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SteveBz

m57 - second attempt

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Hi Guys,

Here are this year's and last year's attempts at M57.

They both use a C8-N with a driven CG5 and DSLR.  They both consist of 30 second fames. The main difference is that this one has a x2 Barlow lens (Televue) and guiding.  The 2018 one had a 2" light train with coma corrector and light pollution filter, which I had to dispense with because the TV Barlow was 1.25".  The DSLR is mains powered here.  Maybe it's my imagination, but I think the RAW frames are a bit noisier.  Neither of them have flats and you can see the vignetting in the 2017 image, which disappears. with the Barlow in play.  Maybe I'll take some flats for this image and apply them, but I don't see much to correct.

This one is:

  • 203 mm Newtonian telescope.  Nominal FL 1000 mm.
  • DSLR Nikon D5000.  ISO6400. 
  • 32 x 30 second subs
  • 30 x 30 sec darks. ISO6400. 6 deg C.
  • 30 x Biases. ISO6400
  • TeleVue 2xBarlow
  • Guiding ZWO ASI120mm + 227mm FL 60 mm Guidescope
  • CG-5 mount with enhanced handset and Arduino control.
  • Processing with DSS and Gimp 9.2 (Exposure and black adjustment only)

The TeleVue has certainly made the image bigger and you can see the white dwarf at it's centre. But it not as good as many of the others on here with similar equipment.

Any suggestions for further improvement?

Regards

Steve.

 

 

 

m57.jpg

M57.jpeg

Edited by SteveBz
Update typos 1600 -> 6400.
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just more time on target, (for 16mins total, it looks really good), match the ISO to the bias/Darks and Stay with 1600iso or even less to reduce the noise.  30s exposures are ok for this target, but you will miss some of the fainer surrounding stuff by doing that.  Just a suggestion:  switch to M27, its alot better for your focal length, and not far away from M57 :)

It's a great result though :)

Mike

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13 minutes ago, mikeyj1 said:

just more time on target, (for 16mins total, it looks really good), match the ISO to the bias/Darks and Stay with 1600iso or even less to reduce the noise.  30s exposures are ok for this target, but you will miss some of the fainer surrounding stuff by doing that.  Just a suggestion:  switch to M27, its alot better for your focal length, and not far away from M57 :)

It's a great result though :)

Mike

Oh, sorry that was a typo.  All the ISOs were 6400.  I'll update it.

Steve.

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35 minutes ago, mikeyj1 said:

just more time on target, (for 16mins total, it looks really good), match the ISO to the bias/Darks and Stay with 1600iso or even less to reduce the noise.  30s exposures are ok for this target, but you will miss some of the fainer surrounding stuff by doing that.  Just a suggestion:  switch to M27, its alot better for your focal length, and not far away from M57 :)

It's a great result though :)

Mike

Hi Mike,

So my issues seem to be:

1) Focal length, which I tried to improve that with the TeleVue x2 Barlow.  Although it says x2, it looks more like x3 or 4 and I haven't cropped either photo.  If it were x3, that would make the FL 3000 mm.  The white dwarf in the centre is not very point-like, and I put that down to the glass in the TV Barlow.  I think If really I want to improve it I need to switch out my x5 Newtonian for a x9 or x10 instrument (for similar aperture). Eg a SC or Mak.

2) Length of guiding.  My CG5 was used and frozen when I bought it.  Although it works nicely now, the guiding error is still 3" which is not the best, so I keep it to short exposures.

My real question is, do you think the TV Barlow has helped or not with DSO photography.  Maybe it's best to reserve for planetary.

Regards,

Steve

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Hi Steve,

the trouble with the Barlow is that although it doubles the focal length (in your case), that also means it doubles the F-Ratio, so your nice fast F5 becomes a slow F10; great for the moon and useful on planets, but not ideal for DSO astrophotography.  You will note from my signature equipment list, i have a Mak127mm, 1500mm F11.8, great for moon and planets, but again not ideal for collecting dim photons from DSO's.  so as you have the F5 i would use that to good effect on things that fit it well.  Thats also why i have the WO61, FL360mm so the North American nebula or Rosette fit that well, and its F6 means its good (could be better with lower F/no, but on refractors that means better quality glass needed) for imaging.  My main imaging scope is the F4.8 250mm Newtonian of course

hope that helps

Mike

Edited by mikeyj1
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To give you an idea, this is what 1hr and 5mins of data looked like

0FjihluU5cJg3Vqmg5bGTNJjJs6nrcnvQVCQ6tg7Z31j5S3fqqCw4_UVZ8_Qr-QQJTljDG7ZifgNG9hvfMKgYBWNoq0eyXbtJ-icFUJh4Ula_mkHmsA3DnT_PrOSDiHyu-2udsq6o_LtsZmRNbJKiylA-TceMZ46wmigaaUsMRneqcgQocaEp3JFEY0aSrb72tujO_fF-zvEamgdaUhQA6fW4g8VwIU8bqb7hVjr1CdwzYi-_WnXXyHHOdOiKzUUg5iBU_2o3RfVgm4ZP9Tv3nEqB_HJWsMcAqthI8YLOf3hb71aDujRh9429LxyP2hqHKCoRG2D49Ijba8xDz9TRBfP8du8hU7bXsdEFy3c3mCioZCWxWc85WzxF9nzGvwDtShOlmg9Jv9Rl0s8wg-rqFcq-H3CvTwlQtm4oBAZ0wW-C9vYOePDZMOJLrvnwMTwUjDCf7iJBKCiELR5oLuD1NubvMw6s4QXap0ZxHnCFMv3d-a76h_U6CZuc2G0dOSImKIlTTnBsCfjifnNirvpPkwmtzoFRW1Ne-jrhZcJALIOKLFcaIsFNb-g9eGfM7PDKt3kiu9V1S9d5T3ekLb7u5RDQEFkwFckKMcTFzJ-kXKx4knqciWBoWL4h_T0BZXL_PZuMfdjNTKNUZc1Rq10lgT6_G-4Yx--u2ZJ7-tLm2KlefG8it_-BXq3GagbY0FLnBXMtFOvjBP2TdmX2Jg=w1359-h905-no

