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Archive 2016 · How can you judge the true sharpness of a lens?

  
 
billsamuels
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p.1 #1 · p.1 #1 · How can you judge the true sharpness of a lens?


I decided to keep one of the many lenses that my dad gave me to sell, it's a Mamiya-Sekor 80mm F/2 C manual focus. I have to use a lens adapter to use it on my Canon cameras, but I think it's the sharpest one that works on the Canon. I'm sure the others are sharp, but probably sharper on a Mamiya, or maybe with a better quality adapter.

I'm trying to figure out how to measure lens sharpness because this has come up several times in the past year. It came up with the EF 400mm F/5.6, and another lens a few months ago, and now I'm trying to figure out if this lens is really sharp or not when I take distant photos. Close up, the photos appear sharp, but distant photos, I can't tell if they're as sharp as a Canon lens. I know when I've asked before, you guys ask me to compare raw vs. jpg, compare an 80mm to an 80mm, etc.

Is there a simple formula or technique I can use?
Thanks.




Canon Rebel SL1, Mamiya 80mm F/2.0, ISO 200, F13, 1/1000 MF




Jan 11, 2016 at 08:11 PM
Imagemaster
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p.1 #2 · p.1 #2 · How can you judge the true sharpness of a lens?


It's not rocket science. Take the exact same photo with lens 'A' and lens 'B'. Simply look at the results to see the difference.

If you can't tell the difference, it does not really matter, does it



Jan 11, 2016 at 08:22 PM
chez
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p.1 #3 · p.1 #3 · How can you judge the true sharpness of a lens?


Are you happy with the results you are getting from the lens? If so, then it's a keeper.

I shoot with many different lenses, some not as sharp as others but provide other characteristics to the images.



Jan 11, 2016 at 08:32 PM
retrofocus
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p.1 #4 · p.1 #4 · How can you judge the true sharpness of a lens?


If it comes down to sharpness evaluation, I prefer to compare against tree branches from a distance and then zoom into the photo up to 200%. This of course assumes that there is no or minimal wind when the photo is taken. This also depends on the focal length of the lens - wide angle lenses are more challenging in this regard because objects in the distance appear smaller in the photo. But you will still be able to make out some small differences between lenses even at shorter FL. Lenses which I own and consider very "sharp" are for example my Leica Summicron-M 50/2 and my Canon 70-200/4 L IS.

As Harry pointed out above, even less sharp lenses can be excellent and have other unique characteristics - just to name the Canon 50/1.2 L lens. Certainly not the sharpest but IMO a keeper lens due to its smooth bokeh effect.



Jan 12, 2016 at 07:59 AM
dhphoto
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p.1 #5 · p.1 #5 · How can you judge the true sharpness of a lens?


IMHO pure 'sharpness' isn't really a major issue with most lenses (and even less so when stopped down a bit) as modern sharpening techniques can often give plenty of apparent sharpness, certainly enough for a big print and that is likely to be the toughest test, looking at 100% crops doesn't really tell you much.

The thing it's still really hard to fake is lens contrast, the thing that sets the really good lens ahead of the merely good. That's only really a personal perception and hard to measure but the finest lens I ever owned was a Mamiya RB67 127mm lens that had the finest contrast I have ever seen (plus it was very sharp). My Hasselblad 150mm Sonnar had fantastic contrast too.

Bokeh again is a personal preference thing and often more important that sheer absolute sharpness IMO.

Again IMO but the tests I have done on medium format Hasselblad and Mamiya lenses on the 35mm format have been less than impressive because the lenses just weren't designed for that small format



Jan 12, 2016 at 08:09 AM
Zenon Char
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p.1 #6 · p.1 #6 · How can you judge the true sharpness of a lens?


I test my lenses on birds. Eyes, beaks, fine feather edges and claws. When those areas look crisp then I'm happy.

~original[/IMG]

This is a crop so not the best as I prefer to test at the original size. You can see the crisp eye and the feather detail under the chin.

~original[/IMG]

Here is a recent and rare shot that I did not have to crop. The detail in the skin and eye. That is what I like to test on.

