pfogle said:
Here (link) is a gallery of 12mm shots with no correction for vignetting - as you can see, it's pretty clean, and less than with the 15mm... there's some, but easy to correct if you want to.
A bit late on the thread but...
🙂
I second Phil, the 12 vignettes less than the 15.
But I now correct all the shots with a simple PS procedures, that works better (for me) than the "Vignetting" filter:
Preparation:
1) Shoot a picture with te intended lens through something translucid and to a uniform light source (I used my light table's surface, after removing ir carefully, shooting through it to a overcast sky). You can even do that with different apertures, although I think that the 15 and the 12 don't deserve the trouble, vignetting is more or less stable. I would give a 1.5 aperture upwards correction, to be near white. And use RAW, keeping the file on 16 bit.
2) Convert to Grayscale and remove dust specks (you'll have them...
🙂)
3) Apply a Gaussion Blur with a 30 radius, so that iamge is very, very smooth (I used 200 ISO but there is always a bit of grain)
4) Import the picture to Photoshp and adjust brightness so that the center (the brightest part of the picture) is pure white.
5) Invert the image. It will look like a center-filter. And it is one...
🙂
6) Save it
In use:
1) Open the image you want to correct (let's call it Image) and convert it to 16 bit
2) Open the "filter" image (and let's call this one Filter)
3) On the Image, add an Adjustment Layer for Brightness/Contrast
4) On the Filter, do Select All, Copy
5) Go back to Image
6) Select the Adustment Layer on the Layers/Channels/Paths window
7) Select the "Channels" tab and then the "Brightness/Contrast" channel
8) Do Edit/Paste. The "filter" image should now be a mask to the Brightness/Contrast adjustment layer
9) Select the "Layers" tab again and bring up the dialog box to adjust Brightness and Contrast. Brightness reduces vignetting and Contrast helps to recover the contrast on the affected areas.
10) If you want to go back to JPG, convert the image to 8 bit and then Image/Flatten Image.
Ok, I know it sounds VERY difficult and LOTS of work but that's not correct. It's easier than it looks and very easy to make a macro to automate all that (even to the point of good "ballpark" values for Brightness and Contrast). It comes handy when you have a few dozens of shots to correct. The real work is taking the "filters" shots and preparing them, especially if you are paranoid enough to do it for every aperture (I did
🙂).
The main advantage is control (and final result: I get better results than the "plain" PS filter"). But I discovered that my 12mm does not vignette symetrically (worse on the right and down the frame). This approach completely corrects the problem. And I now love my 15mm
🙂
Although it sounds complicated, for those with a bit of PS fluency (macro mandatory) it's a very good option, believe me...
I'm planning to do the same with my 6x17 Fotoman and the Schneider Super-Angulon 90/8, as it has a slight hint of fall-off when using slides (but that's to expect - 6x17 cm is a bit extreme...) even at f22 (although much less than the 12mm, let alone the 15mm). Much cheaper than a dedicated center-filter (around 300£...). Below that aperture, the center-filter (or sw correction) is almost mandatory.