How do you go from focal length and fstop to zoom?

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KingKrool

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When you buy point and click cameras, they always list zoom (optical) as 3x, 6x, 10x... or whatever.

However if you go for DSLR, they list it more professionally as say: 18-55mm f3.5-5.6

(This is from Loading deal page of Amazon.com)

I just wondered what this would mean in idiot terms... i.e. what kind of zoom does thing give as compared to a 12x optical zoom canon s2/s3?

I once knew how to do such stuff (back when I was in high school), but I can't remember anymore.
 
A normal lens in a regular 35mm camera is around 50mm .... a 18-55mm zoom lens would be 55/18=3.05 or rounded off to 3x zoom.

In digital cameras most have an angle of view on the wide side equal to anwhere between 28 - 40mm of a 35mm camera ..... different digital cameras have a different wide angle view ..... so a camera with 12x zoom for a lens with a wide view of lets say 40 would be 480mm so this lens would give the zoom view of 40 - 480 when compared to a regular 35mm camera.
 
Thanks dude. My plans of ever buying a DSLR are out of the window if it only gives me 3x zoom on the basic lens... I don't have the cash to afford an 8x lens for 170 USD (not that I have the cash to buy a DSLR for that matter).
 
on the other hand there are quite few non slr digicams with fairly decent zoom. I saw one kodak with a 10X zoom (optical) and i have a 6X zoom.

If you could tell me what your use for this would be, i might be able to help you little more but heres my two paisa on this subject anyway :D

When you do buy a dslr, you could look for a third party lens with no motor control/zoom. you could put a vivitar or sigma zoom lens on a nikon dslr, you would then zoom and focus manually but still use the dslr. Such lenses are cheaper and you can easily pick up a used one as well.

I am assuming that you like the slr for the manual focus use for hobby use.

in general with the smaller (aperture) lenses the fstop ranges are more limited. such as a larger zoom would result in a lens having a smaller f number. (correct me if i am wrong here)

One more thing is - between slrs and point and shoot types, they both have through the lens viewing.(incase of digital)
 
Basically, I want a digicam with at least say 6-8x optical zoom. After that I don't really care. 5-6MP is OK.

The only reason I wanted a DSLR is that I have always wanted to take up photography as a hobby... DSLRs make that possible because they allow you to take photos without the expense of D&P... but if it makes ordinary photography impossible (just 3x zoom doesn't cut it for me), then I will just go to point and click and save me some money. I am in no real hurry to buy anything just yet, but some of the prices available right now are attractive. Thanks for the help.
 
Do not worry about that too much. I know which cams I am likely to buy if I go point and click. As for DSLR, the lower the better. I am not going to be into anything real high end. As of now I am not in a hurry. I was actually looking to buy something next year, but when I saw some of the prices over thanksgiving I started drooling.
 
Don't bother about zoom... look at the reach... a 70-300mm lens will give you way better pics than anything a 10x or 12x optical zoom point and shoot can manage. The former can be had for as low as 150$. A super zoom is not the best solution unless you have an awesome lens like the 18-200mm Nikor VR lens. A lens design performs its best when you use it at a particular range of focal lengths. If what you want to do is take pics of things far away, what you need is telephoto not zoom. Its a popular misconception that zoom lens is used for taking pics of distant objects. A zoom is basically a lens with variable focal length whereas a prime is a fixed focal length lens. Zooms can have focal lengths as low as 10-22mm for super wide angle photos. A rule of thumb is higher than 50mm will basically crop the image over natural field of view and bring farther objects closer to you(telephoto) whereas anything below 50mm is a wide angle lens with more than natural field of view. For reduced sensor DSLRs like the Rebels/EOS 30D/Nikon D40,50,70s,80,200 etc you must multiply the focal length by 1.6 to get the effective 35mm focal length. So basically to get the natural field of view, you need a 30mm lens. Any higher is telephoto. You can take pics of really far away objects even with a 300mm prime lens ;). As a matter of fact in most situations a fixed focal length prime will perform way better than a zoom lens. Primes are generally faster as well so will take sharper pictures wide open.

Also point and shoots get noisy at anything higher than 200 ISO whereas DSLRs can be used upto 800 ISO without much trouble. So if you wanna capture fast motion or u wanna do low light photography, the point and shoots are useless. If you are going the canon route, you can pick up the body for around 520-530. The choice of lenses completely depends on what you want to shoot.
 
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hi,

what exactly is "reach" in photography?

The ISO point is a very valid point. If you need such high ISO's that is. For most hobby uses 400 ISO should be enough for everyone(TM)
 
Reach is the maximum focal length that the zoom can focus at... the higher of the numbers specified. For primes, reach is fixed.
 
From my experience (plainly as a hobby), you would end up taking more wide-angled shots than tele ones. I have a S2 which i bought because of its 12X monster zoom, but i always keep craving for a better wide-angled cam...
 
Suppose I want one of each... one lens for the regular run of the mill stuff.. say at home, or at a party or something.. and one for outdoor trek like scenarios. What would you suggest? The one I have there is 18-55mm which makes it 29-88mm for a 35mm camera. That would be a wide angle lens right? So what should I add on as a telephoto attachment?
 
telephoto attachment for bright day ligh tshooting you could use a 2X or 4X extender- this is available as a clip on attachment for point and shoot cameras.

with an slr you could buy 28-35/35-70/35-170 etc etc any type of lens you want.

extenders give some vignetting and reduce your f number by the same factor.
 
I am considering SLR for the moment. Suppose I get the camera+lens that I have mentioned in the first post. Now I want another lens. Which one?
 
70-310 or similar is a good choice for most outdoor use.

for outdoor trek and indoor party use your 25-88 is very good. treks need wide angles!!

Now if you want telephoto then go for > 88mm for the lower focal length of the lens.
Or you can go the other way as well. namely select an upper focal length, say 300 mm and then go down depending on your budget.

Years ago when i had this(expensive) hobby, with a manual SLR, i found a 35-70, and 70-300 lens enough for my needs. then i was considering a 2X entender to give me 70-140, 140-600 lens range. but then the camera gets limited in terms of the aperture, which becomes f/6 or something like that and you need bright lights, and fast films. My use was very similar with trek and indoor parties and food photography for which i used close up adapters, for ultra macro shots.

My suggestion is to go with a extender now, evaluate it and then later if that is limited them by a good long range zoom.
 
25mm on a APS-C sensor is barely wide angle. You can't compare the focal lengths directly... multiply the 35mm focal length by 1.6 to get the effective focal length. Frankly speaking anything higher than 100-120mm is hard to use without a tripod or IS. If I were you kingy, I'd stay away from any sort of extenders. Consumer telephotos are really slow lenses. You'd not wanna screw them up further by using extenders. My advice... if you are short on budget and want to stay on the canon side of the fence, just get the kit lens and a 50mm f/1.8 prime. These will be good enough for a beginner to learn photography. The latter is an amazing lens.
 
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