Repeatability – (of an experiment, etc) producing or capable of producing the same result again
Predictability – consistent repetition of a state, course of action, behavior, or the like,making it possible to know in advance what to expect
………………………………..wouldn’t that be nice?
Last Tuesday at Tetbury Camera Club we had an inspiring talk by Jay Myrdal who explained how he made stunning commercial images back in the day before Photoshop when it all had to be done in camera – a plate camera quite often. The techniques he explained were fascinating and the results were truly stunning. Some of his images involved taking action shots such as an exploding light bulb – this would be just a part of the image but he would have to shoot it over and over again to get all the timings of the effects just right. He built a rig to automate and adjust the various factors involved so he could tweak the important parameters knowing exactly what he had done beforehand and so migrate towards an optimal set up. He also scrupulously calculated all the angles involved in multi-layered super-imposed images to get things to look right from the perspective point of view.
This got me thinking that I needed to apply his philosophy to my macro photography, which up to now I have been carrying out on a rather hit and miss basis in terms of choice of lens configuration, and adjustment of stacking parameters. So I decided to apply some of Jay’s thinking to the matter.
My rig is pretty much automated already, but the key issue here is recording all the parameters that I have used for each stack in enough detail to enable evaluative decisions to be made after processing (which may be some time later) so that the parameters for the next stack can be improved or consolidated. I already have lots of bits of paper lying around with scribblings of what I have done but no real way of tying these back to the images I have processed. And not everything is written down anyway. It needed organisation and preferably automation.
I was already in the process of updating my Raspberry Pi Python software for my focus stacker to add refinements based on the last few months shooting. As a result, my mind was in tune (as much as it will ever be!) with Python 2.7 and Tkinter, and then two and two came together and for once made four! I decided to automate the logging of my focus stacks using my RPi.
I won’t bore you with the details of how I did it – programming and more programming is all you need to know! But this is what it now does.
There are some user interface windows to enter information that the RPi doesn’t know such as what camera is being used, the lens configuration, the subject matter, and the camera settings. You can also enter a note for each stack. The software gathers up all the info it already knows about the shoot such as the near and far focus points, focus increment and so on; date and time stamps the log, gives it the next shoot number and then (and only) when the shoot sequence button is pressed, the whole lot is appended to a .csv log file.
The .csv file can be read by Exel and as long as the camera and RPi are telling the same time I can figure out which log goes with which image stack.
One hiccup in proceedings is that the RPi is not on the internet, and so the RPi cannot find out automatically what time it is. That’s because it doesn’t have its own real time clock and battery (it apparently kept the cost down) and relies on the internet to reset its clock each time it is turned on. No internet, and the clock just restarts from where it left off last time it was on! Not terribly useful. At the moment I have to enter the time manually into the RPi when I turn it on – it is very easy [sudo date -s “Sat, October 18, 2014 17:21:00] for example. But I might forget.
What would be better is to get the lap top to tell the RPI what the time is. That is all within the realms of possibility. I would have to set up the lap top as an NTP server which Windows 7 does support. It seems to require some mining in the registry to do this, something I am not too keen on doing. There is plenty of advice on the internet, but I will have to nerve myself up before trying this. Then you have to rummage in the RPi’s software settings too. I may have to get my (no-longer) resident expert to help me on this some time.
Finally, I have also made some measurements to establish/check the exact magnifications of my various lens configurations, and have produced a chart to enable me to select the best lens configuration for a given subject size. It requires measurement of the subject height to get it right first time – something I had not been bothering to do. The chart is shown below