Newbie question about zooming

I know that when I zoom, say from 25mm to 300mm, a very steady hand is need, otherwise the picture will blur. The same thing happens to a lesser degree when I zoom from 25mm to 38mm.

Question: Assuming everything else is the same (i.e., same anti-shake feature, same mechanism, same shutter speed, same sensitivity level, etc.), will I ALWAYS get the same amount of "shakiness" when the focal length is the same?

---------------------

Examples

For Camera A with 25-250 mm lens, and Camera B with 40-400 mm lens:

Case1: Camera A is zoomed to 40 mm, while Camera B is at its widest focal length of 40 mm.

Case2: Camera A is zoomed up from 25 mm to 50 mm, while Camera B is zoomed a little from it widest view of 40 mm to 50 mm.

---------------------

Thank you in advance for your help.

Hey Panda,

When referring to absolute focal lengths numbers, we have to factor in the device the glass in mounted on. For example, on a full frame SLR, 300mm is 300mm in 35mm standards (like a golden rule). However or a Canon 40D the 300mm is effectively 480mm and 450mm on Nikon bodys (except the full frame Nikons).

Let's take a look at your examples.

Case 1: Camera A and camera B both are at 40mm. Assuming that their digital sensors (or films) are of the same size, yes, you will need the same shutter speed to avoid camera shakes. It doesn't matter what the "zoom" is, it's the effective focal length that matters.

A rule of thumb photographers use is 1/x shutter speed where x is the focal length. In your example you can go (theoretically) down to 1/40 shutter speed and still be considered safe. However, if you are shooting crop cameras, your minimun safe speed will be more like 1/60.

Case 2: Same. It's the effective focal range that matters. Keep in mind though that anti-shake throws a big donkey bone in what was said above. Different cameras and different lenses have various stabilization mechanisms that can varry greatly from manufcaturer / model to another.

Image stabilization on some lenses claim to give you 3-4 extra stops, so in your example here if you are shooting a crop canon body, your 50mm needs 1/80 or faster shutter speed without stabilizer, but possibly can go down to 1/15 (theoretically).

Well, I'm not sure if I'd agree in all those statements, Xeliex There's the appropiate magnification with regards of the focal length, and then the apparent magnification which is product of the sensor crop.

Now, in 35mm, the rule of thumb of shutter reciprocity to focal length applies specifically to the focal length magnification. The other magnification, the one that comes from sensor crop, is apparent, not real. Hence, I think that it still applies the rule of thumb that you described, despite the apparent behaviour of the focal length.

However this observation, the slowest speed usable for a given focal length depends on a lot of things.

To answer Panda's question, for a given focal length, theoretically the same amount of shakiness would come despite the lens. However, what can you hold more steadily, a 40-300 or a 20-40? Here is when other factors come in: your pulse, balance between camera and lens, etc. This is why is pretty hard to state anything in absolute terms of veracity.

Best,
Sebas.

Thanks, guys.

Panda

Does the optical zoom of a non-SLR digital camera have the same characteristics as that of a film camera's lens? Wide angle and telephoto lenses on a film camera have distinct visual characteristics - compare pictures from a fish-eye to a 1000mm... I've got to do more experimenting, but I suspect that the zoom is cropping... (Samsung S860)

The zoom effect in a compact is optically identical to that in an SLR camera, when considering its effect on either compressing or exaggerating perspective. So in effect, zooming is cropping, as you say. There's a lot more on this on the page about Understanding Camera Lenses.

The only real difference is that most compact cameras zoom in or out using an electronic mechanism, as opposed to the manual hand-twist mechanism in an SLR lens. This has a number of pros/cons...

Dear McQ,
Thanks for clearing that up. The transition from film to digital... so many questions sound idiotic. I need to find a book on the science and engineering of digital imaging and cameras. Any suggestions?
txfred

txfred 'ello mate,

yeah one suggestion springs quickly to mind; keep your money in your pocket, keep using this website and keep practising. I've read so many books (& Ebooks) about digital and every author seems to answer the same question in a different way! The same can be said of digital software.

Mark

The more you magnify, the more camera shake can become evident. In general there are two places photographers magnify: in-camera with focal length or reducing distance to subject, and out-of-camera when enlarging. The reason some folks say you need to consider the crop factor for the old 1/focal length advice is because if you are planning to go to 8x12 from APS then it's a greater enlargement (magnification) than from a larger format enlarged to 8x12.

It should be kept in mind that the 1/focal length hand held rule is a suggestion. There are a lot of aspects that are going to influence how perceptible camera shake will be in the finished photo. Personal testing is a must. If I want really sharp photos when hand holding I try to go with 2 or 3 times the focal length. I can usually see a significant difference from 1/focal length.