Blackmagic Forum

Hello BM users,

I just purchased the Samyang 500mm f8 lens for my telephoto wildlife videography. I just received it in the mail today and put it on my bmcc.

It was then that I noticed when I stopped the lens down dark distinct smudges would appear (this is an image of the clear blue sky)


I immediately assumed it must be dust on the sensor or lens. However when I checked both they were entirely clean;



I double checked the sensor as well, putting on my sigma 18-35 and there were no dark smudges. So do I just have a bad lens that needs to be sent back or is there some way to fix this?

It's certainly dust somewhere on there-- either on the sensor or on the lens, or in the lens. Of course finding one spec of dust which is being magnified by a 500mm lens is going to be.... annoying to say the least. You'll just have to go over all of it with a fine toothed comb, and perhaps even a loop.

AdrianSierkowski wrote:It's certainly dust somewhere on there-- either on the sensor or on the lens, or in the lens. Of course finding one spec of dust which is being magnified by a 500mm lens is going to be.... annoying to say the least. You'll just have to go over all of it with a fine toothed comb, and perhaps even a loop.

Thanks Adrian. Ive gone over the front and rear elements on the lens a dozen times and still cant see anything. Im afraid it may be inside the lens. I dont have any experience with cleaning inside, is that something you can/should go to a lens repair shop for or should I just return the lens?

I'd return it @ that point. It would cost far too much to open it up and clean it for a cheap lens like a Samyang, especially one you just bought. I'd say return it if you've already looked and get another one; of course no promises they have the QC as a builder-- so next one could be better or worse or just the same

Greetings, I've had those spots on my footage as well... Well, just a single spot to be honest, I haven't had that much spots on my footage. I noticed it when I was making a cloud time lapse long ago with a Canon EF-S 18-135mm lens at 135mm.





It is said that it's dust or artifacts over the sensor, it might be dust or artifacts in, or over the lens as well, moisture over filters. It might have happened when changing lenses, exposing them to the enviroment. A few days passed, and when I was going to shoot another cloud time lapse, I wanted to make a test without cleaning the sensor, so I first cleaned my lens, checked the footage, and the spot was gone.



I really can't tell if your lens is damaged. But I can tell you that working at high ASA with really long lenses, like that Samyang, you might notice artifacts, like the sensor grid pattern, and that horizontal line on the center of the footage. Both of these seen on the BMCC's, I can't tell if the glass quality have to do with it. Make sure it's real clean, without signs of moisture or wear. The last thing you can do is to send it back.