Lucky imaging is the next step to high resolution images

  • Posted on: 13 January 2022
  • By: tihomiry

Comparison Pentax K5 and IM178

Atmosphere is the worst nightmare of the ones, who would like to get hight resolution images. Small telescopes can not have adaptive optics but could benefit of there small aperture and the statistical chance to get a clear view for a fraction of a second. The best fit for this is aperture of 100 - 150 mm. It is like being on the bottom of a pool and looking up. You will see a blurred view but for a fraction of a second you have a chance to get a clear view and you could catch this exact moment.
Generally it should be between 10 milliseconds to 2 second depending on the elevation and the state of the atmosphere.
How to estimate it? Record a video and count how much frames is it take before the image change.

frame comparison Almak

For example if you have a change each 10 frames and you shoot 20 frames per second, then you have half a second clear view and your exposure best be set to 0.5x2/3=0.33s. You could use 0.5s of course, but you will have to discard more frames as you are not sure as the state change will be in sync with the exposure interval. For star system use the lowest exposure that you could and for deep sky the highest.

This is image of Almak with my 3 small telescopes in comparison. You could see the differences of the oprical system and how their diffraction limitation looks like:

Almak different scopes

Also SharpCap software have live stack functionality that can stack only frames that are above predefined focus quality FWHM. Witch is best for deep sky. This one is taken under bad seeing conditions due to wind:

Live stack SharpCap

Here is Jupiter with Vixen VMC 110L. No post-processing

Jupiter VMC 110L

VMC 110L

The best thing is that you do not need precise equatorial mouth or autogiding to do that. You need a high speed, low noise, high QE camera that is now becoming cheeper as the advance of the sensor development. More on this topic will come this year as this will be the primary development of my largest telescope SW200pds!

If you have used DeepSky stacker to stack RAW files, maybe you have notice that the resulting image is poor of color saturation. This is because it has a higher number of bits then the display could show.

Last test from passed night put an end of the questions witch is better CCD or CMOS. My old CCD K-m fall back compared to CMOS K-5.

HDR stands from High Dynamic Range. In short it is the number of tones that compose the image. The larger it is, the best capability we have to see details in the bright and dark regions of a scene.

Witch is better. Stack or long exposure? It depends…

NGC 7000, South America nebula in Cygnus, taken by me from NAO Rozhen. 2 shots composed by 45 frames @ 30s, ISO 51200 with SW 200pds and Pentax k-5. Same processing with DeepSky Stacker and LightRoom.