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It's not just about maximum aperture. Even in two lenses with the same focal length and max aperture, one could have a larger diameter. The larger diameter could be because of using larger lens elements, which could have advantages with regard to sharpness and light falloff at the edges of the image circle. Some lenses may even project a larger image circle ...

This looks like a spacer ring, which is used to add space between a lens and a filter (such as close-up filter) or other lens attachment to assist in focusing adjustment or increasing the angle of view. Note, however, that using this could create some vignetting, especially on wide-angle lenses.

The diameter you're seeing is for the filter threads; it's unrelated to image quality. If anything, there are disadvantages to a larger thread diameter (assuming the other specifications are similar): they tend to be heavier, bulkier, and filters to fit them are substantially more expensive. If you are concerned about image quality and handling, you should ...

The only thing you have to be mindful of is with wide angle lenses. You just want to make sure that with the step up ring and filter attached that you don't see the filter edge in the field of view. Slim filters can help with that. Otherwise it's just fine. I do the same myself with 77mm filters.

The only ones I encountered is not being able to use a lens hood and not working at all with lenses which have a built-in lens hood. It is possible it may vignette on some lenses but I have not seen it happen on a DSLR. On one fixed-lens camera I needed a slim step-up ring by the manufacturer to do the trick. Based on the cost of good filters, this is the ...

Step-up rings aren't usually a problem, except that it means you won't be able to use a normal lens hood on the smaller-diameter lenses. That's one of the reasons why square filter holder systems like Lee and Cokin (as well as matte boxes) are popular—they have their own hood systems that can be adjusted (or assembled) to match the field of view of the lens ...

Generally speaking, a larger front element is necessary to achieve a wider maximum aperture. More specifically, a larger front element helps achieve the necessary "entrance pupil" diameter required for a given lens, provides the necessary primary light-gathering power of a lens, and helps achieve the necessary angle of view of the lens. (The entrance pupil ...

Yes a 49mm - 58mm step up ring is what you need. Here is one at BHPhotoVideo for example. And here are a bunch of results at amazon. I would also consider one of the kits that come with multiple step up rings such as this: http://www.amazon.com/Fotodiox-Anodized-49-52mm-52-55mm-55-58mm/dp/B001G445Q4/ref=pd_bxgy_p_text_y

No, a designation of f/1.4 implies the same ratio between focal length and aperture in both lenses. So if you're shooting the same scene, both lenses will give you the exact same shutter speed wide open (unless you vary your ISO...) From what I've read on the Sigma, the larger opening diameter means less vignetting wide open. I haven't observed this ...

To get a smaller threaded lens to work with a 58mm adaptor just requires the appropriate stepping ring. You can get an entire set of these for not much money, or you can measure the lens to find out exactly which size you need (my money would be on the value stated on the lens itself to be the correct one): ...

I think you are comparing way to wide of a range of lenses. Take a simple comparison, such as the Nikkor 85mm f/1.8D AF and 85mm f/1.4D AF. The 1.8 uses a 62mm filter, and the 1.4 uses a 77mm filter. Another great comparison is the following set of lenses, where we have three apertures all at the same focal length. The Canon 50mm f/1.8, 50mm f/1.4, 50mm ...

Most answers given above is great. Also, I'd like to point out one reason not being mentioned -- sensor (or film) size. Nikon DX lenses (for instance) are designed for their 1.5x crop dSLR's, so basically, when you mount one of those on one of their full-frame dSLR's, you will get vignetting in the edges/corners. The size of the image circle being cast by ...

The larger front element doesn't translate directly to a faster aperture -- since they're both rated at f/1.4, they theoretically collect the same amount of light. At least in most tests I've seen, it appears that the Sigma does vignette less than the Nikon though. It also retains relatively round out-of-focus highlights toward the edge of the frame, where ...

The focal length and aperture of the lens are all that really matter in this context. In both cases, the focal length is 50mm and the aperture is f/1.4 which means that the opening that is allowing the light through is approximately 36mm wide. This is true no matter how large the lens barrel is and so the lenses will collect the same amount of light given ...

