Tamron 70-300 TELEMACRO (1:2) stuck @ fixed focal length-

The T-mount is a universal thread developed by Tamron which allows various adapters to couple a lens to a wide variety of camera brands. If a lens is listed as having a T-mount, it means that the lens can be coupled to your camera if you have a T-mount adapter for your camera.

A 2X teleconverter (often called a doubler) enables a lens of a specific to be doubled. For example, the lens referenced above actually is a 650-1300 lens but with the 2X teleconverter the focal length can be doubled to a maximum focal length of 2600.

I have an Opteka 600-1200 telephoto lens which I consider to be a decent lens for its very low price. I also have a doubler which came with my camera kit. That means I can increase the focal length of my lens to 2400 but I cannot imagine any reason to do so. At it's full zoom 1200mm focal length, this lens is very difficult to handle and must be used on a tripod with a remote shutter release.

It is extremely time consuming to focus and must be focused very accurately because it has almost no depth of field. At 1200 mm, the slightest breeze or vibration will cause the picture to go fuzzy from movement.

The lens is also large and does not fit conveniently in a camera bag so it rarely goes with me unless I know for sure that I will need it. It is not particularly good for sports action shots because the action will be over before you are ready to shoot the picture. With very bright light (such as the mid-day sun) and pre-planning and pre-focusing you might be able to get some interesting sports action shots. Say you're at an automobile race and you know a car will be coming into view at a certain spot, you can set up for that spot then trip the shutter when the car pops into view.

All that being said, I think this is a good lens to have in my bag without spending $10,000 plus for a really good lens of this size.

A 35-80 mm lens is 2.3X zoom. Divide 80 by 35 and you'll get the result.

It is usually better to know what the focal length of a lens in "35 mm equivalent" is and judge by that, rather than relying on the "X" power of the lens. For instance, most point and shoot cameras start at about 35 mm and have either a 3X or 4X zoom. This would make it a 35-105 or a 35-140. I've seen some that start at 28 mm, though. A 3X starting at 28 mm is 28-84 and a 4X is 28-112. Neither one is a particularly strong telephoto lens and the 4X is just about the same as the 3X that starts out at 35 mm.

It's also important to realize that tradition dictates that lens focal lengths are usually expressed in terms of "35 mm equivalent," where "35 mm" refers to a 35 mm film camera. This is because of the relation between the sensor size and the actual focal length of the lens and the resultant angle of view of the lens.

I have one point & shoot that is actually a 5.8-24 mm zoom. This is a 4X zoom. The 35 mm equivalent is 28-116 mm. The sensor is 7.2x5.3 mm. (1/1.8") (And I wish I knew someone who could explain how the heck they came up with sensor size terminology!)

I have another point & shoot that is actually a 5.7-17.1 mm zoom. This is a 3X zoom. The 35 mm equivalent is 34-102 mm. "How could a shorter focal length give a longer 35 mm equivalent?" you might ask. It's because the sensor is only about 5x4 mm. (1/2.5")

I have a few Nikon DSLR's and - thankfully - they all have the same size sensor. They all have a "lens factor" of 1.5. This means that you just multiply the actual focal length of the lens to get the 35 mm equivalent and then you can make comparisons accurately from camera-to-camera. Most Canon's, for instance, have a lens factor of 1.6. On a Nikon DSLR, a 28 mm lens is the "35 mm equivalent" of a 42 mm lens. On most Canon DSLR's, the same 28 mm lens is the equivalent of a 45 mm lens.

These example are just to show you how freaking confusing it can all become if you try to make sense of the "X" power of a zoom lens.

Bottom line...

Check the 35 mm equivalent specifications for the lens. This way, you will be leveling the field and comparing apples to apples. More or less.

It's not the lens but the camera that determines the focal length multiplier. On some cameras the 18-270mm lens is an 18-270mm. The XSi's imaging sensor applies a 1.6x multiplier on any lens used with the camera, so the 18-270mm will be approximately 29-430mm.

All canon EF and EF-S lenses work with 500D /T1i model.(yes all)
If your lens is removed from old 500N body and if it has EF marked it will work for every Digital camera model of canon.
Note: its focal length will be multiplied by 1.6 X factor.
(mean 18 mm lens will become 29mm approx.)
If you find this of help rate me.

In low light you need a high ISO setting, probably 1600.
You also could do with a lens with a low F number to let in lots of light. You can get a fixed focal length F1.8 cheap but might find the lack of zoom a problem.
A decent zoom with a low F number is going to be expensive.
The EF-S 17-55mm F2.8 IS for instance has a list price of around £800 / $1200 !!
You can get a non-Canon one which would be more affordable and you also won't need the IS at short focal lengths (although it always helps). Have a look at Sigma and Tamron in the F2.8 to F4.0 range but check the online reviews to make sure they are of reasonable quality.

It will not focus on anything closer than 5 feet.

(From Sigma lens literature) Capable of macro photography, this lens has a 1:2 maximum close-up magnification at the 300 mm focal length. It's the ideal high performance lens for portraits, sports photography, nature photography, and other types of photography that frequently use the telephoto range. It also has a switch for changeover to macro photography at focal lengths between 200mm and 300mm with a maximum close-up magnification from 1:2.9 to 1:2. The minimum focusing distance is 1.5m / 59 in. at all zoom settings.

if it is an auto focus lens that works on one eos camera, it should work on almost all of them. the only known exception is that some high end extenders will not fit the eos1dmarkII as it protrudes into the opening too far.
but a good rule is that if it fits without any obstruction issues, it should work. try cleaning contacts on the lens and camera body. if that doesn't fix it, talk to Tamron. you can use it manually, but will not be as easy and you would get less predictable results.

my suggestion is to always go with lens from camera maker.

sounds like there is an issue with the tamron lens. not the camera.
good luck
mark

There are two versions of this lens.  The Telemacro version takes 77mm filters and is quite good.  It sells for $325-400 depending upon condition.  The other version "APO" is not very sharp and has low contrast.  It takes a 72mm filter and usually sells for approx. $125-$200.  I would not recommend this one for any serious photographer.  The Telemacro version is a nice affordable 400mm lens with decent performance.  Both lenses have slow AF, but the fast focusing alternatives are hundreds to thousands more.

GT APO optical 7x zoom. Focal length: 7.2 - 50.8 mm (equivalent to 28 - 200 mm in 35 mm format) 16 elements in 13 groups (includes two Anomalous dispersion glass elements and two aspheric elements) Maximum aperture: f/2.8(wide-angle position), f/3.5 (telephoto position)

Macro: Wideangle: 0.1m to 1.0m (from lens front) / Telephoto: 1.2m to 2.5m (from lens front) Wideangle: 0.185m to 1.085m (from CCD) / Telephoto: 1.285m to 2.585m (from CCD) Super Macro: 3cm to 100cm (from lens front), 9.5cm to 109.5cm (from CCD), focal length: 10.45 mm (equivalent to 63mm in 35mm format)