I feel like I've stirred up a hornet's nest with some of my comments about focal length. Especially in when discussed in conjunction with depth of field and perspective.
While focal length is part of the equation for figuring both depth of field and perspective, I think a lot of discussions miss the point and give too much emphasis on focal length. Let's look at each of these separately.
First I'll tackle perspective. I define perspective as the relative distance between objects in a scene. When you work close to your subject items appear spread out with a lot of room around them. You could say that the scene is very open and spacious. An example of this situation could be a portrait of a person holding an object in their hand with their hand stretched forward towards the camera with the camera only inches from their hand. That object, be it an apple, a cup of coffee, a tree ornament, or whatever will appear very large. The person holding their hand out will be smaller, and anything in the background will be tiny.
When you work far away from your subject the items appear to all close in on each other and stack up giving a flattened perspective. We are used to seeing this flattened perspective when we see photos of distant overlapping mountain ranges or a distant image of a city with all its skyscrapers appearing to touch each other.
Focal length gets "blamed" for both of the above scenarios. But the focal length of the lens does not cause these issues. In the first example with the person holding their hand out you have to use a short focal length lens to capture the scene. A longer lens would not have a wide enough angle of view or allow you to focus that closely, so you cannot take this image with a long lens. You could turn that around and say that a short focal length lens allows you to capture that apparently distorted scene. But the lens does not cause that distortion. It is a fine distinction, but a very important one. Consider the following passage from a book, Elementary Photography by C.B. Neblette, Frederick W Brehm, and Everett L Priest that was published in 1936...
"A lens should seldom be used with a film the diagonal of which is greater than the focal length of the lens. This is because with a lens of short focus the image is small. To make the image larger the photographer is tempted to get close to the object, with the result that he gets pictures the drawing or _perspective_ of which looks wrong. This effect is caused by the fact that the objects near the camera are drawn on a much larger scale than distant objects. If the picture is viewed at a distance equal to the distance of the film from the lens when it was taken (in the case of 35mm photography, about two inches), the perspective will not appear distorted."
The problem is, how often do we view photographs from two inches away?
The second scenario is easier to show, as you can take a photo of distant mountains with either a short or a long focal length lens. Try this some time. Put your camera on a tripod and point it towards some mountains or skyscrapers in the distance. Take a photo with a short lens (maybe a 28mm or a 35mm) and then _without moving the camera_ switch to a longer lens (maybe 200mm) and photograph the same distant objects. Afterwards make an 8x12 print from each frame. Make the print from the long lens a full-frame image and enlarge the image taken with the short lens so that the objects are the same size as in the long lens print. You will find that the distant objects have the exact same perspective in each print. The quality of the long lens print will be better because of less enlargement. But the perspective is the same. We tend to use a longer lens for this type of photo because it works out better quality-wise. Not because it gives a different perspective.
OK, that one was pretty easy. Now for the trickier subject. Depth of Field.
Everyone has been taught that a shorter focal length lens gives more depth of field than a longer focal length lens. I don't dispute that. But, that description is only half of the story (maybe 1/4 as the missing part is very important). Let's quote Elementary Photography again. "...the shorter the focal length of a lens, the greater its depth of field." OK, that's a given. But then it goes on to say, "However, if the short-focus lens is brought close enough to the object to give the same size image as the long-focus lens, they both with have approximately the same depth of field." That's the part often dropped off or ignored in discussions. So, what does that mean?
Let's take an example. You have a scene in front of you. There is a park bench in the foreground and a wall with a mural painted on it in the background. You want to photograph someone sitting on the bench to make it appear that they are interacting with something in the mural. Maybe they are picking an apple off a tree in the mural or something like that. Also consider that there is a telephone pole off to one side and the edge of the building on the other side and you do not want to include those elements in the photograph. You initially set up with a 100mm lens and find that by setting the tripod up at 15 feet from the bench you can get the framing you want between the person, the mural, and exclusion of the pole and edge of the building. But you also find out that the bench is far enough in front of the mural that you can't get them both in focus, even if you stop down to f/16. What are your options?
A. You might be able to stop down to f/22 or f/32 if the lens allows it.
B. You can switch to a shorter lens.
C. You can just go for it and hope for the best.
D. You can switch to a shorter lens and move in closer to get the subject to the size you wanted and to try to frame the background the way you wanted.
E. You can move further back.
What happens when you try each of these?
A. Not all lenses will stop down as far as f/32. Some may not go down to F/22. And even if they do, you are now well into having to deal with diffraction. The aperture is so small that the light rays have to bend considerably as they pass by the aperture blades that the quality of the image begins to be seriously degraded.
