Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
06-03-2011, 06:02 AM   #31
Pentaxian
cmohr's Avatar

Join Date: Apr 2011
Location: Brisbane. Australia
Photos: Gallery | Albums
Posts: 1,091
QuoteOriginally posted by stanic Quote
ouch
Yes, back then I think the Aussie dollar was 67 US cents, Today Its a different story though, Aussies are buying up big from the US with the current exchange rate AU dollar is worth more than a US dollar.

06-03-2011, 06:12 AM   #32
Pentaxian
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 15,400
Oner of the things to remember, with respect to fast glass, is that many lens designs especially in the past, used spherical elements as these were all that could be easily designed and ground.

As a result, the faster the glass, the bigger in diameter, and the farther from ideal profile the lens gets. This is why, for example, all lenses get sharper when stopped down. you use the central portion only where the spherical element is approaching the ideal profile. Things like lateral CA (which leads to loss of sharpness) get much worse with bigger diameter elements. This can be corrected with today's aspherical lens designs.

Also, the bigger in diameter the thicker the lens gets, so that the difference in refraction of each wavelength gets more noticible. This is why LD glass was developed in part to allow for thicker elements, but also note that in the 80's and 90's Nikon for example started making their 50/1.8 using thinner elements (because it was possible) and this reduced the problems of refraction as well as making lenses lighter and cheaper..
06-03-2011, 06:52 AM   #33
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,795
QuoteOriginally posted by Lowell Goudge Quote
is that many lens designs especially in the past, used spherical elements as these were all that could be easily designed and ground.

good point. For example the Leica noctilux 50mm f/1.2 - released in the 1966 was an aspherical design, and was optically superior to the Canon 50mm f/0.95 which didn't use any aspheric lenses in it's design. Curiously In 1976 Leica produced the Leica Noctilux 50mm f/1.0 - which like earlier canon lens did not use Aspherics. It is only in recent history when Leica announced the Leica noctilux 50mm f/0.95 ASPH when the Leica community sighed with relief that Leica was again producing cutting - edge lens designs. though strangely the Leica noctilux 50mm f/1.0 is actually still in pretty high demand these days because of the Leica "glow" it produced which was nothing more than carefully controlled spherical abberation.

I personally prefer the "classic" 50mm f/1.0 for my work on the Leica M9. The new 50mm f/0.95 ASPH is basically just a faster lens than the summilux 50mm f/1.4 ASPH - at f/2.8 they both render things identically - I like the character the classic noctilux has.
06-04-2011, 08:07 AM   #34
Pentaxian
cmohr's Avatar

Join Date: Apr 2011
Location: Brisbane. Australia
Photos: Gallery | Albums
Posts: 1,091
Look what Pentax Used to make..A 400mm/F4 for the 6x7.





06-04-2011, 09:00 AM   #35
Inactive Account




Join Date: Dec 2008
Location: Ames, Iowa, USA
Photos: Albums
Posts: 2,965
As a first approximation long fast lenses should be really really cheap because as the focal length gets longer and longer the lens curvature gets flatter and flatter.

In the limit of infinite focal length the lens is a simple flat plate which can be very thin so contains no glass at all.

The cost devil is in the details
06-04-2011, 09:10 AM - 1 Like   #36
Loyal Site Supporter




Join Date: Apr 2010
Location: Tennessee
Posts: 5,795
QuoteOriginally posted by Digitalis Quote
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.
I have used the 85L for a long time. It is an excellent lens. The Pentax may very well be better and hopefully Pentax will start making a high grade 85mm again.

I am using the 85L as an example because it is a widely used lens that is still in production and it is faster than f/1.4.

