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Author Topic: Your lens sweet spot...explained technically  (Read 99449 times)

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Offline caterpillar

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Re: Your lens sweet spot...explained technically
« Reply #80 on: November 19, 2008, 08:36:10 AM »
Thanks. Is it correct to say that if there is enough light (including flash?) and a shallow DOF is intended, the sweet spot will give the best picture/color/contrast?

  It depends. A lot variables come into play. Which lens? the scene, zoom or prime, FL etc.?  Also, in terms of MTF, most new lenses have this very high in  the center compared to resolution. And the better lenses tend to have their contrast at the highest already even wide open!

  The new canon ef-s 18-200 IS for example, has a very high contrast and it is almost at it's best even wide open corner to corner all around. But its resolution varies from the center and depending on FL, except in the center w/c is very, very sharp.

  But for all intents and purposes, "in general," yes,  the best resolution/contrast/color is at the lenses' sweet spot.

  But your question is also double edged. You said, if enough light and wide open. Most lenses need to be stopped down 2-3 stops to be at their sweet spot. And that is most. The exceptions usually are the long primes. The 300 f2.8L and 200 f2L's, for example are near or already at their sweet spot even at f2.8 or f2.0!!! ::)    It means, that for most lenses, using it wide open and the its sweet spot don't coincide at all.

  But that should not dishearten you.   :P     The reason is that even if your len's sweet spot is f8, if it is sharp even at f2, then it is still sharp at f2! For example, the 135 f2L is already very sharp at f2. Stopping it down to f8 or whatever it's sweet spot is, will not improve it's overall sharpness. You may have a deeper DOF, yes, but it doesn't mean it's not sharp at f2. It's just sharper at f8 and the differences are not noticeable even if you print at 8x10 unless you really pixel peep.

  I don't have the 135L, but I do have the 50 f1.4 usm and the 100 f2 usm. Wide open, these lenses are already sharp. Getting them to f4 or f5.6 shows improvement in sharpness, but it's not obvious, especially if you just print 5Rs. So, I don't think of the sweet spot when using these lenses. I only think of what aperture is needed/appropriate for the shot based on what I want to come out. The sweet spot is the least on my mind.  :)

  You have to really think hard to why you want to use your lens' sweet spot all the time. The landscape shooter happens to hit it most of the time because he is usually in the f8-f11, maybe even f16 region. But an events shooter can't use f8, much less f11 99% of the time. He simply doesn't have enough light. He has to have multiple flashes to get the subject and ambient light lighted up well at f8! Trouble with that is how will you light up and not destroy the ambiance in a large hall?  So, most of the time, he shoots wide open or near it even at very slow shutter speeds. If he uses a flash, it's only to fill in, or for effect.

  Also, and everyone please take this to heart - when you say sweet spot, it doesn't mean that if I hit f16 or f22, suddenly my sharp lens is a coke bottle! ::)  No!  The effects of diffraction is gradual. In fact, at f11 or f14, most lenses and a crop body starts losing the advantage of a sharpness due to diffraction. But it's not that noticeable till maybe f22 or higher. At f16, the lenses can be as sharp as it was at f4 or f4.5. And if you just print 4Rs or 5Rs, I very much doubt you will see the effects of diffraction at all! It's only when you pixel peep on your monitor (w/c should also be hi-rez) or print very big that you will see the difference.


 In summary, use the proper aperture based on needs. The only time you start thinking of the sweet spot is if you have an application, maybe a large billboard print to be made that really requires the best of your lenses.

