Cocoon Nebula & SIGMA 20mm/14mm ART with IDAS Body-mounted Filters

I think this target might be 1st attempt for me.


BORG 107FL F6 + Cooled Canon 6D + HEUIBII-52 Filter

Today’s SIGMA ART is really high performance lenses. I love them. I’d like to applaud to SIGMA optical designers. But 20mm and 14mm are so critical in its back focus distance. When a filter is set between a lens and a sensor, the light path gets a bit shorter than original design’s. IDAS’s body-mounted filter is 1.1mm thick. It’s relatively thin. But still affected by light path change – 370 micron!! Very sensitive.  So if someone wish to use these lenses with a body-mounted filter, you will have the issue. The camera’s flange back has to be set at 44.00mm as designed, with a filter or without. As far as my experiences goes, 35mm or longer focal length are OK. Only issue is for 14mm and 20mm.  It doesn’t improve even if the aperture is stopped down. So hard to deal.

Your options for the solution are

  • To use 20mm and 14mm without a body-mounted filter (not allowed to set in front of lens physically and optically either)
  • To extend the camera’s flange back distance 370 micron further (In this case, body-mounted filter is set all the time) If you specify that when you order the pre-modified camera from us, we set the flange back based on that – 44.370mm for IDAS filters.
  • To use other brand of lens. I understand these ART lenses are excellent performance though.

My cooled 6D is always used with one of IDAS 52mm filters. It’s 2.5mm thick. So I mechanically adjusted the distance. Now my current 6D’s flange back is 44.83mm.  Then, it works with my SIGMA 20mm well now.





~ by tedishikawa on July 23, 2017.

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