Stan,
If I may offer some constructive criticism without greatly offending you...
This is from an old film photographer who was once pretty damn good in his day, with quite a few published pics.
IMO, your main problem is "depth of field." You're only getting a tiny plane in focus, and stuff in front of it and behind it are out of focus.
There are several factors involved. First, the more your lens is stopped down, the greater the depth of field will be; e.g., f22 or f16 will give you a greater DOF than f2 or f4 or f5.6. I don't know what your lens's wide open aperture is, but DON'T use it! Stop down -- a lot. If you need to switch to a manual mode rather than auto (again, I do not know how your camera works) then you must do so. Perhaps you can set it to "aperture priority" -- then set it for as small an aperture as you can (remember, the greater the f number, the smaller the aperture). Next, of course, since a smaller aperture lets in less light, you do need to take into account the light -- fortunately, reef tanks are brightly lit, to say the least! But, if necessary, increase your ISO (Haha -- we used to call it ASA in the "old days") If your camera has a built-in flash, avoid using it at all costs! Flash flattens things, and produces shadows behind -- I despise flash pictures!
Next factor... focal length. Stan, you have a 90mm macro lens. Many years ago when I was shooting film I used a 55mm MicroNikkor (macro, micro -- just the manufacturer's terminology for "close up lens!" lol). All things being equal, I will get a greater DOF with my 55mm than you will with your 90mm. Bottom line on this: it's all the more important that you STOP DOWN!!! (can't emphasize that enough)
Next factor... distance from subject. The further away you are, the greater the depth of field will be. So... if you have a camera that takes pics with a resolution of 2 zillion by 1 zillion pixels (LOL, of course), get back for a greater DOF and then digitally zoom in by cropping -- I mean... like, are you shooting for publishing on the web, or, for a friggin' 40"x20" poster????!!!!
Next factor... the DOF extends from one third in front of your actual point of focus to two thirds beyond that point.. Which leads us to...
Hyperfocal distance. (Gettin' down into it now!!! LOL) I'm not sure how much of this theory you can apply to these super automatic cameras, but, on my old Nikkor lenses there were color codings right on the focusing ring where you could, for example, on a 20mm lens (my favorite!) set the aperture for f22, then rotate the focusing ring so that infinity lined up with the pink color code of f22... and *everything* from 1.25' to infinity would be in focus -- making it essentially a "point and shoot!" At any rate, what I'm getting at here is that ALL f stops on ANY given lens have a hyperfocal distance. I had tables for every lens I owned -- I have no idea if such things exist these days -- I think the manufacturers just want to make everything as automatic as possible without the user needing to use his brain! (Please, no reflection on you, Stan, just my commentary on yesteryear vs today -- hell, that's always the way it is with us old guys, we long for "the good old days" LOL) But if you had such a table you could for example set your lens at f16 and set the hyperfocal distance to the table that might give you everything in focus from perhaps 4" to 12" -- I'm just throwing numbers out, you really need the manufacturer's table of hyperfocal distances to use this method correctly.
Hope at least some of the above helps to make you a better photographer. Good luck, and looking forward to your viewing your pics.
George
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