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8 minutes ago, mikeyj1 said:

Hi Steve,

the trouble with the Barlow is that although it doubles the focal length (in your case), that also means it doubles the F-Ratio, so your nice fast F5 becomes a slow F10; great for the moon and useful on planets, but not ideal for DSO astrophotography.  You will note from my signature equipment list, i have a Mak127mm, 1500mm F11.8, great for moon and planets, but again not ideal for collecting dim photons from DSO's.  so as you have the F5 i would use that to good effect on things that fit it well.  Thats also why i have the WO61, FL360mm so the North American nebula or Rosette fit that well, and its F6 means its good (could be better with lower F/no, but on refractors that means better quality glass needed) for imaging.  My main imaging scope is the F4.8 250mm Newtonian of course

hope that helps

Mike

Hi Mike,

So you think ditch the Barlow for DSO, reduce the ISO to ISO1600 and take more exposures? Or take longer exposures?  Maybe if the magnification were less, the guiding limitations would not be so obvious.

Possibly I could get the equivalent of greater magnification using dithering on guiding and the drizzle option on DSS ? What do you think?

Regards,

Steve.

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5 minutes ago, mikeyj1 said:

To give you an idea, this is what 1hr and 5mins of data looked like

0FjihluU5cJg3Vqmg5bGTNJjJs6nrcnvQVCQ6tg7Z31j5S3fqqCw4_UVZ8_Qr-QQJTljDG7ZifgNG9hvfMKgYBWNoq0eyXbtJ-icFUJh4Ula_mkHmsA3DnT_PrOSDiHyu-2udsq6o_LtsZmRNbJKiylA-TceMZ46wmigaaUsMRneqcgQocaEp3JFEY0aSrb72tujO_fF-zvEamgdaUhQA6fW4g8VwIU8bqb7hVjr1CdwzYi-_WnXXyHHOdOiKzUUg5iBU_2o3RfVgm4ZP9Tv3nEqB_HJWsMcAqthI8YLOf3hb71aDujRh9429LxyP2hqHKCoRG2D49Ijba8xDz9TRBfP8du8hU7bXsdEFy3c3mCioZCWxWc85WzxF9nzGvwDtShOlmg9Jv9Rl0s8wg-rqFcq-H3CvTwlQtm4oBAZ0wW-C9vYOePDZMOJLrvnwMTwUjDCf7iJBKCiELR5oLuD1NubvMw6s4QXap0ZxHnCFMv3d-a76h_U6CZuc2G0dOSImKIlTTnBsCfjifnNirvpPkwmtzoFRW1Ne-jrhZcJALIOKLFcaIsFNb-g9eGfM7PDKt3kiu9V1S9d5T3ekLb7u5RDQEFkwFckKMcTFzJ-kXKx4knqciWBoWL4h_T0BZXL_PZuMfdjNTKNUZc1Rq10lgT6_G-4Yx--u2ZJ7-tLm2KlefG8it_-BXq3GagbY0FLnBXMtFOvjBP2TdmX2Jg=w1359-h905-no

Great photo.  How long were the frames and how did you process it?  The white dwarf in the centre is clearly visible.

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Well effectively you are compensating for the slow F-ratio with high ISO..but that introduces noise, and you need darks to compensate (you almost took the same amount of time imaging 'blackness' as you did the object ;)).  But M57 is a REALLY small target, so you need long focal length to get the scale.

Thanks for the compliment, my image is cropped a bit (had some issues with camera tilt that night!), but the data is:  63mins from 3 min subs with Flats and Bias, no darks iso 800.  i use APT and dithering these days and get almost as good a result as using darks.

I use DSS and Lightroom to process

if you use SkySafari or similar, you can superimpose your FOV on a target, gives a good idea of what will fill the frame, (most of the big nebulas and some galaxies) and what will get lost (planetaries and doubles, to generalise)

Edited by mikeyj1
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Well, I might try again without the TV and with longer frames, if I get some clear sky.  It's looking a bit wet and overcast this week.

Thanks for the advice and help.

Regards

Steve.

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5 hours ago, mikeyj1 said:

Well effectively you are compensating for the slow F-ratio with high ISO..but that introduces noise, and you need darks to compensate (you almost took the same amount of time imaging 'blackness' as you did the object ;)).  But M57 is a REALLY small target, so you need long focal length to get the scale.

Thanks for the compliment, my image is cropped a bit (had some issues with camera tilt that night!), but the data is:  63mins from 3 min subs with Flats and Bias, no darks iso 800.  i use APT and dithering these days and get almost as good a result as using darks.

I use DSS and Lightroom to process

if you use SkySafari or similar, you can superimpose your FOV on a target, gives a good idea of what will fill the frame, (most of the big nebulas and some galaxies) and what will get lost (planetaries and doubles, to generalise)

So here I re-processed it a little (given that it's raining).  Do you think this is better than before or not quite so good?

m57v3.jpg

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So. i go through the same dilemma steve, stretching it to bring out the colour, but the noise goes up as well, making it look grainy and forced.  i also like the background to be dark, and the only way is lots of subs to improve the signal/noise ratio, and give more dynamic range to the image.  Honestly, i prefer your original, but just go take an hours worth of images in the same way (only lights, you already have the darks and bias), and add it to your original, and i think you will be much happier ;)

 

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