Plieku69 Loc: The Gopher State, south end

Can someone help me understand the why I need one? Or do I?

I think they are used to double the length of a lens, ie: 300mm to 600mm. Also the need for plenty of light as it reduces stops by 2 or more.

I have a Tamron 70-300mm that I like. A Tameron extension would give my a lot more long range reach so to speak, but does it degrade picture quality?

Is a tube really a poor mans long lens, or just a way to keep me poor.

Ken

jerryc41 Loc: Catskill Mts of NY

Extension tubes are for macro photography. They bring objects really, really close, but the lens also winds up being really, really close to the subject. I got the cheap ($10) manual tubes, rather than the auto kind. One tip. Removing them is tricky - but not difficult. There is a little silver release button. When you push (slide?) it the right way, the tubes will come right off. For $10, they worth getting and experimenting with.

https://smile.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=extension+tubes

WayneT Loc: Paris, TN

Extension tubes are used for Macro photography. They will increase your magnification and enable you to get closer to a subject but they are useless for anything other than Macro photography as you will not be able to focus the lens beyond a very short distance. I think what you are looking for is a 2.0x teleconverter that will double your focal length. These are made specifically for your camera body and lens in most cases. There are some generics out there but be carful with those. A 2x converter is powerful but will reduce your light input dramatically. Others here on the forum may be able to give you better examples of how and when they use these, I personally use a 1.4x teleconverter on my Sigma 180mm Macro lens to boost my magnification but I use it almost exclusively indoors with a lot of extra lighting.

Plieku69 Loc: The Gopher State, south end

Wayne you are right, I am asking about a 2x teleconverter.

I have Canon extension tubes and they work OK. It is the teleconverter I have questions about.

Ken

melismus Loc: Chesapeake Bay Country

You are confusing extension tubes with telextenders. Jerry has just explained extension tubes; telextenders are similar size and shape, but contain optics which multiply the focal length. This is the item you have described. Whether you need them (or extension tubes) depends on what you are trying to do.

Wayne types faster than I do.

blackest Loc: Ireland

extension tubes, manual ones, can be quite cheap they increase the magnification of an image. You know how if you have a projector and it is projecting on a wall if you move the projector back then the image gets larger. Think of your sensor as the wall and you should understand whats happening. Because you still get the same light through the lens it is less dense as it hits your sensor this is why you lose a stop or 2 of light.

The effect of an extension tube also reduces the minimum focus distance but it also means you lose infinity focus. This is great for photographing things that are close and small that you want to be as large on the sensor as possible. However the loss of infinity focus means that it is generally impossible for normal distance work to be in focus.

Teleconverters keep infinity focus by introducing new lenses at the rear of a lens, generally these magnify defects in your lens and will lower IQ as well as costing you light, automatic focus may not work in the reduced light. However you do retain infinity focus. Which you lose with extension tubes.

There are also converters that can go on the front of a lens most are poor quality but olympus made some better ones these actually compensate for themselves but again iq can be degraded noticeably.

So no free lunch. For macro photography, extension tubes are useful but ideally need a high quality flat field macro lens to work with.

WayneT Loc: Paris, TN

Teleconverters are great but you will loose light so you will have to compensate somehow to make up for the loss. You also have to be carful that your lens will function with a teleconverter. Not all teleconverters will work with all lenses and they generally are not meant to be used with zoom lenses they are normally used on prime lenses.

mborn Loc: Massachusetts

Every manufacturer makes their TC for specific lenses check online to see what works with your lens many lenses cannot utilize a TC

nikon_jon Loc: Northeast Arkansas

Good tele-converters can be pretty expensive. Cheap ones tend to really degrade your image. Search online for reviews on the brand name you are thinking of buying. They will usually have some samples of photos taken with certain lens/tele-converter combos.

DaveO Loc: Northeast CT

Bobspez Loc: Southern NJ, USA

You need a fast lens for a teleconverter. The 2x teleconverter loses two stops of light, so an f2.8 setting = f5.6 with a 2x TC. An f4 setting = f8, and f5.6 = f11.
That is why Nikon doesn't list the Nikkor 55-300 AFS VR zoom as usable with a 2x TC. At 300mm, that lens has a minimum f-stop of f5.6, so with the TC it =
an f11 setting. That will give it limited usefulness.

mwsilvers Loc: Central New Jersey

Even assuming a 1.4x teleconverter was compatible, if your lens has an f/4-f/5/6 aperture you would need an camera that could handle a maximum aperture of f/8 in order to auto focus. A 2X teleconverter attached to such a lens would not AF even with a camera that supports a maximum aperture of f/8. Now, an f/2.8 lens would be a different matter. As far as IQ, most top of the line lenses don't suffer too much when used with top of the line 1.4x teleconverters. With 2X teleconverters the results are usually more problematic

Bobspez Loc: Southern NJ, USA

Good point. The Tamron 2x TC will not autofocus at 300mm with the OP's Tamron 70-300mm lens. If the OP doesn't mind manual focus and wants to experiment, a manual focus 2x TC can be had for $30 to $50. I bought a used Nikkor TC200 2x manual focus TC on ebay for $32. I haven't found a use for it with my Nikkor 55-300mm lens in daylight. It might work at 300mm for moon shots on a tripod. I haven't tried it on the moon yet.

billnikon Loc: Pennsylvania/Ohio/Florida/Maui/Oregon/Vermont

They are designed to allow you to shorten the close focusing distance of a lens. ie, if the lens minimum focusing distance is 4 feet, and extension tube will allow you to focus closer than that. Many tubes will not work for auto exposure or focusing with your lenses, so make sure that they will. Your depth of field will go to he--. Your IQ will also suffer, you are really better off getting a macro lens for those situations.

camerapapi Loc: Miami, Fl.

You are confusing tele-extender with extension tubes. As has been repeatedly said extension tubes are used to bring the lens closer to the subject. It is a simple way of using macro capabilities without using a macro lens.
If you are interested in macro photography a macro lens should be your first choice. If you want to use a tele extender I would not recommend the use of one for a zoom with large apertures because of the reduction in the light gathering capacity of the zoom lens. Lenses with apertures like f2.8 do better with tele-extenders and even so I would recommend that you use the ones with a 1.5 factor for better sharpness.