Thursday, July 03, 2014

Shutter actuation count

Although the modern DSLR contains a mass of electronics (and more computing power than the average university had when I was an undergraduate!), it is still in many respects a mechanical device. The mechanisms that flip the mirror out of the way and move curtains across the sensor to make an exposure are very similar to those from film SLRs going back to the 1960s. Inevitably, these mechanical devices eventually wear out and fail. The shutter mechanism in particular is quite complex and delicate and must operate at high speeds to make fast exposures. Camera manufacturers test the reliability of their shutter units and rate then for some expected number of actuations before failure. Canon does not publicise this information and it is not quoted in the specifications of cameras on their web-site but, since about 2009, photo-journalists have been ale to get hold of the figures - presumably direct from Canon. For example, the table about 2/3 way down this 2012 review of the Canon 1DX. To summarise this table, consumer models like the 400D are rated at 50,000; models aimed at enthusiasts like the 60D and 70D are rated 100,000 and professional models are rated several times higher, with the 1D X having the highest rating of 400,000.

Your camera keeps count automatically and internally of the number of times you click the shutter. Some manufacturers (e.g. Nikon) include this shutter actuation count in the EXIF information embedded in each photo, but this is not the case with Canon. In fact it is not easy to discover the actuation count for Canon DSLRs! If you Google "Shutter actuation count" you will find plenty of web-sites that claim to be able to give you this information.

Most are based on reading the EXIF data from a photo taken using the camera. Typically they invite you to take a picture (a small, low quality JPEG will do fine) and upload it. A number of these specifically list a whole load of Canon DSLRs amongst those covered (e.g. this one -which lists "Canon EOS 60D"). If you try it, you will find that they tell you that the info is not available. So why include these Canon models amongst those they claim to support?

Another tranche of sites will tell you about a Windows utility called EosInfo. The idea is that you download and install this program (there is a download link about half way down the page), connect your camera to the computer via the USB lead, turn it on and then run EOSInfo. It should connect to the camera via USB and report the info you want. It claims to work on "Canon DIGIC III/IV DSLRs *except* the 1D* series". However, it has not been updated since 2009 and camera models and firmware move on. With my Canon EOS 60D (firmware version 1.1.1), although it is based on DIGIC IV, on connecting the camera and running EOSInfo, the program falls over with a exception error during the connection attempt.

I have found two methods that DO work on my camera:
  1. Astro Photography Tool (APT). From the download page, download the demo version and install it. Connect your camera to the computer via the USB lead, turn it on and then run APT. It shows a black screen with dim-red text (presumably designed to protect the astronomer's night-sight). The shutter actuation count is shown in the bottom-left corner of the screen.
  2. Magic Lantern. This is a firmware add-on for certain Canon DSLRs. If your camera is supported download it and follow the instructions to install it on your camera. Once installed, it has a Debug menu which shows the shutter actuation count - amongst other data. (I have been experimenting with Magic Lantern for many other reasons and will post about it in due course).
Should I be concerned about my shutter actuation count? I am inclined to look at it rather like the mileometer reading on my car. It gives me a rough idea about when I should expect to need a major service and I would take it into account when buying second-hand. It gives some indication whether it has been heavily used by a commercial driver or kept in the garage by one careful owner! And I would expect the price asked to reflect this. After all, the shutter mechanism can be replaced. It would be a major repair and would probably be expensive - but considerably less that a new camera. However, I have had my 60D since Dec 2010 and the actuation count is roughly 28,000 (in 3.5 years). At that rate of usage, I would expect it to take 12.5 years - that is another 9 years - to get to 100K actuations. Well before then, I think I am likely to want a new camera for many other reasons!

Tuesday, May 27, 2014

Dragonfles at Woodwalton

I spent a couple of afternoons at Woodwalton Fen last week photographing dragonflies - especially Libellula fulva (Scarce Chaser). I think there must have been a big emergence recently. When I went on Wednesday there were quite a loy of immature males about which either had not yet developed their blue pruinosity or only had it partially developed. This one has the blue colouring only partially developed down his mid line, with the yellow base colour of the abdomen still showing through down the sides. I think they look rather attractive at this stage.

