Win a Pentax Limited Lens: Raffle Now Live!

Timarete · 06-02-2008, 07:37 AM

Is there any reason why a K100D should show an aperture of f/1.7 for a lens with a maximum aperture of f/1.8?

The lens is a Sigma 24mm f/1.8.

I don't know if the other apertures are registering accurately or not. (I have no way to tell.)

Edvinas · 06-02-2008, 07:45 AM

Originally posted by Timarete

Is there any reason why a K100D should show an aperture of f/1.7 for a lens with a maximum aperture of f/1.8?

The lens is a Sigma 24mm f/1.8.

I don't know if the other apertures are registering accurately or not. (I have no way to tell.)

Probabaly because the lens tells wrong aperture to the camera.

ftpaddict · 06-02-2008, 07:56 AM

Make sure the contacts of the lens and body are clean.

RiceHigh · 06-02-2008, 09:44 AM

Originally posted by Timarete

Is there any reason why a K100D should show an aperture of f/1.7 for a lens with a maximum aperture of f/1.8?

The lens is a Sigma 24mm f/1.8.

I don't know if the other apertures are registering accurately or not. (I have no way to tell.)

Is it a KPR MF lens?

Timarete · 06-02-2008, 10:10 AM

Originally posted by RiceHigh

Is it a KPR MF lens?

The lens is a brand new Sigma 24mm f/1.8 EX DG Macro AF.

joefru · 06-02-2008, 10:34 AM

I've had that happen to me before. I think it was my FA50 when set to f/1.8, the EXIF reported f/1.9. I just chalked it up to it being something like f/1.849, and the lens rounded down, and the camera rounded up. No biggie for me.

Big Dave · 06-02-2008, 10:41 AM

Timarete,
I did a little research and the lens interface codes don't seem the support the F1.8 stop. This would explain why it goes to 1.7, which is the closest stop to f1.8. Here is the link, with pinout and codes.

Dave

Pentax Lens Modifications for Matrix Metering - Mark Roberts Photography

joefru · 06-02-2008, 12:48 PM

Originally posted by Big Dave

Timarete,
I did a little research and the lens interface codes don't seem the support the F1.8 stop. This would explain why it goes to 1.7, which is the closest stop to f1.8. Here is the link, with pinout and codes.

Dave

Pentax Lens Modifications for Matrix Metering - Mark Roberts Photography

At the bottom of that page, it says there will be no effect for Pentax dSLRs. Maybe they read the aperture differently? And I must have been mis-remembering, because I just took a shot with my K10D/FA50 at f/1.8, and the lens, camera, PEF EXIF, and JPEG EXIF all listed f/1.8.

Timarete · 06-02-2008, 02:45 PM

Originally posted by joefru

At the bottom of that page, it says there will be no effect for Pentax dSLRs. Maybe they read the aperture differently? And I must have been mis-remembering, because I just took a shot with my K10D/FA50 at f/1.8, and the lens, camera, PEF EXIF, and JPEG EXIF all listed f/1.8.

Hmm. So then why is my K100D reading this Sigma lens incorrectly? Could it be that only Pentax lenses read the f/1.8 aperture?

ftpaddict · 06-02-2008, 03:02 PM

Originally posted by Big Dave

Timarete,
I did a little research and the lens interface codes don't seem the support the F1.8 stop. This would explain why it goes to 1.7, which is the closest stop to f1.8. Here is the link, with pinout and codes.

Dave

Pentax Lens Modifications for Matrix Metering - Mark Roberts Photography

How can they not support f/1.8? Does the body report another aperture when used with a 31 ltd attached?

Zebooka · 06-05-2008, 08:43 AM

I think that for known own Pentax lenses they have data base of Open aperture numbers (or lens itslef is trasfering in by data contact).
WHile sigma lenses don't transfer this and camera guesses it by other "aperture" contacts on bayonet

axl · 06-06-2008, 12:08 AM

I think there was a thread regarding either the very same sigma lens, or Sigma 28 which was registering as 1.7 as opposed 1.8 that it should. I don't know what was the consensus as for why, but you may try to search the forum. ...

