Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

sgl_imaging_challenge_banner_supernovae_remnants_winners.thumb.jpg.a13d54fa405efa94ed30e7abd590ee55.jpg

JGM1971

The "No EQ" DSO Challenge!

Recommended Posts

1 hour ago, rotatux said:

That Sigma APO seems to fare surprisingly good ! (I like your Orion very much)

How much did you have to close the lens' aperture ? or was it full open at 5.6 ?

Seems only the DG version is available new on the market... did you hear how it compares (optically speaking) to your D version ?

Hello,

 

Forgot to mention the aperture in my original posts. But yes, I shot them at F5.6 so fully opened att 300mm.

 

There is very little information regarding the D version but a few reviews on the DG version and non of them astrophoto related but people seem happy with it though. 

Share this post


Link to post
Share on other sites

Nexstar evolution  mount ,wo 72mm asi294mc .58×60 secs, 20 flats and 20 darks. Had to stop after an hour as  the fanning effect from field rotation was getting close to the flame so lots of cropping. Stacked in sharpcap tweaked in gimp and photoshop Express.

PSX_20190113_215742.jpg

  • Like 2

Share this post


Link to post
Share on other sites

These two done with the same equip but only 10x 60 seconds. No flats or darks but I should of. 

PSX_20190116_210212.jpg

PSX_20190116_210013.jpg

  • Like 4

Share this post


Link to post
Share on other sites

M33 same equip. 45 × 60 seconds. Darks and flats applied.  Galaxys are hard in my humble oppinion. I've tried four or five now and none have any colour to them. 

PSX_20190129_211418.jpg

  • Like 3

Share this post


Link to post
Share on other sites
10 hours ago, Manners2020 said:

Galaxys are hard in my humble oppinion. I've tried four or five now and none have any colour to them. 

I have to disagree. I took a closer look at your jpg of M33. After a quick background gradient removal to remove the worst of the vignetting/light pollution, I only needed to do two boosts to the saturation to see a pale yellow core and lovely blue arms.

I think your problem is not the data but the calibration. I can't stress enough how important flats are to an image. I was terrified by them when I started. However, they are actually really simple to take and can be done the next day if you are careful. Here's what I do:

- When I tear down the kit for the night I am careful to remove the scope/camera as a single unit (leaving it at its last focused position) and I take it all inside and leave it on the dining room table

- The next morning I set up the tripod/mount again and put the scope/camera back on the mount carefully (so as not to disturb any dust)

- I point the scope at any bright area of sky (cloudless or uniform cloud both work)

- I fold about 4 pieces of white A4 paper of the end of the scope to reduce the sky brightness and act as a natural diffuser (white cotton also works but I like paper as I can fold it above and below the scope so it almost holds itself to the scope)

- I then take flats, exposing them until they peak at about 50% of the histogram - typical exposures for me are about 0.1 seconds and I take 25 for each filter

- Having captured the flats I bring it all back inside (you could do it outside but why be cold?)

- I then take corresponding dark frames of the same exposure lengths as the flats (again, 25 flat-darks should be ok) [Note: for DSLRs you might skip darks and only use bias to subtract]

The flats and flat-darks can then be added into your processing software of choice along with your darks and lights

Voila. a much better starting point to begin processing.

Share this post


Link to post
Share on other sites

If you use AV mode (with same iso/aperture) the camera sorts the exposure length for you to get the histogram in the middle.

Edited by happy-kat

Share this post


Link to post
Share on other sites

Or, you could leave it on the table and take the flats by putting a laptop/tablet, displaying a plain white screen, directly in front of the objective. I think you'd still need to diffuse it though, and don't have the screen brightness too high so that you can get a reasonably long exposure (i.e. tenths of a second rather than hundredths or less).

Those images are a good start! But galaxies are hard in the sense that they are generally small in the FoV, which makes them susceptible to tracking errors and field rotation, which will smear their tiny details. Also, as Filroden indicated, it is useful to be able to remove gradients 'easily', and not being a user of Gimp, I don't know whether the Photoshop plugins work with it. It might be worth looking at the range of specialist astro processing software that there is available. Not all are expensive.

