Autofocus mechanism

[WayneF]

a friend of mine shifted habit from regular shutter button operation , to back-button focusing , he feels his images are coming out clearer and really likes this other technique.. but why would this make a difference if this technique is the same as single finger pressing of the shutter release button?

I agree, why would it? My take is the shutter button is placed better to be more able to press it without camera shake. The AE/AL is a programmable function button to change the way focus or exposure is locked, if desired. But you know that if they came out with a radio operated iPhone button, a certain percentage will swear it really helps.

I am old fogy, but other than film speed, cameras have historically had only two controls, shutter speed and aperture. These still work the same today. Shutter mechanisms are faster now, and the CPU chip has made big changes in how focusing is done, but stopping motion still depends on shutter speed in the same way it always did. But of course, we can hear lots of opinions now.

I'm occasionally really cranking up on shutter speed I can gotten up to even 6000th of a sec and I still cant see the same fine scale details that I can on similarly distanced motionless birds but that softness could be for several reasons.

Then I would first suspect a focus issue? Focus on a fast bird is certainly a different situation than a sitting bird.

Another issue , is that Im looking at getting a longer lens , do I need it to have VR if its going to be used at higher shutter speeds as well? If I got a faster lens , would this be better or worse at freezing for detail than trying to use a speedlight If I'm taking my pix in decent ambient light anyway?

The speedlight at low power (close range) will be much faster than any shutter speed, but seems not generally applicable to fast moving or distant birds. For this speedlight advantage to be true, ambient needs to be underexposed at least a couple of stops, so the continuous ambient will not let shutter speed (1/250 second) blur what the speedlight already stopped.

VR does NOT affect focus or subject motion. Its sensor is only about camera motion (shake). Common consensus is to turn VR off if not needed, or said better, turn it on when it is needed. Nikon says turn it off on a tripod, but to me, a fast shutter would seem to be the same thing. If it can't help, it can't hurt to turn it off. But I don't know if it matters or not. It seems clear it cannot help though.

Regardless of the rules of thumb that some folks may find works for them - just physically speaking, without subjective overlay , VR isnt conclusively helping or harming anything in the image at shutter speeds over sync,, so you can just leave it on if you're shooting handheld and have the advantage of a steadier view of your bird.

Dunno, but it seems to me that if shutter speed makes VR unnecessary (shake), then anything VR might do anyway then is unwanted. But VR is never about subject motion or focus, it does not follow the subject.

And a 42.6mph rate of motion is entirely feasible for a vertically moving birds wing.

42.6 MPH is 17.2 inches/second, and in 1/250 second, is 0.068 inches (approx 1/16 inch). This is speaking of shutter slit travel (distortion), exposure and motion freezing can be a few stops faster.

It is said that a 1/25000 second speedlight flash (about 1/64 power at close range) is needed to stop hummingbird wings, but debateably, in practice, 1/8000 seems to do a reasonable job.

This is actually a discussion I did not intend to participate in. But bottom line about the problem, do all you can.

​

 

[Stoshowicz]

I agree, why would it? My take is the shutter button is placed better to be more able to press it without camera shake. The AE/AL is a programmable function button to change the way focus or exposure is locked, if desired. But you know that if they came out with a radio operated iPhone button, a certain percentage will swear it really helps.

One still ends up pushing the shutter button down either way.


I am old fogy, but other than film speed, cameras have historically had only two controls, shutter speed and aperture. These still work the same today. Shutter mechanisms are faster now, and the CPU chip has made big changes in how focusing is done, but stopping motion still depends on shutter speed in the same way it always did. But of course, we can hear lots of opinions now.


True , and distortions like that exhibited in the racecar photo always happened then as well. Electronic shutter control would seem to be the way to go.. at least for high speed photos.



Then I would first suspect a focus issue? Focus on a fast bird is certainly a different situation than a sitting bird.

Well the head is clear , the tracking of the focus is working great ,, you can see this phenom in everyone elses pix as well , at 1000th of a sec there is clearly wingblur , at 2000th most of the wing is stopped nice, at 3000th the tips are frozen ,,, but the very fine detail is still obliterated until the wing speed drops significantly. all you can see at the feather tips is featureless color. It only takes the tiniest smudge- on the order of scale of the detail you want to see.. to render that effect. The strange thing is , the same shutter speeds seem to have the same relative effect on things as different as a swan to a dragonfly.



