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Old 19-07-2018, 05:48 PM
rocco57au (Rocky)
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To clean or not to clean?

What I thought to be really good conditions (no clouds, wind or dew) I set up my gear a couple of nights ago and happily snapped away for a few hours.

The next day I had a quick look at some of the images I had captured and was somewhat disappointed in that the images taken seemed to not be as clear/focused as in the past. I always use a bahtinov mask for focusing and I paid careful attention to get it right.

I'm either using the wrong techniques to capture, stack and process (haven't done anything different to what I've always done) or something is not right with my gear

The attached images are a little bit less in quality than I have been able to achieve in the past and I noticed some dust spots that were not there before. I would appreciate some input regarding what I've captured and should I be considering sending the scope to get the glass cleaned (visually I can faintly see what looks like 'sanblasting' and probably could do with a proper cleaning).

Helix LRGB 1x300 each filter
NGC6559 6x300 Ha7nm

Little in the way of processing... stack and stretch.

Cheers
Rocky
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  #2  
Old 20-07-2018, 05:51 AM
Mickoid (Michael)
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Ricky, I'm not up with mono cameras so I can't really comment with what settings you used for these shots. By the amount of noise showing it looks like you've had to stretch these images a fair bit to reveal any detail. Your focus looks fine to me and the marks I can see look like dust spots on your sensor. I have that pitted look in my refractor after it suffered a severe change in temperature from the cold winter air into a warm car. Condensation formed on the glass elements and it took several days to evaporate. I did not clean it and it doesn't seem to have affected the image quality at all. I would not be cleaning the optics.

Do you use flats? Was there any cloud during your exposures? Were you in a light polluted location when taking these shots?. There can be many reasons and variables why these didn't turn out the way they have in the past. Someone with a mono camera may be able to give you more answers.
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Old 20-07-2018, 06:39 AM
glend (Glen)
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Forget the cleaning for now. Concentrate on getting your exposures and processing right. The LRGB is way over exposed for your apparent location, meaning your showing a lot of skyglow and noise. And frankly 300 sec broadband subs are too long, try stacking many shorter subs. Make sure you shoot Darks and Bias subs as well to build a Master Dark and Master Bias and use them. Forget flats for now, get you basics sorted out.
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Old 20-07-2018, 06:47 AM
Imme (Jon)
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Quote:
Originally Posted by glend View Post
Forget the cleaning for now. Concentrate on getting your exposures and processing right. The LRGB is way over exposed for your apparent location, meaning your showing a lot of skyglow and noise. And frankly 300 sec broadband subs are too long, try stacking many shorter subs. Make sure you shoot Darks and Bias subs as well to build a Master Dark and Master Bias and use them. Forget flats for now, get you basics sorted out.
Agreed!
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Old 20-07-2018, 06:57 AM
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gregbradley
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Yeah definitely clean. Flats remove dust spots but that's a huge one. Sometimes they won't if they are not just right.

Its far better to image with a clean camera and clean filters than rely on flats to remove dust spots in my experience.

So get yourself a rocket blower and some Bintel cleaning fluid and some Q tips and microfibre lens cleaning cloth with a bright torch (you need to shine the torch on the glass surfaces to reveal the dust quite often as it can be somewhat invisible otherwise).

That's my policy, cleaniness is senior to post processing flats etc.

Greg
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Old 21-07-2018, 01:51 PM
rocco57au (Rocky)
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Quote:
Originally Posted by Mickoid View Post
Ricky, I'm not up with mono cameras so I can't really comment with what settings you used for these shots. By the amount of noise showing it looks like you've had to stretch these images a fair bit to reveal any detail. Your focus looks fine to me and the marks I can see look like dust spots on your sensor. I have that pitted look in my refractor after it suffered a severe change in temperature from the cold winter air into a warm car. Condensation formed on the glass elements and it took several days to evaporate. I did not clean it and it doesn't seem to have affected the image quality at all. I would not be cleaning the optics.

Do you use flats? Was there any cloud during your exposures? Were you in a light polluted location when taking these shots?. There can be many reasons and variables why these didn't turn out the way they have in the past. Someone with a mono camera may be able to give you more answers.
Thanks for your reply. I am tending to agree that condensation and dust settling over time has caused that pitted look on the glass. Looking into the tube towards a light globe I can see that it's quite extensive. All of my imaging is done in the same spot in the backyard so nothing has changed in my set up from previous sessions.
There were no clouds and I've never used any flats in the past...

Quote:
Originally Posted by glend View Post
Forget the cleaning for now. Concentrate on getting your exposures and processing right. The LRGB is way over exposed for your apparent location, meaning your showing a lot of skyglow and noise. And frankly 300 sec broadband subs are too long, try stacking many shorter subs. Make sure you shoot Darks and Bias subs as well to build a Master Dark and Master Bias and use them. Forget flats for now, get you basics sorted out.
Thanks for your reply. Yeah, my processing is sort of hit and miss but generally I am happy with the results. The images were processed using the digital development filter in Maxim DL5 and nothing more but even using this filter in the past has produced reasonable results and only use it to see what data has been captured.

It may work out better using shorter subs and I will need to give it a go but I have always used 300s subs since going mono.

Quote:
Originally Posted by gregbradley View Post
Yeah definitely clean. Flats remove dust spots but that's a huge one. Sometimes they won't if they are not just right.

Its far better to image with a clean camera and clean filters than rely on flats to remove dust spots in my experience.

So get yourself a rocket blower and some Bintel cleaning fluid and some Q tips and microfibre lens cleaning cloth with a bright torch (you need to shine the torch on the glass surfaces to reveal the dust quite often as it can be somewhat invisible otherwise).

