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Author Topic: DXO Pro built into raw converter = H3D...  (Read 7427 times)
eronald
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« Reply #20 on: October 23, 2006, 08:30:02 AM »
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Focus shift ?
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Carl Zeiss also paid particular attention to minimal focus shift when developing the lens. The term describes the phenomenon of the focal plane wandering when the diaphragm is adjusted. With Zeiss Ikon lenses, this effect is so strongly reduced that it remains within the depth-of-field range and does not affect the quality of the picture.

http://www.zeissikon.com/news.htm
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Edmund Ronald, Ph.D. 
Graham Mitchell
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« Reply #21 on: October 23, 2006, 09:25:09 AM »
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Thanks, it does seem to be known as 'focus shift' and mainly affects rather old view camera lenses (i.e. 80 years old) and plain poor design/build, from what I could gather after some googling.

"focus shift is the result of uncorrected zonal spherical aberrations. Spherical aberration results from the fact that rays of light from the periphery of the lens are brought to a focus at a different point than rays of light from closer to the optical axis. As you stop down, you eliminate the rays from the periphery of the lens and this zone of focus shrinks. The actual point of best focus doesn't really change, it is just overlaid with out of focus rays from the periphery of the lens and this leads to a larger zone of focus and an apparently better focus - it's partly an optical illusion. If you judge the point of best focus by contrast, you are likley to experience focus shift."

From: http://photo.net/bboard/q-and-a-fetch-msg?msg_id=005H2c&tag=

Has anyone actually experienced problems with H lenses and 'focus shift'? I suspect the effect is not noticeable on these lenses or any other modern MF lenses, so this isn't a problem that needed to be fixed.
« Last Edit: October 23, 2006, 09:35:12 AM by foto-z » Logged

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eronald
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« Reply #22 on: October 23, 2006, 09:44:30 AM »
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Thanks, it does seem to be known as 'focus shift' and mainly affects rather old view camera lenses (i.e. 80 years old) and plain poor design/build, from what I could gather after some googling.

"focus shift is the result of uncorrected zonal spherical aberrations. Spherical aberration results from the fact that rays of light from the periphery of the lens are brought to a focus at a different point than rays of light from closer to the optical axis. As you stop down, you eliminate the rays from the periphery of the lens and this zone of focus shrinks. The actual point of best focus doesn't really change, it is just overlaid with out of focus rays from the periphery of the lens and this leads to a larger zone of focus and an apparently better focus - it's partly an optical illusion. If you judge the point of best focus by contrast, you are likley to experience focus shift."

From: http://photo.net/bboard/q-and-a-fetch-msg?msg_id=005H2c&tag=

Has anyone actually experienced problems with H lenses and 'focus shift'? I suspect the effect is not noticeable on these lenses or any other modern MF lenses, so this isn't a problem that needed to be fixed.
[a href=\"index.php?act=findpost&pid=81759\"][{POST_SNAPBACK}][/a]


Foto-z

 Yes, lots of aberrations can and are well corrected in current lenses. That doesn't mean that it wouldn't be cheaper to have a simpler lens and software correction. H are selling their lenses for  a fortune, and if they can make them cheaply they are sitting on a goldmine. See their 28 which if I understand rightly is cheap to make precisely because it is not well corrected for distorsion.

As for the focus shift correction itself, I wonder if the same mechanism  won't be used to correct for errors in the filmplane to housing distance, and even for lens mounting errors.

 In other words I wonder if H aren't preparing to run the user through a "calibration procedure" for each lens he buys, ostensibly to correct for aberrations, but in fact to correct for manufacturing defects.

 Edmund
« Last Edit: October 23, 2006, 09:45:13 AM by eronald » Logged

Edmund Ronald, Ph.D. 
James Russell
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« Reply #23 on: October 23, 2006, 09:45:10 AM »
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Thanks, it does seem to be known as 'focus shift' and mainly affects rather old view camera lenses (i.e. 80 years old) and plain poor design/build, from what I could gather after some googling.

"focus shift is the result of uncorrected zonal spherical aberrations. Spherical aberration results from the fact that rays of light from the periphery of the lens are brought to a focus at a different point than rays of light from closer to the optical axis. As you stop down, you eliminate the rays from the periphery of the lens and this zone of focus shrinks. The actual point of best focus doesn't really change, it is just overlaid with out of focus rays from the periphery of the lens and this leads to a larger zone of focus and an apparently better focus - it's partly an optical illusion. If you judge the point of best focus by contrast, you are likley to experience focus shift."

From: http://photo.net/bboard/q-and-a-fetch-msg?msg_id=005H2c&tag=

Has anyone actually experienced problems with H lenses and 'focus shift'? I suspect the effect is not noticeable on these lenses or any other modern MF lenses, so this isn't a problem that needed to be fixed.
[a href=\"index.php?act=findpost&pid=81759\"][{POST_SNAPBACK}][/a]


I personally don't believe any of this has anything to do with an H-3 and the 28mm.

I don't get fringing or ca on my leaf files using a 35mm Zeiss or even twisting a 45mm Ukanian tilt shift, or using pentax and hasselblad lenses on my Contax.

Everyone is aware that Hasselblad/Imacon is way behind in Medium Format back sales and they need to find something to allow them to compete.

It must be frustrating to have the #1 camera but be #3 or #4 in back sales, so this was their solution.

Obviously it would do them good to not always be a generation behind Leaf and Phase in features, such as iso and frame rate.

As I mentioned before, Imacon had some lousy samples they presented and early one some awful skin tone color.   This along with some of the demonstrations mentioned here and in other places pretty much sums up why they are #3 or #4, that and the fact Hasselblad seems to be very bad at getting thier message out.

For the photographer none of this really mean anything.

JR
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BJNY
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« Reply #24 on: October 23, 2006, 09:52:29 AM »
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It must be frustrating to have the #1 camera but be #3 or #4 in back sales, so this was their solution.

I wonder how Hasselblad claims to be #2 in digital back sales.
Here in NY, it wouldn't surprise me if the ratio were AT LEAST 50:1 [Phase+Leaf:Hasselblad].
« Last Edit: October 23, 2006, 09:53:37 AM by BJNY » Logged

Guillermo
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« Reply #25 on: October 23, 2006, 09:55:01 AM »
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James

Which adapter/brand are you using to pair a Pentax lens with the Contax 645
and are you referring to 645 or 6x7 lenses from Pentax?

Thanks,
Mark
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Graham Mitchell
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« Reply #26 on: October 23, 2006, 10:19:11 AM »
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Yes, lots of aberrations can and are well corrected in current lenses. That doesn't mean that it wouldn't be cheaper to have a simpler lens and software correction. H are selling their lenses for  a fortune, and if they can make them cheaply they are sitting on a goldmine.

If I understand the focus shift problem correctly, the image quality will suffer due to different parts of the lens having effectively different focal lengths. You will never get good convergence with these lenses and the problem is not fixable by software. I do agree that some aspects of lens performance can be achieved more cheaply through post-correction than by lens design, but they are more likely to be distortion and colour correction. Other aspects of lenses, such as resolution will still depend on the lens.
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