Yes a bit confusing. It is hard to find articles on how to photograph cacti in habitat, but basically it is just conventional flower photography, which in turn is taking a portrait of a plant, therefore is similar to a miniature form of people photography where all the basics of that still apply. Unlike animal or bird photography plants don't run away, but the thinner stemmed ones do move in any breeze. Nevertheless you can spend more time setting up for plant photography than insects or animals.
http://www.ophrysphotography.co.uk/page ... 0tips2.htm
Regarding circular polarisers mentioned in the second link below. A circular polariser does not refer to it's shape, but in the way it polarises light, you can even get square shaped circular polarisers that fit into those Coquin type holders.
The only reason you need a circular polariser is most modern cameras split the light between the viewfinder and meter or autofocus sensor, so a conventional polariser upsets the balance between the two the makers have built in for accurate metering and autofocussing. You can use one of the old linear polarisers (again not a reference to their shape, but how they polarise light) that were used on early film cameras on modern cameras but it may upset the accuracy of the metering and autofocus
http://www.bobatkins.com/photography/te ... izers.html
As stated in the link below, it is true at the same f-number you get greater depth of field on a small sensor. What is not true is that you gain more depth of field on final images of the same size, since the image from a small sensor has to be enlarged more, something which also enlarges the Circle of Confusion, meaning no apparent gain in depth of field if images from different sensors are enlarged to the same final size.
https://www.youtube.com/watch?v=kM0eWP36khk
In the only habitat photography I did, for convenience I broke my golden rule of never using autofocus close up since it is too inaccurate, but to use the human eye to spread the depth of field on the focussing screen. Also I was told not to take a tripod since I would get fed up with lugging it about and stop using it. However I think some form of mini-pod would have helped with the macro work since I could not hand hold below 1/160th second with the lens I was using in order to avoid camera shake. A small tripod would have allowed me to use slower speeds and smaller f-numbers for increased depth of field. Hand holding is convenient, but never as good as a stable tripod.
As an example where autofocus did not work since it did not spread the depth of field available, because the tip of flower is out of focus.
- aerocarpa.jpg (128.68 KiB) Viewed 6842 times
One where it mostly did, but even here if on a tripod rather than hand holding a smaller aperture would have given even greater depth of field.
- weisseri.jpg (149.41 KiB) Viewed 6842 times
If you go out into the field then do not rely on autofocus for macro work.