Blackmagic Forum

Apologies for another potentially newbish BMp$K thread, but just been testing a lens - now it's not a new lens to me, I use it all the time but my workshop backs onto a railway so on a sunny day I will often play with presets whilst shooting trains because they are a handy, covnient subject.

Ive not altered my presets, only shutter speed and iso as it's a bright daym but I noticed in my camera viewfinder a slight lens warp i.e fisheye effect, very slight - the tracks curved up slightly at the edges but thought nothing of it - when ive done the colour in resolve I notice a very definite skew in the photo (look at the edges of the carriages in attached photo). I did another with a slower passenger train and had the same effect.

I just want to sanity check myself that changing ISO and shutter speed (im at the fasted speed at the moment) could cause this?

will keep looking at settings but never observed this with my lens ( LUMIX G 25mm Micro 4/3 Camera Lens - Black
H-H025E-K)

(https://i.postimg.cc/jSXV2f9v/802-2.jpg)

Might be being daft, happy to be set straight

There are a couple of aspects to this image.

The curve at the edges of the track is due to the lens. Wide angle lenses can distort images as you can see here, like a fish eye lens but less extreme. This issue can vary from lens to lens, it's not entirely dependent on the focal length. Some are better than others (search rectilinear lenses).

The carriages are leaning due to the camera having a rolling shutter, not a global shutter. Search rolling shutter or jello effect to find out more.

I hope that helps

There are some budget lenses that likely would be pretty good at minimizing the curvature of the railroad tracks. Take a look at Laowa Zero D lenses for example.

Thanks for suggestions and the info - beleive it or not couldn't find much on google with skewed, so good to know the proper name of the phenomenon.

Bit weird though because I've never had this before (done these kind of test shots a lot), so need to do some homework i think

I think your exposure time is too short. RS is usually covered by motion blur to some degree (apart from some hybrid cameras with really bad one).

If you insert the correct focal length in the camera, you can use the gyro stabilisation in Davinci Resolve, which completely fixes rolling shutter even if you do not need stabilisation !