F/18 is just not sharp enough

[JBW]

[Wavelength]

Why , it is very pleasing.....

[Stagecoach]

Not sure what "F/18 is just not sharp enough" is referring to Brian.

Looking at this image I would consider the following before jumping to any conclusions;

a) What is it? (for those of us that do not know)
b) What was the shutter speed?
c) What was the ISO?
d) Has it been cropped at all?
e) Was it exposed correctly?
f) Could it have moved during the shot?
g) What PP work has been done, because there are some 'dodgy' areas?
h) Was it a single shot?

To me it appears there are some 'sharp' bits within the image and some less sharp bits clearly showing halos.

[Mike Buckley]

Agreed with Grahame on everything. Add to his list the question of whether you tried other apertures and, if so, did any of them yield sharper results?

[Stagecoach]

Agreed with Grahame on everything. Add to his list the question of whether you tried other apertures and, if so, did any of them yield sharper results.

That's an important one I forgot Mike, whilst I have not done much macro for a while one thing I always did after having taken the time to set static subjects up was to take a series at various apertures so I had a good choice of IQ/DoF options for PP.

[george013]

Diffraction?

Use the different diffraction calculators. Especially the macro diffraction calculators for they take in account the image distance of the lens.
http://www.photopills.com/calculators/diffraction-macro

I don't know your exact settings/material but it looks like diffraction.

George

[Black Pearl]

There seems to be a lot of other issues going on with that shot before you start looking at the choice of aperture.

At a guess it was shot at VERY high ISO, it was still under exposed so has been lightened dramatically, its a severe crop and it may have shutter speed issues. Diffraction at very small apertures is a problem but more so at full size - once down-sampled for the web it should be biting sharp.

[Tronhard]

I don't know of many lenses that offer a really sharp image at f-18... most seem to have their sweet spot around the f4-f8 range, although in macro work of course one is seeking a great DoF, still if you want the best results you might want to try focus stacking with a more open aperture...

[george013]

I don't know of many lenses that offer a really sharp image at f-18... most seem to have their sweet spot around the f4-f8 range, although in macro work of course one is seeking a great DoF, still if you want the best results you might want to try focus stacking with a more open aperture...

When having a magnification of 1 the effective f-number, based on the image distance, will become double, f36. And that must be used for diffraction calculations.
George

[JBW]

Why , it is very pleasing.....

Perhaps I have developed an improper desire for sharpness

[Cogito]

And possibly a desire to not answer Grahame's questions? Come on! Own up! And Oh! What's it meant to be?

[JBW]

With apologies to everyone my back went out while I was sleeping so this reply must suffice.

It was a 3 frame stack. It was shot in natural light. It was cropped but not scaled up.

Perhaps what I need to remember is that my Sony is an entry level camera that performs very well in the sweet spot but that spot is somewhat narrow?

[Mike Buckley]

That is one heck of a small crop that includes probably no more than 10% of the original file. That in itself would probably explain whatever dislikes you have with the image unless everything about focus and exposure was absolutely perfect in the capture.

I hope your back issue is resolved as soon as possible.

[Cogito]

Brian, you appear to be using a 90mm macro lens on your A58. Nothing at all wrong with the camera and all (that I know of) 90mm macros are excellent lenses. It's difficult to find a Sony Alpha fit lens with a better reputation than any of the lenses you may own.

[Stagecoach]

With apologies to everyone my back went out while I was sleeping so this reply must suffice.

It was a 3 frame stack. It was shot in natural light. It was cropped but not scaled up.

As I suspected Brian there was more to this than the aperture used, it's a hefty crop and has been played with

Perhaps what I need to remember is that my Sony is an entry level camera that performs very well in the sweet spot but that spot is somewhat narrow?

I would disagree with this Brian and associate it with the saying 'a good workman never blames his tools' ! Your kit does not have a sweet spot that is narrow but a sweet spot that then tails off gradually and the results along the way are dependent upon a number of influencing different variables.

