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Front-End Filter Improves Corner Smearing
  
 
BastianK
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p.80 #1 · p.80 #1 · Front-End Filter Improves Corner Smearing


I was trying to find an adapter short enough to be able to use the Voigtlander VM 50mm 1.5 Nokton with a 5m filter, but no luck.

I got in contact with Novoflex, who were willing to manufacture me a custom adapter with -1mm thickness,
but unfortunately, when just ordering one, the price would have been 150 for the adapter + 300 for the adjustments, so 450 total.

Fortunately I finally found a retired turner who was willing to give this a shot
and after 2 hrs of work I had an adapter 1mm short, probably not as fancy as what Novoflex would have come up with though

So back to the 50mm 1.5 Nokton:

Sharpness_Vm_50mm_1.5_5m

There are a few things to talk about:
1. corners are never particularly great on this lens, especially before stopping down to f/8.0.
So the gain in the corners when attaching the 5m filter was rather small,
as not field curvature but spherical aberrations (and maybe a general lack of sharpness) seem(s) to be the main issue(s) here.
2. the area before the corners (~18-21mm range) showed the greatest benefit, therefore I show this area in the graph
3. there is a slights loss in sharpness in the midfield when attaching the filter, I have seen this with other lenses as well.
Stop down to f/4.0 or further and this is solved.

At f/8.0 you have more even sharpness across frame with the filter attached,
but if this is worth the hassle I am not so sure, the gain is just not as big as with e.g. the Voigtlander 35mm 1.7.



Jun 17, 2017 at 03:12 PM
tr0n
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p.80 #2 · p.80 #2 · Front-End Filter Improves Corner Smearing


thrice wrote:
Manufactured from scratch. Ground and coated to my specs. It's 1mm thick with blacked edges on the glass elements.

Once I've conclusively tested I'll sell off the surplus (had to buy in volume) and hopefully break even.

The pf in out of focus areas is not ideal but it's only a problem in extreme contrast scenarios.



I'd be interested in purchasing one of the pcx filters from you, i pm'd you as well



Jun 20, 2017 at 09:35 PM
Fred Miranda
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p.80 #3 · p.80 #3 · Front-End Filter Improves Corner Smearing


BastianK wrote:
I was trying to find an adapter short enough to be able to use the Voigtlander VM 50mm 1.5 Nokton with a 5m filter, but no luck.

I got in contact with Novoflex, who were willing to manufacture me a custom adapter with -1mm thickness,
but unfortunately, when just ordering one, the price would have been 150 for the adapter + 300 for the adjustments, so 450 total.

Fortunately I finally found a retired turner who was willing to give this a shot
and after 2 hrs of work I had an adapter 1mm short, probably not as fancy as what Novoflex would have
...Show more

The loss of mid-frame resolution is really bad. Thanks for the test Bastian!



Jun 21, 2017 at 04:39 PM
andersd
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p.80 #4 · p.80 #4 · Front-End Filter Improves Corner Smearing


Thanks for the efforts to everyone who contributed to this thread!

I got the coated Optosigma PCX 5m filter and noticed strong improvements with my Zeiss ZM 35/1.4 (bought new). FWIW my lens only had a single golden shim ring under the mount. I could not achieve infinity focus with it in place, and removing it resulted in infinity focus at 1.4 at the beginning of the ∞ symbol using a Novoflex adapter.



Jun 21, 2017 at 10:47 PM
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