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| Should I buy a used 28-70 f2.8? - Page 3 | |
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| Posted: Thu May 31st, 2012 15:26 |
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21st Post |
jk
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I think the D800 will be an examination of our technique. I have said before that teh 36MP is IMHO too many and 24MP would have been better for me but you can only buy what is offered. I have had occasions in the past where the 12MP of the D3/D3S/D700 have not enough when I wanted to make a crop from an image. The 36MP will remove that barrier if the image is sharp in the first place. I have taken note of Dave's point about needing to move up two stops to get rid of shake/vibration. I was thinking that I may go for a 16-35mmf4 but the 17-35mm f2.8 would give me a bit of extra flexibility, but it is more expensive!!
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Thu May 31st, 2012 17:22 |
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22nd Post |
Eric
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richw wrote:Robert wrote: The afd 50mm lens (both 1.8 and 1.4 variants) also suffer similarly in studio lighting with white backgrounds. I was once shooting black boots against white and couldn't stop the hotspot fogging the centre of the image. Interestingly and somewhat puzzlingly, the super duper 24-70 has an atrocious hotspot when used for IR. it's almost 3/4 of the frame...making it unusable. I haven't considered why it works so well with colour images but fails so miserably with IR?
____________________ Eric |
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| Posted: Thu May 31st, 2012 18:20 |
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23rd Post |
Robert
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Way out of my depth here but how about a resonance of light at that wavelength? Something is generating spurious light in the IR wavelengths. I know it can happen with sound, so why not light?
____________________ Robert. |
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| Posted: Fri Jun 1st, 2012 10:53 |
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24th Post |
jk
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Eric wrote:
Must be the something to do with the design and the glass used. I think that the ED or new special high refractive index glasses may not behave so well as the older heavier lenses that were made of all the same type of glass. That is purely a guess ..... Someone out there will know.
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Fri Jun 1st, 2012 12:36 |
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25th Post |
Dave Groen
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I heard that it's more about the reflectivity of the coating used on the rear element of certain lenses. Specific coatings reflect IR light better than others. Coatings that reflect it very well are more efficient at creating hotspots.
____________________ I started out with nothing and still have most of it left |
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| Posted: Fri Jun 1st, 2012 16:25 |
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26th Post |
Eric
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Dave Groen wrote:I heard that it's more about the reflectivity of the coating used on the rear element of certain lenses. Specific coatings reflect IR light better than others. Coatings that reflect it very well are more efficient at creating hotspots. It's those naughty nanos again!
____________________ Eric |
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| Posted: Fri Jun 1st, 2012 17:11 |
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27th Post |
jk
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Maybe then we are better without coatings for IR work.
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Sat Jun 2nd, 2012 04:47 |
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28th Post |
Robert
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Could be a factor but I think there are two fairly obvious factors which are plainly visible, firstly the size of the rear element, and secondly the curvature on the rear face of the rear element. I don't have enough lenses to be able to sort this out but the worst offenders seem to have large and flat rear elements, whereas the better performers have smaller and less flat rear elements. I may of course be wrong, it's only a hunch limited by the small sample of lenses I have.
____________________ Robert. |
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| Posted: Sat Jun 2nd, 2012 05:07 |
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29th Post |
jk
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I know it depends on design but I think larger flat optics for the rear elements are medium/telephoto type lenses. Smaller more curved rear elements are more common on wideangles. Might be completely off base with this. 
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
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| Posted: Sat Jun 2nd, 2012 06:19 |
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30th Post |
Robert
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The 50 f1.4 has a very large and flat rear element, it is also guilty of hot spotting both in Vis and IR. When I get home I will check out all my lenses and compare them.
____________________ Robert. |
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