Pentax 20-40 f2.8-f4

**hjoseph7** · 08-18-2014, 04:08 PM

Does anybody know at what focal lengths does the maximum aperture change on this lens.

imtheguy · 08-18-2014, 04:50 PM

Originally posted by hjoseph7

Does anybody know at what focal lengths does the maximum aperture change on this lens.

On my K-5 it jumps from 2.8 to 3.5 at 24mm.

Adam · 08-18-2014, 05:00 PM

F3.5 is the maximum at 30mm- it seems to scale linearly.

imtheguy · 08-18-2014, 05:08 PM

Originally posted by Adam

F3.5 is the maximum at 30mm- it seems to scale linearly.

I forgot to add that it goes from 3.5 to 4.0 at 34mm. So there you have it;
20-23mm is f2.8
24-33mm is f3.5
34-40mm is f4

If thats what Adam meant by linear scaling then i now understand.

**hjoseph7** · 08-18-2014, 05:15 PM

Thanks !

08-18-2014, 04:08 PM	#1
hjoseph7 Site Supporter Join Date: May 2014 Location: Minnesota Photos: Gallery \| Albums Posts: 2,047	Pentax 20-40 f2.8-f4 Does anybody know at what focal lengths does the maximum aperture change on this lens.

08-18-2014, 05:00 PM	#3
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,595	F3.5 is the maximum at 30mm- it seems to scale linearly. Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
For Sale - Sold: HD Pentax 20-40 mm F2.8-4 WR & 50-200 mm F4-5.6 WR lenses	Vantage-Point	Sold Items	6	09-12-2014 06:02 AM
Cock-eyed Sigma 20-40 f2.8	Wyzard	Pentax DSLR Discussion	3	04-11-2008 02:56 AM
sigma 20-40 f2.8?	OniFactor	Pentax SLR Lens Discussion	3	03-25-2008 06:28 AM

08-18-2014, 04:50 PM	#2
imtheguy Site Supporter Join Date: Mar 2009 Location: Virginia Beach Photos: Gallery \| Albums Posts: 2,950	Originally posted by hjoseph7 Does anybody know at what focal lengths does the maximum aperture change on this lens. On my K-5 it jumps from 2.8 to 3.5 at 24mm.

08-18-2014, 05:08 PM	#4
imtheguy Site Supporter Join Date: Mar 2009 Location: Virginia Beach Photos: Gallery \| Albums Posts: 2,950	Originally posted by Adam F3.5 is the maximum at 30mm- it seems to scale linearly. I forgot to add that it goes from 3.5 to 4.0 at 34mm. So there you have it; 20-23mm is f2.8 24-33mm is f3.5 34-40mm is f4 If thats what Adam meant by linear scaling then i now understand.

08-18-2014, 05:15 PM	#5
hjoseph7 Site Supporter Join Date: May 2014 Location: Minnesota Photos: Gallery \| Albums Posts: 2,047 Original Poster	Thanks !