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

Why is it that all the lenses within a particular range of lenses (eg, Super Angulon), 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 _differing_ angles of view.

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

I'm taking a guess here... Is it because the manufacturers of LF lenses - who don'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 view? Is it for our benefit or theirs, because it doesn't make a lot of sense to me.

-- Chris Bitmead (chrisb@ans.com.au), August 12, 1998

Answers

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.

-- Quang-Tuan Luong (luong@ai.sri.com), August 12, 1998.

I understand that they have different image circles for different formats, but the 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 150mm doesn't have enough coverage. The 355mm is way overkill for those requirements.

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 buy a Schneider G-Claron with an over-kill 444mm image circle when they could make 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 don't want to have to buy the huge Tele-Xenar. (Not that I personally want an 800mm).

-- Chris Bitmead (chrisb@ans.com.au), August 12, 1998.

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 shutters. A lens/shutter combination may well be marked "lens made in Germany, shutter 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 crudely, yes, one design is scaled up and down, giving a family of lenses with the same angle of view, and varying circles of coverage. Actually, it isn't that simple: in the XL series, they have differing angles and circles, but they do have pretty similar geometries.

Schneider could, of course, have a marketing blitz, and rename their lenses by format, and have a 5x4 series, 5x7 series, 10x8, and so on. But this would be artificial too, because a lens suitable for 10x8 with little movement is also suitable 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 between the lenses and bodies, and no longer could we put any lens on any body. Indeed, perhaps we are already on that road.

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

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

-- Alan Gibson (gibson.al@mail.dec.com), August 12, 1998.

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 try reading the archives and subscribe to View Camera magazine where they occasionally have articles about the basic families of lens design.

-- Ellis (evphoto@insync.net), August 12, 1998.

"It seems absurd that a 150mm G-Claron has a really small image circle, just covering 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 them at different distances from the film. A 150mm lens focused at infinity is approximately 150mm from the film, a 305mm approximately 305mm. This being the case, 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.

-- Steve Pfaff (spfaff@hrl.com), August 12, 1998.

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 plane, its circle gets that much bigger. The coverage angle is like a cone, the farther from the apex (lens) you go, the larger the circle of coverage. Also, keep in mind that the specified coverage circles are at infinity focus. As you focus 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 the circle of coverage than it has at its infinity specification. This is all different from angle of view, since that depends on the film size at the focal plane. 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 design affects the parameters also. A 90mm super angulon is made for wide angle views, and must cover the film from a closer position than a 210mm lens, so its ANGLE of coverage has to be much wider. Wide coverage angles are more expensive, because 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 formulas are usable (and cheaper).

-- Ron Shaw (shaw9@llnl.gov), August 12, 1998.

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 lens has a different angle formed by the cone of light. In LF, every lens in a range 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 manufactures 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 too small image circle to cover your favourite format are a case in point.

-- Chris Bitmead (chrisb@ans.com.au), August 13, 1998.

>>... 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 format 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 movements.

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 restricting a lens to a given film format.

I think this is a crucial point: there is no such thing as, say, a 5x4 lens. However, 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.

-- Alan Gibson (gibson.al@mail.dec.com), August 13, 1998.

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 would they determine its design. Make it cover 8x10? How about 11x14? If this was the case, I would have to pay big bucks for a 150mm lens designed to cover 8x10 even if Im shooting 4x5. The difference in cost between a 150 that covers 4x5 well 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 element one covers your film, then it may be a better choice. Also, more complex designs 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 coverage. 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 same optical formula at 300mm on 8x10 (the 'normal' lens). If you are shooting portraits on 4x5, you dont need much in the way of movements, and that nice xenar (at about 375 new)has all the coverage needed. If you are shooting landscapes on 8x10, then you may want the 165mm SA, at whatever that goes for now. Determine the coverage you need for the format and subject matter you shoot, and pick your lens based on that. It doesnt make sense to spend more than necessary, and could actually be detrimental to image quality.

-- Ron Shaw (shaw9@llnl.gov), August 13, 1998.

Chris, You have to admit one thing.....the respondents on this LF site (Alan, Ron, Steve, Ellis, and others) are the most incredibly courteous, patient, and generous (as well as knowledgeable) people you will find anywhere. Sergio.

-- Sergio Ortega (s.ortega@worldnet.att.net), August 14, 1998.

Ron, I wasn't suggesting that they make only one 150mm lens. Only that if they compute the optics for every single lens individually, rather than a common design, the lens ranges might be more useful. Your comment that a 150mm design for 4x5 which is expanded will make a good 8x10 lens is a good point -- if manufacturers made 3 versions of different designs for 4x5, 5x7 and 8x10. But they make a lens in 10 different lengths, some of which are a tad too small image circle for 4x5, and also therefore having gaps in the long lens product lineup because they have no narrow angle of view lenses. I don't want to and shouldn't need a 5 kg , $10,000 lens just because I want a 600mm lens on 4x5.

