Using tiny apertures - Part 4, my preferred setup

By early November it had started getting cold and I wasn't finding any invertebrates in our garden. However, I had another piece of good fortune.  Opposite our house there is a church, and it has some fairly unkempt woodland around it. 

I had never been in there but I had read that springtails can be found in cold conditions and since the leaf litter wasn't cleared out of the wood I wondered if there might be springtails to be found there. I sought and received permission to go into the wood.

It turned out to be a bit of a goldmine. I did find springtails, and some other things too, some almost as small and some larger. Not huge numbers of anything, and it took time to find things that were there, but I found enough to keep me interested and let me carry on experimenting. Here are some of the things I found in November and December, all the way through to 25 December. (Yes, I went over there on Christmas Day. We were having a lockdown "unchristmas"; no family gathering for the first time I can remember.)

By then I had firmed up on what I would use, at least to begin with, in 2021: the A7ii with two 2X teleconverters and a Laowa 100mm 2:1 macro lens, and a Venus Optics KX800 twin flash, which I have been using for several years.

Yes, it's big, it's heavy, but consider this: the spider (?spiderling) below was small, perhaps around a couple of millimetres long. Perhaps it was a bit bigger, I don't know. What I do know is that it was scampering around almost continuously, and fairly fast. Over the course of around 16 minutes I captured around 155 images and 27 of them were to my way of thinking usable, a success rate of approaching 20%. For my visual tastes, for my hands that show a fair bit of hand-shake at 6:1 or whatever magnification I used, and with my definitely not lightning-fast reactions, I count that as a success. And it is something I am confident I could not do with any of my close-up lens setups.

So yes, the image quality isn't of the highest order. Here is one of them as an example. But close-up macro, especially out in the field, especially with smaller subjects, especially with moving subjects, is a game of trade-offs, and I'll obviously try and improve, but for now  at least I'm feeling that I've got a mix of trade-offs that I can live with.

So what is it like to use this big, heavy beast, out in the field?

Well, not too bad actually.

I get from infinity focus to 8:1 magnification with a turn of around 120 degrees of the focus/magnification ring on the Laowa 100. I'm using from 1:1 to 8:1 for these sorts of subjects. At 8:1 the scene size is 4.5mm x 3mm. That is about as small as I can handle, working hand-held as I do. I can get from 1:1 to 8:1 with a turn of around 90 degrees of the focus/magnification ring.

The focus/magnification ring moves very smoothly and easily. Together with the small amount of turning required, this means I can use a technique for finding the subject very similar to what I use with my close-up lens setups. 

Finding small subjects can be infuriatingly difficult. You can see it, you know exactly where it is, but can you get it into the frame so you can see it? Sometimes not, or only after a fair bit of searching. The problem is that you may be pointing straight at it but if the focus plane isn't quite close to the subject it may be invisible, especially at higher magnifications.

What I do is to pull back and reduce the magnification, a lot. This makes it much easier to see the broader picture and locate the subject within it. Having found the subject I turn the focus/magnification ring to increase the magnification, while simultaneously moving the camera to keep the scene somewhat in focus. It doesn't have to be fully, or even much, in focus, just enough so you can keep track of where the subject is. Then I may turn the focus/magnification ring a little to fine tune the framing and then move the camera to fine tune the focusing. 

I don't use any magnification of the image on the screen; I find that too disruptive, and slow. I don't want to be stopping to push buttons at that point. My subject may be momentarily about to move, or it may be in motion, as that little spider was for a number of those shots. How then do I get the focus plane in the right place, especially when just looking at that little screen, and quite possibly not having a particularly clear view to look at? After all, it matters hugely where the focus plane is placed in terms of exactly what ends up in focus.

Well, that is true normally, but bear in mind that depth of field roughly doubles with every two stops reduction in effective aperture. With the apertures I'm using I have a (relatively) large depth of field. I think that what is going on is that because of that much larger than usual depth of field I can get away with not being so accurate about placing the focus plane. 

So what apertures am I using? 

[Note: The effective f-numbers mentioned below might not be right. Please see the next post, here, for more on that.]

I experimented with various f-numbers, and it can get rather complicated because of the variation of effective f-number with magnification. For quite a while I tried to keep up with the mental arithmetic needed to keep the effective f-number constant as magnification changed. Then I had a session with all the wasps and flies on the pigeon carcass where I left the f-number the same, and didn't alter it as I changed magnification. To my surprise, it worked ok.

