IQ sweet sweet spot in m4/3 lenses and cameras

[tsinsf]

I read in Photozone's review of the Olympus 40-150 lens that the sweet spot in micro four thirds cameras is "half" that of full frame equivalents, ie, on this lens f 4.0 rather than 8.0. I decided to do my own simple test with my 40-150 lens and Olympus OMD-5. To my eye, at 1/250 second, 50mm, and mid day sun, f 8.0 was the clear winner. I'm wondering what other peoples experience with "where is the sweet spot" on micro four thirds lenses used with a micro four thirds camera is? Thanks!!

 

[tedolf]

tsinsf wrote:

I read in Photozone's review of the Olympus 40-150 lens that the sweet spot in micro four thirds cameras is "half" that of full frame equivalents, ie, on this lens f 4.0 rather than 8.0. I decided to do my own simple test with my 40-150 lens and Olympus OMD-5. To my eye, at 1/250 second, 50mm, and mid day sun, f 8.0 was the clear winner. I'm wondering what other peoples experience with "where is the sweet spot" on micro four thirds lenses used with a micro four thirds camera is? Thanks!

usually about f/5.6.



You don't have to guess. SLRGear has charts that show you exactly how the lenses perform at each aperture.





Tedolph

 

[CrisPhoto]

This really depends on the lens, or better: depends on your money.

• My 75-300 has its sweet-spot at 75mm/f8 or 300mm/f11
• My 75mm has its sweet spot at f2.0

Olympus 75mm f1.8 test

Anyhow, the f-number is relative. It is the (focal length)/(entry pupil). The entry pupil of a lens and the diameter of the first lens is what makes a lens expensive, the money you want to spend and the focal length determine your individual sweet spot.

If you spend a lot of money, you can buy a Oly FourThirds f2.0 zoom lens, you get a lot of fine glass for a lot of money, the sweet spot is near f2.8 which is remarkable for a zoom lens ...

Olympus 14-35mm f/2

 

[Paul De Bra]

The rule "half of full frame" indeed suggests that f/4 is optimal, but that just means it is how far you can stop down without any potential noticeable diffraction effect. In practice it's not so bad: m43 is still fine at f/5.6, aps-c still fine at f/8 and full frame at f/11. Stop down one more stop and images become visibly affected by diffraction.

For lenses the basic rule is that they are optimal around 2 stops down. So for instance an f/2 lens will be optimal at f/4 but an f/4 lens will only be optimal at f/8. There is clearly a cross-over: When you use a typical f/3.5-5.6 zoom lens the lens will be optimal around f/8 (maybe a bit larger aperture at the wide end and stopped down a bit more at the long end) but the camera system is optimal at f/4 so somewhere between f/4 and f/8 the camera showing more diffraction and the lens becoming sharper will cross over and give you the best you can get with that lens.

An example: my 20mm f/1.7 lens is sharp wide open but very sharp between f/2.8 and f/4 and cannot improve beyond f/4 because the lens is at its best and the camera starts being affected by diffraction. My 12-50 zoom lens is best around f/8. At f/5.6 the camera does better but at f/8 the lens does better... for this reason we really need zoom lenses that are at least as good as f/2.8 (to allow some stopping down before hitting diffraction). We are all anticipating a new Olympus 12-40, especially those of us who don't really want to deal with the purple fringing on the Panasonic lenses.

 

[SkiHound]

Generalizing, I'd say in the f4 to f8 range but it varies from lens to lens. I have the PL25, Oly 45, and Oly 60 and they seem pretty good wide open and very good when stopped down 2/3 to 1 stop. Diffraction probably starts to be a limiter by f8 and certainly by f11. But my old eyes don't really see much degradation even at f11. Of course I'm not pixel peeping and I'm not shooting resolution charts. Folks sometimes talk about f8 to f11 being the indifferent aperture settings with many FF lenses; sweet spot in terms of sharpness and useful when you either don't need or want to limit or maximize DOF.

 

[shihhan]

tsinsf wrote:

I read in Photozone's review of the Olympus 40-150 lens that the sweet spot in micro four thirds cameras is "half" that of full frame equivalents, ie, on this lens f 4.0 rather than 8.0. I decided to do my own simple test with my 40-150 lens and Olympus OMD-5. To my eye, at 1/250 second, 50mm, and mid day sun, f 8.0 was the clear winner. I'm wondering what other peoples experience with "where is the sweet spot" on micro four thirds lenses used with a micro four thirds camera is? Thanks!!

Around f4 to f8 depending on the lens (using the stop down 2 f-stop rule), which typically improves corner sharpness more than the centre. You can look up MTF comparisons on Photozine.

But tbh, what really matters is getting the shot with the right exposure and/or DoF, rather than worrying about where is the 'sweet spot'. (eg. a f2.8 shot is never going to be pin sharp at the corners, but shooting at f4/f5.6 will give you a blurry mess...)

Avoid f22 like the plague though.

 

[ed2002]

i can see wanting f2.8 or f28-3.5 zoom lenses at the shorter focal lengths, but get over 100mm and they start to get big and make you wonder if m4/3 is a good idea;-)

I think a 17-50 f2.8 would be wonderful, maybe sigma can bring one over, but redesign it to be small for the m4/3 and nex systems. Or let it be oly or panasonic. I know its not as wide as people think wide have been interpreted to be, but there is choice of zooms or primes wider, and really many of us do shoot in this range, and want a faster lens with good bokeh that hits some wide to portrait lengths. Let software control some of the CA, make it small and light.

 

[Stan1157]

Thanks for this discussion. Having used a FF Canon, I tend to think F11 or more for architecture because I want good depth of field. When talking "sweet spot" does the "half" rule also apply to depth of field or just sharpness and diffraction? I also shoot stained glass windows both medieval and renaissance and need depth of field to get sharpness from top to bottom when tilting the lenses and then key-stoning with Lightroom or DxO viewpoint. Any suggestions or comments are welcome as I am not really up to speed on lens technicalities.

Thank, Stan