Saturday, December 13, 2008

Lenses-How To Pick One And Read Their Specs: Part 3

Technical data not explained in a lens explained

Lens groups/elements: A lens may seem to be built in a complex way, but in reality its made up of smaller lenses inside it called simple lenses. These lenses are shaped in a specific form so they will create the effect required. When packed together inside the lens, they combine to make the lens you end up holding.

The arrangement of these simple lenses can be in groups or by their own, depending on the lens construction and what kind of lens it is. Each simple lens is called element and a group of simple lenses its called lens group.

When you buy a lens, in the technical specifications its stated how much lens groups and/or elements the lens is made of. Depending on the maker, a lens may contain little or a lot of elements inside it.

Minimum focus distance: In order to bring things in focus, a lens needs to have the proper distance from the subject. There is a limit to how far or how near the subject needs to be from the lens in order to be in focus. The minimum focusing distance is how much distance there HAS to be between your subject and your lens in order to be properly focused. If you dont have this distance, you wont be able to focus.

Unlike high end P&S cameras that require a lot less minimum focusing distance, DSLRS require more, this is determined by what kind of lens youre using and the size of your sensor. Since P&S cameras have a much smaller sensor, they have a much more cropped view, so close ups can be done with the lens practically over your subject.

The only lenses in DSLR system that can do close ups from really close to your subject are macro lenses. The minimum focusing distance varies from lens to lens, its not the same or standard among them, only if you own two identical lenses.

It's important to know this distance for every lens youve got so you know how close you can physicially get to your subject before the lens can't focus. It will spare you of losing moments you may not get back.

Filter diameter: Almost all lenses have a marking in them that tells you what size the front element is so you can attach a filter. The symbol is this one: Ø. This symbol comes with a number. In the Sony 28mm f/2.8 it comes like this: Ø 49mm. This means that if you want to attach a filter to this lens, you need a 49mm sized filter. The Sony 18-200mm f/3.5-6.3 shows Ø 62mm. The lens is bigger than the 28mm, therefore it requires a 62mm filter.

Since lenses vary in size, they size of filters you will need changes a lot. This makes it a problem if you want to put filters on all your lenses, since the variance in sizes may result in one filter being more expensive than others due to rare size or lack of filters due to the size.

Whenever you plan to attach a filter keep in mind two things:
  1. First check if your lens has a thread on its edge to attach a filter.
  2. If you attach a filter, be gentle when attaching and disattaching it. Some lenses have threads more delicate than others, and if youre not gentle, you make break them. This can result in no longer being able to attach a filter and need to buy a new lens.

Finally, some lenses like the Sony 16mm Fisheye lens or the 500mm f/8 Reflex lenses have built in filters included.

Size and Weight: As part of the technical specs of any kind of gear, the size and weight is included. This can be helpful if youre looking for a light and small lens or a big and heavy one. Checking this information before purchasing (especially online) can be helpful to give you an idea of the real size and weight of the lens, since it's common in online stores to display big lenses in a small size and small lenses in a very big size or not display them at all.

Minimum aperture: Since youre more likely to use big apertures instead of small ones, those are included in the lens itself, however, the minimum aperture or big f-number is something you should also know, since it tells you just how dark the lens can be or how much Depth Of Field you can achieve with it (assuming you can have enough light for such small apertures).

Just as the maximum aperture can change if you change focal length, the same happens with the minimum aperture. In the Sony 18-20mm f/3.5-6.3, the maximum aperture at 18mm is f/22, whereas at 200mm its f/40.

In average, in the Sony Alpha lens range the maximum aperture at a lens' shortest focal length is f/22 and at the largest focal length is f/32. Keep in mind this is just an average, not the exact aperture number for each lens.

Angle of view: A very important feature of any lens, its the angle of view it possesses.

The angle of view is basically how much of the scene infront of it the lens can see. The bigger the number, the wider the angle, and the smaller the number, the tighter the angle.

Wide angle lenses have (obviously) wider angles (duh) than zoom lenses or telephotos. However, that depends on the focal length of every lens. If you got a wide angle lens like a 20mm but you also got a zoom lens that has a short focal length of 18mm, the zoom lens can see a bit more than the wide angle lens.

Zoom lenses at their biggest focal length and telephoto lenses have a small angle of view, this is because in order to compress distance and bring subjects closer, you got to sacrifice angle of view. This explains why the closer you get to something, you cant keep the surroundings inside the frame.

How much angle of view you need depends on how much of a scene you want in your picture. You may have a wide angle lens thats including too much in the picture that you dont want or a zoom lens that cant squeeze an extra person in the frame.

One thing you got to keep in mind here is that the angle of view of a full frame lens changes when you use it on a APS-C sensor camera. Remember what I said of focal length multiplier? It applies here. Since a smaller sensor crops out part of the scene that a full frame sensor could capture, this also changes the angle of view.

Example: The Sony 16mm f/2.8 Fisheye lens is designed for a full frame sensor. On a A900, that lens would have an angle of view of 180 degrees, which would make the edges of the frame take a circular shape. If you use that lens on a A700 or else, the angle is reduced to 110 degrees and you wont be able to get the fisheye view the lens is designed to give.

This is why APS-C sensors require specially made wide angle lenses and fisheye lenses. Due to the cropping the sensor does, you would need a lens like the Sony 11-18mm f/4.5-5-6 or a Sigma 10-20mm whereas in full frame a 12-24mm would work as wide angle.

