Lens sharpness.

Having recently bought a DFA 100 2.8 macro I was immediately impressed with the results. They struck me as sharp. This evening I was experimenting and got rather a shock. I took a picture with the 100, then moved the tripod back and took a similar picture with my beloved DA* 300. Both shots were taken with the lenses wide open and the 100 produced a significantly sharper image.

this leaves me with two questions -

1/. What would others have expected?

2/. Should I be comparing both lenses fully open, or at F4 (their largest common aperture)?

Any thoughts appreciated.

It would be a good idea to post both images, so we can see exactly what you shot.

As a general principle I would expect at close distances both to be sharp, but the 100mm macro to have the edge. However, this shouldn't be an issue in general photography, so seeing the images would be very useful.

No answers but the DA* 300 is a very sharp lens.

Somehow it seems that 50mm lenses are simple to make and the further away you get from that the harder it will be. (Maybe it has to do that 50mm is around neutral magnification, or whatever it is called?)
So yes I would expect a 300mm being less sharp then a 100mm one simply because of that.

I would expect that sharpness would be the over-riding goal of a macro lens, and if another lens was sharper, I would wonder what was wrong with the macro.

G

The easiest lens to make in a range is one slightly longer than a standard, so in 35mm film terms a 58mm is often found for faster lenses in the early days of SLRs.

But all lenses in a range should be sharp.

Um that would have been a good idea John - wouldn't it?

DFA 100

[IMG]http://i217.photobucket.com/albums/cc222/Oggy3323/Flower100.jpg[/IMG]

DA*300

[IMG]http://i217.photobucket.com/albums/cc222/Oggy3323/Flower300.jpg[/IMG]

Thanks John.

Subject is on our mantelpiece so hopefully fairly stationary.

Shots taken using the remote, but I'll have a go with with the two second delay to obviate mirror reaction.

The tripod - - it is a throwback to my OM1 days. I've been measuring up the chimney to see which Manfrottos would fit down it.

The DA* seems to do fine when used for aircraft.

Well yes all lenses should be sharp but relative to their focal length.
Since the further away you move from 58mm the more you need to distort the image to fit on your sensor so to say.
What I'm trying to say is that it's easier to make a perfect 1x magnification then a 10x magnification, I know magnification isn't the right worth but it explains better what I'm trying to say here.

Something there rings a bell Stefan. It's about 35 years since I studied any optics, but the phrase "optical angles subtended" comes to mind.

Oggy diffraction is I believe what I meant, not sure though.
I'm quite sure the angles part has something to do with it.

Here it is link

These were taken on the DA* 300

link

The article Stefan linked to discusses optical principles, but we should remember that photographic lenses are not perfect lenses.

In theory, a lens should be at its best at open aperture, but we know this isn't the case. In practice the various compromises mean that the resolution follows a bell shaped curve - best at middle apertures between f5.6 and f11 depending on the design. At very small apertures like f22 diffraction causes a loss of resolution.

Resolution is the ability to reproduce fine detail and is different to sharpness. All correctly focused lenses should be sharp, but DOF and contrast will affect our perception of this dramatically.

The 300mm shots Hyram linked to show the advantages of a 300mm as a close up lens, but No. 3 is not particularly sharp. This is I think either limited DOF at close ditance or maybe subject/camera movement. At 300mm the slightest movement will show when close up. A 100mm macro is much easier to handle at the required distances.