[DeadJohn]

I am using Av mode and auto ISO on a K-5. The camera has a tendency to not want the shutter speed to drop below 1/125s with the Samyang 14mm; it cranks up the ISO instead of using a slower shutter speed. After it hits the maximum auto ISO then it will start slowing the shutter below 1/125. The 14mm doesn't communicate its focal length but I pick the closest setting, 15mm.

For comparison purposes, when my FA43 is used the shutter speed slows down as expected, with speeds around 1/60 or 1/90 in low light.

For now I use TAv with the 14mm, or Av with static ISO, but appreciate comments that will help me understand what's happening.

[Na Horuk]

Hey there.
I would suggest you pick the setting of 12mm instead. I think that makes the SR less likely to blur your photos.
I have the Samyang 14mm, but I wasn't paying attention to the shutter speeds, I usually don't use auto ISO, and I usually like the shutter speed to be at least 1/100, no matter the lens.

[Adam]

I am using Av mode and auto ISO on a K-5. The camera has a tendency to not want the shutter speed to drop below 1/125s with the Samyang 14mm; it cranks up the ISO instead of using a slower shutter speed. After it hits the maximum auto ISO then it will start slowing the shutter below 1/125. The 14mm doesn't communicate its focal length but I pick the closest setting, 15mm.

For comparison purposes, when my FA43 is used the shutter speed slows down as expected, with speeds around 1/60 or 1/90 in low light.

For now I use TAv with the 14mm, or Av with static ISO, but appreciate comments that will help me understand what's happening.

Which program line are you using? If you've set it to MTF, for instance, the camera might behave differently with the 43mm since it has MTF data for that lens.

[DeadJohn]

Hey there.
I would suggest you pick the setting of 12mm instead. I think that makes the SR less likely to blur your photos.
I have the Samyang 14mm, but I wasn't paying attention to the shutter speeds, I usually don't use auto ISO, and I usually like the shutter speed to be at least 1/100, no matter the lens.

I think you're right that 12mm is a better setting than 15mm for a 14mm lens. 12 will undercorrect while 15 will overcorrect. Regardless, that doesn't change the way my camera is setting shutter speed.

I have gotten sharp images as slows as 1/6 sec handheld. A wide angle and SR are a very forgiving combination for low light use.

[DeadJohn]

Which program line are you using? If you've set it to MTF, for instance, the camera might behave differently with the 43mm since it has MTF data for that lens.

Program mode "Normal". I did some more testing and find the 14mm wants to be 1/125 sec or faster in Hyper mode in addition to standard Av.

[Canada_Rockies]

Set your ISO lower and force the camera to go slow. Auto ISO is not ideal for control.

[severalsnakes]

I don't own the Samyang, but I do own many other manual aperture lenses. I understood that in AV mode, the camera shoots wide open all the time, as there is no communication between the camera's brain and the lens' aperture settings. Am I mistaken, or is the Samyang lens different? Would this fact account for the anomalies you're experiencing?

Sorry to add more questions than answers.

[Canada_Rockies]

I did not think of the lens missing an A setting on the aperture ring. If that is the case, you must use Manual mode. It's easy enough to set your aperture and ISO then press the green button to have the camera set the shutter speed. The problem with lenses without an A setting on the aperture ring is that they only shoot wide open in any mode other than manual.

[vonBaloney]

I don't own the Samyang, but I do own many other manual aperture lenses. I understood that in AV mode, the camera shoots wide open all the time, as there is no communication between the camera's brain and the lens' aperture settings. Am I mistaken, or is the Samyang lens different? Would this fact account for the anomalies you're experiencing?

Yes, you are mistaken. Manual focus lenses that have an 'A' setting can use Av mode or any other mode just fine (just no auto-focus). What you are saying only applies to K-mount lenses with no 'A' setting (i.e. no electrical contacts on the mount).

The Samyang does have an 'A' mode, and auto-aperture does work (as long as it actually is ON 'A' mode since it does have an aperture ring).

[severalsnakes]

Yes, you are mistaken. Manual focus lenses that have an 'A' setting can use Av mode or any other mode just fine (just no auto-focus). What you are saying only applies to K-mount lenses with no 'A' setting (i.e. no electrical contacts on the mount).

The Samyang does have an 'A' mode, and auto-aperture does work (as long as it actually is ON 'A' mode since it does have an aperture ring).

I should have been more specific. I was uncertain if the Samyang lens had an auto-aperture setting. I know that engaging the A aperture setting on a lens that has it will allow you to use AV mode, but, like Canada_Rockies pointed out, if there is no A setting on the aperture ring (or if you choose not to engage it), you can Green Button the settings from Manual mode... (after manually selecting the aperture with the ring)

[vonBaloney]

I should have been more specific. I was uncertain if the Samyang lens had an auto-aperture setting. I know that engaging the A aperture setting on a lens that has it will allow you to use AV mode, but, like Canada_Rockies pointed out, if there is no A setting on the aperture ring (or if you choose not to engage it), you can Green Button the settings from Manual mode... (after manually selecting the aperture with the ring)

Yeah, all the Samyangs (and other-named variants) are manual focus 'A' lenses. I don't think anyone is making new lenses for Pentax that don't have an 'A' setting except maybe those Mitakons...

[Na Horuk]

So I just tried the Samyang 14mm on my K-01 and it behaved as you described it. Camera wanted to keep shutter speed above 1/125! Really odd behaviour. Someone should mail Pentax/Ricoh

It was odd because usually the camera keeps shutter to be around 2x the focal length. Or slightly less, actually. So its weird that it would allow a slower shutter speed for a 35mm lens than for the 14mm.

[DeadJohn]

Maybe the "manually selected focal length" that we enter with the 14mm (and other lenses that can't communicate their focal length to the camera) only applies to shake reduction!? Pentax' shutter speed algorithms might be ignorant of what we enter and default to 1/125 second.

We can test this theory by picking a ridiculously long length like 300mm while using the 14mm. Does that make Av mode set the shutter speed faster than 1/300 or does it remain at 1/125?

I wonder how non-Pentax lenses that *can* communicate focal length behave. I think my Tamron 10-24 will go way below 1/125 but I'll confirm later.

[Lowell Goudge]

Maybe the "manually selected focal length" that we enter with the 14mm (and other lenses that can't communicate their focal length to the camera) only applies to shake reduction!? Pentax' shutter speed algorithms might be ignorant of what we enter and default to 1/125 second.

We can test this theory by picking a ridiculously long length like 300mm while using the 14mm. Does that make Av mode set the shutter speed faster than 1/300 or does it remain at 1/125?

I wonder how non-Pentax lenses that *can* communicate focal length behave. I think my Tamron 10-24 will go way below 1/125 but I'll confirm later.

That is correct. Pentax only has the focal length tied to shake reduction not to the other functions like exposure control and flash shutter speed It is one of a few big wants I have for them in software. There is no reason they don't make the camera follow a normal (for the focal length) exposure curve

[Na Horuk]

Ah that explains it. My other manual lenses are all around 50mm, so 1/125 makes sense and I never thought of it