Male Libellula fulva with partially developed blue pruinosity
Since it has been rather warm and sunny, there was a tremendous amount of activity with males chasing each other around and mating pairs also being quite numerous. Male dragonflies (like most insects) produce a packet of sperm called a "spermatophore" which is passed to the female during copulation. She then stores it internally and uses sperm from it to fertilise her eggs before they are laid. The male's genitalia open near the end of the abdomen, but he has "secondary genitalia" located near the base of his abdomen. A spermatophore is loaded into the secondary genitalia before he goes looking for a mate. He will try and grasp any female he encounters. If she is not receptive she will try and evade him and fly off. Otherwise, he grasps her using "anal appendages" at the end of his abdomen which lock into grooves in her pronotum - just behind her neck. These are complex structures with grooves and teeth in both sexes which act like a lock and key, so they will only connect up properly if they are the same species. Male dragonflies are not very discriminating and will try and grapple anything vaguely female-dragonfly like - including other males and individuals of other species! Once they are connected up, the female curls the tip of her abdomen round and inserts it into his secondary genitalia and the spermatophore can be passed across.

Pair of Libellula fulva in cop.
This takes some time in L. fulva and they remain coupled up like this for 15 minutes or more. They usually settle on a reed stem or something similar, but if disturbed they will fly around still coupled up. (I assume only the male uses his wings when they fly in this position).

You can tell a male who has mated because the female's front legs, grasping the males abdomen during copulation, leave a "mating scar" - a dark patch where the blue pruinosity has been scuffed up.

Mature male L. fulva showing "mating scars"
The other species that are common at Woodwalton at the moment are L. quadrimaculata (Four-spotted Chaser) and Brachytron pratense (Hairy Dragonfly). I saw females of both of these ovipositing, so I suspect they emerged a bit earlier and are a bit further on in their season.

L. quadrimaculata male


These shots were taken using a 60D with a Canon 70-200 f2.8L lens at the 200mm end of the zoom range and at an aperture of f8. The closest focussing distance of this lens is 1.2m at which it gives a reproduction ratio of 1:5 (one fifth life size - 0.21x according to Canon's specs). These shots were taken a bit closer than that using an extension tube on the lens. All were taken using a tripod at a shutter speed around 1/160 - 1/200s.

Wednesday, November 06, 2013

How focus stacking software works: image alignment

This is the fourth of a series of posts about taking focus stacked images of insect specimens to illustrate identification guides. The first part was a general overview, the second a description of the setup I use to acquire the stack and the third concerned lighting the specimen. In this post I will start to consider the focus stacking software.

The job of the software is to find the image in the stack where any given point is best focussed and then to combine them into a single, composite image which is as focussed as possible throughout. Obviously, it is not magic - if some feature is not in focus in any of the images in the stack, then it will not be in focus in the final, composite image! The process has the following steps:
  1. Align the images in the stack so that any given feature is in exactly the same position in each image,
  2. Find the image in which any given point is best focussed,
  3. Combine the best focussed parts into a single, composite image.
In this post, I will consider the first step: image alignment.

Why is image alignment necessary?

Since the final, composite image will be built from pixels selected from different images up and down the stack, if features are not in the same place in each of these images, the result will be a confused mess!

Result of combining an unaligned stack


If the camera was mounted on a focus rail when the stack was acquired, why aren't the images already aligned?

Well they probably are - reasonably, but inevitable not exactly.

Firstly, the magnification of the subject inevitably changes as the focal point is changed. This is true whether you move the camera towards or away from the specimen, or fix the camera and change the focus point of the lens. The amount the magnification changes is small, but will noticeably degrade the finished image if not corrected (for example, the multiple rims of the eye in the image above).

Secondly, it is very difficult to fix the camera on a focus rail so that its axis is exactly aligned with that of the rail. If their axes are not exactly aligned, as you move the camera backwards and forwards, the image will shift slightly across the field of view. Given the magnification involved, especially if you are working at large reproduction ratios, even the tiniest deviation from true will be magnified to a noticeable shift.

Finally, if you take the stack hand held in the field, for example by using the continuous shooting mode of your camera to take a series of images as you rock backwards and forwards, then you may also rotate the camera slightly in the process. Rotation should not be an issue if the camera is fixed on a tripod and/or focus rail.

How does alignment work?