The speedlight at low power (close range) will be much faster than any shutter speed, but seems not generally applicable to fast moving or distant birds. For this speedlight advantage to be true, ambient needs to be underexposed at least a couple of stops, so the continuous ambient will not let shutter speed (1/250 second) blur what the speedlight already stopped.

Yep

VR does NOT affect focus or subject motion. Its sensor is only about camera motion (shake). Common consensus is to turn VR off if not needed, or said better, turn it on when it is needed. Nikon says turn it off on a tripod, but to me, a fast shutter would seem to be the same thing. If it can't help, it can't hurt to turn it off. But I don't know if it matters or not. It seems clear it cannot help though.

Well I read the argument for turning it off was that somehow the VR could cause the camera to jump off focus- since its an optical element it could conceivably affect focus. That makes no sense to me though, if the tripod was rock solid then the VR shouldnt adjust anything ,, if the wind vibrated the tripod , well then the VR might dampen the vibrations.


Dunno, but it seems to me that if shutter speed makes VR unnecessary (shake), then anything VR might do anyway then is unwanted. But VR is never about subject motion or focus, it does not follow the subject.

It helps to see what you are looking at while the mirror is down.

42.6 MPH is 17.2 inches/second, and in 1/250 second, is 0.068 inches (approx 1/16 inch). This is speaking of shutter slit travel (distortion), exposure and motion freezing can be a few stops faster.

It is said that a 1/25000 second speedlight flash (about 1/64 power at close range) is needed to stop hummingbird wings, but debateably, in practice, 1/8000 seems to do a reasonable job.

This is actually a discussion I did not intend to participate in. But bottom line about the problem, do all you can.

Yessir it is.

​

 

[Eyelight]

Im impressed with your math But like I said , its to demonstrate principle. But playing along, I never said how dark the background was nor how relatively bright the ball was , nor the fov of the lens , nor the distance to the ball. So those there calculations aren't valid speculations to the scenario. ( besides, I found out that the modern shutters open vertically) And I see you must agree that the ball would be elongated ,, which was the point I was trying to illustrate. And a 42.6mph rate of motion is entirely feasible for a vertically moving birds wing.

Well, your description theorizing a stripe as well as photographing birds and balls in general led to the idea of a small ball relative to the view. Closer ball would be bigger in the view and slower, leading to a blur we could see at some point, but not a stripe across the image. Bear in mind, I'm just thinking along, not really agreeing or disagreeing.

So, let's put some real world stuff into the calculations. What kind of bird are we plotting against and how far away with what focal length are we going for the capture?

 

[Stoshowicz]

Ok fair enough, heres a real example , rather close maybe fifteen twenty feet , not moving very fast, morning light.
You can see the orbital feathers and the edges on the spread tail , but the wing tips which arent spread much further apart than the tail width look smudgey and uniform,, and thats at 2500th of a sec 300mm f5.6 . Its not a perfect choice of pic , but it is what I have at hand. Ill see what Ive got at home which calculates a broader Dof

View attachment 119429

 

[Eyelight]

Ok fair enough, heres a real example , rather close maybe fifteen twenty feet , not moving very fast, morning light.
You can see the orbital feathers and the edges on the spread tail , but the wing tips which arent spread much further apart than the tail width look smudgey and uniform,, and thats at 2500th of a sec 300mm f5.6 . Its not a perfect choice of pic , but it is what I have at hand. Ill see what Ive got at home which calculates a broader Dof

View attachment 119429

Is this full image uncropped??

 

[Stoshowicz]

I think its cropped , I usually do some basic adjustments and drop the big Raw file.
This duck is a clearer example , the wing is still blurred at double what folks ordinarily use on BIFs.
Im thinking the lower margin of the feathers should be as crisp as the leading edge but they arent.

View attachment 119535

If I pan with the birds motion , I really shouldnt need much shutter speed to freeze it, The autofocus should be keeping up with the rate of approach ,so the shutter speed should really oniy be helping much for wing motion. Maybe the VR optical element made a shift during the exposure ? Maybe its just the tip of the wing is fastest , but at this point in the flap , the wing shouldn't be moving very fast up and down , it should be going towards or away from the sensor, and the blur should go all the way around the feather.

