Tuesday, May 05, 2009

20090505 Sun

I fall back to use my Ranger with its original focuser. The 0.5x corrector could no longer be used in the nosepiece of BF10 due to the reduced in-travel, but I placed it on the nosepiece of the DMK at least, I guess the reduction factor is very little, but it's better than absence.

No more motorized focusing, the focus position is less than perfect, but it's acceptable, not too far from the correct position. With a f/12 light cone, you really couldn't go too wrong.

Seeing 3/10, transparency 6/10. Since the corrector is acting in a less powerful way, I have to use "drift method" during capturing and "expand to maximum image size" in registax stack to get full disc. The result is not bad as I can see from the raw.

This is the first attempt at 1519 (GMT+8), notice that the field is not very even, since I stay too much time on the upper part and it's not averaged enough so the sweet spot was shown:-

This is the second attempt, I start drifting the image from the chip as soon as the capturing begins, so the field is surprising uniform, but I didn't stay long enough for the lower part and therefore, the amount of noise is more there.

I shall write a separate article on this interesting technique. This is good in the sense that:

1. Uneven field illumination/bandpass will be averaged out
2. Dust on the chip will be averaged out
3. We have an effectively bigger image area, no need to do mosaic

I shall improve this skill further!

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