There are a number of possible approaches, but the software I wrote tackled this task as follows:
  1. Extract the luminance data from each image,
  2. Extract edges from each image (for example, Laplacian convolution),
  3. For each pair of images down the stack (A:B, B:C, C:D, etc.) calculate a cross-correlation between (a sample of) pixels luminances and vary the x and y shift, magnification and optionally, rotation, of one of the images to maximise this cross correlation (for example, using the simplex algorithm).
  4. This results in a series of estimates of x,y shift, magnification and potentially rotation changes between successive pairs of images.
  5. A new set of images can then be written to temporary storage consisting of a straight copy of the first image and then a re-interpolation of each subsequent image with the estimated x,y shift, magnification and rotation changes applied.
An original image (left), luminosity (centre) and edge extraction (right - colour inverted for clarity)
This can be very nicely visualised by making the images in the stack into the frames of an animation. This is a useful way of checking that the stack has been successfully aligned. If it has, the resulting animation, after alignment, should show no shifts in the image - just the focal point moving through it.

Here is a before and after animation of a rather extreme case. This stack shows a much large lateral shift between images than is typical because it was taken using a camera mounted on one eyepiece of a binocular microscope. Focusing up and down causes quite a bit of lateral shift in the image in this case, because of the bent image path inherent in the design of a binocular microscope:

Before alignment - this stack shows a rather extreme degree of lateral shift because the images were taken using a camera mounted on one eyepiece of a binocular microscope.
After alignment (using align_image_stack.exe).

In a previous post,  I noted that align_image_stack.exe from the Hugin package does a very good job in this respect. Most focus stacking software aligns the images as part of its processing.It may offer the option of turning correction for rotation on or off. If you know that rotation is not a factor (the camera was fixed on a tripod and/or focussing rail) then it is worth turning rotation correction off because that simplifies and speeds up the necessary calculations.

Image alignment can benefit greatly from parallel processing if you computer has multiple CPUs. As described above, the necessary changes are typically calculated for successive pairs of images through the stack and each of these calculations can be carried out by one of the computers processors quite independently. Consequently, two processors will take almost exactly half as long as one, and four processors almost exactly a quarter as long - it scales linearly. Several of the dedicated focus stacking packages take advantage of this to speed up processing if you have a computer with more than one CPU. (Hugin's align_image_stack.exe does not support parallel processing at the time of writing).

In the next post, we will look at finding the most focussed image.

Monday, November 04, 2013

Stag Rock; Willow Tit in Gateshead

We have been away over half term. Visited one of my favourite spots - Stag Rock on the north Northumberland coast. We got there for high tide for the wader roost. Lovely day with low autumnal sunshine, but quite heavy clouds with occasional bursts of rain. It turned out a Bonaparte's Gull had been seen (and photographed) earlier that morning so there were lots of birders about busy examining the flocks of Black-headed Gulls.

Bamburgh Castle from Stag Rock
Flock of Black-headed Gulls takes off in front of a breaking wave
We didn't find the Bonaparte's (it later transpired that it was seen on the sea between Seahouses and Inner Farne in the early afternoon), but lots of stuff around including many Purple Sandpipers.

Purple Sandpiper
An unusual feature was Rook feeding on the beach, along the tide line. This is not a bird I associate with the beach!

Rook feeding on the beach

On Sunday we had a rather wet walk around old haunts in the Derwent Valley (Gateshead). A very welcome sight was a Willow Tit visiting the feeders at Thornley Woodlands Centre. Here they have lost the Marsh Tit, but Willows are still present - the opposite situation to the Peterborough area where Willow Tits are now very rare. This is the first one I have seen in years. Unfortunately, they have lots of problems with Grey Squirrels, so the food is put out for the birds under wire cages - and that is not ideal for photography!

Willow Tit at feeders
When I was based in Newcastle (1975-85) it was Red Squirrels in the Derwent Valley (and the Lower Tyne Valley) and there were no Greys. The Greys invaded around 2000 and, despite an enormous effort to try and stop the invaders, there are now no Reds left in the area. Now, you have to go much further north to see Red Squirrels.

Monday, October 21, 2013

Lighting specimens for focus stacking

This is the third of a series of posts about taking focus stacked images of insect specimens to illustrate identification guides. The first part was a general overview, and the second a description of the setup I use to acquire the stack. In this post I will cover lighting the specimen. The stacks that were shot for Britain's Hoverflies were lit using flash but, more recently, I have been using continuous lighting produced by three Yongnuo YN1410 LED panels. I will compare the results and discuss the pros and cons.

