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View Full Version : Can the center filter be replaced by post-processing?



rpagliari
20-Feb-2019, 17:25
I am in the processing of buying my first 4x5 camera.

I'd like to know how heavy vignetting is with wide angle lenses (Schenider 75mm f5.6 in my case). I can buy the center filter as well but, apart from price, it adds an extra 1.5 stops.

I typically do long exposure and 1.5 extra stops could make the exposure much longer than needed.

Is the fall-off something easy to fix in photoshop (I could not find clear examples on the internet)?

Thank you,

Bob Salomon
20-Feb-2019, 17:36
No!

rpagliari
20-Feb-2019, 17:57
is it worth it with 75mm and above?

Dan Fromm
20-Feb-2019, 17:58
It may be worse than you think, OP.

Rodenstock and Schneider recommend stopping the lens down 2 stops to get the full compensating effect. This is because of mechanical vignetting, which is reduced by stopping down. Center filters compensate only for optical vignetting. Whether this matters for you depends on the apertures you normally use. What apertures do you normally use?

You say you're going to be exposing for 4 to 8 minutes. Do you work in natural dim light or do you make your own with ND filters?

If you use ND filters, the solution is simple. Less density. And don't forget to put the ND filter in front of the center filter to avoid mechanical vignetting.

If you shoot in dim light, well, you'll have to expose longer. There's no way around it.

Spell out what you're doing. This will make it easier for people to help you.

Dan Fromm
20-Feb-2019, 18:01
is it worth it with 75mm and above?

Many photographers shoot 4x5 with lenses as short as 90 mm without center filters. Few 4x5 photographers who shoot lenses shorter than 90 mm use them without center filters. Read this: http://www.galerie-photo.com/center-filters-for-large-format-lenses.html

Re "75 mm and above," which way is up? <75 or >75?

rpagliari
20-Feb-2019, 18:06
I am planning to use f/32 with ND filter and polariser for an exposure between 4 and 10 minutes.

Bob Salomon
20-Feb-2019, 18:27
I am planning to use f/32 with ND filter and polariser for an exposure between 4 and 10 minutes.

Besides the fall off that a center filter corrects you will also be well into diffraction at f32, and you can’t correct that.

rdeloe
20-Feb-2019, 18:34
Maybe, but it depends on lots of things. Working with RAW files (and even JPEGs) in the digital world, we're often dealing with huge amounts of light falloff due to the lens design. Modern lens designs frequently assume that vignetting will be corrected in camera (and the user will never know), or in software. Case in point is a modern lens like the Fuji XF 10-24 mm f/4R OIS. At the 10mm focal length and at f/4, vignetting reaches as high as -1.93 EV according to Lenstip's testing. People who shoot JPEG think it's a terrific lens because the camera evens things out before writing the JPEG file to the card. RAW developers like the one in Lightroom apply the correction on import so you may not even know it happened if you're unfamiliar with the issue.

Film is not a RAW file, but assuming you have information, you can raise the values. However, if the vignetting from the lens was very heavy it could look nasty. You can see for yourself even if you don't own the lens yet. In your workflow, how many EV can you raise the shadow parts of an image you shot on film and scanned before you're unhappy?

Two23
20-Feb-2019, 18:49
I shot this last Saturday with Nikon 75mm f4.5. I cropped a bit off the right side. I did some vignette removal with PS.


Kent in SD

Dan Fromm
20-Feb-2019, 19:11
I am planning to use f/32 with ND filter and polariser for an exposure between 4 and 10 minutes.

Then use a less dense ND filter and ditch the polariser. A center filter will accept one filter with a thin ring. Add more and you'll have problems.

Bob Salomon
20-Feb-2019, 20:23
Then use a less dense ND filter and ditch the polariser. A center filter will accept one filter with a thin ring. Add more and you'll have problems.

Or get a high quality variable ND filter!

Pere Casals
21-Feb-2019, 01:16
Is the fall-off something easy to fix in photoshop (I could not find clear examples on the internet)?

With photoshop: https://www.youtube.com/watch?v=G83PU7iDYhA
With lightroom: https://www.youtube.com/watch?v=90IFl69WFVA

Digitally, it's easy to correct fall-off, there are several ways, but the lens correction tool does it pretty well.

