Difference between f/4.0 and f/2.8 lens?

[jon1000]

Hi, just a quick question

what's the difference between an f/4.0 lens and an f/2.8 lens?

Is just just that the 2.8 will be better in low light?

Thanks.

Just in case it's needed, I was referring to the canon EF 70-200mm F/2.8 & F/4.0.

[JamesF]

An f/2.8 lens won't necessarily be better in low light, but to record the same amount of light on the camera sensor less time will be required because the aperture will be larger than at f/4.0 for the same focal length.

James

[VigdisVZ]

http://en.wikipedia.org/wiki/F-number

The F-number is a measurement how much light the aperture lets in compared to how long the focal length is. T

Yes, the 2.8 will result in more light. There is more to it, just as James hints, but generally the lower the F, the better.

For instance the zoom lens youre refering to has a focal ratio of 2.8 at 70mm and 4.0 at 200mm. The aperture stays the same, but since youre zooming, youre collecting light from a smaller area, thus less light.

[cfpendock]

For some images I use both f2.8 and f4 because I find that I get sharper stars at f4 but more faint details at f2.8. Also when photographing objects with relatively bright areas, combining the two exposures can reduce the saturation (burned out look) of brighter areas whilst maintaining the detail and contrast of the faint areas. In particular, although perhaps regarded as "impure", I like the diffraction spikes which I can get on brighter stars at the smaller aperture - probably due to the lens construction.

Chris

[VigdisVZ]

Yeah, lenses behave very differently on different apertures. It's not just the amount of light, its diffraction spikes, depth of field, lens flares etc

I also like the spikes on small aperture

[jon1000]

Thanks for all of your comments, I bought the canon ef-s 55-200mm f/4.0

I think it will be ok for me as a new user of DSLR cameras, I have just bought the canon 1100d with 18-55mm lens and I also got a good wireless timer/shutter from eBay for just £30.

[markfftang]

Just to clear up a point the Canon 70-200mm f/2.8 and 70-200mm f/4 L lenses are constant aperture across their zoom ranges; the first is just a stop brighter wide open than the second. And an extra stop of aperture will halve your exposure time (at the same ISO).

[Cuffbertt]

I've used both the f/2.8 (for a wedding) and f/4 (for motorsport) versions of the lens, and they're both fantastic. I use a sigma 120-300 f/2.8 for motorsport nowadays and the image quality from it isn't nearly as good as either of the Canon's But that's what I got for trying to save money

They both also come in two varients, with and without image stabilisation (IS). They IS versions cost quite a lot more and are a bit heavier but they offer weather sealing when attached to a weather sealed body. However IS needs to be turned off when it's attached to a tripod or similar as it'll get confused and reduce image quality haha.

Never used the 55-200 f/4 though as it's an EF-S and is not compatible with my 5D2, so I can't comment on that puppy

[Davey-T]

Be aware that Canon lenses with "s" designation are not compatable with clip in LP filters same is true of the "kit" lens if that is the 18/55mm .

Just in case you're thinking of buying one.

Dave

[ollypenrice]

You don't have to stop down by using the diaphragm. (This will create big diffraction spikes.) You can do it like this with a home made aperture mask;

Olly

[laser_jock99]

Difference between f/4.0 and f/2.8 lens?.........a couple of thousand pounds!

[VigdisVZ]

Difference between f/4.0 and f/2.8 lens?.........a couple of thousand pounds!

*comedy drum roll*

[petercoxphoto]

Also should be noted that the 55-200mm lens is actually f/4-f/5.6. At 55mm (zoomed all the way out), the maximum aperture is f/4. At 200mm (zoomed all the way in), it decreases to f/5.6 - this halves the size of the aperture, resulting in exposures that will be twice as long for the same image brightness.

In general with camera lenses, they perform better stopped down by at least one, and preferably two stops. So at 200mm, the lens will perform better stopped down to f/8, or even f/11. I imagine this would make it too slow for astrophotography, however. Just be aware that at f/5.6 the stars in the corners of the image will not be as sharp as what you get in the centre.

