Crescent Nebula DSLR Woes

[imakebeer]

31 minutes ago, alacant said:

I just checked a 450d and 1024 is correct. Here is a 1/4000s dark.

@imakebeer are you certain you have the viewfinder covered?

Yep, I have some tape over the viewfinder but can double check it's not peeling off - this would be more of a concern for flats as they're often taken in the daytime, right???

Surely a 1/4000s is a bias??? But I think the point you're making from that table is that a constant offset of 1024 is pretty much spot on???

[alacant]

20 minutes ago, imakebeer said:

a 1/4000s is a bias

Is it? It's a 1/4000s frame taken in the dark. I don't know what the current English usage be 😟
But it gets the right answer!

Edited September 19 by alacant

[Padraic M]

I'm not sure this is particularly relevant looking at your original image, but the 150PDS is a fine scope that leaks light like a sieve. It's good practice in any event to seal up the standard trouble-spots - around the focuser drawtube, and at the rear around the primary mirror.

You can check this in a dark room by sticking the camera on a loop (1 second exposures will do), cover the scope front opening, and shine a bright flashlamp all around the OTA. You will see bright streaks on the image wherever the light is getting in. It usually looks like a diagonal off-centre arc. 

I use tinfoil to seal the drawtube, allowing enough flex for the focuser to move, and I use a woolly hat to cover the rear end. The usual recommendation is a black swim cap, but I didn't have one of those 🙂

 

[wesdon1]

3 minutes ago, Padraic M said:

I'm not sure this is particularly relevant looking at your original image, but the 150PDS is a fine scope that leaks light like a sieve. It's good practice in any event to seal up the standard trouble-spots - around the focuser drawtube, and at the rear around the primary mirror.

You can check this in a dark room by sticking the camera on a loop (1 second exposures will do), cover the scope front opening, and shine a bright flashlamp all around the OTA. You will see bright streaks on the image wherever the light is getting in. It usually looks like a diagonal off-centre arc. 

I use tinfoil to seal the drawtube, allowing enough flex for the focuser to move, and I use a woolly hat to cover the rear end. The usual recommendation is a black swim cap, but I didn't have one of those 🙂

 

@Padraic M Brilliant advice regarding light leaks. My SW 200P also leaked light terribly, so I did exactly same things. I use a woolly hat for the rear main mirror, and use foil for drawtube. I also use black insulating tape to cover the viewfinder of my DSLR camera. before doing all this I had dreadful gradients in my subs from light leaks.

[Padraic M]

There might be money to be made in astrophotography-quality woolly hats!

[TiffsAndAstro]

44 minutes ago, Padraic M said:

There might be money to be made in astrophotography-quality woolly hats!

Normal woolly hat £5,

astrophotography certified woolly hat £50.

I think we're onto a winner

[TiffsAndAstro]

51 minutes ago, wesdon1 said:

@Padraic M Brilliant advice regarding light leaks. My SW 200P also leaked light terribly, so I did exactly same things. I use a woolly hat for the rear main mirror, and use foil for drawtube. I also use black insulating tape to cover the viewfinder of my DSLR camera. before doing all this I had dreadful gradients in my subs from light leaks.

Not sure woolly hat is better than a black swimming cap

I reached out to Adidas and Timberland for this unbiased review......

Edited September 19 by TiffsAndAstro

[Elp]

3 hours ago, wesdon1 said:

It's likely then due to my old 600D's low quantum efficiency?

Low QE doesn't help, but I got decent signal with my modded 600d when I had it, even with vintage lenses at F5.6.

[imakebeer]

3 hours ago, Padraic M said:

I'm not sure this is particularly relevant looking at your original image, but the 150PDS is a fine scope that leaks light like a sieve. It's good practice in any event to seal up the standard trouble-spots - around the focuser drawtube, and at the rear around the primary mirror.

You can check this in a dark room by sticking the camera on a loop (1 second exposures will do), cover the scope front opening, and shine a bright flashlamp all around the OTA. You will see bright streaks on the image wherever the light is getting in. It usually looks like a diagonal off-centre arc. 

I use tinfoil to seal the drawtube, allowing enough flex for the focuser to move, and I use a woolly hat to cover the rear end. The usual recommendation is a black swim cap, but I didn't have one of those 🙂

 

Do you know what, exactly that thought went through my head (i.e. in one ear and out the other!) when @alacantmentioned taping up the camera viewfinder. 

I have heard this before about the 150P/PDS so I should set about it - thanks 👍 

Edited September 19 by imakebeer

[imakebeer]

2 hours ago, TiffsAndAstro said:

astrophotography certified woolly hat £50.

AP certified woolly hat with the SGL logo on it £75! 🤣

(I'm kidding, it's very nice here 😊)

[TiffsAndAstro]

1 hour ago, Elp said:

Low QE doesn't help, but I got decent signal with my modded 600d when I had it, even with vintage lenses at F5.6.

Yeah er I think my vintage glass is very vintage. Though my Pentax f1.7 50mm might be decent. But it was very cheap way to start.

