diffraction - f3.5 to f22 using 35 macro [imgs]

[Brent Lossing]

Follow up to this thread:
http://forums.dpreview.com/forums/read.asp?forum=1022&message=35967033

Well. I was going to use the 14-54 for this test but it appears that at 14 mm it focuses a bit shy of infinity. I never noticed because I never used an aperature low enough for it to show....

So I did the test today using the 35 mm (my next widest lens) and shot at several different apperatures. There may have been a stray breeze through some of the leaves - but overall quite quiet. The closest bushes are about 15 feet away, the ones across the center about 50 and the furthest trees back about 200 feet. I used live-view and focused on the trees furthest back - put it in Manual focus and never touched it again, remote w/ 2sec delay plus 2 sec MLU, IS off (this time , tripod, ESP metering (I used some compensation to keep the path from blowing out), shot in RAW - just used CS4 defaults and saved right to jpgs.

I will follow up with at least a summary and answer any questions. Picts are in my dpreview Challenge gallery. Feel free to download (I assume that is possible?) and they will also be in the next post.

--
Thanks,
brent

http://lossing.zenfolio.com/

 

[Brent Lossing]

 

[robert j]

They all look good to me.
--
Coolpix L1, E-500, E-510, 14-42,18-180 & 70-300

http://www.flickr.com/photos/40113950@N05/

 

[Brad Ross]

they all look the same to me,,maybe I just dont have a discerning eye, but unless someone tells me what small detail to look at,,I don't see the differences

but then again I look at photos in a rather non technical way unless there is some blaring difficulty with a photo,

also looking on a 20 in flat screen monitor, maybe that makes a difference
--
Brad Ross

 

[LinusP]

Looks as expected to me...the foreground is DOF-limited at f/3.5 and f/4 and the background is diffraction limited from f/11 to f/22. The one at f/5.6 is my favorite overall - the f/8 shot seems just a touch softer, especially in the background.

Of course, they're all perfectly adequate for typical print sizes.

Brad Ross, check out the foreground leaves on the left, and compare f/5.6 to f/22. Depending on your monitor, you may have to zoom them in a bit to see the difference, but it's definitely there.

 

[Brent Lossing]

Look at the resolution charts here:
http://www.photozone.de/olympus--four-thirds-lens-tests/473-oly_35_35?start=1

You will see at the center the resolution goes from
3.5 = 2001
5.6 = 2278
11 = 1784
16 = 1373

just based on these charts (not taking DOF into account) you would expect the sharpest image to be 5.6, then 4, then 11, then 18 for the images I shot. The drop off from f5.6 to f18 is due to diffraction.

A confounding factor is DOF. I was curious how this would affect sharpness across a broad DOF. You can tell what areas should be sharp if you look at the DOF charts
http://olympusamerica.com/cpg_section/product.asp?product=1342&page=specs

I focused at about 200 feet (really infinity) so we would expect:
3.5 = sharp from 65 feet to infinity
5.6 = 39 feet out
11 = 20 feet out
16 = 15 feet out

Here are cutouts from different distances for all of the fstops. NOTE - I mixed wide and narrow aperature so you could clear see the differences at close, mid and far distances. Look at this at the original size or you probably won't see the differences.





--
Thanks,
brent

http://lossing.zenfolio.com/

 

[emsig]

Well done Brent.

I appreciate this work very much. It shows that we have to think more careful about using a certain aperture in a given situation.

Cheers
Emilio

 

[Great Bustard]

Look at the resolution charts here:
http://www.photozone.de/olympus--four-thirds-lens-tests/473-oly_35_35?start=1

You will see at the center the resolution goes from
3.5 = 2001
5.6 = 2278
11 = 1784
16 = 1373

just based on these charts (not taking DOF into account) you would expect the sharpest image to be 5.6, then 4, then 11, then 18 for the images I shot. The drop off from f5.6 to f18 is due to diffraction.

A confounding factor is DOF. I was curious how this would affect sharpness across a broad DOF. You can tell what areas should be sharp if you look at the DOF charts
http://olympusamerica.com/cpg_section/product.asp?product=1342&page=specs

I focused at about 200 feet (really infinity) so we would expect:
3.5 = sharp from 65 feet to infinity
5.6 = 39 feet out
11 = 20 feet out
16 = 15 feet out

Here are cutouts from different distances for all of the fstops. NOTE - I mixed wide and narrow aperature so you could clear see the differences at close, mid and far distances. Look at this at the original size or you probably won't see the differences.