  But in most instances, in the bigger scheme of things, you shouldn't choose your aperture based on the sweet spot alone. And most people actually don't worry about it.  Most are concerned about other issues like, light, DOF, slow shutter speeds, composition, etc. The sweet spot is a nice thing to know. But you shouldn't be constrained to stay on it. Use the opening you think you need to get your shot. Use the sweet spot if you will be printing really large prints, and you have really good reason to get the best out of the lens.  ;)


--- Caterpillar ---

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Re: Your lens sweet spot...explained technically
« Reply #80 on: November 19, 2008, 08:36:10 AM »

Offline maligo

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Re: Your lens sweet spot...explained technically
« Reply #81 on: November 23, 2008, 10:19:00 PM »
much appreciated caterpillar. thanks a lot for taking the effort to explain it technically. I guess I need to shoot more to actually experience and understand better the things that you have explained. More power to you :)


Offline amateur photog

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Ho to test for Your lens sweet spot
« Reply #82 on: December 03, 2008, 12:37:45 PM »
Caterpillar,

Just got to reading your first and other posts on the lens sweet spot.  Thanks a lot for such valuable information.

One question:  would you be able to suggest a procedure for testing a lens' sweet spot - both fixed focal and zoom?

As you mentioned in your article, while we should not be ruled by the sweet spot, it is good to know where this is.

Thanks a lot.

Offline thugs28

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Re: Your lens sweet spot...explained technically
« Reply #83 on: December 05, 2008, 09:11:46 PM »
very nice info.......
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Offline attydenden

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Re: Your lens sweet spot...explained technically
« Reply #84 on: December 13, 2008, 07:26:52 PM »
thanks sir caterpillar for the exhaustive explanation. so basically, as the saying goes. Wala sa pana yan, nasa indian. hehe ;D

Offline i_am_bishop

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Re: Your lens sweet spot...explained technically
« Reply #85 on: December 24, 2008, 10:41:59 PM »
wow! learned a lot. thanks for the info. particularly those extensive helpful comments of caterpillar. merry christmas!
"Do or do not... there is no try." -- Jedi Master Yoda

Offline Eclipse

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Re: Your lens sweet spot...explained technically
« Reply #86 on: January 16, 2009, 10:52:16 PM »
I was glued to my seat!  ;D  many thanks for the info's.
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Offline zymo4

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Re: Your lens sweet spot...explained technically
« Reply #87 on: January 17, 2009, 12:12:01 AM »
Very Informative... napa nganga ako while reading!

astig ang mga Pinoy....  8)

Offline Kodakan

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Re: Your lens sweet spot...explained technically
« Reply #88 on: January 23, 2009, 10:26:40 PM »
great info..thanks soo much for sharing
 

awesome..=)

Offline mikeng

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Re: Your lens sweet spot...explained technically
« Reply #89 on: January 24, 2009, 08:09:27 AM »
nice info :) any guys? do you know whats the sweet spot for the canon 17-40L ?

Offline Shutter_Speed

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Re: Your lens sweet spot...explained technically
« Reply #90 on: January 24, 2009, 09:13:52 PM »
Very well explained man. I didn't even know that there was even a technical term for sweet spot. Thanks for the tip.  :)
"It's not about having the right gear that makes you a photographer. Its how you  capture and freeze those scenes and events that unfold in front of you that matters. This would result a connection between you and your audience."

Offline theman2

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Re: Your lens sweet spot...explained technically
« Reply #91 on: February 05, 2009, 11:48:02 PM »
very nice nice indeed!

sa akin lang naman. were talking about sweet spots about lenses eh ang pinakaunang tanong.. kelan ba magbabaan ang mga presyo ng mga lenses ha. ang mamahal eh.

maka OT lang :)

Offline Harima

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Re: Your lens sweet spot...explained technically
« Reply #92 on: February 10, 2009, 02:31:40 PM »
Wow! I learned a lot in this thread! Thank you very much sir for the more in-depth explanation of the sweet spot! ^^

Offline theman2

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Re: Your lens sweet spot...explained technically
« Reply #93 on: February 10, 2009, 07:54:14 PM »
@caterpillar

sir, tatanong ko lang which lense would you prefer a:

50mm 1.8 or a 85mm 1.8?

much much cheaper and 50mm but i dont know about sa 85mm quality of pic. can you share some inputs po?

salamat po.

