Im considering the Tamron AF 18-270mm F/3.5-6.3 Di II VC LD Aspherical (IF) Macro vs Nikkon 18-200mm, as such does the additional 70mm from the Tamron actually makes a difference in terms of quality against nikkon at maximum zoom. This is mainly used outdoor in the day for scene, cars and street candid with occasion of night shoots.
Is aperture impt for High Power-Zoom lense?
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If you're in need for the range, then go with the Tamron. but note that the Nikon has VR which may help a bit esp if you're not tat steady yet.
i notice a lot of garbage among the various answers in here.
anyway, answering the first post:
the only reason why aperture or rather low aperture setting is required, as aperture control the depth of field, or rather simply to selective focus in or out of the subject. it doesnt matter using zoom lense or whatever "prime" lense or whatever "high-power" .. bokeh is often associated with aperture, however it does not make sense to mention about it here.
anyway, answering the first post:
the only reason why aperture or rather low aperture setting is required, as aperture control the depth of field, or rather simply to selective focus in or out of the subject. it doesnt matter using zoom lense or whatever "prime" lense or whatever "high-power" .. bokeh is often associated with aperture, however it does not make sense to mention about it here.
Yes the smaller F-stop mean more light it also mean a thinner field of depth. Thinner field of dept would be useful when u wanna isolate yr subject from the background with bokeh (blur)
To better understand f-stop value, f-stop is a ratio between the diameter of the aperture in the lens and the focal length of the lens..The smaller the f-stop number the bigger the diameter of the lens.
To better understand f-stop value, f-stop is a ratio between the diameter of the aperture in the lens and the focal length of the lens..The smaller the f-stop number the bigger the diameter of the lens.
The smaller the f-stop, the larger the aperture?
http://en.wikipedia.org/wiki/Exposure_(photography)
yea... the smaller the f-stop number the bigger the "hole"
maybe said hole is easier to understand for guys:bsmilie:yea... the smaller the f-stop number the bigger the "hole"
My sifu Nakedtoes.. reaaly knows how to explain clearly ..
:nono: Not true... DOF is not the only reason for a low aperture setting... Actually IMO there are several questions raised by the TS's original question, "Is aperture impt for High Power-Zoom lenses?":
1. What is aperture? This is the opening or 'hole' through which light passes.
2. How is aperture measured? Using the f-number, which (as nakedtoes explained), is the ratio between the diameter of the lens aperture and the focal length. Smaller f-number = bigger aperture = faster/brighter lens.
3. Is aperture important? YES. There is onlyone substitute for a large aperture: an even larger aperture... ;p
4. Why is (large) aperture important? For four reasons:
(a) A larger aperture means more light reaching the sensor. As weixing explained, this usually means (i) can use faster shutter speed = capture moving subjects better + reduce effects of camera shake; (ii) can use lower ISO = less noisy image; and/or (iii) can shoot in lower light = more able to capture pooly-lit subjects.
(b) A larger aperture means a thinner depth of field. As zac08 and nakedtoes say, this allows you to isolate a subject better. A fast (large aperture) lens can always be stopped down to give a large DOF; but a slow (small aperture) lens cannot be opened up to give a thin DOF!
(c) A larger aperture means a brighter image on the viewfinder and sensor. Allows you to see better, and as DeSwitch mentioned, allows the camera to autofocus better.
(d) A larger aperture lens usually means it's larger, heavier and more expensive. They're larger because of the physics involved (in getting more light through the lens). They're heavier because it needs to be larger (= larger pieces of glass). They're more expensive because they are more complex to design (= pay more to engineers!) and more expensive to build (= more difficult to make an optically-good piece of lens that's also large).
5. What are "high power zoom lenses"? Not sure what the TS is referring to, but could be either (a) super-zooms / large zoom ratio lenses, e.g. 18-200, 18-270; and/or (b) zoom lenses that reach the telephoto range, i.e. 70mm and beyond.
6. Is aperture important for "high power zoom lenses"? Well, aperture is important for all lenses. Why? See point 4....
A fast (large aperture) lens gives you more options (higher shutter speed, thinner DOF, etc), but it will cost you more in terms of money, size and weight!7. What do the f-numbers mean on a zoom lens? If a range is given (e.g. 70-300mm f/4.5-5.6), this means at 70mm the largest aperture is f/4.5 and at 300mm the largest aperture is f/5.6 = "variable aperture zoom". If only one number is given (e.g. 70-200mm f/2.8) then it means the lens can be opened to f/2.8 throughout the entire zoom range = "constant aperture zoom". In general, constant aperture zooms are larger, heavier and more expensive than variable aperture zooms in the same zoom range.
