Macro using high megapixel cameras

[pnodrog]

Now I am confused. I think DOF limitations are linked to diffraction by their shared correlation with aperture. Here is how I think of this. Someone tell me if I am wrong.

First, let's hold print size, viewing distance, eyesight, and sensor size constant to get a minimal contrast: higher vs. lower pixel density, and therefore smaller vs. larger pixels.

Pixel size is negatively correlated with the physical aperture at which a lens becomes diffraction-limited: the smaller the pixels, the larger the aperture at which diffraction limits resolution. OK so far?

So, if you want to limit yourself not to shoot at narrower apertures than those at which diffraction becomes a factor (a limitation I don't impose on myself), moving to a sensor with smaller pixels means imposing a larger maximum aperture (smaller f-stop number). This will give you narrower DOF.

What am I missing?

Semantics is the problem. As you point out in practice there is a point at which stopping down to increase DOF will not help because the softening by diffraction becomes unacceptable. Yes they relate to totally different effects but they do have a shared factor. Depending on reproduction and viewing distance it is possible to increase DOF by reducing aperture beyond the point at which diffraction can first be resolved by the sensor. Hence the calculator Manfred provided a link to.

[chauncey]

It is often said that lenses perform their best if stopped down several stops above wide open...why?

[Dave Humphries]

It is often said that lenses perform their best if stopped down several stops above wide open...why?

Because the design and manufacture of anything involves compromises.

Think of it like Depth of Field;
If they made it work best wide open, it would all be downhill (in one direction) from there.
If they make it 'best' in the middle, you get the roll off from 'best' equally either side of that.

HTH, Dave

[xpatUSA]

It is often said that lenses perform their best if stopped down several stops above wide open...why?

Bob Atkins explains it it well:

The optimum aperture of a lens, i.e. the aperture at which it is sharpest, varies from lens to lens, but as a general rule it's between 1 and 3 stops down from the maximum aperture for the center of the field. Why is this?
First you have to understand that no lens is perfect. They all have aberrations which reduce their performance. Classically there are five so called "Seidel" aberrations. They are sometimes called third order aberrations based on the mathematics used to model them. They are:

• Spherical aberration
• Coma
• Astigmatism
• Field curvature
• Distortion

All lenses have these aberrations and they are worse in fast lenses. Stopping down a lens greatly reduces Spherical aberration and to a lesser extent reduced the effects of Coma, Astigmatism and Field curvature on image sharpness. Distortion is unaffected by aperture. A 6th aberration, Chromatic aberration, is to a first approximation unaffected by aperture too.

More good stuff here:

http://www.bobatkins.com/photography...ffraction.html
.

[Bear]

Because some lenses are not uniformly optically correct from the corners to the best optical characteristics of the center portion of the lens, when you make the aperture smaller you are eliminating the lesser optically correct part of the lens and selecting the better part of the middle, therefore comes the old stop down for sharpness assumption. Stopping down, of course, reduces the amount of light that can pass through to the sensor which brings on another set of problems such as higher ISO, lower shutter speeds, etc.

Some of the newer lenses, such as the new 100-400 II, has optically correct lenses from the center to the corners giving consistent sharpness from wide open to the small apertures. Old habits die hard, so as I learned to forget the old stop down for sharpness ditty and just shoot at the aperture applicable to the light and the desired image, it was liberating.

The main thing with the 5DSR is not to motion blur the tiny pixels which will give you soft images and negate the advantages of the higher resolution, meaning the newest IS systems and half to double the shutter speeds you would use with a lower res camera. The 100-400 II gives you the newest 4 stop IS technology, MFD of about 3 feet, magnification of .71, optical excellence, 100-400mm zoom for working room, etc., make it great for macro. The EF 100 f/2.8L IS Macro with 4 stop hybrid IS is another one to look at.

My experience with the 5DSR is that it is easy to use and will bring out the best of any lens you clap on it, but naturally the better the lens, the more you will get out of the camera. I think most good lenses will out res the camera. It is more a matter of selecting the lens for your application, but particularly your technique in consideration of the tiny pixels that will give you success.

[chauncey]

Aha, now I get it...sort of a CYA for "within specs".

[pnodrog]

Semantics is the problem. As you point out in practice there is a point at which stopping down to increase DOF will not help because the softening by diffraction becomes unacceptable. Yes they relate to totally different effects but they do have a shared factor. Depending on reproduction and viewing distance it is possible to increase DOF by reducing aperture beyond the point at which diffraction can first be resolved by the sensor. Hence the calculator Manfred provided a link to.

Before the above is picked on I would like to add a caveat.

As mentioned above you may gain some meaningful DOF by stopping down even beyond the point at which the diffraction can first be detected.

BUT even the parts of the image that are well and truly in focus will become progressively softer.

Initially applying additional sharpening by increasing the threshold etc may offer an acceptable comprise.

[William W]

My current lenses of choice mounted on my Canon 1Ds3 are a 300mm f/2.8 or a 180 macro...both are noted for great MTF tables.

I don't think either DOF or resolving power will be much of an issue. If the sensor outresolves the lens, you just won't get all the additional detail that the sensor can offer.

The EF180 F/3.5L USM and the EF 300 F/2.8L IS USM (I assume the 300 is as IS lens) are good lenses, no argument.

But each was built upon science and technology and (probably most importantly) to meet the resolving capacities necessary in 1996 and 1999 (respectively) and if your 300 is not an IS Lens, then that's 1987 technology.

A considered point is that according to Canon Technical Support: it is NOT a question of 'if'' you will not get the resolving power to meet the 5DS /5DSR from the two lenses that you mention, the salient point is: you won’t.

The question for you to consider is about how much of an issue will be the incapacity of your lenses.

To assess any difference you’d really need to do or source an A/B with the 180/3.5 and one of the 100/2.8 and another A/B with your 300/2.8 and the 300/2.8 MkII IS.


I don't mind how you spend your money and in this respect I agree with Manfred: "Just enjoy your new toy if you end up getting it and stop worry about the details."

But I merely re-iterate the mention of the list of lenses Canon recommend for the 5DS / 5DSR, because you specifically asked a question that would involve picking nits and as a consequence this conversation has evolved where it seems there certainly is not being equal weight placed upon all considerations.

To put it another way, (as Manfred already mentioned) there is much picking nits about one issue of cropping and DoF and seemingly much less addressing the issue of initial resolving power of the lenses you will be using.

To my thinking that’s inconsistent.

In my opinion is also not Objective Thinking especially as we are discussing Marco work, where getting "all the additional detail" seems to me to be a very good initial concept and one of the cornerstone premises for making a purchase choice of a 5DS / 5DSR . . . specifically for Macro Work.

WW

[george013]

In my opinion is also not Objective Thinking especially as we are discussing Marco work, where getting "all the additional detail" seems to me to be a very good initial concept and one of the cornerstone premises for making a purchase choice of a 5DS / 5DSR . . . specifically for Macro Work.

WW

But with lenses that suit the pixelsize of the new camera.

Not so much heard, using a sensor with a lot of pixels to get a crop with many pixels means you have to choice for another CoC, meaning another DOF and another diffraction limitation. Also when shooting a 1:1 macro means you must recalculate with a double f-number. So f16 becomes f32.

George

[dem]

Thanks all...great points to consider...especially the DOF limitations due to diffraction.

A subtle point. Both excessive drinking and wearing wrong glasses can make ones vision blurred. That does not mean that wearing wrong glasses makes you drunk.