[APML] Orion Mosaic preview

[Wei-Hao Wang <whwang@asiaa.sinica.edu.tw>]

Hi,

I have an incomplete picture to share with everybody and would like 
to hear any suggestions you may have.

http://www.ifa.hawaii.edu/~wang/misc/orion-center.jpg

This is a quickly processed 4-frame mosaic, combined in registar.  
After calibration in registar, I didn't match each frame further in 
PhotoShop, so you can barely see that there is still some seams and 
frame to frame difference.  The image you are seeing now is 16.5% of 
its original size.

Each frame is taken with my 105mm refractor at F5.1 and a Pentax 67 
camera.  The film is E100S (push 1) and exp time is 90min.  I have
three more frames that are not included in this image.  I plan to
take totally 18 frames to cover the body of Orion.  Perhaps in Feb
I can add five more.  I don't think I can collect all 18 this year.

The major difficulty I had in processing these images is vignetting
correction.  As you can see, faint nebulas are everywhere in these
images.  Because of this, I cannot generate an accurate sky 
background image and use it to correct the vignetting.  If the 
accuracy of vignetting correction is limited by faint nebulas, 
then vice versa, enhancing the faint nebulas is also limited by
the inaccurate vignetting correction.

What I plan to do is, to borrow the flat-field technique used by
CCD guys.  Take a shot of some uniform brightness target and use
this image to correct the vignettign pattern.  Because film is not
linear, I'm not sure how good the results will be.

It has been snowing for most of the time on Mauna Kea since 
Christmas.  Hope I can grab some good weather next month.

Clear Sky.

Wei-Hao

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