I got a 200mm f3.5 in a case and mint for £15. It rubbish, but passable at f5.6 looks nice though.

[alacant]

Adobe woolly hat: €120 then €15 per month.

Edited September 19 by alacant

[wesdon1]

On 19/09/2024 at 18:40, TiffsAndAstro said:

Not sure woolly hat is better than a black swimming cap

I reached out to Adidas and Timberland for this unbiased review......

 

@TiffsAndAstro LOL in fairness I agree with you mate! A swimming cap is better for blocking light! 

I have white LED street lights literally shining down the OTA of my 'scopes, they drive me nuts! ( anyone got a shotgun I could borrow please!?? 😂 )

[wesdon1]

On 19/09/2024 at 18:39, TiffsAndAstro said:

Normal woolly hat £5,

astrophotography certified woolly hat £50.

I think we're onto a winner

@TiffsAndAstro haha oh don't get me started on the subject of astro gears prices!! I don't understand why but astro gear costs are "astronomical!" ( sorry! LOL )

[imakebeer]

Well I've been having some fun.....

First of all I've managed to source a used 2" Optolong L-eNhance AND L-Pro - both have been delivered and screw straight into my coma corrector 👍 The former is in place and ready to go if it ever stops being cloudy again so I can have another bash at the Crescent Nebula and see what difference it makes 🤞🙏 The latter will hopefully be useful to improve imaging of galaxies - the Crescent Nebula will soon be dropping a bit low for me, but M31 will be accessible soon (if not already) which is where I started my DSO AP journey 2 years ago.

Then I went down a rabbit hole of comparing the different Optolong filters to understand how they differ and why that's interesting. Which led me to doing a bit of Google research into atoms, ions, electrons and photons so I have a better idea why this all matters (which happened to overlap nicely with my daughter's school homework!).

Somewhere along the line I also found some time to tidy up the rats nest of cables on my rig so that's looking more trick now 👌

And at some point last week there was enough clear sky to get some more imaging of the Crescent Nebula, although unfortunately this was before the filters arrived 😕 But this did give me an excellent opportunity to stack roughly double the data and see how that affected the image (before & after below, TLDR: Better, more detail, but still blotchy) - and that meant I had to learn how to combine data from different imaging sessions in Siril, which has got to be a useful skill to have in the locker, right? (old post here if you're interested).

Before: (one night's imaging - awful)

 

After: (two night's imaging - slightly better, a bit more detail coming out, but still blotchy and poor)

[wesdon1]

2 hours ago, imakebeer said:

Well I've been having some fun.....

First of all I've managed to source a used 2" Optolong L-eNhance AND L-Pro - both have been delivered and screw straight into my coma corrector 👍 The former is in place and ready to go if it ever stops being cloudy again so I can have another bash at the Crescent Nebula and see what difference it makes 🤞🙏 The latter will hopefully be useful to improve imaging of galaxies - the Crescent Nebula will soon be dropping a bit low for me, but M31 will be accessible soon (if not already) which is where I started my DSO AP journey 2 years ago.

Then I went down a rabbit hole of comparing the different Optolong filters to understand how they differ and why that's interesting. Which led me to doing a bit of Google research into atoms, ions, electrons and photons so I have a better idea why this all matters (which happened to overlap nicely with my daughter's school homework!).

Somewhere along the line I also found some time to tidy up the rats nest of cables on my rig so that's looking more trick now 👌

And at some point last week there was enough clear sky to get some more imaging of the Crescent Nebula, although unfortunately this was before the filters arrived 😕 But this did give me an excellent opportunity to stack roughly double the data and see how that affected the image (before & after below, TLDR: Better, more detail, but still blotchy) - and that meant I had to learn how to combine data from different imaging sessions in Siril, which has got to be a useful skill to have in the locker, right? (old post here if you're interested).

Before: (one night's imaging - awful)

 

After: (two night's imaging - slightly better, a bit more detail coming out, but still blotchy and poor)

@imakebeer Wow me and you have been doing astrophotography for roughly the same amount of time, circa 2 years! 

Oh wow I cannot wait to see your reaction when you start getting data on a Neb' with that L-Enhance and your astro-modded DSLR! I was blown away when I first saw my subs on my DSLR screen! Go for the Vale Neb, if you don't have obstructions blocking it, that really pops with the L-Enhance! If not try the Heart Neb' or the North America Neb', they both look stunning with the L-Enhance! 

 

[alacant]

16 hours ago, imakebeer said:

still blotchy

Hi

Reminder: get rid of ALL the edge artefacts whilst the image is still linear BEFORE attempting any processing.

Edited Monday at 08:55 by alacant

[imakebeer]

On 23/09/2024 at 09:54, alacant said:

Hi

Reminder: get rid of ALL the edge artefacts whilst the image is still linear BEFORE attempting any processing.

