Saturday, September 30, 2017

Focus Bar Update

Just a quick post to say I've updated my focus bar script (FOCUS on the right).

This version provides additional near depth of field distance information when you are optimising infinity focus.

If the full info option is selected (default) then you see both near and far depth of field infinity focus sets of data, ie:
  • In the far field, ie at infinity, you get a breakdown of the defocus, diffraction and total blurs in microns;
  • In the near field you get the depth of field distances that correspond to three 'blur scenarios', eg: infinity defocus blur, twice the infinity defocus blur and the ML CoC set defocus blur.
The script as provided is good for a visible band, full frame 5D3. For a cropped Infra Red camera, for example, you will need to tweak the script.


Thursday, September 21, 2017

Unlocking the power of the Hyperfocal Distance

I assume everyone reading this post is aware of the hyperfocal distance (HFD) focusing concept?

Simply focus at the HFD and everything from half the HFD to infinity will be ‘in focus’ according to a specified criterion, or more correctly not so out of focus that you can see the defocus.

If we ignore diffraction, the HFD is simply a function of the focal length, the aperture number and a blur criterion, usually called the Circle of Confusion (CoC).

If you have read my previous posts, you will know that the HFD is only ‘just’ acceptable, ie at infinity the defocus blur is the CoC. You will also know that you can achieve a far superior result by simply focusing at, say, Y times the HFD, as calculated with your ‘just acceptable, CoC: which will reduce the blur at infinity by the CoC/Y. Thus at a focus of 2xHFD(CoC), the blur at infinity will be the CoC/2.

With a typical (just acceptable, and no diffraction accounted for), full frame CoC of 0.03mm, ie 30 microns, you can therefore get a far field focus, all the way to infinity, that is always better than, say, 15 microns throughout the focus field: dropping to 0 at the point of focus. But of course in doing this you have reduced the near field depth of field.

Of course if we focus at infinity we achieve a blur of zero at infinity, but at the cost of reducing the near depth of field, ie HFD to infinity. Also defocus blurs less than two sensor pixels are rather meaningless. Thus you are over focusing with a digital camera if you focus at infinity.

To achieve the ultimate, of (very) near to infinity focus, you need to use focus stacking. That is you focus overlap various images and post process them to achieve an image with as large a depth of field that you want.

As readers of my blog know, if you have a Canon DSLR or EOSM, you can use my Magic Lantern Lua scripts to automate the process: taking all the guess work out, and automatically accounting for diffraction.

But what if you don’t have Magic Lantern. How do you know where to focus and how many focus brackets to take?

This is where knowing the HFD for your focal length and aperture helps.

As most photographers seeking out large depths of field will be ‘landscapers’, they will know that you need to ‘balance’ the blurs caused by defocus (from the lens) and diffraction (from the aperture alone). Without proof, you want to be ‘in the middle’ with your aperture, ie not at F/2.8 or at F/16, if you wish to balance out the two blurs. Say, between F/8-F/11 on a full frame DSLR.

So we have now set one of the HFD variables: the aperture number, eg, say, F/8 (N). The focal length (FL), of course, will be fixed once you have composed: so that is known (and permanently fixed on a prime lens). This leaves the CoC, which we will leave at the accepted ‘just acceptable’ number of 0.03mm for 35mm full frame format.

Note for on screen/web presentation we could increase this and for high scrutiny print exhibition/judging we should consider reducing this ‘base’ CoC. For now, we will assume normal quality is an infinity blur or 30 microns and a high quality print blur at infinity will be between 10-15 microns.

Previous posts gave the HFD formula, which, in its (approximate) simplified form, is FL*FL/(N*CoC). Thus for a FL of 24mm, at F/10 and a CoC of 0.03, the HFD comes out at 1920mm (ie about 2m). Giving a depth of field of 1920/2 mm, ie 960mm through to infinity (at a defocus blur criterion of 0.03mm).

But what if you had a ‘point of interest’ at, say, 400mm, what focus bracketing strategy should you use? How many brackets should you take?

