Why aren't center filters built-in?

[John C Murphy]

Why don't manufacturers of wide angle lens just incorporate the center filter into the lens? Is the exposure change the only problem? Or are there other reasons?

[Leonard Evens]

Not everyone wants to use a center filter in all circumstances. Since you have to increase exposure to compensate for the reduced intensity at the center, the question of how to balance that against uneveness of illumination should be left to the photographer.

[Bob Salomon]

Not only don't all users want a center filter building one is very complex and making it part of the lens would also raise the cost of the lens. Even for those who don't want or think they want a CF.
Additionally some people like the look of darker corners and refer to it as a wide angle effect. They would not get that effect with the filter built-in.
So the only way that would make sense would be to include one with the lens rather then selling them as an accesory and, having been selling Rodenstock, Schneider and Nikon lenses at the wholesale level since 1976 I can tell you that most lenses are sold without the filter and the sale of lenses is far greater then the sale of the filters. That should tell you that the market is not interested in having the filter included with the lens.

The only exception in our case to the above is the sale of the 72mm SA for the Technorama 617S III. Most buyers of the lens for this camera do buy the CF.

[David A. Goldfarb]

It would be much easier of course to have a little fan that you could swing out of the way when it wasn't needed, or just use for part of the exposure.

[Ernest Purdum]

Is Andrew hiding under yet another name?

[Bob Salomon]

"Is Andrew hiding under yet another name?"

Probably not. This is a rather common question at shows and on the phone.

[Kerry L. Thalmann]

John,

As others have mentioned, not all users want or need a center filter for all applications. In fact, the use, or not, of a center filter is a very personal matter. Some users swear they need them with a 90mm (on 4x5), others claim they never see the need even when using a 65mm lens (on 4x5). With such diverse opinions, it doesn't make sense for the manufacturers to go to the expense and trouble of incorporating a center filter into every lens they sell. It makes much more sense to offer it is an option and let the user decide.

Although I prefer to use a center filter with all my lenses shorter than 90mm (on 4x5), I compose and focus without the center filter installed and then add the filter and adjust the exposure just prior to exposing the film. It's hard enough to compose and focus wide angle lenses without adding another 1.5 - 2.5 stops of density. Think of it this way, many users pay extra money for faster f4.5 and f5.6 wide angles for the sole reason that the brighter ground glass makes focusing and composition easier. Trying to convince those same users that it's in their best interest to charge them more money for a lens that is effectively 1.5 - 2.5 stops slower is a losing proposition. Giving them the option of focusing and composing without the CF and then adding it as necessary seems to be the best solution.

One other possible option to reduce fall-off in large format wide angles would be to come out with a series of retrofocus (reverse telephoto) wide angles. However, there is no free lunch. Retrofocus designs have inherently more distortion than standard wide angles. To achieve comparable optical performance requires designs that are much more complex and have many more elements. This would result in wide angle lenses that are much larger, heavier and more expensive. So again, a standard wide angle design with an optional center filter seems to be the best compromise for optimal performance, size, weight and cost. Which is probably why all four current makers of large format wide angle lens makers have chosen this route.

Kerry

[Eric Leppanen]

Film type often plays a large role in determining the need for a center filter. Chrome film responds relatively quickly to differences in lighting, and I find myself frequently using center filters when using this type of film. I rarely use center filters with B&W and color print film.

[David A. Goldfarb]

You can sometimes compose around the hotspot as well, for instance applying front rise with a landscape and maybe tilting the camera downward (when the composition is amenable) to darken the sky, or using shift to move the lens axis toward one part of the image or another and put the hotspot over the item of interest.

[Alan Davenport]

--Center filter reduces illumination on the film, requiring the photographer to incorporate the filter factor into his/her exposure calculation. If the CF were incorporated into the lens, some photographers would not be smart enough to get a decent exposure, others (even dumber) would publicly attack the manufacturer for selling an f/5.6 lens that is only f/9 on the film (or whatever.)

--Manufacturer and retailer both get extra money from selling the filters. If the CF was incorporated into the lens, the mfgr would probably lose money because they'd still have to sell the lens priced to compete with others that didn't have the filter. No, that's not logical but neither are shoppers.

--Building the CF into the lens would lock everyone into your way of seeing, or at least the way the lens designer saw things at the time. As others have mentioned, not everyone likes, wants or needs a CF. My widest lens at this time is 90mm (on 4x5) and I have no desire for a center filter at this time.

[Kerry L. Thalmann]

My widest lens at this time is 90mm (on 4x5) and I have no desire for a center filter at this time.

But what if you were to use that same 90mm lens on 5x7? Then you may find a center filter necessary. Yet another reason not to build the center filter into the lens. The 110mm Super Symmar XL is one of my all time favorite lenses. I bought it originally for 4x5, and have used it on that format for years without ever feeling the need for a center filter. Once I began using the same lens on 5x7, and more recently 4x10, I found a center filter absolutely neceesary (for my needs).

Fortunately, it takes the same center filter that I use with my 80mm Super Symmar XL on 4x5. And, yet anopther reason still not to build the center filter into the lens - one filter can be used with multiple lenses.

Kerry

[M Brian Mills]

And one other reason...
I have a Schneider 65mm f8 that was not intended for 4x5 use because the image circle is too small and would have tons of fall-off on the edges, but I use it for 4x5 photomacrography. If I had to adjust my uber-long exposure times to be 2 stops longer because the center filter was on the lens I would have exposures that were upwards of 4-6 hours. Yikes!

[Bob Salomon]

"I would have exposures that were upwards of 4-6 hours. Yikes!"

What aperture are you shooting at now?

[Will Strain]

ah reciprocity multipliers... how I love thee.

[M Brian Mills]

Hey Bob,
I usually shoot wide-open at f8, but use ambient light indoors.
I’m also getting about 10:1 magnification.

[Bob Salomon]

"I usually shoot wide-open at f8, but use ambient light indoors.
I’m also getting about 10:1 magnification."

Then a center filter would not work at all for your application.

But then again if you were using a lens optimized for that magnification and stopped down to it's optimal aperture you would get better results - unless you aren't after the sharpest possible results.