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Making of Center ND Filter


Lord Lucan

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Hello everybody,Please read and advise.

Scenario: I know a local opthalmic optician who has in-house fecility to make spectacle lenses and apply tint of various degree.

If I take a simple UV filter and request him to tint center area leaving just less than 25% area for grey tint.

Do you think the completed job would be equal to prof'nally made commercial filter?

These kinds of filters are not easy to find and they are costly.

Thank you.

Regards.

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.... they are costly...

Think about the possible reason for this!

Center filters are not easy to fabricate and speciallcy optimised for one lens only.

Super-Angulon needs another one than Hologon and so on...

 

Most reputated manufacturer I know:

http://www.schneiderkreuznach.com/en/photo-imaging/product-field/photo-lenses/products/large-format-lenses/centerfilter/

 

So they are easy to find, but no bargains!

 

To your question asked:

No, I don't know the abilities of your optician, but I'm quite sure, that his result will be not comparable to professional filters.

2 tips from me:

1. If you need a center filter, your lens will cause magenta corners on digital sensor, much more on Sony (thicker sensor glass) than on Leica, but results will not satisfy. Only cam working is Monochrome!

2. as a DIY-project just for fun take an UV filter and blacken the center over candleflame, work with great caution not to overheat the glass, do test before with a pice of glas. Mention that this soot is very touch and might cause black contamination to clothing!

Good success

Thomas

Edited by duckrider
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I tried the centre filter produced for the Hasselblad X-Pan 30mm lens on the f/3.4 Super Angulon and it helped lighten the corners but was not a perfect match - to precisely even up the image adjustments were still needed to the image files but were less substantial. If you look at data on vignetting for different lenses you will find that the degree of vignetting probably does vary a little for each lens and so the precise variability of the filter factor across the frame probably needs to be matched to each lens. If you look long enough you will probably find centre filters eventually which will fit or can be adapted to your lenses but they will cost you a fair amount. Whether your optician is prepared to experiment to sort out a matching filter for your lens and whether this is likely to cost less is something that you need to look into. In all honesty I now realise that my Super-Angulon works best if I allow it to vignette and shoot it as a monochrome lens - its great then - so I no longer use a centre filter which I sold off.

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I tried the centre filter produced for the Hasselblad X-Pan 30mm lens on the f/3.4 Super Angulon and it helped lighten the corners but was not a perfect match - to precisely even up the image adjustments were still needed to the image files but were less substantial. If you look at data on vignetting for different lenses you will find that the degree of vignetting probably does vary a little for each lens and so the precise variability of the filter factor across the frame probably needs to be matched to each lens. If you look long enough you will probably find centre filters eventually which will fit or can be adapted to your lenses but they will cost you a fair amount. Whether your optician is prepared to experiment to sort out a matching filter for your lens and whether this is likely to cost less is something that you need to look into. In all honesty I now realise that my Super-Angulon works best if I allow it to vignette and shoot it as a monochrome lens - its great then - so I no longer use a centre filter which I sold off.

Are you really basing your opinion after trying the xpan's 58mm filter on a super angulon that require a 48mm filter? No wonder it didn't work.

The xpan's 49mm filter (which is a 1 stop filter) would have been a much better bet.

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It is far more simple to address the vignetting in postprocessing, be it from a digital file or from a scan. The best way to do so is to use the flat field plugin in LR or the LCC profile in C1. It will get rid of vignetting,  any colour casts and remove dust too.

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It is far more simple to address the vignetting in postprocessing, be it from a digital file or from a scan. The best way to do so is to use the flat field plugin in LR or the LCC profile in C1. It will get rid of vignetting,  any colour casts and remove dust too.

I understand that. I also wonder why were there such fliters in first place? Is it because software usage was not as wide spread as it is today?

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I understand that. I also wonder why were there such fliters in first place? Is it because software usage was not as wide spread as it is today?

What software? These filters were in use from the beginning of wideangle lenses. I don't know when the first was made, but it must be in the order of a century and decades ago. They are still needed for a completely analog photographic process. Dodging and burning a print  in a wet darkroom to remove strong vignetting is a serious hassle and very hard to do perfectly.

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It is far more simple to address the vignetting in postprocessing, be it from a digital file or from a scan. The best way to do so is to use the flat field plugin in LR or the LCC profile in C1. It will get rid of vignetting,  any colour casts and remove dust too.

 

The problem with post (not a big problem usually) is that correcting vignetting is effectively boosting ISO (or amplifying the gain) in the corners. Depending on how you shoot and your subject matter, this can boost noise in the corners and it has cost me the odd shot which has become less effective as a result. As a general rule I would advocate software adjustment, but there are times when a centre filter is a better solution even if further software correction is needed to fine tune things.

 

Are you really basing your opinion after trying the xpan's 58mm filter on a super angulon that require a 48mm filter? No wonder it didn't work.

The xpan's 49mm filter (which is a 1 stop filter) would have been a much better bet.

 

Sorry. I meant 49mm - not up on Xpan stuff so I'd sort of 'remembered' it as the w/a centre filter offering - incorrectly.

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But, using a centre stop filter effectively boosts the ISO across the whole frame. Surely the former is preferable?

 

No, its a neutral density filter with a graduation which is darker in the centre, so it effectively lightens up the corners as far as the camera is concerned (or darkens the centre - same difference) before the image is taken, and the resulting image file has less, or if matched correctly, no vignetting within it, so exposure is more consistent across the frame. Exposure will shift slightly when using one.

 

Using software means lightening the corners so an increase in noise (or in effect, boosting the ISO in the corners).

Edited by pgk
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No, its a neutral density filter with a graduation which is darker in the centre, so it effectively lightens up the corners as far as the camera is concerned (or darkens the centre - same difference) before the image is taken, and the resulting image file has less, or if matched correctly, no vignetting within it, so exposure is more consistent across the frame. Exposure will shift slightly when using one.

 

Using software means lightening the corners so an increase in noise (or in effect, boosting the ISO in the corners).

 

 

My underlining.

Your presumption that lightening the corners and darkening the centre are the same is incorrect. Remembering that the corners are already darker, that's the issue we're tying to fix, so darkening the centre means we now have darkened the entire frame and you will need to shoot at a higher ISO - all else being equal. 

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My underlining.

Your presumption that lightening the corners and darkening the centre are the same is incorrect. Remembering that the corners are already darker, that's the issue we're tying to fix, so darkening the centre means we now have darkened the entire frame and you will need to shoot at a higher ISO - all else being equal. 

 

Simple choices:

 

1. Use no centre filter and correct in software - increases noise in the corners.

2. Use a centre filter and increase ISO which will increase the noise throughout the image.

3. Use a centre filter and use a slower shutter speed and keep noise minimised thoughout the image.

4. Use a centre filter and use a wider aperture and keep noise minimised thoughout the image.

5. Don't bother correcting.

 

I used to operate choice 3 myself on my Super-angulon-M which worked ok, but I now operate option 5 becaue I've realised that I rather like the characteristics of the lens. We have to make choices in life and in this case its the above ;) .

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Thank you all for very healthy contribution,I am sure,this topic could become educational for many.

Another point.

Center ND filter Vs Software correction for image quality. Any pros and cons?

@pgk  your five points evaluation should be noted.

I also feel that all lens manufacturers should offer this filter with their ultra wide lenses.

Edited by Lord Lucan
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