The subject of this thread is about lens speed not a pissing match between camera brands.
06-04-2011, 09:21 AM   #37
Veteran Member




Join Date: Mar 2009
Location: Midwest
Photos: Gallery
Posts: 1,407
QuoteOriginally posted by cmohr Quote
Look what Pentax Used to make..A 400mm/F4 for the 6x7.
Believe me, I've thought about getting the adapter and picking one of those up. There's one on ebay right now with a Buy It Now price of ~$1300USD. I've seen them sell at auction for as little as $699 (for the black ones). I've also considered picking up a 6x7 body and an adapter, and then just collecting lenses when they sell for cheap on ebay. Saw a 150 f2.8 sell for $129 a couple of months ago.
06-04-2011, 09:41 AM   #38
Loyal Site Supporter




Join Date: Apr 2010
Location: Tennessee
Posts: 5,795
QuoteOriginally posted by bdery Quote
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.
The subject of the thread is about fast glass in general, not fast 200+mm lenses. Pentax has made f/1.2 glass in the past and they can make high quality f/1.2 glass in the future. Pentax needs to bring back modern versions of the 50mm f/1.2, 85mm f/1.4 (or faster) and the 135mm f/1.8. A 300mm f/2.8 and a 400mm f/4.

Since Pentax is now optimizing for a 50% smaller sensor it should be easier to design fast high quality glass. Hoya is one of the largest producers of optical glass in the world, and lens coatings and manufacturing technology has improved quite a bit since lenses like the A* 135mm f/1.8 were designed. I read an article on Sigma a couple years back where they talked about how far computer modeling had come and they could now run models of hundreds of lens designs before actually having to make a physical copy to test. This has brought Sigma's R&D costs way down and improved the quality of their lenses.

Other companies do make 200mm F/2 lenses. Canon made a 200mm F/1.8 which was a good lens at f/1.8 under the right lighting conditions. I have rented the 200mm f/2 for several events and it is an excellent lens.

Define what is "practical & economical". Is the Leica S2 practical or economical? Is the Pentax 645D practical & economical? What about a 60MP P-1 back? Is spending $1,000 for a 77mm f/1.8 practical or economical? If the 77mm f/1.8 can sell for $1,000 then so can a 50mm f/1.2 if it is of high enough quality.


Last edited by Winder; 06-04-2011 at 09:53 AM.
06-04-2011, 08:07 PM   #39
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,795
Three of the fastest pentax lenses I use these days. note that the front elements on all three of these lenses are very similar in size.

( I know the FA*85mm f/1.4 should be in there but I prefer the smaller FA77 f/1.8)

Last edited by Digitalis; 01-28-2015 at 12:36 AM.
06-06-2011, 05:22 AM - 1 Like   #40
Pentaxian
bdery's Avatar

Join Date: Mar 2008
Location: Quebec city, Canada
Photos: Gallery
Posts: 5,830
Winder, I may be reading you wrong but you seem almost angry in your posts. I sure hope you're not. I'm sharing what I know about lens design, you're free to believe me or not, I can only give you my credentials and share the knowledge and experience I do have.

QuoteOriginally posted by Winder Quote
Since Pentax is now optimizing for a 50% smaller sensor it should be easier to design fast high quality glass. Hoya is one of the largest producers of optical glass in the world, and lens coatings and manufacturing technology has improved quite a bit since lenses like the A* 135mm f/1.8 were designed. I read an article on Sigma a couple years back where they talked about how far computer modeling had come and they could now run models of hundreds of lens designs before actually having to make a physical copy to test. This has brought Sigma's R&D costs way down and improved the quality of their lenses.
a smaller sensor allows for a smaller lens (better price) but not an easier design. There are little fundamental differences between designing a full frame or an APS-C lens.

Hoya is one of the biggest manufacturers of glass in the world, I have ordered from them and designed with their glass in the past. But thinking it can have any significant impact on how Pentax design their lenses is mostly wrong. There is about a dozen of major glass manufacturers in the world, each with their catalog of glass with different properties. When designing a lens, you look up the glass with the properties you want, and include it in your design, whatever manufacturer offers it. If Pentax limited themselves to Hoya, they would be unable to work, essentially.

