Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
01-20-2011, 07:13 AM   #16
Site Supporter
GeneV's Avatar

Join Date: Oct 2008
Location: Albuquerque NM
Photos: Albums
Posts: 9,775
QuoteOriginally posted by Spock Quote
Given that APS-sized sensors are smaller than FF, and a 30mm lens in APS gives a similar field of view as a 50mm in FF, shouldn't it be possible to build a 30mm F1.4 or F1.2 that is no bigger than an old fast fifty? If not, why not?
I'd add to what Rico said that whether it is possible to build such a lens is a different question from whether it is possible to build, market and sell it at a profit.

01-20-2011, 10:12 AM   #17
Veteran Member
RioRico's Avatar

Join Date: Jun 2008
Location: Limbo, California
Posts: 11,264
QuoteOriginally posted by GeneV Quote
I'd add to what Rico said that whether it is possible to build such a lens is a different question from whether it is possible to build, market and sell it at a profit.
And there we get to the question of just what a target audience (prospective buyers) would want or do with something WIDE and FAST. Mid-range is something else, and a 30/1.4 is mighty damn tempting from a low-light perspective, but it bumps against the DOF issue. Y'see, part of what makes ultra-Fast Fiftys (f/1.2, f/0.95, etc) exciting is ultra-thin DOF. The DOF of a 30/1.4 is only slightly thinner than a 55/2.8, and is rather thicker than a 58/2 like the cheap Helios-44. Note that the DOF of a 50/1.2 is slightly thinner a 55/1.4, and slightly thicker than an 85/2.

[You may ask: How d'ya knoiw that DOF stuff? And my answer is, the comparative DOF index: Divide the focal length by the maximum aperture; higher quotients mean thinner DOF. Y'all can build your own spreadsheet to compute this.]

Anyway, a shorter lens means thicker DOF, and that's just how optics works. If a large chunk of a target audience wants thin DOF as well as low-light performance, they WON'T be in the market for that wide fast lens. Would a 15/2 or 14/1.4 be tricky to use? A dSLR version would certainly be huge and costly. So, how many buyers will fork-out US$5K+ for such a monster? I'll guess that the bean-counters at the glass foundries have figured it's not enough, else we'd see some around.
01-20-2011, 10:41 AM   #18
Site Supporter




Join Date: Nov 2008
Location: Minneapolis
Photos: Albums
Posts: 588
To the OP: suggest you frame a number of shots at 28 and 35mm. If 35 is wide enough, consider the 35 F2.4 or 35 F2.8 Macro.

I'd particularly recommend the DA 35 F2.8 Macro. If you're out there fly fishing and whatnot, the macro capability will be fantastic. No, it's not alot faster, but it is much more capable.

I have the A 28 F2.8 as well, but use it more often on a film camera.
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!
da, f1.4, f2.8, k-7, k-mount, lens, light, pentax lens, pentax-a 28mm f/2.8, slr lens, smc pentax-a 28mm
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Travel Lens Final Decision : Pentax 17-70 SDM Vs Sigma 18-250 HSM Christopher M.W.T Pentax SLR Lens Discussion 34 02-22-2010 10:54 AM
Good complement to 18-55mm kit lens? jonathan1984 Pentax SLR Lens Discussion 22 12-14-2009 07:05 PM
Travel Kit Help shiestmiester Pentax Camera and Field Accessories 1 02-27-2009 01:39 AM
Pentax Travel Kit: cny3123 Pentax DSLR Discussion 33 10-27-2008 12:49 PM



All times are GMT -7. The time now is 02:15 PM. | 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