Sergio: I'll agree with your statement, but does it have anything to do with lenses? :-)

-- Chris Bitmead (chrisb@ans.com.au), August 14, 1998.

Chris, LF lenses are a specialty market; Your reply smacks of frustration with the manufacturers, but keep in mind that there are other options: you don't want to spend $10,000 for a 600mm lens (by the way a Nikon Nikkor T 600mm f/9 telephoto is listed in the B&H book at US$2499.00)? Fine, buy a 6x7 or 6x9cm roll film back for US$450 (6x7)>$750 (6x9) and you will have effectively turned your 300mm M-Nikkor into a 600mm ( or near it.). one of the beauties of large format is that one can crop, sometimes radically (see Arnold Newman's portrait of Igor Stravinsky), and not lose much image quality. Something you cannot do with smaller formats. there really is a different way of thinking to LF photography as you will find out, then there is to 35mm work. Both can complement the other -Ellis

-- Ellis (evphoto@insync.net), August 14, 1998.

No, I'm not really frustrated Ellis. I'm just trying to understand why things are the way they are. I've never seen anyone bring up the topic of why LF lenses are designed this way.

-- Chris Bitmead (chrisb@ans.com.au), August 15, 1998.

Chris, I have a feeling that you haven't seen the subject brought up because in the over all scheme of things, it doesn't matter.

Large format photography is a lot different than miniature (35mm)photography, in a lot of ways. I think you will find that LF photographers tend to do a lot more, and talk a lot less, because, there isn't a lot of the type of information available that there is for 35mm photography.

LF uses a lot of older equiptment, how many 35mm photographers use a 100 year old lens for thier primary optic? I and a lot of others do. I would be hard pressed to tell the difference between an 8X10 contact print made with my freinds late model 300mm Fuji and my 90 year old 12" Turner and Reich Convertible.

I don't know the specs for the Convertible, it covers 8X10 with all the movements I have available, and if it didn't I would take it back to the gentleman that sold it to me and get one that did. I make that arrangement before I even start to haggle price. LF can be very daunting in that respect, we fly blind quite a bit. This forum is a good source of accurate information, and frustrated or not, I think as you start to create some images, you will find that the specifics of lens design will have nothing to do with your creative output.

Wait until you start to retouch dust and lint out of your negatives, you'll see what I mean.

-- (mthompson@2clinton.net), August 15, 1998.

LONG response to Chris: With all due respect, I don't believe anyone could really satisfactorily answer your question as it's been posed, though many have tried. To quote Strother Martin, from Cool Hand Luke, "Boys....I think what we have here....is a failure to communicate!". So, let's set up a few basic parameters here, before going any further. You stated, the various focal lengths within the Schneider SA line (or G-Claron, or Apo Symmar lines) all have wildly differing image circles, yet they pretty much have the same angles of view. Don't confuse angle of view with angle of coverage. Other respondents have explained this important difference very well, review their responses.

These differences may not make any sense initially, but this is a very good thing. It is for the consumer's benefit. They are not just saving money, or taking the easy way out.

As you know, each of the LF film sizes (4x5, 5x7, 8x10, etc.) requires a specific image circle size to adequately "cover" the particular film area in question. Adequate "coverage" is simply determined by the diagonal measurement of the film size in question; the distance (expressed in mm's) from the opposite corners of the film area, plus about 20% extra to allow for displacement of the image circle due to LF movements.

A lens is said to adequately "cover" a film size when the image circle it projects onto the film area, at infinity focus, and stopped down to about f16 or f22, provides even illumination and image quality across the entire film plane, corner-to-corner. Any more "coverage" than necessary for the film size in question is a waste of lens capacity.

The closer you focus a lens from infinity, increasing the distance from the nodal point of the lens to the film plane, the larger your image circle becomes. That is why all image circle dimensions are given at their smallest usable size: at infinity focus. (Note: Schneider often provides image circle dimensions for their G-Claron lenses at closer than infinity focus; the huge image circles sometimes quoted for G-Clarons are given at magnification ratios of up to 1:1, double the bellows extension needed for infinity focus. Schneider touts these lenses as optimized for close-up work.)

Another misconception about image circles is that they get physically larger as the lens is stopped down from maximum aperture. Image circles do not increase in size as the lens is stopped down to f16 or f22 from maximum aperture; the illumination just becomes more even, and the image quality gets better, across the entire image circle, as the lens is stopped down to apertures of f16 or f22. (Source: Schneider Optics)

Now, to apply this, let's say that my favorite focal length in 35mm is my 50mm, or "normal" lens. I want the equivalent focal length when I use the 4x5 format. Conversion tables tell me I need a 150mm LF lens to achieve the same angle of view for the 4x5 film size.

