Schneider Super-Angulon 90 mm f/5.6 ND center filter

[prince fritz first]

Hi,

I just received my center filter and wanted to ask a question about a darker spot that I'm noticing in the very center of the filter... Can anyone confirm this is normal in theirs as well, please.

Thank you!

[Mark Woods]

Yes. The image from the lens is closer to the film at the center and the image has to travel further to the film at the edges. The filter is correct for very wide lenses.

[djdister]

The neutral density center filter should appear darker in the center of the filter and taper off to next to no neutral density at the edges, as this one appears. In this way, it counteracts the tendency of the wide angle lens to vignette at the edges of the lens. You should give the film extra exposure when using this ND filter - whatever the filter factor is (perhaps 1 stop)?

[Bob Salomon]

The neutral density center filter should appear darker in the center of the filter and taper off to next to no neutral density at the edges, as this one appears. In this way, it counteracts the tendency of the wide angle lens to vignette at the edges of the lens. You should give the film extra exposure when using this ND filter - whatever the filter factor is (perhaps 1 stop)?

You must stop down a minimum of two stops for the filter to work and then apply the filter factor.

[prince fritz first]

Thank you for your responses. I do understand how a ND filter works and what its’ appearance should be. This one seems to have a very defined darker spot of about a 1/4” in the very center of it. That’s the part I was inquiring about.
I'm attaching two images which should point this out best. Same image, just the second one has the mentioned darker spot encircled.


Just found another filter someone is selling and here's a picture of it. It doesn't seem to have the same spot in the center.

[Lachlan 717]

I can't tell the difference.

It looks like both of my CFs.

[stawastawa]

I dont recall the one I had having a central spot.
https://www.flickr.com/photos/stawas...7663351104743/

If you have a very good densitometer you could try and measure it... I imagine the spot is simply some sort of optical illusion. I do think I see it on yours, but barely, and not 100% of the time.

[Corran]

Okay I was going to write a description of what a center filter was but I see now there may be a tiny little center spot darker. Maybe. Have you tried just cleaning the filter? I doubt it would be at all a big deal in real use.

[hiend61]

Your filter has a normal appearance, and wil perform as it should. If you have a spot meter, take a measure of a white subject with the center part of the filter in front of the meter, then take other measure through the outer part of the filter, the clearest one. If the difference between the two readings is 1,5 - 2 F stops, your filter is OK.
And remember that the filter will work properly when you use F16 and beyond.

[faberryman]

I would send it back if there were any question. They are expensive. I wouldn't want something nagging me in the back of my mind when making images.