Dans cet article, nous allons passer en revue tous les critères liés à un objectif photographique
Technical Qualities of the Lens
Technical quality is a good starting baseline.
- Focus: Does the lens have autofocus, and if so, what kind of autofocus? Newer methods are usually faster quieter, but not always. What focus modes do the lens allow?
- Focus breathing: Does the focal length change dramatically depending on where you’re focusing? How will this affect any images you plan to make?
- Colour rendition: How does the lens render colour? Is it incredibly accurate it or does it mute some tones?
- Lens coatings: How are the lens elements coated? Coatings are an effective method for minimising chromatic aberration but they can negatively affect light transmission. If you’re shooting black and white, less coated elements is better. For colour, you need multiple coatings to deal with aberration.
- Coma: How are off-axis point sources of light rendered? Does the lens suffer from a lot of comatic aberration or do they remain points?
- Distortion: Barrel and pin cushion distortion affect the straight lines in your images and wide angle lens are more prone. How are the edges of the image distorted by the lens? Is the distortion too much for your needs?
- Light falloff: How does light fall off towards the edge of the image? Is there a heavy vignette or is the image evenly exposed?
- Use with filters: Can you use the lens with standard 77mm screw on filters or is it an unusual size, needing adapters?
- Flare and ghosts: How does the lens react to off-axis light sources? Do they cause dramatic lens flares and ghosting? Do you want this effect?
- Lateral colour fringes: How much does the lens correct for chromatic aberrations? Are all your images going to end up with colour fringes or will they be barely visible?
- Macro focusing and minimum focusing distance: How close can the lens focus?
- Sharpness: How sharp is the lens wide open? What about at its sharpest aperture? Is it sharp from corner to corner or just in the centre? Do you even need tack sharp images?
- Spherochromatism: Similar to lateral colour fringes but caused by a different optical property. Will they be a problem?
- Sunstars: How will bright light sources look at smaller apertures? How many blades is the aperture diaphragm? That’s what determines the appearance of sunstars.
Aesthetic Qualities of the Lens
A lens might not be technically perfect but still have aesthetic character that makes it worthwhile.
- Lens family: Is the lens based on a classic design? There are plenty of imperfect-but-aesthetically-pleasing lenses that have become cult favourites. Maybe a particular photographer used this lens in their most famous works?
- Bokeh character: How do the bokeh look at wide apertures? Do they add or detract from the kind of images you want to create? Are they unusual or interesting in any way?
- Microcontrast: How does the lens render small changes in colour? Does it flatten them out or leave microcontrast intact?
- 3D-ness: How does the lens render 3D objects? Are things compressed so they appear on the same plane or do they maintain their fullness?
The lens housing is almost as important as the lenses themselves.
- Material: What’s the lens made of? Metal lenses are hardier but plastic lenses are cheaper. Do you need tough lenses?
- Focal length: What’s the lenses focal length? Is this a focal length you want to work with?
- Angle of view: What’s the adjusted focal length of the lens if you’re using something other than a 35mm/full-frame camera? Is that too wide or tight for your needs?
- Maximum reproduction ratio: For macro shots, what’s the ration between the size of the subject and it’s reproduced size on the centre?
- Hard infinity focus stop: Does the lens stop focusing at optical infinity or can you focus past that? Do you need to be able to quickly focus to infinity or can you eyeball it as you work? Are you going to be working in a wide variety of environmental conditions where optical infinity will noticeably change?
- Focus scale: How small are the focus increments? If you’re going to be doing a lot of manual focusing, the smaller the better.
- Depth-of-Field scale: many older manual-focus lenses have markings on the barrel to help you do hyperfocal focussing.
- Filter thread: What size is the filter thread? Is it common? Do you have the filters that fit it? Is it metal or plastic?
- Mount: How is the lens mounted to the camera, and is it compatible with your camera? Is it a plastic or metal mount? How far does the flange project into the body?
- Size: How big is the lens? You do have to carry it. Some lens manufacturers like Sigma and Sony make big lenses while others, like Leica and Voigtlander, make smaller lenses.
- Weight: How heavy is the lens? Again, you have to carry and work with it.
- Caps: How does the lens cap attach? Is it easy to remove? Is it going to fall off easily?
- Hood: Does the lens come with a hood to protect against lens flare?
- Case: Does the lens have a case? Is it capable of protecting the lens?
This last measure is entirely subjective. How does the lens feel when you use it? Is it balanced with your camera? Do the aperture ring and focusing controls move smoothly? Is it a nice beefy portrait lens, good for working slowly? Or is it a diminutive pancake lens, perfect for street photography? Lens feel is, in some ways, the most important characteristic. You can read internet reviews all day long about ‘perfect’ lenses but it’s the lens in you hands that you’ll use in the real world. It has to feel good.