Yongnuo YN1410 LED video light with plain diffuser
Yongnuo produce quite a range of LED panels with anything up to 300 bright white LEDs. The more recent models have tended to be a bit thinner and lighter and to have rather more sophisticated brightness controls. Part of the reason I went for the YN1410 (which is an older, and probably superceded, model by now) is that it has a DC power socket. Many of the more recent units don't have this. They can be powered using 6 AA batteries or battery packs made by Pansonic or Sony for video cameras. The battery packs are expensive (quite a lot more than an LED panel!) and I didn't want to have to keep 18 AA batteries recharged! Instead, I bought a 60W, variable voltage DC power supply (panels need 7.2 - 9V) from Maplin and a 4-way splitter cable (I could only find 2-way or 4-way splitters!). This happily powers all three units for however long a session I want and means I don't need to cope with all that extra weight of batteries - which makes attaching and positioning them easier.

The LED panels have very simple controls: an on/off switch and a pair of buttons to increase or decrease the light output over 16 steps. They are quite well daylight balanced, but tends to be a little towards the blue side at max output (5800-6000K). I find that, with the camera set to auto white balance, I get very acceptable colour reproduction.The max light output of each panel is rated at 960 lumens. What is probably a more useful way to describe it is that, for the MP-E 65 macro at 1:1 reproduction ratio and f8, the exposure is around 1/60-1/80 second at ISO100.

Specimen lit with 3 x Yongnuo YN1410 panels
Hilara matrona (Empididae, Diptera) male. LED lighting.
100% crop

In the past I have used three flash guns: the two heads of my Canon MT-24 EX and the Yongnuo YN565EX as the third. These require some diffusion, so in the picture below, the MT-24 heads are fitted with plastic diffusers which roughly double the effective area whilst the 565 is fitted with a large, home made soft box. The flash exposure is manual and with the 565 set up as a slave controlled by the MT-24. For this particular shot, the MT-24 heads were both set to 1/16 power and the 565 to 1/64 power. This is best judged by taking test shots and assessing the image and histogram on the camera's rear LCD panel. (The articulated LCD screen of the Canon 60D really scores here. It makes it easy to view the screen without having to go through contortions to get down and directly behind the camera! Being young and bendy would probably be equally effective ...) For this sort of shot in the 1.5-2:1 range, the flash power require  is generally low. This has the advantage that the flashes recharge very quickly. At higher reproduction ratios, say 4-5:1 for shots parts of the animal, more flash power may be required. For things like tarsi details at 5:1 you may even need full power. In these cases the StackShot's programming will need adjusting to allow a longer pause between shots to allow the flashes time to recharge.

Three flash heads with diffusers. The YN565 has a large, home made diffuser head fitted.
Stronger specular highlights. Note those on the hind femur.
100% crop
Comparing the two images, the greater contrast and more pronounced specular highlights in the flash lit shot are obvious differences. More diffuse flash can be obtained by building a soft box around the specimen. This is especially necessary for more shiny and metallic specimens with strong specular highlights. One way I have often done this is to use plastazote sheets (ideally 6mm thick - the ones shown are thicker than I usually use!) to build a soft box around the specimen (note that, in this case, I didn't also use diffusers on the flash heads):

Plastazote softbox built around the specimen
Another idea is to use an expanded polystyrene vending machine cup (the sort of thing soup is sometimes sold in). Cut the bottom off, so you get a cone, narrowing outwards, and pin that to the backing sheet so that it surrounds the specimen.

Note that the MT-24 head is mounted on a small ball & socket head. I find these extremely useful for mounting lights and flashes. They can be bought quite cheaply off eBay.

Small ball & socket head, metal flash "cold-shoe" mount and standard 1/4 inch photo screw, all bought off eBay, are very useful for mounting lights.

