Monday, September 20, 2021

Landscape Bracketing Script (M3): now with a simulated ND filter option

Just a quick post to say I've brought the M3 version of my CHDK Landscape Bracketing Script, into line with the non-M3 version.

The M3 version, downloaded from the right as usual, now has a menu item called "ND Filter?", with values of 0 to 5.

If 0 is selected then no ND brackets will be taken. If the value of this menu item is between 1 and 5, then a simulated ND bracket set will be taken, as part of the focus and exposure bracket set.

An ND2, will take 2 images that you can post process, whereas an ND5 will take 32 images. Each ND bracket set can be processed in Photoshop, for example, to create a Long Exposure image for blending with the others in the bracket set, eg the focus images and the sky ETTR capture.

The ND images are taken at the foreground exposure value, ie the one used for focus bracketing.

As with the sky exposure bracket, the ND filter bracket set is taken at the infinity focus point that you set, eg three times the hyperfocal, say.

Once captured, the bracket set is easily identifiable in Lightroom, as the script makes use of dark frame bookends at appropriate places, eg:

In the above we see that the entire bracket set has bookends at the start and end of the bracket set, and the ND set is also delineated, eg the 4 images towards the end, in the above example. Also seen are (4) focus brackets, at the start: two before the hyperfocal, one at the hyperfocal and one at, in this case, 3 times the hyperfocal, for a defocus infinity blur of about a third of the overlap CoC, which was set at 15 microns in this test capture.

The script automatically took the focus brackets, as, in this case, I had selected the X2Inf option. Thus all I needed to do was to focus on the foreground point of interest, note the number of focus brackets and accept or adjust the aperture, focus or focal length.

Then, with a single button press, the M3 captured a perfect focus bracket set, plus capturing a simulated ND bracket set for 'statistical processing in Photoshop, and an ETTR sky image at infinity. 

Once the focus and ND bracket sets are pre-processed, these two images can be blended with the sky ETTR image, eg using masks.

As usual I welcome any comments on this post or any of my posts.

Wednesday, September 1, 2021

If it's good enough for a Large Format camera; then it's good enough for my Canon M3

Once you get into photography you begin to look at the various categories of equipment. From large format film cameras down to point and shoot digital technology.

From my perspective, with a bias towards the science and technology of photography, I'm always interested to look backwards for 'new' ideas, ie ideas that we can exploit today.

This post is about one of those necessities from the large format, view camera world, that is virtually ignored today. Namely a dark cloth, which is also called a focusing cloth or hood, The dark cloth being a piece of light-proof material that covers your head and the back of the camera. It eliminates stray light to allow for proper viewing of the relatively dim image on the camera ground glass during framing and focusing.

Although today's digital cameras don't require us to inspect focus on a piece of ground glass, we often find ourselves looking at the LCD screen , eg to read camera info, carry out focus peeking or, in my case, drive Magic Lantern or CHDK.

But try and look at a camera's LCD screen in bright sunlight, or if your eyes are 'getting older', as mine are.

I've tried various 'solutions', but I found all of them lacking at some level. Plus things can get complicated if your camera has an articulating screen, rather, say, than the fixed screen on my 5D3.

Also, as a photographer who likes getting low, I envy the cameras of old, where you can look down into the camera:

As my 5D3 has a solution in the form of the Swivi S5 (see below), I decided to 'hack' my M3.

As I didn't wish to buy more 'stuff' I decided to use what I had and not to compromise my base Canon M3 configuration, which looks like this:

That is any solution needed to fit around a cage and a handle, and enhance my low level photography needs, when I have the screen deployed like this:

The base set up ended up looking like this, where I adapted a collapsible Hoodman Loupe, with a diopter adjustment, via a cold shoe mounted, miniture ballhead:

But this base arrangement still suffers from light hitting the screen.

The final configuration benefited from me having a wife who is an expert sewist. She quickly knocked up the following Mark 1 version of my idea, which will likely end up the final version for me. Thank you Jean :-x

Here we see my 'dark cloth' for a DSLR :-)

So far it's a 100% success: allowing me to use the camera in bright sunshine, low on the ground, whilst focus peeking and controlling CHDK scripts.

