Flats not correcting dust motes properly...

[Adam1234]

I (think) I may have fixed the issue with my filter wheel- I done an experiment this evening:

1) Took 2 sets of flats with no filter change, calibrated one set with the other - result: flats calibrated fine & cancelled each other out (already done this last time but done it again to make sure)

2) Took 2 sets of flats with a filter change between each set (going back to original filter before the 2nd set, calibrated one set with the other - result: as expected due to the misalignment on filter change, I saw the moon crater pattern

3) Re-calibrated the filter wheel

4) Took another 2 sets with a filter change between each set, calibrated one set with the other - result: flats calibrated ok and cancelled each other out

 

This seems to suggest that re-calibrating the filter wheel may have done the job, so hopefully for future images I take, my flats correct for the dust motes properly - assuming that the calibration holds and it doesn't come out of alignment again any time soon. We shall see next time I manage to get out and image. Just in case, I think it will still be worth me cleaning the filters at the weekend.

I'm not sure I'll be able to save the images I took before I noticed the issue, but I'll try and take a full set of flats and see. Probably will depend on whether the filter wheel came out of alignment before or after I took the images. At least it was only a nights worth of images I'll lose if not. 

But fingers crossed all is good for future images!

 

Edited February 10, 2021 by Adam1234

[Adam1234]

Taking the plunge and just about to clean my filters. Armed with nitrile gloves, Baadar Optical Wonder Fluid (if needed), Kim Wipes and a rocket blower. 

Wish me luck! I'm a bit nervous about cleaning them actually, but it needs to be done 

 

 

[Adam1234]

Well I've no idea if I've made the filters better, worse or made no difference! 

They certainly don't look as if they've just come out of the factory that's for sure. 

May or may not have made the luminance filter worse - used the rocket blower to remove loose dust first but some refused to come off so I tried using the wonder fluid on the L filter, but I seemed to just move bits around, possibly introduced bits from the kim wipes and I don't think the wonder fluid dried so well and left round spots 😐 May have even scratched it as well 😭

I did not risk the RGB and NB filters so just used the rocket blower on them.

Filter wheel now back together, going to take a few flats and see how they look...

[Adam1234]

Well some good news for a rainy day - I don't think I ruined my luminance filter! No obvious artefacts at least anyway.

Flats for all other filters seem ok I think, and only 1 spec of dust missed on the Sii filter, but I'm not going to worry about that one, unless the filter wheel alignment issue persists. Not sure what the streaky bit is on the Sii flat, but as long as it corrects my images I'll be happy. Just need to take proper flats at some point as these were only 20 test flats of each filter, with no camera cooling or dark frame subtraction. 

Now the real test will be to actually shoot some images of the cosmos...no idea when that will be....🌧️

In the meantime, here's the stacked 'test' flats in the order of L > R > G > B > Sii > Ha >Oiii

 

[bvalente]

Hi Adam1234

A friend pointed out your post to me

I had (have) the exact same issue as you. Maybe you are more fortunate than me? it took me 3 years to figure it out ;)

I could never get the filter wheel to register consistently every time. I ended up shooting flats for each filter right before i shot that filter, and made sure never to change the filter between flats and lights. I shoot flats every night, for every filter

The only way i retained my sanity is by using a flip flat so the flat panel automatically drops into place, shoot the flats, then it raises back up

 

Good luck

Brian

 

 

[Adam1234]

On 03/03/2021 at 16:01, bvalente said:

Hi Adam1234

A friend pointed out your post to me

I had (have) the exact same issue as you. Maybe you are more fortunate than me? it took me 3 years to figure it out

I could never get the filter wheel to register consistently every time. I ended up shooting flats for each filter right before i shot that filter, and made sure never to change the filter between flats and lights. I shoot flats every night, for every filter

The only way i retained my sanity is by using a flip flat so the flat panel automatically drops into place, shoot the flats, then it raises back up

 

Good luck

Brian

 

 

HI Brian, I like the idea of the flip flat, do you have a picture? Must have been frustrating having to shoot flats every night, especially when the nights are short and/or you want to image with multiple filters on a night.

I'll hopefully be able to tell you next week if I've been fortunate - I done some imaging last weekend but haven't got around to taking my flats yet. I'll let you know how it it turns out!

Edited March 4, 2021 by Adam1234

[Sp@ce_d]

Here you go.. I'm still saving for one  ... https://www.firstlightoptics.com/flat-field-generators/optec-alnitak-flip-flat-gen2-flat-fielder-and-dust-cover.html