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My Flats, opinions please

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10 replies to this topic

#1 inoxtrim

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Posted 17 March 2019 - 07:48 AM

I am starting in astrophotography with DSLR NIKON 5500 camera, & Nikon backyard

celestron 102SLT AVX Mount
I have some doubts when it comes to obtaining the flats during the session.
I am using a led ligth pad, I try  center the  histrogram as much as I can , but I do not get it, I attach a file of one of my flats so you can take a look and give me your opinion. regards !!!!

 

Thanks 

 

https://drive.google...iew?usp=sharing


Edited by inoxtrim, 17 March 2019 - 05:21 PM.


#2 Gipht

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Posted 17 March 2019 - 10:02 AM

No picture attached.


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#3 mxpwr

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Posted 17 March 2019 - 10:56 AM

I've had good results with using a blank A4 page at 45 degree angle towards the optical axis and have that illuminated with a light source of about 6000k (or just plain on a sunny day).
This way you have no vignetting from the light source.
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#4 inoxtrim

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Posted 17 March 2019 - 05:21 PM

Sorry, now is attached



#5 kyle528

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Posted 17 March 2019 - 05:41 PM

There doesn't seem to be much agreement on what a perfect flat should look like. Your attached flat looks almost exactly like the flats I end up with, and they seem to work fine. I just use a white shirt pointed at the morning sky. I don't pay much attention to the histogram on the flats (not saying this is right, but it works for me), I just let aperture priority take care of it. I've not had a problem with this process yet. 


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#6 gcardona

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Posted 17 March 2019 - 06:21 PM

The most important thing to consider when taking flats is that you want your flats to be as bright as possible without saturating the sensor. This is why you should look at the histogram to make sure the right hand shoulder is not near the edge.


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#7 mxpwr

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Posted 18 March 2019 - 01:03 AM

I've noticed some luminosity gradient in the upper left corner of your flat.

At least for me, flats show fairly symmetric vignetting, and if not, I got uneven illumination, when taking the flat.
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#8 44maurer

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Posted 18 March 2019 - 04:08 AM

 

Something is odd with the bottom and the top of you flats.


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#9 inoxtrim

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Posted 18 March 2019 - 08:39 AM

In trying this time with sunlight and a white shirt and I think the result has improved a lot, what I can not get in the histrogram is to join RGB, the blue is always more to the right than the others, I do not know what to do?

Attached Thumbnails

  • Flat.jpg


#10 mxpwr

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Posted 18 March 2019 - 10:50 AM

If you look at raw data, RGB histograms rarely overlap perfectly.
That's a function of incoming light spectrum (e.g. color temperature) and the sensor response, which is not the same for the three colour channels (usually modelled after human eye response).
Anyway, that's why you white balances afterwards.
But for the flat you should just make sure that RGB are not too far apart, otherwise you might add unnecessarily noise to your image and potentially complicate later white balance.


Edited by mxpwr, 19 March 2019 - 01:01 AM.

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#11 inoxtrim

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Posted 19 March 2019 - 07:06 AM

Thanks !!!!




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