Ian

Edited by The Admiral

Share this post


Link to post
Share on other sites
1 hour ago, Filroden said:

I have to disagree. I took a closer look at your jpg of M33. After a quick background gradient removal to remove the worst of the vignetting/light pollution, I only needed to do two boosts to the saturation to see a pale yellow core and lovely blue arms.

I think your problem is not the data but the calibration. I can't stress enough how important flats are to an image. I was terrified by them when I started. However, they are actually really simple to take and can be done the next day if you are careful. Here's what I do:

- When I tear down the kit for the night I am careful to remove the scope/camera as a single unit (leaving it at its last focused position) and I take it all inside and leave it on the dining room table

- The next morning I set up the tripod/mount again and put the scope/camera back on the mount carefully (so as not to disturb any dust)

- I point the scope at any bright area of sky (cloudless or uniform cloud both work)

- I fold about 4 pieces of white A4 paper of the end of the scope to reduce the sky brightness and act as a natural diffuser (white cotton also works but I like paper as I can fold it above and below the scope so it almost holds itself to the scope)

- I then take flats, exposing them until they peak at about 50% of the histogram - typical exposures for me are about 0.1 seconds and I take 25 for each filter

- Having captured the flats I bring it all back inside (you could do it outside but why be cold?)

- I then take corresponding dark frames of the same exposure lengths as the flats (again, 25 flat-darks should be ok) [Note: for DSLRs you might skip darks and only use bias to subtract]

The flats and flat-darks can then be added into your processing software of choice along with your darks and lights

Voila. a much better starting point to begin processing.

I have wondered if my flats have been doing anything to be honest. I've been doing them with a t shirt and white light on a tablet straight after my darks which I've been doing straight after focussing.  I've been doing it that way because I've convinced myself the focus would be out if I left it until the next day eith the change in temp.  The darks I can see what good they are doing but I wouldn't  recognize if my flats were or not . I'll try what you suggest with the paper and sky next time. And I've just had a thought. If my focus tube is in the exact position but focus is off due to temp change , would that still count as the same focus for the flats? Also would you mind posting that pic of my image you tweaked, I'd live to see the colour in it. Thx for the pointers.

Share this post


Link to post
Share on other sites
12 minutes ago, The Admiral said:

Or, you could leave it on the table and take the flats by putting a laptop/tablet, displaying a plain white screen, directly in front of the objective. I think you'd still need to diffuse it though, and don't have the screen brightness too high so that you can get a reasonably long exposure (i.e. tenths of a second rather than hundredths or less).

Those images are a good start! But galaxies are hard in the sense that they are generally small in the FoV, which makes them susceptible to tracking errors and field rotation, which will smear their tiny details.

Ian

Just a quick one on the histogram.  I've been adjusting exposure and gain until sharpcap gives me a green ok.  The image for the flats is always a pale muggy brown .  Should I maybe not be paying too much attention to the ok and more on the actual  histogram? 

Share this post


Link to post
Share on other sites
38 minutes ago, Manners2020 said:

would that still count as the same focus for the flats? Also would you mind posting that pic of my image you tweaked

I've never noticed any issues with my flats due to focus changes. On closer inspection, maybe the gradients are all pollution related rather than flats? It's just that each image appears to be vignetting.

Here's a crop with the gradient removal and saturation boost. Pre-processed low res JPG isn't the best starting point but it should show you there is colour hidden in there.

PSX_20190129_211418(2).jpg.646bdff07191a119358e7ff88228e809.jpg

  • Like 2

Share this post


Link to post
Share on other sites
24 minutes ago, Filroden said:

I've never noticed any issues with my flats due to focus changes. On closer inspection, maybe the gradients are all pollution related rather than flats? It's just that each image appears to be vignetting.

Here's a crop with the gradient removal and saturation boost. Pre-processed low res JPG isn't the best starting point but it should show you there is colour hidden in there.

PSX_20190129_211418(2).jpg.646bdff07191a119358e7ff88228e809.jpg

Thanks for that image, also glad to hear about the focus .

Share this post


Link to post
Share on other sites

As a cost guide StarTools (excellent wipe tool included) is give or take the same cost as the gradient exterminator plugin for photosghop, and startools has so much more then just gradient removal. The full license is free to trial just you can't save (but screen grabs are useful while trialing)

Share this post


Link to post
Share on other sites
Just now, Manners2020 said:

Thanks for that image, also glad to hear about the focus .

