[StephenBatey]

On the original topic, I can provide a reasonable explanation that would account for the differences between the image size at a nominal 70mm that you found with the 18-70mm and the 55-200mm lenses. Can, but won't as it involves maths that I've found most people don't want. So, although I hate saying this (because it's entirely possible that I've made a slip and if I gave my workings it could be checked) you'll have to take my word for it.

On related topics, I've found that photographers have a "herd instinct" in what matters to them. Megapixels, noise at high ISO are important to them, even if they never make large enlargements or use high ISO settings, or rarely do. How big a subject brightness range their cameras can successfully record (even though it affects every single photograph they take) is of no interest. I once asked on another forum if anyone had ever tested their camera. The only person that ever commented (a professional) said he had no idea and had never checked. So, don't expect people to have any interest in a topic just because it's of immense practical importance.

You may be right that people have difficultly stringing words together, but two points to bear in mind:

1. The internet opens you up to seeing written communications from people whose writing you would never have seen before.

2. Educational standards have dropped seriously from former times.

As to comments - well, I can string words together reasonably well, and I don't make comments on people's photos now unless explicitly asked, simply because I am too plain and easy to understand. I usually offend simply because I point out what should have been obvious, but no-one else either sees or dares to mention.

Finally - I don't know if the number of people able to fully understand you is diminishing, but again consider the nature of forum communications. It's not like receiving a letter, where you can read carefully and reply at leisure. The immediacy encourages a fast read and a fast response. and that in turn encourages people to assume that they understand without actually reading. If you use certain words, it's more likely to trigger an emotional response that will block out your true meaning, as I found on another forum. I mentioned in a thread that I'd had bad treatment while in hospital. This triggered (apparently) the following sequence of thoughts: "bad treatment = criticism; criticism = wants to dismantle the NHS" and a full blooded attack on my principles for wanting to privatise the NHS followed on my post.

Back on topic, if you want a reasoned answer to your query (so that you can see if you agree) let me know and I'll send one privately.