Nikon D70 - Sun images
In preparation to the Venus transit, I tested the D70 for Sun imaging.

The instrumental configuration
I tested Sun imaging with 2 differents configuration:

- With a 180mm Nikon lens and a Mylar filter

- With a refractor of 70mm diameter, 400mm of focal, a perl Halley 70

Two configuration used: first one with a 180mm lens with a mylar filter (Mylar not shown) and the second one on the right, with a Perl Halley 70 refractor on azimutal mount.

In both case, I used the Nikon Capture Software to store the images directly to the PC. As the exposure are not "Bulb exposure", Nikon Software is useable. I used the remote IR command (palm with Omniremote) to avoid vibrations. See more on Nikon D70 camera here.

  • For the 180mm configuration, I centered the sun on the central sensor of the auto-focus and let the camera do the focus. I bracketed the exposure to get the adequate exposure time.

  • For the Halley70 configuration, I did the focus manually, step by step by looking at the image on the PC. I set the Nikon capture software to download the image and check the image under Iris, this is faster than opening the image with Nikon Capture Editor. I registered both jpg and raw image to have direct access of camera settings in the exif format (see exif command in IRIS) for a fast decision on the best exposure.

The observatory is quite unusual here as it is in Paris downtown - with just one hour frame for observation as the sun goes on top of the street.

The sun image processing

No dark, no offset, no flat... maybe not the best way to do. I select the best image and convert it inton r,g,b, images. I then pick only the green one and convert it from 48bits to 16bits to get a Black and White image. I then apply an unsharp mask with IRIS of 1.5 - 2
The B&W conversion is made to increase the final resolution by not interpolating the color layers.
Results

With the 180mm lens - 18th of May 2004, 12:46 TU

  • 1:1 image - color image - 1/400s F/5 ISO200

  • 1:1 image - Black & White image with unsharp mask

With the 70/400 Perl Halley refractor - May 29th 2004, 08:14 TU

  • 1:1 image - color image

  • 1:1 image - Black & White 1/200s ISO200 - unsharp mask

  • 1:2 zoom on the sunspots region with wavelength filter

More to come with the Venus transit from Iran !!!