Cheers,

Peter

[ollypenrice]

Also should be noted that the 55-200mm lens is actually f/4-f/5.6. At 55mm (zoomed all the way out), the maximum aperture is f/4. At 200mm (zoomed all the way in), it decreases to f/5.6 - this halves the size of the aperture, resulting in exposures that will be twice as long for the same image brightness.

In general with camera lenses, they perform better stopped down by at least one, and preferably two stops. So at 200mm, the lens will perform better stopped down to f/8, or even f/11. I imagine this would make it too slow for astrophotography, however. Just be aware that at f/5.6 the stars in the corners of the image will not be as sharp as what you get in the centre.

Cheers,

Peter

Four times as long, no?

Olly

[petercoxphoto]

Olly -

From f/4 to f/5.6? That's one stop so under normal conditions at least it will double exposure time. F/4 to f/8 would be four times as long.

Perhaps there's some funkiness that happens in AP, but that's how it is in regular photography.

Cheers,

Peter

[stem1989]

An f/2.8 lens won't necessarily be better in low light, but to record the same amount of light on the camera sensor less time will be required because the aperture will be larger than at f/4.0 for the same focal length.

James

what he said

[ollypenrice]

Olly -

From f/4 to f/5.6? That's one stop so under normal conditions at least it will double exposure time. F/4 to f/8 would be four times as long.

Perhaps there's some funkiness that happens in AP, but that's how it is in regular photography.

Cheers,

Peter

Sorry, 'Halves the size of the aperture' meaning halving the size by area. Of course you are right. Halving it by diameter would reduce the time by 4. Grovelling apologies!!

Olly

[Digz]

Another thing to consider is you generally need to stop a lens down a couple of stops in aperture to hit the sweet spot. What this means on an f2.8 lens is, once stopped down, the aperture is still fairly wide open giving desirable bokeh effects and allowing you to maintain fast shutter speeds and low ISO compared to a stopped down f4 lens.

Both lenses, however should still perform adequately wide open.

[petercoxphoto]

Olly - no worries! In regular photography we never discuss aperture in terms of diameter, it's always referred to by the focal ratio.

So from where I come from size always refers to area in this regard

[laser_jock99]

Another thing to consider is that F2.8 lenses are mainly 'pro series' lenses and are usually better quality than standard lenses of similar focal length. The bigger 'glass' lenses are hugely expensive to make and the lens bodies are metal as opposed to the plastic consummer lenses. Costly but supperior products- however even the best f2.8 pro lenses aren't great for astro 'wide open' since stars are the ultimate optical quality test. So even the best lenses will need stopping down a bit.

See how the price goes up as F ratio goes down!!

http://www.calumetphoto.co.uk/eng/product/canon_ef_400mm_f_5_6l_usm_lens/321-258d

http://www.calumetphoto.co.uk/eng/product/canon_ef_400mm_f_4_do_image_stabilization_usm_lens/321-259s

http://www.calumetphoto.co.uk/eng/product/canon_ef_400mm_f_2_8l_is_ii_usm_super_telephoto/321-445b

When I said the price difference was a couple of thousand pounds- It's actually £7000!!

[Mr Spock]

If you want to guage an ideal aperture for the 55-200, lens tests are useful as a starter, such as here: http://www.photozone.de/canon-eos/193-canon-ef-55-200mm-f45-56-usm-ii-lab-test-report--review?start=1

You can see there you aren't losing much by using it wide open at 200mm.

[JasonScott]

On a side note, the 70-200mm f/2.8L IS II is one of the most beautiful lenses you will ever use!

[Digz]

On a side note, the 70-200mm f/2.8L IS II is one of the most beautiful lenses you will ever use!

In either flavour as well I absolutely love my Nikkor version.

[andyboy1970]

I think a lot of people get confused because in the photographic world lenses are quote by focal length ie. 100mm f1.4 whereas telescopes are quoted by apature ie. 200mm f5

The above examples are - 100mm f1.4 has an apature of 76mm and 200mm f5 has a focal length of 1000mm.

[springbok]

On a side note, the 70-200mm f/2.8L IS II is one of the most beautiful lenses you will ever use!

The 70-200mm f/2.8L IS MK I aint to shabby either I've had mine around 10 years now, and it has never failed me. It's a keeper for sure.

I was surprised at the price increases since I bought my L glass.