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| Losing the low pass filter - Page 2 | |
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| Posted: Tue Feb 26th, 2013 02:10 |
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11th Post |
Robert
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richw wrote:I think sometimes we get too caught up in some of this, for most of us it will make no difference to the overall impact and quality of our images. Of course Rich, Nikon employ the appropriate configuration for their particular needs, but it does no harm to understand what is going on inside. Particularly for those of us who are pushing the boundaries using old lenses and making Infra Red images. Those using up to date equipment and making 'normal' images are not affected.
____________________ Robert. |
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| Posted: Tue Feb 26th, 2013 03:30 |
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12th Post |
Eric
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Robert wrote:richw wrote: Actually that's not true! If you put a current 50mm lens (1.8or1.4) on any body and photograph dark footwear against a white background in studio...you get a very distinct hot spot. I had to routinely digitise this out ...for several years!! Whilst even this may not be classed as 'normal' photography it demonstrates that the hotspot from even some modern lenses, without any camera adaptations, is still there. It's only the confusion of colours and detail in general photography that disguises it. Try taking any high contrast subjects centred in the middle of the frame and you run the risk of seeing a hotspot.
____________________ Eric |
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| Posted: Tue Feb 26th, 2013 03:40 |
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13th Post |
Robert
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I stand corrected! I am easily fooled. What would your recommendation be to make a side by side test for hotspot Eric. Last time I used a sunlit pebble dashed wall, I don't have any black shoes! Perhaps a concocted still life scene with a dark object across the centre?
____________________ Robert. |
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| Posted: Tue Feb 26th, 2013 03:48 |
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14th Post |
Eric
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Robert wrote:I stand corrected! I am easily fooled. When I get a moment I will see if I can go back through my archives and find an example of a raw imageI never edited to show the effect. It was the bane off my existance at the time and caused me to use longer, slower lenses just to avoid the extra work.
____________________ Eric |
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| Posted: Tue Feb 26th, 2013 04:45 |
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15th Post |
jk
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It would be very interesting to see that image Eric. I havent used my 50mm f1.8 for serious shooting for a while. Another thing to check when I get back from my travels. BTW: What was your Photoshop method of removing the hotspot?
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Tue Feb 26th, 2013 05:00 |
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16th Post |
Eric
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That took some finding! 2003! D1X and 50mm lens. The hotspot is a magenta spot arrowed. On white boots it didnt show...on coloured boots the discolouration disappeared but on black boots! I bought 3 different 50mm f1.8 lenses ( kept returning them to Jessops - no wonder they went bust!) Bought 2 50mm f1.4 lenses from another source - still the same! Tried all combinations of lighting to see if it was an errant reflection...even with a time exposure with modelling lights it showed this hotspot. In the end I shot the images with the 17-35 at 35mm .....and a little closer. The 17-35 is now my standard IR lens ...as it has no hotspot at all! Edit - This was an untouched nef file resampled for viewing but it doesnt show up as much when posting on the forum???? So to make the hotpot more clear on all screens I have just run a saturation brush over the area to make it a tad more obvious. Attachment: hotspot2.jpg (Downloaded 19 times)
____________________ Eric |
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| Posted: Tue Feb 26th, 2013 05:46 |
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17th Post |
Robert
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OK have taken some test images with the D1x normal body and the body with the LPF removed. I have managed to reproduce the hot spot effect you describe but only at f16 it is just visible at f8 and gone altogether with wider apertures. The hotspot is present on both bodies but not as distinct on the one with the LPF removed. I will take a set with the IR camera then put them up here after lunch.
____________________ Robert. |
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| Posted: Tue Feb 26th, 2013 06:10 |
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18th Post |
Eric
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Robert wrote: OK have taken some test images with the D1x normal body and the body with the LPF removed. Yes the small apertures (I think these boots were f16) do focus and intensify the effect. In fact I invariably keep the aperture I use for IR at between 5.6 an 8...which may be a subliminal recognition of your observation? This step alone probably increases the range of lenses that are 'usable'. Ironically and bizarrely, one of the current flagship lenses (24-70) has a horrid IR hotspot even at f5.6! Which contradicts previous thinking... as its not evident when shooting in colour even at small apertures? So there is more to this than meets the eye. :baffled::baffled:
____________________ Eric |
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| Posted: Tue Feb 26th, 2013 06:14 |
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19th Post |
Eric
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PS...I have now got to go and shoot some large black batteries against a white background. Guess which lens I won't be using? 
____________________ Eric |
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| Posted: Tue Feb 26th, 2013 07:31 |
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20th Post |
Eric
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Okay - I supposed after what I said I shouldnt be surprised. As I was doing the lighting set up for these batteries I thought I would try the 24-70 on this black on white scene. Below the result (left) and the repositioned shot with the 80-200 (right). This does show that the acknowledged IR big hotspot (Bjorn agrees by the way!) on this lens IS still there in colour....albeit at f16 and black on white. Although this is a very specific lighting set up and extreme settings...its not uncommon for catalogue work and frankly I cant help feeling its a big failing in this supposedly top quality lens. I now have to go and clean these batteries before I shoot them.  Attachment: _DSC7526.jpg (Downloaded 17 times)
____________________ Eric |
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