As usual I welcome any feedback on this post or any of my posts.

Monday, August 30, 2021

M3 Landscape Bracketing Script: minimum focus to focus position mode

Just a short post to say I've updated my M3 bracketing script to include a new auto focus mode, to cover when you wish to focus bracket from the minimum focus distance of the lens, to a fixed point. For example, when you don't want a sharp image throughout the scene.

To enable the new feature simply select it in the menu. But remember the caveat with this script, it’s not designed for macro focus bracketing at high magnification.

Once selected, to use this new mode simply:

  • Set the lens to the minimum focus and focus the camera on the nearest part of the object of interest, ie by moving the camera - the front of the tea bag in the example below;
  • Then move focus, with the lens, to the far part of the object of interest, ie the top of the tea bag in this example;
  • Then run the script.

To get an estimate of the number of focus brackets, simply take note of the difference between the number of brackets reported at each focus station, ie the minimum and the farthest focus point of interest.

Finally, you can also use sky bracketing with the new Min2X feature.

In this example, shot at F/4 at an 11mm focal length, the script took 6 images, which I processed in Helicon Focus:

As usual I welcome any feedback on this post or any of my posts.

Addendum to "Continuing insights into Macro Photography: Part 2"

In part 2 I showed how we can work out the 'best' aperture for macro photography based on the following variables:

  • The optical magnification (m)
  • The pupil magnification (p)
  • The acceptable total circle of confusion (c)
  • A factor, k, to account for the post production impact of the diffraction, ie 0 means ignore diffraction, 0.5 assume a 'weakish' impact and 1 assume the 'full' Airy impact.

I also showed how you can find the pupil magnification through the PhotonsToPhotos optical bench hub. Of course if your lens is not in the list of lenses, you will need to measure or guess the pupil magnification yourself.

As many macro photographers will be using a lens set to a specific optical magnification, there is no need to worry knowing the focus distance, as we do in non-macro photography. We thus 'only' need to solve the following to arrive at an estimate of the total depth of field (d) in mm; where m, p, c and k are the four variables that you need to know to match your camera/lens settings and presentation needs:

Note that c in the above is in mm, with the other input terms being dimensionless.

As some will look at the above and be intimidated by the maths, here is a link to a WolframAlpha page (no need to supply any personal details) that allows you to input your m, p, k and c values on the input line at the top of the WolframAlpha screen; with WolframAlpha doing the maths for you to solve for d and, on the way, highlight the optimum aperture (N). Note that you need to select approximate in the Solution box to get a decimal output, also use a small k value to switch off diffraction, say 0.1, else you will get a ‘no solution’ result.

As an example, lets take a Canon 100mm macro lens and use the PhotonsToPhotos Hub to find the pupil magnification at an optical magnification of 1. Note the aperture of F/10 is arbitrary, ie the pupil magnification does not change with aperture:

Here we see that at a magnification of 1, the lens has a pupil magnification of 0.28. Let's assume a circle of confusion of 0.03mm, ie 30 microns, and that we can use our software tools to recover some of the diffraction softening, thus we will use a 'weak diffraction model' and a k value of 0.5.

Plugging the above into the WolframAlpha link gives the following:

Here we see that, if shooting with the Canon 100mm macro at unity magnification, we will maximise the diffraction aware depth of field by shooting at F/6.5, which will result in a total depth of field of about 1.3mm, ie about 0.65mm either side of the plane of focus.

The above is all useful information if we are focus stacking with a rail (more on this in a future post). 

If handholding, single shooting or attempting to focus bracket by moving the camera's position relative to the subject, this depth of field is very challenging, unless you are Thomas Shahan, say :-)

However, we have a few things that can help those of us that need it. 

First, modern sensors tend to have a good resolution, thus, although a magnification of 1 is great, we could get away with a magnification of, say, 0.5, ie about half the linear resolution on the object, relative to unity magnification.

