Calibration Frames

[Herzy]

The last few nights I've wasted.  Although I took maybe 40-70 lights, I didnt take any calibration frames. I'm going to explain my procedure and please tell me if I'm doing it right.

Darks: Put lens cap on telescope and take pictures that are the same exposure and ISO as my lights. Take them directly after taking lights.

Flats: During daylight place a white t-shirt over telescope. Take pictures at the same exposure and ISO as my lights.

Bias: Same as darks but at the shortest exposure time my camera can do. Same ISO as lights.

Edited April 23, 2016 by Herzy

[geordie85]

For your flats you don't want the same exposure time as they'll just be washed out.

If you have a canon DSLR turn the knob to AV. That should give a decent exposure time for flats

[ollypenrice]

Darks: Put lens cap on telescope and take pictures that are the same exposure and ISO as my lights. Take them directly after taking lights.

Be careful. This won't work on a Newt which has a light-leaky optical tube. Ideally darks should be done with the camera fully blacked out but lens cappiing a refractor might be OK.

Flats: During daylight place a white t-shirt over telescope. Take pictures at the same exposure and ISO as my lights.

Again, on a Newt you' may get light leakage in the daytime. Take you flats at short exposures which put the histogram peak about a third of the way to the right.

Bias: Same as darks but at the shortest exposure time my camera can do. Same ISO as lights.

Yes. Also use bias as dark frames to subtract from your flats.

Olly

Edited April 24, 2016 by ollypenrice

[Owmuchonomy]

....and because I know about your other threads makes sure all the calibration subs are taken in RAW like your light frames should be.

[geordie85]

9 hours ago, ollypenrice said:

 

Flats: During daylight place a white t-shirt over telescope. Take pictures at the same exposure and ISO as my lights.

Again, on a Newt you' may get light leakage in the daytime. Take you flats at short exposures which put the histogram peak about a third of the way to the right.

Olly

Do you have any advice for t-shirt flats?

I'm using a skywatcher 200p with an atik 383l. When I tried taking flats, even at 1 second, they were completely washed out.

[Astroboy239]

If you are clicking at night hold a white screen/laptop covering the aperture and click ur images or make a light box. Not exactly day light but twilight or Grey sky

 

 

Varad 

[Marky1973]

Hi Herzy - this is my cheap and cheerful method for getting flats using my ED80 - might not be ideal for a reflector, depending on the size, but it works okay for me!

 

 

[ollypenrice]

Try a twilight sky and more T shirt, I guess.

Olly