SA f8/75mm - how to use a centerfilter?

[Patrik Roseen]

Hello, I have a Schneider original center filter for the Super-Angulon f8/75mm lens. I know it is supposed to even the lightfalloff by darkening the center of the lens. I then assume I need to add some stop to the lightmeter reading to get a correct exposure. 1) Does anyone know how much stop I should add to the lightmeter reading?

I think that the light falloff varies with the aperture size (?)
2) Does the centerfilter only add value when the lens is not stopped down or is it useful regardless of aperture?

3) When should I use this filter and when should I not use it?

Kind regards, Patrik.

[Bob Salomon]

To use a center filter you must stop the lens down at least 2 stops for it to work. That means with a f8 lens you have to be stopped down to at least f16. In addition the center filter requires an exposure correction of about 1 and 1/3rd stops. Do not open the lens larger then f16 or the lens will not "see" the filter.

[Richard Littlewood]

I use a 65SA f8, very much like the 75mm. I can get away with using a centre filter at f11 without any nasties happening, although it is best to go smaller than that. The Schneider centre filter for the 65 robs 1.5 stops, and as far as I know the dedicated 75 centre filter will be about the same. I focus without it on the lens as it makes a dim lens even dimmer to look through. The worst aspect of the centre filters is keeping them clean. The design of the filter housing at the lens side seems made for retaining muck.

[Patrik Roseen]

Bob Salomon, thanks this is exactly what I was asking for...
When looking through previous threads talking about centerfilters there are some people complaining about the effect when using tilt and so on. Is this beacuse they did not stop down enough or is there any specific reason why the filter should have a negative effect under certain circumstances?

Richard, I see what you mean...looking through the camera with the filter on is a nightmare! The centerfilter also looks very sensitive to scratches since there is very little protecting it from anything you put it on, i.e. hardly no distance at all between the glass and the outer threads. The leather filter compartment it came in has a button lock which I do not dare to use since the inside of the button will press against the filter when closing it!

[Bob Salomon]

Patrik,

The negative is that center filters are not totally neutral and under some conditions will cast a greenish or magenta cast on spectrals. This is most obvious on aluminum buildings in bright sunlight. Of the three major filter suppliers, Schneider, Rodenstock and Heliopan the Rodenstock are the most neutral.

Most people that have contacted us with questions egarding problems other then a color shift were not stopping down enough for the filter to work.

But the most frequent complaint was not that the filter did not work or that their was a color shift. It was to complain about the fall off as they did not use a center filter and did not know that they exist or what they did or how to use them..

As an aside we stock Schneider, Rodenstock and Heliopan center filters. Rodenstock and Heliopan are the best sellers to our dealers.

[Andrew_4548]

Bob, this might be a naive question but I assume it's possible to fit one manufacturer's centre filter to another's lens and get decent results?

Obviously, there's the physical thread sizes to match or use stepping rings but are the neutral densities sufficiently similar to allow it? Are there lists of the ND values to compare filters?

I've not felt the urge to rush out and buy C/Fs for my wideangle lenses (90 f5.6 SA XL and 75 f/6.8 Grandagon) as I'm using B&W vitually all the time and the price of the filters here in the UK can be up to a quarter of the price of the lens in the first place :eek:. You never know - I might find a bargain someday...