THIS is the chassis of the Sigma

[JR1]

150-600

Now I know whey it weighs so much

[Manfred M]

Interesting, Jeremy.

What it tells us people who understand manufacturing processes is that they don't expect to sell a whole lot of these lenses, as the slower, more expensive all-metal construction was chosen over producing the injection moulds that would have been required to go to an engineered resin lens body.

That also tells me that the price of this lens is not going to drop all that much over time as the base manufacturing costs using CNC machining are going to be there. With a resin body, the manufacturer can afford to reduce the price quite drastically, after the R&D and tooling costs have been amortized. With this lens the R&D costs amortization are the only costs that impact future price reduction potential; the machining costs, will at best stay the same, but more than likely may go up a bit.

[NorthernFocus]

Interesting in this age of plastic, CF, etc. Oldschool.

Manfred, that's a good hypothosis. But it may simply be the size of the lens and they decided to stay with metal for technical reasons. Or fear of the unknown with it being the largest/longest zoom lens that they have produced.

[Manfred M]

Manfred, that's a good hypothosis. But it may simply be the size of the lens and they decided to stay with metal for technical reasons.

Of course the other explanation is that this is the prototype housing; prototypes are often made out of metal and the actual production lens will be injection moulded. Not having access to the original (and being Japanese, a translation of the information, we are only guessing here.

What drives me to this speculation is that I looked at the Sigma USA website, and the one important piece of data missing on that lens is weight. All the other dimensions are there. That tends to suggest to me that all the final manufacturing decisions had not been made at the time the lens was put up on the site.

It's a large lens, so keeping the weight down by using resins would have been the direction I would have pursued in designing this beast.

[NorthernFocus]

Of course the other explanation is that this is the prototype housing...

And a very likely scenario particularly if the image is/was being used as advertisement.

It's a large lens, so keeping the weight down by using resins would have been the direction I would have pursued in designing this beast.

Then it stands to reason you'd also manufacture all of the big primes out of engineered materials as well? That is interestingly one area that most of the optics folks haven't yet ventured. They are attacking the weight via lighter glass rather than extensive use of engineered material for barrels etc. One could argue they are simply sticking with what they know but they sure spend plenty of R/D and build prototypes with different glass all the time. One would think they's be trying out different structural materials as well. But we're assuming the decisions are made purely for engineering purposes. Many Japanese companies are highly integrated and they may use certain materials simply to support another branch of the company.

[DanK]

The weight is given on the B&H website as 6.3 lb (2.86 kg). Ouch. The Tamron 150-600 is given as 4.30 lb (1.95 kg).

[ajohnw]

I've taken a couple of lenses definitely from the early 70's late 60's apart and even though the construction is basically metal the actual running gear multistart threads etc is add on plastic at least on one half. A much earlier one was metal on metal. I've handled a couple of these as well. Not so nice a feel and heavier greases had to be used. Some even focused by moving the entire lens. It's an interesting area. Olympus was criticised for a lens with a loose centre section that moved when focusing and zooming. It turns out that switching the camera on locked it in place - something to do with the focus drive. The MKII is stiffer on or off. So rather than pointing things out they "fixed" it.

Personally I would welcome the sensible use of more plastics for the weight savings. As things stand I suspect some lenses are apparently very solid due to the casings but may be rather flimsy inside.

The glass wieght savings are really cost savings bought about by fluorite like glasses becoming available. The prices of the glasses that are very fluorite like are supposed to have rocketed of late. Hot pressing rather than grinding is also very common now.

John
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[Manfred M]

Then it stands to reason you'd also manufacture all of the big primes out of engineered materials as well? That is interestingly one area that most of the optics folks haven't yet ventured. They are attacking the weight via lighter glass rather than extensive use of engineered material for barrels etc. One could argue they are simply sticking with what they know but they sure spend plenty of R/D and build prototypes with different glass all the time. One would think they's be trying out different structural materials as well. But we're assuming the decisions are made purely for engineering purposes. Many Japanese companies are highly integrated and they may use certain materials simply to support another branch of the company.

A couple of thoughts here.

The cost of moulds has gone down fairly significantly over the past decade. In instances where I would have gone with aluminum moulds because of cost (but lower life), the upcharge for steel ones is now minimal.

Yes, the larger Japanese companies are definitely vertically integrated, but the smaller ones less so. Canon and Nikon are multi-billion dollar businesses, whereas 2014 sales for Sigma were in the $50 million range, so definitely a mid-sized player, and hence also less integrated.