I check all the manufacturer's product literature and find several lenses in this focal length: the G-Claron 150, the Nikkor 150 W, the Apo Symmar 150, the Apo Sironar-N 150, the 150 Super Symmar 5.6, the Super Symmar 150 XL, the Nikkor 150 SW, the Grandagon 155, and many others. Why all the choices? Am I being played by the manufacturers? I'm confused!

Remember, all these 150mm's will provide the same angle of view when used on the 4x5 format, not the same angle of coverage. Additionally, all will vary wildly in their respective sizes of image circle, their physical size (filter and shutter size), and their prices (from several hundred to several thousand dollars). Which one should I choose?

From a "user's point of view", if I had a bottomless bank account, strong and willing porters or beasts of burden to carry all my equipment, and a 4x5 camera large and strong enough to handle any 150mm lens available, I could choose any of the above lenses for a "normal" lens for the 4x5 format. But why choose, and pay for, a Super Symmar150 XL, or a Nikkor 150 SW, for 4x5 format? Why not the G-Claron or Sironar N?

From a "user's point of view", if I wanted to do studio tabletop/product photography work, I'd get the G-Claron--lot's of coverage when focused closer than infinity, and optimized for close-up work. If I wanted a versatile field lens for general landscape/portraiture work, I'd get the Apo Symmar, or Sironar N, or Nikkor W--great image quality at infinity, light, small and cheap, and more than sufficient coverage for the intended purpose: 4x5. If I were a "perfectionist", and wanted the sharpest "normal" lens made for 4x5, I'd get the Super Symmar 150 5.6, damn the cost! And If I were a complete fool, I'd get the Super Symmar XL, the Nikkor 150 SW, or the Grandagon 155.

To summarize, Chris: When choosing a LF lens, in a particular focal length to achieve a particular angle of view FOR a specific film size, for a specific photographic purpose, that will adequately "cover" the film size in question, I should/would choose the lens brand/design that will do all these things for the most reasonable cost, weight, and size. Anything else would be wasteful.

The only exception to this common sense rule would be if you wanted to use the same lens on a different size format; to achieve a different angle of view on that format, of course. In that case, you could conceivable get a 300 Nikkor M for both 8x10 and 4x5, providing a "normal" angle of view for the 8x10 format, and a "short telephoto" angle of view (comparable to about a 100mm lens on a 35mm camera) for the 4x5 format.

Have any of you noticed the increased use of this forum lately? Is it just the heat outside? Or is it the "All Monica, All the Time" crap on TV these days?

Hope this helps, Sergio.

-- Sergio Ortega (s.ortega@worldnet.att.net), August 15, 1998.

Thanks for your response Sergio, I learnt several good points from it.

I do understand the difference between angle of view and angle of coverage. Perhaps I can crystalise my question even further by putting it like this... The Schneider Super-Angulon 58mm XL has a 166mm image circle. The Super Angulon 90mm XL has a 259mm image circle. I can see several possible reasons for this....

1) A big image circle is more useful on a 90mm lens than on a 58mm lens? 2) A 72mm lens with a 259mm image circle would cost so much they wouldn't sell any? 3) They can't make a 72mm lens with a 259mm image circle? 4) They are just being lazy by using the same optical design for the 58mm and the 90mm lens and that's just how it happened to pan out? (Both lenses have a 110 degree angle of view)

-- Chris Bitmead (chrisb@ans.com.au), August 17, 1998.

1. Yes, for a given film format, I find larger image circles more necessary for longer lenses, because Scheimpflug needs more tilt, and controlling parallel lines needs more shift.

2. The size, weight and cost of an LF lens will be largely dependant on the angle of coverage. And cost varies with volume.

3. The current design limits for rectilinear lenses are about 120 degrees. This depends on the definitions of acceptable aberrations and fall-off, as well as types of glass and manufacturing methods.

4. Being lazy? It seems to me that designing lenses is a computationally difficult process. And pushing the envelope, 120 degrees and wider, is also a marketing issue: what trade-offs will the market bear?

If I was a manufacturer of LF lenses, I think I would take advantage of, say, a new glass formula or new manufacturing process to design a new series of lenses, that could do something more than my previous series of lenses. The market seems to want ever greater angles of coverage. I suspect there is also a market for pushing other envelopes, for example getting high quality at larger apertures. Perhaps Schneider et al don't think that market is large enough.

-- Alan Gibson (gibson.al@mail.dec.com), August 17, 1998.