 

[Eyelight]

This is more interesting with photos. I've been playing with wing beat speeds and learned a few things that may make my own bird photos a bit better. Your blackbird and duck are better than any of my BIF shots.

There are similarities between the duck shot and the blackbird shot.

Here is my take on the duck shot. Could tell more with the original RAW file, but what I see in these appears to be a combination of the wings getting into the fringe of the DOF and some motion blur.

Assuming the duck is in straight flight, or at least that both wings are in the same motion, the near wing is not as sharp as the far wing. This is the DOF indicator. If you can post the uncropped shot, I can esti-calculate a distance and determine an approximate DOF.

The leading edge of the far wing appearing sharper than the tips of the primaries is an indication of motion blur, due to the tips sweeping and/or a bit of flutter. The tips of the primaries would actually be the fastest moving parts during the upward/forward wing movement (I'm not a duck expert, so it's my guess this is a forward wing movement moment)

Now, looking back at the original question, is there something about the duck shot that leads us to think there is an issue with anything other than DOF or motion blur??

 

[Stoshowicz]

This is more interesting with photos. I've been playing with wing beat speeds and learned a few things that may make my own bird photos a bit better. Your blackbird and duck are better than any of my BIF shots.

There are similarities between the duck shot and the blackbird shot.

Here is my take on the duck shot. Could tell more with the original RAW file, but what I see in these appears to be a combination of the wings getting into the fringe of the DOF and some motion blur.

Assuming the duck is in straight flight, or at least that both wings are in the same motion, the near wing is not as sharp as the far wing. This is the DOF indicator. If you can post the uncropped shot, I can esti-calculate a distance and determine an approximate DOF.

The leading edge of the far wing appearing sharper than the tips of the primaries is an indication of motion blur, due to the tips sweeping and/or a bit of flutter. The tips of the primaries would actually be the fastest moving parts during the upward/forward wing movement (I'm not a duck expert, so it's my guess this is a forward wing movement moment)

Now, looking back at the original question, is there something about the duck shot that leads us to think there is an issue with anything other than DOF or motion blur??

Well , you may be exactly correct , about the cause of the wingtip blur ,, its very difficult to say conclusively otherwise - I was making a rough approximation , that the lower wing is really pretty much in the field of decent focus because its roughly at the same distance as the tail and face,, and that the wing was pivoting basically toward or away from the sensor rather than overall down or up.
So the distribution of the blur was the main thing suggesting to me a vertical bias for smudge.
I dont know if feather edges flutter at some high frequency, thats an interesting possibility.
I'm trying to rule issues out so as to do better. I google to try to find discussion on fine scale artifacts that show up on moving objects but couldn't find much.
They say you cant really freeze action completely with shutter speed and Im seeing some confirmation of that. But when you go to use a strobe, the distance makes the effect weak and the ambient light shows the ghost of motion superimposed on the flash image ( if you know what I mean)

 

[Stoshowicz]

Leaving the other issue aside for a moment .
Heres another example of a technical issue that I just cant explain , but is readily visible , the anhinga is soaring so the wings are moving at the same relative motion as the rest of it. The upper trailing edges of the nearer wing show a blue margin , the lower trailing edges show a yellow margin , and on the far wing there isnt much color cast it looks brown .. but then on the head and bill one doesn't see the color margins at all ,, are the feathers polarizing the light or something? Should I get a polarizing filter? or is this just unavoidable.
View attachment 119550

 

[Eyelight]

Leaving the other issue aside for a moment .
Heres another example of a technical issue that I just cant explain , but is readily visible , the anhinga is soaring so the wings are moving at the same relative motion as the rest of it. The upper trailing edges of the nearer wing show a blue margin , the lower trailing edges show a yellow margin , and on the far wing there isnt much color cast it looks brown .. but then on the head and bill one doesn't see the color margins at all ,, are the feathers polarizing the light or something? Should I get a polarizing filter? or is this just unavoidable.

I can't see the margins that well at the upload resolution. If you wanted to upload the original to DropBox or similar and post or PM the link, I would be interested to look. I'm guessing by what you describe that it is simply colors in the feathers that are being accentuated by the way light is hitting, reflecting and being interpreted by the lens and sensor.

