[Digitalis]

Canon also had a 50mm/F1.0 I believe.

The Canon lens got it's rear element handed to it by the Leica Noctilux-M 50mm f/1.0 - and now Leica have the Noctilux-M 50mm f/0.95 ASPH

I own a canon EF 200mm f/1.8L and yes it is very very good for sports, but lately I have been using my Nikkor AF-S 200mm f/2 VR on my D3s - the Nikkor being optically perfect to my eyes, The canon 200mm f/1.8L has some pretty nasty purple fringing at large apertures.

[Kim C]

Cosina now do a 50/1.1 and the 35/1.2 is due out soon.

If you need the speed then all of these superfast lenses are almost essential. However, I do feel that there is a trade off. Not only are they expensive but also difficult to design and make.

There is nothing else that can perform like them wide open but once they are stopped down to even a moderate aperture, there are many lenses out there which some perceive as giving better results.

Kim

The Canon lens got it's rear element handed to it by the Leica Noctilux-M 50mm f/1.0 - and now Leica have the Noctilux-M 50mm f/0.95 ASPH

I own a canon EF 200mm f/1.8L and yes it is very very good for sports, but lately I have been using my Nikkor AF-S 200mm f/2 VR on my D3s - the Nikkor being optically perfect to my eyes, The canon 200mm f/1.8L has some pretty nasty purple fringing at large apertures.

[bdery]

I understand that that Aperture is = (FL/AD) where FL = Focal length and AD = Aperture diameter.

I'm stepping it late, but I'm an optical designer so I'll help.

The aperture diameter you refer to is not the diameter of the front element of the lens, it is the MINIMUM aperture in the optical path (more accurately named the aperture stop). Usually, but not always, that's the iris.

Why can't they design a 200mm F/1.8 or faster? which would have AD=111.11mm. Is it that the lens barrel would be to large, and thus the front element being HUGE?.

Is it just not cost effective to do so or is there physical design restraints?

Any light that could be shed on the subject to calm my curiosity would be great

You can design anything. The constraints in your particular case are:

-cost : such a lens would be very expensive if only because of the amount of glass used, so there might not be a good market case

-size : it would need to be huge, bordering on the unusable for many, again working against the business case

-design cost and compromises : it would cost a lot of money to design and develop such a lens. There would be many optical compromises necessary, and it would probably NOT be amazing optically, especially in the corners. Aberrations would probably be quite ugly wide open. You would need to employ, among other things, lots of exotic (expensive) glass to mitigate that, increasing the cost even more

There are other challenges involved, these are the main ones. Starting with a slower lens design, I could make you a 200mm f1,8 lens in half an hour. To make a GOOD lens would take me a lot of time, and I'm not sure I could do it (photographic lens design is not my particular specialization).

Edit : added the "not" in bold. I meant the opposite of what I wrote...

[Digitalis]

there are also lens mount constraints to take into consideration -E.g: Canon changed over from the FD to the EF mount which can support a 50mm f/1.0 lens, the FD mount was maxed out at 50mm f/1.2

[jstevewhite]

I'm stepping it late, but I'm an optical designer so I'll help.

Interesting information... Can I ask you another question, not specifically related to aperture, but...

How closely related to photographic/optical coatings are the anti-reflective coatings my optometrist puts on my daughter's glasses? And would there be any benefit to getting an old lens' elements coated like that?

(just a curiosity I've always had)

[bdery]

How closely related to photographic/optical coatings are the anti-reflective coatings my optometrist puts on my daughter's glasses? And would there be any benefit to getting an old lens' elements coated like that?

They basically serve the same purpose : lower reflections and improve light transmission.

Getting a lens coated the same way glasses are coated would probably be impossible without disassembling the lens, because of the way glasses coatings are applied.

In addition, those coatings would not work very well in most cases. Coatings need to be matched to the glass on which they are applied, there's no "one-coating-fits-all" process, sadly. In addition, the human eye and a CCD/CMOS sensor do not gather light exactly the same way, so the coatings need to take this into account too.

coatings for glasses are quite resistant, but also quite simple optically. coatings for photographic lenses are more complex to design and manufacture.

Does that help?

[jstevewhite]

They basically serve the same purpose : lower reflections and improve light transmission.

Getting a lens coated the same way glasses are coated would probably be impossible without disassembling the lens, because of the way glasses coatings are applied.

In addition, those coatings would not work very well in most cases. Coatings need to be matched to the glass on which they are applied, there's no "one-coating-fits-all" process, sadly. In addition, the human eye and a CCD/CMOS sensor do not gather light exactly the same way, so the coatings need to take this into account too.

coatings for glasses are quite resistant, but also quite simple optically. coatings for photographic lenses are more complex to design and manufacture.

Does that help?

Absolutely, thanks. Disassembly is no issue, but it sounds like it wouldn't be particularly beneficial. I was just curious. Thanks for taking the time!