As for the diffraction angle which so often is raised with quotes to calculators and theoretical figures look at these which I have posted in the past. Focus was on the vertical hanging curly hair just above the centre of the match head. The image at f/57 was accidentally underexposed by over a stop due to lack of flash power, exposure raised in post, de noised because of this and sharpened slightly more than the other two. The images were not cropped at all.

f/16


f/40


f/57 (min aperture for lens)


Taken with a camera that I suspect has an older sensor than yours and a lens of which some say the Tamron is better

Yes, there are differences but their significance will vary differently to those viewing.

[Manfred M]

Brian - when you start cropping that heavily, you are going to get into resolution issues as you are magnifying a very tiny part of the overall image, so any focus errors and camera movement will be magnified. You are also going to get into issues where you could be getting into lens resolution issues as well - the more you magnify, the more you will push the limits of what your lens can reproduce cleanly.

I think you are pushing the limits very hard here, so I'm not at all surprised that the results are not quite what you are hoping for.

[george013]

Taken with a camera that I suspect has an older sensor than yours and a lens of which some say the Tamron is better

Yes, there are differences but their significance will vary differently to those viewing.

I must admit they're beautiful images. I don't know how much pp was involved.

I just added the diffraction to the list, I missed it.It's a logical thought reading the title of this thread.

The f-number you used is the effective f-number. Again with a magnification of 1 the nominal f-number would be something as 32. The minimum on your lens.
I assumed, Brian didn't mention anything, that the mentioned f18 is the nominal f-number. As far as I know only Nikon gives the effective f-numbers. I could be miss.

It turned out that Brian enlarged the picture very much, he used a crop. That's ok but when he wants sharp images, than he has to calculate with another coc as the standard of 0.020 mm for his camera.

George

[Stagecoach]

I must admit they're beautiful images.

I find that a subject with fine hairs is ideal for demonstrating a real world example for macro sharpness.

I don't know how much pp was involved.

On the f/16 and f/40 examples the only PP was basic image and downsizing sharpening that I use on 95% of all my shots. I use USM figures recommended by a previous member here, Colin Southern.

The f-number you used is the effective f-number. Again with a magnification of 1 the nominal f-number would be something as 32. The minimum on your lens.
I assumed, Brian didn't mention anything, that the mentioned f18 is the nominal f-number. As far as I know only Nikon gives the effective f-numbers. I could be miss.

That is correct, Canon and Sony only indicate nominal aperture. But what is significant on the examples is that they work through a range to a 'minimum' physical aperture that is the same for each lens, Nikon, Tamron and Canon.

It turned out that Brian enlarged the picture very much, he used a crop. That's ok but when he wants sharp images, than he has to calculate with another coc as the standard of 0.020 mm for his camera.

I have to admit I have never undertaken a single calculation with respect to CoCs or even considered it in my macro work

[Mike Buckley]

I find that a subject with fine hairs is ideal for demonstrating a real world example for macro sharpness.

I am going to be doing some experimental macro work soon using rented equipment to determine the best fit with my needs before making a purchase. Your idea about that is very helpful, especially because I probably would not have thought of it on my own.

[DanK]

I agree with Grahame--diffraction is a red herring in this example. Although I have not pushed the limit as far as he has, I routinely shoot at nominal apertures of f/13 at greater than 1:1, and I have gone considerably higher. Most often, the greater DOF has a far greater positive impact an the perceived sharpness of macro images than minor negative impact of diffraction.

I wouldn't go as far as saying that a good workman never blames his tools, but Brian, your tools are fine.

It is really hard to tell from this one severe crop, but the image does suggest to me that the DOF was not as deep as I would want it, because the back of the spotted piece is in focus but the front appears not to be. Brian, given that you are stacking, the solution in my opinion is not a smaller aperture. It may be that you had too few images in the stack, or that they didn't have an optimal difference in focus. I generally shoot my flower stacks at f/7.1 or 8.

Mike--If you are going to be doing studio work, any reputable macro lens should be sharp. IMHO, the main issue in studio work is working distance (because of lighting and limits on the size of your working space). In addition, if you want high magnification, the amount of magnification from any length of extension is inversely proportional to focal length. I have done all of my studio work with 60mm and 100mm lenses. I always use 100mm with my full frame (my 60mm won't fit on it), but I used both when I did this work with a crop sensor.