Light is a funny thing and does not always behave like we think it should and a DSLR doesn't always know what to do with what it sees.

 

[Eyelight]

Well , you may be exactly correct , about the cause of the wingtip blur ,, its very difficult to say conclusively otherwise - I was making a rough approximation , that the lower wing is really pretty much in the field of decent focus because its roughly at the same distance as the tail and face,, and that the wing was pivoting basically toward or away from the sensor rather than overall down or up.
So the distribution of the blur was the main thing suggesting to me a vertical bias for smudge.
I dont know if feather edges flutter at some high frequency, thats an interesting possibility.
I'm trying to rule issues out so as to do better. I google to try to find discussion on fine scale artifacts that show up on moving objects but couldn't find much.
They say you cant really freeze action completely with shutter speed and Im seeing some confirmation of that. But when you go to use a strobe, the distance makes the effect weak and the ambient light shows the ghost of motion superimposed on the flash image ( if you know what I mean)

It's a mix of cold hard facts and perception. The CHF is that if something is moving it will have some motion blur at even the highest shutter speeds. But, we can only see so much detail and if the detail looks sharp, we perceive a frozen subject. If you zoom in enough on any sharp detail, it will get soft, even for a motionless subject. What high shutter speed and/or flash do is capture such a small amount of movement, we perceive and think there is none.

Back to the duck, if this is level straight flight, then the near wing is extended toward the camera in the same position as the far wing. In that position the near wing extends farther into the near DOF than the far wings extends into the far DOF, and that is kind of what I see in the blur of the two wingtips. However, almost looks like the duck may be turning away from the camera, and if so, I'm not sure how that affects the wing positions, other than the near wing could be moving in a faster motion.

 

[Stoshowicz]

It's a mix of cold hard facts and perception. The CHF is that if something is moving it will have some motion blur at even the highest shutter speeds. But, we can only see so much detail and if the detail looks sharp, we perceive a frozen subject. If you zoom in enough on any sharp detail, it will get soft, even for a motionless subject. What high shutter speed and/or flash do is capture such a small amount of movement, we perceive and think there is none.

Back to the duck, if this is level straight flight, then the near wing is extended toward the camera in the same position as the far wing. In that position the near wing extends farther into the near DOF than the far wings extends into the far DOF, and that is kind of what I see in the blur of the two wingtips. However, almost looks like the duck may be turning away from the camera, and if so, I'm not sure how that affects the wing positions, other than the near wing could be moving in a faster motion.

Yep I agree, about all that and about the inevitability of SOME motion , and I could just attribute any blur to simply speed because I just dont know the wingtip velocity of a banking ring-necked duck.
Im just looking close at the clearly visible artifacts of the photos to determine cause.
I loaded up that copy of the anhinga to flickr ( you could google stoshowiczz -at flickr and youd see my more recent photostream if you were curious) , but its a downsized copy and you cant really see what I'm talking about well there either. Ill do like I did with the duck , crop in close on a sharper image and repost it up tomorrow which would probably be easiest, if your patience is so great as to continue till then.

 

[Eyelight]

Yep I agree, about all that and about the inevitability of SOME motion , and I could just attribute any blur to simply speed because I just dont know the wingtip velocity of a banking ring-necked duck.
Im just looking close at the clearly visible artifacts of the photos to determine cause.
I loaded up that copy of the anhinga to flickr ( you could google stoshowiczz -at flickr and youd see my more recent photostream if you were curious) , but its a downsized copy and you cant really see what I'm talking about well there either. Ill do like I did with the duck , crop in close on a sharper image and repost it up tomorrow which would probably be easiest, if your patience is so great as to continue till then.

I found the stream, but not that shot. But, I try never to be in a hurry and cropping from the original would give the best detail.

Bear in mind when imagining the DOF that it is an arbitrary system to yield distances related to our perceptions of what we see when looking at a certain size image from a certain distance. Just as motion blur is always there, but sometimes not perceived, blur starts at the focal plane and increases to the near and far. We don't call it blur until we perceive it. When viewing an image at 100% we are in effect, reducing the DOF by increasing the blur nearer the focus point. So, a wingtip that is nearer (or farther away) than the focus point is always going to be in less sharp focus.