Is that with startools?

Share this post


Link to post
Share on other sites

Oh yes,  I should give startools another try. I followed a almost three hour tutorial  twice but without  calibration files. 

Share this post


Link to post
Share on other sites

All I did was oepn that jpeg in startools and reversed the stretch, ran it through Wipe (sorted gradients and colour) and then saved as tiff, opened in paintshoppro purely to save the tiff as a jpeg to upload here.

 

PSX_20190129_211418.jpg.5c578753042bdd85de5ebca0b4c248fa.jpg.jpg

The colour module did bring out the green in the middle but I didn't like it. I am sure there is more in the original autosaved fits file from DSS.

Common process would be open > crop > bin 50% > wipe > develop > then see what you have ... maybe colour > contrast  then save as tiff. A basic quick process.

Edited by happy-kat

Share this post


Link to post
Share on other sites

Here is mine. 

Sony A7s 218 sub x 8s . ISO 6400. Any Suggestion how to denoise for this one? I stacked with median and average setting in DSS and the noise is really bad. 

Celestron Nexstar 8SE51454128_10205331847771208_4938457236365115392_o.thumb.jpg.ccd50fb33ae58474e3b2accd604cfc8a.jpg

  • Like 1

Share this post


Link to post
Share on other sites

I like median kappa clipping for the lights, I would add flats, dark flats and bias and stack again and see how the noise is.

  • Thanks 1

Share this post


Link to post
Share on other sites
6 hours ago, Minhlead said:

Any Suggestion how to denoise for this one?

So the best way to reduce noise is...drum roll...more data. You only have 29 minutes of data using relatively short subs where read noise will have a greater impact. Although the nebula is bright and you have a lot of aperture, you will always have noise, even using the best stacking algorithms etc. Some post-processing noise reduction (using masks to apply the effects more strongly in the weaker signal areas) will help but the reduction is likely to be as noticeable as the noise.

  • Thanks 1

Share this post


Link to post
Share on other sites
7 hours ago, Minhlead said:

Any Suggestion how to denoise for this one? I stacked with median and average

Use an algorithm which selects best samples before combining. Such as those with "sigma clipping" or "range clipping" (just a wild guess, I'm not a DSS user). They will make a *huge* difference. When you have bad data (does not seem your case), use more selective parameters.

From your number of frames, best is probably "average sigma clipping" because with a high number of frames, averaging statistically recovers more signal depth than median. Median is best with low number of frames because it converges faster (than average) to its target value, at the price of resulting precision (it would recover at most 1 bit of signal depth, when average could recover many more).

Once you use the right algorithm, only way is more data, as Ken said. Most post-processing algorithms (such as median and other linear and non linear filtering) will only smear out your image, loosing detail; Some however will help, I personnally use wavelet denoising, but I'm too young on the subject to give advice.

Edited by rotatux
  • Like 1
  • Thanks 1

Share this post


Link to post
Share on other sites
On 06/02/2019 at 16:26, happy-kat said:

I like median kappa clipping for the lights, I would add flats, dark flats and bias and stack again and see how the noise is.

Thanks. Id try again and let you guys know

Share this post


Link to post
Share on other sites
On 06/02/2019 at 18:24, Filroden said:

So the best way to reduce noise is...drum roll...more data. You only have 29 minutes of data using relatively short subs where read noise will have a greater impact. Although the nebula is bright and you have a lot of aperture, you will always have noise, even using the best stacking algorithms etc. Some post-processing noise reduction (using masks to apply the effects more strongly in the weaker signal areas) will help but the reduction is likely to be as noticeable as the noise.

Yeap. I have exposed for longer but after selection and throw away the blurry ones I left with those 200 frames. I'd try again later and try to capture more frames. Thanks 

Edited by Minhlead

Share this post


Link to post
Share on other sites
On 06/02/2019 at 18:35, Stub Mandrel said:

Here's a quick hit with the 'Astra Image Stick':

m42_not_mine.png.d69622b4bd97a94389b90cf94535a80c.png

Looks like the denoise algorithm of Astra is somewhat better than lightroom but you still lose detail when do the denoising in post so I'm looking to optimize my stacking workflow. But thanks for the suggestion :D

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   1 member

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.