LF lens manufacturer philosophy

[Chris Bitmead]

The range of lenses offered by LF manufacturers is baffling to someone coming fr om medium or small format.

Why is it that all the lenses within a particular range of lenses (eg, Super Ang ulon), have roughly the _same_ angle of view with _differing_ image circles? In the 35mm world of course, different lenses have the _same_ image circle and _dif fering_ angles of view.

It seems absurd that a 150mm G-Claron has a really small image circle, just cove ring 4x5, whereas the 305mm G-Claron has a huge image circle which can cover 8x1 0. It would have seemed more sensible if all G-Clarons had the same image circle .

Similarly, Super Angulons range from the 47mm with a very small image circle, to the monster 210mm with a MASSIVE image circle, but roughly the same angle of vi ew.

I'm taking a guess here... Is it because the manufacturers of LF lenses - who do n't sell many compared to 35mm manufacturers, are saving money by just designing just one good lens, and providing the lens in different sizes. i.e. Just taking the design drawings and expanding it to make a longer lens?

Or is there a good reason for this state of affairs from the user's point of vie w? Is it for our benefit or theirs, because it doesn't make a lot of sense to me .

[QT Luong]

Depending on your application you might need to be able to make a lot of adjustments or not, which would call for various image circles. Also, the lenses are not dedicated to a particular format, remember that the angle of view changes when you keep the focal constant but change the format.

[Chris Bitmead]

I understand that they have different image circles for different formats, but t he way they arrange things doesn't make much sense to me.

Like, let's say you decide "I want several lenses, I don't care about aperture ( f9 is fine), and I need enough coverage for 4x5 with a little bit of movement". You can't just buy several - say G-Claron lenses of whatever focal length. The 1 50mm doesn't have enough coverage. The 355mm is way overkill for those requireme nts.

It would make more sense to me if they had a Small, Medium, Large and Very Large image circle ranges of lenses. As it is, it seems like they have gaps in their range. Like, let's say I wanted a small/light 350mm lens. Why should I need to b uy a Schneider G-Claron with an over-kill 444mm image circle when they could mak e something smaller/lighter/cheaper. (I'm just using this as an example. I don't necessarily want a 350mm lens). Or let's say I want an 800mm lens for 4x5. I do n't want to have to buy the huge Tele-Xenar. (Not that I personally want an 800m m).

[Alan Gibson]

One of the delights, for me, of LF is that it doesn't suffer the same marketing gizmos of 35mm (or, heaven forbid, APS). It is more deeply rooted in tradition. Here is a case in point.

Lens manufacturers are just that. As far as I know, Schneider just makes lenses, for various purposes, including photography. They don't make cameras, or even s hutters. A lens/shutter combination may well be marked "lens made in Germany, sh utter made in Japan". The lenses and cameras come from different manufacturers, and the buyer of LF equipment needs a greater depth of knowledge than for 35mm.

To Schneider, lenses go in families, characterised by their geometries. Put crud ely, yes, one design is scaled up and down, giving a family of lenses with the s ame angle of view, and varying circles of coverage. Actually, it isn't that simp le: in the XL series, they have differing angles and circles, but they do have p retty similar geometries.

Schneider could, of course, have a marketing blitz, and rename their lenses by f ormat, and have a 5x4 series, 5x7 series, 10x8, and so on. But this would be art ificial too, because a lens suitable for 10x8 with little movement is also suita ble for 5x4 with a lot of movement.

And then they could go further, with lens manufacturers joining with the camera manufacturers, creating specialist mounting systems, with data interchange betwe en the lenses and bodies, and no longer could we put any lens on any body. Indee d, perhaps we are already on that road.

For my money, I like simplicity, which means I have to know about circle of cove rage.

Chris may have a point, that there are no LF lenses that cover 10 degrees or les s. The reason may be economic: too little demand. If everyone who wants these le nses lobbies the manufacturers, they might make them.

[Ellis Vener]

Chris, the answer to your good question is fairly straight forward: you are mistaking angle of view (what the film sees) with angle of coverage (what the lens shows). I agree it appears to be a paradox, perhaps better semantics would help. Also t ry reading the archives and subscribe to View Camera magazine where they occasio nally have articles about the basic families of lens design.

[Steve Pfaff]

"It seems absurd that a 150mm G-Claron has a really small image circle, just cov ering 4x5, whereas the 305mm G-Claron has a huge image circle which can cover 8x10."

