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Archive 2017 · 100-400 ii backfocuses when stopped down

  
 
technic
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p.6 #1 · p.6 #1 · 100-400 ii backfocuses when stopped down


monky wrote:
That's interesting, because my experience is different. I've tested both near MFD (maybe 5 feet) and at farther distances, and both seem to yield similar results for me with regard to both image quality and the focus shift issue.


Maybe your experience is different because you are working at different apertures or different focus distance? The glow problem is worst full open and near MFD, the backfocus and focus shift gets worse when you stop down or focus closer. The real IQ and focus shift problems only start really close, below 2 meters or so.

My lens has no detectable focus shift or backfocus above 10 meters, below that the problem gets bigger when focus distance gets smaller. I don't have exact measurements because that is difficult to do out in the field, but 3-5 meters distance definitely requires some MFA (-5 or so) if you want the best IQ and near MFD you would need -20 or even more ... someone else posted more exact measurements for MFA with this lens depending on focus distance (there could be copy variation involved as well).



Aug 28, 2017 at 01:05 PM
johnlg
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p.6 #2 · p.6 #2 · 100-400 ii backfocuses when stopped down


I've seen the soft glow on images with mine when operating at MFD - seems to be sensitive to light though. I too have had similar shots of damselflies with an almost halo type appearance.

I just assumed it was slightly OOF and due to the light, usually when very bright.

Having said that, it does do quite well with macro too (I accept this isn't a great shot BTW):

Dragonfly by John Gardiner, on Flickr



Sep 01, 2017 at 10:34 AM
technic
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p.6 #3 · p.6 #3 · 100-400 ii backfocuses when stopped down


johnlg wrote:
I've seen the soft glow on images with mine when operating at MFD - seems to be sensitive to light though. I too have had similar shots of damselflies with an almost halo type appearance.

I just assumed it was slightly OOF and due to the light, usually when very bright.

Having said that, it does do quite well with macro too (I accept this isn't a great shot BTW):

https://farm5.staticflickr.com/4331/36559465375_77e4af6db6_z.jpgDragonfly by John Gardiner, on Flickr


Yes, it's quite sensitive to lighting, in low contrast conditions you will hardly notice the 'glow' and it just looks a bit soft. Especially with damselflies (which by definition is close to MFD) the halo effect can be really ugly; it gets worse because of the slender bodies that emphasize the superimposed 'glow' from the OOF background. The problem is usually worst with darker subject against brighter background but it's difficult to predict and you cannot see it very well on the LCD ...

When using PDAF the image can also be 'soft' due to backfocus, the glow will only be very obvious until f/8 or so. You can do good macro within the limitations (avoid minimum MFD and f/4.5-f/8, use Liveview to reduce backfocus). But for me, for my style of shooting, it's a bit too much problems conspiring against the photographer and very few situations where this lens would be my choice for closeups (irrespective of the weight and cost ...).



Sep 01, 2017 at 12:42 PM
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