What the eye can see?

[carl geyer]

The final product of a photograph is a print. The gold standard in many member's mind would be a contact print taken with an 8 x 10 large format camera. Many of us know what is needed to produce such a print. But, sadly there are other factors which limit our perception of that final print.

The eye itself is probably limited to 40 to 50 lp/mm. The resolution of a lens is highest at large apertures and deteriorates with smaller apertures. Large format cameras use smaller f-stops to increase depth of field, the diffraction limit is never reached because of the size of the film and, more importantly, camera movements come to the rescue. However, resolution still deteriorates with smaller apertures.

The digital domain. It is diffraction limited. The need for fast lenses is increased. To achieve 40 to 50 lp/mm is feasible, but at a cost. Larger apertures. Usually f/ 5.6 or f/8. Because of the larger CCD size medium format cameras and great lenses may push this to f/11. However, with smaller CCD's depth of field is increased. There is no longer a need for smaller f- stops.

So can the eye see the 40-50 lp/mm with a digital system. The answer is that depends. If the viewer is over age 60 many of us have cataracts. The light reaching the retina is diminished. Why do I bring this factor into play. The answer is because many of us use manual focus lenses. Why spend a great deal of money on camera and lenses if your eyes are rate limited to begin with at whatever age. My answer is a simple one. Have cataract surgery if you need one. I recently had cataract surgery in my left eye. I am a new person.

[Jody_S]

Thankfully I just stocked up on popcorn.

[Jac@stafford.net]

There are so many unclear assertions in the original post that I will just enjoy some popcorn, and maybe a beer, too.

[Mark Sawyer]

The resolution of a lens is highest at large apertures and deteriorates with smaller apertures. Large format cameras use smaller f-stops to increase depth of field, the diffraction limit is never reached because of the size of the film and, more importantly, camera movements come to the rescue. However, resolution still deteriorates with smaller apertures.

I'm not sure where this is coming from. Most LF lenses have an optimum aperture around f/16 to f/32, a relatively small aperture. Diffraction limits have nothing to do with film size. And camera movements don't have anything to do with lens resolution other than moving the film/sensor on and off the plane of focus.

But I'm glad your cataract surgery improved things! :)

[Dan Fromm]

Roast goat, anyone?

[carl geyer]

Diffraction limits are related to the size of the CCD in the digital world. Since there is no CCD that is 4" x 5", I merely stated that there is no diffraction limit for practical purposes. However, if you were to think about resolution in terms of lp/mm at f/16 or f/32 it is significantly less than f/5.6. The eye is many times limited by diffraction limits, resolution and, finally, aging. In terms of popcorn, it is full of saturated fats. That may take the aging part out of the equation.

[Nathan Potter]

OK guys take it easy. This fine fellow sold me a 110SSXL for a fine price. I happened to be in the area of his home with my wife so could pick up the lens in person. Had a nice visit, a hot cup of coffee and a tour of his orchid greenhouse, all greatly appreciated after being on the road for 2 months.

Carl how are you and the greenhouse. What are you using now for orchid photography?

Nate Potter, Austin TX.

[sanking]

So can the eye see the 40-50 lp/mm with a digital system. The answer is that depends. If the viewer is over age 60 many of us have cataracts. The light reaching the retina is diminished. Why do I bring this factor into play. The answer is because many of us use manual focus lenses. Why spend a great deal of money on camera and lenses if your eyes are rate limited to begin with at whatever age. My answer is a simple one. Have cataract surgery if you need one. I recently had cataract surgery in my left eye. I am a new person.

You are right about manual focus lenses. In that respect some of the split screen focusing on good SLR cameras was vastly superior to the focusing on some of the top DSLRs.

As for cataract surgery, I had it about five years ago. Before the surgery my far vision sucked but I had great close vision and could easily focus all of my cameras, including view cameras on the ground glass. Post surgery I have 20/20 + vision at any distance over about twenty feet, but close viewing (and focusing cameras) is a pain in the ass.