Whenever you buy a lens, be sure to know the angle of view the lens has and if it will be reduced if you mount it on a APS-C sensor or smaller.

Number of aperture blades: In a lens, the more blades it has, the better picture quality since the degree of blurring it can achieve is better.

Another data thats specified in the specs its if the aperture is normal or circular. Circular aperture is better since it renders the out of focus subjects smoother than the normal aperture.

In the Sony Alpha range, the average aperture blade number is 7, and the G and Carl Zeiss lenses almost all have 9. Also worth mentioning is that almost all the lenses in the Alpha line have circular aperture, the 28mm f/2.8 is one of the exceptions.

If it has special glass elements or coatings: Usually lens makers include special lenses among the elements to correct possible light aberrations that can occur. One very common these days is the APO lens. APO is an abbreviation of apochromatic, which means it corrects the color aberrations that the other elements can cause. The APO lens element was an element used by Minolta in its range of telephoto lenses.

There are all sorts of special glass elements used by lens makers in order to correct aberrations or to further enhance the effect the lens is designed for. They usually specify them when promoting a lens.

As for coatings, whenever the lens maker doesnt specify if the lens has a special coating on the lens, it will on the specifications.

Magnification ratio: Another important value of a lens is its magnification ratio.

In simple terms, it means how much it will enlarge small things. This is something really important in macro lenses, since they are designed to enlarge things.

When you see something through a lens, its size can increase or decrease. The magnification ratio is how much that lens can bring subjects to their real size. This ratio is expressed like this: 1.0 or this 1:0.

When a lens says its magnification ratio is 1.0 it means it shows the subjects on their real size.

Magnification comes in all lenses, in some its not so visible and in others it is. However, even telephoto lenses can have a high magnification; the Tamron 70-300mm f/4-5.6 LD Di has a magnification ratio of 1:2. That means that it can make subjects appear half their real size, which effectively makes this lens into a telemacro lens: a telephoto with macro capabilities.

If it comes with any other accesories: Some lens makers supply their lenses with additional accesories such as lens hoods, carrying cases, filters, cleaning cloths, etc. It's important that you check if any accessory is supplied with every lens you purchase, otherwise you wont know if something is missing.

Questions about lenses that you have but you're afraid to ask

Does an expensive lens guarantees a good photo?

No. An expensive lens may have a lot more bells and whistles than a cheaper lens wont have, but no matter how fast, light, full of special glass, etc. the lens is, if the photographer doesnt know how to handle it or doesnt have the enough vision to create a compelling picture, not even the most expensive lenses in the world will guarantee a good picture. It all depends on the photographer and its creativity.

Is lens sharpness that important?

It's common these days for photographers to be really picky about lens sharpness. The holy grail is a lens thats sharp all around including corners and at any aperture.

The truth is, such thing hasnt existed so far, and probably will never exist.

Modern lenses are sharp enough to get good pictures, sure, some are sharper than others, but the only way in which you will scientifically measure how sharp a lens is from another is with controlled tests at a lab.

And a lab isnt the only place for photographs you can use.

Ken Rockwell points out on an article he wrote about sharpness that usually the problem is not the lens, but a bad focus, camera movement or subject movement. You can find the article here.

Sure, you dont want your pictures coming out fuzzy or not sharp enough to see the subject, but lenses these days wont fall into that unless they have a defect.

A very very very underrated lens is the Sony 28mm f/2.8. A lot of people and testers disregard this lens because its not as sharp as other more expensive wide angle lenses are.

The truth is that this lens is sharp, may not be sharp enough to cut bread, but it sure is sharp, and Ive managed to get great portraits with it indoors.

Again, its more important what you conjure up for a picture than if your lens is sharp as a shark's fang.

Is it best to go for the expensive lens instead of the cheap one?

Well, if you got money to blow, then get the expensive one, if not, the cheap one.

Price only determines three possible things in a lens: Status, quality and options.

You can buy a Sony 70-300 f/3.5-5.6 G lens and blow 800 dollars on it instead of the Sony 75-300 f/4.5-5.6 that costs 223 dollars, you will be seen as someone with serious equipment and youll have as many buttons on the lens as you do on your camera.

However, that doesnt mean that you will get great pictures with it if you dont know how to use it. You only got a long lens with lots of buttons, better glass and a lens hood that will surely scream out to everyone else: HEY, I GOT AN EXPENSIVE LENS!

To get great pictures you dont have to own the best lenses. To think that you need the best lens to get better pictures is just as stupid as to think you need an Aston Martin or a Ferrari to make it to work on time.

Its the results you create with a lens that get you awards, jobs or praise. Viewers dont think of what lenses you use when looking at your pictures. They watch the results.

A 1800 dollars lens like the Carl Zeiss 24-70mm f/2.8 T* Vario Tessar wont make you a better photographer, nor will create masterpieces nor will take pictures on its own. The only results it will get depend on what you do with it. What YOU do with it.

Expensive or cheap? Doesnt matter, its the result you get from it that counts.


This concludes our article about how to pick a lens and read their specs. I hope that now the basic terms and concepts are now clear to you and you can get a better idea of what to look for in a lens when you purchase one.

And remember, its what YOU the photographer do with a lens that matters, not the lens itself. If you ever won a prize, it certainly wouldnt go to the lens you used, would it? A lens doesnt do anything on its own afterall.

James Bond uses a Walther PPK 7.65mm gun, which is a tiny gun, and yet he always does his job. Its how you use it, not what brand or size.

Until next time.

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