General questions about lenses

Abstract said:

I still don't understand (at all)*cough* are lenses, and what I need.

Here's one of many (many many) questions I have about lenses: Why would you want to get a 28-70 mm lense at all when you can just get a single 28-200mm lense? One goes to 70 mm, while the other goes to 200mm. I realize that the price, glass, etc, is different, but why not just get one with the largest range of numbers possible? Is that silly?


What about the "G" in front of f/3.5-5.6G? Sometimes it says "D" instead of "G". And why do some lenses not give you a range of apertures at all? Why would someone want only f/2.8 and not more options?

I have more, but can't think right now.

Click to expand...

To start with your lens, (and you may know this already) - in digital photography your lens will typically have a different 'effective' ratio than a traditional lens - say, around 1.5x greater. Thus, a lens that's 24-120mm would actually be the equivalent of, say, 36-182mm. As far as getting the greatest range - I suppose you'd have to weigh what you typically shoot with cost, weight of lens and what you're willing to accept in terms of lens speed and quality. A great quality lens can cost a LOT of $ with a large range.

My 'guess' on lack of aperture ranges would be that since the Nikon G lenses are designed for camera-body driven aperture control, you'd change this with your body instead of your lens. The D is for 'distance' - lenses that are made to give you distance accuracy for flash & ambient light. I don't shoot with Nikon's, but that's my understanding of their series.

Abstract said:

Here's one of many (many many) questions I have about lenses: Why would you want to get a 28-70 mm lense at all when you can just get a single 28-200mm lense? One goes to 70 mm, while the other goes to 200mm. I realize that the price, glass, etc, is different, but why not just get one with the largest range of numbers possible? Is that silly?

Click to expand...

Generally speaking the greater the zoom ratio (28-80 is 2.8x zoom, while the 28-200 is a 7x zoom) it is felt that the optical quality of the lens falls off. But not everyone sees the quality differences.

I thought about it and may actually just get the D50 body and buy my lenses separately. The question is which one, and for my understanding, why?

Click to expand...

It depends on your needs. I went with the D50 and the 18-200VR for shear ease of carrying on my European trips. I will still have for the time being my Rebel XT kit with a great set of three different zooms for times that I demand the sharpest images. Add to that,the VR on the 18-200 will allow me to take virtually shake free images down to 1/15 of a second.

I also don't understand the "lingo" is when it comes to lenses. Looking at Nikon lenses, what does AF and AF-S mean? How about DX? I figured out what IF and ED is though (yay!).

Click to expand...

AF is focusing by gear connection. This is noisier and slower than with AF-S which focuses with a silent wave motor built-in to the lens.

What about the "G" in front of f/3.5-5.6G? Sometimes it says "D" instead of "G". And why do some lenses not give you a range of apertures at all? Why would someone want only f/2.8 and not more options? In fact, lenses that say f/2.8 never give you a range. I find it strange to not give you any choice. In fact, I don't understand why it would be so hard for them to just give you a much larger range of aperture sizes. Is it a physical limitation?

I have more, but can't think right now.

Click to expand...

As mentioned, the G means that there is no aperture ring. The D means that the lens cpu communicates distance information to the camera. This is used for 3d Matrix metering and 3d flash metering. Can help in getting that much better of an exposure.

All lenses have a range of apertures (save for special purpose lenses). A 2.8 aperture lets in lots of light compared to an f/4 lens. Sometimes lens will only show you the maximum aperture, sometime the entire range.

Hope this helps.

Abstract said:

Why did you get the D50 and the 18-200 VR lens for stability when the D50 doesn't even have a mirror lock-up feature? Doesn't NOT having the mirror lock-up feature, which is present on the D70s, defeat the purpose of getting such a nice zoom lens with VR? I know the D70s is a lot larger, but still....

Click to expand...

Usually it is only macro people who use mirror lockup consistently - so they wouldn't be using a VR lens anyway.

Abstract said:

...And why do some lenses not give you a range of apertures at all? Why would someone want only f/2.8 and not more options? In fact, lenses that say f/2.8 never give you a range. I find it strange to not give you any choice. In fact, I don't understand why it would be so hard for them to just give you a much larger range of aperture sizes. Is it a physical limitation?

Click to expand...

