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28

You probably didn't find much because you were searching on the wrong term. The phenomenon isn't commonly called 'The Newton Effect,' it's usually called 'Newton's Rings.' Briefly, Newton's Rings are an optical property of physics that occurs between two pieces of glass when one piece of glass is convex and the other piece is flat and there is airspace ...


16

Given that you have explicitly disqualified fungus and dust inside the lens, then the answer is no. A lens will not "naturally" lose sharpness with age. Glass is glass. It is a fixed medium, and assuming a 100 year old lens is in good condition without any extraneous wear and tear like fungus, dust, or a strong enough jolt to misalign one of the internal ...


14

You ask whether a lens can lose sharpness over time, but then go on to say: Please note, I am not talking about general wear and tear, or dust inside the lenses, nor am I talking about fungus in the lens. Which are exactly the reasons lenses lose sharpness over time. So the answer is no - once you exclude all the factors which causes lenses to lose ...


12

Real fastest value at the exact focal length. But, this is just a rule of thumb — it's not necessarily exactly two stops in every case. For the question of what two stops mean, see What does f-stop mean?. In short, each stop is approximately the-square-root-of-two times the previous one. That means half the light is allowed in (which is why the ...


10

All lenses will show dust with a flashlight shown through them, even brand new ones. Here are a couple of detailed articles on how to evaluate a used lens, from Calvin Foo and TechARP. Finally, scratches matter less than you might think. Check out this lens.


9

There are numerous kinds of optical abberations that you may encounter with a lens. Chromatic Aberration is only one of them. Some are more drastic, others are more subtle. Lens Flare Probably the most commonly known aberration is lens flare. Flare occurs when non-incident light enters the lens and reflects off of the various lens elements and/or ...


8

Good things are not cheap and cheap things are not good. This is true of all lens manufacturers. There is a small premium for brand name lenses usually but price is largely proportional to quality. For example, Sigma produces plenty of cheap low-quality lenses but they also produce some excellent lenses and, guess what?, they are far from cheap. When ...


8

When comparing lenses, it is important to look at all the qualities and features. In this case, those really are not comparable lenses. The Sigma is their base line, whereas the Nikon is a stabilized, internally focusing, high quality glass lens. The Sigma would compare better to this lens from Nikon, also compatible in price. When comparing lenses, its ...


6

I'm trying to write down a more photographer oriented answer. So the different lens-related issues are: Vignetting - corners of the frame are darker than the center noticeable in viewfinder/on screen to avoid - stop down your aperture, filters only make it worse, so you might want to try without post-processing - relatively easy to correct special ...


6

I've had limited use of a Composer and Muse. The build quality was acceptable, and I know they've held up well for the owners who use them regularly, though it's a pretty clear step below kit lenses in terms of fit and finish. I think the amount of enjoyment you get out of a Lensbaby is most directly correlated to the optic you choose and your expectation ...


5

Simply, those are not the same lenses, so no, they do not perform the same. Dig for optical formulas and you'll find that they are often changed between lenses. Example: the 50 1.8G is 7 elements in 6 groups. 50 1.8 AF-D is 6 elements in 5 groups. That's not to say some formulas won't change, but more often than not they will be different. I think the next ...


5

The first thing is to buy used from reputable sellers. Many Buy and Sell forums have a feedback system which allows you to make an informed decision. The next step is to do your homework. Used lens hold their value, unless badly mistreated, or made obsolete (in some cases this can increase the value). If the lens is way off what you find on B&S Forums ...


5

Well, the lighting in the photos look like lights on the background, and two relatively large lights illuminating their face (you can see the catchlight in the eyes), very possibly some rim light too. You're spot on about the large aperture, even the ears are out of focus. However, considering how sharp the photos are, its possibly stopped down a bit (but ...


4

I use DxOMark to compare technical lens data. They use a standard test process to measure and compare the following lens parameters: Resolution Transmission Distortion Vignetting Chromatic aberration These data points are taken at different focal lengths (for zoom lenses), at different apertures and are tested on a variety of camera bodies. ...