Once again, not wishing to frighten off readers off with lots of equations, the number of brackets can be estimated from dividing the closest point of interest (400mm above) into half the HFD (and round up to the next integer.

Thus, in the example above we simply do the following calculation: 1920/(2*400), or 2.4, which we round up to 3. That is we need to take three brackets to capture the full near field.

But this begs the question: where do I focus those brackets?

Once again, the HFD comes to the rescue.

Without proof, and assuming each focus bracket just touches its adjacent bracket, the nth bracket needs to be focused at HFD/(2n-1). For example in our above three bracket example we would focus at HFD, HFD/3, HFD/5. The near and far depths of field of each bracket being HFD/(2*n) and HFD/(2(n-1)).

For the ‘perfect’ bracketing set, I would also take a bracket at 2*HFD, which would result in the following (illustrative) focus strategy. Note in this example we have not addressed the bracket to bracket overlap. We will deal with that in a subsequent post.





Bottom line: for those that tend to do landscape photography and use a ‘sweet’ spot for focal length and aperture, it is relatively easy to remember the HFD (or HFDs). Once you know the HFD, all you need to do is multiple or divide this by integers, typically between 2 and 9.

In future posts I’ll deal with focus overlapping when focus bracketing.

Tuesday, September 5, 2017

Revisiting some basics

In previous posts I have discussed the ‘normal’ hyperfocal distance (HFD = H) and why it is not (sic) the optimum focus strategy for landscape and architectural photographers trying to get high quality depth of field images, from near to far.

Assuming a ‘simple lens’, and ignoring diffraction, the HFD may be estimated from the following:

Where f is the focal length, N the aperture number and B the defocus blur at infinity, eg what some call the Circle of Confusion, eg for a full frame camera this is often quoted as 0.03mm (30 microns).

If we assume that f term is (very) small relative to the other term and that the blur at infinity can be less than the minimum acceptable blur, then the above simplifies to:

Where Q is a focus quality term, relative to the normal, minimally acceptable blur. Q will typically be between unity and, say, 2ish. For example, if Q is 2, then the blur at infinity would be 15 microns, rather than the ‘normal’ 30 microns.

Understanding this very simple equation is the starting point for maximising the focus quality in your (landscape) images.

Before moving on, it is worth remembering that (defocus) blurs less that two sensor pixels are ‘meaningless’. Thus if we assume, for illustration, a sensor pixel size of, say, 7 microns, then the sensible defocus blur range is between 14 microns (2 x 7) and 30 microns: which leads to Q being between 1 and 2ish.

To emphasis this point, for on-screen work you will ‘get away’ with blurs of 30 microns, or more. For high quality printing, at close scrutiny, eg by judges or in a gallery, you should use defocus blurs of, say, half of this, say 15 microns on a full frame.

Remember that diffraction will always add additional blurring to your image, and that diffraction blurring varies linearly with aperture, ie shooting at F/16 will double the diffraction blur compared to an image captured at F/8.

For high quality work, it is not advisable to push the aperture too much: unless you have to. Most would suggest a ‘sweet spot’ for a full frame DSLR of between F/8-F/11.

The key take away from the above is that, for full depth of field photography, you should focus beyond the (minimally acceptable) HFD, but not more than twice that HFD.

But what if you want to really maximise your depth of field, ie from infinity to near. Well we know the ‘secret’ here is to focus bracket, ie recover the defocus in the near field.

If you are a Canon shooter you can make use of the various Magic Lantern tools at your disposal, including my auto landscape bracketing script and my focus bar script. But what if you don’t have Magic Lantern. Is there a simple focus bracketing approach?

The answer is yes.

Without proof, the optimum (high quality) two-bracket focus stacking approach is to take the first image at Q times the (normal) HFD and the second one at Q times the HFD divided by 3.

Thus if Q is unity and HFD is the ‘just acceptable’ HFD, ie a defocus blur of the minimum quality, that is often used, then focus your two focus brackets at the (usual) HFD and at HFD/3.