Well done, well done! I must say, an impressive effort in putting the numbers into visual form!

OK, here's what I see -- the issue of DOF most certainly is a confounding variable, especially as the DOF we see at 100% is somewhat more narrow than what a DOF calculator would give us.

The left crops show the effect of DOF combined with diffraction, whereas the middle and right crops show the effects of diffraction alone.

To my eyes, it is difficult for me to discern any differences from f/3.5 to f/5.6 for the middle and right crops. I mean, I can see differences, but nothing that I, personally, would call "significant". What's interesting about this observation is that, per the lens test, the resolution at f/5.6 is 10% better than f/3.5, which means that, for my QT (quality threshold), differences of 10% or less seem to be insignificant.

However, past f/5.6, the image degradation is visible, and progressively worse as we close down the aperture.

Others, of course, may see things differently than I do, and that's just fine. However, your tests seem to well reflect what the lens tests show, and serve as an outstanding example to put the numbers of a lens test into a visual context.

So, next time someone is citing the "obvious superiority" of one lens over another because it resolves 2000 lines / image height vs 2100 lines / image height (photozone uses lines / ih as opposed to DPR's linear pairs / image height), I think a link back to this test is in order.

Again, allow me to express my appreciation for a test well done!

 

[LaMesa]

Your elaborate test is a useful demonstration of diffraction, something many of us are aware of, but had no idea of the real effect.

Thanks and Regards, Herbert
--
http://www.pbase.com/herbRD
Olympus E-1, E-330, Vario-Elmar 14-150mm

 

[FrankyM]

Excellent work, Brent, and very informative!

Frank

 

[Paniko]

Very well done. Plain simple.

Thank you Brent!
--
still trying to learn...

http://paniko.zenfolio.com

 

[Brent Lossing]

Nice to come in after a long day and read such positive comments

thanks,
brent

 

[ginsbu]

First, great work, Brent! Especially nice visual presentation of the results in your follow up post.

However, past f/5.6, the image degradation is visible, and progressively worse as we close down the aperture.

Something is definitely looks off about the f/8 shot. Examining both the near and far crops, f/11 looks marginally sharper than f/8. At 1/200 wind shouldn't be an issue, but perhaps a slight jostle to the setup. Regardless, I would bracket the f/8 result.

What surprises me most, actually, is that there isn't more visible degradation from f/11 to f/18, while the drop off to f/22 is much more pronounced.

 

[Brent Lossing]

First, great work, Brent! Especially nice visual presentation of the results in your follow up post.

However, past f/5.6, the image degradation is visible, and progressively worse as we close down the aperture.

Something is definitely looks off about the f/8 shot. Examining both the near and far crops, f/11 looks marginally sharper than f/8. At 1/200 wind shouldn't be an issue, but perhaps a slight jostle to the setup. Regardless, I would bracket the f/8 result.

What surprises me most, actually, is that there isn't more visible degradation from f/11 to f/18, while the drop off to f/22 is much more pronounced.

What is also interesting is that what drops off is contrast.

 

[Brent Lossing]

0. At web size you cannot tell the difference between any of the shots
1. All the shots from 5.6 to 11 were acceptable to me
2. 5.6 is the one I would pick in a side by side comparison.

3. for the furthest reaches (f3.5 & f22) the image is compromised - though not impossibly so. I have shot and kept images with lower IQ shot with ISO 1600

4. Even though 5.6 to 11 are all acceptable, for a different shot I might choose one or the other (or outside of the range). For example if there was movement - perhaps 5.6 may be a better choice. It I was shooting at 70mm f11 may be better.

5. Most shooters that shoot a lot of landscape instinctively (through trial and error) know approximately what is best. Either through composition (grouping item within the DOF that is sharp) or through aperature.

I thought overall it was good to have reasoned discussions. I think Greg (daddyo) said it well - something like: when I see some one just making a blanket statement like anything over f11 is bad or only shoot the best aperature according to the charts... Well we as photographers make the choices we do either through choice or maybe we just used the settings from last night (ooops!) but it is a hobby not a religion.

As my friend at church said - who will be at your funeral if you are always right?

Thanks for all of the input - it was fun,
brent

 

[Stefan Kaben]

Agreed.

Brent, between the lead-in thread and this one, I learned a lot - not so much new information as putting known information together in useful and meaningful ways for real-world photography. Got me thinking differently about what I thought I might've known. Thank you!
--
Cheers,

• Stefan

http://skaben.zenfolio.com/