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05-16-2016, 03:48 PM   #1
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wide open soft vs F4 sharp

this is a hypothetical question with opinions not facts
let's say you have a 2.8 lens wide open and it is soft.. doesn't sharpen until F4. you have another lens that is F4 but sharp wide open.
what is the use in paying the extra money, extra weight, etc? bokeh better sure but if it's not unusable wide open what is the point?

All opinions welcomed!

thanks

randy

05-16-2016, 03:50 PM   #2
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Hmmm...do you have a specific example?


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05-16-2016, 03:57 PM   #3
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QuoteOriginally posted by stevebrot Quote
Hmmm...do you have a specific example?


Steve
My Sigma 70-200 F2.8 doesn't get sharp until f4. the I heard the *60-250 I sharp right from the get go

Randy
05-16-2016, 04:00 PM   #4
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QuoteOriginally posted by slip Quote
My Sigma 70-200 F2.8 doesn't get sharp until f4. the I heard the *60-250 I sharp right from the get go

Randy
If true sounds like a no-brainer to me assuming that the DA* at f/4 is as sharp or sharper than the Sigma at both f/2.8 and f/4. What you lose is 1 stop of viewfinder brightness and and 1 stop of both meter and PDAF range.


Steve

05-16-2016, 04:07 PM   #5
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QuoteOriginally posted by slip Quote
but if it's not unusable wide open what is the point?
you meant to say not usable wide open? define that.

because most f/2.8 zooms should be usable in the center, wide open.
05-16-2016, 04:11 PM   #6
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QuoteOriginally posted by osv Quote
you meant to say not usable wide open? define that.

because most f/2.8 zooms should be usable in the center, wide open.
I guess the term unusable is up to the user. the point is won't it be worth the weight saving and price difference?

Randy
05-16-2016, 04:12 PM   #7
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QuoteOriginally posted by stevebrot Quote
If true sounds like a no-brainer to me assuming that the DA* at f/4 is as sharp or sharper than the Sigma at both f/2.8 and f/4. What you lose is 1 stop of viewfinder brightness and and 1 stop of both meter and PDAF range.


Steve
Imaging Resource rated the Sigma 70-200/2.8 "as good as" the Pentax for the shared range of apertures and focal lengths. Their copy of the Tamron 70-200/2.8 equaled the Pentax and bettered the Sigma wide open.


Steve
05-16-2016, 04:16 PM   #8
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QuoteOriginally posted by slip Quote
I guess the term unusable is up to the user. the point is won't it be worth the weight saving and price difference?

Randy
FWIW, I use two vintage manual focus Tamron zooms, both with fixed f/3.5 maximum aperture, and don't miss the 2/3 stop and do appreciate the somewhat smaller form factor. As for price difference, I thought the DA* was 1/2 again more expensive than the Sigma. At least it was when both were available new.


Steve

05-16-2016, 04:46 PM   #9
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Basically I expect any lens I use ** will be much sharper and have less coma/other problems when stopped down, although other fine attributes that are not about sharpness may come into play when fully open.

Every lens is a compromise and a choice of some attributes over others. I think expecting high sharpness wide open means you lose something--usually:
-- money
-- the lens is larger/heavier (more elements and possibly it starts out stopped down some)
-- that unsharp, less clinical, full open character

You would expect the wide open sharpness/coma, etc. to be worse, but it allows a better focus--assuming the focus shift w/ aperture is not significant. I basically anticipate stopping down 1/2 to 1 stop--unless I am looking for the unsharp dreamy look.
___
** Well any fast or reasonably fast general purpose lens, which I assume is the point of this discussion. Many slow lenses (e.g., SMC 35mm f/3.5) do have good sharpness fully open--although they still are better/best about 2 stops closed down. Also some very fast solely for macro lenses are best full open--but again it is about what compromises the lens designer chooses.

---------- Post added 05-16-16 at 05:17 PM ----------

Another point touched on in my comment, but not with enough emphasis is the need to stop down for better (safer) focus, particularly in situations where focus cannot always be optimum. This is (for me) why I want a fast lens, unless it is wide focal length where I zone focus. In fact I do mostly theatre photgraphy, and yet almost always stop down 1 stop from full open--for the focus margin it provides.

Last edited by dms; 05-16-2016 at 05:20 PM. Reason: added footnote/clarification
05-16-2016, 08:55 PM - 1 Like   #10
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QuoteOriginally posted by slip Quote
what is the use in paying the extra money, extra weight, etc?
brighter viewfinder; better AF ability at low light; F2.8 when necessary (you don't need razor sharp all the time, particularly in the corners, and speed might be more critical)
05-16-2016, 09:37 PM   #11
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Soft image vs blurry image caused by 1 stop slower shutter speed. What would you choose?
05-16-2016, 09:46 PM   #12
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^This.

It depends what you are using the lens for. For event work, indoor sports, etc, sometimes that extra stop is very useful. Better to get a shot that's less than tack sharp than to have motion spoiling it completely.
05-17-2016, 05:10 AM   #13
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QuoteOriginally posted by slip Quote
this is a hypothetical question with opinions not facts
let's say you have a 2.8 lens wide open and it is soft.. doesn't sharpen until F4. you have another lens that is F4 but sharp wide open.
what is the use in paying the extra money, extra weight, etc? bokeh better sure but if it's not unusable wide open what is the point?

All opinions welcomed!
People using the 16-85 and 60-250 have asked themselves that very question, and come up with the most satisfying answer possible

I tend to agree, I'd rather have a smaller lens that's a bit slower but sharp at all apertures, instead of a fast lens that's useless wide open. I have primes when I want super wide apertures. On the other hand, sometimes there's no solution other than using a fast lens...
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