[Lowell Goudge]

Hi guys,
I have question regarding the design restraints on max aperture of a lens. I am pretty ignorant in respect to the physics behind it so please bear with me.
I understand that that Aperture is = (FL/AD) where FL = Focal length and AD = Aperture diameter. But the reason I ask is Nikon Produce a 800mm F/5.6 thus has a AD = 142.85mm yet the fastest 200mm lens I have seen is the 200mm F/2.8 giving AD = 71.4mm.

Why can't they design a 200mm F/1.8 or faster? which would have AD=111.11mm. Is it that the lens barrel would be to large, and thus the front element being HUGE?.

Is it just not cost effective to do so or is there physical design restraints?

Any light that could be shed on the subject to calm my curiosity would be great

they can, but if you consider your AD of 111.11 mm, it is not the lens barrel that limits the aperture, but the lens diameter that drives the barrel.

and yes it is because of the size and cost of the front element.

the aperture is placed in the light path where it is convenient to constrict the light further from the wide open case, and is also put in a place where the size of the actual diaphram can be reduced to an economical and practical size for fast response.

[cmohr]

that is quite a difference...maybe also dependant on calibration of exposure system if he was using multi-segment metering
I`d also say that such expensive lens gets better element coating with higher than average transparency (no proof though)

Haha, yeah I'm ready to concede the metering system in an EOS-1n may have been better than my old "dunked in a river a few times" MZ-5..

I remember spending a small forture way back then on the FA 200/2.8. Here in Australia back then Pentax FA lenses cost two arms and two legs, plus first born. I got a fairly good price for the time. List prices were $3300.00AU and my 85/1.4 was something like 1800.00AU.

[Winder]

You can design anything. The constraints in your particular case are:

-cost : such a lens would be very expensive if only because of the amount of glass used, so there might not be a good market case

No more expensive than the Canon 85mm f/1.2.

-size : it would need to be huge, bordering on the unusable for many, again working against the business case

No larger than the Canon 85mm F/1.2

-design cost and compromises : it would cost a lot of money to design and develop such a lens. There would be many optical compromises necessary, and it would probably NOT be amazing optically, especially in the corners. Aberrations would probably be quite ugly wide open. You would need to employ, among other things, lots of exotic (expensive) glass to mitigate that, increasing the cost even more

No more optically amazing than the Canon 85mm f/1.2

There are other challenges involved, these are the main ones. Starting with a slower lens design, I could make you a 200mm f1,8 lens in half an hour. To make a GOOD lens would take me a lot of time, and I'm not sure I could do it (photographic lens design is not my particular specialization).

Edit : added the "not" in bold. I meant the opposite of what I wrote...

Pentax has made f/1.2 glass in the past and it was very good. The 50mm f/1.2 was an excellent lens. Making a high quality lens like an 85mm f/1.2 that is optimized for APS-C is easier than making the same lens that is optimized for 36x24mm sensors. Pentax could make a DA* 85mm f/1.2 that is every bit as good or better than the 85L since they are working with a smaller image circle.

Your post reads like it is next to impossible to make high quality fast glass, but it has been done in the past and is currently being done by other manufacturers for larger & more demanding sensors.

[RioRico]

It is very easy to build very fast lenses very cheaply. Merely stack some +dioptre close-up adapters onto a focusing helicoid. However, being simple uncorrected meniscus lenses, the IQ will totally suck. Don't try this at home, kids.

[/me considers such a frankenlens, and shudders...]

[Digitalis]

No more optically amazing than the Canon 85mm f/1.2

the canon 85mm f/1.2 gets it's rear element handed to it by the pentax FA*85mm f/1.4 - so if I were you I would stop using the Canon 85mm f/1.2L lens a some shining example of goodness. I use a Leica 80mm f/1.4 on my canon FF bodies because the Leica lens doesn't have the awful focus by wire mechanism that the Canon 85L does- and the Leica lens has better aberration control.

[stanic]

I got a fairly good price for the time. List prices were $3300.00AU and my 85/1.4 was something like 1800.00AU.

ouch

[bdery]

Pentax has made f/1.2 glass in the past and it was very good. The 50mm f/1.2 was an excellent lens. Making a high quality lens like an 85mm f/1.2 that is optimized for APS-C is easier than making the same lens that is optimized for 36x24mm sensors. Pentax could make a DA* 85mm f/1.2 that is every bit as good or better than the 85L since they are working with a smaller image circle.

Your post reads like it is next to impossible to make high quality fast glass, but it has been done in the past and is currently being done by other manufacturers for larger & more demanding sensors.

There is a world of difference between designing a 85mm f1,2 and a 200mm f2. Try it

Next to impossible, absolutely not. I even said I could try it, even though that's not my particular specialty. Practically and economically however, it's a different matter. If making a 200 f2 lens was a simple and marketable tool, other companies would do it before Pentax.

[8540tomg]

Nikon had $29,000 300/2 a few years ago. Not surprisingly it didn’t sell all that well and was discontinued. Pentax also had a 300/2 prototype in the late 70’s. It is referred to towards the end of the attachment.

Nikon F 300/2

Evidently this Pentax 300/2 monster never made it into production. This was back in the days when Pentax was still something of a leader in SLR photography.

Tom G