Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
07-23-2011, 09:14 AM   #31
Veteran Member




Join Date: Mar 2011
Location: Arizona
Photos: Albums
Posts: 330
QuoteOriginally posted by reeftool Quote
I would think that light transmission could easily be different in one brand of glass to another. The f stop is a ratio of the aperture to the length. Putting a neutral density filter on a lens doesn't change the aperture but certainly changes the exposure.
Put the it is TTL metering. Meter is looking at what light makes it through the glass. Putting a neutral density filter on your lens wouldn't change anything as far as correct exposure if you are still using auto exposure. All it will do is slow down the correct settings.

QuoteOriginally posted by hoojammyflip Quote
The only way to compare transmission effects, without aperture affects confounding your results, will be to shoot wide open.
Easier said than done. The 31mm is a 1.8 and the 28mm is a 2.8. So it is not a direct comparison even still. Never the less, the image would represent exactly what the meter thought. Thats why is you read up higher we were talking about metering through whatever the selected aperture was. Any picture with the Zeiss is metered at the chosen aperture while the Pentax is metered at 1.8 then calculated to the chosen aperture.

07-23-2011, 09:25 AM   #32
Loyal Site Supporter




Join Date: Jun 2009
Location: Tumbleweed, Arizona
Photos: Gallery | Albums
Posts: 5,002
Original Poster
QuoteOriginally posted by atlnq9 Quote
Easier said than done. The 31mm is a 1.8 and the 28mm is a 2.8. So it is not a direct comparison even still. Never the less, the image would represent exactly what the meter thought. Thats why is you read up higher we were talking about metering through whatever the selected aperture was. Any picture with the Zeiss is metered at the chosen aperture while the Pentax is metered at 1.8 then calculated to the chosen aperture.
... and that is exactly what was going on, in particular with the Av mode. In full manual, each of the lenses had the manual aperture rings set to f4, but the camera body still knew that the 31 was a f1.8 lens. On the CZ 28 being a f2.8 lens (and no reporting capability), the body assumed a constant f2.4 for the lens (apparently a default for all pure K mount lenses).

The images were always wonderful - never a complaint (other than my poor manual focusing ability - but that another story). The main reason for this thread was I happen to see the wide differences in shutter times, and essentially wondered why....

Inquiring minds - and the like...
07-24-2011, 04:55 AM   #33
Veteran Member




Join Date: Aug 2009
Posts: 381
There will be differences between glasses...at best, one will transmit 100% and the other at worst 99%, thanks to the coatings. Say you have 10 surfaces, this works out at 100% vs 90%...which equates to -0.15EV...and thats no way near the noted 0.5EV, and realistically, Pentax coatings let through 99.9% not 99%.

I am not a solar PV expert, but I expect that the constant exposure to sunlight and expense of installation and replacement means that they have very different design requirements to consider, which may conflict with transmission. For example, degradation of glues in the PV panel making the thing fall apart after 5 years. Plus, they are built to a cost specification, whereas a FA Ltd or Zeiss lens aren't, at least they are more of a luxury item.
07-24-2011, 10:32 AM   #34
Pentaxian
reeftool's Avatar

Join Date: Dec 2007
Location: Upstate New York
Photos: Gallery | Albums
Posts: 8,012
I would think you could easily test the light transmission differences by setting up a test with both lenses at the same aperture and shutter speed. Use good artificial lighting so you know there will be no differences at all in the light. In theory, they should both be the same.

07-24-2011, 12:46 PM   #35
Veteran Member




Join Date: Aug 2009
Posts: 381
QuoteOriginally posted by reeftool Quote
I would think you could easily test the light transmission differences by setting up a test with both lenses at the same aperture and shutter speed. Use good artificial lighting so you know there will be no differences at all in the light. In theory, they should both be the same.
what happens if the f-stop is incorrectly calibrated, as alluded to before? Although you can have f5.6 loaded up on the aperture ring, if the diaghram moves differently, that will override any meaningful interpretation of the quality of the glass. I really think measuring the transmission properties of the glass, when the difference is likely to be 0.1EV at most, is futile.

Its all a bit moot anyway, if you know a lens overexposes, just alter the EV setting on the body.
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!
glass, images, k-mount, lens, lenses, pentax lens, sec, sets, shutter, slr lens, zeiss
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: PENTAX, ADAPTALL, ZEISS JENA LENS AND PROMASTER (Worldwide) rajubhai55 Sold Items 7 03-16-2011 01:41 PM
SR efficiency the main difference between K-7 and K-r? JoepLX3 Pentax DSLR Discussion 3 09-21-2010 09:41 PM
Rare Carl Zeiss Jena STASI lens set for M42 Pentax mt. netuser Pentax SLR Lens Discussion 6 02-18-2010 06:07 PM
Zeiss lens to a pentax mount? Is there a way? Nubi Pentax SLR Lens Discussion 4 10-04-2009 01:12 PM
What Zeiss lens in Pentax mount? FLASH Pentax SLR Lens Discussion 8 11-18-2007 06:27 PM



All times are GMT -7. The time now is 06:05 AM. | 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