~original[/IMG]



Jan 12, 2016 at 08:39 AM
Scott Stoness
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p.1 #7 · p.1 #7 · How can you judge the true sharpness of a lens?


Let me add - the performance of a lens can vary between close and far based on field curvature.

For landscape resolution, I would find a scene that is pretty perpendicular to you with trees far off in the distance, focus near centre with live view, use a tripod, and mirror lockup, and take 3 pictures and then use the sharpest. Do the same for the comparator and decide if there is a difference, centre, middle, and right vs left and top vs bottom edge.

Do this wide open but if you are comparing a f4 to f5.6, do them both at f5.6. In fact to be through do them at open, open plus 2 stops, and f8. Sometimes a good lens is not good wide open.


Then repeat with the focus close to the edge and repeat.

Then pick the set (focus centre vs focus edge) that is sharper and compare. And not whether centre focus or edge focus is sharper for future use.

I would also do a similar, but not as many, closer in with a brick wall to see what kind of distortion is introduced.

A really quick version of this is to set the lens up on a tripod, focus centre with live view, and then do a x 10 mag and see how focussed. Chang from edge focus to centre focus. And redo. This only checks wide open though. And you have to remember what you saw on the other lens.



Jan 12, 2016 at 09:01 AM
nntnam
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p.1 #8 · p.1 #8 · How can you judge the true sharpness of a lens?


For me sharpness = resolution + micro-contrast. It really depends on viewing distance to tell which lens is sharper. Zooming to 100%, lens with higher resolution will look sharper, but at 12% or 25%, lens with higher micro-contrast may look sharper (if its resolution doesn't fall too far behind). I have both canon and zeiss lenses, and I can tell that. My canon lenses usually have better resolution but lower micro-contrast than my zeiss lenses, but canon's images don't always look better or sharper.

So, IMHO 'true sharpness' is kind of sharpness works best for your photography. I prefer my zeiss for landscape, Canon for portrait.



Jan 12, 2016 at 09:48 AM
mttran
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p.1 #9 · p.1 #9 · How can you judge the true sharpness of a lens?


nntnam wrote:
For me sharpness = resolution + micro-contrast. It really depends on viewing distance to tell which lens is sharper. Zooming to 100%, lens with higher resolution will look sharper, but at 12% or 25%, lens with higher micro-contrast may look sharper (if its resolution doesn't fall too far behind). I have both canon and zeiss lenses, and I can tell that. My canon lenses usually have better resolution but lower micro-contrast than my zeiss lenses, but canon's images don't always look better or sharper.

So, IMHO 'true sharpness' is kind of sharpness works best for your photography. I prefer my
...Show more

+1, and use the bodies that can best your focal planes in realtime.



Jan 12, 2016 at 10:44 AM
Zenon Char
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p.1 #10 · p.1 #10 · How can you judge the true sharpness of a lens?


There is a lens sharpness chart you can use that gives you an objective result. I don't have a link. General images are subjective and what is sharp to one person may be different to another. As long as you are happy with your images that is what counts. When I shoot birds for sharpness tests I know what to look for and what makes me happy. If I'm happy I just move on.



Jan 12, 2016 at 10:50 AM
Gunzorro
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p.1 #11 · p.1 #11 · How can you judge the true sharpness of a lens?


I use a tripod and run complete aperture range on various convenient subjects and various distances around the yard or neighborhood. Often, I use a dual camera mount and switch lenses between two cameras to get an even better impression of the results. LV manual focusing. Do 100% A-B comparisons in LR with "Control/C" on PC.

I'm checking sharpness, contrast, CA, field curvature, and vignetting for the most part.



Jan 12, 2016 at 10:51 AM
jcolwell
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p.1 #12 · p.1 #12 · How can you judge the true sharpness of a lens?


I use a variety of ways to assess individual lens performance, and to compare relative performance between lenses.

There are a variety of test charts to assess resolution. I prefer these two:

USAF test chart pdf http://photo.net/learn/optics/USAF1951.pdf
- (from http://photo.net/learn/optics/index)

ISO 12233 test chart http://www.graphics.cornell.edu/~westin/misc/ISO_12233-reschart.pdf

I use the spreadsheet developed by Rob Studdert (Digital Image Studio) to calculate resolution from USAF 1951 test results. Rob's site is much reduced these days. I recall corresponding with him through FM a few years ago, and so maybe he'll pop up.

