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While awaiting the center filter for the 45mm lens I need to do some quality panoramic work. What Photoshop program must I use or hire someone to use which will compensate for the lack of a center filter. Is it terribly complex?
You can use photoshop to correct at least part of it. However, if you can minimize the effect to start with you will be "ahead of the game".
Use color negative film as much as possible. Not using a center filter is more obvious on transparency film due to less latitude in this type of film. Using F/8 or higher will also help no mater what film is used.
To minimize vignetting with the 45, always stop down to at least f/8, as Robert suggests. If this is not possible, see if you can't compose in such as way as to have darker tones frame the shot, thus masking the dark corners.
You didn't mention what type of film you'll be using, but again as Robert writes, negative film is more forgiving w/respect to vignetting. With b&w film, you may not even notice it.