If I had it to do over I would probably have put off the cataract surgery for a few years.

Sandy

[carl geyer]

You are right about manual focus lenses. In that respect some of the split screen focusing on good SLR cameras was vastly superior to the focusing on some of the top DSLRs.

As for cataract surgery, I had it about five years ago. Before the surgery my far vision sucked but I had great close vision and could easily focus all of my cameras, including view cameras on the ground glass. Post surgery I have 20/20 + vision at any distance over about twenty feet, but close viewing (and focusing cameras) is a pain in the ass.

If I had it to do over I would probably have put off the cataract surgery for a few years.

Sandy

[carl geyer]

Nathan: The last time I saw you, I had decided that the digital world was and still is an inviting world. I have since purchased yet a third large format system and am toying with going to an 8 x 10 system. I have followed the world of Jack Dykinga. A Nikon D3x, a Nikon 800e and a 4 x 5 system.
Sandy: There are many alternatives to the lenses one can use in cataract surgery. I was born with one eye being 20/20 and far sighted and one eye being extremely myopic. The myopic eye was the one which had the cataract. The lens I have focuses at 15" to 20" and is 20/20. Most people do have lenses that are similar to the one you had implanted. They wear reading glasses. Because of my oddball combination, I have no need for glasses.

[bobwysiwyg]

You are right about manual focus lenses. In that respect some of the split screen focusing on good SLR cameras was vastly superior to the focusing on some of the top DSLRs.

As for cataract surgery, I had it about five years ago. Before the surgery my far vision sucked but I had great close vision and could easily focus all of my cameras, including view cameras on the ground glass. Post surgery I have 20/20 + vision at any distance over about twenty feet, but close viewing (and focusing cameras) is a pain in the ass.

If I had it to do over I would probably have put off the cataract surgery for a few years.

Sandy

I 'm coming up on this now with my right eye. It's difficult to see well under low-light conditions as the pupil dialates putting the edge of the cataract in the field of view. The occasional break with my Nikon F100 is welcome. God bless auto-focus sometimes. :)

[Jac@stafford.net]

Diffraction limits are related to the size of the CCD in the digital world.[...]

Perhaps someone can yea/nay this: "Diffraction is related to absolute aperture size." IOW, an aperture of 8mm diameter will not likely cause significant diffraction. On a 12" lens 8mm might be F/16, while F/16 over a 35mm format would be much smaller, far more susceptible to diffraction.

Carl - good luck with your surgery.

[sanking]

Perhaps someone can yea/nay this: "Diffraction is related to absolute aperture size." IOW, an aperture of 8mm diameter will not likely cause significant diffraction. On a 12" lens 8mm might be F/16, while F/16 over a 35mm format would be much smaller, far more susceptible to diffraction.

Carl - good luck with your surgery.

No, I believe that is not correct. Diffraction is determined by the aperture number itself, not the actual size of the aperture.

There are several formulas for determining diffraction, they vary somewhat based on color of the light. For general purposes I use the formula given in Leslie Stroebel's View Camera Technique, R =1800/f-N, where R = resolution and f-N is the aperture of the lens. For example, the diffraction limit of any lens at f/16 with this formula would be 112 lpm. Not that you would get that much resolution with any lens, but the diffraction limit is such that you can not get more.

Sandy

[Jac@stafford.net]

Thank you, Sandy.

I think the formula you gave has a congruence relation to the focal length. As the focal length grows larger, light rays travel farther to the film/sensor and thus the diffraction is increased. There is an equilibration of the relationship of aperture across focal lengths. Then there is the acceptable CoC.

'nuff to wonder about. I have not made errors due to diffraction since learning how it behaves in actual practice long, long ago.

[paulr]

I'm not sure I understand the original post. This idea of how much resolution we can capture with one system or another is dependent on many things, but directly dependent on the degree of enlargement, which isn't getting addressed. The post also seems to be conflating image quality with theoretical resolution numbers. There are many factors that are more important.



