Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
09-10-2015, 04:36 PM   #31
Veteran Member




Join Date: Jun 2008
Location: Flyover America
Posts: 4,475
QuoteOriginally posted by quant2325 Quote
the amount of light that is collected by a particular lens is proportional to the surface area of the aperture.
Correct.

QuoteOriginally posted by quant2325 Quote
I hope I have the above right. If not, someone correct me and I'll edit my comments.
Your numbers are for the clear aperture of the lens so your numbers reflect the linear diameter of the lens in mm not the surface area of the lens in sq mm.
Given that, doubling the diameter increases the area 4x (from 1964 mm sq to 7854 mm sq) thus really increasing the weight and bulk of the complete lens assembly.
You pay a lot for a fast lens and it isn't just in cost.

Your overall point is well taken.

09-14-2015, 08:01 PM   #32
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 32,712
QuoteOriginally posted by bassek Quote
More pixels result in smaller pixels that require more light.
Those darned smaller pixels!

QuoteOriginally posted by Rondec Quote
I think a lot of folks shoot faster apertures to achieve shallow depth of field and not because they are pushing the extremes on iso.
No way!

QuoteOriginally posted by bassek Quote
I fully agree with you.
Well...I guess there might be something to it.


Steve
09-14-2015, 08:05 PM   #33
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 32,712
QuoteOriginally posted by Pål Jensen Quote
I'm sure folks will be shocked by the size and weight of the coming D-FA* 24-70/2.8.
I expect it will make the new FF look like petite. If they had shrunk the range by a few millimeters (28-70/2.8), much of that pain might have been averted.


Steve
09-14-2015, 08:19 PM   #34
Otis Memorial Pentaxian
Loyal Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 32,712
QuoteOriginally posted by quant2325 Quote
Lenses have to be bigger if they are faster since the amount of light that is collected by a particular lens is proportional to the surface area of the aperture.
Uh, huh...actually, it is the diameter of the entrance pupil, but close enough, I fancy. For a 50mm lens, that is only 25mm to make f/2.0. I have a couple of very petite 50mm f/2 FF lenses with a barrel diameter of only about 45mm and an overall length about the same. Both are very well corrected and quite sharp too. That being said, they were made for use of 35mm rangefinder film cameras.

I am not saying that maximum aperture is not a factor. It is, but it is not the entrance pupil size that is driving the increase in size, nor is it those pesky tiny pixels. The huge front elements have more to do with allowing a mirror box that is deeper than the lens focal length and while also providing a decent sized entrance pupil while providing flat field and excellent optical correction.


Steve

(...has a 28/2.5 that is three times the volume of the FA 77/1.8 Limited and which takes a 77mm filter. The FA 77 takes a 49mm filter...go figure...)


Last edited by stevebrot; 09-14-2015 at 08:27 PM.
09-15-2015, 03:54 AM   #35
Loyal Site Supporter
Loyal Site Supporter




Join Date: Mar 2015
Photos: Gallery | Albums
Posts: 6,294
QuoteOriginally posted by stevebrot Quote
I have a couple of very petite 50mm f/2 FF lenses with a barrel diameter of only about 45mm and an overall length about the same. Both are very well corrected and quite sharp too. That being said, they were made for use of 35mm rangefinder film cameras.
The original mirrorless ILC!!!

All of this probably explains why there was never a 50mm f/1.2 lens in the Pentax-M series. Even the 1.4 looks like it barely fits within the casing dimensions. Plus the 1.2 K was probably still in series production back then, and anyone who really needed the extra half-stop (and was willing to pay for it) could easily have got one. Not worth the pain and cost for the engineers and designers at Asahi to try to cram all that into an M-sized package.
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!
camera, cameras, corner, f/1.4, k-mount, lens, lenses, macro, pentax, pentax lens, plane, primes, sensor, sharpness, slr, slr lens, slr lenses
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Nature Some cats are bigger than others ...... daacon Post Your Photos! 13 06-21-2015 05:56 AM
Additional lenses for a film SLR newbie chiaroscuro Pentax SLR Lens Discussion 5 11-16-2014 12:02 PM
getting bigger&closer macro shots happyprince Troubleshooting and Beginner Help 4 03-21-2013 01:17 PM
What are your favorite SLR lenses for under $100? briankemper Pentax SLR Lens Discussion 135 07-18-2012 05:22 AM



All times are GMT -7. The time now is 05:23 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