stopping down hurts?

[arthurking83]

Ok I've seen a few images around here where the exif says ... f=22 or similar.

diffraction!

There's usually no issue and the images have appeared fine, but(!!) I've been seeing a lot of lens tests/comparisons where the tester has noted things like "diffraction causes problems from f/16, as is to be expected..." or words to that effect.

It appears to afflict certain cameras worse than others, they all do it, but to what degree?

As I've read many lens tests proclaim it to be a problem, I tend to use a min f/11-13(f/16 on some occasions) for any landscapes where there's excessive light... many at f/8.

I'm wondering if any folks here are aware of this 'problem'?

I finally found a technical link that many folks can "visually understand" (meaning I finally see what they're on about ).

THE TECHNICAL LINK!

the site is interactive, so you can see what diffraction does to an image, and explains technically what's happening within you camera(the sensor).

OK here's the catch! The sharper the lens the WORSE the diffraction appears!!

It actually makes sense really, if your lens is sharp as a tack(hey Dowden, you still got that 70-200? ) then you will notice any blurry abberation more than you would if the lens was already softish

[Knawful]

Hmm, gunna have to experiment tomorrow me think's.
I usually shoot f2.8 - f11 with the 70-200 and havent really noticed to be honest.

[arthurking83]

I'd like to see some samples of a brick wall at f8 and f16(and smaller) just to see.

f/5.6 is supposed to be the sharpest setting on that beast..

I don't think I have a lens sharp enough to really make a definitive example...but all those MTF tests and info like that link can't be wrong

brick wall(maybe a paling fence?) is good because of the texture, and focal plane!

ps I'll stop posting tonight, and post my 1000th post tomorrow .... headache/cold is wearing me out... and it's only 12:30!

[dejavu]

Diffraction is noticable from around f16 and up (exclusive). Now, the thing is why do you want to shoot at f22+?

The increase of DoF from f22 to f32 is absolutely minimal, even in macro. There are much more effective methods of achieving higher DoF without resorting to bumping the aperture up that high.

Be careful reading some of those image test online though. Unless the tests have been conducted with the strictest standards, the test will biase against high aperture settings since the longer exposure will be more susceptible to vibrations.

[xpantz]

Diffraction is noticable from around f16 and up (exclusive). Now, the thing is why do you want to shoot at f22+?

There are much more effective methods of achieving higher DoF without resorting to bumping the aperture up that high.

Got tips? :-)

[xpantz]

Got tips? :-)

hey I got one of my own. :-)

poking around looking for technique to increase DOF I came across a couple of pieces of softare to help you do the job.

it's like HDR for DOF

Helcion Focus
http://heliconfilter.com/pages/index...e#heliconfocus
and
CombineZ5
http://www.hadleyweb.pwp.blueyonder..../combinez5.htm

I used Helcion to create this image... perfectly in focus from back to front.



Created from these 6 images.. focus moving from back to front in steps.
All shot at f/11







I've only used the Halcion software so far but I believe the CombineZ5 does the same thing and is free. Halcion costs 30$ for the basic version and 70$ for the pro which can clone and copy bits from any of the source images to the processed image and a few other tricks... you can just live with the lite version I rekon.

Really easy to use.. just take a few shots with focus ranging from one side to the other... open them up in the Helcion softare and hit the process button.

if you can get your bug to sit still long enough you can have him from focus from eye to tail.

kinda feels like cheating but hey :-) it works!

[arthurking83]

Diffraction is noticable from around f16 and up (exclusive). Now, the thing is why do you want to shoot at f22+?

.....

The point I was trying to establish, for anyone coming from film (me!) when shooting landscapes, I was 'taught' to stop down for DOF.

I suppose p&s(digital) folks probably never had this issue ... (dunno.. .. I've never had one)

I have seen some folks shooting at f22, I felt compelled to point this phenomenon out.


My main concern with those MTF charts and lens comparisons are more about sample variation... more so, than controlled environments...
I have no reason to suspect (nor seen evidence to the contrary) that they are not done to a standard.... ie. consistent environments.
Further to that, many lens tests seem to report similar findings anyhow ... that Lens X is generally sharper than Lens Y, yet Lens Y may have better color or CA control, or it may feel less robust.. etc.... a pattern does emerge (only from what I've read on the lenses that I have any interest in!)

[DAdeGroot]

The point I was trying to establish, for anyone coming from film (me!) when shooting landscapes, I was 'taught' to stop down for DOF.