The move to resin bodies has been a relatively recent move, so the older bodies are still metal. I have the Nikkor f/2 105 DC, and it is one of my more recent purchases. It has a metal body. Unless they come out with a new lens design, updating these relatively low volume lenses to reduce cost / weight is going to be a pretty expensive proposition and likely is not going to happen.

Lighter glass? Most glass used in lenses is selected for its optical properties, i.e. index of refraction (IR). Some of the lower end lenses with aspherical elements use a combination of an injection moulded resin that is bonded to a glass element, so that approach is there. The IR of resins is a lot lower than glass, so that is one reason we don't see this in faster lenses is the size factor. Moulded glass elements are used in the higher end aspherical elements; the manufacturers have given us that much information, but the exact process used is not being shared by the manufacturers.

That being said, so far as I can tell some of the recent Canon and Nikon lenses that use fresnel elements will likely have to have resin based optical elements. So far as I know, these ultra-fine etched elements can only be done in resins; unfortunately, this is proprietary information, so I can get any really decent information on the technology, outside of marketing documents.

The weight is given on the B&H website as 6.3 lb (2.86 kg). Ouch. The Tamron 150-600 is given as 4.30 lb (1.95 kg).

This could definitely explain the difference between the two lenses; but the the Sigma is longer and has a larger diameter. Until the Sigma ships, we are just guessing as to the construction.

[NorthernFocus]

As I understand it the weight savings in the big primes is due to the flourite glass being used for a few of the larger elements. That's also the explanation for the significant increase in price. I haven't researched it in detail. Just going by Nikon's advertising and a few articles that I've seen. One thing for sure is that the new version of the 400 2.8 is a couple of pounds lighter and a couple thousand dollars heavier. Indications are that the 600 f4 is next. Presumably they are upgrading those two with the flourite glass because there is the most weight savings to be had with the huge glass elements.

[Manfred M]

Flourite? Made of wheat? I suspect you mean Fluorite...

I think some of my old Leica lenses have some fluorite elements; which partially explained the high costs. A bugger of a maerial to work with is what I had always read. I was under the impression that some of the speciality ultra low dispersion glasses had generally replaced fluorite glass elements; lighter, less fragile and less susceptible to humidity changes..

[ajohnw]

My understanding is that the bulk of aspheric lenses are hot pressed even in compacts. Ohara for instance will price up very precise billets of glass for them. I'd hope that better quality lenses are at least heat treated afterwards to even out the refractive index.

The lighter glass weight is down to the dispersions that are available now. There used to be too little difference in available crowns and flints so more elements were needed for the same order of chromatic aberration. Fluorite was the ultimate and only available in sizes suitable for microscope objectives. Now there are glasses with very similar characteristics and I believe that real fluorite crystals can actually be grown now. Interesting stuff to work. It's soluble in water. Even the atmosphere corrodes it. The glasses have similar problems as well. Many have for some years. Manufacturers in the past would avoid them as even the internal elements would have to be coated. They all are now thanks to SD glasses etc.

I've wondered about how they would make Fresnel elements. The traditional methods are a combination of moulding and fabrication in the case of items such as light house lenses. For camera lens types I'd guess some form of etching similar to the ones used for semiconductor production. There could be several different ways of achieving this even what is basically ion beam machining.

This link mentions a lens which can be optimised for 3 distinct wavelengths.

http://www.rpcphotonics.com/optical.asp

There used to be a lot of mention of optical plastics showing great promise but I've never managed to find any suitable for general use other than what goes into spectacles and IR optics.

John
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[Manfred M]

Hmm. The techies have hijacked another thread...

[NorthernFocus]

Flourite? Made of wheat?..

I think they only use the wheat glutin. But I may be confusing flouride coated lenses...

The spelling may be influenced by fourteen hours of air travel having gotten home at 0230 this morning

[ajohnw]

I think they only use the wheat glutin. But I may be confusing flouride coated lenses...

The spelling may be influenced by fourteen hours of air travel having gotten home at 0230 this morning

It curious how canon and nikon coat lenses with fluorine as mentioned on the web. They must have some mysterious way of keeping a highly toxic gas in place. But really they should be calling it a fluoride coating. Some compound of fluorine probably a metallic. One that also forms part of the anti reflection coatings.

John
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[JR1]

Surely one of the reasons the "S" lens is so well designed and metal used so much is that unlike the cheaper "C" lens it is intended to be well used by sports photographers, it will take the daily hammerings

[ajohnw]

I would doubt if there is much in it running metal on metal Jeremy what ever it's cased in. Photography is an odd area buyer wise. There is a certain Nikon lens that they plastic coated so that it wouldn't be cold to the touch. KR reckons that these are bargain as people would rather have them without the coating even though the internals are identical.