If you wish to capture a higher (optimally focused) quality bracket set, then focus at 2xHFD and 2xHFD/3.

The resulting blur (defocus) field for a high quality (single) capture (Q = 2) looks like this – compared to the defocus field for a (normal) HFD shot, say a B of 0.03mm:
 


Here we see the real advantage of focusing at 2xHFD, ie the far field, beyond H never gets ‘worse’ than a blur of B/2, ie you have doubled the far field focus quality.

Once again, without proof, taking HFD (or H) as that given by the minimal acceptable blur (say 0.03mm), we can take a high quality focus bracket set at 2xHFD and 2xHFD/3, that results in the near field depth of field being better than if we had focused a single image at the (normal) HFD.

What has been gained is quality of focus in the near field, to complement the far field, as illustrated below, ie for a Q of 2, the near DoF at a blur of B is 2*H/5, ie Q.H/(3+Q).

Finally, I appreciate that not everyone likes reading posts with equations or numbers: in fact some get ‘really turned off’. However, the fact is, to get the most out of your cameras you do need to understand some of the (basic) ‘science and maths’ that is going on behind the scenes.

Monday, August 28, 2017

Summer is designed for Infra Red photography

It's August Bank Holiday here in the UK and a chance to get out and explore the local area from my house, on foot, with my IR converted EOSM, with an 11-22mm lens. The explorations today included a local moated house.

The camera is also 'hacked' with two grips and an LCD viewer from http://www.clearviewer.com/index.html.


My post processing is mainly (totally for the images below) in LR.

After applying a linear 'gamma' and an IR DNG profile to recover the white balance to a more reasonable starting position in LR, I then make good use of dehaze and other LR sliders to get the look I'm after.





 As usual, I welcome any feedback on my post and images.

Saturday, August 12, 2017

Something different

Most of my posts are about achieving the best exposure or focus that you can: so I decided a while ago to 'try something different'.

Pinhole photography!

The other day my new lens arrived: a pinhole lens from thingyfy


Unlike other pinhole lens, or one you make yourself, the Thingyfy lens has variable apertures. From 0.1 to 0.8mm.

The lens has a focal length of 50mm, which can be changed by using extension tubes.

The ability to dial-an-aperture is the real selling point for me, as the Prober-Wellman equation in the visible bands shows the optimum pinhole size varies with focal length and M, the magnification, which is simply the focal length divided by the subject distance from the aperture:
Others have plotted the above for various focal lengths and magnifications:
For landscape work, where M approaches 0, for a 50mm focal length the optimum pinhole diameter is about 0.25mm.

So what does an image look like with my new lens?

Here are a few test images taken this afternoon. Both typical scenes around us at the moment: crops and cricket (note I shot when the bowler was running).

Both images benefited from being ETTRed via Magic Lantern, of course; and were post processed in Lightroom and Photoshop. At ISO100 the ETTR exposure was 5s on one and 3.2s on the other.

One of the downsides of pinhole photography is that you are shooting at very high f/stops, ie in the above images at F/200. At such F/stops you will see every dust particle and therefore you will need to carry out a bit of post processing. I'll be writing about post processing in another post.

Obviously pinhole photography is a statement: it creates ethereal images that are the antitheses of every thing I tried to do in photography, up until now. I'm looking forward to exploring the new lens, including IR pinhole photography.

 
 

Sunday, August 6, 2017

Macro is difficult enough, with out this...

As we know, macro photography is difficult, ie even with closed down apertures we still have very narrow depths of field.

On top of that, macro photography can take the environment out of the image: leading to rather subject-fixated images.

A while ago I bought a rather unusual lens: the Laowa 15mm f/4 Wide Angle Macro:

Billed as the world’s widest 1:1 Macro Lens, it features an ultra-wide 110 degrees angle of view of with 1:1 maximum magnification. Thus achieving focus very close to the subject but at the same time, able to include background details, ie to show where and how the subject lives. Rather unusually, it also has with a +/- 4mm shift feature.