B. The shorter lens will give more depth of field because the image is smaller (less magnification). But, as noted, the image is smaller. Now that telephone pole and the edge of the building are in the image. You need to crop the image and enlarge it more to make the print. Enlarging it will reduce the quality and will also reduce some of the depth of field that you gained by switching to the shorter lens. Or you can go with it as is and be limited in how large a print you can make. Smaller prints will display more depth of field than larger prints of the same crop.
C. Nothing different happens. This is the original setup.
D. By moving closer to the subject you are increasing the magnification and your depth of field is diminishing. When the subject is the same size in the viewfinder (same magnification) the depth of field is going to be approximately the same, no matter which lens is used. And by moving closer you have altered the perspective relationship between the person and the background, changing your concept.
E. Moving back will give less magnification and greater depth of field. Like in B, you will then have to crop and enlarge the image, sacrificing some image quality. Plus, like in D, by moving the camera (back this time) you now have a different perspective on the scene. The person on the bench will not have the same relationship with the mural in the background. Your grand concept now has to be altered. You will get more depth of field. But you will be making a very different photograph.
Of these options, which is best? B is the only option that maintains your original concept. But you may find out that you have to limit the size that your image can be printed (maybe no larger than a 5x7 print). Or you have to accept that at 16x20 something in the image that you wanted to be in focus (either the person or the background) is going to be soft. The silver lining here is that with a larger print the viewer will tend to stand back and view from a greater distance. So it may all balance out. But you really haven't gained any additional depth of field, you will get about the same DOF results in a print from either lens because the final image magnification is the same.
Friday, January 18, 2008
Tuesday, November 13, 2007
Closer and Closer
It has been a while, hasn't it?!?! Got to start writing again.
Right now I'm going to go back to macro and close-up photography. Something I started back at http://cornicello.blogspot.com/2007/05/which-macro-lens-should-i-get.html
Here I want to talk about the various ways to do close-up photography, especially concentrating on supplementary lenses (sometimes called Closeup Filters).
They typically come in powers or diopters, such as +1, +2, +3, +4
These affect the working distance (distance from the lens to the subject), as opposed to focusing distance (distance from film/sensor to the subject). They shorten the focal length of the lens they are attached to. The shorter the original lens, the less effect. And because they shorten the lens focal length you run into issues like short working distance (no room for lights, too close to some live subjects) and too much background coverage (you see the house next door, the sky, etc., etc.). My suggestion is to use the longest practical lens you can for the situation. Minimum 100mm for full-frame Macro (or 60mm for a crop factor digital camera). But preferably 150 to 200mm. This is so you can isolate your subject from the background. 50mm macro lenses are great for flat copy type work (postage stamps, etc.). But in the field they are generally too short for most situations.
The formula for figuring out the new focal length is 1000/((1000/focal length)+diopter)
Examples:
50mm lens with a +3 diopter
1000 / ((1000/50)+3)
1000 / (20+3)1000 / 23 = 43.5mm
24mm lens with +2 diopter
1000 / ((1000/24)+2)
1000 / (41.7+2)
1000 / 43.7 = 22.8
100mm lens with +1 diopter
1000 / ((1000/100)+1
1000 / (10+1)
1000 / 11 = 91mm
100mm lens with +3 diopter
1000 / 13 = 77mm
No matter what the original focal length of the lens, it will focus at the same distance. At infinity that distance will be approximately 1 meter divided by the diopter power. A +1 lens focuses at 1 meter (~39 inches) in front of the lens. A +2 focuses at 1/2 meter (~19.5 inches). A +3 at 1/3 meter (~13 inches). A +4 focuses at 1/4 meter (~10 inches), etc. You can combine them. For example a +1 and a +3 would equal a +4 and focus at a maximum of .25 meters. You lose distant/infinity focus when using closeup lenses. If you combine closeup filters put the stronger one closer to the camera and don't stack more than two.
As all lenses with the same closeup lens attached focus at the same distances, the longer lenses will show more magnification. But with the increased magnification you run into sharpness issues, especially around the edges of the frame.
Canon and Nikon make dual-element close up filters that are better quality with longer lenses. Canon offers two. The 500D is a +2 diopter and the 250D is a +4 diopter. The names come from the working distance. A +2 diopter lens focuses at a maximum 1/2 meter (500 mm) and a +4 focuses at a maximum 1/4 meter (250mm). They recommend the 250D for lenses from 28mm to 135mm and the 500D for lenses from 75mm to 300mm. The 250D is available in 52mm and 58mm sizes. The 500D is available in 52mm, 58mm, 72mm, and 77mm sizes.
The Nikon closeup filters have names like 0, 1, 2, 3T, 4T, 5T, and 6T. The 3T and 4T are for medium telephoto lenses (like the Canon 250D) and the 5T and 6T work with longer lenses. The 0 through 4T filters are 52mm in diameter, the 5T and 6T are 62mm.