I find the test charts are best suited for short and medium test distances, and real world images are well suited for all distances, as long as you have a more-or-less stationary or constant subject. I've been recently testing at relatively long distances to compare a variety of prime and zoom lenses for scenic photography, like these,

EF 16-35/4L IS test images https://www.fredmiranda.com/forum/topic/1313373/0#12531288
Comparison of Zeiss 25/2 ZE and Canon L lenses https://www.fredmiranda.com/forum/topic/1403832

...and other stuff,

Best 135mm? [135/2L vs SMCP-M] https://www.fredmiranda.com/forum/topic/1368392/0#13040912
100-400L IS (Mk I) vs 70-200II + 2x III https://www.fredmiranda.com/forum/topic/1154527
[85mm bokeh & detail images] https://www.fredmiranda.com/forum/topic/952008/0&year=2010#9001461

Unfortunately, images are no longer available for many older FM threads, such as the 85mm bokeh tests linked above.

As Jim (Gunzorro) mentioned above (and has often been discussed here), it's important to use a careful, systematic, and repeatible approach to doing these tests; otherwise, the results aren't of much value. Here's some more info on this,

50 MP 'resolution' [sum of recips] https://www.fredmiranda.com/forum/topic/1346296/3#12869085
FM thread on 'testing lens resolution...' https://www.fredmiranda.com/forum/topic/1261919/0#12017003
FM thread on 'guides for comparative testing' https://www.fredmiranda.com/forum/topic/1255884/0#11957157
Takinami PDML lens test procedure http://www.takinami.com/yoshihiko/photo/lens_test/pdml-procedure.html
Monaghan's Magasite Camera and Lens Testing Tips http://www.jcolwell.ca/MM/TestingTips.pdf

Also, there are specialty charts to test AF accuracy, which is usually part of a set of AF microadjustment tests (AFMA), which I won't mention further here, ...except to say "snapsy" and "LensAlign II".

Whatever you do, don't post colour-comparison tests...

Lens colour difference test https://www.fredmiranda.com/forum/topic/1386031



Jan 12, 2016 at 01:25 PM
Scott Stoness
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p.1 #13 · p.1 #13 · How can you judge the true sharpness of a lens?


nntnam wrote:
For me sharpness = resolution + micro-contrast. It really depends on viewing distance to tell which lens is sharper. Zooming to 100%, lens with higher resolution will look sharper, but at 12% or 25%, lens with higher micro-contrast may look sharper (if its resolution doesn't fall too far behind). I have both canon and zeiss lenses, and I can tell that. My canon lenses usually have better resolution but lower micro-contrast than my zeiss lenses, but canon's images don't always look better or sharper.

So, IMHO 'true sharpness' is kind of sharpness works best for your photography. I prefer my
...Show more

I am an engineer and I am of the school that if you can't measure it - it does not exist.

I agree that micro-contrast may be important but I find the label vague.

The best definition I have seen is that some lens are better at resolving really tiny lines vs larger lines.

It is verifiable by examining the mtm of the lens at greater and greater lines per inch. Eg look at thedigitalpicture mtm measures and compare the lower curves, the higher the curves are the better the microcontrast.

Incidently the gap between sold and dash lines indicates astigmatism.

So what you can discern from the curves is microcontrast (higher bottom curves), astigmatism (gaps between dashed and solid) and resolution (higher is better). The image will have a brighter /crisper feel to it when you look at it.

Unfortunately it does not help for field curvature, copy variation, and color, and ca.

I appreciate being corrected if someone disagrees.



Jan 12, 2016 at 02:40 PM
David Baldwin
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p.1 #14 · p.1 #14 · How can you judge the true sharpness of a lens?


Focus the lens at infinity and take some star trails at varying apertures. This is an extreme "torture" test for any lens, and will give you a very quick way of assessing basic sharpness. The slightest aberrations or decentering will be obvious.


