DSLR – Pentax Body

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All that you need to know before you buy a lens:

Before you make a decision about buying a lens (and to understand how photos are affected by various settings), you need to understand the basics. If you don’t understand something, just keep reading as it will become clearer towards the end.

Types of lenses:

• – Prime lenses – fixed focal length (no zoom – just one angle of view). Why? Because you get very high quality for a relatively low price. Achieving the same quality with a zoom lens is a big challenge, so the price goes up.
• – Zoom lenses – pretty obvious (variable focal length, but lower quality)

Zoom lenses can be classified as with:

• Fixed maximum aperture (or f/ number) – the same amount of light falls in across the whole zoom range.
• Variable maximum aperture – amount of light falling in decreases with zooming in (getting close to the object, so faster shutter speed is required to avoid motion blur)

Wide - A wide angle lens is a lens which has a shorter focal length than that of a ‘standard’ lens, allowing a much wider area to be brought into frame. To obtain a wider view, the centre lens has to be closer to the sensor (or film if you are using a film camera) of your camera, which means the lens must be shorter in overall length. A lens with a lower focal length (in millimetres) is always wider angle than a lens with a higher focal length. For example, an 18mm focal length is wider angle than a 55mm focal length. Wide angle lenses for digital cameras typically range from about 8mm to 35mm.

Standard - A standard lens is one which is in between wide angle and telephoto. Standard lenses for digital cameras typically range from about 35mm to 80mm.

Telephoto - A telephoto lens allows you to zoom in on far away subjects. The telephoto range is the widest range of focal lengths, ranging from under a hundred to over a thousand millimeters. These lenses are also the longest and bulkiest of all lenses, and it is not uncommon for a telephoto lens to weigh a pound or more. Telephoto lenses for digital cameras typically range from 80mm to 1200mm or more.

Fisheye - A fisheye lens is an extremely wide angle lens which captures at least a 180 degree field of view, and takes distorted pictures which bulge outwards in the middle, similar to a fish eye. Fisheye lenses were originally developed for use in meteorology and astronomy, but became popular with photographers for the unique images that they produce.

Macro - A macro lens is a lens of any focal length (but typically standard or short telephoto) which allows an extremely close minimum focusing distance to the subject. True macro lenses also feature a 1:1 (life size) reproduction ratio. Macro lenses are used for extreme close-up photography.

Parameters:

Focal length – is the distance between the sensor (or film in film cameras) and the lens (the nearest piece of glass to the sensor) or how far you zoom in or zoom out, that’s why zoom is given in mm as it reflects the focal length, which is measured in mm.

Focal length at Wikipedia

Aperture / f-number: Size of the opening inside of your lens that regulates the amount of light falling in, and also, as a side effect, it regulates the depth of filed (area of sharpness in the picture). The higher the f-number, the smaller the aperture (like that makes our life easier, but f-number is a mathematical value of focal length divided by aperture diameter in mm). Aperture can be set both in the camera and on the lens (although many lenses do not have that option), but the change happens in the lens only.

Aperture at Wikipedia

Depth of field – the length (distance) which will be in focus in the photo. It depends on the aperture and the size of sensor. Compact cameras have very small sensors, so the effect is difficult to observe.

At f/32, the background is distracting.     At f/5.6, the flowers are isolated from the background.

Depth of field at Wikipedia

Sharpness—or the lack of it—is immediately noticeable when you look at a photograph. If you are making a portrait, you want only the person to be sharply focused, but not a distracting background. In a landscape, on the other hand, often you will want everything sharp from close-up rock to far away mountain. Once you understand how to control depth of field, you will feel much more confident when you want to make sure something is—or isn’t— sharp.To control depth of field, you have three factors to work with.

• Aperture size. The smaller the aperture, the greater the depth of field. The larger the aperture, the shallower the depth of field.
• Camera-to-subject distance. As you move father from the subject you are focused on, you increase depth of field. As you move closer, you decrease it.
• Lens focal length. Using a wide-angle lens or zooming out increases depth of field. Using a long lens or zooming in decreases it.

Each of these three factors affects depth of field by itself, but even more so in combination. You can get the shallowest depth of field with a lens zoomed in on a nearby subject using a large aperture. You get the greatest depth of field when you are far from a subject, with the lens zoomed to a wide angle, and using a small aperture.

Stop – this usually refers to one step between one f-number and another (just another way of describing aperture changes). Each stop up increases light intake by 100%, and each stop down decreases light intake by 50%. If in automatic mode, the camera will compensate this by slowing down or speeding up the shutter speed. Cameras and lenses can usually operate in steps of 1/2 or 1/3 stops.

Resolution – similarly like the camera, a lens has resolution, but it’s more difficult to measure and it changes between the centre of the lens and its edges. Kit lens might have resolution of around 10M pixels or less, while good lenses will have up to 50M pixels (don’t quote me on that as I’m not an expert). You won’t find any info on lens resolution on the box as it’s not that important and subject to debate.

