Effect of pan and tilt on dark subtraction?

[timh]

Hi Robin,

I often use the facility in Sharpcap to capture frames that are not full sized but that are cut down to dimensions that best frame the object of interest (and because the file sizes are then smaller).

Sometimes I will then use Pan and Tilt to get the object of interest nicely centred.

However - I assume (perhaps incorrectly?) that pan and tilt work by shifting the particular part of the sensor that is being read and recorded into lights?

However does that now mean that any darks and flats used to calibrate and do cosmetic correction should also be panned and tilted in exactly the same way in order for them to then accurately line up with the lights?

Or is this just an imaginary issue because Pan and Tilt only alter what you see but not what is actually captured ?

thanks
Tim

[admin]

Hi Tim,

pan and tilt do change the area of the sensor being used, so you have two options here

1) hard way- capture darks and flats at exactly the same pan/tilt as you intend to use

2) easy way - capture full frame darks and flats - SharpCap will automatically cut the right region out of them when you use ROI features and pan/tilt.

Note that the ability to use full frame darks/flats is moderately recent (last 6 months or so), so you need to have a recent SharpCap 4 for it to work.

cheers,

Robin

[Tiago Ferreira]

Hi Tim,

pan and tilt do change the area of the sensor being used, so you have two options here

1) hard way- capture darks and flats at exactly the same pan/tilt as you intend to use

2) easy way - capture full frame darks and flats - SharpCap will automatically cut the right region out of them when you use ROI features and pan/tilt.

Note that the ability to use full frame darks/flats is moderately recent (last 6 months or so), so you need to have a recent SharpCap 4 for it to work.

cheers,

Robin

I tried that recently with updated version, full frame and it did go wrong. So i made darks only for that region which allow me only to pan/tilt a bit to avoid all the mess hided around the first ROI position.
I deducted it was because i'm using a focal reducer with high distortions outside the ROI and for some reason it did not work.
After reading you Robin, i wonder if i should try it again to double check. Should i?

[timh]

Hi Robin,
Many thanks once again for the answer and suggestions! Don't like the look of the hard way - I didn't know that the full frame flats and darks now work so that is very useful to know.

Tim