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how to take flat field for dslr


doseri
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hi guys

i would like to know what is the best flat field??????!!!!!!!!!!! , and what is the  correct way to take the flat field !!!!!!, i was thinking to do a flat field light box, i have my new gso Newtonian 8 inch f/5 with gso 2" Coma Corrector on DSLR, last niight i was  imaging  but unfortunately the images need the flat field what l should  do for that ????????

please help me & waiting your advise .

regards,

SAM

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Stretch a white t-shirt over the end of your telescope tube secured with an elastic band, aim at a laptop screen showing a white background, camera in Av mode with the same ISO as the light frames and snap away.

Always works really well for me.

cheers

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I never bothered with a light box or EL panel when I had a DSLR, it's really simple to point at the dull daylight sky - set the camera to AV and 100iso and the camera will take the right length flats for you. 

If the sky is too bright you can put a T shirt over the aperture, or sheets of typing paper (I made a paper mask for this). 

You're only problem would be if you can't leave your kit set up until the next day, but if you can remove the scope with camera still attached and unmoved, you could still do them the following day (I have done this on one occasion).

Carole

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I didn't know about light leaking on Newtonian's Olly, this might account for some of my problems with my Newtonian last year when I was blaming a light leak on the Manual FW.  Must give this further investigation when I get the Newtonian out again, though I have a feeling sky flats worked OK with the DSLR. 

Thanks for that info Olly. 

Carole

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I didn't know about light leaking on Newtonian's Olly, this might account for some of my problems with my Newtonian last year when I was blaming a light leak on the Manual FW.  Must give this further investigation when I get the Newtonian out again, though I have a feeling sky flats worked OK with the DSLR. 

Thanks for that info Olly. 

Carole

 Dear Sub Dwarf

Thank you  for the info , can you tell me more about the setup for the sky flats ( ISO, RAW ,EX )and  and what is  avg frames ,

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Unless I'm mistaken you need to leave the ISO at the same setting as the light frames so it is able to pick up everything in the optical train that might be in your light frames; dust, smudges, dirty great thumb prints etc, basically you are trying to capture lights but without the image data. If your lights are in RAW format then you should use the same format for the flats, bias, darks etc.

I always leave the ISO as per the light frames, selecting Av mode means you specify the ISO (same as lights) and the camera should calculate everything else for you, exposure, aperture etc.

I have found that sky flats are OK but the light at dawn changes brightness and temperature quite quickly so I got inconsistent results.

Horses for courses though :)

cheers

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Unless I'm mistaken you need to leave the ISO at the same setting as the light frames so it is able to pick up everything in the optical train that might be in your light frames; dust, smudges, dirty great thumb prints etc, basically you are trying to capture lights but without the image data. If your lights are in RAW format then you should use the same format for the flats, bias, darks etc.

I always leave the ISO as per the light frames, selecting Av mode means you specify the ISO (same as lights) and the camera should calculate everything else for you, exposure, aperture etc.

I have found that sky flats are OK but the light at dawn changes brightness and temperature quite quickly so I got inconsistent results.

Horses for courses though :)

cheers

thank you Star Forming

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You don't need to use the same ISO etc as you used for the lights. All you are doing is photographing the inequalities of illumination in your light path. There is no magic connection between settings used for flats and for lights. Darks, on the other hand, must replicate the capture of lights exactly. Use a low noise setting for flats so that they don't introduce noise into the final image. Calibrate flats with a master bias used as a dark. (Just tell your stacking programme that the master bias is a dark-for-flats.)

Olly

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Can just jump in here and ask a question "is the reason I am getting a magenta sky when I stack in Registax because I don't have any flats or darks to include in the processing? What I can't understand is that some of the pictures I shot had black backgrounds to the stars, so why didn't this come through on the final stack.

Last night was the first time I tried Astrophotography and I was blown away when I saw the Orion Nebula on my laptop. I worked on one image through Photoshop and the colour seemed fine. I got the reds and blues etc, but when I tried to use Registax everything went magenta. Help please!!

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Why are you using Registax - this is for stacking videos/AVIs?  Try using Deepsky stacker (free) and see what your results are like on that.

Darks are not essential while you are just practising, as they reduce noise, but flats are important as you can't really process an image properly without due to vignetting.  I am presuming you are using a DSLR from your signature. 

However the lack of darks and flats should not affect the colour. 

Carole

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Thanks for that Carol, and I'll have a go at Deepsky.

Yes, my DSLR is the one in my signature as I have come to Astrophotography from my love of photography.  It's not bad as  camera's go, but I don't think I'll have it converted as I also use it for my photography work generally.  I am however interested in trying my IR camera on the Moon as think the high contrast will be good for that.  We just need some clear skies now.

Brenda  :smiley:

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Calibrate flats with a master bias used as a dark.

Although ISO for the flats doesn't really matter, I would just make sure you use biases for the flats which are at the same ISO. This might not be necessary, but better safe than sorry.

NigelM

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  • 2 weeks later...

Unless I'm mistaken you need to leave the ISO at the same setting as the light frames so it is able to pick up everything in the optical train that might be in your light frames; dust, smudges, dirty great thumb prints etc, basically you are trying to capture lights but without the image data. If your lights are in RAW format then you should use the same format for the flats, bias, darks etc.

I always leave the ISO as per the light frames, selecting Av mode means you specify the ISO (same as lights) and the camera should calculate everything else for you, exposure, aperture etc.

I have found that sky flats are OK but the light at dawn changes brightness and temperature quite quickly so I got inconsistent results.

Horses for courses though :)

cheers(

do i do the flats in GRAY (b&w) or in same colore space

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