RiceHigh · 06-06-2008, 02:46 AM

Originally posted by Timarete

The lens is a brand new Sigma 24mm f/1.8 EX DG Macro AF.

So, it is just an incompatibility problem where the lens told the camera a not-so-exact reading.

cardinal43 · 06-06-2008, 06:11 AM

Not trying to be a wise guy, but does it really matter between 1.7 & 1.8? I'm a newbie, and just curious.

ftpaddict · 06-06-2008, 06:33 AM

Originally posted by cardinal43

Not trying to be a wise guy, but does it really matter between 1.7 & 1.8? I'm a newbie, and just curious.

Technically, it's 1/4 a stop. You decide if that's important to you or not.

06-02-2008, 07:37 AM	#1
Timarete Inactive Account Join Date: Apr 2008 Location: Berkeley, CA Posts: 49	K100D registers wrong aperture Is there any reason why a K100D should show an aperture of f/1.7 for a lens with a maximum aperture of f/1.8? The lens is a Sigma 24mm f/1.8. I don't know if the other apertures are registering accurately or not. (I have no way to tell.)

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Loss of aperture control on K100D	teamgs	Pentax DSLR Discussion	4	09-25-2010 01:00 PM
Constant Aperture vs Variable Aperture	Netsoft	Pentax SLR Lens Discussion	13	01-11-2010 07:29 AM
Use of Aperture-Ring 43mm/1.9 -> no aperture data	Deimo	Pentax SLR Lens Discussion	7	06-24-2009 03:25 PM
using an aperture ring lens on the K100D Super	burntsienna	Pentax DSLR Discussion	3	02-25-2009 02:10 PM
For Sale - Sold: K100d with broken aperture control	junkdon	Sold Items	0	10-17-2008 03:45 AM

06-02-2008, 07:45 AM	#2
Edvinas Veteran Member Join Date: Sep 2006 Location: Kaunas Posts: 1,458	Originally posted by Timarete Is there any reason why a K100D should show an aperture of f/1.7 for a lens with a maximum aperture of f/1.8? The lens is a Sigma 24mm f/1.8. I don't know if the other apertures are registering accurately or not. (I have no way to tell.) Probabaly because the lens tells wrong aperture to the camera.

06-02-2008, 07:56 AM	#3
ftpaddict Veteran Member Join Date: Jan 2008 Location: Yurp Photos: Gallery Posts: 4,666	Make sure the contacts of the lens and body are clean.

06-02-2008, 09:44 AM	#4
RiceHigh Veteran Member Join Date: Nov 2006 Location: Hong Kong Posts: 1,934	Originally posted by Timarete Is there any reason why a K100D should show an aperture of f/1.7 for a lens with a maximum aperture of f/1.8? The lens is a Sigma 24mm f/1.8. I don't know if the other apertures are registering accurately or not. (I have no way to tell.) Is it a KPR MF lens?

06-02-2008, 10:10 AM	#5
Timarete Inactive Account Join Date: Apr 2008 Location: Berkeley, CA Posts: 49 Original Poster	Originally posted by RiceHigh Is it a KPR MF lens? The lens is a brand new Sigma 24mm f/1.8 EX DG Macro AF.

06-02-2008, 10:34 AM	#6
joefru Senior Member Join Date: Mar 2008 Location: South Louisiana Photos: Gallery Posts: 210	I've had that happen to me before. I think it was my FA50 when set to f/1.8, the EXIF reported f/1.9. I just chalked it up to it being something like f/1.849, and the lens rounded down, and the camera rounded up. No biggie for me.

