If I have a 200mm lens, and want to focus at, say, 450mm from the camera, two questions:   can I (do I need to) use bellows to achieve this? is there a formula for how to work out how much extension I need on the bellows to achieve the minimum focal length?
19998
There must be a mathematical description of the difference that an extension tube makes to a lens -- is it something that can be easily described?  (For example, with teleconverters you can say things like "a 2x teleconverter will turn a Y-mm lens into a 2Y-mm lens, and will lose you 2 stops." Is there something similar for extension tubes?)  If there's nothing much you can say about magnification, in general, what about the change in closest focal distance? Is that also lens-dependent?  What about if we factor out the lens: is there any general way to compare the effects of (say) a 12mm and a 24mm extension tube on the same lens?
72190
For example, if I have a lens that is 16mm-50mm, which focal length would be the closest to the human eye's view? (I don't have a camera yet, so I'm just curious.)   Would 50mm be more zoomed in than "normal"?  I imagine 16mm would be wider than the normal human point of view?
117985
I read following in a web site ()     Lenses with maximum apertures of f2.8 allow the camera to use all high   precision sensors. In low light or other situations that are hostile   to autofocus, that’s a big deal. Lenses with a maximum aperture of   f4.0 use only the center focus sensor in its “high precision” mode,   and use the other sensors in their “horizontal line” only mode. Lenses   with a maximum aperture of f5.6 use all sensors in their   “horizontal-only” mode, and lenses with a maximum aperture of f8 use   only the center sensor point, and that with horizontal sensitivity   only.   I want to understand if this is completely true? I am raising this because recently I have purchased a Nikon 70-200 f/4 lens and would like to understand if I have made a wise investment, or, should I collect some more money and buy a 70-200 f/2.8 VR-II lens.
28936
I am new to the photography field, there are few things which I am not able to understand. I am playing around with my Nikon D90 along with its kit lens (18-105mm).  While reading about Depth of preview, the author asks to do some basic exercise to better understand DOF, like this:   set your aperture to smallest number f/2.8, f/3.5, f/4 with 70mm or longer lens.   When I tried to set aperture to f/3.5, and tried to change focal length, my camera is setting aperture automatically in every possible mode (which I know of). It is changing aperture in the following fashion:  1. 18-24 ----&gt; 3.4 to 4 2. 18-35 ----&gt; 4.5 3. 18-50 ----&gt; 5 4. 18-105 ---&gt; 5.6   But if i set my aperture to 5.6 or higher, it does not change when I change the focal length of my camera. I know I am not doing some basic thing right, but I'm still not sure why this is happening. Can some one help me to understand this?
9002
There seems to be a preference for to have the    18 mm - 55 mm 55 mm - 250 mm   lenses, but no mention of why they're better than a single 18-200mm. Could someone please explain why the two separate are better than the one combined, and if anyone has quantified this difference?  (I'm curious about Canon in particular.)
97341
How do extension tubes affect focusing distance? More specifically, what I mean to ask is : why does the maximum focusing distance become shortened when an extension tube is attached? - Why does the maximum focusing distance become reduced (from infinity to XYZ)? I don't understand why moving the image plane further back would have any effect :( On a related topic, am I correct in stating that the reason the minimum focusing distance decreases (when a lens is used with extension tubes) is because the lens's focal length stays the same, but the light has to travel further to reach the sensor/film? Does that make any sense, it does (kinda) in my head - but I am a silly person aha ;)   I should make it apparent that I have tried to look for an answer, but I have yet to find an explanation. I have read from multiple sources e.g. (   ,  )  If you could provide a basic answer as well as a more technically savvy answer that would be greatly appreciated :) Also, I know it is a lot to ask, but you guys please provide a picture or a video in your answer? &lt;3 :)  I would like to thank you all in advance for your answers and support! :)
66623
(This could turn out to be a bone, practical, product-specific query, but this is the internet so the worst that could happen is a 0 rather than a 1.)  Anyhoo: is it possible to lock a zoomable lens to a certain focal length? Is this a typical feature for a lens?  I want to keep my SELP1650 at X mm to help with some creative experiments, but the thing shifts whenever I move my hand against the lens ring. Does SELP1650 (or the body, Sony A6000) specifically have this option?  Or... is there a reasonably non-goofy DIY trick I could pull off, without bricking the thing? (anticipating a sarky 'duct tape' suggestion)
39102
I've read a few threads on here that mention some  of macro lenses and found some marketing fluff in the box for my Canon about them as well, but being a complete novice I was left a bit confused.  Can someone please provide me with a top-to-bottom explanation of what a macro lens does?
