Zoom confusion

[Solarflare]

One thing I haven't seen anyone hit on that might help OP is a focal length of about 50mm is what the human eye sees. So you can judge from that the distance the lens can see.

I frankly dont get what this even means.

Obviously, human beings have a 14mm lens because we have a nearly 180 degree vision (horizontally, anyway).

But I've read that our actual field of view, the area where we really see sharp, thanks to enough light sensitive cells in that area, is just 3 degrees, which is about 800mm.

And if I view through my viewfinder, the image I get with my 50mm equivalent is nowhere near the image I would see without the camera. I guess that also depends upon the magnification factor of your viewfinder.

So where exactly does one get this "50mm is near what the human eye sees".

What I get is that its pretty close to the actual size of the sensor, which is 43.3mm (thats the diagonal of a 36x24mm full frame sensor).

 

[John27]

To me, the 'x' number is just a mass-marketing gimmick. Used to make a '10x' lens somehow better than a '5x' zoom to the uneducated buying public.

Bingo. It's kind of like wattage on audio equipment. You gotta look on the box for the real numbers. Your "500 watt" amp is nowhere near 500 watts. That's PMPO (Peak Music Power Output) which is a number that happens so quick the human ear can't even hear it. It's basically made up! It's all marketing gimmicks. It might actually be around 120 watts RMS (actual, sustainable, constant MAX power)

It doesn't mean the products are bad, but, if they can find some way to have a bigger number (any number) than the other guy, they will. Because a lot of un-informed, un-researched customers will compare it, based on numbers, with what is on the shelf. In fact, I was at Best Buy on black friday (they had the 430 EX II on sale) and while I was in the DSLR aisle I heard a lady talking to the associate. She said "Okay, now, why is the 5D so much more than the 7D", "Well the 5D is a better camera" said the ever-so-knowledgeable associate. Then she said "How can that be, this is a 7, that's a 5?" To which the associate replied "Oh yeah, that's true... I dunno then"

Bigger number. Must be better. Maybe Canon uses that system knowing that it's high dollar cameras are going to educated consumers, whereas the cheaper systems are more likely to be bought by a window shopper. They'll think that 500D is such a great deal, a tenth the price of the 5D! And it's 495 more D's!

The craziest one is megapixel though. Yes, high resolution has it's advantages, but whether DSLR or PnS there are way to many factors to focus in on that one. In the days of 1 and 2 megapixel cameras perhaps, but nowadays with these incredibly high resolution images (remember your big screen high definition TV is around 2 megapixels. Which is impressive considering it's 24, 30, or 60 2 MP images each second, but still!), the quality of the lens, features, and sensor are sooo much more important. Yet so many consumers will look down the aisle and find the highest 'megapixels' camera they can find, assuming bigger must be better!

 

[Solarflare]

Actually, how much you get depends upon your loudspeakers.

That is because the degree of efficiency varies extremely between different loudspeakers. If you get a cheap one with meager traditional magnets, or a highend one with huge neodyn magnets, or a horn loudspeaker (who are much more efficient than other types of loudspeakers) will make the same 20 watt input result in very different levels of loudness.

And of course every loudspeaker also has a maximum loudness, too. No use to have a 400 watt amplifier and a 20 watt loudspeaker.

Also, people who buy hifi equipment on the basis of "the more watt the better" are truely extremely clueless. Most people know that better hifi equipment has better sound quality, but not necessarily more loudness.

Its pretty much like cameras, too.

 

[Kolia]

Solarflare,

The image, zoom compression and general feel delivered by a 50mm lens on a FF sensor will be similar to what you could see if you were standing and the spot where the picture was taken.

You might just perceive 3 degrees FoV but that doesn't matter. You never look at a whole picture at the same time.

As for your audio concept. The material used in the construction of the driver is irrelevant to the amp. It only see the speaker's resistance.

A 400W amp powering speakers made for 20W will still sound better than with a 50W amp because it will run lower in its power range.

We use very little power to generate sound. Just look at the rated efficiency of your speaker. 86dB at 1m with just 1W of power is loud !

 

[Solarflare]

I'm sorry, I dont get your comments on audio.

How good an amplifier sounds is a much more complex issue that what you describe and most amps are really not bothered that much on what output they produce, in respect to the sound quality they produce.

Whats true though is that, if you have a 200 watts box, its a good idea to have a 250 or 300 watts amplifier, because that will protect your tweeters. When an amplifier gets beyond its maximum output, a lot of high frequencies are produced and that may kill the tweeter.

Audio is a very, very complex issue though and completely offtopic in this forum.

 

[DirtySocks85]

To me, the 'x' number is just a mass-marketing gimmick. Used to make a '10x' lens somehow better than a '5x' zoom to the uneducated buying public.

While we're at it we should probably touch on how much of a crap marketing feature "digital zoom" is.

 

[480sparky]

To me, the 'x' number is just a mass-marketing gimmick. Used to make a '10x' lens somehow better than a '5x' zoom to the uneducated buying public.

While we're at it we should probably touch on how much of a crap marketing feature "digital zoom" is.

Um.............

 

[DirtySocks85]

To me, the 'x' number is just a mass-marketing gimmick. Used to make a '10x' lens somehow better than a '5x' zoom to the uneducated buying public.

While we're at it we should probably touch on how much of a crap marketing feature "digital zoom" is.

Um.............

Ah, I must of missed that. My mistake. Anyway, it makes me cringe when I see people (read: my mother) constantly using the zoom feature on their iPhone and then wondering why it looks so bad.

 

[panblue]

18 x 1 = 18
18 x 2 = 36
18 x 3 = 54

18-55mm = ~x3 zoom capability

I am really confused about zooming in DSLR's. In P&S's the ability of zoom is defined by X's, like 10X zoom, 15X zoom etc. In DSLR's, it is described as 18-55mm, 70-200mm. The first thing I want to know about is that if a 18-55mm lens provides 3X zoom, what will a 70-200mm provide? How to convert DSLR zoom units to P&S zoom unit?
Second confusion is, Can we zoom using a lens that has fixed focal length? like Nikkor 35mm f1.8, 85mm, 50mm.

No; fixed is fixed. Zoom is variable, not fixed. 1.8/35 is a fixed focal-length. Commonly referred to by stills photographers as 'a prime lens' although I've read that actually zooms can be termed 'primes' in cinematography but that is more obscure usage of the term.

 

[Solarflare]

I mostly like the term "prime lens" because its not such a mouthful as "Festbrennweitenobjektiv" in my own language

 

[CFPAalex]

Wow! Learned a lot! thanks for every here.

 

[480sparky]

Shall I further muddy the water by mentioning varifocal lenses?

 

[BrianV]

"Zoom lenses" have mechanical/optical compensation to maintain focus across the range of focal lengths of the lens.
"Varifocal lenses" rely on the user to correct the focus as the focal length is changed. They were not very popular on SLR's, Vivitar 35"ish"~85"ish"/2.8 (I forget the exact range) is the only one that pops into mind. Leica offers the "Tri-Elmar", essentially varifocal lens with 3 set positions. The RF cam of the lens changes to maintain coupling with the camera. You can take apart most fixed-focal length lenses and make them into a vari-focus lens. Just make it so the spacing between front and rear groups can be changed.

 

[Sarmad]

Thanks guys, that was quite helpful!