I also have the Macro Twin Flash KX-800 from the same company: https://www.venuslens.net/
To complement the set up, as I like getting low, I also have a PlatyPod Max and the ReallyRight Stuff  BC-18 Micro Ball:



Finally, I need to add in my Varavon Multifinder, which allows me to access LV from above the camera:
Pulling all this together you end up with a 5D3 that now looks like this on my kitchen work surface:

As for what all the above can do: all I can offer at the moment is a test image from the garden and a row of mushrooms:
This image was taken at not a very large magnification, with the manual aperture of the lens closed down to F/32 and a downward shift of a few millimeters. 

Clearly this is not an award-winning image: just a test capture; and I have much more practicing to do with this rather unique set up. Look out for more reporting :-)


Auto Landscape Bracketing Script Update

Just a quick post to say I've updated my Auto Landscape Bracketing Script: V5 on the right.

This update fixes a problem in ML's depth of field calculation.

...and what about diffraction?

In this post I'll carry on talking about focusing with the focus bar script and introduce the diffraction blur.

Without any equations, the diffraction may be considered a fixed blur that degrades focus across the image and into the scene. The only camera variable that impacts diffraction is the aperture. The smaller the aperture, the more diffraction blur will occur.

Graphically it looks like this:
We now see two blurs that are degrading the image and reducing the depth of field: the defocus blur (still showing the defocus only depth of field), which varies with focus, aperture, focal length and the CoC; and the diffraction blur, which only varies with aperture.

As mentioned in previous posts, these two blurs are added in quadrature, that is the root mean square or: Total_Blur = SQRT(Defocus_Blur^2 + Diffraction_Blur^2).

Illustratively the total blur curve looks like this, showing that even at the point of focus there is a degradation in focus because of diffraction:
Finally, the impact on the depth of field looks like this:
In other words the depth of field has 'shrunk' and the blur at the point of focus will not be less than the diffraction blur.

Bottom line: The last two posts have discussed the two contributions to depth of field and achieving tact sharp images. The focus bar manages both diffraction and defocus, and allows you to find the optimum focus.
 

Saturday, August 5, 2017

Understanding focus blurs

As readers will know from a previous post, I'm aware that some find my focus bar too complex and too confusing. Hopefully this post will help those struggling to understand the focus bar.

First, let's talk about focus and depth of field. 

The depth of field is simply the zone where our brain and eyes see things 'equally' sharp, ie in focus. Outside this zone the focus falls away. The following illustrates a simplified sensor-lens arrangement:
In the real world, what is called object space, we recognise three distances. The point of focus (d2), the near depth of field distance (d1) and the far depth of field distance (d3).

On the sensor, in the image space, there is a so-called circle of confusion, ie a blur, that if we are inside this circle, then we perceive things as 'in-focus'.

For a full frame DSLR you will typically see this CoC stated as 29 or 30 microns, or 0.03mm. For a crop sensor camera, this CoC is reduced by the crop.

We won't complicate things here, but we will note that a CoC of, say, 30 microns, is only just acceptable, ie good for digital projection, but not necessarily for high quality (close scrutiny) print viewing, where a CoC of, say, 15 microns would be considered a better criterion.

So far we haven't mentioned diffraction, which is an additional blur that 'adds' to the defocus blur from the lens. Without proof, it is normal practice to 'add' the defocus and diffraction blurs in quadrature, ie Total_Blur = SQRT(Defocus_Blur^2 + Diffraction_Blur^2).

Handling defocus and diffraction blur are the two 'secrets' to getting a tact sharp image.

Sticking with just defocus blur for now, it is important to understand how the lens defocus blur varies through the image. This next cartoon is illustrative:

 
Here we see the classical defocus curve. At the point of focus the blur is zero. As we move away from the point of focus the blur increases, but the near and far curves are not the same. That is the defocus towards the camera is different than towards infinity.

