Using a Center Filter

[John Brady]

Is using a center filter any different than using any other filter? I will soon have a Schneider SS-XL 150mm and the center filter for it. I have never used a center filter before.

Getting back to the original question, it is very simple to use a center filter. I would recommend composing and focusing your image and then screwing in the filter. This will make it easier since the intended purpose of a cf is to restrict light in the center of the image and then gradually go to clear at the edge.

While holding the filter take a meter reading with a spot meter of an evenly lit area through the center of the filter and then compare another reading without the filter. I suspect it will be around 1 to 1.5 stop difference. You will need to adjust for this every time you use the filter (just like other filters).

Are you using the 150 on 4x5 or 5x7 or 8x10? For 4x5 you probably don't need a center filter with this lens, especially for black and white. For 8x10 (does it cover?) you probably do.

I use 2 stop center filters with extreme wide angle lenses, like 47xl on 4x5 or 90xl on 8x10.

I hope this was the kind of info you were looking for.
jb
www.gladesgallery.com

[Diane Maher]

I plan to use the 150 mm on whole plate (6½ in. x 8½ in.), 8x10 and 5x12.

[Nathan Potter]

Ah, thinking about this now maybe I know what you're saying Bob. It's an issue of Depth of Field. As one stops down the lens the actual center filter begins to show a real image of itself at the film plane while with the lens wide open the center region is simply a full blurr. Thus the recommended two stops down or so is a compromise for partial imaging of the filter at the film plane while still utilizing the maximum resolving power of the lens. Beyond f/11 or f/16 maybe the maximum effect of the radial density compensation is already achieved. This would be a bit of suttlety I've never thought much about.

Nate Potter, Austin TX.

[Bob Salomon]

Ah, thinking about this now maybe I know what you're saying Bob. It's an issue of Depth of Field. As one stops down the lens the actual center filter begins to show a real image of itself at the film plane while with the lens wide open the center region is simply a full blurr. Thus the recommended two stops down or so is a compromise for partial imaging of the filter at the film plane while still utilizing the maximum resolving power of the lens. Beyond f/11 or f/16 maybe the maximum effect of the radial density compensation is already achieved. This would be a bit of suttlety I've never thought much about.

Nate Potter, Austin TX.

The other way we phrase it when someone calls and asks is that you have to be stopped down at least 2 stops for the lens to "see" the filter. Same thing you just figured out.

[Steve M Hostetter]

center grad filters are graduated filters but unlike regular grad filters need compensation to work

[Diane Maher]

So, if I read all of these replies correctly, I'm going to need to apply a filter factor for not only the center filter, but also for any other filter I choose to put over the lens.

Thanks for all of your replies. As soon as the center filter gets here, I hope the weather is nice. The lens arrived yesterday and I'm looking forward to using it.

[Bob Salomon]

So, if I read all of these replies correctly, I'm going to need to apply a filter factor for not only the center filter, but also for any other filter I choose to put over the lens.

Thanks for all of your replies. As soon as the center filter gets here, I hope the weather is nice. The lens arrived yesterday and I'm looking forward to using it.

Correct, and the center filter has to mount directly to the lens and any other filters mount to the front of the center filter. So you will need other filters the size of the front of the center filter. Not the size of the lens thread.

[JimL]

Regarding the 2 stop thing, I would think that at 2 stops down, only the optical falloff is present (assuming no camera movements are used); at full aperture there is additional falloff due to mechanical vignetting.