06-02-2008, 10:41 AM	#7
Big Dave Veteran Member Join Date: Jan 2008 Location: San Antonio, Texas Photos: Gallery Posts: 547	Timarete, I did a little research and the lens interface codes don't seem the support the F1.8 stop. This would explain why it goes to 1.7, which is the closest stop to f1.8. Here is the link, with pinout and codes. Dave Pentax Lens Modifications for Matrix Metering - Mark Roberts Photography

06-02-2008, 12:48 PM	#8
joefru Senior Member Join Date: Mar 2008 Location: South Louisiana Photos: Gallery Posts: 210	Originally posted by Big Dave Timarete, I did a little research and the lens interface codes don't seem the support the F1.8 stop. This would explain why it goes to 1.7, which is the closest stop to f1.8. Here is the link, with pinout and codes. Dave Pentax Lens Modifications for Matrix Metering - Mark Roberts Photography At the bottom of that page, it says there will be no effect for Pentax dSLRs. Maybe they read the aperture differently? And I must have been mis-remembering, because I just took a shot with my K10D/FA50 at f/1.8, and the lens, camera, PEF EXIF, and JPEG EXIF all listed f/1.8.

06-02-2008, 02:45 PM	#9
Timarete Inactive Account Join Date: Apr 2008 Location: Berkeley, CA Posts: 49 Original Poster	Originally posted by joefru At the bottom of that page, it says there will be no effect for Pentax dSLRs. Maybe they read the aperture differently? And I must have been mis-remembering, because I just took a shot with my K10D/FA50 at f/1.8, and the lens, camera, PEF EXIF, and JPEG EXIF all listed f/1.8. Hmm. So then why is my K100D reading this Sigma lens incorrectly? Could it be that only Pentax lenses read the f/1.8 aperture?

06-02-2008, 03:02 PM	#10
ftpaddict Veteran Member Join Date: Jan 2008 Location: Yurp Photos: Gallery Posts: 4,666	Originally posted by Big Dave Timarete, I did a little research and the lens interface codes don't seem the support the F1.8 stop. This would explain why it goes to 1.7, which is the closest stop to f1.8. Here is the link, with pinout and codes. Dave Pentax Lens Modifications for Matrix Metering - Mark Roberts Photography How can they not support f/1.8? Does the body report another aperture when used with a 31 ltd attached?

06-05-2008, 08:43 AM	#11
Zebooka Veteran Member Join Date: May 2008 Location: Russia, Siberia, Novosibirsk Posts: 323	I think that for known own Pentax lenses they have data base of Open aperture numbers (or lens itslef is trasfering in by data contact). WHile sigma lenses don't transfer this and camera guesses it by other "aperture" contacts on bayonet

06-06-2008, 12:08 AM	#12
axl Veteran Member Join Date: Mar 2007 Location: Nove Zamky, Slovakia Photos: Gallery \| Albums Posts: 7,183	I think there was a thread regarding either the very same sigma lens, or Sigma 28 which was registering as 1.7 as opposed 1.8 that it should. I don't know what was the consensus as for why, but you may try to search the forum. ...

06-06-2008, 02:46 AM	#13
RiceHigh Veteran Member Join Date: Nov 2006 Location: Hong Kong Posts: 1,934	Originally posted by Timarete The lens is a brand new Sigma 24mm f/1.8 EX DG Macro AF. So, it is just an incompatibility problem where the lens told the camera a not-so-exact reading.

06-06-2008, 06:11 AM	#14
cardinal43 Veteran Member Join Date: Oct 2007 Location: Virginia Photos: Gallery Posts: 2,412	Not trying to be a wise guy, but does it really matter between 1.7 & 1.8? I'm a newbie, and just curious.

06-06-2008, 06:33 AM	#15
ftpaddict Veteran Member Join Date: Jan 2008 Location: Yurp Photos: Gallery Posts: 4,666	Originally posted by cardinal43 Not trying to be a wise guy, but does it really matter between 1.7 & 1.8? I'm a newbie, and just curious. Technically, it's 1/4 a stop. You decide if that's important to you or not.

K100D registers wrong aperture

Win a Pentax Limited Lens: Raffle Now Live!