Let's now add in the CoC (or blur) criterion that we mentioned above, which then allows us to see the 'in-focus' zone:
Without any equations, we can see how the focus zone appears to us. The curves illustrate that focus is not a 'black and white' affair, and thus the CoC blur criterion part of a continuum of defocus from the point of focus.

Let's now start using this knowledge of defocus: in this post let's continue to ignore diffraction. 

Let's focus at the hyperfocal distance, which is simply where the infinity depth of field's blur is at the CoC blur criterion:
We now see that the depth of field goes from a near field distance, that is HFD/2, to infinity. But we also see one of the limitations of HFD focusing. That is, for a large part of the image, all the way to and at infinity, the blur is close to the barely acceptable CoC blur criterion.

Of course if we were to focus at infinity, then at infinity the blur would be zero. But as we know, if we do this we loose a lot of depth of field in the near field. Clearly there must be a better place to be, ie between the HFD and inifinity. 

This is where the focus bar helps you decide where that optimum focus is. This next cartoon illustrate that optimum focus point:
But how far should I focus away from the HFD and towards infinity?

Fortunately we have a very easy way to know when to stop focusing. Without proof, we stop focusing when the defocus blur becomes less than twice the sensor's pixel pitch. Thus on my 5D3, with its 6.3 micron sensor pitch, I will not seek out defocus blurs less than, say, 13 microns. This last cartoon shows the sensor limit, which the focus bar alerts you to. Thus, if you use the focus bar, you will always be able to set the optimum focus, ie an infinity blur between the HFD (CoC criterion) and the sensor limit.
The focus bar tells you what the infinity defocus blur is and provides you information on the  defocus blur, the diffraction blur and the total blur of the defocus and diffraction blurs combined in quadrature. 

In future posts I will talk about diffraction blur in more detail. For now, I hope this post has helped those struggling with the focus bar, and the concept of infinity blurs, understand the difference between the CoC blur criterion and the defocus blur that varies as you adjust focus.

Friday, August 4, 2017

EOSM Infrared Conversion Test

Finally the UK's weather changed today and I managed to get a test image with my 'new' Infrared converted EOSM. 

The conversion was done by Alan Burch at http://www.infraredcameraconversions.co.uk. The service was great: personal, fast and reasonably priced. Based on my experience with Alan I can recommend him.

The test image is of one of our local churches. Here is the OOC image - the wind was blowing, so there is movement in some of the trees:


The image was captured at 11mm and an aperture of F/6.3. I used Magic Lantern to set the ETTR shutter at 1/100s. 

I choice the rather open aperture, as IR diffraction is more than in the visible region, by a factor of around 850/550, say about 50% more. I will be looking to see how far I can close down the aperture, to gain greater depth of field and get closer to the lens MTF sweet spot.

As for focus, I used my focus bar script and optimised the infinity focus, ie between the HFD and infinity.

I had already used the Adobe IR Profiler to create a custom profile for Lightroom. One that recovered the highlights via a linear gamma and reduced the red cast. This profile is my starting position for post processing.

I then used Lightroom and luminosity masks in Photoshop to get a reasonable look to the image: which is still a little 'muddy' for my taste, ie more post processing practicing required

This is the resultant image. From a camera that will now become part of my 'travel light' bag: together with its brother, the non-IR converted EOSM.

 

Monday, July 31, 2017

For goodness sake Garry: KISS



As we know, KISS means Keep It Simple Stupid. Well, from feedback, it is clear my focus bar fails the KISS test :-(

As I’m introducing a ‘new’ way of (landscape) focusing Canon cameras with the focus bar, ie optimising focus between the hyperfocal distance and infinity, I clearly need to do a better job of explaining what is going on: that is in KISS language.

Having said that, if you are using a DSLR, then you are using a complex piece of hardware and software, ie you are not a point & shoot person. In addition, if you are using Magic Lantern you most probably are aware of depth of field and want to get more out of your camera.

As we know the defocus, that occurs as you move away from the point of focus, is a function of the focus distance, the focal length, the aperture and a blur criterion, usually called the circle of confusion (CoC).

