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.

[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

[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