Other factors related to the lens, although not regulated by the lens:

Shutter speed – how long the sensor is exposed to light while the photo is taken. The shorter the time, the less blur in the photo, but less light falls in, so you need to have more light on the object photographed. If the photo is still dark and you cannot slower the shutter speed, you can decrease the f/number and/or increase ISO. This is set in the camera and does not affect the lens directly, but your camera might decide to change aperture of the lens to reflect the shutter speed changes (depending on the camera mode currently in use).

35mm equivalent – this matters only when coupled with a camera. It’s a standard that tells you how big or small angle of view is. You can compare it to different currencies; to know the value of something in another currency, you need to know what the exchange rate is, but in if everybody used, for example, only Euro, you would not have to calculate. So in photography we use the equivalent, so we do not have to calculate it ourselves.

E.g. with some cameras 18mm lens will give you the same angle as 28mm with other cameras, that’s why we use the equivalent, so 35mm equivalent of 28mm is always the same on each camera, although real distance will be different (I know, the more I explain, the less you understand). 35 mm is the size of a standard film exposure; hence this has become the baseline for other sizes. Digital SLR’s usually have smaller sensors (with factor of 1.5 or 1.6 – so called APS-C size), but there are some full frame (35mm) DSLR’s – they are usually more expensive and for professional use. All Pentax DSLR bodies are APS-C, so 18mm will always be equivalent of 28mm on 35mm (18×1.5=28). Check Wikipedia article if you need more explanation: 35mm equivalent

Please, let me know in the comment if you need more explanation or if you need answers to some other issues.

Regards

Kamil

One, two or more lenses with your Pentax DSLR?

Whether we talk about Canon, Olympus, Nikon, Pentax, Samsung or Sony DSLR, I guess this is a question that runs though the minds of all the owners of DSLR’s: How many lenses and what lenses?. If you’re a pro, the answer is obvious, but for a rookie (like I was just a few years ago) this is a sleep depriving challenge. Let me help you decide:

Typical scenario:

You love taking photos and you are planning to buy a DSLR camera, and you ask yourself and others around you whether to go for the kit lens, or two lenses (typically 18-55mm and 50-200mm or 70-300mm) or go for one universal lens (18-250 mm).

This applies to at least Pentax, Canon, Nikon, Sony and Samsung DSLR’s. Olympus has a bit different zoom length values, but in general it’s all about the same.

Pros and cons:

1. Kit lens only:

• - cheap
• - suitable for most everyday snaps
• - light

but

• - zoom only 3x
• - resolution usually below 10M pixels that your camera is capable of, if not more
• - shooting airborne planes and other distant objects is out of question

2. Kit lens plus long range lens (I would recommend Tamron 70-300mm):

• - not expensive (a lot of bundle offers, and anyway 70-300mm is quite cheap on it’s own)
• - very long zoom coverage (16.6x combined)
• - very good quality (for the price) of the long range lens (70-300mm) – perfect for portraits, macros (close-ups) and of course for peeping your neighbour from 50m away

but

• - two lenses to carry with you all the time (bigger bag, heavier)
• - inconvenience of changing lenses frequently
• - possibility of missing the perfect shot because the right lens is in the bag
• - getting tired of frequent lens changes and losing interest in taking photos etc.

3. Universal lens (Tamron 18-250mm or 18-270mm):

• - one size fits all – perfect lens for most shooting situation (unless you’re a pro and need really high quality, but if you were a pro, you would not be reading this, so don’t get distracted by those shouting “but the quality sux!” – believe me, it doesn’t)
• - a lens that you won’t need to upgrade for years (you might want to compliment it, but definitely not replace)

but

• - expensive
• - barrel distortion is quite visible while shooting geometrical shapes at wide angle (18-25mm), but if you only shoot (or photograph, to be precise) people and nature, you can neglect it
• - pretty high vignetting (or light fall off in the corners) in many situations, however most people won’t notice it, or it will actually add some charm to your photos, and it can be easily corrected in software that you are going to use anyway. Also, even the most expensive lenses suffer from this (just a little bit less, that’s why you pay more – much more)

So what should you do?

I have gone through all those scenarios above, so I know what each one feels like, and I can say: go for the last one – Tamron 18-250mm). Since I finally bought this lens, I don’t remember when the last time I swapped it was. I still love my Tamron 70-300 (brilliant lens), but I can’t really be bothered to carry two of them when I go for some fun shooting (most situations in the life of an amateur). So borrow, steal or earn that additional cash and get it right from the start to avoid my mistakes.

Remember, you are likely to change your camera every 2-3 years, but the lenses will stay with you for 5-10 years.

Summary:

Still not convinced or hesitating? Answer these questions:

1. Do you want convenience of one universal lens so you never need to compromise on zoom?
2. Do you really want to spend the money twice? (Sooner or later you’ll buy that universal lens)
3. Do you want to buy a bigger camera bag and carry it with you instead of just the camera?
4. Do you want to feel that you made the right choice?
5. Do you sometimes feel that you can’t take that perfect photo because of insufficient zoom?

I hope now you know what to do. So it’s either option 3 or 2. If you choose option one, you should buy a compact, not a DSLR (just kidding ).

Enjoy your shopping experience.

Kamil

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