Offline caterpillar

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Re: Your lens sweet spot...explained technically
« Reply #94 on: February 10, 2009, 08:33:13 PM »
@caterpillar

sir, tatanong ko lang which lense would you prefer a:

50mm 1.8 or a 85mm 1.8?

much much cheaper and 50mm but i dont know about sa 85mm quality of pic. can you share some inputs po?

salamat po.


   I presume you are talking of canon lenses here.  Regardless, comparing the 50mm and the 85mm is, to a degree, unfair.  Both are different focall lengths. Even if they are of the same build, same AF, etc., there's a 30m gap that could be disadvantageous or advantageous, depending on application.

   The 50mm is hard to get wrong. The design is old but reliable, and time tested. If you look at the schematic of the 50mm f1.8 mk2, mk1, 1.4 version, they are the same with minor differences. The 50 f1.4 usm, for example, just has an extra glass.  The 50 f1.2L is a tad different, but there are similarities. In short, as far as sharpness goes, they can't be far off each other. And 50mm is an easy design and easy to get it right.

  The 85mm is popular as a portrait lens. In my experience, the 85 f1.8 is prone to CA on wider apertures.  And there can be variances in copies.  Some have more CA than others. I've used 3 or 4 of these and only 1 was truly a gem. In fact, it was perfect even at f1.8. Normally, it's softer at f1.8. You have to stop it down to f2 o f2.2 to get that bite in the image.  Again, the rest weren't duds. I guess, it's just the nature of the lens. It's harder to get a perfect copy that was exceptional at f1.8 with minimal CA.

  For me, for portraiture in a crop body, the 85 f1.8 usm is perfect in FL. That is for portraiture only. For events, however, on a crop body, the 50mm is better for me. Again, a matter of preference, not lens limitations.  But as far as AF speed, the 85 f1.8 (and 100 f2 usm) are the speed champions, perhaps in all of the canon lens lineups. You will love it for almost instant AF.

  For 35FF. 85mm for portrait is too short for me. This is why I went for the 100 f2 usm.  It's 1/3 stop slower,  but has less issues. The lens is too long, however for cropped bodies. The 100 f2 usm has less CA, and less copy variance. My copy is very sharp at f2. It's also easier to find a perfect or near perfect 100 f2 than an 85 f1.8 usm. But there are less 100 f2 owners here than 85 f1.8 owners.

   I've gone the 28 f1.8/50 f1.4/100 f2 trio for my primes. I use the 50mm the most, since I have a crop body. There is no doubt, I'll be using the two other lenses more if I ever move to 35FF. In fact, this is the reason why I have these lenses, even if the two sees less use.

  I say, the 50mm is more useful and practical for  a crop body. But the 85mm is perfect for a crop body if you do lots of portraiture. In fact, if one can afford it, one must have both if one is a portrait type of person.
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Offline ramzchillin

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Re: Your lens sweet spot...explained technically
« Reply #95 on: February 12, 2009, 11:23:58 AM »
a worthy thread :D thanks for sharing , indeed sir  caterpillar is right. use aperture depending on situation :D

Offline icko

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Re: Your lens sweet spot...explained technically
« Reply #96 on: February 17, 2009, 12:05:25 AM »
good info!  ;D

Offline owyzzz

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Re: Your lens sweet spot...explained technically
« Reply #97 on: February 17, 2009, 07:14:36 PM »
nice! So, can I also spot this in shallow DOF?
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Offline alanebs

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Re: Your lens sweet spot...explained technically
« Reply #98 on: February 19, 2009, 09:58:09 AM »
this is such a great thread! i learned a lot... bookmarked!

Offline marklee_15

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Re: Your lens sweet spot...explained technically
« Reply #99 on: February 19, 2009, 10:25:20 AM »
nice thread. Very helpful

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