115772
I have a 17-85mm Canon lens which I was using at the beach the other day. A sudden hard blow of wind caused sand to be thrown on me and my camera. Afterwards, the camera would give the Error 01 code related to faulty camera communication. I figured out this would always happen if I used a smaller aperture than the widest one possible. So my conclusion is: the diaphragm is stuck due to sand intrusion and only works when no closure is required. I already bought a new one but would like to try and fix the old one as a backup. Does someone have a guide or experience which can be of help here?  Update  Actually my "new" lens also has an issue (it not actually brand new, it was first used by my parents and is outside warranty noz). The issue is that the focus gets stuck in certain ranges at the extremes of the zoom. When at 85mm (and a bit below), the focus works well in the entire range but it gets stuck at infinity once it got there. Same at the 17mm end, but there the focus gets stuck at lower focal ranges. In the middle it moves freely. When in manual focus it is also impossible to move the focus out of these ranges. You can feel some slight resistance on the focus ring when moving towards the middle zoom region. Any thoughts on this as well? I noticed there were focus problems before but never really bothered, so the problem has been around for a while but it is "workable" by realising the focus using the ~40mm part of the zoom.
36764
I'm looking to buy a compact camera, and having a very wide angle is important to me. I know that review sites often list the real focal length of the lens, but what I'm looking for is something that will show me current models with actually wide field of view. Is there such a resource?
37447
I understand that the simple idea that f-stop is focal length divided by aperture really applies to a simple single-glass lens, not the compound lens systems used to provide good image quality in modern lenses.  I've heard that in this case, what matters is the ratio of the aperture as it appears through the front element. Why the front element, and not the back (which would be the "point of view" of the sensor or film)?  What about for effects such as diffraction? Does the literal physical aperture size matter, or is it the effective size?
24241
I'm wondering, technically, why and how does the out of focus areas blur more when using a bigger aperture. I think it'd help a lot if I presented a problem that's been driving me nuts for a long time:  I've read that the f-number of the human eye varies from about f/8.3 in very bright light to about f/2.1 in the dark. But from what I've tested, I always see out-of-focus areas with the same amount of blur.  Which leads me to ask: how does this aperture thing work, why does it create a blur from the technical point of view, and does it also apply to eyes, or is it just a "failure" in the camera lenses we've come to like and never wanted to "fix"?
56586
Once you know the MFD (minimum focus distance) for a particular lens, is that the distance from the subject to the front of the lens or to the camera sensor?
42537
I have a kit lens which has no markers. What would be a recommended way to find infinity focus on this lens?  I plan to shoot objects at night -- not necessarily stars or the moon. So, adjusting the focus using the viewfinder may not be an option.
120374
I can understand that a zoom lens with a maximum aperture wider than f/2.8 would be difficult and costly, but it seems like something pros would kill for.  Surely it can't be more expensive (if its possible) than some of the $10k+ lenses and they exist to sell in limited quantities.  Is it just near impossible or is there another reason we don't see zoom lenses faster than f/2.8?
40389
I am new to dslr's and got a nikon 3000 with 18-55 lens as a gift.  I already see some limitations with the lens for walking about or on trails.  So my question is being new should I go with a 55-200 or 55-300 or is there another step before I go with a telephoto lens.
23865
I have a Nikon D3200, which doesn't have an autofocus motor. Therefore, I'm mostly deterred by lenses that don't have focus motors in them. But the ones that do have it are much more expensive.  Take the Nikon 70-300 for example:  AF Zoom-Nikkor 70-300mm f/4-5.6G: $172.95 AF-S VR Zoom-Nikkor 70-300mm f/4.5-5.6G IF-ED: $589.95   So is it possible to have an autofocus motor as a separate attachment to the camera? This would go between the camera and the lens, like an extender. I think it should be doable in principle, but not sure if anyone makes them..