Empty (No) Filter in EFW2: Individual Image Sub and Calibrated Image Sub (niteman1946)

Empty (No) Filter in EFW2: Individual Image Sub and Calibrated Image Sub

Upper L/H: Line Profile of Individual Sub image

Lower L/H: Individual Sub image

Upper R/H: Line Profile of Calibrated image

Lower R/H: Calibrated image

This Individual Sub image was shot through an open port on the EFW2 filter wheel. Consequently, there was more clearance for the light path than when the Luminance filter was used. As with the other examples, this is a stretched version which results in the hot spot. Note how little the Individual Sub curve drops as a result of the "shoulders".

From discussions with knowledgeable folks on the Cloudy Nights forum, I have learned that ......

" ....... If a line profile through your images shows these "shoulders" you can assume the optical cone is being restricted by an aperture stop, possibly the filters. If the curve is smooth, even if it drops off dramatically in the corners, the light falloff is most likely a natural consequence of the telescope optics.

As a quick test, you could remove one filter and shoot through the empty filter position. If the vignetting changes (or not) you'll know if it is caused by the filter."

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Number/6011701/page/4/view/collapsed/sb/5/o/all/fpart/2/vc/1

#6020892

Note the fairly normal ADU pattern of the Calibrated Sub curve. It starts at about 37k on the left, drops to the 36k value and then finishes just below 36k on the right. You can also see that the stretched version of the Calibrated sub shows none of the distinct vignetting that plagues the Luminance version. It appears that in this case, the flats did do their job. There is some gradient from left to right, which I believe can be removed through processing.

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