Sweet Spot

All,

 

Its a rookie question i guess. I understand sweet spot will be different for

different lenses. But will the sweet spot be different for different pieces of

the same lens as well ? The reason I am curious is, can I look up the sweet spot

for a canon 70-200 f/4L lens from the forums and assume its the same for my

piece as well ?

 

Thanks in anticipation

Sankar

You're over analyzing this. That's a great lens all around. Just buy it.

Trebor, I just gave that as an example. Its a general question with curiosity to understand

Oh, ok. There are really two things that people refer to the seet spot in lenses.

 

One is the center of the image area. As in a crop body only uses the central region so most of the image is in the "seet spot". But a FF body uses the whole image area and may show softer corners. But I dont' think that's what you mean.

 

I think you mean the Zoom range sweet spot. Many zooms are a little soft at thier longes, or shortest focal lenght.

 

Then again, you cold be refering to the Aperture sweet spot. This was once considered F8 across the board back in the days of film.

 

But now it's usually closed down one or two full stops form open.

 

Regardless if you want to investigate a lens for potential purchase I like photozone.de. http://www.photozone.de/canon-eos

 

Check it out.

Hello Sankar. I read recently in a digital photography handbook that on most lenses, the "sweet spot" is 2 F-STOPS down from the maximum aperture. Now the max aperture is going to vary, lens by lens. But if that info is true, then take the max aperture (smallest f-stop #), and bump it up 2 clicks, and you should be near the sweet spot. Thats what this book said, though he provided no hard references to any specs or data sheets for any specific models.

 

Perhaps the pro can correct me on this if i'm mistaken, or fill this point in with more accurate knowledge.

Kind of depends what your shooting, for lanscapes you could get a sweet spot around f11, for portrait maybe f5.6

All ,

 

Thanks a lot for all your replies.

However my original query is : Say I buy a 70-200 f/4L lens today and click a few pics and find out its sweet spot. Tomorrow if I replace it with another piece of 70-200 f/4L, should i again go about finding its sweet spot ?

 

Thanks

Sankar

Varies from lens to lens...

 

Check out <a href="http://www.kenrockwell.com/nikon/50-comparison/f-stops.htm" target="_blank">http://www.kenrockwell.com/nikon/50-comparison/f-stops.htm</a><div></div>

Format also makes a difference. Likely to be at a smaller aperture with FF compared to

crop.

>>[Trebor Navilluso]>> if you want to investigate a lens for potential purchase I like photozone.de. <a href="http://www.photozone.de/canon-eos" target="_blank">http://www.photozone.de/canon-eos</a>

<p>

I agree.

<p>

I owned (and enjoyed) the 70-200 F/4L but I had the fever to upgrade, so I considered the f4L IS, the 2.8L non-IS, and the 2.8L IS.

<p>

I ended up going with the f4L IS because several sites demonstrated that the 2.8 isn't really sharp until F/4 anyways, but the f/4L IS is sharp wide open. IS on the f/4L is newest generation too. So less $ and less size/weight, I decided I'd go with the f4L IS.

<p>

OTOH, with the 2X extender, the 2.8 would've given me the option for 400mm IS AF... which would be roughly equal to the 100-400 IS I've also been pondering. The f/4L can do AF/IS with the 1.4X extender, but MF only with 2X.

<p>

These are some other useful sites with pixel peeping "sweet spot" measurements:

<p>

<a href="http://www.slrgear.com/reviews/showproduct.php?product=999" target="_blank">http://www.slrgear.com/reviews/showproduct.php?product=999</a>

<p>

<a href="http://www.dpreview.com/lensreviews/canon_70-200_2p8_is_usm_c16/page4.asp" target="_blank">http://www.dpreview.com/lensreviews/canon_70-200_2p8_is_usm_c16/page4.asp</a>

<p>

But IMHO, the sweet-spot really depends on the trade-offs of your shooting environment and style. Do you prefer fast shutter? prefer large DoF for more of the scene in focus? prefer less DoF for intentional background blur? prefer lower noise from lower ISO? Do you typically have plenty of light to work with? Do you have good flash(es)? Prefer sharpness of primes or composition flexibility of zoom (without having to swap lenses)? Prefer IS or tripod? Displaying large prints or mainly 5x7 or web resolutions?