The aperture that is listed with a lens like that is not the only aperture that the lens is capable of. What it represents is the maximum aperture of the lens.

For example, the f/2.8 lens you mentioned means that it can be 'opened up' to as much as f/2.8. It still can have the apertures of f/22, f/16, f/11, f/8, f/5.6, f/4 as well as f/2.8, plus fractional stops in between. Thus, for an f/2.8 lens, it will have 7 "full" stops worth of adjustment between f/2.8 and f/22.

BTW, you'll sometimes find apertures beyond f/22, but I'm ignoring them here. Similarly, there's some mirror-based 500mm lenses that are only f/8 - its an exception to the rule.


From a photo crafting standpoint, having more adjustment range is always better. However, it is technically more involved to make a lens with more light-gathering power (f-stops with low numbers), so these lenses will be more expensive and heavier...that's the trade-off you're faced with. For example, Canon makes an f/2.8 300mm telephoto and an f/4 version too. The latter's lighter and less expensive.

Aperture Ranges:

When you see a lens such as a 75-300mm f/4.5 - f/5.6, what this means is that the maximum available aperture is not constant across the zoom range.

Typically, the lens will be the 'faster' (f/4.5 here) aperture on the wider end and the 'slower' (here, f/5.6) on the telephoto end.

Again using f/22 as the minimum, this particular lens would have 5 stops of adjustability on the f/5.6 telephoto end, and 5.5 stops on the f/4.5 wide end.

Overall, this is just another engineering design technique to make a lens be less expensive & lighter, which will of course have its trade-offs.

FWIW, notice that I've not said anything yet about image quality. This is still just basically looking at the "trade space" between physical size and the light-gathering abilities for a certain focal length/diameter/etc. For example, in the 75-300mm lens group, Canon sells IIRC 3 different designs, which range from $200ish to $1000.


-hh

"Why would you want to get a 28-70 mm lense at all when you can just get a single 28-200mm lense? One goes to 70 mm, while the other goes to 200mm. I realize that the price, glass, etc, is different, but why not just get one with the largest range of numbers possible?"

Different lenses fulfill different needs at different times. At home, I very often prefer to use my long and heavy 70-200mm f/2.8 VR lens, especially in low light conditions. Right now I'm about to take a trip (to SF, to MacWorld!). Of course I'll want to shoot photos out there and of course I want the long reach of a 200 mm lens....but I DON'T want to take that very heavy, large lens with me, nor do I want to take several other lenses in order to make up a decent range of focal lengths. Instead, as Chip mentioned, there is the new Nikon 18-200 mm VR lens, which I will be taking instead. That and the 12-24 mm lens will give me plenty of range in just those two lenses. Tradeoff is that I might not be able to get some of the same images that I could with a lens that has f/2.8 throughout the lens focal lengths, but the convenience is worth it and I'm anticipating that the VR on the 18-200 will make a difference. I've shot with the Tamron 18-200 mm and found that I didn't always have satisfactory results. We'll see how the new lens works for me out in SF...

OTB

Mirror lock-up is normally used for long exposures on a tripod, and Nikon suggests turning off the VR on the 18-200 when the lens is on a tripod.

"If you have a 70-200, and an 18-200mm lens, they both have the same reach as you put it, but different magnification."

Both lenses have the same magnification, which is

mX = [Focal Length] / 50 = 200 / 50 = 4X.


"So basically, I'd think that the 70-200, which has a magnification of ~3x, would have a longer barrel, while the 18-200mm would have a very short barrel."

A 70-200 lens has a zoom range of

zX = [Maximum focal length] / [Minimum focal length] = 200 / 70 = 2.86, or approximately 3X.


The Nikkor 70-200 mm f/2.8 lens is long and heavy because it is a constant-aperture lens with a fixed barrel length.


"And these lenses have the same reach, but what does that mean anyway if the magnification is different on each?"

The maximum magnification may be different between lenses because their minimum focusing distances are different. This magnification is the size of the subject on the film at the maximum focal length and the minimum focusing distance.

"And with an AF Nikkor 50mm f/1.8D, wouldn't I only be able to focus on objects at a very specific distance, as 50 mm is non-adjustable?"