I then tried doing this in more sessions. I ended up leaving the f-number somewhere around f/45. The effective aperture would then vary from around f/90 at 1:1 to around f/400 at 8:1. It worked. Why would that be? I suspect that as subjects get smaller they need a smaller effective aperture to get enough depth of field to cover the same proportion of their body etc as I like to have with larger subjects (for example, for a winged insect, the head, body, near side legs and preferably near side wing in focus). By leaving the f-number set on the camera to a constant value the effective f-number increases as the magnification increases, and perhaps this is just what is needed to keep the depth of field coverage fairly constant in relation to the subject and its size in the frame. Anyway, for whatever reason, it appears to work. I need to firm up on this, or make alternative arrangements if it turns out not to be so satisfactory after all. But for now, I'm regarding it as a very helpful simplification.  

And what does using f/45 mean in terms of depth of field, compared to what I get with my close-up lens setups?

Well, with my close-up lens setups I use apertures that give the same depth of field as f/45 on full frame like the a7ii. With f/45 set on the A7ii/lens, at 1:1 the effective f-number is f/90, which means that it will have twice the depth of field as a close-up lens image of the same scene. At 2:1 the effective f-number is around f/132 and by 3:1 the effective f-number has reached f/180, which means that it will have four times the depth of field as a close-up lens image of the same scene. By 7:1 the effective f-number has reached f/360, which means that it will have eight times the depth of field as a close-up lens image of the same scene, and a bit more than that at the setup's maximum magnification of 8:1. These are rather significant increases in depth of field, and I like that a lot.

There are of course other factors, both positive and negative.

It is great to be able to be able to cover all the scene sizes I want to work with without having to make any changes to the kit. That for example, makes it practical, irrespective of subject size, to do one of my favourite manoeuvres, which is to move frequently back and forth between whole body, environmental and closer-in shots, including when I'm tracking a moving subject. This sort of thing (only more so sometimes, especially at the environmental end of the spectrum).

Flash can be a bit of a problem. With close-up lens setups the working distance remains fairly constant irrespective of magnification as long as you don't change to a different close-up lens, and even if I change between a Raynox 150 and a Raynox 250 the working distance is not affected enough to disrupt flash usage. 

With the double teleconverter setup the working distance gets very large out towards 1:1 with the result that the flash heads are distant from the subject and also pointing in the wrong direction. The KX800 has flexible arms, but I don't like moving them around too much. They are a bit fragile. I have broken one of the arms on one of my KX800s several times and have had to superglue the broken joints together, which reduces their flexibility. Also, having to move the flash heads breaks the flow of the capture routine and also slows me down. The kit is also a bit heavy to hold one-handed while adjusting the bendy arms of the KX800 with the other hand, and those adjustments work better, with less danger of causing damage,  using both hands, which would mean putting the kit down. That can be problematic in wet conditions and/or with brambles etc all over the place. And of course it puts paid to any thought of moving smoothly closer in and further out. 

To some extent I can compensate for the increased distance by increasing the ISO rather than making a big adjustment to the bendy arms, but that doesn't solve the problem of the flash heads pointing in the wrong direction, which does require physical manipulation of the arms. I may have some fine tuning to do on this front.

Very small apertures require a lot of illumination. I don't like running the flash at more than 1/4 power because of the impact on recycle times. That in turn means that it isn't possible to use base ISO. In fact I'm typically using ISO 1600 and 3200. I'm not too bothered about this as ISO 3200 gives about the same amount of noise as base ISO with my bridge cameras, and I can live with that. Of course, higher ISOs also lose details. However, the diffraction effects are so strong that the details that would be lost through higher ISOs may have already gone anyway, and with modern noise reduction things seem to work out ok for my purposes.

Another problem is dust spots. Using tiny apertures makes any dust etc on the sensor show up very clearly, especially with the rather strong post processing that the images need (see next post), and the more so as the aperture gets smaller. And it is not just dust on the sensor. There are another eight surfaces on which dust etc can settle: the front and back of each of the teleconverters, the front and back of the macro lens, and the front and back of a UV filter which is permanently attached to the front of the macro lens. The effect on the image of dust on any of those surfaces becomes  larger and more diffuse the further away the surface is from the sensor. That can make the spots more difficult to handle during post processing. 

I have tried very hard to get the A7ii sensor completely clean so that no spots show up. Despite many efforts, and despite deploying an air purifier to remove dust in the air of the room I use for sensor cleaning, I have yet to get the sensor so clean that it shows no spots at the effective apertures I am using.

Despite the problems, overall I'm getting fairly comfortable with the capture workflow with the A7ii double teleconverter setup.

Being able to capture images is one thing. Being able to make something presentable out of them can be quite another. Next up, post processing and image display.