Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
06-02-2011, 03:36 AM   #16
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,525
QuoteOriginally posted by cmohr Quote
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.

06-02-2011, 03:48 AM   #17
Senior Member
Kim C's Avatar

Join Date: Dec 2006
Location: Lincoln, UK
Photos: Gallery
Posts: 229
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

QuoteOriginally posted by Digitalis Quote
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.

Last edited by Kim C; 06-02-2011 at 05:13 AM.
06-02-2011, 05:09 AM   #18
Pentaxian
bdery's Avatar

Join Date: Mar 2008
Location: Quebec city, Canada
Photos: Gallery
Posts: 5,650
QuoteOriginally posted by Chaos_Realm Quote
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.

QuoteOriginally posted by Chaos_Realm Quote
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...

Last edited by bdery; 06-02-2011 at 06:57 AM.
06-02-2011, 05:16 AM   #19
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,525
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

06-02-2011, 06:22 AM   #20
Veteran Member




Join Date: Mar 2009
Location: Midwest
Photos: Gallery
Posts: 1,407
QuoteOriginally posted by bdery Quote
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)
06-02-2011, 07:02 AM   #21
Pentaxian
bdery's Avatar

Join Date: Mar 2008
Location: Quebec city, Canada
Photos: Gallery
Posts: 5,650
QuoteOriginally posted by jstevewhite Quote
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?
06-02-2011, 07:27 AM   #22
Veteran Member




Join Date: Mar 2009
Location: Midwest
Photos: Gallery
Posts: 1,407
QuoteOriginally posted by bdery Quote
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!
06-02-2011, 07:44 AM - 1 Like   #23
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,312
QuoteOriginally posted by Chaos_Realm Quote
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.

06-02-2011, 04:54 PM   #24
Pentaxian
cmohr's Avatar

Join Date: Apr 2011
Location: Brisbane. Australia
Photos: Gallery | Albums
Posts: 1,085
QuoteOriginally posted by stanic Quote
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.
06-02-2011, 06:24 PM   #25
Loyal Site Supporter




Join Date: Apr 2010
Location: Tennessee
Posts: 5,412
QuoteOriginally posted by bdery Quote
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.
QuoteOriginally posted by bdery Quote
-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
QuoteOriginally posted by bdery Quote
-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
QuoteOriginally posted by bdery Quote
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.

Last edited by Winder; 06-02-2011 at 06:30 PM.
06-02-2011, 08:12 PM   #26
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
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...]
06-02-2011, 09:06 PM   #27
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,525
QuoteOriginally posted by Winder Quote
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.
06-02-2011, 10:35 PM   #28
Veteran Member
stanic's Avatar

Join Date: Aug 2010
Location: PB
Photos: Gallery | Albums
Posts: 380
QuoteOriginally posted by cmohr Quote
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
06-03-2011, 05:10 AM   #29
Pentaxian
bdery's Avatar

Join Date: Mar 2008
Location: Quebec city, Canada
Photos: Gallery
Posts: 5,650
QuoteOriginally posted by Winder Quote
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.
06-03-2011, 05:56 AM - 1 Like   #30
Pentaxian
8540tomg's Avatar

Join Date: Feb 2008
Location: Waterloo, Ontario
Photos: Gallery
Posts: 4,444
Pentax 300/2

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

Last edited by 8540tomg; 06-03-2011 at 06:04 AM.
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
200mm, ad, aperture, design, k-mount, lens, max, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
DA 55-300 Max Aperture? L33tGreg Pentax SLR Lens Discussion 3 03-22-2011 08:34 AM
Max Aperture f1 Squier Pentax DSLR Discussion 13 10-14-2010 01:37 PM
Theory/Engineering question on lens max aperture Michael Barker Photographic Technique 9 07-26-2010 07:45 PM
Confused: Adaptall Pk/A Adapter Max. Aperture Issue pbo Pentax SLR Lens Discussion 13 09-15-2009 08:43 PM
Aperture Limitations In Manual Mode? jshurak Pentax DSLR Discussion 6 07-26-2007 01:25 PM



All times are GMT -7. The time now is 11:50 PM. | See also: NikonForums.com, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top