Luminous Landscape Forum
Equipment & Techniques => Medium Format / Film / Digital Backs – and Large Sensor Photography => Topic started by: evgeny on May 25, 2015, 04:05:16 pm
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Hi,
I shot the attached picture to test Heliopan 95mm Neutral Density Slim (ND) 3.0 Filter on the Hasselblad HCD 28mm f/4.0 Wide Angle Prime Lens.
ISO 100, 6 sec, f/8.0.
The picture is exported from PHocus as unprocessed JPEG Medium Size.
I think this amount of vignetting is not accessible.
How much vignetting should be expected from 3.0 to 4.5 ND filters on wide angle Hasselblad HCD 28mm lens.
How to eliminate or reduce vignetting at shoot time?
Can Phocus help to eliminate vignetting in post production? Please give a step by step detailed instruction, if possible.
Thanks!
Evgeny
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I've used B+W ND filters on my HCD28mm and HC35mm. I noticed vignetting if I mounted the ND filter (ND 3.0) over a UV filter. It was barely noticeable if I mounted the filter directly on the lens without the UV filter. I think the vignetting is from the thickness of the filter itself. I don't see a way to correct it from Phocus, but you most certainly can via Photoshop.
I switched to using 150mm square filters - Firecrest from FormattHiTech. It works very well Linhof's filter holder and adapter rings.
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Hi,
I shot the attached picture to test Heliopan 95mm Neutral Density Slim (ND) 3.0 Filter on the Hasselblad HCD 28mm f/4.0 Wide Angle Prime Lens.
ISO 100, 6 sec, f/8.0.
The picture is exported from PHocus as unprocessed JPEG Medium Size.
I think this amount of vignetting is not accessible.
How much vignetting should be expected from 3.0 to 4.5 ND filters on wide angle Hasselblad HCD 28mm lens.
How to eliminate or reduce vignetting at shoot time?
Can Phocus help to eliminate vignetting in post production? Please give a step by step detailed instruction, if possible.
Hi Evgeny,
The oblique rays have a longer path to travel through the thickness of a mass colored filter than the chief rays. That's why they will always pick up more density or color from such a filter. In addition, some (non-retrofocus) wide angle lens designs will cause some shading effects on digital sensors as well, in addition to the lens vignetting and light fall-off.
I'm not familiar enough with Phocus, but what you need is a solution that's called LCC in the Capture One Pro Raw converter. Maybe Phocus has a similar solution, I just don't know.
You can also try RawTherapee, a free Rawconverter, which handles all sorts of file formats, and it can automatically remove the type of vignetting you are experiencing if you supply it with one or more flat-frame shots taken with the the lens and filter set at the same focus distance.
Cheers,
Bart
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C1 and LR both have great tools to remove the vignetting. LR would work on the raw if LR will open it. C1 will not support a raw from Hasselblad. But you could work on a tif.
Phocus does have a LCC correction however not as robust as C1. However it should remove the vignetting. You will need to shoot a separate LCC frame and process it against the files you wish to work on.
Paul
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Oops, I had to say that I stacked Heliopan ND 3.0 filter on front thread of Hasselblad UV filter.
Will re-test ND 3.0 tomorrow again just to better understand the difference.
Anyway, I cannot shoot in outside without protection filter. Here is too much dust and salty sand in our climate.
Looks like I need to learn how to shoot an LCC frame and apply it in Phocus.
Thanks
Evgeny
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If you are shooting with a CMOS back then you shouldn't have severe vignetting due to the crop factor;
otherwise, a CCD back is a horrible choice for ND 3.0 shots (poor dynamic range, darkframe NR, lithography partition, unusable LiveView with ND 3.0 etc).
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I want to shoot a wide, distant scene. I focused 28mm lens to infinity.
It's not clear how can I shoot an LCC frame at the same focus distance? I mean, what should be the size of white (or gray?) calibration target to completely cover the frame?
Thanks
Evgeny
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There's a Phase One video explaining LCC use here: https://www.youtube.com/watch?v=3xsOzYKXg04
The translucent card is placed directly against the front of the lens, so focus is not an issue.
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The translucent card is placed directly against the front of the lens, so focus is not an issue.
That depends on the actual shooting distance.
For the best result, one best uses the same focus distance setting, but with the translucent card flush with the lens (and thus out-of-focus). Changing the focus distance will change the angle of view a bit, so one gets the most accurate results with the same LCC settings (focus/tilt/shift/aperture) as for the actual shot.
Cheers,
Bart
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Now it's clear. Thanks!
Evgeny