Diffraction existed in the film world too - on a 135 format (full frame in the digital world) body, you'll start to get diffraction from f/16. The issue with film is most people weren't shooting high quality, low grain film in order to notice it.

On an APS-C body, diffraction creeps in from f/11 onwards. You can usually get away with f/16 and not notice too much, but beyond that, and with a sharp lens you'll see softness compared to a wider aperture.

So while stopping down will get you more depth of field, you will lose sharpness past the diffraction point of your camera system. It should be noted that the point at which diffraction becomes noticeable is related to the size of your film/sensor and the lens construction. Thus, large format shooters using 8x10" film can happily shoot away at f/32, while small format (135 format) users cannot without getting a fairly soft image.

[TOM]

diffraction is dependant on two variables

1. the distance fromt he lens, of the object affected by diffraction
2. the size of the lens being used

one cannot simply say, diffraction kicks in at fxx.

[Tannin]

~~ Huh?

Neither of those have anything at all to do with diffraction. Zip. Nothing. Nada.

[Kym]

Diffraction can work for you! The 'star' effect is due to diffraction.

f/16, 30 seconds, ISO 100, 43 mm

[TOM]

Neither of those have anything at all to do with diffraction. Zip. Nothing. Nada.

the amount of diffraction is determined by lens size, and the amount of affect that diffraction has on part of your image, depends on how far that part of your image is from the lens. so for an image with a film camera (not that sure with a Digital Camera), i work on s=D/1600d where s is the diffraction limited size of object, D is the distance from the lens in feet, and d is the lens size (focal length/f stop). so if i am photographing the on the Sturt Reserve in Murray Bridge with a 35mm lens at f11, and the twin bridges are 1km in the background, i know that anything that is just over a half a foot in size or larger will be rendered sharply in my image. So as you can see, by using a larger aperture, we get better resolution and less diffraction, however our dof is limited. But just over half a foot (16) allows me to render the basic structure of the bridge, but rivets and the shape of the beams are not detectable.

so beams of light travel ina straight line, but when they are squeezed through a diagraphm opening, they divert. they still travel forward, but now at an angle, so obviously the further away an object is from the lens, the more that diffraction will affect said object. now with a Digital Camera, you can just chimp, but if you ever graduate to a larger format camera, you may not have that luxury. the above calculation doesn't have to be worked out every time, you will become familiar with these figures. i know that for max dof for most of my scenic shots, that f9.5 on my 35mm will give me great results.

as for lens size, Ansel Adams named his school "f64". this was an f stop that he often used. the lens that he was quite partial to was a 300mm lens, and he used this for alot of his work. Lens size = 4.6mm

[Steve Axford]

the amount of diffraction is determined by lens size, and the amount of affect that diffraction has on part of your image, depends on how far that part of your image is from the lens. so for an image with a film camera (not that sure with a Digital Camera), i work on s=D/1600d where s is the diffraction limited size of object, D is the distance from the lens in feet, and d is the lens size (focal length/f stop). so if i am photographing the on the Sturt Reserve in Murray Bridge with a 35mm lens at f11, and the twin bridges are 1km in the background, i know that anything that is just over a half a foot in size or larger will be rendered sharply in my image. So as you can see, by using a larger aperture, we get better resolution and less diffraction, however our dof is limited. But just over half a foot (16) allows me to render the basic structure of the bridge, but rivets and the shape of the beams are not detectable.

so beams of light travel ina straight line, but when they are squeezed through a diagraphm opening, they divert. they still travel forward, but now at an angle, so obviously the further away an object is from the lens, the more that diffraction will affect said object. now with a Digital Camera, you can just chimp, but if you ever graduate to a larger format camera, you may not have that luxury. the above calculation doesn't have to be worked out every time, you will become familiar with these figures. i know that for max dof for most of my scenic shots, that f9.5 on my 35mm will give me great results.

as for lens size, Ansel Adams named his school "f64". this was an f stop that he often used. the lens that he was quite partial to was a 300mm lens, and he used this for alot of his work. Lens size = 4.6mm

This doesn't seem right to me. The diffraction works from the iris to the sensor (film or digital), not from the subject to the iris. Am I missing something?

I find that f18 is the limit for my 180mm macro (at close distances). For my MP-E it is f16, which is the maximum. It is worth remembering that the effective aperture is also dependent on how close is the subject (angle of incidence to the lens). This really is irrelevant for most lenses, but for the MP-E it can change the f16 to f64 at 5x magnification. For some of the other lenses it may be a little less, maybe f13. This is for the 1Ds Mk3, but it would be less for a camera with higher pixel density. You really need to experiment a little to find what is best for your lens/camera combinations.