Whilst all the stacks for Britain's Hoverflies were shot using flash, I have more recently almost entirely switched to using continuous lighting provided by the Yongnuo LED panels. I find that this approach solves a few niggles I had with using flash:
  • With flash, you need another light, such as desktop halogen lamp or an anglepoise lamp, to provide the light to to view the specimen for focussing and setting the start and end points. You then need to move that out of the way and move the flash heads into the correct position before you shoot.
  • You generally need several test shots to get the right flash exposure and to adjust the diffusion and flash head positions to manage specular highlights.
  • The exposure of successive flash shots can sometimes be a bit variable (probably an indication that the flashes did not have sufficient time to fully recharge between shots). This can impact on the quality of the finished image.
With continuous lighting, these are avoided. The main lighting for the shot is also used to focus and setup and, whilst you are focussing and setting up, you see shadows, highlights, etc. So everything is done in one operation and it is unusual to need more than one test shot to confirm the exposure. I have not found any detectable exposure variation between shots using the LED panels. All in all, faster and more convenient!

In the next post I will talk about software for processing the stacks.

Wednesday, October 16, 2013

Setup for focus stacking

This is the second of a series of posts about using focus stacking to photograph insect specimens to illustrate identification works. The first part is here and provides a general overview. In this post I want to describe the setup I use to acquire the stack of images:

Setup for taking focus stacks ofa specimen
The photo shows my Canon EOS 60D with the MP-E 65 macro lens mounted on a Stackshot motorised focussing rail. This is mounted on a homemade jig which allows me to position the specimen vertically on the back wall of the jig and slide it sideways and up and down to center it in the field of view. The specimen is lit using three Yongnuo YN1410 LED video lights which give a bright, daylight balanced white light (I will write a separate post about lighting).


The jig

The jig. The insets show the vertical slider without the specimen carrier in place (bottom left) and the way in which the three flash brackets, used  for mounting the lights, are attached (top right).

My home made jig is built mainly from MDF. The base consists of a 32x14cm piece of 18mm MDF and the back wall is 25cm high, also 18mm MDF. They are joined by a couple of right angled steel brackets. The vertical and horizontal sliders on the back wall and the tracks they run in are all built from 3mm MDF. Three "Kood straight flash brackets" (bought off eBay) are attached to the back wall. These are used to mount the lights. The flash shoe has been removed from each of these brackets and an 8mm diameter hole drilled through the bracket where the shoe was located. These fit over three captive bolts glued into a piece of 2x1 which is then screwed to the top of the back wall. The brackets are fixed to the bolts using a butterfly nut so that they can be angled as required and held in place simply by tightening the nut.
Underside of base
The base has a 6x14cm slot cut in it and a 3mm Aluminum plate (14x20cm) attached over the slot. The plate has a series of 6mm holes drilled along its centre line. The focussing rail is mounted using a standard 3/8 inch photographic screw (also purchased off eBay). The black strip down the middle is a piece of cycle inner tube glued on with contact adhesive and helps prevent the focus rail from rotating out of alignment too easily.

Specimen carrier

Specimen carrierMounting pin
The specimen carrier consists of a 20x8cm piece of 3mm MDF which acts as the horizontal slider on the back wall. A 7x12 sheet of 12mm plastazote is stuck to it using double sided carpet tape (I usually get plastazote sheets from Anglian Lepidopterists Supplies). The background consists of a piece of paper pinned to the plastazote. A mid-grey background was used for specimen photos in Britain's Hoverflies, but a plain white background is shown here. I often see backgrounds with a coloured gradient on photos online - this could easily be achieved by printing the desired gradient using an ink jet printer and then cutting out a suitable sized piece to pin to the specimen carrier.

The actual specimen is mounted on a plastazote stage on a long pin to get it well in front of the background so that stays completely out of focus. The plastazote stage into which the specimen's micro pin is mounted has been coloured blue using a standard highlighter pen. This makes the mount easy to mask out of the finished image because this florescent blue is not a colour that is likely to occur naturally! (I will talk about post processing the stacked images in a later post.)

The second sheet of 6mm plastazote pinned to the bottom of the specimen carrier simply acts as a reflector. It throws some light upwards and tends to fill in any shadows underneath the specimen arising from the fact that there is no light below the specimen in my setup (although there is no real reason why you could not mount a fourth light on the base of the jig, below the specimen, if required, to get really flat, all round illumination).


Stackshot focussing rail
Stackshot controller
The StackShot "focus stacking macro rail" is a wonderful piece of kit, but is not cheap! As far as I know, it is only available directly from Cognisys in the USA ($525 + carriage at the time of writing). Remember that you will also have to pay import duty and VAT to HM Revenue & Customs when you import it!