Simply put, the circle of confusion is the defocus blur that ‘just’ looks sharp on the sensor, ie a larger blur would look out of focus.

Thus to get the best out of the focus bar it is essential to understand the basics of depth of field and the concept of blurs.

For a full frame DSLR producing images for digital display, ie on the web, a CoC or blur of 29 or 30 microns is considered (just about) OK. For more exacting work, ie a judged print, a CoC of about 15 microns might be a better choice. This is a simplification and in reality you should choose the blur to fit the viewing conditions, the size of the print and the distance that the viewer is away from the print. But let’s keep it simple for now.

For the full frame landscape photographer, simply set the Magic Lantern CoC to 29 or 30 microns. For a crop shooter reduce this by the crop factor. That’s it: don’t touch this again :-)

So let’s look at an example: a FF camera and a 16mm lens, at F/8 and focused short of the HFD, the defocus field (without diffraction) looks like this:


The left hand axis shows the blur, with a unity blur being the set CoC criterion, ie 30 microns. The plot clearly shows a zero blur at the point of focus and the focus field defocusing either side. By definition the depth of field is between the curve where it crosses the unity blur line. In this zone, our eyes think everything is tact sharp (relative to our criterion of 30 microns). Out side this zone the image gets progressively out of focus. Note that the near and far fields behave radically differently, ie the focus field is not symmetrical about the point of focus.

Let’s now move the focus to the hyperfocal distance. Now we see the classical HFD focus field, ie the near field depth of field (unity blur) is just short of the focus point, i.e. at HFD/2, and the far field (unity blur) is at infinity (although it is not shown here you can see the far field curve approaching unity blur, i.e. 30 microns in this illustration, where it will at infinity):


Finally, let’s now focus beyond the HFD and short of infinity, ie use the focus bar. This is where the focus bar ‘magic’ starts. As you can see the far field curve now asymptotes to a blur that is half of that at the HFD. Remember, in all the charts the unity (CoC) blur remains constant at 30 microns.


Finally, to emphasise what has happened, let’s show the depth of field curves for the HFD case and for the focus bar, together:


Here we see the advantage of using the focus bar to tell us when to stop focusing short of infinity. In other words, by focusing slightly beyond the HFD, ie at about 2m in this illustrative case, we have created an infinity defocus blur, ie no diffraction effect yet, of half of the ML set 30 microns; ie half of the HFD blur. 

Put another way, we have focused for a high quality print, with a near depth of field of about 1 meter at a blur of 0.5 of the CoC, ie about 15 microns, or a slightly larger depth of field if you accept the 30 microns blur for the near field.

Finally, for defocus blur you really can’t do much better than two sensor pixels; and on a 5D3, for example, that means a defocus blur at infinity of about 13 microns. Therefore the full frame guidance is to aim for a reported (defocus) focus bar blur at infinity of, say, 29 or 30 microns, for digital projection; and about 15 for high quality print work.

Note, the ML set CoC stays at 30 throughout. All we need to do is act on the reported focus bar blurs.

I truly hope this post has helped those that are struggling with using the focus bar; as I believe for landscape photography, the focus bar is about the best you will get from a focusing perspective.

Saturday, July 29, 2017

Travelling light: at all frequencies

Although I have an infrared converted camera (a 50D), it is rather large. Therefore, if I wish to travel light, the 50D and my 5D3 just don't fit...literally!

For visible band photography, my go to travel camera, because it runs Magic Lantern and my focus bar script, is my EOSM. I did have a Sony 6000 as my travel camera, but I missed Magic Lantern so much, that I sold that, and now all I buy are 2nd hand EOSMs. Yes I have two.

So last week I decided to get one of them converted to IR. I decided to keep with the 720nm cut, that I have in my 50D, as I believe it to be a good middle ground between a 'full spectrum' conversion and a deep IR one.

Here is a chart to illustrate how a digital sensor responds to light:


 
The black curve shows the typical response of a CMOS sensor, showing that the sensor can capture more data that we can see, which is reflected in the 'hot mirror' curve.