So can the eye see the 40-50 lp/mm with a digital system.

Perceptual science doesn't support these numbers, or anything close to them.

There are two questions implied here, which are not terribly related: what can the eye see, and what does the eye need to see in order to perceive high quality in a print?

The answer to the first question will vary, based on the quality of the eyes, the viewing distance, the lighting, and the contrast of the fine detail in question. In very controlled tests, with high contrast transparent test targets lit from behind, people with excellent eyes have been able to discern detail that would correspond with a maximum of 21 lp/mm at close print viewing distances.

But this has nothing to do with photographic detail, reflected light, and normal viewing conditions. Under these cirucmstances, the finest discernible detail is generally 11 to 14 lp/mm. In most cases, since photographic detail loses so much contrast at high frequencies, the real value is significantly less than this.

But the second questions makes the first question irrelevant. It's been found that we form our impressions of sharpness, detail, and clarity almost exclusively with detail in the 1 lp/mm to 5 lp/mm range at close viewing distances. Detail finer than this doesn't contribute anything. If the finer detail is low in contrast, which is likely, it can actually reduce our sense of subjective quality, because we just perceive it as fuzz, and it can lower the apparent contrast of the 5 lp/mm detail.

In other words, if you make a print with real detail in the 1 to 5 lp/mm range, with this detail rendered at high contrast, the print will look like a contact print. It can in fact look sharper and more detailed than a contact print that actually has more fine detail visible with a loupe.

This perceptual theory is all widely available now, and thanks to digital tools is easy to demonstrate at home.

[carl geyer]

What the eye can see is a very complex question. The number of 40-50 lp/mm is referring to the fovea which maybe as great as 200 lp/mm. Standard eye tests employ a reading distance of 25 cm or 10 inches using the letter e which is equivalent to 5 lp/mm. The retina can make an image at least 3 times per second. It summates these images over time. Resolution of the naked eye is 1'(arcminute) or 1/60 of a degree.:)
Resolution alone is clearly not the entire answer when we look at a print. I listed this reference in another post, but it illustrates in a controlled fashion different imaging systems with the gold standard being 8 x 10 film camera. The apertures were selected to achieve the sharpest imaging possible. I refer you to the article to compare digital systems to film.
http://www.onlandscape.co.uk/2011/12/big-camera-comparison/

[paulr]

1 minute of arc corresponds with 7 lp/mm at 25 cm. This number is the result of viewing tests under specific viewing conditions ... under other conditions you'd see somewhat lower or higher numbers. But you'd never see 5 or 6 times this. Any seeing test takes into account the eye's temporal behavior (and of course the limitations of the eye's lens).

Measurements of the MTF curves of the fovea are interesting, but don't tell us anything about actual vision.

I'm still not sure what you're getting at with all this.

[Doremus Scudder]

.... Sandy: There are many alternatives to the lenses one can use in cataract surgery. I was born with one eye being 20/20 and far sighted and one eye being extremely myopic. The myopic eye was the one which had the cataract. The lens I have focuses at 15" to 20" and is 20/20. Most people do have lenses that are similar to the one you had implanted. They wear reading glasses. Because of my oddball combination, I have no need for glasses.

There's an idea! Lens implants optimized for ground-glass viewing! Of course then we'd all be extremely myopic otherwise and need big progressive-lens eyeglasses for normal functioning. Or, we could do as Carl, and just get one eye optimized for ground-glass viewing and the other for the "everyday" world. But that would make getting reading glasses a bit more complicated...

Sandy, I sympathize, since I was fine for many years viewing the ground glass with just naked eyes except for fine focusing with a loupe. Now I find I need to carry +4-diopter reading glasses with me for ground-glass viewing (and I haven't even had cataract surgery...). I'm pretty used to it, however, and am simply thankful that I live in a time where magnifying glasses are available.

Best,

Doremus