[Tannin]

Hoolie doolie that's a hard way of thinking about an easy subject Tom! To summarise, you are saying that you can .... no, that's too hard for me. My brain hurtz when I try to summarise what you just wrote. Let's do it the other way:

Diffraction depends on your f stop.

Wasn't that easier? And it also has the advantage of being 100% correct. Diffraction increases as aperture gets smaller; the higher the f/ number, the more the diffraction. For any given camera, no other factor is relevant. Diffraction depends on your f stop. End of story.

[arthurking83]

Yep! it's definitely related to both sensor resolution(more than size) and lens design.

I haven't fully tried to see any differences with the 70-200 Tammy between the D300 and the D70, and I may have erred with the f/8 shots I took.. MLU, multiple shots. remote(when it was working ) and focus confirmed with Live view.

But the 300/2.8 with TC's is the spanner in the works, and I suspect that other may see similar results with stacked TC's on their lenses too.
The F/22 shots on the Tammy with a 1.4x and 2x TC stacked are definitely crisper than the f/16 shots were.

What may cause confusion to members that haven't fully tested their gear, is that there is a general consensus that f/11 is the limit for an APS-C sensor, or a sensor with a x.yz pixel pitch, or whatever.. but that doesn't take into account the lens used, and as Steve mentioned, his macro lenses work very well up to and beyond f/11(his example of f/16 and f/18 are noted). I've seen similar results from the 105VR micro too.. where f/16 and even f/22 don't look overly diffracted.... as, say, the 10-20mm Siggy does.
I max my Sigma 10-20 at f/11 by default(exif in tact and you'd notice that 99.9% of my images from the 10-20 are at f/11. If I'd remembered to check camera settings my last image taken with the Tammy 28-75 at f/11 would never have happened.. I generally stick to f/8 as maximum(or minimum depending on your preferred terminology) on that lens.

That's why it's important as Steve said, for those that think it's of value to them, to test their lenses(chimp it as TOM reckons ) to see what variables they need to get their lenses work effectively.

I remember reading a quoted line of text by a very professional photographer and tester, where he said that the theory is only valid once the practice proves it to be true. Until then it's only theory(translated to mean useless in the real world if not proven to be true )

DOF and diffraction are two of those elements that haven't actually been proven by any formula... because a lens engineer can easily design one, to make them look as silly as they appear to be. What may work for one lens, may not work for another.

[TOM]

Tannin, lens size is most certainly the more accurate way to talk. F11 on a 35mm lens is a smaller aperture than f11 on a 75mm lens. lens size is lens size, no matter the focal length, no matter the format.

Okay, a quick summary...for landscape or shots where max dof is required, use a lens size between 3 and 5mm.

[Steve Axford]

Tannin, lens size is most certainly the more accurate way to talk. F11 on a 35mm lens is a smaller aperture than f11 on a 75mm lens. lens size is lens size, no matter the focal length, no matter the format.

Okay, a quick summary...for landscape or shots where max dof is required, use a lens size between 3 and 5mm.

True, but the diffraction effects are constant, irrespective of lens size. Of course this does not explain why some lenses show diffraction effects at lower fstops than others??

[TOM]

it's funny how there is this mystique surrounding some Leica lenses and the way that the images from these lenses have a "glow" to them. This is known as the "Leica glow", but this glow is caused by light bouncing off the diagraphm blades. It was something unique to these lenses, and it is highly unlikely that it was unintention, at least not the first lens designed with the inherant property.

[Tannin]

Ouch! First, "lens size" is a ridiculous term to use when actually you seem to mean physical aperture - most people would assume you are talking about focal length. Second, physical aperture ("size of the hole") doesn't control depth of field or diffraction, it is physical aperture in combination with focal length.

So either you keep two different factors in your head and do sums with them .... OR you recall that, as it happens, there is a very convienent single number already calculated that tells us all we need to know about diffraction. It's called the f/ratio.

[TOM]

lens size is a term that has been used for decades, and i didn't make it up. it is a logical term that everyone should be familiar with. if you use f16 with a 15mm lens, and f16 with a 35mm lens, diffraction limitations/affects will be different.

doesn't control depth of field or diffraction, it is physical aperture in combination with focal length.

?? that is exactly what lens size is...focal length/aperture=lens size. a 3mm lens size on a 300mm lens is exactly the same size as a 3mm lens size on a 35mm lens.