In a darkroom it's also easy to correct it in the printing process, we have several techniques for that. First we can use an enlarging lens that has fall-off that will compensate the fall-off in the negative, we also may print a mask in a transparency and we may make a sandwich with the negative and a diffuser sheet, and we can also manipulate the illumination of the enlarger to make it compensate what the negative has, we also may place a mask in the light path instead making the sandwith with the negative.

But, as Bob Salomon noted, the fall-off in the taking may bring on problems because it can exagerate the dynaming range the scene has, making more difficult to capture all scene range with quality.

So in scenes with narrow Dynamic Range we always may make the correction in the post, for scenes with large DR we may have problems, but also all depends of the ammount of fall-off we have depending also on focal and aperture, and the film latitude, with slides we have to be careful with that.



I'd recommend this reading by Ken Rockwell that (IMHO) sports a lot of wisdom in that, it shows when CF it's worth or not, and even how you may take advantage of fall-off as a creative resource:

https://kenrockwell.com/tech/center-filters.htm
https://web.archive.org/web/20180224133122/http://www.kenrockwell.com/tech/center-filters.htm

rpagliari
21-Feb-2019, 01:33
Then use a less dense ND filter and ditch the polariser. A center filter will accept one filter with a thin ring. Add more and you'll have problems.

What kind of problems would I run into?
I typically use the lee system with polariser and one nd filter.

Thank you

pgk
21-Feb-2019, 02:10
FWIW. I have an early Leica 28mm f/2.8 Elmarit-M - the version 1 which had some design input from the Super-Angulon according to some sources. It shows significant vignetting. Sometimes I use in an a Sony A7II and being of a curious nature I try different lens 'pre-sets' during the RAW conversion to see whether any suit it. Surprisingly if I set it as being the Sony 28mm f/2 FE lens, a great deal of the vignetting is dealt with. Which suggests to me that the Sony lens has substantial vignetting which is mostly dealt with in software one way or another.

However, using a centre filter has the advantage, as already stated, of dealing with 'uneven' exposure at the taking stage and as such is technically a 'better' option, depending on what you are going to do in post processing later. In extreme conditions where substantial adjustment is needed to an image in post processing I suppose both tonality and noise might become an issue although I doubt this will happen often.

And also FWIW I did use a Hasselblad XPan 49mm centre filter on a Super-Angulon-M for a while but actually found that some of the 'character' of the lens was lacking in that evening out exposure across the frame did emphasise the lower lens performance (mushier detail) at the edges and corners.

Lastly, I have learnt practically that stacking filters which include a polariser has sometimes produced soft corners so I tend not to do so.

Just my POVs though.

rpagliari
21-Feb-2019, 02:27
I shot this last Saturday with Nikon 75mm f4.5. I cropped a bit off the right side. I did some vignette removal with PS.


Kent in SD

Thanks for sharing this Two. This result is very acceptable to me, in fact, I could not tell the difference.

Huub
21-Feb-2019, 02:32
The main risk you will run when stacking filters is that of vignetting as it will decrease your image circle, next to possible quality loss due to adding extra surfaces that might cause reflection and other forms of image degradation. I am not sure how that would work out with the Lee filters you are using.

I agree with others that you could try to leave out the ND filter and replace it with the center filter. Otherwise you could try for yourself and see what happens before buying the center filter. I am using both a 75mm and a 58mm without the center filter and compensate in the darkroom. For the 75 mm I overexpose about half a stop and for the 58mm I use a whole stop to make sure i keep enough shadow detail in the corners. But then: i do only b&w and when using slides it will be a complete different story.

And one more thing: stopping down a 75mm to f32 brings you well into defraction range. Defraction can be noticed when the physical size of the diafragma becomes less then about 5mm, which translates to f16 for a 75mm lens. Whether this loss of sharpness is acceptable is something you have to decide for yourself.

Dan Fromm
21-Feb-2019, 05:54
What kind of problems would I run into?
I typically use the lee system with polariser and one nd filter.

Thank you
With an ultrawide lens and a center filter?

As has already been said, vignetting.

Folks, the OP has stated very clearly that he wants to take long exposures, in the 4 to 8 minute range.

JimboWalker
25-Feb-2019, 16:28
I have had limited experience with this , but I have investigated this very same issue with my new (old) S-K 65mm f8 Super-Angulon. I do not have center filter. The filters cost more than the lens! Try exposing one stop over and even out the vignetting in PS. My limited testing seems to have real possibilities. You do not want to drastically underexpose the vignetted areas of the image to loose shadow detail. Good luck, Have fun!