>The Great Orion nebula and the filters

  • Posted on: 11 November 2020
  • By: tihomiry

Some shots from Sofia. A very bright sky place. Zenith sky brightness info (2015): SQM 19.13 mag./arc sec2 Brightness 2.41 mcd/m2, Artif. bright. 2230 μcd/m2, Bortle class 6.

However I think that with the LED lights nowadays it is much worse as I can see only the 7 bright stars of Orion.
So I did another comparison of different filters to compare which one is best for my observations.

You can notice that the IR image gives the most stars, as most of the artificial LED lights do not emit IR. However IR is less then 20% of the QE of the sensor and we do not have much details here. The best details and colours we have with the UHC-S as it is narrow band for hydrogen and oxygen. The nebula is reach of those elements. The general light pollution filter (Omegon city lights filter) is also good but my one do not have AR coating and cast some glows. However it is my default choice when shooting at sky with any kind of pollution. It is more universal then UHC-S and I can use it for galaxies as well. Here is the place to check your sky : light pollution map

Orion nebula comparison

No fake :) My filters tested with my hand made spectrum analyser and looks good. The light pollution filter cuts all the yellow. UHC-s cuts IR but pass blue light.

Mars spectrum with filters

I am so impressed with the K5 ability to quickly gather signal from nebulas (Quantum efficiency) and galaxies, so I decide to take one more K5 and to remove the IR-cut Filter of the old one.

Recently I got one very good lens the Asahi Takumar 135mm 1:2.5. This is fast telephoto lens and from my point of view a good lens should be with aperture from 1:1,2 to 1:2,8.

Moon at 45% illumination and 70x magnification. With aperture of 200mm,14,1 stops dynamic range, color depth of 23.7 bits at this image there are slight color variation on the moon surface that reveals it’s structure.

This is the beginning of my research on how dark the sky could be and what is benefit of a dark sky for astrophotography. I was inspired from those 2 sites. First one presents mathematical model of how dark the sky is.

You can find my last DSLR Astrophotography article in Bulgarian at page 76. I am sharing my last findings for this publication, Specially written for the Institute of Astronomy.

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