Question on image distortion

[reahducks]

Hi there,

currently I only own a Dahua HDBW2431R-ZS-S2. Bein a varifocal I ordered it to get a feeling of what fixed lenses I need for my coming installations.
Now I know and I see it's getting hard getting cameras with one of the standard focal length for my desired field of view. So I'm thinking about getting all varifocals.

But what I noticed is that at least my 2431R distortes the image quite a bit in the wider settings. That's nothing to wonder about, but what I want to know is, if a fixed focal lens at e.g. 2,8mm or 3,6mm does distort the same amount or if it's the zoom lens were that effect if pronounced.

Thanks,
Reah

 

[Perimeter]

You will have to specify, exactly what kind of image distortion you mean. Are you refering to straight lines showing up as bend?

 

[wittaj]

A picture is always helpful.

 

[reahducks]

You will have to specify, exactly what kind of image distortion you mean. Are you refering to straight lines showing up as bend?

Yes, that's what I mean.

 

[reahducks]

A picture is always helpful.

You’re right. See the gutter in the attachment.

 

[SpacemanSpiff]

That is not distortion, but the effects due to the nature (curvature) of the lens optics.

You will experience the curvature of objects, like the gutter in the image, regularly (though infrequent). It is a result of the object being so close to the outer edge of the lens optics (glass).

 

[Mike A.]

It will be basically the same with a fixed lens. The wider (lower mm number), the more of that effect.

 

[reahducks]

Okay, understood. I thank you for the insights. So regarding this effect there is no advantage using a fixed focal length.

 

[Perimeter]

So regarding this effect there is no advantage using a fixed focal length.

Not with the same angle of view. The fixed focal may deliver slightly better image quality but usually geometry will not improve much.
What the fixfocals sometimes offer is a setting called LDC (Lens distortion correction). The existance of this setting tells you that they also suffer from this problem. LDC simply keeps the inner part of the picture and deletes the distorted outer part. You get less pixels, less field of view and less distortion.