The Importance of Focal Length over MP in camera selection


Getting comfortable
Mar 18, 2022
Reaction score
Now what about daytime, can you get away with more digital zoom then?

So here are comparable daytime pics taken at the same time (noon) of the same vehicle from just slightly different angles - one from the 5442-ZE 4MP set to 3.6mm that I digitally zoomed to make the vehicle about the same size as the vehicle in the 2MP 5241-Z12E varifocal optically zoomed. You can make out the phone number in the 2MP optically zoomed picture, but not in the 4MP digitally zoomed picture.

FedEx daytime 4MP digital zoom.jpg

FedEx daytime 2MP optical zoom.jpg

As expected, with enough light, the digital zoom is more effective, but it isn't perfect either.

The 2MP camera is 4092 CBR bitrate and the 4MP is 8192 CBR bitrate, which are appropriate for their relative resolutions. Both at H264. H265 is even worse digital zoomed due to how it blocks for compression.

Digital zoom uses an algorithm to achieve that zoom and that also introduces additional noise and artifacts as the algorithm tries to fill in missing pieces and interpolate as the digital zoom gets bigger. It isn't like taking a magnifying glass to a hard copy of something. Digital zoom introduces artifacts not present in the original size.

Economically, the sensor size simply isn't available to us (nor would we want the size of the camera to accommodate it) to provide us with meaningful digital zoom beyond just a little bit.

I tested all of this when I got the camera by digital zooming to something across the street and changing bitrates until I saw a difference - I wanted to try to squeeze as much digital zoom as I could out of it, and the simple fact is you just can't do a lot.

By comparison, the non digitally zoomed 4MP image looks great and something within the DORI number for IDENTIFY looks great. But when you digital zoom, this is what you get, unless you are in a movie or on TV and then you are seeing nose hairs when digital zooming LOL.

There is a trade off with every camera. Do you want a wide field of view but lose details at distance, or a narrow field of view but able to get details at distance.

Most of us have a wide angle fixed camera as an overview to OBSERVE a wider view and can serve to IDENTIFY when a subject is within the DORI distance for that particular camera, supplemented with optical zoomed cameras zoomed in to pinch points or other points of interest further out.

Again, it is why we say one camera cannot do all, be all, see all. A 2.8mm or 3.6mm fixed cam is a great overview camera to get a big wide picture, but it isn't going to be used to IDENTIFY a stranger at 60 feet, especially at night. You need another camera optically zoomed to that area.
TL : DR...
More megapixels is better...

Yes, I was kidding.

@wittaj when you are digitally zooming are you using zoom on the camera, BI, or after it's recorded? I always understood it that any type of digital zoom should be done after the image (in this case video) is captured. Any type of digital zoom introduces error, and if done after you have more options how to "enhance" the image. This how I understood it for photos, video may be a little different?


Known around here
Aug 8, 2018
Reaction score
Spring, Texas
Here are a couple of shots with a Dahua SD12203T-GH 2.7-8.1mm PTZ cam which is 2MP on a 1/2.8" sensor.

First shot is the 2.7mm wide angle shot.
Driveway Window 2.7 mm.jpg

The second is at full optical zoom of 8.1mm.
Driveway Window  8.1 mm zoom.jpg

The third shot is full optical zoom and full digital zoom as done in the camera. I do not know what the lens equivalent would be here. I just zoomed it as far in as the controls would allow.
Driveway Window  full optical and digital zoom.jpg

And here is the full optical zoom photo then zoomed in digitally in MS Photos to about the same view as the digital zoom within the cam. You can see additional digital artifacts.
Driveway Window  8.1 mm  digitally zoomed photo.jpg
Last edited:


IPCT Contributor
Apr 28, 2019
Reaction score
Since this thread is about proper camera selection, I thought it would be good to mention a little bit about running cameras in color versus B/W.

While color is obviously preferred, sometimes we have field of views that just do not have enough light and need to be in B/W with infrared.

Like many here, I use both to help ensure maximum opportunities to capture a clean image.

While infrared is great, because it is in B/W, sometimes you can get cleaner captures for like a face or something, but color determination is way off, and some colors are problematic with infrared.

So I notice this non-descript plain white truck go by so I got suspicious:


So I pull up a color camera to see what is going on and this is the truck:


Now that you know it is a Kroger truck, you can kinda see it in the B/W photo, but wow!

Now imagine if this were someone that had damage done to say a parked car hit by this vehicle and all they had were B/W cameras going, nobody would suspect this truck!

If at all possible, one should try to run some overview cameras in color - even though they clearly are not for IDENTIFY purposes, they help paint a better picture as to color and some other details that may be lost with infrared and B/W.