Markarian's chain

[TiffsAndAstro]

Probably another stupid question by me, so apologies, but how long is a 'good amount' of time centering on m87 to get markarian's chain?

took the attached last night for 45mins dodging cloud and expected nothing, but got quite a few very very small galaxies with my 200mm f5.6 canon 600d 120sec subs.

would i be likely to get more definition on those tiny galaxies with a lot more total integration time, with my set up? Or is that pretty much always obviously so, irrespective of gear?

[DaveS]

Yep, more (Much more) integration time. Signal / Noise goes as the square root of integration time, so to double your S/N requires four time the integration, but as that's still only 3 hours it's well worth doing. For Markarian's Chain I might be thinking of 12+ hours (Sorry).

I would also be inclined to rotate the camera by 90 degrees for better framing.

[ollypenrice]

More integration is always better but the benefits are very target-specific. If you are chasing faint signal like tidal tails, faint galaxy arm extensions, accretion loops, outlying nebulosity, IFN, etc., then the benefits are enormous. When you are trying to drag something faint out of the background sky, you will never have enough.  If you have a reasonably bright object already but would like to sharpen its brighter details, the benefits are considerable. You need signal to sharpen. Multiply by four and you'll see a difference. If you are imaging an old elliptical galaxy with little structure, more signal will make it cleaner and smoother and, quite probably, a little bigger but the benefits will not compare with the previous examples.

With a screamingly fast F2 system, cooled CMOS camera and a very, very dark site we regard 2.5 hours as a minimum, so that would equate to about 11 hours in a small refractor of comparable focal length.

Olly

[TiffsAndAstro]

1 hour ago, DaveS said:

Yep, more (Much more) integration time. Signal / Noise goes as the square root of integration time, so to double your S/N requires four time the integration, but as that's still only 3 hours it's well worth doing. For Markarian's Chain I might be thinking of 12+ hours (Sorry).

I would also be inclined to rotate the camera by 90 degrees for better framing.

Well m87 is up most of the time for me, but I'll need to Google how to combine multiple nights.

Maybe I can do 5 hours at a time.

No way of rotating my camera until I get a better lens with a collar ;(

[TiffsAndAstro]

12 minutes ago, ollypenrice said:

More integration is always better but the benefits are very target-specific. If you are chasing faint signal like tidal tails, faint galaxy arm extensions, accretion loops, outlying nebulosity, IFN, etc., then the benefits are enormous. When you are trying to drag something faint out of the background sky, you will never have enough.  If you have a reasonably bright object already but would like to sharpen its brighter details, the benefits are considerable. You need signal to sharpen. Multiply by four and you'll see a difference. If you are imaging an old elliptical galaxy with little structure, more signal will make it cleaner and smoother and, quite probably, a little bigger but the benefits will not compare with the previous examples.

With a screamingly fast F2 system, cooled CMOS camera and a very, very dark site we regard 2.5 hours as a minimum, so that would equate to about 11 hours in a small refractor of comparable focal length.

Olly

Hmm that's not terrible sounding. Hopefully combining multiple nights isn't too horrible to learn.

 

Ty both for your advice.

[TiffsAndAstro]

one other thing if you zoom in there is a sort of streaky noisy pattern. any ideas what this is? is it an artifact from too little total integration time or something else? 

same effect is in these two also   over processing by me? 

[WolfieGlos]

1 hour ago, TiffsAndAstro said:

one other thing if you zoom in there is a sort of streaky noisy pattern. any ideas what this is

The first image looks like walking noise to me. Using a DSLR, I found that it can be partially calibrated out by taking dark frames, but the effect is still there.

The best way to remove it, is to use dithering. This shifts the image slightly (say 5px) in a random direction, which will effectively "trick" the stacking software to isolate the signal from the fixed pattern noise generated by your DSLR. I didn't catch what mount you are using, but if using a guided setup with a mount with tracking in RA and DEC (i.e. not a Star Adventurer 2i), then dithering can be enabled and will be carried out by your guiding software (i.e. PHD2).

With 3 minute frames, I'm currently dithering every 3 frames with my 800D and I get no walking noise. With 5 minute frames, I dither every 2, but if I shoot 6 minute frames, then I found I needed to dither every frame. This was found by trial and error for my setup. On this basis, if you're shooting 2 minute subs, then you might get away with every 4 or 5 frames.

If you are not using a mount like this, then you can still dither, but you will need to do it manually by physically moving the RA/DEC ever so slightly. Just remember to stop the imaging run, and resume after you've dithered, and let the mount settle from the vibrations.

