Dark Frame and Flip

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jsawaski
Posts: 19
Joined: Tue Mar 14, 2017 2:06 am

Dark Frame and Flip

#1

Post by jsawaski »

When creating and using dark frames the manual is specific about certain parameters being help constant; gain, exposure, temperature, etc. However, "Flip" is not mentioned.

I experimented by creating a dark frame of a brick wall in the daylight. If I apply the dark to a light with the same "Flip" setting I see a black screen; as expected. However, if I set the "Flip" control to anything other than what the dark was created I see a rather ugly image. This make me believe that the dark frame must be used with the same "Flip" setting as the light frames.

This has implication for both EAA as well as post processing astrophotography. I also believe flats would have the same issue.
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Re: Dark Frame and Flip

#2

Post by admin »

Hi,

Yes you are correct that you must use flats and darks with the same Flip orientation as the captured frames. I think this is only a problem on ZWO cameras because most other brands of cameras don't offer the option to flip if you are capturing raw frames. I will try to make sure this makes into the documentation for the next update

Cheers, Robin
jsawaski
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Re: Dark Frame and Flip

#3

Post by jsawaski »

Yes, I use ZWO cameras. This expalins why sometimes I such poor results during EAA secissions and some astrophotography images. Knowing this will make a big difference for me.

Is it possible, during live viewing, to make SharpCap check compatibility of all the appropriate parameters of the dark and flat with the current camera settings? And if an error exists issue a warning? The user could ignore the warning, but at least the user was warned. I guess the real question is, are these parameter stored in the FITS file of the master dark and flat?
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Re: Dark Frame and Flip

#4

Post by admin »

Hi,

I pretty sure that the flip settings will not get saved in the meta data of a master flat or master dark image file, which would mean that SharpCap would not know which flip orientation should be checked and using those frames. Of course I could make it save that data in future, but that wouldn't help for any existing flat or dark file libraries.

I wonder if it might be better to take away the current flip controls and add a separate set that only flip the image on screen and do not adjust the saved image orientation. Then every saved file would have normal orientation and the flip controls would just change how the image looks on screen which is all they are really good for anyway.

Cheers, Robin
jsawaski
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Re: Dark Frame and Flip

#5

Post by jsawaski »

Yes, that sound good.
BlackWikkett
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Re: Dark Frame and Flip

#6

Post by BlackWikkett »

We've had a request for this from some time back.

viewtopic.php?f=5&t=1279
jsawaski
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Re: Dark Frame and Flip

#7

Post by jsawaski »

Apparently I did a poor job of searching to see if this issues was already reported. Sorry for the duplication.

But I guess all that maters is that we make people aware of this and improve Sharpcap.
cmooney
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Joined: Tue Apr 03, 2018 1:18 pm

Re: Dark Frame and Flip

#8

Post by cmooney »

+1 for having the dark frame follow camera orientation one way or the other. Preferably maintaining orientation to the saved file.
Maybe "mirror, flip, and mirro+flip" could be added as a preview effects FX filter?

I like to run remote EAA Star Parties and I like to have everything north-up on the GEM, so I double flip the camera after a maridian flip.

I only realized the dark fame flip issue recently (just started using the GEM) and I'm planing on stating a new dark frame library and manually labeling "east side" & "west side" dark's. Luckily I'm only using a newt, so I don't have to worry about the different refactor mirror

SharpCap as awesome!
-Corey
ZepHead
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Re: Dark Frame and Flip

#9

Post by ZepHead »

I have a question about camera orientation and how dark frames are taken and then applied.

I understand that dark frames can be taken with the camera sensor covered, and this how I've typically created my dark calibration frame library. I have an 8" Celestron SCT, which I use with a f/6.3 focal reducer at the rear cell as well as a HyperStar connected to the front corrector plate. I have the flip setting set to "Vertical" which is how I took my most recent dark frames. My camera is an ASI533MC Pro.

How would I know which way I should orient the camera depending on if it's connected to the rear or front of the OTA in order to properly correct for noise and hot pixels? Would I need a dark frame library for each configuration?

Thanks in advance,

Frank
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Re: Dark Frame and Flip

#10

Post by admin »

Hi,

you will need to make sure your dark and flat frames are taken with the same 'flip' setting as your light frames. If you regularly change flip settings then you will need (as you say) to have versions for each orientation that you use. Personally I tend not to bother with the flip functions, since there is no real 'right way up' for astronomical images. If I was taking terrestrial images then it would make more sense to me to use them to get the image the right way up/right way round.

cheers,

Robin
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