Focusing and composing can be quite different in macro photography than in general photography. If you are interested in reproduction ratios, for example you want to get an image that has a 1:1 size relationship between the subject and the image projected onto the film/sensor) you would set the lens focus for the 1:1 ratio and then move the entire camera back/forward to achieve focus. If you turn the lens's focusing ring you change the reproduction ratio. If you are not as concerned with an exact scientific number, you can combine lens focus control with camera distances. But it may be a little confusing at first. And you have to remember that you will have a maximum focusing distance and infinity focus will not be available.
Other alternatives for close-up photography are teleconverters and extension tubes.
Teleconverters magnify the image while maintaining the same closest focus distance of the lens. So a 100mm lens with a 1.4x converter becomes a 140mm lens, but still focuses as close as it did without the converter allowing you some extra magnification.
Extension tubes move the lens further away from the camera body, allowing the lens to focus on objects closer to it.
Both converters and extension tubes involve light loss, but through-the-lens metering should compensate. Still consider that you will need more light or longer exposures with these. And you can combine them, too.
Macro lenses are the best option if you will be doing a LOT of macro work. Their downside is extra cost. Again, my preference is for something at least 100mm focal length with a full frame camera. With a cropped sensor camera, I would start at around 60mm or longer.
Right now I'm going to go back to macro and close-up photography. Something I started back at http://cornicello.blogspot.com/2007/05/which-macro-lens-should-i-get.html
Here I want to talk about the various ways to do close-up photography, especially concentrating on supplementary lenses (sometimes called Closeup Filters).
They typically come in powers or diopters, such as +1, +2, +3, +4
These affect the working distance (distance from the lens to the subject), as opposed to focusing distance (distance from film/sensor to the subject). They shorten the focal length of the lens they are attached to. The shorter the original lens, the less effect. And because they shorten the lens focal length you run into issues like short working distance (no room for lights, too close to some live subjects) and too much background coverage (you see the house next door, the sky, etc., etc.). My suggestion is to use the longest practical lens you can for the situation. Minimum 100mm for full-frame Macro (or 60mm for a crop factor digital camera). But preferably 150 to 200mm. This is so you can isolate your subject from the background. 50mm macro lenses are great for flat copy type work (postage stamps, etc.). But in the field they are generally too short for most situations.
The formula for figuring out the new focal length is 1000/((1000/focal length)+diopter)
Examples:
50mm lens with a +3 diopter
1000 / ((1000/50)+3)
1000 / (20+3)1000 / 23 = 43.5mm
24mm lens with +2 diopter
1000 / ((1000/24)+2)
1000 / (41.7+2)
1000 / 43.7 = 22.8
100mm lens with +1 diopter
1000 / ((1000/100)+1
1000 / (10+1)
1000 / 11 = 91mm
100mm lens with +3 diopter
1000 / 13 = 77mm
No matter what the original focal length of the lens, it will focus at the same distance. At infinity that distance will be approximately 1 meter divided by the diopter power. A +1 lens focuses at 1 meter (~39 inches) in front of the lens. A +2 focuses at 1/2 meter (~19.5 inches). A +3 at 1/3 meter (~13 inches). A +4 focuses at 1/4 meter (~10 inches), etc. You can combine them. For example a +1 and a +3 would equal a +4 and focus at a maximum of .25 meters. You lose distant/infinity focus when using closeup lenses. If you combine closeup filters put the stronger one closer to the camera and don't stack more than two.
As all lenses with the same closeup lens attached focus at the same distances, the longer lenses will show more magnification. But with the increased magnification you run into sharpness issues, especially around the edges of the frame.
Canon and Nikon make dual-element close up filters that are better quality with longer lenses. Canon offers two. The 500D is a +2 diopter and the 250D is a +4 diopter. The names come from the working distance. A +2 diopter lens focuses at a maximum 1/2 meter (500 mm) and a +4 focuses at a maximum 1/4 meter (250mm). They recommend the 250D for lenses from 28mm to 135mm and the 500D for lenses from 75mm to 300mm. The 250D is available in 52mm and 58mm sizes. The 500D is available in 52mm, 58mm, 72mm, and 77mm sizes.
The Nikon closeup filters have names like 0, 1, 2, 3T, 4T, 5T, and 6T. The 3T and 4T are for medium telephoto lenses (like the Canon 250D) and the 5T and 6T work with longer lenses. The 0 through 4T filters are 52mm in diameter, the 5T and 6T are 62mm.
Focusing and composing can be quite different in macro photography than in general photography. If you are interested in reproduction ratios, for example you want to get an image that has a 1:1 size relationship between the subject and the image projected onto the film/sensor) you would set the lens focus for the 1:1 ratio and then move the entire camera back/forward to achieve focus. If you turn the lens's focusing ring you change the reproduction ratio. If you are not as concerned with an exact scientific number, you can combine lens focus control with camera distances. But it may be a little confusing at first. And you have to remember that you will have a maximum focusing distance and infinity focus will not be available.
