Deep sky with Nikon D70
Acquiring Deep Sky images is the real test to estimate the performances of the Nikon D70. Opportunity at Pic du Midi observatory was given under good observing conditions, this 2004 summer.

Observations procedures
Two configurations have been tested:
- in parallel to the refractor on the GP-DX equatorial mount, no guiding, using two diffrent lens: 180mm f/2 Nikon and 28mm f/2.8 nikon
- at the focal plane of the Astropysic ED120 refractor, GP-DX mount, no guiding

All the images have been acquired in Raw format.

To avoid the "stars filtration" effect, the mode 3 is used:

- Set the camera in "noise reduction" mode
- At the end of the exposure, the camera will start automatically the dark image acquisition. Shut-down the camera. The green light indicating that the camera is writing the image on the memory card is flashing.
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When it stops flashing, power-on the camera to take the next exposure.
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The exposure being triggered by the IR remote controller, it requires that you select again this mode as the IR device is deselected when shutting-down the camera.
- You are now ready to start the next exposure.

The focus has been made "on the fly", using camera zoom or "hand-modified" olympus magnifier "vari-magni" to be attached on the camera viewer. This is clearly the weakness of the procedure, and it would have been better to transfer the image to the PC for a full-resolution display and iterative adjustment.

The image processing has been done using IRIS software. Three dark exposures have been acquired at the same exposure duration. The .NEF images are converted into .pic image with IRIS, dark subtraction, then converted back in rgb .pic images (convert to CFA). White balance is sometimes tricky to adjust. Additional processing using either ddp or modified equalization to enhance white aera and increase contrast.

Raw ".NEF" image Dark Image Raw Same dark, with thresholds adjusted to enhanced contrast Final processed image

Milky Way - 28mm lens

Images have been reduced and compressed compared to original size.

Milky Way
one shot of
5 min exposure - 400ISO - 22th July 2004 - white balance Nikon program: "Cloudy" +2
Milky Way - cygnii area
one shot of 5 min exposure - 800 ISO
Milky way
one shot of 5 min exposure - 800 ISO
Messier object - 180mm lens

Images have been reduced and compressed compared to original size.

Andromeda Galaxy M31
two shot of 5 min exposure - 800 ISO - cropped
North America nebula
two shot of
5 min exposure - 800ISO - 25th July 2004
H & X perseus
one shot of 5 min exposure - 800 ISO
Dumbell
one shot of 5 min exposure - 400 ISO
Omega Nebula
one shot of 5 min exposure - 400 ISO
Lagoon Nebula
one shot of 5 min exposure - 400 ISO
Messier object - Focal plane of 120mm refractor
Dumbell - M27
five shot of 30sec exposure - 400 ISO
Conclusions
  • Images with wide-field lens like the 28mm are quite spectacular, 5 minutes exposure with no guiding is acceptable.

  • Images with 180mm tele-lens provide good view of messier object, with the vision of the sky around. With no guiding, some exposures have been rejected. Also, additional exposures would have been useful to increase the signal to noise ratio

  • Images at refractor focal plane was quite challenging. Focus was done using a bright star. With no guiding, 30 seconds was the absolute limit and about 50% was rejected due to guiding glitchs. The temporay installation of the GP-DX mount did not help to prefectly aligned the mount, and no PEC was used. Few minutes of exposure is clearly not enough, the image quality can really be improved that way.