Of course in IR photography we are not looking at thermally-emitted IR, ie from hot objects, but reflected solar IR:

The IR conversion removes the hot mirror and, in my case, replaces it with a 720nm filter, giving the following sensor characteristics: 


As I wait for my EOSM conversion to arrive, I thought I would revisit an IR capture that I made with my trusty 50D. The image is of the Seven Bridge and as a RAW capture, ETTRed with the help of Magic Lantern, it doesn't look that impressive:


The LR histogram clearly shows that this was an ETTRed image:


Here we see one of the first 'problems' with IR photography. Bluntly, just looking at the image, you would initially be tempted to mark this as a 'reject'. In other words, never discard an IR image by just evaluating the RAW: always post process first!
As usual with digital photography, there are many ways to post process an IR image. The only thing you can say with confidence is, that there is no right or wrong way.

The general workflow I follow goes like this:
  • First I use a custom profile in LR that I have made. This processes the image with a linear gamma curve, and pulls out more highlights, which goes with ETTRing. This profile also reduces the red cast, because LR on its own can't handle IR images;
  • I then get the basics of the image looking right in LR;
  • I then do a round trip to Photoshop to tiding things up, ie clone stamp etc and use luminosity masks to give the image the look I'm after;
  • Finally, in LR I will carry out any last minute tweaks.
Following the above, the Seven Bridge image is transformed into the following:


Look out for more IR postings once I get my EOSM back from its conversion.

Thursday, July 20, 2017

Your Choice

A short post to say I've expanded the choices in the focus bar to allow you to decide what criterion you wish to use to calculate the near depth of field when in infinity blur mode.

This is useful when refining the focus beyond the hyperfocal distance, ie focusing between the HFD and when the focus distance reaches infinity. 

In this focusing zone the far DoF is meaningless, as the far DoF distance is infinity. But the infinity defocus blur in this zone still has meaning, as represented by the blur gauge on the right hand side of the focus bar.

The four sensible choices that are available to calculate the near DoF are:
  • The defocus blur alone, ie the green/red vertical bar
  • Twice the defocus blur alone
  • The defocus and diffraction blur taken in quadrature, ie the total blur
  • Twice the defocus and diffraction blur taken in quadrature
The default may be set by changing the menu item at the end of the script.

Finally, the bottom DoF info shows the defocus blur at the near and far DoFs, and updates to show the infinity defocus component if in the infinity focus mode. 

Tuesday, July 18, 2017

Warping can be fun



Modern lenses are incredible feats of engineering. Likewise, modern software is also incredible. Bring the two together with Magic Lantern and, well…you can get incredible images.

To illustrate what can be achieved, consider a standard EOSM 11-22mm lens, at 11mm. The minimum focus distance is 15cm, giving a near depth of field at 19 microns total blur (defocus and diffraction), at F/10 of about 13cm. But what if I wanted to focus closer, say right in front of the front of the lens, and (sic) get the background in focus.

I could use a tilt shift. But let’s say I don’t have one…I do really ;-)

One way is to combine focus stacking with a vertical pano; and because we can , throw in the need to cover a wider dynamic range than a single image can capture: so we’re use Magic Lantern Dual ISO as well!

Let's look at a single Dual-ISO image test (indoor) capture [ignore the artistry ;-)]

 
As we can see, the near field doesn't capture the full scene and is out of focus.

So lets take the first focus bracket set by pointing the lens down to capture all the scene from near to far, ie with five dual-ISO focus brackets.

 
Now repeat for the ‘normal’ image, once again capturing five dual-ISO focus brackets.


Ingest all ten images into Lightroom. Process the Dual-ISOs and export each five set bracket to Helicon Focus. Giving us two images ready for pano processing:


Do a round trip to AutoPano Giga to process the two perspectives, giving the following image, which is tack sharp from zero to infinity:


Bottom line: Extreme photography requires extreme processing. Yes, I could have captured a similar, in focus, image using my tilt-shift lens. But clearly there are alternatives and post processing can be fun ;-)