05-23-2012, 12:17 PM
(This post was last modified: 05-23-2012, 12:30 PM by Brightcolours.)
[quote name='PuxaVida' timestamp='1337603117' post='18389']
I was a good read, a really good read, yet it still remains unclear what causes this phenomenon...
I don't remember where here in this thread exactly, but somebody mentioned about a reflection from the sensor/film to the lens' rear element and then back... I doubt that... I think this kind of "ghosting" would show itself on any location on the image, not as a purple halo perfectly surrounding the blown highlights. Or am I missing something?...
I gave up chasing "what are the possible causes", I rather question "what cannot be the cause" <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />...
And then, I have samples to share/ask opinion. I guess the below sample is like a mixed salad (please excuse the quality of the image, but I believe it's an appropiate sample to bring in <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='
' />...). It's a 100% crop. Taken by the old 135mm CZJ Sonnar @f/3.5. The rocks look slightly OOF (maybe because it's a native M42 mount lens, which is unable to focus at infinity on Nikon). Check the blue surroundings on the left-bottom. Any ideas?... Or the purple halos all over the image, they look like BF but there are more purple halos towards the rocks (near to the in-focus area) and that confirms PF I guess...
![[Image: _SKT9812_019_NX2_sample.jpg]](http://i1172.photobucket.com/albums/r571/SerkanKet/Test%20Shots/_SKT9812_019_NX2_sample.jpg)
Another one, taken with the 28mm AiS @f/11, 100% crop from the right bottom corner... No PF, no visible other CAs, just a tad haze maybe reducing the global contrast (I believe it's a decent lens as reported <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='' />). So, what can be the reason why we don't see a PF here?
![[Image: _SKT9808_012_NX2_sample.jpg]](http://i1172.photobucket.com/albums/r571/SerkanKet/Test%20Shots/_SKT9808_012_NX2_sample.jpg)
[/quote]
You will only see that kind of "ghosting" as you labeled it surrounding very bright spots, simply because that is the only part where the light is strong enough to reflect back in enough quantity. For the rest of the image one would only see a light contrast lowering.
The 28mm f11 image... well, first of all you shot it at f11. This will mean that the light is of MUCH lower intensity, so much less light will reflect back.
A much more interesting aspect is the back element design, though:
135mm f2.8 STF:
![[Image: 308_2.jpg]](http://www.dyxum.com/images/Lenses/308/308_2.jpg)
Nikon 28mm f2.8:
![[Image: 28mmnikkoroptic.jpg]](http://www.mir.com.my/rb/photography/companies/nikon/nikkoresources/28mmnikkor/28mmnikkoroptic.jpg)
Look at the shape of the back elements.
The STF has a virtually flat back element, the 28mm Ai-S' back element has a strongly curved surface. The STF will reflect "straight" back, the 28mm will spread any reflection out over a larger area.
I was a good read, a really good read, yet it still remains unclear what causes this phenomenon...
I don't remember where here in this thread exactly, but somebody mentioned about a reflection from the sensor/film to the lens' rear element and then back... I doubt that... I think this kind of "ghosting" would show itself on any location on the image, not as a purple halo perfectly surrounding the blown highlights. Or am I missing something?...
I gave up chasing "what are the possible causes", I rather question "what cannot be the cause" <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/biggrin.gif' class='bbc_emoticon' alt='
' />...And then, I have samples to share/ask opinion. I guess the below sample is like a mixed salad (please excuse the quality of the image, but I believe it's an appropiate sample to bring in <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='
' />...). It's a 100% crop. Taken by the old 135mm CZJ Sonnar @f/3.5. The rocks look slightly OOF (maybe because it's a native M42 mount lens, which is unable to focus at infinity on Nikon). Check the blue surroundings on the left-bottom. Any ideas?... Or the purple halos all over the image, they look like BF but there are more purple halos towards the rocks (near to the in-focus area) and that confirms PF I guess...Another one, taken with the 28mm AiS @f/11, 100% crop from the right bottom corner... No PF, no visible other CAs, just a tad haze maybe reducing the global contrast (I believe it's a decent lens as reported <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='
' />). So, what can be the reason why we don't see a PF here?[/quote]
You will only see that kind of "ghosting" as you labeled it surrounding very bright spots, simply because that is the only part where the light is strong enough to reflect back in enough quantity. For the rest of the image one would only see a light contrast lowering.
The 28mm f11 image... well, first of all you shot it at f11. This will mean that the light is of MUCH lower intensity, so much less light will reflect back.
A much more interesting aspect is the back element design, though:
135mm f2.8 STF:
Nikon 28mm f2.8:
Look at the shape of the back elements.
The STF has a virtually flat back element, the 28mm Ai-S' back element has a strongly curved surface. The STF will reflect "straight" back, the 28mm will spread any reflection out over a larger area.