4

Personally, I just try just taking photos of a nice smooth surface (white paper for example) at the smallest possible aperture. Similar to sensor dust, scratches won't be apparent at the larger apertures (small f numbers). Of course, that all depends on whether or not it's possible to use the lens. That only covers scratches though. A used lens may have ...


4

Ignoring that fact that a large aperture lets in more light allowing faster shutter speeds etc. there are a number of reasons you'd want to use a larger aperture other than for subject background separation: Wide apertures let you shoot through certain obstacles. It's a common technique in amateur motorsport photography to shoot through a chain-link fence ...


3

The reason a lens would loose sharpness would most likely be because of wear and tear, dust, or fungus. I would think the glass itself is unlikely to warp unless faced with extremes in temperature. I imaging if you kept a brand-new lens in a dust sealed, climate controlled environment, it would stay sharp for quite some time. But most lenses will need ...


3

I have the VC version (Nikon mount). I have tested it alongside my 50mm prime and found it to be just as sharp at f/3.2. It is very slightly softer at f/2.8, but only when looking at an artificial test pattern. That's one person's opinion based on a sample of one. I have tested other non-professional zoom lenses (Nikon and Sigma) and the Tamron is far, ...


3

I think your first stop should be at Imatest, which offers many different suites of tests widely used by large commercial & industrial customers. That said they also cater for the individual, check out in particular the Imatest Master. The downside is the purchase price (although there seems to be trial version available) and you may need extra test ...


3

"Stopping down" is a throw-back term to the good ol' days of film and manual cameras. Apertures were set by the ring on the lens. Each setting, the ring clicked, or "stopped". Each stop is a full setting, with digital cameras allowing you to "stop" by 1/3 of a stop or 1/2 a stop, etc. Your "base" aperture that you're referring to is very simply the ...


3

Strictly 'optical' (ie wavefront) aberations are: Defocus Spherical aberration Coma Astigmatism Field curvature Image distortion But the ones that are mostly likely to affect your photographs are: Chromatic aberation - different colors are focused to different positions in the image, this gives rainbows around bright objects, especially on the sky. ...


3

There is one factor not yet mentioned by any of the other answers: separation of elements glued together. As a lens ages the glue that holds some elements to each other can degrade, allowing air to infiltrate between the two lens elements. The areas with air will refract light differently and affect the overall sharpness of the lens. In the context of the ...


2

Used lenses lose their value fast if they have scratches, on the barrel but especially on the surface of the front or back lens. Those scratches may not show up in pictures, but that's the psychology of buying and selling used gear. I would spend more attention on other features. Check if the AF works properly, if the lens doesn't wiggle too much when you ...


2

Also, do not forget post editing. Slight sharpening, careful highpass filtering, to highlight all skin details.


2

Here's a detailed review from DPreview on one of the Lensbaby lenses (the Composer Pro). They cover the build quality shortly on the second page.


2

The edited question: "Does the higher price lens always reflect better quality regardless of it being 3rd party or not?" can be generalized for any product: Does the higher price product always reflect better quality or not? The answer, in general, is "it depends" Sometimes higher prices reflect higher costs (better engineering, better material, better ...


2

"The Digital Picture" has an excellent lens comparison tool that should give you a very good idea (under test chart conditions) http://the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=400&Camera=474&Go.x=1&Go.y=7&FLI=0&API=0&LensComp=679&CameraComp=474&SampleComp=0&FLIComp=0&APIComp=0 However test ...


2

The word homogeneity itself refers to the uniformity of a substance. A substance that is of uneven thickness, uneven colour or uneven polarising properties will cause a slight measurable difference in the uniformity of the resulting image in different parts of the frame. In particular, the homogeneity test you linked will be sensitive to differences in ...


2

"Am I simply not seeing it with my unexperienced eyes, or is it that the effect of streaks in a filter are not visible at computer screen resolution? I don't see it even when pixel peeping." It's not visible like that in the image. As the filter is completely out of focus, any flaws will affect most of the image, not single pixels. It would mostly ...



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