Perhaps the concept youre missing here, Chris, is that since LF lenses (unlike MF and SM lenses) do not have internal focusing, they are focused by placing the m at different distances from the film. A 150mm lens focused at infinity is app roximately 150mm from the film, a 305mm approximately 305mm. This being the cas e, even if the angle formed by the cone of light as it leaves the lens (angle of coverage) were the same for both lenses, the image circle would be about twice as big for the longer lens. Hope this helps.

[Ron Shaw]

Steve is correct. Both the 150mm G-Claron and the 305mm G-Claron have about the same ANGLE of coverage. Since the 305 will be twice the distance from the film p lane, its circle gets that much bigger. The coverage angle is like a cone, the f arther from the apex (lens) you go, the larger the circle of coverage. Also, kee p in mind that the specified coverage circles are at infinity focus. As you focu s closer (rack OUT the bellows), your lens gets farther from the film plane, and the circle of coverage gets larger (ANGLE of coverage remains the same). The G- Clarons are made for approx. 1:1 image scales, and at 1:1, the 150mm has twice t he circle of coverage than it has at its infinity specification. This is all dif ferent from angle of view, since that depends on the film size at the focal plan e. A 150mm LF lens has the same image scale at the film plane as a 150mm lens on 35mm, but since the film is larger, the angle of view is wider. Also, lens desi gn affects the parameters also. A 90mm super angulon is made for wide angle view s, and must cover the film from a closer position than a 210mm lens, so its ANGL E of coverage has to be much wider. Wide coverage angles are more expensive, bec ause they require more corrections than a 210mm lens would. The longer the focal lenght, the smaller the needed angle of coverage becomes, and simpler optical f ormulas are usable (and cheaper).

[Chris Bitmead]

The fact that both a 150mm and 305mm G-Claron (or Anglon or whatever), have the same shape cone of light is exactly the point I am trying to make. It looks like a tad lazyness on the manufacturers part. Every different focal length 35mm len s has a different angle formed by the cone of light. In LF, every lens in a rang e has the same angle cone of light.

I'm not saying this is disasterous. To a certain extent the larger image circle is more useful on longer lenses. All I'm saying is that the range of lenses manu factures make would be more useful if they custom designed every lens instead of aiming the shrinking ray gun at a single design. Lenses that are just a shade t oo small image circle to cover your favourite format are a case in point.

[Alan Gibson]

>>... if they custom designed every lens instead of aiming the shrinking ray gun at a single design.

It seems to me that the lenses in a given design are not merely shrunk, but are then tweaked, presumably to modify the trade-offs.

>> Lenses that are just a shade too small image circle to cover your favourite f ormat are a case in point.

Yes, frustrating isn't it, but don't forget that a lens that doesn't quite cover your favourite format will cover the next size down, with room for some movemen ts.

35mm generally doesn't have movements, so lens manufacturers go for the smallest cone they can get away with. LF does have movements, so there is no point in re stricting a lens to a given film format.

I think this is a crucial point: there is no such thing as, say, a 5x4 lens. How ever, there are some lenses that will cover 5x4 with movements, and other lenses that cover 5x4 with no movements, or 6x9cm with plenty of movements.

[Ron Shaw]

I guess Im sort of missing the point. It seems to me that the broad selection of lenses available is a benefit. If a mfr. made only one 150mm lens, then how wou ld they determine its design. Make it cover 8x10? How about 11x14? If this was t he case, I would have to pay big bucks for a 150mm lens designed to cover 8x10 e ven if Im shooting 4x5. The difference in cost between a 150 that covers 4x5 wel l and a 150 that covers 8x10 is a big difference. If you need wide coverage at a given focal length, you can pay for that exotic 8 element lens, but if the 4 el ement one covers your film, then it may be a better choice. Also, more complex d esigns often are outperformed by simpler formulas in absolute sharpness (within thier coverage circles, of course). As for the angle of coverage being constant with different focal length lenses of a common formula seems fairly clear to me. Just like a flashlight. The farther from a surface, the larger the circle of co verage. This happens with lenses as well, and seems nice and orderly. A 150mm on 4x5 (the 'normal' lens) will give about the same amount of movements as the sam e optical formula at 300mm on 8x10 (the 'normal' lens). If you are shooting port raits on 4x5, you dont need much in the way of movements, and that nice xenar (a t about 375 new)has all the coverage needed. If you are shooting landscapes on 8 x10, then you may want the 165mm SA, at whatever that goes for now. Determine th e coverage you need for the format and subject matter you shoot, and pick your l ens based on that. It doesnt make sense to spend more than necessary, and could actually be detrimental to image quality.