Canon 100mm L f2.8 macro_IS or no IS? Sharpest aperture?

[Cunha]

I´m using a new Canon 100mm L Macro f2.8 lens, with a tripod to shoot a square (25x25cm) print on paper on the floor for reproduction purposes. I´m also using the mirror lockup function to avoid shaking. And a Canon ETTL flash (600 EX-RT).

a) Should I use the IS lens stabilization also?

b) Which aperture is the most sharp and all in focus with this lens?

Thank you very much.

[RobertTheFat]

a) Not unless your studio is located over a subway line or in an area unusually prone to minor earthquakes.

b) Check the specs on the Canon Web site, but it should be around f/6.3 to f/8. "All in focus" doesn't mean much in this context, though, since the subject will be at a single fixed distance from your camera. 

[Cunha]

Dear RTF, thank you for your help.

a) ok .-) I guess the IS is just for handheld work.

b) Thanks too. I´ve been searching for answers and it seems that 6.3 is the sharpest spot fot this lens.

Best regards to Boston .-)

[ebiggs1]

"a) Should I use the IS lens stabilization also?

b) Which aperture is the most sharp and all in focus with this lens?"

A = no

B = f8

[Cunha]

Thanks ebiggs1.
f8 is sharper than f6.3 in your opinion?

[ebiggs1]

Yes.  

[Cunha]

f11 is worst again/diffraction?

[Skirball]

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@Cunha wrote:
f11 is worst again/diffraction?

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Technically, yes.  But the lens is fine at f/11.  I'll go all the way up to f/18 for product photography - where detail counts.  The lens is remarkably sharp and really doesn't suffer from noticable diffraction until f/22 or so.  That said, if I don't need the widest DoF that I can get I usually don't go above f/13.  These are just rules of thumb based off my experience, but it'll give you an idea.  I'd use f/11 without the slighest hesitation.

Edit - I should add that I'm using a full frame camera, so the effects of diffraction are less compared to a crop camera (it doesn't actually have anything to do with the crop, but crop cameras usually have a smaller pixel size, which does affect it).  It's a combination of many things - the lens, the sensor, the AA filter, etc.  I wouldn't worry about it too much, just know if you're too wide open it'll be soft due to the wide aperture, if you close down too much it'll be soft due to diffraction.  Somwhere in the middle is where you like to be.   And all this goes out the window when dealing with fast primes  🙂

[ebiggs1]

Quite possibly you should do some test shots to determine for yourself which is going to meet your requirements.

Most lenses will see f8 as the 'sweet' f-stop. However some don't as all lenses are individuals.

[TCampbell]

Diffraction depends on the camera model... the idea is that as the aperture size is reduced, diffraction causes each "point" of light to actually result in a small spot (not a single spot).  That "circle of confusion" is typically smaller than any one pixel when shooting at low focal ratios so it cannot be detected.  But at high focal ratios, the spot can grow to be larger than a pixel.

For most APS-C cameras, if you're below f/11 then the diffraction is low enough that it's "sub-pixel" level... on the sensor.  Full frame cameras usually have larger photo-sites so they usually get at least an extra stop before they start noticing the diffraction issue.  But it does depend on the specific size of the photo-sites on the sensor.

But that's still not the whole story... because typically most output sizes tend to not use all of the pixels the camera has to offer.  Which means even if diffraction is larger than one pixel on the sensor... it still may not be more than one pixel on whatever your output medium happens to be.

Unless you're using very large output sizes... you probably wont see diffraction issues even at high f-stops.

Also it is a continuum... it's not like you have diffraction or you don't... it's the degree to which you have diffraction.  f/11 is typically not enough for people to notice it because even when it's there... it's probably not enough to be noticeable.