|
|
|
|
|
#1
12-30-2007, 05:31 AM
|
||||
|
||||
Go
Here is a link on photog glossery terms:
http://www.floccinaucinihilipilifica...raphy:Glossary I think that there may be some confusion regarding f-stop verses focal length or maybe focal plane? Depth of Field Depth of Field refers to range of distances such that elements are in focus. An image with a narrow depth of field has a very small amount in focus. An image with a large depth of field has a lot in focus. f-stop The f-stop is the unit of measure for the aperture. The f-stop is the the size of the aperture expressed as a fraction of the focal length of the lens. This is why some zoom lenses have different minimum f-stops based on the amount zoom. An f-stop of f/16 (f being the focal length), means that a 200mm lens has an aperture openning of 200/16 = 12.5mm. A 18mm lens has an aperture openning of 18/16 = 1.125mm. For a given f-stop any lens, regardless of focal length, transits the same amount of light to the sensor or film. Focal Length The focal length is the distance from the front element of a lens to the sensor (or negative). The focal length can be used to describe the effect that the lens has on the produced image. A long focal length (say, 50mm and up) make objects look closer (like a telescope). Short focal lengths (24mm and smaller) capture a wider view, making object smaller. Lenses with short focal lengths are sometimes refered to as wide angle. As you can see the focal length does have an effect on magnifying the object , however a macro lens will still allow the lens to be positioned closer to the object. I still stand my ground on that DOF is greatly controlled by the f-stop or aperature setting. Try shooting with your DSLR on Aperature Priority and set it to f/2.8. Focus on a subject 4 ft away from you with some background objects. Take a the shot. Next, set your aperature to f/22 and focus again on the same subject. Take a shot. Compare the 2 shots and I can gaurantee you that your DOF difference will be huge, not just cm but in ft. At f/2.8 your focus will only be for the first few feet. At f/22 the focus should be from the subject to infinity. Therefore DOF is largely controlled on by the f-stop. Jason, I'm trying to understand your point. Is there another way of explaining what you are talking about? ________ silver surfer vaporizer Last edited by Gooly001; 01-25-2011 at 05:01 AM. 
|
|
#2
12-30-2007, 05:17 PM
|
|||||
|
|||||
|
I think we have gotten way off topic and I feel bad for highjacking Kyle's thread
But we are talking about 2 different situation. A True Marco photo taken so that the image is 1/2 the oringonal size or greater relys far less on f-stop then magnification as discribed by this equation DOF~2NC[(M+1)/M2] Sorry hard to write in text it should be M squared J
|
|
#3
12-30-2007, 06:11 PM
|
|||||
|
|||||
|
pm sent, hopefully I can help out.
Some general info for D70 owners. I have had my D70 for just over 3 years now and have taken a few photography classes in that time. One of the instructors had a D70 also and said that they have basically been recalled, and you can take it into Nikon in Richmond and they will fix it for free. I got mine in New York so I am not eligible but can pay for the upgrade but have not just yet. I don’t recall the exact problem it was having but they have problems with different flash cards like Lexar. It’s been quite some time since I heard this so I would contact Nikon directly to clarify.
|
|
#4
12-30-2007, 06:17 PM
|
||||
|
||||
|
Go
Jason,
I agree about the highjacking of the thread, so if you would like to further pursue this we can start another thread on this subject of photography technical formulaes. I am assuming that this is what your point is regarding: "Close-up When the subject distance s approaches the focal length, using the formulae given above can result in significant errors. For close-up work, the hyperfocal distance has little applicability, and it usually is more convenient to express DOF in terms of image magnification. Let m be the magnification; when the subject distance is small in comparison with the hyperfocal distance, \mathrm {DOF} \approx 2 N c \left ( \frac {m + 1} {m^2} \right ), so that for a given magnification, DOF is independent of focal length. Stated otherwise, for the same subject magnification, all focal lengths give approximately the same DOF. This statement is true only when the subject distance is small in comparison with the hyperfocal distance, however. The discussion thus far has assumed a symmetrical lens for which the entrance and exit pupils coincide with the front and rear nodal planes, and for which the pupil magnification (the ratio of exit pupil diameter to that of the entrance pupil)[4] is unity. Although this assumption usually is reasonable for large-format lenses, it often is invalid for medium- and small-format lenses." Now I'm not a very formula oriented type of guy and I'm sure a lot of people here viewing this thread isn't either. But if you could explain in laymen's terms on how the formula will help in understanding macro photography better, it would be greatly appreciated. At this point, I've figured myself to be a decent photog and actually took 2 years of photography school but frankly you've gotten me quite confused. From my understanding of photography, and there are many links that I've provided to support my claim, f-stop DOES play an important role in DOF. Other factors that influence DOF are: Focal length Subject distance Film or Sensor format Here is another website that explains my theory in laymens terms with photo samples: http://www.dpreview.com/learn/?