# Focal length question on powershot sx120



## Achaicus (Aug 31, 2013)

I have got the idea of f stop changing focal range down, and have encountered the concept on how to maximize focus range but am having trouble translating that concept to practice with my particular camera with any assurance that I am getting it. It is possible that I don't understand the idea fully also.*

I have a Powershot sx120 is. *this point and shoot comes with a 10x15 zoom, but I don't use that most of the time.*

Now the manual focus jumps from 10 feet to infinity, now I'm not sure... is the 10 feet setting the idiot's point of max focus? or is it at another point, and would f stop change that. For snapshots this camera does well on auto, but I've been taking shots that my own settings come out better and so I have been trying to learn where I can improve.


Thank you in advance, and let me know if I left any information out of my question that would help with the answer.

Frederick


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## grafxman (Sep 1, 2013)

Can you control the f stop with that camera? The specs suggest that the f stops available are 2.8 in wide angle and 4.3 in telephoto. If I'm reading the specs correctly you aren't able to change the f stop.


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## radiorickm (Sep 1, 2013)

From reading your post, I don't think you have some of the concepts down at all. Your book for the camera is not explaining some things well either. So we need to get some definitions clear, to understand things.

Focal range refers to the distance from the camera an object needs to be, for the camera to be able to focus on it. If your ZOOM is set to the wide angle position, it will focus on something as close as 2 inches away. If it is set to Tele-Photo, it will focus on something as close as 39 inches or so. In both cases that is the CLOSEST you can be to what ever you are taking a picture of. It can be any distance farther away, and the camera will focus correctly. So, at wide angle, you have a focal range of 2 inches to infinity; when zoomed to telephoto, you have a focal range of 3.3 feet to infinity.

The aperture, or F-Stop's have nothing to do with the focal range; What they affect is called the depth of field. Remember, our human eyes can change focus areas very rapidly between items, We don't even notice that this happens. The camera has to focus on one thing, and that thing is a certain distance from the camera. Because of this, things in front of, and things behind your intended subject may or may not be in sharp focus. This is called, Depth of Field. It is affected by the F-stop you (or the camera) select, but is all affected by the focal length of the lens, or which zoom setting you are using.


By their nature, wide angle lenses have a very deep depth of field. For instance (only a made up example) using the wide angle setting of the Zoom, and a small f-stop of F-16, you could take a picture of a flower 1 foot from the camera, and have the mountains in the background come out sharp also.

Now on the other hand, if you set your zoom to Tele-Photo, and the F-stop to F-4, then took a picture of a person 6 feet away from you, the person would be very sharp (focused), but the mountains in the background would become completely fuzzy, or out of focus.

Don't be afraid to use the ZOOM. There is so specific point, or as you say, "_now I'm not sure... is the 10 feet setting the idiot's point of max focus? 

_Good luck learning, and remember these things are not specific to your camera. They apply to all cameras. So, Google and You-Tube are your friend!


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## Achaicus (Sep 1, 2013)

grafxman
I do have f stop control: f2.8- f8.0 wide angle, and f4.3-f8.0 full telephoto. *6.0-60.0mm lens

radiorickm
Thank you, I knew when I launched into this I didn't know the vocabulary to ask the question I wanted to ask. I don't have a book on this camera, and most of my time with a camera has been with a point and pray, so to have to think about this is something new. I did grab the Andsel Adams photography lesson book from the library at one point, which is how I have some non verbal understanding (spent just enough time with the book to be able to know which end was up on the f stop-shutter speed and f stop- depth of field interactions). I have spent several hours playing with my camera since then to get the basics of those concepts.

Now that you have helped me with vocabulary, I would like to restate my question. In that book was instructions on how to maximize depth of field. To maximize depth of field, the focus would be set to just beyond the near edge of the depth of field that would exist when focus is at infinity.*

I see in my camera manual focal range jumps from infinity to 10 feet with no settings in between. My question is whether the 10 foot focal point would be that maximum depth of field setting (idiots point because of the jump) or if a focal point closer would be it. Assumed wide angle f8.0 used for the basis of this question. A related question would be what would be the maximum depth of field possible with my camera?


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## grafxman (Sep 1, 2013)

I practically never read manuals. I just play around with things until I figure them out. Here's what I suggest you do. Instead of being "hung up" on what the manual says, find out for yourself what the depth of field is and how much control it gives you. Go out into a lawn area and focus on the grass about 6 or 8 feet in front of you. Use the minimum zoom setting and the smallest f stop. In other words, the lens's aperture will be wide open which will give a minimum depth of field. Take a photo. Then set the f stop to the maximum which will close the aperture down to its minimum size. Take another photo of the same spot. This will give you the greatest depth of field.  Perhaps you should use a leaf or a rock as a focus point. Then zoom out to maximum and repeat the process with maximum and minimum aperture settings. 

Here's what you should see on a computer when examining a magnified image. With the lens set to both wide angle and zoomed to the max more blades of grass will be in focus with the smaller aperture setting of f8 than are in focus at the wide open aperture settings. That's how depth of field works. A smaller aperture means more stuff is in focus. A wider aperture means that just the item of interest is in focus and perhaps a few other things that are the same distance away. This photo may partly illustrate what I'm talking about:

IMG_4114 | Flickr - Photo Sharing!

As stated in the information area, that's a 1000mm hand held shot taken 4 years ago. However, see how the bird is in focus but the beach on each side of the bird is out of focus. If I had used a greater f stop and closed the aperture down smaller I would have had more depth of field and more of the beach would have been in focus. 

Focus control and an understanding of depth of field can be critical when it comes to getting certain wildlife photos. Examine this photo:

IMG_0752 | Flickr - Photo Sharing!

Notice how the bird's eye is in focus through the foliage. The intervening leaves are out of focus. That 500mm shot was with the aperture wide open. If I had closed the aperture down any, all the foliage would have been in focus and the bird's image would have been lost in the clutter. I hope this helps you some.


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## Achaicus (Sep 1, 2013)

I found a website that satisfies my inner geek, and nicely answers my question.
Online Depth of Field Calculator

The theoretical max depth of field focus point for my camera is 3 feet, which gives a depth of field from 1.5 feet to infinity. Which isn't much gain from setting it at infinity.*

Sweet, I have a camera with all of the basic controls available. Now I just wish for RAW, but I think that it isn't capable of it... Oh well I still have plenty to learn.

Thank you all for your kind nudges of direction.*

Regards,
Frederick Miles


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