September 2, 2013 18 Comments
Clearly, H-alpha astronomical imaging would greatly benefit from a modified camera. A lot more nebulas are now within feasible exposure time. Yet this pose another hurdle to use the camera in daily photography as its color balance is compeletely thrown away. Preset WB is a way to go but scene are so variable from one another that it becomes a chore to keep a sheet of white paper with me. And besides, preset WB only correct for one light source. The correction ratio for different color temperature is no longer the same with modified spectrum in the sensor. Spatial varible lighting, street lights plus moonlight as an example, will be a real chanllenge to correct. This will all add an insurmountable task in post-processing.
A genius solution will be taking advantage of the original factory filter and making it switchable! So, here’s the plan, I designed a filter rack just like the one offered by Hutech LPS front filter, which now could hold the ICF stack in it. After measuring the rack and dimension of Nikon lens mount, I drafted the 3D model in CAD and exported the final version as STL file, which is an universal format in 3D printing.
The 3D rendering of the filter rack. I named it ICF-FF-N4
The printing process is accurate up to 0.1mm in XY, the precision in Z is not as high. But none the less, horizontal accuracy is needed for filter mounting. It turned out the filter could just be secured inside the frame without any screw. The dent in the upper beam is reserved for an extra bump in the middle of the reflex mirror while it flips up.
The waveplate must be in between the 2 antialiasing layer. Since we move the ICF from behind the dust filter to in front of it, we need to make sure the AA layer is facing the lens.
Now the only thing left is to spray the filter rack black. The ICF is multilayer coated. We could now take away the clear filter installed in front of the sensor as the original focus could be restored. But a offset in the focusing system is still needed, because the AF sensor has an additional piece of glass in front of it.