Optical Zoom Vs Digital Zoom ?

[tenghsu]

Hi Everybody,
I have just started working in a IP camera manufacturer company and I am taking a training to understand more about cameras.
There was a question that my trainer asked and I don't know the correct answer (he refused to say...)
Hope you guys can enlighten me.

Let's say I have 2 cameras:
1. Camera A with Optical Zoom x35 with max resolution 704x480
2. Camera B with Optical Zoom x20 with max resolution 1920x1080

Since the Camera B is megapixel I can zoom it digitally, so the megapixel could be counted also as a zoom.
Here are my questions:
1. Which camera is better for the same image when I use the max zoom (both digital and optical)?
2. Since the the width - height relation is different for these two camera, how does it affect in the calculations?
3. What is the total zoom of each camera (adding optical and digital)?

Thanks!

[Shadowman]

I hope your trainer isn't a member of this forum. See the following tutorials.

https://www.cambridgeincolour.com/tu...lr-cameras.htm
https://www.cambridgeincolour.com/tu...era-lenses.htm
https://www.cambridgeincolour.com/tu...ensor-size.htm


And welcome to the group.

[Geoff F]

I would say that your question includes a number of different items.

Firstly, and put rather simply, different size zooms magnify a scene by different amounts. Such as a dslr camera with either a 50 mm lens or a 500 mm lens. Obviously the larger lens produces the most magnification but at the expense of loosing much of the scene edges; subject to sensor size when comparing different bodies.

But with some cameras, we have both optical zoom, which is simply based on the lens magnification and digital zoom which increases the size of your image by 'increasing the number of pixels' in much the same way as you can enlarge an image on a computer. This can sometimes also reduce the amount of visible scene where you have a limitation such as print size.

If you need to use 'digital zoom' to increase a shot beyond the capabilities of your camera lens I would say it is better to do that on a computer where, with suitable software, you will be totally in charge of the process of 'adding more pixels' so you can select the best method which results in a smoother and sharper end result.

In camera 'digital zoom' may produce a coarser result.

So, if you need maximum zoom I would say go for the camera which produces the greatest magnification by simple optical zoom; but also be aware of different sensor sizes. Which I suspect is what the original question meant.

And consider print sizes. For example 704 pixels wide would only allow you to print at 3.52 ins using 200 ppi, while 1920 pixels would produce a 9.60 ins print. This may well be the significant point here.

[Ricco]

Answer - the more expensive camera.

But more seriously, I think the theoretical answer is camera b. with camera b, at maximum zoom, you have 1080 pixels high vs 480 and thus could "zoom" another 2.25 times for an equivalent of 20x2.25= 45.
However there are practical aspects to this as Geoff points out.

[Ricco]

Sorry - didn't answer question 3. Mainly because I don't think it is possible to answer. I'm not sure that the following is clear when I write it but I'll try.

You need to consider the size of what you are trying to print and the quality of that print. Lets say you were after a print that could be produced from an image on your sensor of 480 pixels high at 35x zoom.

In camera a, you zoom all the way in, take the snap and use every available pixel to produce e print. All good.

In camera b, you zoom all the way in but get a larger view of the picture (1.75 times more picture than with a - 35\20). However, there is more picture as you have more pixels. But now your picture is on about 620 pixels (1080/1.75) so you throw away the balance and end up with a slightly higher resolution for the same image or same effective zoom. But if you actually only want 480 pixels, you could zoom in that little bit extra more or up to another 30% (620/480).

So you see, your question can't be answered direct as it depends on what your final image size is.

(I should qualify that I am not an expert on the above and it represents my best understanding - I'm pretty sure it is right, but perhaps worth checking with our resident expert or trainer. Let us know what he reckons.)