[TiffsAndAstro]

33 minutes ago, WolfieGlos said:

The first image looks like walking noise to me. Using a DSLR, I found that it can be partially calibrated out by taking dark frames, but the effect is still there.

The best way to remove it, is to use dithering. This shifts the image slightly (say 5px) in a random direction, which will effectively "trick" the stacking software to isolate the signal from the fixed pattern noise generated by your DSLR. I didn't catch what mount you are using, but if using a guided setup with a mount with tracking in RA and DEC (i.e. not a Star Adventurer 2i), then dithering can be enabled and will be carried out by your guiding software (i.e. PHD2).

With 3 minute frames, I'm currently dithering every 3 frames with my 800D and I get no walking noise. With 5 minute frames, I dither every 2, but if I shoot 6 minute frames, then I found I needed to dither every frame. This was found by trial and error for my setup. On this basis, if you're shooting 2 minute subs, then you might get away with every 4 or 5 frames.

If you are not using a mount like this, then you can still dither, but you will need to do it manually by physically moving the RA/DEC ever so slightly. Just remember to stop the imaging run, and resume after you've dithered, and let the mount settle from the vibrations.

that's brilliant ty. from youtube i thought it was walking noise and tried to post process it out and im working on a guidescope and camera. i have a sw gti via nina which seems good.

ty so much for this.

[WolfieGlos]

13 minutes ago, TiffsAndAstro said:

 tried to post process it out and im working on a guidescope and camera. i have a sw gti via nina which seems good.

You're welcome 🙂 Unfortunately, now you have the walking noise, there's nothing you can do about it for these images. As I said, I have had some success with dark frames (I actually found they were partially masking my walking noise before I learnt of dithering!), but they don't wholly remove it. You can try and take some if you can match the temperatures of the lights, but otherwise, that's it. It might get masked if you shot, say, another 10 hours of data......

The GTI and NINA should be fine for dithering with a guidescope. I use NINA, in conjunction with PHD2, the ZWO miniguider and a HEQ5, and have no problems at all. It's fairly easy to setup NINA to do this, just experiment with the settle time. Mine works with 30 seconds with a 102ED refractor.

HTH 

[TiffsAndAstro]

6 minutes ago, WolfieGlos said:

You're welcome 🙂 Unfortunately, now you have the walking noise, there's nothing you can do about it for these images. As I said, I have had some success with dark frames (I actually found they were partially masking my walking noise before I learnt of dithering!), but they don't wholly remove it. You can try and take some if you can match the temperatures of the lights, but otherwise, that's it. It might get masked if you shot, say, another 10 hours of data......

The GTI and NINA should be fine for dithering with a guidescope. I use NINA, in conjunction with PHD2, the ZWO miniguider and a HEQ5, and have no problems at all. It's fairly easy to setup NINA to do this, just experiment with the settle time. Mine works with 30 seconds with a 102ED refractor.

HTH 

confession time: i only took 5 dark frames. also i used 'library flats' because i am lazier than cuiv and it was just another test. wasn't really expecting to actually see any galaxies and i gave up counting at twenty. i think i've managed to clean the finger print off the front element that i think caused the black hole.  

its good to know the cause and likely solution. im rushing a bit into more complexity, but so far its been ok. most problems are with niggly usb things. and focus. and clouds. i need time to fail more then fail bit less the next time  

[ollypenrice]

1 hour ago, TiffsAndAstro said:

confession time: i only took 5 dark frames. also i used 'library flats' because i am lazier than cuiv and it was just another test. wasn't really expecting to actually see any galaxies and i gave up counting at twenty. i think i've managed to clean the finger print off the front element that i think caused the black hole.  

its good to know the cause and likely solution. im rushing a bit into more complexity, but so far its been ok. most problems are with niggly usb things. and focus. and clouds. i need time to fail more then fail bit less the next time  

Many DSLR users don't use darks because they add more noise than they remove, and using only 5 will certainly do that. A large dither (12 pixels) is by far the best way to go.

Shooting multiple nights is perfectly simple provided you have the camera consistently aligned. I always align along RA and Dec (either in portrait or landscape) because it is repeatable. Once set up, simply slew slowly in one axis while taking an exposure of about 3 seconds. You'll get star trails and these will show the current orientation of the camera. Once they are horizontal or vertical on the chip you're good to go.

You can plate solve to reframe, though I never used to do this, working manually. I just looked at the star pattern round the edges of the chip.

