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| Night Time Photography - Page 5 | |
| With D200... | Rating: 
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| Posted: Fri Nov 27th, 2015 02:42 |
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41st Post |
Robert
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Not wishing to split hares... All normal cameras must have a low pass filter, even such as the D810, otherwise the images would be contaminated by infra red and ultra violet imagery. This would result in an extremely hazy and wooly image. My understanding is Nikon have stopped dipping the glass filter in front of the lens in acid which created a micro etch to diffuse the light rays in an attempt to reduce the ugly moire effect when fine parallel lines appear in photographs. I think this has in part been enabled by higher resolution in some of the high end bodies which reduces the tendency for the moire effect to occur, and possibly built in software to correct it although that is a guess on my part. A pass band filter to remove light below about 400nm (ultra violet) and above about 680nm (infra red) is pretty well essential for a clear image. I have often wondered what would happen if I used an ultra violet <400nm and an infra red filter >680nm in combination on my full spectrum D200, given that it has no low pass filter just a piece of extremely thin quartz glass in front of the sensor. The downside would of course be a lot of messing with filters and potential ghost images due to the two filters being in front of the lens in tricky lighting, instead of just in front of the sensor. It would be so much easier if Nikon had provided the facility for the user to easily change the sensor filter. [OK, I know it's splitting the wrong hair but I rather liked the typo, so being in a obtuse mood I left it!] 
____________________ Robert. |
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| Posted: Fri Nov 27th, 2015 05:00 |
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42nd Post |
jk
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If you can catch the hare then you can split it. Even shooting them is very difficult much less running and catching them! Sometimes these typos intentional or otherwise bring humour into the internet world.
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Tue Dec 1st, 2015 06:51 |
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43rd Post |
Robert
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Well I'm back home with the luxury of my 24" screen again! I have revisited the images I took last week at Glenridding of Ulswater in moonlight. I sifted through the 50 odd images I took and settled for one of the last which was taken with a full, unobscured moon. The details are as before, D200 (normal, not IR or UV), Nikkor 20mm f2.8, @ f2.8 with an 8 second exposure, Hi-ISO NR, normal; long exposure NR, ON. With my larger monitor and easier working I have been able to have a better look at the fringing. Here is my best effort at processing the image: I am still unsure about the tint towards sepia, but reducing the saturation seems to detract from the effect?  I am very pleased with it, If I had realised how good the D200 was going to handle the extremely difficult lighting I would have gone home for it at the previous full moon. The water was as flat as a mirror and the reflections were perfect, but that's life as they say. The fringing. It appears to come in three colours depending on the orientation of the contrast junction with which it is associated. Horizontal seems to be grey, vertical on the left seems to be magenta and to the right, cyan. These screen shots have been taken in Photoshop at 400% I have manually remove much of the fringing in the image above, I tried using the CA removal tool in Lightroom but it didn't do anything, I think there is one in Ps but I couldn't find it. The skyline of the large mountain:  The branches of the nearby tree:  The cyan and magenta fringing can be clearly seen in this screenshot. The fringing seems to change to grey on the horizontal branches. Very strange, I have removed most of the cyan and magenta fringing but the grey was much harder and where the branches were tightly packed I gave up!
____________________ Robert. |
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| Posted: Tue Dec 1st, 2015 15:01 |
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44th Post |
Eric
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Robert wrote:Well I'm back home with the luxury of my 24" screen again! If you overlay magenta on top of cyan..what colour do you get? Maybe the grey is just the result of close interaction of tightly packed different color fringes? Have you examined the individual channels?
____________________ Eric |
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| Posted: Tue Dec 1st, 2015 15:47 |
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45th Post |
jk
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Like I said before I think there is a CA effect. It may be in the Adobe algorithm, or in the sensor capture process or even in the lens but if you havent noticed it in the lens before I would think it is a sensor or algorithm artifact as long exposures do not behave 'normally'.
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Tue Dec 1st, 2015 16:46 |
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46th Post |
Robert
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Eric wrote:If you overlay magenta on top of cyan..what colour do you get? I dud wonder about that... My new En-suit sink... Nothing do with the topic but I thought you might like to see it!!!   Back on topic! I have converted the image to CYMK and taken a screen shot of each channel: Fringing CMYK.  Fringing C.  Fringing M.  Fringing Y.  Fringing K.  Fringing CM.  Over to you Eric... Do those images tell you anything? They are taken from an un-adjusted NEF.
____________________ Robert. |
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| Posted: Tue Dec 1st, 2015 17:13 |
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47th Post |
jk
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I'm lost. Nice bathroom. I know more about plumbing than CA and fringing problem resolution.
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Tue Dec 1st, 2015 17:23 |
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48th Post |
Eric
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Robert wrote:Eric wrote: Using the channels you get a clearer picture of where color problems lie....although you had already deduced there was a magenta/cyan issue. You can play a lot of games tweaking channels, like copying the black Chanel outline onto magenta and cyan channels to lose the difference. 
____________________ Eric |
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| Posted: Tue Dec 1st, 2015 17:24 |
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49th Post |
Robert
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jk wrote:I'm lost.  Same here! I can see some sort of effect but what the cause is I haven't a clue, the fringing is definitely cyan and magenta with the magenta one side and cyan the other, where there is no definite 'side' it becomes grey, a mixture of cyan and magenta overlay. It seems to happen at high contrast boundaries. Perhaps it's the lens? I only used the 20mm f2.8 so I don't have anything else to compare with. It was also evident in the low contrast images taken with the moon obscured by the heavy cloud cover.
____________________ Robert. |
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| Posted: Tue Dec 1st, 2015 17:30 |
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50th Post |
Robert
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Eric wrote:Using the channels you get a clearer picture of where color problems lie....although you had already deduced there was a magenta/cyan issue. Thanks Eric. It's getting late now but can that be done in layers, then by increasing or reducing opacity of the layers adjust the effect, this is way beyond my experience...
____________________ Robert. |
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