What technical terms do you not understand?
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You’ll probably want to buy a Macro Lens and a Tripod and Head at the very least, so you need to factor those into your budget.
I forgot to mention that it would be nice if the camera had LIVE VIEW or similar (for critical Focusing) and also a retractable/swing- out Monitor Screen (for ease of Focusing in live view when the camera is on odd positions) would be useful. I don’t know if that camera has those two facilities.
I think that the solution need not be a DSLR.
I am not necessarily opposed to the idea of a bridge camera being a very good option for you. I would like it to be able to capture raw and I think that the point about the long Working Distance that I raised above requires adequate investigation.
But I really don’t think you should rush in and buy anything just at the moment.
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I think that Kathy and (I know that) I hold a fairly strong opinion that is predicated on giving advice so we do not encourage people to assume that buying more gear will necessarily solve the issues that they encounter.
So (now speaking for myself only) – I never stated nor was I ever suggesting: "don’t buy anything else– just use your Fuji" . . .
What I am stating (bluntly and this is just as one example) is this:
If you haven’t mastered the skills of Manually Focusing using the Fuji X100s to get a submerged Object in good focus at a Shooting Distance of about 6 inches, then buying a DSLR and a Macro Lens (or any other camera) will probably not fix that.
Moreover I honestly don’t think buying something else at the moment will make the task of Manual Focusing (and also other tasks like White Balance; Critical Focusing; Lighting) any easier for you to master, when you have a perfectly good tool with which to hone your skills and learn more about what are the specific design requirements of the camera/lens/lighting that you really require.
WW
By the way and simply as an example of practicing -
I submerged a Flower in a glass of water:
The leaf is about the size of my pinkie. The glass was CURVED (that means a much more difficult shooting scenario than if the glass were FLAT).
I then made two photos using my Fuji X100s, one from the side, shooting through the glass and also shooting through the water and the second shot shooting from above only shooting through the water.
These were made using the Marco Mode and the Working Distance was 6 inches.
The object of the exercise was simply to attain good focus on the front of the flower in each photo.
I used Manual Focus, looking through the EVF and using the magnified assistance.
Both photos are JPEG SOOC (Jpeg file Straight Out Of Camera), and each has been cropped as would be necessary to get the equivalent of about 1:1 magnification in the final image.
The top photo was pulled at: F/16 @ 1/250s @ ISO320 and I used a Tripod.
The bottom photo was pulled at: F/11 @ 1/500s @ ISO320 and the camera was hand held – critical focusing was achieved by moving the camera position in and out, not using the Manual Focus Ring on the camera. It required two attempts to get the Hand Held shot.
Here are the results:
WW