Thanks for the reminder on this - I don't think that's the first time you've said it and I wasn't ignoring you, just focusing on getting my head around scripting in Siril 💪

I did go back to the original linear stacked image and cropped it before going any further but I'm damned if I can get it to a point where I'm happy with it. I swear once I start stretching the cropped image in GIMP I'm getting edge artifacts that just aren't there in the uncropped one. So in the end my solution was simply to crop the edge artifacts out of the previous image! And I think it is better, not having the eye distracted by the ugly edges:

[alacant]

1 hour ago, imakebeer said:

I'm getting edge artifacts that just aren't there

Hi. Post a -link to- the unprocessed image if you like. Then we can take a look.

[imakebeer]

2 hours ago, alacant said:

Hi. Post a -link to- the unprocessed image if you like. Then we can take a look.

Thanks @alacant, that's very generous of you. Zipped FIT file of the stacked unprocessed image here:

https://drive.google.com/file/d/1P-RGgRk_4tUOi2tC_8qEat7CmwJAq1j0/view?usp=sharing

FWIW I wouldn't expect miracles, as we've been discussing in this thread I might do better with a filter, which is now installed, and so far the forecast for Friday night is looking good 🙏🙏🙏🤞🤞🤞

[alacant]

Hi
The filter may help; we find a simple UHC works wonders on targets such as this. However I think it's fair to say that budget sw reflectors aren't too clever out of the box.

When troublsooting processing, you need to be able to eliminate the hardware from the equation. For a pds, this means

• Line the inside of the tube with matt black velvet cloth (not sure of the current SGL or English term for this)
• Paint the inside of the focuser, the outer edge of the secondary and the fasteners protruding into the tube matt black.
• Fit a rigid spider to hold the secondary. Paint it matt black
• Fit a felt ring on the outer focuser barrel to prevent light entry.
• Remove the fleixible rubber from the focuser
• Tape around the focuser base plate radius where it attaches to the tube.
• Place an opaque shower cap over the primary end of the tube.
• Remove the primary mirror clips and seal it to its cell using double sided silicone adhesive pads. Or if you must, an aperture mask. Still fix the primary to prevent lateral movement.
• Refit the primary using 1.4mm wire springs. Three to replace the existing models and three passively using the lock screws as retainers.
• Fix the tube rings wider apart on a Losmandy dovtail plate.
• Tie the top of the rings with rigid 3mm wall rectangular aluminium profile rail.
• Mount the guide telescope directly to the rail.
   

If a little time consuming, none are particularly difficult, but will certainly help you move forward.

--- --- ---

Processing wise, any idea what the circular artefact may be? Any flat frames appear to have worked, but have not corrected whatever the former. Maybe scroll the individual frames looking for cloud? Clean the camera sensor and ff? Dunno...

Anyway, working with your data, go minamilist perhaps?

 

Edited 5 hours ago by alacant

[Elp]

Agree on the dark patch, is it a light leak? it's restricting what you can do with the data:

[TiffsAndAstro]

2 minutes ago, Elp said:

Agree on the dark patch, is it a light leak? it's restricting what you can do with the data:

i had a go with free tools and couldn't get it reduced as much as you have.

i assumed it was some kind of colimation error, but the halo does seem to match the shape of the crescent nebula itself....rather than circles or similar....

[imakebeer]

@alacant many thanks for the tips (from what I read around here I think the word for the matt black lining in the tube is "flocking" 😉). Not the first time I've heard about or seen these mods mentioned for a PDS 👍If I have to take things to pieces I'm very nervous about the idea about having to (I assume) re-collimate afterwards mind you, but I'm sure I could learn.....

More generally, thanks for the processing attempts everyone, very generous of you all @Elp & @TiffsAndAstro No idea what that ring is around the target - that stack comes from 2 nights worth of imaging and the ring present in both. Could it be light from the target bouncing off the various lenses in the imaging train (primary & secondary mirrors, coma corrector???). I've never had this issue with any other targets so it's very odd.

Still, fingers crossed for clear skies tomorrow night and I can give the L-eNhance filter a test drive 🔭🙏🤞👍

[TiffsAndAstro]

5 minutes ago, imakebeer said:

@alacant many thanks for the tips (from what I read around here I think the word for the matt black lining in the tube is "flocking" 😉). Not the first time I've heard about or seen these mods mentioned for a PDS 👍If I have to take things to pieces I'm very nervous about the idea about having to (I assume) re-collimate afterwards mind you, but I'm sure I could learn.....

More generally, thanks for the processing attempts everyone, very generous of you all @Elp & @TiffsAndAstro No idea what that ring is around the target - that stack comes from 2 nights worth of imaging and the ring present in both. Could it be light from the target bouncing off the various lenses in the imaging train (primary & secondary mirrors, coma corrector???). I've never had this issue with any other targets so it's very odd.

Still, fingers crossed for clear skies tomorrow night and I can give the L-eNhance filter a test drive 🔭🙏🤞👍

im really not experienced enough to make a judgement, i just wanted to point out the shape looks similar to crescent nebula so maybe a reflection from something?

good look with it, it seems a minor thing a tweak will fix