K-1 and Samyang/Rokinon 135mm f2

TSC992 · 12-24-2019, 08:47 AM

I recently purchased a Samyang 135mm f2 for my K-1. It takes fantastic pictures, but I noticed that some pictures are exposed too dark at f-stops between f 2.2 and f4.0 when the apertuerering was in A-position. I checked how the aperture behaved with different f-stop-settings (camera in TAV or AV-Mode) by looking through the frontlens and sometimes the blades were closed much too far (f 2.2 looked like f4). The same effect could be observed when using the DOF preview. I also tried the lens on my K-5, here it seems that this problem does not exist, the aperture blades were reliably closed as far as expected.
Therefore I have the question for those who use a Samyang/Rokinon 135mm on their K-1 whether the aperture is always set correctly at small aperture values like f 2.2 or f 2.5 with the aperture ring in A-position ?

dcpropilot · 12-24-2019, 09:11 AM - **1 Like**

I have never had this particular problem with my Samyang 135/2.0 on my K-1.

stevebrot · 12-24-2019, 09:26 AM

Welcome to the Pentax Forums!

Two questions...

What happens if you use the aperture ring?

Do you see similar problems with other lenses on your K-1?

Steve

TSC992 · 12-24-2019, 09:36 AM

When I use the aperture ring and M mode, the aperture blades are set exactly as I expect them be and the exposure is correct. When I discovered the problem on the Samyang, I immediately tested a few other lenses on the K-1. All the other lenses work correctly. So I think the problem must be somehow with the lens, even though it seems to work correctly on the K-5. Fortunately, I still have my warranty.

**BigMackCam** · 12-24-2019, 09:48 AM

Originally posted by TSC992

When I use the aperture ring and M mode, the aperture blades are set exactly as I expect them be and the exposure is correct. When I discovered the problem on the Samyang, I immediately tested a few other lenses on the K-1. All the other lenses work correctly. So I think the problem must be somehow with the lens, even though it seems to work correctly on the K-5. Fortunately, I still have my warranty.

The lens' diaphragm linkage mechanism probably needs minor adjustment. My Tamron 10-24 had a similar problem, though in that case the diaphragm wasn't closing down at all until around f/5.6, if I remember correctly...

biz-engineer · 12-24-2019, 10:11 AM

I didn't have that issue with the Samy 135 2 and K1.

TSC992 · 12-24-2019, 11:36 AM - **1 Like**

Okay, thank you very much for your answers. I think I'll return it to the dealer in the next days.

12-24-2019, 08:47 AM	#1
TSC992 New Member Join Date: Dec 2019 Photos: Gallery Posts: 7	K-1 and Samyang/Rokinon 135mm f2 I recently purchased a Samyang 135mm f2 for my K-1. It takes fantastic pictures, but I noticed that some pictures are exposed too dark at f-stops between f 2.2 and f4.0 when the apertuerering was in A-position. I checked how the aperture behaved with different f-stop-settings (camera in TAV or AV-Mode) by looking through the frontlens and sometimes the blades were closed much too far (f 2.2 looked like f4). The same effect could be observed when using the DOF preview. I also tried the lens on my K-5, here it seems that this problem does not exist, the aperture blades were reliably closed as far as expected. Therefore I have the question for those who use a Samyang/Rokinon 135mm on their K-1 whether the aperture is always set correctly at small aperture values like f 2.2 or f 2.5 with the aperture ring in A-position ?

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12-24-2019, 09:11 AM - 1 Like	#2
dcpropilot Veteran Member Join Date: Mar 2010 Location: Vermont Photos: Gallery \| Albums Posts: 941	I have never had this particular problem with my Samyang 135/2.0 on my K-1.

12-24-2019, 09:26 AM	#3
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Welcome to the Pentax Forums! Two questions... What happens if you use the aperture ring? Do you see similar problems with other lenses on your K-1? Steve

12-24-2019, 09:36 AM	#4
TSC992 New Member Join Date: Dec 2019 Photos: Gallery Posts: 7 Original Poster	When I use the aperture ring and M mode, the aperture blades are set exactly as I expect them be and the exposure is correct. When I discovered the problem on the Samyang, I immediately tested a few other lenses on the K-1. All the other lenses work correctly. So I think the problem must be somehow with the lens, even though it seems to work correctly on the K-5. Fortunately, I still have my warranty.

12-24-2019, 09:48 AM	#5
BigMackCam Digitiser of Film Join Date: Mar 2010 Location: North East of England Posts: 20,702	Originally posted by TSC992 When I use the aperture ring and M mode, the aperture blades are set exactly as I expect them be and the exposure is correct. When I discovered the problem on the Samyang, I immediately tested a few other lenses on the K-1. All the other lenses work correctly. So I think the problem must be somehow with the lens, even though it seems to work correctly on the K-5. Fortunately, I still have my warranty. The lens' diaphragm linkage mechanism probably needs minor adjustment. My Tamron 10-24 had a similar problem, though in that case the diaphragm wasn't closing down at all until around f/5.6, if I remember correctly...

12-24-2019, 10:11 AM	#6
biz-engineer Pentaxian Join Date: Feb 2015 Photos: Gallery Posts: 12,249	I didn't have that issue with the Samy 135 2 and K1.

12-24-2019, 11:36 AM - 1 Like	#7
TSC992 New Member Join Date: Dec 2019 Photos: Gallery Posts: 7 Original Poster	Okay, thank you very much for your answers. I think I'll return it to the dealer in the next days.