Lenses and their types

[gymak90]

Hi!

I've got a couple of questions regarding lenses. Hope I can some advice from the folks here

1) How is macro-focusing different from normal focusing? Take 2lenses for example, both are zoom lenses of 70-300mm. But there are 70-300mm Macro lenses. Can't a normal 70-300mm do macro-focusing?

2) So far I've been using zoom lenses. There are standard focal length lenses out there, e.g. 50mm. Again, why is there a need for such standard focal length lenses, when a zoom lens e.g. 17-85mm can also be set to 50mm?

Thanks for the help!

[Dream Merchant]

In the example you mentioned, 'macro' means 'can focus closer' than other types of 'non-macro' zooms.

It's not, in the true sense of the word, capable of 'macro' focusing where the lens is able to get you close enough to obtain a life-sized reproduction (1:1).

Any lens that is not designated with 'macro' or 'close-focusing' is generally not capable of going very close to the subject (e.g., so called 'macro' zoom can focus to 3 feet, wehreas non-macro lens of the same focal length can only focus as close as 7 feet).

Don't get mislead by marketing terms - just look at the specs of the lens (online) and look for minimum focusing distance(s) and maximum reproduction ratio(s). The closer you can go, and the higher the repo ratio, the larger the object will appear in the viewfinder at any given focal length.

[J-Chan]

70-300 macro lenses aren't "true" macro lenses.. they just focus nearer than normal, giving something like 1:3 magnification, but not true 1:1

You mean prime lenses.. no doubt a zoom lens covers a said focal length, but the main advantage primes have against zooms is their aperture size.. 1.4 vs 4.5 at 50mm for example..

[giantcanopy]

Originally Posted by gymak90 2) So far I've been using zoom lenses. There are standard focal length lenses out there, e.g. 50mm. Again, why is there a need for such standard focal length lenses, when a zoom lens e.g. 17-85mm can also be set to 50mm?

1) Because the prime lenses are smaller and lighter. if you have no need for zoom for an event or if you do not mind changing prime lenses on the fly

2) They have a slightly better IQ compared to current variable aperture zoom lenses although the gap is closing up and most of us cannot tell without magnification. And to get better image, the option of buying the prime lens is cheaper than buying a professional constant aperture zoom.

3) They might still be slightly more flare resistant than the zoom lenses since they have fewer elements within the,. The usage of coatings however has managed to contain this problem somewhat

4) Many of the consumer zooms often have more marked distortions compared to the prime lenses.

5) If you are referring to the 50mm prime, yes the aperture is much bigger than what you can get from the 50mm in your zoom. There is a 28mm f1.4 prime as well

Ryan

[gymak90]

Thanks a lot guys. Appreciate the help

I realise there aren't many lenses that can do 1:1 repo, and they are expensive. Haha, what about lenses that can magnify? Say taking a photo of an ant, how is that ant magnified?

About the prime lenses,

Quote: 4) Many of the consumer zooms often have more marked distortions compared to the prime lenses.

What are the distortions mentioned here? Is it due to aperture? What I know of aperture is that it controls the amount of light entering.. and some blurring of the background can be achieved if the aperture is wide.
Are there other usages of aperture? Lenses with constant aperture are more expensive, does that mean they are more favoured?

[J-Chan]

what 1:1 magnification means is that the image projected onto the sensor/film is exactly the same dimensions as the object itself.. for your taking a photo of an ant case, 1:1 won't cut it.. just cos the ant is so much smaller than the sensor, it would just occupy a small area of the image.. you would need a specialised (and expensive) lens, ie the MP-E 65mm 1-5x Macro lens, 5:1 magnification ratio, stuff just 1/5th the size of the sensor can fill the frame..

distortion here refers mainly to barrel and pincushion distortions.. a simple way to put it, straight lines don't appear straight, either curving inwards or outwards..
other usages of a wider aperture you mean.. other than blurring of background, aka shallow DoF, you'll get faster shutter speeds which helps alot in low light..

[2.8photography]

Originally Posted by gymak90 About the prime lenses, What are the distortions mentioned here? Is it due to aperture? What I know of aperture is that it controls the amount of light entering.. and some blurring of the background can be achieved if the aperture is wide. Are there other usages of aperture? Lenses with constant aperture are more expensive, does that mean they are more favoured?

in this case, i think giantcanopy is mainly talking about barrel distortions which are mainly caused by the lens and focal length
this shld explain http://en.wikipedia.org/wiki/Barrel_distortion but its quite technical

as u mentioned, i think the amount of light and blurring of bg (bokeh) are the 2 main uses. others include sharpness and CAs etc but those are again variable, and depend on the lens

lenses with constant aperture are generally more favoured cos they usually have large max. apertures (eg f/2.8). thus they allow more light in, and can be used when lighting is dim.

[giantcanopy]

Originally Posted by gymak90 Lenses with constant aperture are more expensive, does that mean they are more favoured?

Often heavier than their variable aperture counterparts, it takes more effort to maintain the constant aperture. I would think they are more favoured by many unless weight becomes an issue

There are some quality variable aperture zoom lenses as well. Canon has a few variable aperture lenses that are designated L.

Ryan

[gymak90]

I see!

That explains the results from some photographic tests on dpreview.com

Thank you all very much for the help!