I actually started this thread writing "CoC" and replaced it with "Airy disk" before publishing. My problem with using CoC was that the term is used for depth of field analysis and I wanted to direct the thinking toward downsizing improving sharpness due to diffraction effects, not considering depth...

Nice comparison of the different methods. Most of the programs I would use to down-size an image have no obvious way of changing the sampling method. What method would be used in, for instance, Canon's Digital Photo Professional, the free software that comes with Canon cameras? That's generally what...

While it's always possible to speculate about "effective DOF", "effective diffraction limit" and so on, if I were developing some sort of terminology for describing this situation, I'd always use "system, limited by ..." term to describe it in general. All games about reduction of image resolution ...

Can you explain what you mean by this? "the underlying optical physics are not mapped, just their effects" Sure...once the image is recorded as digital data, the connection to the optical domain ceases. The principles of optical physics no longer apply to the image; only the principles of the digit...

No pushback there. Very few photography forums are sophisticated enough to worry about the details, just the outcome. Not being an Optical or DSP engineer, I started this thread to make sure I was describing the sharpening effect correctly, and to make sure my presumption of the underlying physical ...

I don't mind bringing in DLA to explain the issue, but I don't think I want to lead with it since it always brings up lots of questions and is a controversial topic. DLA is just the onset of diffraction softening, yet the words imply that the image is diffraction-limited, which is not true. I also p...

Sure, just the other way to look at it. To you, OK. But to me, the words "Apparent Effective Aperture" immediately suggest that there must be something like "Apparent DOF". Can you tell me what that is, and how it is affected by downsizing? --Rik Your point is well taken. If anything, the sharpenin...

Now, does this make sense? I assume that DLA means Diffraction Limited Aperture. If so, then what you're trying to do makes sense, but the way that you've been talking about it has made you sound FOS. Even this latest explanation seems roundabout, requiring a new term and all. Here's my proposal fo...

I know it's not the same, and it's not strictly correct to use the optical terms, but I am indeed trying to relate the downsizing effect on image sharpness to the original optical system that created the image to explain/guide a downsizing philosophy versus effective aperture. A relevant factor that...

Yes, you are of course not affecting the original optics at all. I suppose it's the same as replacing the sensor with another sensor of 1/4 the number of pixels but the same physical size. But isn't it also the same as changing the eyepiece of a microscope from, say a 10x to a 5x? Doesn't this chang...

I've been making statements on another forum and want to make sure I'm not FOS... When an image is downsized, my presumption is the effective aperture is increased. For instance, if the image is taken at nominal f4 at optical 2x magnification on a 6000x4000 pixels sensor, the effective aperture is f...

I think I have a SK 90mm f4.5 HM. Not sure, looking for a picture on ebay, I found they do/did an Artar 1:1. Never heard of that one! http://www.ebay.co.uk/itm/Schneider-75mm-f4-HM-APO-Artar-MC-1-1-Lens-743-/141640163759?hash=item20fa6961af:g:j-wAAOSwBahVMGNW I've been looking at that one for some ...

Ray - any particular reason why there are no Schneider enlarger lenses in the group? It's not really intentional, just that I don't own any in this focal length range. I have purchased several in the past, but each one had problems and had to be returned. I have had very poor luck getting good exam...

ray you seem to have interpreted my post as recommending an $1100.00 lens..., I suggest you read my post again... I was suggesting beginner coin photographers look at slightly more expensive enlarger lenses( US$200- $400) they perform very well with out stacking. A number of years ago I tried you a...

I take your point that most coin collectors may want to take small sized photos for ebay or keeping a record of coins. That still doesn't change my view that a much higher quality enlarger lens will be far better value for money as those same collectors will probably not be focus stacking Thanks fo...