Macro Lens Image Sharpness

Please, could somebody suggest a practical method of determining the 'sharpness' of a macro lens? By that I mean proving that the image quality is what one would expect of a particular lens namely, in this instance, my Sigma 105 EX DG.

I am well aware that this is not an easy type of lens to use with its critical focussing and extremely short depth of field - even at small apertures. I have seen many superb shots obtained by others with this lens but I seem unable to achieve the level of sharpness I expected - indeed, except for extreme close-ups I get as good or better from my DA16-45mm.

After all, it's no good going back to SRS if my incompetence is the real problem


Roger.

Have a read here. If used at around f5.6 it's optimum aperture you should get excellent sharpness. Try focus stacking at this aperture and then use unsharp mask in photoshop. Have never had any issues with sharpness on this lens.

Hi Roger, are you talking sharpness or Depth of Field? Some sample images may help.

If talking DoF then most macro lenses retain most of there resolution down well beyond f/5.6 my Tamron 90mm will do very nicely at f/16 and I'm sure the Sigma will too, before diffraction sets in and reduces image quality. At such small apertures you may well require the support of a tripod for the slow shutter speeds or some additional light, ring flash etc

The 16-45 will have greater DoF due to the shorter focal lengths involved, is this what you are seeing in your results?

John

John has the answers: stop down a lot, focus stack, plenty of light and a strong tripod so the camera cannot move even a smidgen.

That said, I took this single frame at 1:2 hand-held in available light.

[IMG]http://farm6.static.flickr.com/5184/5635928077_1ddd06b1f2_b.jpg[/IMG]

You need to post some images so we know what your expectations and problems are.

Macro images generally need lots of light so that you can use faster shutter speeds to 'stop' motion, and/or smaller apertures for larger depth of field.

For static subjects like flowers, additional lighting is not always necessary. For bugs, you'll quite often need extra light from a flash and suitable diffuser.

If you have any kind of filter fitted to the front of the lens, remove it for best results.

To actually check the sharpness of your lens you'll need a fancy chart like this one.

This explains all.

Thank you all for your responses, there is a lot in them for me to think on.

JohnWhit: Basically I am talking sharpness, at the same time having looked through scores of (unsatisfactory) shots, I am very aware how difficult it is to separate depth of field from achieving optimum sharpness at true macro! Regarding the 16-45, the comparison here was using the Sigma as a prime (and why not? ). I wanted to make up a reference picture of a large number of different Helebore blooms mounted on wire mesh. I used the Sigma as it was the best quality lens I have. At the same time I duplicated each shot with the 16-45 set up to produce the same image size. There was virtually no difference in IQ between the two lenses.

Robin: My tripod is a fairly rigid Linhof I have used for about 40 years, however I have noticed than when the K20 + 55-300 is mounted thereon, the viewfinder image is seldom absolutely still which I suppose must be ground vibration caused by nearby traffic.....I had supposed this would be largely negated by very short shutter speeds. And as for your picture - in my dreams . I do have some likely images (in fact I have a great many) which I may upload when I find a straightforward way of so doing. Some shots will show that at about 1:4 the Sigma is very sharp - my problems start when attempting to shoot at or near to 1:1.

Mannesty: I suspect such a chart (if I could download it) might answer my original question rather quickly.

I find the 105 quite sharp at 1:1 as well as at lower magnifications.
These are recent examples:
[IMG]http://i156.photobucket.com/albums/t5/Prieni/4%20in%20a%20row/2011-04%20Diagonals/_PRI1539sm.jpg[/IMG]

This one was taken wide open:
[IMG]http://i156.photobucket.com/albums/t5/Prieni/4%20in%20a%20row/_PRI0801.jpg[/IMG]

And this one with aperture closed at 16
[IMG]http://i156.photobucket.com/albums/t5/Prieni/4%20in%20a%20row/_PRI1053sm.jpg[/IMG]

If you want to make sure that the lens is o.k. try setting it up on the tripod and focus carefully. Then do a series of exposures with slightly changed focus distances. If one of them is sharp you know that the lens is ok.
Prieni

If the vibration is visible in the viewfinder then the tripod is not doing its job. It should take a whole lot of vibration to get that much shift. Even vibrations you cannot see will blur the image at high magnifications, so vibrations you can see are way too much to tolerate.

I posted that since it is nothing anyone shouldn't be able to easily do. This was with the Vivitar Series 1 105mm, which is a very nice macro but then again so are many others. If 1:1 is a problem I suggest sticking with 1:2 until you have perfected your technique. Cutting back the magnification by half makes an enormous difference in usability but can still give you some cool images.

The insect was not moving at the it me. Real challenges occur when plants are moving in a breeze (to give one common example).

great shot.

errrr, what is it?

Others seem to have answered your queries already, all I'd add is that the Sigma 105 is a very very sharp lense that your kit lense shouldn't be able to get near !

Two other points for macro, one mentioned already :
1. you need as much light as possible to keep your shutter speeds up otherwise movement blur - even minute - will make your shots suffer. So think about how you are lighting your subjects.
2. Often people suggest MF over AF for macro, however you can have success both ways. In either way digital saves the day and you can take hundreds of shots to get the one you want. This shot was taken by using a rocking motion and keeping that shutter button depressed - as you can see without focus stacking the DoF is absolutely minute !

Ignore the title .... it's a hover fly not a bee !

Thanks Smeggy! For the benefit of the young folk on the forum: This is a book. We used it in the old day to read all kinds of stories and facts. This was, of course, before we had computers, smartphones and tablets. The letters were printed with ink on paper and once printed couldn't be altered (a kind of single use display, it always shows the same content, which may seem a bit pointless these days).

Depicted here is a book seen from the side with single pages folded back to the middle of the book (called spine; that's another term many people these days don't know anymore). The example in the shot, btw. is a PhD thesis in applied physics (not that this really matters).

Prieni

P.S.: Smeggy, I don't think that you are too young to know books from own experience and I appreciate that without any scale it might be hard to figure out what it is. I just couldn't resist

Brilliant

Hi Roger,
I've owned both the 16-45 and Sigma 105 (not DG model) at one time, I found the 16-45 very good, the Sigma was very sharp even wide open at 2.8, in fact I only sold the Sigma because I wanted something slightly shorter to go between a DA-70 and FA-135. Whether the difference would be noticeable in macro work well I don't really know.
It may be worth checking the micro focus adjustment as your camera supports the feature and adjusting accordingly, you would need a test chart for this. The advice offered by others regarding tripod/lighting is relevant, any slight movement at such high magnification will have a major affect on your images.

John

I should mention in passing that it is a myth that macro lenses are sharper than others. People get this impression since they are seeing small things writ large due to the magnification power, but comparing objects at the same magnification tells a different story.

The DA 16-45mm is indeed sharper than the FA 100mm or D-FA macros, for example. Though the sharpest lens in the Pentax line-up is likely the FA43 Limited. (I say "likely" since Photozone has not tested every lens.) The maximum MTF values are 2320, 2100, 2200 and 2420 respectively, though this does not tell the whole story. The FA macro attains this peak at f/8 and the D-FA at f/5.6. Stopped down to a more realistic f/16 the values are significantly reduced.

But intrinsic lens sharpness is by no means as important as your macro shooting techniques. Getting greater DOF puts more of the subject in focus which is preferable to a slightly sharper but thinner DOF.

I cannot compare the Photozone values for the Sigma in question since it was tested on a Canon. However, it came out lower than the Pentax equivalents. Again: not a real issue.