Lens coatings improve transmission, but do nothing to reduce aberrations.

Computer design of optical elements is something I do everyday in my job. It has been around for some time... the first version of the Vivitar 70-210 was computer designed. You can even dab your hands at it by downloading the educational (free) version of OSLO, one of the most advanced lens design tools. The 450 pages manual is in fact an introduction class to optical design.

the process of designing a lens, nowadays, is like this:

1-look up existing designs (you can purchase CDs with 10 000 designs on them, look up any optical science magazines).

2-find the design closest to what you want to do

3-adapt its specifications (focal length, aperture, etc)

4-look at the aberrations involved, start to swear

5-play with the values, glass types, thicknesses, and so forth, until you find balance.

The art of optical design is all comprised in that fith step.

QuoteOriginally posted by Winder Quote
Define what is "practical & economical". Is the Leica S2 practical or economical? Is the Pentax 645D practical & economical? What about a 60MP P-1 back? Is spending $1,000 for a 77mm f/1.8 practical or economical? If the 77mm f/1.8 can sell for $1,000 then so can a 50mm f/1.2 if it is of high enough quality.
For the record, the 645D is a 10k camera competing with 40k cameras, so yeah, it's economical.

We are now exiting optics territory and entering marketing/sales territories. I am not trained in those fields. I will use my logic, such as it is, and propose that with all the talent we know is available at Pentax, if a lens such as a 200mm f1.8 WAS a good and profitable move, it would have been done already.
06-06-2011, 07:31 AM   #41
Pentaxian
Digitalis's Avatar

Join Date: Mar 2009
Location: Adelaide.
Posts: 8,795
QuoteOriginally posted by Winder Quote
Since Pentax is now optimizing for a 50% smaller sensor it should be easier to design fast high quality glass.
I think you are forgetting that they are still using exactly the same lens mount and flange distance as they have been using for to past 50+ years. The reason why Leica M cameras are able to have such fast lenses designed for them is because their short flange distance - which is 27.80mm the pentax flange is 45.46mm - almost twice that of the leica.
06-06-2011, 08:12 AM   #42
Loyal Site Supporter




Join Date: Apr 2010
Location: Tennessee
Posts: 5,795
QuoteOriginally posted by bdery Quote
Winder, I may be reading you wrong but you seem almost angry in your posts. I sure hope you're not. I'm sharing what I know about lens design, you're free to believe me or not, I can only give you my credentials and share the knowledge and experience I do have.



a smaller sensor allows for a smaller lens (better price) but not an easier design. There are little fundamental differences between designing a full frame or an APS-C lens.

Hoya is one of the biggest manufacturers of glass in the world, I have ordered from them and designed with their glass in the past. But thinking it can have any significant impact on how Pentax design their lenses is mostly wrong. There is about a dozen of major glass manufacturers in the world, each with their catalog of glass with different properties. When designing a lens, you look up the glass with the properties you want, and include it in your design, whatever manufacturer offers it. If Pentax limited themselves to Hoya, they would be unable to work, essentially.

Lens coatings improve transmission, but do nothing to reduce aberrations.

Computer design of optical elements is something I do everyday in my job. It has been around for some time... the first version of the Vivitar 70-210 was computer designed. You can even dab your hands at it by downloading the educational (free) version of OSLO, one of the most advanced lens design tools. The 450 pages manual is in fact an introduction class to optical design.

the process of designing a lens, nowadays, is like this:

1-look up existing designs (you can purchase CDs with 10 000 designs on them, look up any optical science magazines).

2-find the design closest to what you want to do

3-adapt its specifications (focal length, aperture, etc)

4-look at the aberrations involved, start to swear

5-play with the values, glass types, thicknesses, and so forth, until you find balance.

The art of optical design is all comprised in that fith step.



For the record, the 645D is a 10k camera competing with 40k cameras, so yeah, it's economical.

