GX617, 90mm lens, no center filter: photoshop/LR lens correction good enough?

[EinstStein]

How is a 90mm lens on GX617 without center filter? It's almost impossible to find the original matching center filter, and a new third party center filter costs about 1300 USD.
Since I have no set up to do wet print, is Photoship/Lightroom lens correction good enough?
Or, what about crop it to 6x12?

[E.J. Peiker]

You are likely to get some color and aritfact issues as you get to the edge of the frame.  An alternative would be to take two transparencies - one at your intended exposure and one 1.5 to 2 stops brighter.  Then composite those by constructing a photoshop layer mask to smoothly blend the transparency with the correct exposure from the center with the one with the correct exposure from the edges.  Of course, for this to work well it needs to be a static scene.

[EinstStein]

You are likely to get some color and aritfact issues as you get to the edge of the frame.  An alternative would be to take two transparencies - one at your intended exposure and one 1.5 to 2 stops brighter.  Then composite those by constructing a photoshop layer mask to smoothly blend the transparency with the correct exposure from the center with the one with the correct exposure from the edges.  Of course, for this to work well it needs to be a static scene.

You mean, take one (expose to the edge) according to the normal light reading, another (expose to the center) with 1.5~2 stop under exposure?
If so, can it be done with just one normal exposure (expose to the edge), but create the 1.5~2 stop underexposure in LR, then blend them?
Or simply use the lens correction in LR?   

[E.J. Peiker]

You can try it but, like I said, I think if you expose it properly for the center and then try to lift the edges it won't be that good.  Film has such a limited dynamic range that the corners will not look very good at all.  Transparency film has a dynamic range of maybe 5 stops so if you are underexposed in the corners by two stops due to exposing properly for the center, after raising that in post processing, you are only left with a grainy 3 stop dynamic range area of the photo.  Depending on the subject, that could look pretty bad.  On the other hand if you take one shot that is exposed properly for the center and then another properly exposed for the corners and build a smooth blending mask in Photoshop you can get a really great result.

[EinstStein]

You can try it but, like I said, I think if you expose it properly for the center and then try to lift the edges it won't be that good.  Film has such a limited dynamic range that the corners will not look very good at all.  Transparency film has a dynamic range of maybe 5 stops so if you are underexposed in the corners by two stops due to exposing properly for the center, after raising that in post processing, you are only left with a grainy 3 stop dynamic range area of the photo.  Depending on the subject, that could look pretty bad.  On the other hand if you take one shot that is exposed properly for the center and then another properly exposed for the corners and build a smooth blending mask in Photoshop you can get a really great result.

Now I get it. Thanks.

[elliot_n]

You're better off shooting colour neg, and over-exposing a stop or two.

[BobShaw]

Lens correction is not the problem. You have a graduated exposure reducing 2 stops towards the edges.
The procedure E.J. suggested should work though.
I would avoid neg film as that introduces more problems than ir solves.

[elliot_n]

Lens correction is not the problem. You have a graduated exposure reducing 2 stops towards the edges.
The procedure E.J. suggested should work though.
I would avoid neg film as that introduces more problems than ir solves.

What problems does colour neg introduce?

(The problem that it solves is that it has a much greater dynamic range than transparency, and therefore - as long as you give it enough exposure for the corners - you can capture everything in a single shot. So shot 400ISO film at 100ISO, and you're good to go.)

[BobShaw]

What problems does colour neg introduce?

The massive colour cast on the base substrate when you scan it.

[EinstStein]

Thanks a lot for everyone’s suggestion.
Are these all according to your personal experiences?

[BobShaw]

Are these all according to your personal experiences?

I had the centre filter on the G617 (earlier) using Velvia so no experience in not having a centre filter.
Scanning experience yes though. Velvia was easy to scan using the Epson V700. Negatives are harder to get right using standard software.

[elliot_n]

Thanks a lot for everyone’s suggestion.
Are these all according to your personal experiences?

Yes. My comments are based on shooting a lot of colour neg film, rated 2 stops over,  with a 90mm f8 lens without a centre filter. Not with the GX617, but with a 4x5 camera (I believe the issues are the same). The film is then scanned on an Imacon. I have no experience of the technique blending two transparencies.

[elliot_n]

The massive colour cast on the base substrate when you scan it.

I'm not sure what you mean.

[EinstStein]

Yes. My comments are based on shooting a lot of colour neg film, rated 2 stops over,  with a 90mm f8 lens without a centre filter. Not with the GX617, but with a 4x5 camera (I believe the issues are the same). The film is then scanned on an Imacon. I have no experience of the technique blending two transparencies.

I am thinking 2 stop over expose with B&W negative too. I am waiting for the GX617 to try that.
For Velvia 50, I will try 0.5~1 stop over exposure. This is based on my old experience that Velvia 50 worked best with 1/2 stop over exposure, in the hope that 1 stop over exposure should actually put the center to 1/2 stop over exposure while the corner 1/2 stop under exposure. Then try to duplicate it to two copies for blending, one to brighten it by 0.5~0.75 stop, the other to darken it by 0.5~0.75 stop.     

 

[BobShaw]

The variation from the centre to the side edges is 2 stops on the 617 from my recollection.

[EinstStein]

I guess the simple answer to my own question is,  don't shoot this wide lens without center filter.