Taking flats

[joecoyle]

I need to start taking flats.

Bearing in my I have zero DIY capability, what is the best way to take flats ? And when? After darks? Are they temp dependent ?

I don't want to leave kit out overnight in case of the impending rain that occurs in Manchester on a near daily / nightly basis!

T shirt and torch ?

Plastic bag?

Paper?

MacBook screen ?

And, with no Av mode on a CCD what duration etc should they be? How many should I take? 50?

Cheers

Joe

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[Davey-T]

You need to take them with the camera scope in the same position as when the images were taken, so don't remove the camera until you've taken them but if you can carry the scope indoors with camera attached you can do them next day.

You need some way to measure them either by observing a histogram or software that can analyse them to get a measurement around 20000 / 30000 adu to achieve this you need an adjustable light source or adjust exposure times.

Not particularly temp dependant .

I generally take 16 / 20 after which you get the law of diminishing returns.

Dave

[joecoyle]

Yeah fair enough. Won't moving the scope potentially dislodge any dust ?

What do you use? A light box ?

What's ADU?

I'll be using Nebulosity. Does that tell you ADU?

Joe

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[Jokehoba]

I struggled to find a consistent way of obtaining flats and the best way I found was holding a panel monitor over the scope! So as I had a couple of broken laptops, I used the screen from one to make a light panel. Then I read that someone used something like this: http://www.amazon.co.uk/dp/B00AYXNR5S?psc=1. I think you can get them cheaper on ebay.

Optimum exposure will place the (luminance) peak at about half-way along the histogram, i.e., no black/white clipping.

John 

[StargeezerTim]

I use a light pad that you can get from Amazon or Ebay for just under £30. Seems to work well enough.

http://www.amazon.co.uk/MiniSun-Modern-Ultra-Slim-Design-LightPad/dp/B00AYXNR5S/ref=sr_1_1?ie=UTF8&qid=1436822638&sr=8-1&keywords=light+pad+a4

[joecoyle]

This hobby is escalating in cost by the second haha. Another bit of kit to buy!

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[StargeezerTim]

This hobby is escalating in cost by the second haha. Another bit of kit to buy!

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Tell me about it!

[Ouroboros]

I use a light pad that you can get from Amazon or Ebay for just under £30. Seems to work well enough.

http://www.amazon.co.uk/MiniSun-Modern-Ultra-Slim-Design-LightPad/dp/B00AYXNR5S/ref=sr_1_1?ie=UTF8&qid=1436822638&sr=8-1&keywords=light+pad+a4

I like the look of this. It's an even illumination you reckon?

[joecoyle]

How do you attach it? Just hold it over ?

[StargeezerTim]

I like the look of this. It's an even illumination you reckon?

How do you attach it? Just hold it over ?

Seems to be an even illumination, it was suggested in another thread to adjust the way it sits on the aperture once or twice during the taking of flats just to equalise out any variations across the pad. I just point the scope up and rest the pad over the opening. It's quite bright and not adjustable. The flats (without filter) come out at 1/4000 sec exposure with the histogram about a third/half way across.

Its the most convenient way of taking flats i've found so far. hope this helps, Tim.

[ollypenrice]

I like about 23000 ADU max. Depending on your vignetting you will see a minimum value maybe 3000 ADU below that. Temp isn't important at all other than that higher temp has more noise, so take more flats to compensate if you feel like it.

What hasn't been mentioned, and is mighty important, is the need to take darks for flats. If you don't they will over correct. But don't panic, it's not as bad as it sounds. All you need by way of darks for flats is a set of bias, or a master bias. (The flat exposures are so short that thermal noise doesn't build up and so most of the noise will be just in the bias.) You do need to tell your stacking software that the file(s) you may have labelled 'bias' are being used, in this case, as darks for flats.

I do panel flats and I do them in the dark because, when I don't, I get light gradients in my flats. Not everyone seems to find this.

Olly

[joecoyle]

So in terms of workflow then:

1. Stack darks into master

2. Stack bias into master

3. Calibrate flats into master using master bias

4. Calibrate lights using master dark and master flat

5. Stack

What do people tend to use for stacking?

A) I know people use DSS but I'm a Mac user and really hesitant to install parallels.

Nebulosity for calibration / stacking then pix insight for processing?

C) pix insight for both stacking and processing?

Thanks

Joe