So is the A7Sii better?

I bought the A7sii on the grounds that it might produce better results than the A7ii because of its smaller number of larger pixels. The suggestion had been that post processing involves floating point arithmetic and this involves errors that can accumulate along a chain of operations. Starting with better data for individual pixels might cause the calculation errors to be smaller and accumulate slower, giving a better final result.

In this post at photomicrography.net Rik Littlefield agreed that starting with better pixel level data might be advantageous for some post processing operations, although not mainly for reasons of floating point error accumulation. 

So it doesn't seem like an intrinsically silly idea that my heavily processed images might end up better if starting from better pixel level data.

Within 10 days of getting the A7sii I had had seven sessions with it, and I was pleased with the results I was getting. I was curious as to whether these were better than I could get with the A7ii; had my purchase been worthwhile in terms of image quality? I know from experience that doing effective comparisons can be very difficult, even if you can reduce a lot of the variability by doing like for like tests in a controlled environment. However, I also know how difficult it is to draw real world conclusions from highly controlled comparisons. And it was real world results that mattered to me. So I tried a real world comparison.

Since image by image like for like comparisons were impractical out in the field, I decided to try comparisons at a session level. In the previous four days I had had three sessions with the A7sii with the 100mm Laowa 2X macro lens with 2X plus 1.4X teleconverters, using f/40 for the whole of two of the sessions, f/45 for one session and f/36 and f/32 for the other session. All four sessions were in the church grounds opposite our house.

I decided to do another session in the church grounds, using the same setup apart from using the A7ii rather than the A7sii. I would use f/40 throughout the session. The images I kept from the session are in this album at Flickr. The images from the four sessions with the A7sii are here, here, here and here at Flickr.

And my conclusion?

I can't convince myself that, at the session level, what I got from the A7ii session is any worse (or any better) than from the four A7sii sessions. There may be differences that someone more observant than I am might notice, but as it stands, I'm not seeing it.

So do I regret getting the A7sii?  No, I'm comfortable using it, I like the results I'm getting from it, I think it is giving me stronger focus peaking signals than the A7ii, although even there I'm not 100% sure about this; it is something else that is rather difficult to test in real world use. But if it is giving better focus peaking signals that will probably be improving my focus success rate. Having the A7sii means that the A7ii is freed up for other things. And if I hadn't got the A7sii I would have had a permanent niggle in the back of my mind that perhaps I could do better by using a low pixel count camera.

And I have this feeling, which may of course be no more than wishful thinking, that it may in fact be giving me better results, at least some of the time, but I just can't put my finger on it. Anyway, I'm entirely content to go forward with the A7sii as my primary camera for photographing invertebrates.

Using less teleconversion

 Using the A7ii and subsequently the A7sii with the Laowa 100mm 2X macro and a pair of 2X teleconverters opened up new possibilities for me. Previously I had occasionally managed to get a half decent image of small subjects such as globular springtails and aphids, but it was difficult and had a very high failure rate, so for the most part I avoided subjects that small. Now I found I was able to capture better images of these small subjects, and to do so with a much higher success rate. My photographic opportunities had widened significantly.

However, there turned out to be a downside at the other end of the spectrum; photographing larger subjects had become problematic, especially more "environmental" shots of larger subjects from further out. The problem was working distance. The problem is usually having not enough of it. Now the problem was having too large a working distance. At 1:1 the working distance was around 380mm and was increasing fast as the magnification decreased any further. This large working distance made it difficult to throw enough light on to the scene (and I need to throw a lot of light on to the scene because of the very small apertures I'm now using).

There were two problems. One was simply the distance. Illumination decreases with the square of the distance between the light source and the subject, and by 1:1 the illumination had become very diluted. And that was if the flash heads were pointing at the subject. But at lower magnifications they were not, and that was the second problem. If the flash heads were pointing so as to illuminate small, close subjects then they were far away from pointing at distant, larger subjects and not providing them with much light, necessitating uncomfortably high ISOs. And if the flash heads were adjusted for larger subjects the smallest subjects got no illumination at all. It is true that adjusting the direction the flash heads were pointing had become much more feasible with the Yongnuo YN24EX than it had been with the Venus Optics KX800, but making any adjustments to the physical flash setup was very unattractive; it would be very disruptive for some of the sequences I like to capture, where I move freely between a wide range of magnifications, sometimes taking shots as frequently as every two seconds or so while change magnification from shot to shot.

I went back to my close-up lens setups and did some measurements to give me some context. I used my FZ330 small sensor bridge camera with Raynox 150 and Raynox 250 close-up lenses, as this was my most used setup, and the one with the widest range of magnifications.

The Raynox 150 was by far my most used setup with the FZ330 (sometimes I would have sessions with the FZ330 where I only used the Raynox 150 and didn't use the Raynox 250 at all). This let me photograph scenes from around 75mm wide down to 13mm wide. Using the Raynox 250 instead of the Raynox 150 gave me scene widths from 43mm down to 8mm. So by changing between the two close-up lenses I could photograph scenes from 75mm wide down to 8mm wide.

In contrast with the A7ii, the 100mm 2X macro and a pair to 2X teleconverters:

• I could go down to a scene width of 4.5mm, much smaller than with the Raynox setups. (I had more powerful Raynox close-up lenses, and I could stack Raynoxes for example a Raynox 150 and a 250, or two 250s. However, I had found it difficult to get good results with these setups.) 
• But I was limited for larger scenes to around 36mm scene width, which was very restrictive compared to the 75mm scene width I could get with my much used Raynox 150.

I did some measurements on the A7sii with 100mm 2X macro with one 2X and one 1.4X teleconverter. This would give me a minimum scene width of 6.4mm, which was still slightly smaller than I could get with the FZ330 and Raynox 250. At the maximum feasible working distance of around 380mm it gave me a scene width of around 53mm. That was not as good as the 75mm scene width I could get with the Raynox 150 on the FZ330, but it seemed like swapping out one of the 2X teleconverters and using a 1.4X in stead would give me a closer fit to what I needed.

So I experimented. It turned out that there was an adjustment I could make to the bendy arms holding the Yongnuo flash heads that brought them down a bit and let them point a bit more forwards and a bit less downwards and that was enough to let me use a slightly longer working distance, and that was all I needed to get to the sort of scene width I could get with the FZ330 and Raynox 150. So with the 2X plus 1.4X teleconverter setup I could cover the full range of scene sizes that I could with the FZ330 and Raynox 150 and 250, and could do so seamlessly, unlike with the Raynoxes which required changing close-up lenses to go between magnification ranges.

The other question was whether the 2X plus 1.4X teleconverter setup would give me enough magnification for what I wanted to do.  Although the double 2X teleconverter setup gave me up to 8X magnification, I had been feeling for a while (without doing any careful measurements) that I was rarely using much beyond 6X or so. It turned out in practice with the 2X plus 1.4X setup that I didn't often feel I was missing the extra 5.6X to 8X magnification range that the double 2X setup gave me.

So I decided to transition to a 2X plus 1.4X setup. So far it has worked well. Indeed, for reasons I don't understand, it turns out that I am using lower ISOs with this setup than the double 2X setup. I think that may be down to the adjustments I made to the position and direction of the flash heads. I'm sometimes using ISOs as low as 400, which gives me a three stop noise advantage over the FZ330 setup,  for which base ISO 100 is similar to ISO 3200 on full frame. And I'm rarely using ISOs as high as 3200, so there is at least a little noise advantage over the FZ330 setup for almost every shot, and sometimes a rather larger noise advantage.