Whats up with the clear plastic bag flats???

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barnstorm
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Whats up with the clear plastic bag flats???

Post by barnstorm »

I have seen two references to making H A flats using a clear plastic bag over the front of the scope.

Is this like Snipe Hunting or is it real?


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Re: Whats up with the clear plastic bag flats???

Post by EGRAY_OBSERVATORY »

Personally and IMHO I don't really know why for Solar purposes there is need to worry about flats - unless the camera has far-too many bad pixels.

In some cases (say in the black-surrounds of the Solar-disk), if pixels are detected and can't be cropped-out, then usually for some, could be
either ignored or with either PaintShopPro or Photoshop at least, be dealt with by one or other method...

I have never really had to deal with flats for either Solar or Lunar imaging, as they don't usually interfere with the result and if so would have been dealt by PaintShopPro.

Obviously for DeepSky/night imaging where the blackness of no stars etc. are showing stars that don't exist there, then yes flats may well be required - if the camera has hot/bad pixels..

Terry


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Re: Whats up with the clear plastic bag flats???

Post by marktownley »

Yes, clear plastic bags work as a diffuser for flats. You would use them to remove the influence of dust bunnies from the camera chip, and also unevenly illuminated solid etalons, namely Quarks.


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Re: Whats up with the clear plastic bag flats???

Post by Montana »

Yep, absolutely vital for an instrument such as a Quark.

https://www.flickr.com/photos/alexandra ... 535593245/

Alexandra


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Re: Whats up with the clear plastic bag flats???

Post by barnstorm »

Thanks, everyone!

I have used flats for deep-sky work but until I found out my QHY-183m had pattern issues I did not even realize people used flats for solar work.

I was confused about using a CLEAR bag especially but it looks like the bag should be not entirely clear??


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Re: Whats up with the clear plastic bag flats???

Post by Montana »

It depends, you want to get a diffuse image with the gradients on. I find the fruit bag (as shown) to be perfect for my Solarscope, but it does not let enough light through for the Quark. So I used to use cling film instead for that. You have to experiment. The image will be darker but you can ramp up the exposure to insane levels and the gain and it doesn't matter. So long as you collect at least 100-200 frames and load these into Autostakkert to make a reference flat.

Alexandra


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Re: Whats up with the clear plastic bag flats???

Post by OregonAstronomer »

Flats also eliminate Newton's rings. My mount is so well polar aligned that the sun sits in the exact same spot on the sensor for hours, even with a 2x Barlow in Coronado SM 70mm. Using clear bag flats sure beats the heck out sitting there and manually dithering. Newton's rings are gone in the final image.

They work best when the sun completely fills the field of view. Nevertheless, I have used them on full disk images where the sun is surrounded by black sky because it is stationary on the sensor. Does require a little more tweaking in post-processing, however, to deal with the circumferential gradient in the black area just around the sun due to the flat being blurred while the image is sharp in this area. That being said, full disk images are taken without the Barlow and so Newton's rings are much less of a problem.

When my kids were little I used to send them snipe hunting all the time. As a stay-at-home dad, it was the only time I could ever get anything done! :lol:

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Re: Whats up with the clear plastic bag flats???

Post by marktownley »

barnstorm wrote: Wed Nov 24, 2021 2:00 pm
I have used flats for deep-sky work but until I found out my QHY-183m had pattern issues I did not even realize people used flats for solar work.
It is very unlikely a flat will get rid of the fixed pattern noise inherent with this camera at Ha wavelengths...


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Re: Whats up with the clear plastic bag flats???

Post by Merlin66 »

Yeah,
Bag flats can and do work.
FireCapture allows you to take a flat and then automatically apply it to the SER video. Instantaneous feedback!
I had the ZWO equivalent camera the ASI 183....didn't work for solar, they accepted it back and I got the ASI 1600 which I now use.
Extract from the ZWO website following my (and others) problems with H alpha imaging.
""
Notice: After receiving user feedback, it has been brought to our attention that this IMX183 sensor has grid pattern noise when doing Ha solar imaging. To alleviate this issue, please take flat frames for calibration (out of focus or add a Barlow lens to take flat frames). We recommend our ASI1600/ASI174 mono camera for Ha solar imaging.
""


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Re: Whats up with the clear plastic bag flats???

Post by SeamusBorst »

In January 2021, a law passed in our country banned plastic bags, except for those designed to pack goods. I believe that this law is unnecessary and useless. Regular plastic bags are stronger, more convenient, and sold everywhere. But a huge plus is that the environment will be many times cleaner. Due to such events, I started using Kraft bags, also called bags. At https://www.interplas.com/stand-up-bags/kraft-stand-up-pouches, I can buy them in any size for different needs. And what is your opinion, was it the right decision made by the government, or is there some benefit in it?
Last edited by SeamusBorst on Thu Oct 20, 2022 11:25 am, edited 1 time in total.


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Re: Whats up with the clear plastic bag flats???

Post by Montana »

Yes, unfortunately they are becoming less common. I cherish my 2 fruit bags as they are precious and irreplaceable now.

Alexandra


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Re: Whats up with the clear plastic bag flats???

Post by Sol seeker uk »

On one of Marty's excellent videos he gave 2 versions of flats using firecapture.. first is the standard de-focus method where you can defuse the whole fov of the sensor.. second is the bag method ( like what you find in a cereal packet) for use with full disc fov


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