Teleconverter question

stsinner · Feb 12, 2009

I've seen a lot of recommendations of a 1.4 or 1.7x teleconverter, but never a 2. Is there a problem with going to 2x? Does it enhance the shortcomings of a lens more or something?

Thanks.

Big Mike · Feb 12, 2009

The stronger the teleconverter, the more light it eats. A 1.4 eats about one stop and a 2X about two full stops. For most cameras, this means that you need to start with F2.8 lenses, otherwise the TC will render your AF useless (not enough light).

tsaraleksi · Feb 12, 2009

A TC basically blocks part of the lens' image circle and magnifies the part that is not blocked. This reduces the light and shows the lens' shortcomings-- think about how cropping a picture might make more obvious motion blur, or something similar.

Judge Sharpe · Feb 12, 2009

In the old days, before AF 2x and even 3x were common. It was an inexpensive way to increase your lens collection with out spending big bucks. Some were good, most were OK for the purpose.
I wonder if you could use a 2x and manually focus your camera?
I found out that the reason that circular polarizeing filters are used today is because the old type linear filters is that the linears mess up AF's split beam system. Go figure. Anything to make it more expensive.
Judge Sharpe

Overread · Feb 12, 2009

1.4 TC block one stop of light and give a 1.4 times inrease in focal length. They also generally have very little imapact on the image quality that the lens will deliver - on good primes and high end zooms the image quality loss is harly noticable.

2TC block 2 stops of light, which means that if you don't have an f2.8 lens you will lose AF on any canon camera that is not a 1D line make and whilst on nikon you will keep your AF after f5.6 AF accuracy takes a nosedive. Further this TC will have a noticable impact on overall image quality - it will make things much softer. On a lens like a 70-200mm L zoom its noticable and limits its use - on a pro end prime like a 300mm f2.8 the impat on image quality is still noticable, but images remain sharp enough to still use.

A 1.4 is a good investment and will likley see a lot of use - whilst a 2TC is a more tricky bit of kit, likley to be used less often (unless you have pro prime lenses) and often only in certain conditions (such as very bright weather)

Overread · Feb 12, 2009

Judge Sharpe said:
I wonder if you could use a 2x and manually focus your camera?

Its certainly possible but there are limits:
1) if your shooting sports or moving targets AF is normally far quicker than the human hand

2) DSLRs don't have focusing aids like the old film cameras did - thus manual focusing is even more tricky to do - especailly when you try to tell the difference between in focus and tack sharp in focus.
(note that whilst split screens can be put into many midrange DSLRs they do mess up the AF system as a result)

3) with 2 stops of light lost the image through the viewfinder is now much darker - in dimmer lighting conditions (or if your shooting macro this can make focusing much harder to do since you have less light to see the image.

ksmattfish · Feb 12, 2009

Judge Sharpe said:
I wonder if you could use a 2x and manually focus your camera?

Most AF systems start crapping out when the max aperture gets beyond f/5.6 or so (there's just not enough light for it), but manual focus still works (if you can still see through your viewfinder at f/5.6 or smaller).

A x2 teleconverter on a f/2.8 lens changes it to f/5.6, so AF should still work on most cameras.

Image quality concerns are often mentioned about teleconverters. I once saw an article where this guy was stacking up to 4 x2 teleconverters to shoot surfers against a huge sun. His photos looked pretty good. In a choice between image quality and getting the shot, he chose getting the shot, and counted on exciting subject matter presented in a unique way to overcome any technical quality issues.

stsinner · Feb 12, 2009

Thanks everyone! I have noticed what you describe. The AF is useless indoors, but I didn't know what to attribute it to-I thought that maybe since my lens was telling the camera that it was a 70-300 but the focusing didn't make sense, it just couldn't make sense of the shot.. Learning that it's light makes sense.

I should put my 2x TC on my 500mm and see what happens... The sun will probably be the only thing I can take a picture of... LOL

Overread · Feb 12, 2009

were the example shots webshots or was he giving examples of fullsized shots?
I have used two 2TC and got reasonable results that - when resized and sharpend for the web - do not look half bad. The trick is to get the subject filling the frame - you can't really get away with cropping or havin a smaller subject to background - but if they fill the frame enough details are generally caught for a good usable shot

gsgary · Feb 12, 2009

stsinner said:
I've seen a lot of recommendations of a 1.4 or 1.7x teleconverter, but never a 2. Is there a problem with going to 2x? Does it enhance the shortcomings of a lens more or something?

Thanks.

No problem at all with the 2X on a prime lens i use the Kenko on the 300F2.8L for cricket and get great results
Gary Clarke : photos : Derbyshire Phantoms V Surrey Brown Caps- powered by SmugMug

table1349 · Feb 12, 2009

Part of the problem is what people are putting TC's on. They are not designed for anything less than a 100mm lens. Off brands like, Tamron, Kenko, Tokina and Sigma will fit virtually any lens where as Canon's TC's will only fit on certain Canon Bodies. I don't know about Nikon TC's as to what lenses they will or will not fit. Putting a 2X TC on a 50mm provides a poor substitue for a 100mm lens. Even a consumer grade 100mm lens in most cases.

Along with all the other things mentioned above, keep in mind that a TC whether it is a 1.4, 1.5, 1.7, 2.0 or 3.0 will multiply the Image Quality defect by that amount. If you are using a consumer grade lens that is not razor sharp then that lack of sharpness is going to be enhanced by the TC resulting in softer photos. Most shooters don't have a 300 f2.8, 400 f2.8 500 f4.5 600 f4.5 or 800 f5.6 to use with the TC When you put a top quality TC on a top quality piece of glass like that you can get very good results.

I only use my Canon 2.0 TX on my 300 f2.8L and 400 f2.8L. For my 70-200 f2.8L I never use anything but my Canon 1.4. The 2.0 just doesn't provide the results that I expect.