Olly

[TiffsAndAstro]

9 hours ago, ollypenrice said:

Many DSLR users don't use darks because they add more noise than they remove, and using only 5 will certainly do that. A large dither (12 pixels) is by far the best way to go.

Shooting multiple nights is perfectly simple provided you have the camera consistently aligned. I always align along RA and Dec (either in portrait or landscape) because it is repeatable. Once set up, simply slew slowly in one axis while taking an exposure of about 3 seconds. You'll get star trails and these will show the current orientation of the camera. Once they are horizontal or vertical on the chip you're good to go.

You can plate solve to reframe, though I never used to do this, working manually. I just looked at the star pattern round the edges of the chip.

Olly

Im hopping i can just slew and center m87 in nina over multiple nights. dslr dark frames might not be an issue for too much longer. i think its telescope and astro cam time. 

after what i can only assume is a decent 3ppa, it slews and is usually about 4000 pixels out. then it adjusts and is about 40 pixels out, then one last and its a couple of pixels out. 

Edited April 1 by TiffsAndAstro

[ollypenrice]

1 hour ago, TiffsAndAstro said:

Im hopping i can just slew and center m87 in nina over multiple nights. dslr dark frames might not be an issue for too much longer. i think its telescope and astro cam time. 

after what i can only assume is a decent 3ppa, it slews and is usually about 4000 pixels out. then it adjusts and is about 40 pixels out, then one last and its a couple of pixels out. 

In that case you'll find nothing difficult about multiple night imaging. Have fun!

Olly

[TiffsAndAstro]

58 minutes ago, ollypenrice said:

In that case you'll find nothing difficult about multiple night imaging. Have fun!

Olly

Ty, it's good to have someone to blame

[TiffsAndAstro]

On 31/03/2024 at 23:49, WolfieGlos said:

You're welcome 🙂 Unfortunately, now you have the walking noise, there's nothing you can do about it for these images. As I said, I have had some success with dark frames (I actually found they were partially masking my walking noise before I learnt of dithering!), but they don't wholly remove it. You can try and take some if you can match the temperatures of the lights, but otherwise, that's it. It might get masked if you shot, say, another 10 hours of data......

The GTI and NINA should be fine for dithering with a guidescope. I use NINA, in conjunction with PHD2, the ZWO miniguider and a HEQ5, and have no problems at all. It's fairly easy to setup NINA to do this, just experiment with the settle time. Mine works with 30 seconds with a 102ED refractor.

HTH 

Do you think I would be able to get away without guiding?

I seem able to do upto 5 mins unguided if I take care with setting up, but that's at a much much bigger fov.

Edited April 2 by TiffsAndAstro

[ollypenrice]

59 minutes ago, TiffsAndAstro said:

Do you think I would be able to get away without guiding?

I seem able to do upto 5 mins unguided if I take care with setting up, but that's at a much much bigger fov.

The need for guiding, and the necessary precision when guiding, depends entirely on your resolution in arcseconds per pixel. The error in your guiding (the RMS in arcseconds) needs to be no more than half your image resolution in arcsecs per pixel. That's actually quite a tall order and a very tall one when unguided with a non-premium mount. People often regard round stars as proof of acceptable tracking or guiding but this is an error. If your tracking/guiding errors are about equal in both axes you'll get round stars however bad your tracking is. They will just be large round stars and all fine detail will be blurred out.

Guiding is a wonderful thing. It allows a £1000 mount to perform like a £10,000 mount.

Olly

[TiffsAndAstro]

4 hours ago, ollypenrice said:

The need for guiding, and the necessary precision when guiding, depends entirely on your resolution in arcseconds per pixel. The error in your guiding (the RMS in arcseconds) needs to be no more than half your image resolution in arcsecs per pixel. That's actually quite a tall order and a very tall one when unguided with a non-premium mount. People often regard round stars as proof of acceptable tracking or guiding but this is an error. If your tracking/guiding errors are about equal in both axes you'll get round stars however bad your tracking is. They will just be large round stars and all fine detail will be blurred out.

Guiding is a wonderful thing. It allows a £1000 mount to perform like a £10,000 mount.

Olly

Yeah I was really asking but knowing the answer

I'm trying to use my very limited budget to get the biggest improvements to my end product.

I'll have to stick with unmodded dslr but get a scope, guide cam and scope and the required bits.

Also my £5 flea market  tripod maybe iffy with more stuff

Edited April 2 by TiffsAndAstro