Second, we have software that purports to 'recover' the image quality by 'AI algorithms', for example the new Adobe Enhance feature.

Based on this, let's now look at backing the optical magnification off to, say, 0.5; which results in the following lens characteristics:

Here we see that the pupil magnification has now changed to 0.58, resulting in the following DoF estimate:

That is our diffraction aware depth of field is now estimated to be about 5.3mm, shooting at F/16. Although the object will take up about a quarter of the sensor area of the previous set up, with a modern sensor this should be OK: as long as we are not seeking to create too large a print and the exposure is still ok. 

I hope this addendum has helped some, and, as usual, I welcome any feedback on this post or any of my posts.


Sunday, August 29, 2021

Continuing insights into Macro Photography: Part 3

In the last couple of posts I've addressed some of the theory behind macro photography; in particular the depth of field and impact of diffraction when undertaking macro photography. 

We have seen that, although we can ignore lens asymmetry, pupil magnification, for non-macro photography, we can't when shooting at magnifications greater than, say, 0.5.

We therefore know that with depths of field measured in a couple millimeters, at best, and likely sub millimeters, attempting to handhold during macro photography is a skill that needs to be practiced. 

So far it is a skill I have yet to perfect. For example, I went out yesterday with my Canon 100mm macro, attached to my 5D3, and tried to grab a few handheld shots. 

I had previously tried without a flash, but on this occasion I used a flash with a diffuser, to soften the light and reduce harsh shadows.

From these early experiments, flash and a diffuser is clearly the way to go.

Although I will carry on trying to perfect my handheld skills, my instinct is to move on to the next macro technique that should give better results than handholding: namely focus stacking.

So, to bring this post to an end, I'll simply post a few images from yesterday's shoot.

As usual I welcome any comments on this post or any of my posts.

Wednesday, August 25, 2021

Continuing insights into Macro Photography: Part 2

In the last two posts I have looked a macro depth of field using a simple lens model, but one that accounts for pupil magnification, and noting that magnification is estimated from the front principal of the lens (or perfectly by taking an image and calculating the 'exact' magnification.

The source of the DoF model is Jeff Conrad's excellent 'Depth of Field in Depth', first published nearly 20 years ago, but still one of the best insights into depth of field, albeit originally mainly written for a large format audience.

Conrad gives us the following expression for the 'macro' depth of field, based on magnification:

The above being the same as I present two posts ago, albeit in a different form.

The above may also be written as follows:

Where B is the so-called bellows factor, ie (1+m/p).

As before, if we wish to make the defocus circle of confusion (c) diffraction aware, we can use the Airy model and add this in quadrature to the defocus blur. 

However, as has been pointed out on one of the DRPreview forums (thank you Alan) using the 'full' Airy disk and using an RMS approach to couple the defocus and the diffraction blurs, will likely result in a worse case view of the depth of field.

Alternative approaches to using the 'full' Airy model are discussed here, but the bottom line is that, if we accept that using the Airy disk is a worse case model for accounting for diffraction, a more 'forgiving' approach, albeit still, for simplicity, using quadrature to ‘add’ the two blurs, would be to reduce the Airy disk by up to, say, a factor of 2. 

We thus have a diffraction range that we could use, influenced by our experience and faith in some of the latest software, that claims to reduce the impact of diffraction softening.

In an attempt to get a working model up and running, in this post I will use the fallowing to model the diffraction blur: 4kNB/3000.

Where k can be used to 'dial back' the influence of the Airy disk, ie k being between, say, 1 and 0.5; and B is the standard bellows factor. Note the above is the diffraction blur in mm, using an infinity aperture, ie the value quoted by the camera, at least for a Canon camera, ie not the effective aperture.

The resultant expression for the diffraction aware depth of field now looks like this, where c is in mm:

To find the 'best' aperture, all we need to do is differentiate the above with respect to N, set this to 0 and solve for N. Resulting in the following simple expression for the 'best' aperture that maximises the depth of field:

Which pragmatically we can 'round' to the following 'Rule of Thumb' expression for the ‘optimum’ aperture number:

Where c is in microns.