The word plastic doesn't mean much on it's own either. They use fillers, probably fibre glass. The only company that have owned up to what they used is Olympus on the 4/3 lenses some of which cost extra ordinary amounts of money. It's not a cheap option and it's very tough stuff. These days the sections on some are thinner and I have no idea what filler they are using. It wouldn't surprise me if carbon fibre cropped up at some point, It's used on fishing tackle, reels and things like that to replace metal. People had the same reluctance to change. These days it's often the metal bits that are weak as they can't be seen and are made too thin - or inadequate plastics used for some parts.

There are probably 2 ways of making metal lens shells. Castings, maybe with some subsequent machining and machining from solid or tube on machining centres. The Olympus pro lenses look very much like the latter due to the finish of the barrels. It also looks like they will be standardising part of the lens on all models. The running costs of these machines is on the high side. Forget conventional cnc, they can turn, mill, grind and do all sorts of things and even handle the parts automatically. I would have a shrewd guess that apart from capitol recovery aspects items made like this would cost less than more conventionally produced ones. The plant costs a lot of money. That has to be offset against tooling costs making them the other way. In other words machining from solids may be cheaper unless volumes are rather high. The camera market is shrinking so more metal may be on the way.

Manfred mentions aluminium moulding tools - rather a long time ago now but we even tried wood with very little added metal. Mostly just for plastic flow parts as it's rather hot.

John
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[JR1]

I'm no engineer but would CF not be the way ahead for lenses, top end telescopes are made from it.

[NorthernFocus]

I'm no engineer but would CF not be the way ahead for lenses, top end telescopes are made from it.

From a pure technical standpoint that seems to make the most sense. However CF is typically more expensive than non-exotic metals. So from a competitive standpoint it's difficult to go there unless the industry comes along with you. There is the potential for weight savings but in the consumer market they are already using other plastics at much lower cost. So it comes down to economics on the high end gear. If it costs more to manufacture than current materials then to maintain profits, the cost must be passed on to the customer. So how much weight can be saved and are people willing to pay the associated premium? Presumably the manufacturers think not. Though if one considers tripod sales, the evidence suggests that people are in fact willing to pay the premium. It is an interesting question. Maybe there are issues that, in spite of our collective technical prowess, we just haven't yet thought about.

[Manfred M]

Both carbon fibre and fibre glass are really not terribly suitable materials for lens component. Both materials fall into the category of fibre re-enforced resins and are generally made into sheets or tubes.

Production methods are fairly simple and often manually prepared, with sheets of fibres laid down and resin applied between sheets. By orienting the sheets of fibres in different directions during the layup process, is how the strength properties can be varied. These are then placed in a press during the curing process. If a thermoplastic is used, the sheets can be heated to soften the material and then vaccuum formed to create shapes.

Tubes are made in one of two ways. The first is a layup process over a round mandrel and the second method method is pulltrusion where the fibre is pulled through a tool that is quite similar to an extrusion die.

The material can also be injection moulded, but this is not particularly straight forward, as rather than strands or matts of fibre, the material is chopped into short pieces and mixed with the resin prior to being forced into the mould under high pressure. Tool life is shorten because the fibres are quite abrasive and gains in tensile strength are not nearly as good as when mats or strands of fibre are used. Because of the random orientation of the fibres, these can result in rough surfaces that can caused cuts when handled. If these parts are used in a way that people will handling them, an additional layer of surface protection must be added, i.e. they are often painted, and here problem is that the risk returns should the protective layer be worn off.

One of the projects I was involved in that involved in a couple of years ago involved some pulltruded, glass fibre reenforced parts, but ultimately we went with a more expensive powder coated metal solution because of the risk of cutting as the material wore.

This is really why we only see these materials in fairly simple shapes, like tripod legs and not in more complex components like lens bodies. High pressure injection moulding and turning aluminum parts on a CNC lathe are really still the best options here, given current materials and manufacturing technology.

[NorthernFocus]

...This is really why we only see these materials in fairly simple shapes, like tripod legs and not in more complex components like lens bodies. High pressure injection moulding and turning aluminum parts on a CNC lathe are really still the best options here, given current materials and manufacturing technology.

Again, Manfred, doesn't it boil down to cost? Single piece molded CF aero bicycle frames are extremely complex shapes and difficult to manufacture. But there is a market segment willing to pay for them so there they are. Early on CF bikes were simply CF tubes bonded into metal joints. But the market supported the development and higher cost of monoque (sp?) frames and now they are fairly common on high end bikes.