Other alternatives for close-up photography are teleconverters and extension tubes.
Teleconverters magnify the image while maintaining the same closest focus distance of the lens. So a 100mm lens with a 1.4x converter becomes a 140mm lens, but still focuses as close as it did without the converter allowing you some extra magnification.
Extension tubes move the lens further away from the camera body, allowing the lens to focus on objects closer to it.
Both converters and extension tubes involve light loss, but through-the-lens metering should compensate. Still consider that you will need more light or longer exposures with these. And you can combine them, too.
Macro lenses are the best option if you will be doing a LOT of macro work. Their downside is extra cost. Again, my preference is for something at least 100mm focal length with a full frame camera. With a cropped sensor camera, I would start at around 60mm or longer.
Wednesday, June 27, 2007
Update on the Bare Images art show
Original blog entry: http://cornicello.blogspot.com/2007/06/legs-2.html
Bare Images show schedule:
Friday Night Preview Party:
7:pm-11pm
Show hours:
Saturday July 7th 10:00am to 8:00pm
Sunday July 8th 10:00am to 5:pm
(I plan to be there on Sunday to meet guests)
Live Life Drawing sessions:
Saturday 11-1pm and 3-5pm.
Sunday 10:30-12:30pm and 2:30-4:30
Bring your favorite medium and Paint, Draw, Sculpt or Photograph (bring along a model release form)
A talk By Prof. Mark Storie on "The nude in art" (Time to be announced)
BBQ and Beverages all weekend
Gift shop (I will have some greeting cards available in the gift shop)
Camping and RV sites
If you have questions regarding the show or if you wish to be on the mailing list for next year contact:
Russ Riddell
(360)420-0786
rrphoenix@netzero.net
Park Info and camping rates contact:
LARC...(Lake Associates Recreation Club)
(360) 445-6833
http://www.larcnudists.com/
Directions: http://www.larcnudists.com/Directions.pdf
Kudos... Raves... Awards...
Just wanted to share some recent comments and awards.
From class evaluations for the Martha Casanave Portrait and Figure class that I assisted in at the Coupeville Arts Center...
"John Cornicello ranks among the best class assistants in my experience. He was equally attentive to both the teacher and the students, was organized and prepared, anticipated what would be needed, and was a pleasure to interact with."
Don't forget that I am teaching an introductory class on how to use your camera at Coupeville in October, 2007.
And from the Seattle Photographic Society... Last night I was given a bunch of year end awards (the club's year is June to May)...
First Merit Award in General Division
Second Merit Award in General Division
Honors Achievement Group for General Division (avg score of 40.9 points)
First People's Choice award in General Division
Photographic Excellence 2006/2007 First Place General Division (avg 40.9 points)
Third Place for total points accumulated in General Division (476 points)
Third Place for "Best General Image/Projected" category for "Aurora Twilight"
Third Place for "Best Nature Image/Projected" category for "Pelicans"
Honorable mention for "Best Creative Image/Projected" for "Savings"
I really wan't expecting all that. So thank you to everyone who voted throughout the year.
You can view the images I've shown at the Seattle Photographic Society meetings on my Flickr stream.
From class evaluations for the Martha Casanave Portrait and Figure class that I assisted in at the Coupeville Arts Center...
"John Cornicello ranks among the best class assistants in my experience. He was equally attentive to both the teacher and the students, was organized and prepared, anticipated what would be needed, and was a pleasure to interact with."
Don't forget that I am teaching an introductory class on how to use your camera at Coupeville in October, 2007.
And from the Seattle Photographic Society... Last night I was given a bunch of year end awards (the club's year is June to May)...
First Merit Award in General Division
Second Merit Award in General Division
Honors Achievement Group for General Division (avg score of 40.9 points)
First People's Choice award in General Division
Photographic Excellence 2006/2007 First Place General Division (avg 40.9 points)
Third Place for total points accumulated in General Division (476 points)
Third Place for "Best General Image/Projected" category for "Aurora Twilight"
Third Place for "Best Nature Image/Projected" category for "Pelicans"
Honorable mention for "Best Creative Image/Projected" for "Savings"
I really wan't expecting all that. So thank you to everyone who voted throughout the year.
You can view the images I've shown at the Seattle Photographic Society meetings on my Flickr stream.
Sunday, June 24, 2007
Art Show coming up in July
On July 7 and 8 some of my prints will be on display (and available for sale) at the Bare Images art show near Mt. Vernon, WA. I will have five 11x14 prints (matted in 16x20 frames) in the show. More information is available at the LARC website.
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