/key=depth_of_field All lenses have the ability to allow you to change its' aperature therefore allowing you to control the amount of light entering the lens. Because of this control, it causes the lens to change its' point of focus due to the adjusted lens elements focusing onto the film or sensor plane. The smaller the aperature ie f/8-f/22 the greater the focus range. The larger the aperature ie f/1.4-f5.6 the shallower the focus range. Please correct me if I am wrong here. Macro lenses are specialized lenses that are constructed in a way that allows the photographer to get closer and focus closer to an object that most conventional lenses will not let you. True macro lenses also magnify at a ratio of 1:1 meaning that the lens will reproduce the image to full life size as the photographer is seeing it through the lens. Some lenses advertise that they are macro but are only 1:2 meaning that they will focus close but will only magnify half the life size of the object that it is focusing on. Please correct me here if I am wrong. Wider lenses ie 28mm have greater DOF sometimes up to f/32 however they also have an aperature ring that will allow you to control DOF. Meanwhile telephoto lenses may have shallower DOF but most have minimum of f/16. You are saying that the higher the magnification the greater the DOF? Is there something else besides a formula that can explain this? From my experience shooting with a prime Nikon 105 macro f/2.8 and a Nikon macro 80-200 f/2.8, I can tell you that I see a difference in my DOF when I am shooting aperature priority. Do I know the manufactures specifications on how my lens works, No. All I know is that I control light entering my camera so that I can take a photo but manipulating the lens' iris and my cameras' shutter. Because of this manipulation, there are other factors that need to be considered ie DOF, Bokah, Cirlce of Confusion etc...Unless you are striving to become Annie Lebowitz or the next Ansel Adams most amateur photogs just want to know what they can do to take a better photo. A formula with no explanation will not help them IMO. Photography is best learned through trial and error. Formulas in my opinion does not really help in understanding how the camera and lens work together. ________ BMW R47 Last edited by Gooly001; 01-25-2011 at 05:01 AM.
|
|
#5
12-30-2007, 06:38 PM
|
|||||
|
|||||
|
Quote:
Half way through this thread I realized that what I'm talking about only relates to Marco photography where the subject is being exposed at a ratio of 2:1 or greater. Meaning the exposed image is 1/2 the size of the original or larger (the Image is actually larger than the original subject). For example if you where to take a picture of 1 polyp of an SPS or LPS and fill the frame with that polyp the actual image would be larger than the subject. The closer you get to a 1:1 ratio the less F-stop effects DoF. So in reality with the tank glass and the distance from the class to the subject it would be very uncommon to get such an instance where this would play a significant role. But having said that. A true macro lens does not react the same way your standard 50mm or what ever does in terms of DoF. the Classic DoF experiment would be to take a standard lens and stand at a picket fence. focus part way down the fence and then take exposures adjusting the aperture between each frame. This shows the effect of DoF. Now if we were to shrink this test and say set up dominos on the floor and perform the same experiment with a Marco lens you would never achieve the same degree of DoF regardless of f-stop. Just for some background I too took photographic sciences in school. But instead of taking pictures we built emulsions on glass plate, Built lenses and shutters. then created images from what we constructed. I still work in the industry but gave up on shooting years ago. J
|
|
#6
12-30-2007, 07:08 PM
|
||||
|
||||
|
Go
Quote:
Regarding the limited DOF when you are shooting at 1:1 ratio. You are right in saying that f-stop does not affect the DOF because there is no longer a DOF. Because the object is taking up so much of the frame there is nothing else in the frame that would give you the ability to see the difference it makes in DOF. You are simply so close that only the closest object is in focus filling up the entire frame. You only can see the DOF difference if there is something else that is in the frame that is further of closer then the object that you are photographing. So your example of filling up the frame with only one polyp and having no DOF is correct because only that one polyp will show up as being focused, there is nothing else in the photo. All that I am trying to communicate is that a 50mm non macro and a 50mm macro both shot using your picket fence example will produce the same result if all the variables are considered the same. ie subject distance and point of focus and aperature/shutter value. ________ Suzuki GS500E Last edited by Gooly001; 01-25-2011 at 05:01 AM.
|
|
#7
12-30-2007, 10:38 PM
|
||||
|
||||
|
But what are the results using his domino example? It seems to me you two are on different pages and almost talking about different things.
If you have a magnifing glass and put your hand at a right angle to it and focus on the first finger....is the fourth finger out of focus or is it DOF? Scott
|
|
#8
12-30-2007, 10:51 PM
|
|||||
|
|||||
|
Quote:
Since this was not the main focus  of this thread. Maybe we could focus again on Kyle's original concernJ
|
|
#9
12-31-2007, 03:40 PM
|
||||
|
||||
|
Quote:
__________________
If it is alive, I can most certainly kill it
|
Hybrid Mode