For example, if we assume a symmetric lens at a magnification of 1, the bellows factor, B, is simply (1+1/1) = 2. If we also assume the 'worse case' diffraction model, ie the 'full' Airy disk, then k = 1. Thus the 'best' aperture, for a c of 30 microns, ie a typical, reasonable quality, full frame circle of confusion, is indicated at 30/(2*2) = F/7.5, say, F/8.

On the other hand, if, from experience, we believe that using the full Airy diffraction is 'too aggressive' a model, and post processing software will help reduce the diffraction softening, we could dial that back by using a k of, say, 0.5. Indicating an aperture of 30/2*0.5) = F/15, say. F/16.

Finally, if we are so inclined, we could model the pupil magnification impact by making use of PhotonsToPhotos Optical Bench Hub (Thank you Bill) to gain insight into our lens.

For example, let's take a Canon 100mm macro lens at a magnification of 1. The optical bench tells us the pupil magnification, at a magnification of 1, is about 0.28, eg:

From the above we can now estimate the 'best' aperture based on our experience and software, eg using a k value of 0.5 in this case: 30/(2*(1+1/0.28)*0.5) = 6.5, around F/6.3.

So what's the bottom line here?

I think it is that macro photographers should use the above as a background read. The bottom line is: get out there, capture some images, process some photos and get to know where you are comfortable shooting your macros. Experience should be your best friend.

However, if you are interested in a few numbers, I hope this post has helped you get your head around macro depth of field.

As usual I welcome any feedback on this post or any of my posts.

Sunday, August 22, 2021

Continung insights into Macro Photogtaphy: Part 1

In the last post I took a quick (re)look at the depth of field issues we face with macro photography. In doing so I took a first step at accounting for diffraction in the circle of confusion, but, as I flagged up, this ignored the impact of magnification on the diffraction blur, ie I assumed a fixed (infinity) diffraction.

The expression for the infinity-based, diffraction aware CoC, used in the previous post, was:

Where N is the aperture, as stated on the lens, ie at infinity. 
BTW the 4N/3 estimate of infinity diffraction is one of several models that could be used.
For macro work, we need to use the effective aperture in the above, ie multiple N by the so-called bellows factor (1+m/p):
If we ignore the magnification and assume a symmetric lens, ie a pupil magnification of 1, the above collapses to the first expression. However, the above is a better model to use for macro photography, especially high magnification macro.

The depth of field expression, accounting for magnification, pupil magnification and diffraction, now looks like this:

One interesting feature of the above DoF expression  is that it says nothing about the focal length of the lens or the crop factor. All such 'complications' are compressed into simply thinking about the acceptable total blur, ie c above.
So what does the depth of field look like as we vary the aperture? 

To keep things from getting too complex, let's first assume a symmetric lens (p=1) at unity magnitude (m = 1). Let's use a total CoC of 0.03mm, eg we are on a full frame sensor and not seeking to create a large print. The depth of field (mm), now looks like this:

Here we see the horrible truth about macro photography. The 'full', diffraction aware, depth of field is really small and we should adjust the Rule of Thumb we used in the last post, which ignored the magnification impact on the diffraction blur.

A more enlightened Rule of Thumb, to find the optimum aperture for the macro, diffraction aware depth of field, appears to be more like: divide the total blur you can accept, in microns, at least by, say, 4. But note in reality you also need to account for the pupil magnification when calculating the diffraction and, critically, the above is only 'true' at a magnification of 1. At higher magnifications things just get worse, for example:

In the above DoF contour plot, where we are varying m and N for a symmetric lens (p=1), we see how the depth of field, the vertical axis (mm), falls off, as does the optimum aperture, as we increase magnification:

The bottom line now appears to be:

  • If you are using a 'normal range' macro magnification, ie around m=1, then a reasonable Rule of Thumb for the 'optimum' aperture is about a quarter of the total CoC you are using;
  • If you are using higher magnification, ie greater than 1, then your optimum aperture needs to less than that for a unity magnification.
As usual I welcome any comments on this post or any of my posts.