Jan 12, 2016 at 02:46 PM
tuantran
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p.1 #15 · p.1 #15 · How can you judge the true sharpness of a lens?


I think we should start with some basic questions:
1. What is your budget? This should include the cost of the lens adapter + your time figuring out whether what to keep.
2. How much do you value your time? This can be as simple as how much do you get pay per hour for your job. If you get paid $125 and you spend 5 hours to do all this, wouldn't it be cheaper to buy a good lens from recommendations?
3. What are you shooting? Events and Wedding with a manual focus is a little painful.
4. How much are you shooting? If you are going to use it once every 4 months, then spending hours to figure out if you want to use it is a waste.

I think Chez is right. Shoot something, blow it up to 20x30 and see if you're happy. This takes little effort and cost is minimal especially at Costco where 20x30 is like $10?



Jan 12, 2016 at 03:03 PM
billsamuels
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p.1 #16 · p.1 #16 · How can you judge the true sharpness of a lens?


Scott Stoness wrote:
Let me add - the performance of a lens can vary between close and far based on field curvature.
For landscape resolution, I would find a scene that is pretty perpendicular to you with trees far off in the distance, focus near centre with live view, use a tripod, and mirror lockup, and take 3 pictures and then use the sharpest.
Do the same for the comparator and decide if there is a difference, centre, middle, and right vs left and top vs bottom edge. Do this wide open but if you are comparing a f4 to f5.6, do
...Show more

This seems like fairly easy method to come up w/ realistic idea of whether the lens is sharp or not. I'm trying to figure out if my Mamiya 80mm F/2 is worth keeping for my Canon cameras or should I sell it The other two Mamiya-Sekor lenses aren't real sharp on a Canon, but they were real sharp on a Mamiya. When I had the Mamiya, they worked like a charm, but the camera had light-leaks so I sold it to KEH because they gave me a lot more than I ever thought the camera was worth. I kept the lenses, because I thought the lenses would be fun to use, but each lenses wasn't all that exciting or sharp on a Canon, except I think the 80mm seems sharp close-up, but I haven't figured out if it's sharp in distance shooting.

After shooting yesterday (see photo above) I think it is fairly sharp, but compared to a Canon or a Zeiss, it's not as sharp, but then again, I don't have an 80mm Prime lens.

I'm going to try Scott's technique and see if I can get a handle on sharpness, but only on distance, not close-up.

Then just to play around, maybe I'll test it close-up against my Canon 24-100mm and 70-200mm, both set at 80mm using the 6D (or maybe my new 5DSR if I really want to have fun!).






Jan 12, 2016 at 04:25 PM
Chris.P
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p.1 #17 · p.1 #17 · How can you judge the true sharpness of a lens?


I usually setup a tripod in my backyard and shoot at a wooden fence that has lots of little details. You'll see quickly the difference between the center and the corners and overall the lens sharpness characteristics.


Jan 13, 2016 at 10:45 AM
Sy Sez
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p.1 #18 · p.1 #18 · How can you judge the true sharpness of a lens?


That lens is currently available from KEH, with a 180 day warranty, for $65

You'd be lucky to get $25 for it, so it would seem hardly worth the bother of trying to sell it.

My advice is, If you have a use for it, & get images that are acceptable for the purpose, keep it & use it----If not, post it on some "free" sales site, or stow for memorabilia.

Leigh
http://www.leighwax.com



Jan 13, 2016 at 12:08 PM
PeterP1D
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p.1 #19 · p.1 #19 · How can you judge the true sharpness of a lens?


I've fooled around with this a few times.

http://www.normankoren.com/Tutorials/MTF5.html



Jan 13, 2016 at 01:50 PM
Scott Stoness
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p.1 #20 · p.1 #20 · How can you judge the true sharpness of a lens?


Chris.P wrote:
I usually setup a tripod in my backyard and shoot at a wooden fence that has lots of little details. You'll see quickly the difference between the center and the corners and overall the lens sharpness characteristics.


The trouble with this technique is you are tsting the lens relatively near. Field curvature might cause good results that don't repeat at infinity. You will need to repeat relatively far (trees on mountains near infinity).




Jan 13, 2016 at 02:30 PM





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