> IR-cut filter removal improvement on Pentax K5

  • Posted on: 8 March 2019
  • By: tihomiry

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. The same thing I have done in the past with Pentax KM and I got significant improvement of 2.5 stops. Here is a short article on that: http://planetarium-gb.eu/pentax_astrophotography.pdf
Since I have K5, I almost stop using KM as K5 has huge advantage in terms of QA and noise levels. There is no amplifier glow and no need of dark frames and cooling.
In fact K5 is one of the best DSLRs for astrophotography which is using Sony IMX071 Xmor CMOS sensor. Same as ASI071MC Pro (color) (https://astronomy-imaging-camera.com/product/asi071mc-pro)
Thus after the modification the Ha sensitivity improvement is far less then what I expected. But this camera is great unmodded, so it seems that Pentax IR-cut filter is letting most of the Ha spectrum to the sensor. Below is comparison of M42 Orion nebula with UHC-S filter of 1.Modded (without IR-cut) K5 and 2.Unmodded. There is very slight difference but well enough to show far great results, when push it to the limit with a fainter objects and stack of 100+ frames.

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.