited January 6 by alacant

[Stefan73]

44 minutes ago, alacant said:

We neither. I question the need for adding yet another layer electromechanical interference to a train. If anything, our stars improve as the night progresses

By contrast in the UK last night it dropped 1.5C over the first half an hour to hour of imaging I did last night and the 10" F4 GSO reflector I've recently got definitely needed refocusing.  It's just a function of temperature change and a massive metal tube I guess.; I don't think I've ever needed as obviously to refocus my Samyang lens during the night no matter how brutal the temperature change has been.

When it's below zero outside I'm very, very grateful for my AEF and autofocus routines too!

[WolfieGlos]

12 hours ago, Elp said:

You know, in three years of imaging I've never refocused during an imaging run (unless a camera lens has shifted due to a cable tug with its dew heater).

It must just be me then! Since I set up for every session, the scope goes from being inside at circa 20 degrees, to outside ... at currently say 1 degree. Initial focus is circa 10 minutes after setup, so that's why I put it down to temperature.

The focus doesn't change by a large amount, now I have the EAF it tends to register as small as 10 steps up to 40 at the worst. I'd dare say with a mask you wouldn't notice it; I just spot it in NINA's HFR reading creeping up from, say, from circa 2.1 to 2.6. A refocus sorts it out, and then that's it for the rest of the night. My initial thought for Mr Green, is that that might have happened too.

[Mr Green]

Had a response from FLO and turns out that I do indeed have sensor tilt which is pretty bad luck as fixing the issue is way beyond my limited skill set.

I had a couple of evenings on the Iris Nebula this week and the images stacked fine but the tilt makes the stars look dreadful regardless of whether I am focused and guiding is running smoothly.

Is sensor tilt really that common or is it worth sending the camera back and ordering another one?

 

 

[Elp]

Yes it's common, the larger the sensor the more it'll bother you. For me, the target is what's important rather than the hundreds of insignificant stars around it which can usually be cropped out. For AP, it's useful to have a set of spacing rings and a few less than 1mm ones too for correcting this exact issue.

[Mr Green]

I've had a set of spacer rings arrive today. There's 0.5mm, 0.8mm & 1mm in the set.

Will adding one or two of these help do you think?

I really don't want to mess with the tilt plate on the camera as I'd have no idea what I am doing and will only make things worse.

[Elp]

Do you have a Vernier caliper at hand, it's essential for measuring your total backfocus distance. The rule for distorted stars at the edge of field is if the stars are streaking out as lines from the centre of fov, your backspacing is too short, if they are elongated as curved lines appearing to rotate around the centre of fov, your backspacing is too long. Streaked into triangle shapes on one side of frame is usually tilt.

Measure your distance and add approx 0.3-1mm to the total backspacing for a flattener/reducer for any general filters. It's quite a frustrating task, one I've never truly conquered out of choice because I'm always chopping and changing my optics and cameras and setup and breakdown every time, I just keep a log of various setups on my phone to reference, and the Vernier stays with my rings set, I've also tippexed the sides of each ring with their size, even the thin 4mm ones with dots so no need to measure in the dark.

[WolfieGlos]

Another way to do it, is if you are still in the returns period, see if you can return the flattener and spacers and get an adjustable flattener. I didn’t know of this, but it makes it a lot easier to figure out backfocus and will do away with taking apart your imaging train. I have this for my Starfield 102ed, and I thought FLO had a Stellamira version for the Evostar 72ed but I can’t find it at the moment.

With regards to tilt, I tried these and had a little success. Something Like this would be better and can be fine tuned.

I never fully fixed it with my 72ed, there’s a long thread here on SGL started by  @AstroNebulee where we both (and others) tried to figure it out. He managed to sort it, I didn’t quite get there. As I recall, with my DSLR, it was supposed to be 55mm backfocus; I ended up with about 60 IIRC. Like Elp, I gave up caring and cropped the edges out. It’s definitely a frustrating issue, and one I left until a Full Moon was out….

Edited December 1, 2023 by WolfieGlos

[AstroNebulee]

26 minutes ago, WolfieGlos said:

Another way to do it, is if you are still in the returns period, see if you can return the flattener and spacers and get an adjustable flattener. I didn’t know of this, but it makes it a lot easier to figure out backfocus and will do away with taking apart your imaging train. I have this for my Starfield 102ed, and I thought FLO had a Stellamira version for the Evostar 72ed but I can’t find it at the moment.

With regards to tilt, I tried these and had a little success. Something Like this would be better and can be fine tuned.

I never fully fixed it with my 72ed, there’s a long thread here on SGL started by  @AstroNebulee where we both (and others) tried to figure it out. He managed to sort it, I didn’t quite get there. As I recall, with my DSLR, it was supposed to be 55mm backfocus; I ended up with about 60 IIRC. Like Elp, I gave up caring and cropped the edges out. It’s definitely a frustrating issue, and one I left until a Full Moon was out….

@Mr Green I will try to find the thread mentioned. In the meantime here's a diagram of my imaging train. I have 60.5mm of backspacing. I do have a tilt plate on my zwo asi294mc pro, though I believe this is only just pinched up and not tilting the camera. The rotator from RVO really helped me as no slop in it. 

Lee 

[Mr Green]

Thanks all for the help and support, it's much appreciated. I've spent way more than I should have done the past month therefore won't be buying anymore kit for a while.

I think I'll take the advice of cropping images for now and do my best to focus before taking any images.

I was half tempted to mess with the screws on the tilt plate and keep a mental note as to what I've done so that I can undo any mistakes..... what's the worst that can happen as my images are naff anyway.

[AstroNebulee]

41 minutes ago, AstroNebulee said:

@Mr Green I will try to find the thread mentioned. In the meantime here's a diagram of my imaging train. I have 60.5mm of backspacing. I do have a tilt plate on my zwo asi294mc pro, though I believe this is only just pinched up and not tilting the camera. The rotator from RVO really helped me as no slop in it. 

Lee 

I think this is the thread 

Lee 

Lee