The focussing rail is driven by a stepping motor which is controlled by the programmable controller. There are many options, but I use the one where you set the start and end point (by driving the rail forward and backwards using the "Fwd" and "Back" buttons on the controller) and step size. I set the step size using a Depth of Field table for the MP-E 65mm macro lens. I choose a step size that is 30% less than the Depth of Field for the F-stop and reproduction ratio I have set on the lens. This gives some overlap of the parts that are in focus between shots which helps the stacking software to merge the shots successfully. So, if the chart says that the Depth of Field is 0.5mm for my chosen lens settings, I would set a step size of 0.35mm (0.7 * 0.5). The controller works out how many steps of that size are needed to travel from the selected start to end points. When you tell it to start shooting the stack, the controller moves the rail to the preset start position, fires the shutter, moves by one step of the selected size, fires the shutter, etc. until it arives at the preset end position.

There are many options to control how fast the rail moves and the length of time between operations. For example, you can set how long to pause between the rail arriving at the next position for a photo and the shutter being triggered (i.e. how long to allow for vibrations caused by the rail's movement to damp down). It can be very useful to modify these settings, for example, to make the time between shots longer to allow a flash to recharge (if you are using flash to expose the shots). It also has an option to trigger the shutter twice for each shot so that you can use mirror lock up (as I normally do).

In the next post I will consider the lighting and compare flash and continuous LED lights.

Tuesday, October 15, 2013

Photographing of insect specimens using focus stacking techniques

This is the first of a series of posts describing the methods I have used to photograph specimens of flies to illustrate "Britain's Hoverflies" and various identification keys using focus stacking.

Ceratinostoma ostiorum (Diptera, Scathophagidae), male. Focus stack of 25 shots taken in July 2013 at approx. 1.5x life size using Canon 60D with MP65 macro lens, processed using Zerene Stacker.

Why is focus stacking necessary?

When you look at an insect specimen through a microscope, you focus up and down and move the specimen around and what you "see" is a 3D model formed by your visual system - the combination of eye and brain. If you take a photograph of the same specimen at the same sort of magnification the resulting image is often rather disappointing! It fails to match your perceptions because, due to the limited depth of field, it is not all in focus. It is possible to increase the depth of field of a photo by decreasing the aperture of the lens (selecting a higher F-number) but, as the magnification you are trying to achieve increases, the depth of field available is simply not sufficient. It is not possible to decrease the aperture, and hence gain more depth of field, beyond certain limits because diffraction leads to unacceptable image degradation.

The way out is "focus stacking" - taking a series of photos (the "stack") at different focal points and merging the most focussed parts into a single, composite image that is in focus throughout. The result, like the one shown above, satisfyingly matches our perceptions of what the specimen ought to look like!

Whilst this technique has been known for a long time, the availability of computer hardware and image processing software that will do a good job in a reasonable amount of time and at a cost affordable to an amateur enthusiast is relatively recent development. Sufficiently powerful home-computers with enough memory have only become available and affordable over the past decade or so (say, since 2000).

My experiences of focus stacking

I have been interested in the technique for a long time. I first encountered it when I was a PhD student at Newcastle University (1975-78). At that time, the camera microscope and image capture setup cost something in the high tens to low hundreds of thousands of pounds and the processing software needed the resources of a university mainframe computer! In Dec 2002 I bought a Nikon Coolpix 4500 and used that, mounted on a binocular microscope, to capture focus stacks which were processed using software I wrote myself (called "DeepFocus") written with Delphi 7.

Sphaerophoria scripta (Diptera, Syrphidae). Focus stack of 14 images taken in April 2004 with Coolpix 4500 mounted on binocular microscope and processed using self-written "DeepFocus" software.

More recently, Roger Morris and I produced about 180 images of  hoverflies for the WildGuide "Britain's Hoverflies". Producing this number of images at the sort of quality required for publication in a book, was only really possible because I had developed better and faster techniques.

Melanostoma scalare (Diptera, Syrphidae), female head. Focus stack of 15 shots taken in April 2011 at approx 3x life size using Canon 60D with MP65 macro lens. Processed using Helicon Focus.
My latest projects are an update my key to the British Scathophagidae and a Field Studies Council fold-out identification card on Garden Hoverflies (still in preparation). For these, I have been shooting a series of whole-animal images.

In the next post I will describe the setup I have developed to acquire the stack of images.