Looking for advice on how to improve photo sharpness

I just got a strobe, which has improved the quality of my photos tremendously, however I am still struggling with sharpness. I'd appreciate any suggestions on what I can do to achieve sharper pictures.

Here is a photo of a white lined dirona that I took, and a full size enlargement. I was using a Canon EOS-M, 18-55mm lens, shot at f/8, @1/125th, ISO 200, +1 diopter filter, with an Sea&Sea D2 strobe on TTL metering.

[edited to include shutter speed]

You left out a critical parameter - what shutter speed was used?

I shoot mostly in manual mode, fixing shutter speed, aperture and ISO, and letting my flash power vary. Without setting manual mode that way, I end up with shutter speeds as low as 1/30th. Or apertures wide open. (Or ISO 8000...)

I shoot in the fastest shutter speed my strobes can reliably sync at. My camera would normally do 1/250th, but underwater with onboard flash firing strobes I can't get reliable results there. 1/160th is generally as fast as I can go. If there is any ambient, I get a chance at freezing some motion, usually my own. But if the flash contributes all the light, shutter speed is almost irrelevant.

So, besides trying to keep a reasonable shutter speed, here are some more tips:

1. Have your subject centered in the frame. Resolution falls sharply at the edges.

2. Be sure you are achieving proper focus. Didn't say what technique or issues you might have there.

3. When shooting almost anything white underwater, your strobes are likely to blow out a lot of detail. If your camera has a lot of headroom in the files (like my D810), you can pull down the highlights slider in Lightroom (or similar), and a lot of hidden detail may pop out.

4. Don't be afraid of F22 when shooting macro. Or backing up just a bit for better depth of field, and cropping off poor edges.

5. if you are shooting macros, getting a lembeh stick to hold yourself in place against things can be very helpful.

@phxazcraig

Thanks so much for the tips. I shot with 1/125th. I’ll try faster shutter speeds and stopping down further for macro shots like this. There wasn’t much detail left in the highlights in Lightroom, but i’ll tey adjusting the exposure comp on the flash ttl to not blow out the highlights.

What size and resolution are you shooting at?

Obtaining sharp focus is not always easy with macro shots, as tiny movements of the camera can have big effects on sharpness. Stability is easier said than done when floating!

If you're using a strobe, shutter speed is not very important for sharpness as the flash duration is in microseconds, i.e. two orders of magnitude faster than the shutter.

Lenses have an optimum aperture. Generally, diffraction becomes an issue at smaller apertures, so f8 should be safe, but you could do some research to see if there are any issues with your lens. Or just set up a tabletop experiment and shoot the same subject at varying apertures to see if there are apparent differences as you stop down.

I was shooting raw 18MP. Looking again, it does seem that there is more detail that can be recovered from the white tips, but simply adjusting the highlight seems to make the translucent parts too dark. So potentially more work with the curves could help with this...

I was shooting at 31mm zoom. I've attached the full, uncropped image. It sounds like maybe getting closer would help? Or maybe not because it would shrink the depth of field?

It sounds like the blur is most likely coming from camera movement. Is that correct? I was also a little uncertain about the autofocus, since the EOS-M has notoriously slow auto focus, and it can be a bit hard to gauge if it has settled correctly from looking at the live screen through the housing.

The "sweet-spot" for this lens is f/8-11, so maybe going down another stop could help smooth over focus issues.

It's a bit hard to judge anything from the small image size you've posted. You need to look and see if there are some closer areas that are also in focus meaning the DOF is shifted towards you.

I suspect a lot of the issues are related to your movement, it can be very difficult to avoid movement to and from the subject. Consider using a pointer stick to help stabilise yourself and adding a focus light to help out the auto focus. Hold the camera with both hands with the pointer held in your left hand and also holding the housing. Of course watch where you put the pointer. You could try stopping down a little to f11 (equivalent to f18 on a full frame) but don't expect a dramatic improvement in depth of field.

Now that I see the full image and realize how much you have cropped, and with the caveat that I have not used your lens, I suspect you've done about as good as can be expected. First, from that distance, small movements of the camera are less important than when you are 50mm away from your subject. Second, you're shooting through a lot of water. Third, you just can't expect the sharpness of a dedicated macro lens if you're that far from the subject with a kit lens. I have had various Olympus m4/3 systems and I can tell you that moving from the 14-42 zoom lens to the 12-50 with macro switch was a revelation, then moving to the dedicated 60 mm macro was another quantum leap.

Not to say you can't get great results of course. And practice is fun! As a final thought, see if you can borrow a wet diopter to get closer to the subject, and what changes when you do. They aren't that expensive if they do produce the results you want.