Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
07-22-2021, 05:26 PM   #31
Site Supporter
Site Supporter
RobA_Oz's Avatar

Join Date: Nov 2008
Location: Tasmania, Australia
Photos: Gallery
Posts: 8,182
QuoteOriginally posted by house Quote
I've done some more lazy googling and found Hoya patents for anomalous partial dispersion glass recipes dating back to the early seventies. As well as lots of recent info from Schott, Leitz etc. So its most certainly a (actually many different, a whole category) type of material that is different from other optical speciality formulations.
Although it’s unlikely, the Pentax version may have substituted a different glass for the one element identified differently, but (from what I gather about anomalous dispersion glass having a different property near the UV end) its dispersion and refractive index in the visible region would have to be close to the Tamron original.

As I said, though, I don’t regard it as likely.

07-23-2021, 03:55 AM   #32
Site Supporter
Site Supporter
Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
Photos: Gallery | Albums
Posts: 17,869
Everyone needs to step back and recall that many manufacturers share design aspects etc.

The K28mm F2.0 is actually a Zeiss optical design and Pentax and tamron have in the past have codeveloped lenses

Why is anyone surprised about a similar optical design.

The differences can be coatings, weather sealing and build quality. And these can be important
07-23-2021, 04:12 AM   #33
Pentaxian




Join Date: May 2015
Photos: Albums
Posts: 3,304
Original Poster
QuoteOriginally posted by Lowell Goudge Quote
Everyone needs to step back and recall that many manufacturers share design aspects etc.

The K28mm F2.0 is actually a Zeiss optical design and Pentax and tamron have in the past have codeveloped lenses

Why is anyone surprised about a similar optical design.

The differences can be coatings, weather sealing and build quality. And these can be important
The assumption since release has been that the lenses are identical.

I'm showing that they describe the optical design differently opening up for the (unlikely) possibility that Pentax actually sells one that has been tweaked with anomalous partial dispersion glass and other minor differences in glass types whilst maintaining the general optical design.

If they are identical its curious and something to be critical about that they describe the lenses so differently. Its also interesting to know whether Pentax is lying about materials or Tamrons is underselling their optics.

Last edited by house; 07-23-2021 at 04:20 AM.
07-23-2021, 05:20 AM   #34
Pentaxian
bdery's Avatar

Join Date: Mar 2008
Location: Quebec city, Canada
Photos: Gallery
Posts: 9,352
QuoteOriginally posted by RobA_Oz Quote
Although it’s unlikely, the Pentax version may have substituted a different glass for the one element identified differently, but (from what I gather about anomalous dispersion glass having a different property near the UV end) its dispersion and refractive index in the visible region would have to be close to the Tamron original.
Changing a class element would mean modifying the whole optical design, to smaller or larger extents. One cannot simply change a component, the elements are interdependent.

07-23-2021, 06:52 AM   #35
Site Supporter
Site Supporter
RobA_Oz's Avatar

Join Date: Nov 2008
Location: Tasmania, Australia
Photos: Gallery
Posts: 8,182
QuoteOriginally posted by bdery Quote
Changing a class element would mean modifying the whole optical design, to smaller or larger extents. One cannot simply change a component, the elements are interdependent.
Yes, I understand that. If you look at what I said, it boils down to replacing a glass with another that has essentially identical properties in the part of the spectrum the lens is designed for. I think I should just leave it at that.
07-23-2021, 07:09 AM   #36
Pentaxian




Join Date: Apr 2007
Location: Romania
Posts: 15,132
QuoteOriginally posted by bdery Quote
Changing a class element would mean modifying the whole optical design, to smaller or larger extents. One cannot simply change a component, the elements are interdependent.
How about two or more components?
07-23-2021, 08:41 AM   #37
Pentaxian




Join Date: May 2015
Photos: Albums
Posts: 3,304
Original Poster
Yeah those "xr" elements near the front arent labelled as anything special in the Pentax. Xr may be a marketing name though.

Didnt pentax do one of their ancient uwas in two versions one with special glass but otherwise the same formula? Asph?

07-24-2021, 11:26 AM   #38
Pentaxian




Join Date: May 2015
Photos: Albums
Posts: 3,304
Original Poster
Came across the Voigtländer APO-LANTHAR 50mm F2.0 which seems to be one of the most "perfect" lenses out there at the moment. Had a look at it's optical diagram...