 

[Stoshowicz]

I found the stream, but not that shot. But, I try never to be in a hurry and cropping from the original would give the best detail.

Bear in mind when imagining the DOF that it is an arbitrary system to yield distances related to our perceptions of what we see when looking at a certain size image from a certain distance. Just as motion blur is always there, but sometimes not perceived, blur starts at the focal plane and increases to the near and far. We don't call it blur until we perceive it. When viewing an image at 100% we are in effect, reducing the DOF by increasing the blur nearer the focus point. So, a wingtip that is nearer (or farther away) than the focus point is always going to be in less sharp focus.

Yep Im on the same page with that. So Im trying to pick images where the parts look like they pretty much are at the same distance from the sensor ,, so the bird is its own frame of reference.
( if you typed in only one letter Z it would show you an older thread from before they abandoned the old log in venue, I had to start the second after that because I couldnt actually merge the two together, Id have had to reload everything, and since , hopefully ,I'm getting better with time put in ,, I didnt want to mess with stuff I popped in there for various reasons like for reference in conversations or solely bird ID confirmation.)

 

[Eyelight]

I was looking at the one Z stream. In regards to ZZ

a picture speaketh a bunch of words.

 

[Stoshowicz]

I was looking at the one Z stream. In regards to ZZ

a picture speaketh a bunch of words.

View attachment 119590

Ummm I didnt say to go about it that way

View attachment 119599View attachment 119600

 

[Stoshowicz]

Ok heres the closer view of the color artifacts , as you can see , they dont go all the way around the perimeter. Id like to know why it is where it is, and is not ,,where its not.

View attachment 119716

 

[Horoscope Fish]

Ok heres the closer view of the color artifacts , as you can see , they dont go all the way around the perimeter. Id like to know why it is where it is, and is not ,,where its not.

Are you talking about the purple-ish halo around some of the edges? That's Chromatic Aberration. It occurs at intersections of high contrast and most often manifests in shades of purple or green. In this case it's purple. It's pretty easy to remove, typically, using your post processing software. Adobe Camera RAW has some sliders in the Lens Corrections module dedicated to removing CA.

....

 

[Eyelight]

What Mr. Fish said.

It's how the light makes it thru the lens and different colors that make up the same point on the subject not always getting focused on the same point in the image. Sometimes worse with digital sensors. Sometimes easy to fix and other times not.

I am guessing it is different on different edges because light reflects as different colors off of different angles of the same object and the wavelength of light is different with different colors.

There is a lot of reading out there on the causes and what can be done. Lenses are designed to reduce it and some more so than others.

 

[Eyelight]

Been studying on bird flight and freezing their variety of motions. Here is the blackbird with the PS grid turned on and set to the size of the D7100 sensor. The main grid lines represent millimeters and the lesser tenths of millimeters. So, this is the image of the bird sized to the sensor.

Shutter Travel: The bird size on sensor is roughly 5.72 mm. Shutter curtain with a travel time of 1/250 top to bottom will pass the bird in 1/681 second. Just considering roughly 1 inch of wingtip (about 1 mm on the sensor), the curtain will pass it in 1/3900 second and pass each tenth millimeter of image in 1/39,000 second.

In a shot like this the flight speed is offset by panning the camera and effectively reduced to where the body and head is perceptibly sharp. Wings are a different matter. Depending on the movement and angle of movement, the wingtips move across the sensor at a variety of speeds, but the fastest would seem to be the forward/upward movement across and parallel with the sensor plane.

Assuming a few numbers, such as 11.25" average b-bird wing length, WAG of 17.67" wingtip travel and 10 wing beats per second gives an average wingtip speed of 15.6 meters per second in real life. The bird is reduced in size by the lens and this reduces the speed relative to the shutter travel speed (noted above). The duration of the shutter speed then captures a fraction of the wingtip movement of roughly 0.10 mm. Hard to tell because the screen capture of the blackbird is not so high res, but it looks like the wingtip may have moved about that much.



Edited to add: The sizing of the grid is based on the image being a full uncropped image. If the image was cropped then the bird would be smaller on the sensor and movement in relation to the sensor and shutter would be less.