Comment:
For starters, I especially don't care for studio-type work done in plain-Jane daylight. I can't quite put my finger on why, and it's not a critical reflection because of the circumstances under which these photos were taken, but it just doesn't look right. Maybe it's got something to do with setting up a formal pose in an arbitrary lighting regime, and one that is rather plain at that. The light makes the photos prosaic and the shadows get in the way, or something.
Thus, a lot of these that might have looked decent in a studio setup don't look all that great with the lighting they've got.
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You handled the pose pretty well. Needs some fill lighting to control the shadows, especially those on his face.
Select-1
It doesn't work well as a portrait (doesn't really showcase the person) or as a formal (no emphasis on form), and those facial shadows are really harsh. You've lost both his eyes.
Select-2
I feel that the lighting as it is flattens the hand, arm, and torso too much.
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More flattening (not flattering) lighting. Another disadvantages of not doing this in a studio: clothes/props/settings should work with the poses for a unified impression. The pose suggests grace, the clunky shoes and plain old clothes don't. Form and figure being the main element of the shot, the background happens to distract from it with the haphazard detail in the grass and the chunky horizon line. Better to have a sweep or a deliberate set.
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Two more where the lighting and background just aren't right. The big old shadows blasting across the model don't contribute to the picture, and the background really takes away (especially in the second one, with all that fiddly detail in the plants).
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Finally, a shot where the lighting at least highlights form instead of just shining across it randomly! The background still doesn't help, though. If you don't use a sweep to remove everything but the subject's form from the photo, another approach is to integrate that form with the background, e.g. by mimicking another significant shape in the scene.
Select-8, Select-9
Flat lighting again. You've also got the background brighter than the model in -9, which steals attention from her face. I'd quibble with the posing and framing in these as well; there could be a much stronger compositional connection between the two models. If you had any directorial input during this shoot - and I don't see why you would not have - it would have been a good opportunity to ask them to make small alterations in the pose for better effect and framing.
Select-10, Select-11
Where you have selective lighting, you have a very easy way to emphasize certain things, be they faces, shapes, or details. In this case what is being emphasized is random parts of the frame, which does nothing for the photo. Even using 'found' lighting, you have to make it work for you however you can instead of just accepting it.
Select-12
Much better. A respectable portrait at least.
Select-13
The most interesting parts of the photo are the fellow's face and arm, as his chest and the sky behind him are plain expanses. In light of that, I feel you gave his face short shrift when you framed it; this is another instance where some directoring would have been helpful.
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Nice. The texture of the water is well-represented. A little more space above the long plants might be good, though.
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With much different and more deliberate lighting and without the ring, it would be possible to make a shot like this that I'd find interesting. This one just gets a colossal "Meh" from me; it's far too straightforward to be an abstract body shot.
Select-16
Get some fill light from the right side and then expose a little less so the sunlit part of her face isn't so bright. Also, it would be nice if her eyes were either more open or totally closed.
Select-17
A respectable portrait. The lighting could be better, but at least what you had was workable.
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If you're going to include the photographer, he should be included in a more definite way. There's little enough here that the shot almost looks like a misfire.
Select-19
Best of the bunch. The lighting is decent and the shape of the hand and foot and the interaction between them is well-caught. The only thing I don't like is the triangle of shadow under the foot, because it looks like like a gray mush instead of a full shadow or an unshadowed wood surface. The foot and table merge there in a rather ugly way, and I think it would be better if the two were kept more distinct. Controlled lighting would have been useful.
Select-20
This one is kind of plain to be a decent portrait, and that arm could have been excluded (or included) in a much better way than it was.