A 50 mm prime lens has a fixed focal length, not a fixed focusing distance. A real issue with focusing distances is the infinity focusing distance, outside of which everything is in focus. If you desire a blurred background, you need to be inside the infinity focusing distance of the lens.

Wanted to post this reference link earlier, but it took me a few days to remember where I'd seen it.

http://bythom.com/lensacronyms.htm

Hope it helps re: some of the naming conventions/meanings re: Nikkor lenses.

Frank

arogge said:

A 70-200 lens has a zoom range of

zX = [Maximum focal length] / [Minimum focal length] = 200 / 70 = 2.86, or approximately 3X.


The Nikkor 70-200 mm f/2.8 lens is long and heavy because it is a constant-aperture lens with a fixed barrel length.

Click to expand...

Maybe should add to that, this lens is designed to meet the greatest expectations at all focal lengths and apertures.

A lens can have the same focal lengths and apertures; but be vastly different in size. In the past "larger" lenses were though to be better "corrected" than those of similar values.

f/2.8 is the max end of the scale

Abstract said:

In fact, lenses that say f/2.8 never give you a range. I find it strange to not give you any choice. In fact, I don't understand why it would be so hard for them to just give you a much larger range of aperture sizes.

Click to expand...

If you can aford it you WANT the lens marked "f/2.8" That number referes to the MAXIUM aperture size. Some zooms are marked f/4.6 - f/5.6 which means the maximum usable aperture will be in the range of 4.6 to 5.6 depending on the zoom setting ALL lens
allow you to stop them sdown to f/16 or f/22 so they never advertize the other end
of the scale.
BTW that number "2.8" is the ratio of effective lens diameter to focal lenght. A smaller number means a larger diameter and in "lens speak" aperture means diameter.

Next question: why not get a 28-300 zoom? because you can't get a zoom that wide in f/2.8 and for a given price point the shorter range willhave better quality.

At the extream end of this I bought a fixed foal lenght lens (a non-zoom) because I could get it with f/1.4 max aperture and zooms typical can be found in f/2.8 at best,

arogge said:

"If you have a 70-200, and an 18-200mm lens, they both have the same reach as you put it, but different magnification."

Both lenses have the same magnification, which is

mX = [Focal Length] / 50 = 200 / 50 = 4X.


"So basically, I'd think that the 70-200, which has a magnification of ~3x, would have a longer barrel, while the 18-200mm would have a very short barrel."

A 70-200 lens has a zoom range of

zX = [Maximum focal length] / [Minimum focal length] = 200 / 70 = 2.86, or approximately 3X.

Click to expand...

FWIW, I think the confusion here was the concept of the...do we call it "zoom ratio"?

For example, looking the max/min ratio of a 70-200mm, we get 200mm/70mm = ~3x, whereas a 28-200mm is 200mm/28mm = ~7x

I think the source of the confusion was that IIRC, the comment was made that zooms with larger zoom ratio's tend to be inferior to ones with smaller zoom ratio's...ie, a "7x" won't be as good as a "3x" for image quality (at the same price point, of course).

Briefly, the underlying physics here is that any zoom lens needs to move its glass elements around to be able to zoom, and the broader the zoom adjustment range (7x vs 3x) is, the further they have to be moved.

Since a longer telescoping barrel will have more barrel flex, barrel twist, etc...stuff that degrades the optical allignments...either the quality of the lens has to go down, or you put in more engineering technology to keep it in allignment, so it becomes more expensive.

As such, the generalization is that a lens with a significantly broader focal range "will have to" ... at the same price point, etc ...produce an inferior image to the lens that has less focal length range.

Do notice that when we take this generalization to the extreme, we get another common generalization, namely: "a zoom lens can't ever be as good as a prime lens".


-hh

Chip NoVaMac said:

A lens can have the same focal lengths and apertures; but be vastly different in size.

Click to expand...

Here's (halfway) an example (note: the two camera bodies are alligned to each other, even though it doesn't quite appear that they are)

Obviously, the white lens on the left is physically bigger than the black lens on the right, but its maximum is only 200mm, whereas the black lens's max is 300mm, which is 50% more magnification!