There are a few other related issues, but not directly dealing with aperture size...
(1) What is the relationship between high zoom ratio and aperture? As giantcanopy pointed out, a constant aperture lens with a large zoom ratio would be "too heavy, bulky and expensive". Not only that, high zoom ratios (e.g. 18-200mm) always compromise on image quality. Why build a large, heavy, expensive constant aperture lens that can't take pictures with good image quality?
(It's like putting a 900 cc engine into a Porsche.)(2) What is the relationship between the aperture size, DOF, and quality of bokeh? Two issues here. A 50mm lens at f/1.4 will give less DOF than at f/8 - this is a quantitative measurement. You can calculate this objectively in millimetres, centimetres, metres, etc. But how 'nice' the bokeh is a qualitative and mostly subjective measurement. What is 'nice' bokeh to one person may not be 'nice' to another. Having said that, why do large aperture lenses usually give 'nicer' bokeh? Well, quality of bokeh depends on several factors: DOF, lens design, number of blades used for the aperture diaphragm, shape of the aperture blades... Mirror lenses are cheaper, but tend to give ring-shaped bokeh. More blades in the aperture diaphragm usually mean a nicer bokeh (because the opening is more circular). Curved blades usually mean a nicer bokeh (because the opening is more circular). But more blades and curved blades = more cost. So, no point designing a fast lens with a large aperture, and then use a poor/cheap aperture diaphragm design. That's why fast lenses usually have a nice bokeh: not only because of the large aperture, but because the manufacturers have put in a good aperture diaphragm design.
(3) What is the relationship between shutter speed, moving subjects, effects of camera shake, vibration reduction/image stabilisation, and aperture? High shutter speed = 'freeze' moving subjects + reduce effect of camera shake. If you have steady hands (i.e. not much camera shake), you can use a slow shutter speed and photograph stationary subjects, but you will not be able to 'freeze' moving subjects. Similarly, if you have VR/IS on the lens/camera (i.e. reduce effect of camera shake), you can use a slow shutter speed and photograph stationary subjects, but VR will not help you to 'freeze' a moving subject! The only way to 'freeze' a moving subject is with a high-enough shutter speed. That's one reason why there's no substitute for aperture: in poor lighting, with your ISO at maximum, the only way to capture a moving subject with a high-enough shutter speed is to use a larger aperture.
Okie, these are my $0.02 on this topic....
:nono: Not true... DOF is not the only reason for a low aperture setting... Actually IMO there are several questions raised by the TS's original question, "Is aperture impt for High Power-Zoom lenses?":
Okie, these are my $0.02 on this topic....
An excellent overview of "Aperture", thanks.
Indeed a very comprehensive coverage on aperture..
Actually, I was wondering, is there a way to measure bokeh "quantitatively"?
As in, by looking at the focal length and aperture opening.
If we have a 50 f/1.8 and 50 f/1.4, we can tell that the f/1.4 will give more bokeh, because it has a larger aperture.
But suppose we have a 50 f/1.4 and 85 f/1.8 lens.
How can we tell which one will give more bokeh?
One has a larger aperture, but the other has a longer focal length.
Another factor that affects bokeh is the focusing distance.
So let's assume that the focusing distance is in such a way that the object fills the same size in the frame (that means, closer with the 50 lens, and a bit further with the 85 lens).
Actually, I was wondering, is there a way to measure bokeh "quantitatively"?
As in, by looking at the focal length and aperture opening.
If we have a 50 f/1.8 and 50 f/1.4, we can tell that the f/1.4 will give more bokeh, because it has a larger aperture.
But suppose we have a 50 f/1.4 and 85 f/1.8 lens.
How can we tell which one will give more bokeh?
One has a larger aperture, but the other has a longer focal length.
Another factor that affects bokeh is the focusing distance.
So let's assume that the focusing distance is in such a way that the object fills the same size in the frame (that means, closer with the 50 lens, and a bit further with the 85 lens).
Hmmm.... There are some ways of 'quantifying' bokeh, but not really using the focal length and aperture size as you suggested. For example, you can look at the out-of-focus areas of the picture, and look at the OOF 'discs'. These may be uniformly bright, brighter near the edge, or brighter near the center. A related 'measure' is whether there double-lines seen in areas where there are straight lines. These characteristics can be different for objects in front of or behind the object in focus (depends on the lens design). But which one gives the 'nicest looking' blurry areas? It really depends on what kind of photo you are taking, and also on personal taste. This is the 'subjective' bit about bokeh. What may be 'nice-looking' bokeh for one person may be 'unacceptable' bokeh for another.
