Full Manual Lenses, does anyone have experience with Rokinon/Samyang? Exposure Issue

Started May 10, 2014 | Questions thread
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ShutterWorth New Member • Posts: 8
Full Manual Lenses, does anyone have experience with Rokinon/Samyang? Exposure Issue

Hi, I am sort of a newbie to the photography world and technical stuff. But I will try and explain my issue best as possible.

I have the Nikon D600 and have only used these 2 lenses on it. Rokinon 14mm and 35mm, both Cine lenses. This of course means that it has a smooth aperture ring.

I usually shoot at Aperture Priority mode, only adjusting the Aperture ring on the lens and setting ISO and WB. I've never been able to adjust exposure any other way, and to be honest I prefer it that way. When I turn the aperture ring, the same aperture setting the lens is at, gets displayed on camera.

My photos have always been correctly exposed, but lately its doing something very strange, on both my lenses. I'll use my 14mm as example:

At F2.8, at ISO 200 and WB Auto, my camera chooses a shutter speed of 1/25s and my photos are now slightly under exposed. Turning the aperture ring to F22, the shutter speed are now at 3 seconds, which completely over exposes my photos.

Switching to Manual Mode, I use the exposure meter in the viewfinder, and it suggests the same values, with the same results.

I have now started looking at the actual iris of my lenses. Detached from the camera, the iris opens and closes nicely and smoothly between F2.8 - F22. When set at F22, I can see the iris opening and closing when I push the lever at the back of the lens. But as soon as I attach the lens to the camera, the iris gets pushed open and stays open, regardless of what aperture the lens is set. When I move the aperture ring, it changes the F values on the camera but it doesn't look like the iris opens and closes. I'm not sure if it's supposed to though... I was under the impression that it has always opened when on camera, but I have now read elsewhere that I am only supposed to set the lens at F22 and only use the front dial to change aperture values, which sounds strange to me, as I don't think I have ever been able to do that!

I can play around with some settings to get my shots correctly exposed at around F2.8 (or F1.4 on my 35mm) But anything smaller, all the way up to F22 gets increasingly harder and it's impossible to do any long exposure shots.

So is this a problem with my lenses or should I have Nikon take a look at my camera?

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Nikon D600
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