Filter wheel

Focusers, Filters, Barlows etc..

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Rodd
Posts: 54
Joined: Fri Mar 11, 2016 8:58 pm

Filter wheel

Post by Rodd » Thu Apr 25, 2019 4:58 am

I use the EFW 7 with the ASI 1600 and have never had a problem with calibration. Lately, if I do not take flats immediately after my subs the flats will not line up properly and I wont be able to calibrate. I even lost the first sub of the night because I rotated the filter wheel after the first sub, but then decided to stick with lum instead of doing LRGB--well, because I rotated the filter wheel,. the flats I took at the end of the night did not work on the first sub--dust donuts are visible. The flats worked on the other subs. I used the INIT tool to INIT the filter wheel at the beginning of the night--so it cant be that.

Please help me--I should not have to worry about loosing flats if I rotate the filter wheel--the wheel should be accurate enough to do this--what if I do want to image an LRGB sequence--I wont be able to because I wont be able to calibrate the subs.
Rodd

wvreeven
Posts: 18
Joined: Mon Apr 01, 2019 7:06 am

Re: Filter wheel

Post by wvreeven » Thu Apr 25, 2019 6:47 am

My first reaction was "why would you want to rotate the filter wheel?" but I suppose this is because of balancing issues. In any case, could you explain why you (need to?) do this?

Anyway, dust specks on the filters may introduce donuts in your lights so that's why it is essential that the flats are taken with exactly the same focus, orientation, etc as the lights. I am surprised that this used to work and I think that was just sheer luck if you don't mind me saying so. So I am afraid that your statement "I should not have to worry about loosing flats if I rotate the filter wheel" is not correct.

"what if I do want to image an LRGB sequence" If possible try to avoid rotating the filter wheel. If that is not possible then I am afraid you need to take flats before rotating it.


HTH, Wouter

Rodd
Posts: 54
Joined: Fri Mar 11, 2016 8:58 pm

Re: Filter wheel

Post by Rodd » Thu Apr 25, 2019 12:26 pm

Are you kidding me? I rotate the filter wheel to shoot through another filter--that is how LRGB imaging is done....The filter wheel should rotate from filter to filter at the same spot--flats should be able to be used for more than 1 night. In teh case of last night, the filter weheel rotate to teh SII filter once after the first sub (then I decided to stick with Lum and the first lum sub would not calibrate.

Rodd
Posts: 54
Joined: Fri Mar 11, 2016 8:58 pm

Re: Filter wheel

Post by Rodd » Thu Apr 25, 2019 12:27 pm

I have previously been able to use my flats successfully for months--the filter wheel is not lining up correctly. Flats shoul not be out of alignment simply becuase the filter wheel rotated.

Rodd
Posts: 54
Joined: Fri Mar 11, 2016 8:58 pm

Re: Filter wheel

Post by Rodd » Thu Apr 25, 2019 12:32 pm

Sean--please chime in. I have been imaging for several years and I know how to shoot LRGB images. Everyone I know that is very accomplished does not lose flats simply due to changing filters. The filter wheel is supposed to lock in place VERY ACCURATELY as it has in the past. Something has changed and I am loosing initialization, or alignment or something.

wvreeven
Posts: 18
Joined: Mon Apr 01, 2019 7:06 am

Re: Filter wheel

Post by wvreeven » Thu Apr 25, 2019 2:22 pm

Aaaaahhh you mean to say that you are CHANGING FILTER from e.g. R to G!!! I thought you were rotating the filter wheel, i.e. the physical device, for balancing or so and then continued imaging with the filter that was previously selected.

OK, going back to the start: you need flats for every filter that you use. So if you use 8 filters, you need to shoot flats for all 8 filters, create master flats for each filter individually and apply those flats for the lights of the corresponding filter. If you do not do that then a dusk spec on, say, the R filter will (not may, WILL) become visible in all the images taken with other filters (G, B, Ha, OIII etc) when the R flat is applied to them.

Once again, the fact that this worked before is sheer luck. With all due respect but this is the first lesson learned when shooting multi-filter images and it is so basic that I honestly thought that you could not possibly mean that. Apparently I was wrong.

Rodd
Posts: 54
Joined: Fri Mar 11, 2016 8:58 pm

Re: Filter wheel

Post by Rodd » Thu Apr 25, 2019 2:29 pm

Come on man....give me a break! Of course I shoot flats for every filter. I am saying that my lum flats will not work with lum subs if I rotate teh filter wheel. So if I take 10 lum subs then 10 red subs then shoot my lum flats the lum subs will not calibrate

Got it?

wvreeven
Posts: 18
Joined: Mon Apr 01, 2019 7:06 am

Re: Filter wheel

Post by wvreeven » Thu Apr 25, 2019 6:08 pm

Gotcha. That sounds like a hardware problem to me.

Rodd
Posts: 54
Joined: Fri Mar 11, 2016 8:58 pm

Re: Filter wheel

Post by Rodd » Thu Apr 25, 2019 6:20 pm

Hence the question--what is wrong with the filter wheel.

wvreeven
Posts: 18
Joined: Mon Apr 01, 2019 7:06 am

Re: Filter wheel

Post by wvreeven » Thu Apr 25, 2019 6:35 pm

Have you tried opening up the filter wheel and use your software to change filter and then back to the first one? Perhaps a visual inspection might give you a clue.

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