Lens on left:
Canon 70-200mm f/2.8 IS
Roughly 3 lbs
77mm filter

Lens on right:
Canon 75-300mm f/4.5-5.6 IS
Roughly 1.5 lbs
58mm filter


-hh

You don't need a long lens

One interresting observation: New or beginner photographers always think they want ahuge telephoto lens. Putting a 200 zoom (be it a 70-200 or 28-200) on a D50 is like putting a 300mm on a 35mm format film camera. a 300mm lens is really a specialized lens that is not usful most of the time. OK there are uses for long lens. Sports and wildlife photographers use them and the latter group always with a tripod

In general a wide lens is much more usfull. Ge the widest and fastest one you can afford.

Why do you need a 200mm lens? Try and list the subjects you would shoot with it. Basically you list should include ONLy subjects that are physically impossable to get close to lke animals in zoos and wll not much else. Unless someone has put up a physical or legal barier it's always best touse you feet rather then the big lens.

One good Nikon Lens is the kit lens that comes with the D70. It happens t have a longer zoom ratio than the D50's kit lens but it is a FAR BETTER lens. It is also 3X more expensive. The autofocus motor is MUCH faster and more silent and it has the fast manual over ride (just grab the focus ring and the autofocus shuts off) and a non-rotating front ring (a must-have feature for many of us who like polerized filters) and better quality physical construction It's about $350. You could use it until you can name some shots you've missed due to the lens' inability. I'll bet that list will include comments like
1) low light, need faster lens
2) Could not back up through wall, need wider lens
3) camera was to large to cary, left it at home
Very few comments will say "subject appeared to smal in viewfinder" because you
can always crop the image

Abstract said:

I also read somewhere else that the telephoto lens that I get doesn't matter very much anyway, so getting a cheaper one isn't so bad, and that I should invest in a great wide-angle lense rather than a great telephoto.

Click to expand...

I think the simple bottom line is that if you get hooked, you're going to dump a ton of money no matter what

I think I read it on Ken Rockwell's site, but his reviews seem so indifferent and insouciant in all his reviews and advice about lenses and cameras ("It really doesn't matter what camera or lens that you use because they're all good to me!!").

Click to expand...

I'd have to go look at what "class" of lens he reviews, because there are some pretty lousy lenses out there - - in particular, the 'cheap' telephoto's.

The goodnews/badnews aspect of this is that if you never print anything larger than a 4"x6" print, this small print size covers a lot of shortcomings in optics - - oldtimers like myself will grin and recall that "way back when", even prints from ancient 110 film cameras looked "Okay" with this print size.

The underlying question here is one of how much "reserve capabilty" do you want to have inherantly built into your image capturing system so that when you do get that lucky fabulous shot, you can successfully enlarge it?

FWIW, in our dining room, I have an 8x10 photo of a chinese wood duck hanging up. I absolutely *loathe* it. The reason why its still hanging up is because my wife loves the shot - - I love it to ... but in 4x6! When we enlarged it to 8x10, the grain in the 1980's vintage ISO 400 speed film became very, very evident to my eye, which ruins it for me personally.

Lesson learned: even if you're just woodchuck hunting, load for bear.

I have a chance to get (prices include taxes):

1. D50 + 18-55 mm lense for AUD$1200 (or US$901)
2. D50 + 18-55 mm kit lense + 70-300 mm G Nikkor lense AUD$1500 (or US$1127)
3. D50 + 18-55 mm kit lense + 55-200 mm Nikkor lense AUD$1600 (or US $1202)
4. D50 + 18-70 mm lense AUD$1600 (or US$1202)

Click to expand...

I'd probably go for either #1 or #4. Basic philosophy is to focus today on a good WA capability, and put off any healthy telephoto for awhile...work on one thing at a time, and do it well, rather than dilute yourself and do neither well.

For #1 vs #4, I'm of split opinion. On the one hand, the higher cost of the 18-70mm infers that its probably a "better" lens. On the other hand, I might be inclined to opt for a little more $ for the 18-35mm f/3.5-4.5D, which I think is a full frame lens? And on the third hand, I'd say "now is the time" to buy a good Nikon 35mm body before they become scarce, so I might put some of the budget towards that if I didn't already have that base covered (FWIW, since I use Canon, I'm looking at some options at or above the EOS-3). Fortunately, its your decision, not mine


-hh