That's my policy, cleaniness is senior to post processing flats etc.

Greg
Thanks for your reply. I wear prescription glasses and can see the remarkable difference when I give them a "proper" clean with lense cloth AND cleaning fluid. Lense cloth alone does an OK job as far as I can see.
I've thought about cleaning the glass myself and have looked at some youtube clips and read about the do's and don'ts but now I'm leaning towards sending the OTA away for professional cleaning... it will cost some dollars but not sure I want to risk doing it myself
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Old 23-07-2018, 12:04 PM
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sil (Steve)
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I dont think the OTA is in need yet of major cleaning, The spots are really closer to the imaging sensor mainly. So if you are swapping gear around expect them to keep building and cleaning eacjh time is your only solution. If you leave all your gear attached at all times, give them a solid clean and put back in place and leave them alone. Typically a sensor blower bulb is all you need, to gently remove dust particles. Turn the exposed optics or sensor on its side to blow, or better upside down just make sure the blower tip doesn't touch anything. Physical contact cleaning always carries the risk of catching a hard particle and dragging it back and forward scratching sensor or optics. So yes avoid if you can and are uneasy about it. But if you're not swapping gear on and off much you should spend the time to take a good set of flats especially if your gear is always setup in place you can use the flats for all imaging. If you find vignetting in your flats you really should use them always purely for that rather than dust too.

BTW Bintel sell a mild cleaning solution and if you have camera gear and crappy scopes use those to practice cleaning on before tackling you good gear. Avoid cleaning solution alternatives, some may contain additives that can coat and attract dust or even damage protective coatings on glass, just grab the bintel stuff. If your scope needs disassembling to clean you may want to find someone able to do that to help you out, but dont if you really dont have too. My guess is there is only dust on your imaging sensor thats visible in your shots.

Your shots look fairly sharp though and possibly the extra water vapour in the air is slightly hazing things. Also while you've always used 300s subs your camera characteristics will degrade over time so maybe its producing too much noise for your acceptability (imaging is personal and i dont think its a problem, your images show as a quick stretch what I would expect in a single sub anyway.) Theres no obvious vignetting in there either but if you want to make mosaics you really should take flats to help get an even background across joins. But a light pollution filter would probably suit you well. The filter wheel may have gaps allowing dust to get in onto filters, flats taken with each filter should clearly show changing dust features while persistant ones or on optics or sensor. Sensor is most common and people tend to have it open faced up so they can visually inspect it but gravity is carrying particles down into this "bucket" constantly, a fan can cause eddies sucking dust into the sensor too. inspect, but then turn upside down and use puffer to gently blow anything that had just fallen in and keep it facing down maybe cap it. You want the sensor exposed to open air as short a time as possible and try to give gravity a hard time dropping stuff into it. then there's humity and static electricity.

My guess is you have some large dust dirt particles on the sensor that may be large enough to see visually with a moving torch aimed at the sensor. use a bulb blower to shift. Anything that refuses to move try an evaporating cleaning solution, first with a drop at an angle to run over the particle and maybe carry it away on its own or with a qtip or fine artist brush with fluid to dislodge it. With cleaning optics I plan ahead and try to reduce the time they are exposed to air and always facing down as much as possible. reassembling from ota outwards cleaning each step and covering too to reduce airborn particles being carried into the cavity. Slow and careful and gentle as you go and once reassembled try to avoid swapping out parts if you can, my gear is essentially in permanent setup, so only dust on the front element of OTA is of any concern and theres nothing noticeable in my subs like yours and I havent cleaned ota in 2yrs. I spent a weekend or so cleaning the backside, OTA to imager basically, clean, test shoot, examine subs, disassemble, clean, test shoot etc to be confident there are not insects living inside the train or anything obviously causing issue. Technically there will be particles in there that would make a quantifiable difference, but I'm happy with where I'm at with my images. Like I said earlier imaging is often personal where you draw the line in the sand with your efforts and whats an acceptible loss of quality for gains elsewhere.
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Old 30-07-2018, 06:14 PM
rocco57au (Rocky)
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Hi sil, thanks for your lengthy and detailed reply.
My set up is normally fixed and nothing changes and only recently have I taken it apart to add an OAG... that is another story. I've gone back and used a blower to remove any surface dust that may have found its way onto the optics... filters, camera and front of OTA glass. The imaging sensor is sealed and I couldn't see anything obvious on the glass but that could be my aged eyes playing funny tricks with me
I put everything back together and played around with the setup the other night to get focus on both the imaging camera and guiding camera... it's proved to be a bit of a challenge and still not got it right On first appearance, images taken, and they were purely for focusing the guide camera, it seems that I have removed whatever was causing the large dust spot. It clouded over quicker than I could set up so not many test shots taken. I haven't attempted to do anything else with the OTA glass at this stage until I am able to get a good night, and all the planets are aligned, for me to be able to get out there and give it another shot... that can be some time away as I am not always feeling up to it when skies do happen to be clear. From what I can see, the glass is in definite need of a proper clean but I'm not sure that I am up to the task. I don't want to risk causing any irrepairable damage to the glass so for now I'll keep doing as in the past.

As for mosaics, I have attached a couple if images of Eta 4x4 mosaic. One is straight out of MaximDl and the other I have only adjusted the levels in Photoshop... very minor. This was taken back in Feb this year when I believe the optics to have been in a better state than now. I know that I have a lot of work to do when it comes to processing as it is not one of my strengths so I am happy with the "trial and error" approach for now and to be honest I don't think that will improve in a great hurry
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