Lots of dirt on image train - should I do anything ?

[teoria_del_big_bang]

My flats now seem to show an awful lot of dust motes / bunnies or just pure dirt not sure which within the image train.

I have not finished all the pre-processing yet on latest images to see if the flats are removing all of these blemishes but should I be doing anything about this. From what I recall from instructions when I first started a couple of years ago I was told basically never clean any lenses, I guess I am okay to clean the cover to the sensor ? and what about the filters ?

Or do I just leave it?

Below is an autostretched flat in PI.

Steve

[discardedastro]

There's a handy calculator here http://www.wilmslowastro.com/software/formulae.htm#Dust which will tell you har far away the dust is from your sensor plane - worth making sure you know which bit of the optical train needs cleaning before you go at anything.

Everything including the sensor cover on an AP camera will have some form of coating and be sensitive to scratches, but cleaning isn't impossible - you just need a very soft lint free cloth (disposable) and isopropyl alcohol. For loose dust, compressed air can work but can also cause scratches depending on how you use it, so I'd stick to very careful use of disposable lint-free cloths. When you have your optical train in bits, do so in a dust-free environment and keep everything face down or covered with dust caps.

With that much contamination, particularly the thing going on bottom right, I'd probably be looking to clean that, myself. While dimming from dust shadows will get taken out in calibration, blockages won't, and you are throwing away perfectly good light if you have shadowing across too much of the glass.

[gilesco]

5 hours ago, teoria_del_big_bang said:

My flats now seem to show an awful lot of dust motes / bunnies or just pure dirt not sure which within the image train.

I have not finished all the pre-processing yet on latest images to see if the flats are removing all of these blemishes but should I be doing anything about this. From what I recall from instructions when I first started a couple of years ago I was told basically never clean any lenses, I guess I am okay to clean the cover to the sensor ? and what about the filters ?

Or do I just leave it?

Below is an autostretched flat in PI.

Steve

Hi Steve,

I've seen the Australian guy on his star stuff you tube channel apparently routinely cleaning his lens with a regular house dusting cloth, and his pictures seem to remain great. I would avoid chemical cleaners, or anything that has an abrasive feel to it, I tend to use compressed air cans from amazon, to get rid of dust on the imaging train, without an actual visual inspection it is difficult to give advice, if there is an obvious blemish on your optics through a visual inspection then you will need to remove it. But it might be best to consult with the manufacturer of the optics first to get an idea of the chemical concentrations of any fluid you might think of applying to clean it off.

[Merlin66]

IMHO...

Access all the filters and use a Rocket blower to remove as much dust as you can. Then, as said by Discardedastro, you can use KimiWipes (non shedding) and IPA to clean each surface.

For the camera do the same for the front of the glass cover plate....hopefully this should remove the problem.

However....I do solar imaging and found there were still small motes and small (very small) rings.....on/in the camera!

These didn't really appear on flats taken at f5 ( I cover the objective with a clear plastic bag and image a bright daytime sky) but they looked absolutely horrible at f15. The larger f ratio seems to show much more.

It took a few iterations with the IPA/ KimiWipes on both surfaces of the front cover glass and the sensor cover to fix the problem.

It could be for "normal" AP this is not a major issue, but I found for solar imaging it was a nuisance I could do without.

 

[teoria_del_big_bang]

I have looked for those wipes before and never found a supplier in UK. I will try again.

I need to look at this again. I used the calculator in @discardedastro post and the best I can see it comes out at about 7.8 mm and there is nothing in the path around that, so I guess I am working something out wrongly. Nearest is the cover of the camera itself. The filters are probably more than 0 mm away but the positions of these marks are the exact same on all filters so it is not the filters.

Also thinking about it if some of them are that bad it comes out black on a stretched flat image (one in bottom right corner) then would I not be able to see at least something on a stretched image where there are plenty of stars, but the image below is an image from the same session and I can see nothing like that. Left is a raw Ha image and right with flats, dark-flats and darks applied. These marks do not seem to be present in either, that I can see anyway.

Steve

 

[Merlin66]

I found the KimiWipes we’re stocked by a medical supply company.....

[Laurin Dave]

The difference in light transmission of the dust bunnies is only a few percent ..  it’s the auto stretch that makes it look black..  check the ADUs in the affected/ non affected area to see the actual difference..  I use a rocket 🚀 blower to clean them and hold them upside down 

[Merlin66]

Hmmm, if you use >f15 you don’t need to stretch the image to see the small motes!!

[discardedastro]

2 hours ago, teoria_del_big_bang said:

I have looked for those wipes before and never found a supplier in UK. I will try again.

Amazon stock them in bulk, or RS supply them in lower volumes: https://uk.rs-online.com/web/p/multi-purpose-wipes/1223087/

Chemtronics also do these which are effectively the same thing premoistened with isopropyl alcohol: https://uk.rs-online.com/web/p/fibre-optic-cleaning/2361981/

Both are lint-free and will work great for cleaning optics. Using a blower to remove any large-scale debris is always a good starting point though.

There's a lot of hearsay around cleaning optics - I have a spare AR-coated clear Baader I might sacrifice to science while I have a high-zoom stereomicroscope on hand since I have boxes of fibre optic cleaning supplies lying around along with coarser options.

[Merlin66]

I used a pressurised air can, until I found it just spread small "motes" on the sensor.... now I rely on the Rocket blower.....

[discardedastro]

1 minute ago, Merlin66 said:

I used a pressurised air can, until I found it just spread small "motes" on the sensor.... now I rely on the Rocket blower.....

Yeah, canned air is risky because if you're near the end of a can or hold it wrong you can quite easily dump a load of very cold propellant out on the surface you're trying to clean, which can induce damaging temperature differentials. Plus the velocity is high, so it can cause scratches (is the received wisdom). Blowers/puffers don't suffer either of these issues.

[teoria_del_big_bang]

2 hours ago, discardedastro said:

Amazon stock them in bulk, or RS supply them in lower volumes: https://uk.rs-online.com/web/p/multi-purpose-wipes/1223087/

Thanks for the link ordered a couple of boxes next day delivery 🙂 

I am surprised @FLO don't stock them

Steve

Edited March 30, 2020 by teoria_del_big_bang

[teoria_del_big_bang]

3 hours ago, Laurin Dave said:

The difference in light transmission of the dust bunnies is only a few percent ..  it’s the auto stretch that makes it look black..  check the ADUs in the affected/ non affected area to see the actual difference..  I use a rocket 🚀 blower to clean them and hold them upside down 

Okay, I see now (I think). I am going to have a got seeing where they are coming from and see if I can make it better when I get the wipes.

Steve