For point 1., I can see that you would need less tilt for Scheimpflug effect for a shorter lens. But I would have thought you would need _more_ shift for a shorter lens. The shorter the lens, the closer you will need to move to your intended subject, and I would have thought therefore the greater shift. I'm imagining being right up close to a tall building.

-- Chris Bitmead (chrisb@ans.com.au), August 17, 1998.

Yes, you are right, for the same magnification, a shorter lens will be closer to the subject, and will need more shift. Slightly confused thinking on my part: I was thinking of the situation where the camera position didn't change.

-- Alan Gibson (gibson.al@mail.dec.com), August 17, 1998.

Chris, I believe that the Super Angulon 72mm XL does have an image circle approaching 259mm, or at least pretty close. Alan has one, he could probably verify this.

Perhaps LF lens designers could come up with a 58mm XL or a 47mm XL with a larger image circles than 166mm; a new line of XXL's? Schneider and Rodenstock have been offering shorter lenses with larger and larger image circles in recent years. I think that trend is great; they shoud keep on pushing the envelope.

The cost might be prohibitive, though. And I question whether the demand (or need) for such lenses would justify the high design and manufacturing costs. I'm not a lens designer, but I would think that at some point certain design limits will be reached.

But, as it stands now, these lenses (45mm, 47mm, 58mm) provide a marginal usable image circle for 4x5. That makes them more difficult to use well. It is very easy to displace such a small image circle. That is why most people would advise against getting one of these as your first WA lens.

These ultra-wides do work particularly well for interior architecture, particularly in tight, cramped situations, precisely because they are often focused at distances much closer than infinity, increasing their usable image circle. This greater bellows extension, and the resulting increase in usable image circle, will allow for greater movements in situations when they are most needed.

I believe Alan is correct--the longer the focal length for a given format, the greater the need for larger image circles to allow for movements. For a variety of reasons, the degree of Scheimpflug tilts/swings necessary with wide angle lenses is much less than with longer lenses.

I believe this would also hold true for shift movements. (You know, I cannot recall the last time I actually used a shift movement with a WA lens.) Your plausible theory that greater shift movements might be necessary with WA lenses, particularly when the lens is positioned closer to a subject, would probably be offset by the very substantial decrease in magnification with WA lenses, when compared to longer lenses.

Have you noticed how very tiny things look on a 4x5 groundglass with a 58mm WA? I would not take much of a shift with a 58mm to achieve the desired effect, no matter how close the subject.

Keep up the questioning attitude. Take care. Sergio.

-- Sergio Ortega (s.ortega@worldnet.att.net), August 17, 1998.

If your desire is to get a 600mm lens cheaper because its optimized for 4x5 is isnt reasonable because the cost you are paying for that 600mm isnt because its hard to make, but because its a limited market. Long lenses are easy to make, optically. Even narrow angles of illumination end up with far more coverage than you need. Thats just the way lenses work. You can make a very usable lens for 4x5 with only 1 element. Or maybe, try no lens at all. (check out the latest issue of View Camera mag. for an article on pinholes on LF. Surprisingly sharp!) Maybe have some fun and experiment. Order a cheap lens element from Edmond Scientific for a couple of dollars, and see what you get on the ground glass. If you really want a super image, spring for an achromatic (2 element) lens. Try even longer focal lengths. The longer the better, optically. Try mounting them in a lens cap or something. The image you get on the ground glass may suprise you with its quality. It will be better than a pinhole, which is already pretty good at these focal lengths, and its fun, too. Get your kids involved, as well, as this is something they will enjoy.

-- Ron Shaw (shaw9@llnl.gov), August 17, 1998.

Regarding the 72mm lens: yes, the claimed circle is 226mm, rather than 166 for both the 58mm and 47mm. It seemed to me that Chris was getting confused between the 58mm and 72mm, but it didn't substantially affect the conversation, so I didn't mention it.

I also don't shift very much. I do tilt/swing, and just remember not to tilt/swing the 47mm lens, but to do this to the film back instead.

I was exploring a cupboard the other day, and came across my experiments that were pretty much as Ron describes. Close-up lenses, single element, +2 and +3 dioptre (500mm and 333mm, or 200mm with both screwed together). A cardboard lens panel, with a step-up ring glued in place, to take one of the close-up lenses. Black cardboard circles, with holes, making the apertures. The shutter was of the "hold your hat over the lens" variety. I was playing with 5x4 and 10x8, and the results were, well, OK. Much better than pinholes, but much worse than "real" lenses. Also, of course, very much cheaper than "real" lenses.

Kids are an accessory I don't have, but I suppose they would be useful for lugging the gear around.

-- Alan Gibson (gibson.al@mail.dec.com), August 18, 1998.