You could use a full-aperture solar filter that's appropriate for astronomy use. Orion sells many: http://www.telescope.com/catalog/search.cmd?form_state=searchForm&keyword=solar+filter Advantage of this kind is that it would be safe to look through with your eyes.

If you're not hung up on the Hoya brand name, you can get neutral density filters in 2.4, 2.7 and 3.0 log densities (8, 9 and 10 stops) in the large square formats for Lee and Cokin filter holders, which will also make them usable on your other lenses. (The links are to product list pages at B&H.)

Usage of color filters in digital photography has already been covered in another question. There certainly are at least 21 lenses with 49mm filter size, all of them for Pentax and Sony. Also, some compact cameras use that filter size, e.g. Fuji X100 (with either AR-X100 adapter or an extra 49mm filter frame).

I'm using a '49mm-52mm Step-Up Ring' and a '52mm Macro Reverse Adapter Ring for Pentax K' to reverse mount my SMC PENTAX-A 1:2 50mm lens which has a 49mm filter thread. It's working great and I don't see any disadvantage. Of course it would be cheaper and simpler to use a '49mm Macro Reverse Adapter' but I was unable to find one in the local store (many ...

Have you considered using a ruler? There are 2-3 millimeters (or more, in the larger sizes) between standard filter thread diameters. Simply measuring across the filter thread will give you a diameter that's just about 1mm less than the actual thread size, so if you measure 48-and-a-bit millimeters, your lens takes a 49mm filter; 51-and-a-bit takes a 52mm, ...

With regard to your second question about whether the step up ring would affect picture quality, the answer is that it shouldn't. You are putting a larger filter on a smaller lens so it won't obscure the lens in any way. The quality of the 58mm filter will be the same as a 49mm filter (assuming the same manufacturer etc.) If you leave the step up ring ...

The lens barrel of Z990 should have a 48.5 mm thread. This is not a standard filter size, but looks like some people have succeeded in modifying 49mm filters to fit by filing the thread slightly smaller. Another option is to use a filter adapter tube, but it seems very likely that the tube will black out corners and edges on shorter focal lengths.

I just looked at mine to be sure, and Pentax SMC M 50mm f/2 does not have the thread diameter marked on the lens either on the front (as pictured) or on the edge. Many lenses do indicate it usually in combination with a diameter symbol "⌀", but this one doesn't, probably because there's not much room with the writing that's already there. The 50mm is just ...

I bought an extension tube and 58mm reverse adapter ring for the EF-S 18-55mm canon lens but as you can guess, I can't control the aperture You can actually control the aperture using the following way: With your lens connected to the camera body, Set your camera to aperture priority and choose an aperture value. After choosing the aperture value, press ...

There seems to be some confusion between closeup lenses and filters. What you linked to is a set of closeup lenses. They do mount on the front of your lens like a filter, but are not filters. The purpose of a closeup lens is to let the camera focus on something closer than the bare lens would by itself. This is the same principal as you looking thru a ...

Indeed as @dpollitt said, the lens you have has a 49mm filter-thread. If you look across the entire NEX lens lineup, it is the most common thread size with only the 18-200mm using a 67mm thread. You could go with a 49mm filter or a larger size such as 67mm or 77mm with adapters. Personally, I choose the adapter route because then I only need to buy one set ...

Quick edit, I suddenly realized that the second measurement was the diameter, kind of confused me, for a moment... The nutshell answer then is that it doesn't really. I'll leave the rest of my answer to explain what does matter... Focal length and aperture do effect image quality, but they're hardly the only things! The ability of the lens to transmit light ...

Essentially a larger diameter allows the lens to be designed with a larger maximum aperture. More light means shorter shutter speed which means less motion blur when holding the camera directly, IS or not. The benefit of a large aperture is that you will be able to bring down the ISO sensitivity to reduce noise when shutter speed isn't a priority.