I've not seen anything like that before. No wonder it's performing ok 5 elements are partial dispersion glass!

The dfa*50 has 3 but just one asph might make for a better bokeh.
08-06-2021, 06:02 AM   #39
Pentaxian
bdery's Avatar

Join Date: Mar 2008
Location: Quebec city, Canada
Photos: Gallery
Posts: 9,352
QuoteOriginally posted by Kunzite Quote
How about two or more components?
Sorry for the late reply, I was in vacation.

1, 2, 4 or more elements, the same reasoning applies. Finding different glass formulas with the same optical properties doesn't really make sense, they would be the same glass.
08-06-2021, 06:10 AM   #40
Pentaxian




Join Date: Apr 2007
Location: Romania
Posts: 15,132
QuoteOriginally posted by bdery Quote
Sorry for the late reply, I was in vacation.

1, 2, 4 or more elements, the same reasoning applies. Finding different glass formulas with the same optical properties doesn't really make sense, they would be the same glass.
I'm talking about changing the properties of one or several elements being compensating through changing the properties of another or several other elements to roughly get the "same" optical design.
08-06-2021, 09:03 AM   #41
Pentaxian




Join Date: May 2015
Photos: Albums
Posts: 3,304
Original Poster
Figured out the old uwa I was talking about. The 15mm f3.5 was first made with an asph.

Version 1 (asph)


Version 2
08-07-2021, 03:24 AM   #42
Pentaxian




Join Date: May 2015
Photos: Albums
Posts: 3,304
Original Poster
Bumped into another one but I information is contradictory about whether the design is different or not.

Zeiss 35mm f2 classic vs Milvus




https://www.zeiss.com/consumer-products/int/photography/milvus/milvus-235.html

The purplish element is made of anomalous dispersion glass in the milvus version. Some suggest its "normal " glass in the classic version.

Last edited by house; 08-07-2021 at 12:44 PM.
08-07-2021, 12:54 PM   #43
Pentaxian




Join Date: May 2015
Photos: Albums
Posts: 3,304
Original Poster
This page suggests they both have anomalous dispersion glass
Carl Zeiss Classic Distagon T* 35mm F/2 ZE / ZF / ZF.2 / ZK / ZS
ZEISS Milvus Distagon T* 35mm F/2 ZE / ZF.2

Scroll down to "Lens construction" in the table to see AD glass listed in both versions.
08-07-2021, 01:11 PM   #44
Pentaxian




Join Date: May 2015
Photos: Gallery
Posts: 1,930
QuoteOriginally posted by house Quote
The assumption since release has been that the lenses are identical.



I'm showing that they describe the optical design differently opening up for the (unlikely) possibility that Pentax actually sells one that has been tweaked with anomalous partial dispersion glass and other minor differences in glass types whilst maintaining the general optical design.



If they are identical its curious and something to be critical about that they describe the lenses so differently. Its also interesting to know whether Pentax is lying about materials or Tamrons is underselling their optics.
There was another relatively recent thread where a similar discrepancy between a Pentax lens and the HD equivalent I think. It turned out two drawings existed for one of the lenses, one labelled "Anomalous Dispersion" glass and the other labelled "Extraordinary low dispersion" glass for the same element.

09-17-2021, 08:07 PM   #45
dbs
Pentaxian




Join Date: Jun 2010
Location: Clare Valley S A
Photos: Albums
Posts: 7,558
No different than a bonnet or hood on a car ..... they are the same thing ... right
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!
diagrams, dispersion, glass, k-mount, lenses, pentax, pentax lens, pentax vs tamron, post, slr lens, tamron
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Spotmatic F circuit diagrams brint c Maintenance and Repair Articles 4 06-15-2021 02:04 PM
Lens Construction Diagrams Sought bclaff Pentax SLR Lens Discussion 8 06-30-2020 09:29 AM
K-5 vs MZ-S vs LX vs PZ-1p vs ist*D vs K10D vs K20D vs K-7 vs....... Steelski Pentax K-5 & K-5 II 2 06-28-2017 04:59 PM
Optical IS (in lens) vs optical SR (body sensor shift) vs DS (pixel tracking) rburgoss Canon, Nikon, Sony, and Other Camera Brands 10 10-20-2014 07:07 PM



All times are GMT -7. The time now is 12:25 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