We are now exiting optics territory and entering marketing/sales territories. I am not trained in those fields. I will use my logic, such as it is, and propose that with all the talent we know is available at Pentax, if a lens such as a 200mm f1.8 WAS a good and profitable move, it would have been done already.
I'm not angry. Companies have been making fast glass for years. I realize it is a challenge, but Pentax has done it in the past. Other companies have done it. Sony has a patent on a new 50mm F/1.2.

The 200mm f/1.8 is not practical for Pentax because they don't have the user base and they don't have the AF that the people who buy that type of lens would demand.

Olympus 150mm f/2 (excellent lens)
Sony CZ 135mm f/1.8 (excellent lens)
Canon 85mm f/1.2 (excellent lens)
Nikon 24mm f/1.4 (never used)
There is a long list of really good fast glass.

Pentax only has one lens that is f/1.4. Samyang makes more fast glass than Pentax. If Pentax is going to focus on APS-C then they need to offer glass that is optimized for APS-C (faster and sharper).

Pentax users already pay a premium for glass. The Pentax 55mm is the most expensive lens in its class. The 50-135mm and 16-50mm can all be bought from Tokina for less money. Pentax charges extra for the luxury of SDM.....

Pentax is already making limited runs of glass for the 31mm, 43mm, & 77mm. They could do the same for an 85mm & 135mm.
06-06-2011, 08:19 AM   #43
Inactive Account




Join Date: Dec 2008
Location: Ames, Iowa, USA
Photos: Albums
Posts: 2,965
QuoteOriginally posted by Digitalis Quote
I.... The reason why Leica M cameras are able to have such fast lenses designed for them is because their short flange distance - which is 27.80mm the pentax flange is 45.46mm - almost twice that of the leica.
Doesn't the short registry distance give rise to image circle problems? I guess the answer is likely no for long focal lengths but why then does the shorter registry distance matter?
06-06-2011, 09:56 AM   #44
Pentaxian
bdery's Avatar

Join Date: Mar 2008
Location: Quebec city, Canada
Photos: Gallery
Posts: 5,830
QuoteOriginally posted by Winder Quote
entax only has one lens that is f/1.4. Samyang makes more fast glass than Pentax. If Pentax is going to focus on APS-C then they need to offer glass that is optimized for APS-C (faster and sharper).

Pentax users already pay a premium for glass. The Pentax 55mm is the most expensive lens in its class. The 50-135mm and 16-50mm can all be bought from Tokina for less money. Pentax charges extra for the luxury of SDM.....

Pentax is already making limited runs of glass for the 31mm, 43mm, & 77mm. They could do the same for an 85mm & 135mm.
Now your talking again of marketing strategies, and apparently expressing disappointment with Pentax. We're not talking about lens design anymore, but about market development strategies.
06-06-2011, 10:28 AM   #45
Loyal Site Supporter




Join Date: Apr 2010
Location: Tennessee
Posts: 5,795
QuoteOriginally posted by newarts Quote
Doesn't the short registry distance give rise to image circle problems? I guess the answer is likely no for long focal lengths but why then does the shorter registry distance matter?
It depends on the lens design. If I am not mistaken the shorter distance meas that light is striking the edge of the sensor at a sharper angle and this causes several different problems for digital sensor (soft edges and vignetting). Olympus uses a telecentric lens design but that adds to the size of the glass. You want the light to strike the sensor at a 90 degree angle. This is one reason Olympus glass is sharp from edge to edge, but is just as large as the FF equivalent glass. This is also why Olympus ZD glass is so expensive.

Four Thirds | Four Thirds | Standard
Telecentric Lens Systems

The center of the image circle is always at 90 degrees so that will be the sharpest (in a perfect world). As you move away from center the the angle at which light is striking the sensor changes and distortion starts to occur. Smaller sensors only use the center part of the image circle so they show less distortion and vignetting edge to edge.
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 11:26 AM. | See also: NikonForums.com, CanonForums.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