Here are some links that discuss more about bokeh (but be warned they don't always agree with one another!! ;p):
http://en.wikipedia.org/wiki/Bokeh
http://www.rickdenney.com/bokeh_test.htm
http://www.luminous-landscape.com/essays/bokeh.shtml
Erm, I don't think you can really 'quantify' bokeh by saying 'more' or 'less' bokeh.... ;p Basically the 'bokeh' refers to the parts of the picture that are out-of-focus; the OOF areas contribute to the overall 'bokeh' of the picture.
From the example you mentioned (50 f/1.8 vs 50 f/1.4) I'm guessing that when you say "give more bokeh", you mean that more of the picture will be out-of-focus. If that's what you mean, then yes, 50 f/1.4 can create more OOF areas -- but this is because f/1.4 gives you thinner depth-of-field.
Again, I think what you're actually referring to is DOF, not bokeh.
If that's what you mean, then yes, you can calculate how thin the DOF will be. There are several factors you need to consider:
1) Type/size of sensor or film
2) Focal length of lens
3) Aperture setting
4) Subject distance.
For example, if you are shooting with a Canon EOS 50D, and your subject is 2m away, 50mm f/1.4 will give you a DOF of 8 centimetres, while 85mm f/1.8 will give you a DOF of 4cm.
You can try it out here: http://www.dofmaster.com/dofjs.html
And if you're interested in the mathematics, here: http://en.wikipedia.org/wiki/Depth_of_field
In real life, this means that if you're using a Canon 50D, 50mm, f/1.4 shooting something 2m away, anything that is more than 4cm in front of or behind your focus point will be rendered OOF, and become part of the 'bokeh' of the picture. But if you change to 85mm, f/1.8, you have less DOF for the same subject distance. Things that were in-focus (not part of the bokeh) in the 50mm picture may become OOF (part of the bokeh) using the 85mm, because of decreased DOF.
True, bokeh can change according to focusing distance, but actually it's (again) a function of DOF...
(1) If the camera, focal length and aperture are the same, then the DOF increases the further you are from the subject. e.g.:
85mm f/1.8, subject 2m away, DOF = 4cm.
85mm f/1.8, subject 8m away, DOF = 59cm.
At 8m, a lot more of the picture will be 'in focus', and therefore a lot less OOF, and hence less of the picture contributing to the bokeh.
(2) If the subject looks the same size on the frame, it means your subject distance has changed as well. Then you're introducing additional variables.
85mm f/1.8, subject 8m away, DOF = 59cm
On a 50mm lens, the subject will need to be 4.7m away to appear the same size in the frame.
50mm f/1.8, subject 4.7m away, DOF = 59cm (focal length & subject distance change)
but...
50mm f/1.4, subject 4.7m away, DOF = 47cm (focal length, subject distance and aperture different).
Essentially, if you change the subject distance such that it appears the same size on the frame, and use the same aperture setting, the DOF doesn't change significantly. But if you're comparing different aperture settings, then that's an additional factor....
So why bother with an 85mm f/1.8, when you can get the same DOF on a 50mm f/1.8, if you go closer? Well, it comes down to what you're shooting. For example, say you're shooting a portrait of someone at 2m away, you would need to go up to less than 1.2m to get the same DOF. Moving nearer changes the perspective, so your subject/client may end up looking like he/she has a huge nose. Plus, he/she may not be very comfortable with the photographer coming so close.... ;p
Hope this helps! :cheers:
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You have a sound conclusion, yet not entirely complete.
Flash can travel far enough for the 300mm =P Whether the picture is a good one or not, is a different story, but if you push your ISO up to say 800, flash can easily clear 20m with an F5.6 lens and give you a good exposure (of the subjects it hits).
2nd thing you might want to consider. a 300mm lens does not imply that your subjects are far away. A 5-8 meters range subject can call for a 300mm sometimes (talking about an APS-C crop sensor), depending on how tight you want your framing to be. (Coincidentally, a good flash will do very well here at night)
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To the thread-starter (TS), you might want to consider sharpness issues. Generally F2.8 lenses will be sharper in comparison, given similar apertures.
oic. the only flash i'd used so far is only my pop up flash ha. thanks for filling in the gap.
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