How do you do your flats?

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HAL
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How do you do your flats?

Post by HAL »

Bag method - I can never find a bag with the right level of translucency. Loads of people seem to swear by this method. I don't know what I'm doing wrong.

Featureless defocussed area - I can't often find an area that is featureless enough near the centre of the disc and find that there are light and dark spots on my flats as a result. This also doesn't work for my little Lunt because the field of view is too big. Also, such a pain having to defocus.

So.... I pretty much never do flats. I think solving my flat field woes is the next step in levelling up my imaging.

I wonder if the illuminated discs you can buy are worth the expense.

How do you do yours?


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Re: How do you do your flats?

Post by marktownley »

I don't do flats at all.

What are you trying to flat with - full disks, closeups? Why do you need to flat?


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Re: How do you do your flats?

Post by HAL »

Hi Mark,

Close ups mostly. I want to do them to get rid of any issues in my images due to dust specks and also to create a more even contrast when doing mosaics.


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Re: How do you do your flats?

Post by Rudi »

I tried with a DIY diffuser, a couple of layers semi transparent bag to be used in focus. Works perfect for Herschel wedge flats, but it was rubbish for my Quark.
Then I tried an out-of-focus flat with the sun centered with the Quark. Also gibberish…
Perhaps I didn’t de-focus enough? Or the strong vignetting is too much?
So with my Quark, I haven’t succeeded in making a usable flat yet. With Herschel wedge, the in-focus diffuser works perfect.


/Rudi
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Re: How do you do your flats?

Post by marktownley »

HAL wrote: Fri May 24, 2024 4:56 pm Hi Mark,

Close ups mostly. I want to do them to get rid of any issues in my images due to dust specks and also to create a more even contrast when doing mosaics.
If it is dust specks just clean the sensor.


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Re: How do you do your flats?

Post by HAL »

Sounds like you are having similar struggles Rudi! I hope you find a solution.

I could just clean my sensor. However, sometimes you don't necessarily notice issues until post-processing, so wouldn't have known to clean, sometimes the dust isn't on the sensor but elsewhere in the imaging train, and cleaning doesn't correct problems of uneven illumination etc. I usually manage fine without flats but would like to find a workable way of doing them so that I have the option.


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Re: How do you do your flats?

Post by Dennis »

Rudi wrote: Fri May 24, 2024 5:00 pm Then I tried an out-of-focus flat with the sun centered with the Quark. Also gibberish…
Thats the way to go for close ups with the Quark.

The Lunt you just have to tune correctly. I myself are no expert there but this is what i could get with a Lunt 40 without flats. The etalon itself is not completely on band but thats another story.
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Re: How do you do your flats?

Post by Rudi »

Thanks Dennis. The four sequences I recorded, was all only partially covering the solar disk. Have very strange skewed results when flat was subtracted.


/Rudi
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Re: How do you do your flats?

Post by Dennis »

Rudi wrote: Sat May 25, 2024 9:32 am Thanks Dennis. The four sequences I recorded, was all only partially covering the solar disk. Have very strange skewed results when flat was subtracted.
Yes for this method the field needs to be completely covered with surface details. If not possible i used a white t-shirt or a plastic bag in front of the scope with success.


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Cameras: imx432 + imx462
Barlows:
-2x Gerd Düring 2.7x
-2x TMB 1.8x
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Re: How do you do your flats?

Post by HAL »

Lovely shot Dennis!


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Re: How do you do your flats?

Post by Rudi »

@HAL (oh - that username gives associations to a certain AI in a book I read in the 80’es ;-) ), how are you imagining the Sun? Which equipment and FOV?


/Rudi
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Re: How do you do your flats?

Post by HAL »

I am indeed named for the famous misunderstood AI!

I am either using my 150 mm refractor + Quark, 80 mm refractor + Quark, or Lunt LS60MT with ZWO ASI174MM.


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Re: How do you do your flats?

Post by rigel123 »

I used to use flats at times but found they mostly did more harm than good, and sometimes made the image just look, well, flat! I found that using an IR cut filter in front of the chip window at all times helps to cut down on dust that could show up in images and I’m sure to blow that off before any imaging session.


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