<p>

So AFAIC the sweetspot of sharpness at any measured aperture is just another tradeoff. Sure, knowing that the 70-200 is sharpest at f/5.6 (or whatever the "sweetspot" may be) is worth considering, but it gets tossed in my mental exposure tradeoffs just like everything else... that's where experience and practice to become familiar with your equipment comes in play... bracket as many of those variables as you can and you continually improve your understanding of what permutations work well. That's where the real sweet spots are.

Sankar:

 

You still aren't telling us what the heck you mean by Sweet Spot. It can mean anything. But I'll assume you mean aperture sweet spot.

 

Whatever it is, yes there can be some copy varience as we call it here on Canon Lenses or any brand for that matter.

 

But I think it would affect overall image quality rather than the magical sweet spot specifically.

 

Unfortunately there is no way to tell if you get a good copy unitl you can get your hands on the lens. This is why I no longer buy lenses online and go to a store where I can try them out. Or if I do buy online, i make sure I can return it no hassle.

 

Do a search on lens testing here and you'll see lot's of threads on how ot do that.

> However my original query is : Say I buy a 70-200 f/4L lens today and click a few pics and find out its sweet spot. Tomorrow if I replace it with another piece of 70-200 f/4L, should i again go about finding its sweet spot ? <

 

No, there should be no need to go about finding a new sweet spot for the same model lens.

 

The `sweets spots` are basically intrinsic to the design of the lens.

 

If the overall production line has good quality control, each lens of the SAME design will have the same sweet spots.

 

The above is a very simplistic answer and is generally correct for the THREE aspects of any zoom lens, each of which are commonly referred to as having a `sweet spot`:

 

1. Aperture Sweet Spot (best aperture to use for overall Image Quality)

 

2. Zoom Sweet Spot (The point in the zoom`s range where there is the best overall Image Quality)

 

3. Image Circle Sweet Spot (the sharpest part of the whole image)

 

Sweet Spots 1 and 3 also apply to Prime Lenses

 

***

 

1. The Aperture Sweet Spot is usually two or three stops down from the widest aperture

 

 

2. The zoom Sweet Spot, is usually not really at any one point but rather, the IQ of a zoom lens gradually tends to drop off at the extremes of the zoom.

 

Often more degradation is seen at the wide end than at the telephoto end for normal view and wide angle zooms. (eg 14 to 35 and 28 to 85 etc)

 

But there is usually more degradation at the telephoto end, for telephoto zooms. (eg 100 to 300)

 

Often for Super Zooms, the zooms that are usually more than 4x or 5x zoom (eg 50 to 250) there is noticeable Image Quality degradation at both the wide and telephoto ends.

 

3. The image circle sweet spot is usually at the centre of the image and degradation is noticed at the extremities, especially the corners.

 

That is why, for example, many photographers might choose to use the EF28F1.8 with a 40D, but not with a 5D.

 

All the above points are are generalizations: there will always be exceptions.

 

WW

William.. that was exactly what I wanted to know, nice, elaborate and clear.. Thanks a bunch..

 

Thanks to everyone .. you guys are great in offering your help to amateurs like me..Heartily appreciate it !

Sankar,

<p>

If you want to distill the essence of what you want to know then grab any lens - stop down 3 stops - and you're good to go.

<p>

Keep in mind that correct sharpening technique will have a larger effect on image quality (in general terms) than the differences between being "in" and "out" of "the sweet spot".

<p>

Cheers,

<p>

Colin

You`re welcome, no problem.

 

Cheers,

 

WW

all that being said, with the 70-200 lens series, you can't really go wrong. I use mine wide open all the time and it's typically as sharp as i've ever seen a lens get.

Thanks everyone for your kind suggestions.

I just joined this forum and am a neophyte with blogs. I do know some stuff about photography, however. My question/comment pertains to the accepted theory that a lens' sweet spot is +/- 2 stops from wide open. I shot my 28-70 2.8 L with my old film Elan and now with my Mark III. The sweet spot is still staight uo f/8. What are the theories behind the 2 stops off and do they differ between film and digital?

Thanks,

John

Hi John, You might visit http://www.bobatkins.com - he has lots of good info on most things optically related and probably explains the technicalities involved when stopping a lens down. I think it's safe to say that stopping most lenses down a couple of stops helps sharpen things up. It's sort of the same reason we squint when we want to see something better. If you wear eyeglasses you can punch a tiny hole in a piece of cardboard and hold it up to your eye just right with your glasses off. If you catch it right you might notice things look pretty sharp through that tiny hole, even without your glasses. It's just not very practical! ;-)