Teleconverter question

Started Feb 26, 2014 | Discussions
billslatteryjr Contributing Member • Posts: 544
Teleconverter question

OK say one usually lands up cropping away 1/4-1/2 of a bird, insect, animal... photo. Now they use a 1.4 teleconverter that causes a 5%-10% loss in sharpness. But that same shot now gets a lot less cropped away. Wouldn't one get a better photo using the teleconverter as long as the shutter speed stays fast enough for the subject?

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larrywilson
larrywilson Veteran Member • Posts: 5,939
Re: Teleconverter question
1

If your converter and lens is auto focus fine tuned to get a good sharp image then yes its better to use a converter.  I have found that the tc 1.4EII requires af fine tuning with my long lens to get a sharp image.  In most cases it the number of pixels on your subject that determines resolution if your camera is focusing well with your lens setup.

Larry

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joejack951 Senior Member • Posts: 2,682
Re: Teleconverter question

billslatteryjr wrote:

OK say one usually lands up cropping away 1/4-1/2 of a bird, insect, animal... photo. Now they use a 1.4 teleconverter that causes a 5%-10% loss in sharpness. But that same shot now gets a lot less cropped away. Wouldn't one get a better photo using the teleconverter as long as the shutter speed stays fast enough for the subject?

It's a little more complicated than that.

First, admit that you pulled that 5-10% number out of your @ss!

As you noted, a teleconverter takes away at least a stop of lens speed, meaning you are shooting at a higher ISO or a slower shutter speed. Neither is good for sharpness.

A teleconverter slows down focus speed as the AF sensors have had the light available to them cut in half at least (up to 4X less light with a 2X TC). Lens sharpness is irrelevant if you can't get the subject in focus.

However, a teleconverter also allows one to utilize all of the camera's pixels on a smaller subject than otherwise possible. It also magnifies the subject in the viewfinder which could allow for more accurate focusing.

I own and use a TC14EII and have generally been happy with it (used with an 80-200/2.8 AF-S and 105VR micro). I bought and sold a Sigma 2X TC that left me a bit disappointed with every shot where it was used (on a rented Sigma 120-300/2.8 OS).

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Leonard Shepherd
Leonard Shepherd Forum Pro • Posts: 13,366
Re: Teleconverter question

billslatteryjr wrote:

Now they use a 1.4 teleconverter that causes a 5%-10% loss in sharpness. But that same shot now gets a lot less cropped away.

Some recent reliable (IMO) tests and my own experience indicate loosing around 7.5% image information using a TC14e which obviously only fits on a good lens.

Cropping by the equivalent amount reduces MP by 75% which, depending on body and lens, is about 25% image resolution reduction.

If you cannot afford or have the strength to carry a longer pro grade lens IME a TC14e is the next best option - after getting closer to the subject

I do not disagree the not so fast AF and darker viewfinder. As using a 1.4 x gives 1 stop more depth of field than the same crop with a longer lens you can open up 1 stop to get the same shutter speed and dof, or loose a shutter speed and gain 1 stop dof.

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Leonard Shepherd
Great images are often of good subjects.
If they are great images does what lens, body or technique was used matter more than the skill of the photographer?

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Bob GB Senior Member • Posts: 1,730
Re: Teleconverter question

billslatteryjr wrote:

OK say one usually lands up cropping away 1/4-1/2 of a bird, insect, animal... photo. Now they use a 1.4 teleconverter that causes a 5%-10% loss in sharpness. But that same shot now gets a lot less cropped away. Wouldn't one get a better photo using the teleconverter as long as the shutter speed stays fast enough for the subject?

There is no simple answer to this question. The lens, sensor, magnification of the image and post processing form a complicated transfer function producing the end image.

Adding a TC to a lens is similar to magnifying the image formed by the lens in this case by a factor of 1.4. Doing so, you reduce the resulting sharpness (resolution) of the lens by the same factor (1.4) which is a reduction of 29%. The TC itself is also a lens with its own aberrations which will be added to those coming from the main lens.

If this reduced sharpness (by 29%) still is better than the sensor in your camera you are probably in good shape. But as others have pointed out you also lose 1 f/stop demanding either more ISO or a longer exposure time. I would say using one of the exotic long lenses this is probably the case. If you add a TC to a zoom lens the 29% reduction of resolving power would perhaps make the lens fall below the D800 sensor.

However, the impact on the image might be a little different comparing a sensor limited picture to a lens limited picture. It is really up to your preference. I strongly suggest you try it out with the lens in question.

OP billslatteryjr Contributing Member • Posts: 544
Re: Teleconverter question

Wow Bob. That is very much different than the results they got here.

http://photographylife.com/image-degradation-with-nikon-teleconverters

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Dr Bob
Dr Bob Senior Member • Posts: 1,319
Re: Teleconverter question

billslatteryjr wrote:

OK say one usually lands up cropping away 1/4-1/2 of a bird, insect, animal... photo. Now they use a 1.4 teleconverter that causes a 5%-10% loss in sharpness. But that same shot now gets a lot less cropped away. Wouldn't one get a better photo using the teleconverter as long as the shutter speed stays fast enough for the subject?

You've got some good information here in all of the posts. I've only just started playing round with a TC 1.4 on a prime (not a zoom) and as long as you have enough light (you loose your stop with the TC and you need to stop the lens down a touch to retain sharpness) then you will not be compromised too much. You can therefore do you normal cropping and have more reach.

One thing not mentioned is that if you use a TC, the focal length is longer (obviously) hence you get better subject isolation - quite important if you are shooting birds.

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larrywilson
larrywilson Veteran Member • Posts: 5,939
Re: Teleconverter question

Yes I have read the article concerning using tc's and how much sharpness you lose.  I think it states around 5% loss using the lens tested which I think was a 70-200 zoom.  The sharpness loss on an exotic lens such as a 500 or 600 may be even less than the 5%.  I have tested my 500 alone, then used the tc 1.4EII with the 500 of course mounted on a tripod and used a timed release.  When I cropped the 500 image to the same size as the image with the convertor, the image using the converter was sharper.  If a person is going to print an image to say a 12 X18 then it even becomes more important to get as many pixels on the subject as you can.

I use the tc 1.4EII all the time with my Nikon 500 and the focus speed and image is really sharp.  The converter works well if a person has auto focused fine tuned the converter and lens combination to the camera.  Without fine tuning with my tc 1.4EII the images are not sharp.  Mine is set to a +15 to eliminate the front focusing using the converter and lens combined.

Larry

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Minnesota_Steve Contributing Member • Posts: 512
Re: Teleconverter question

What lens are you considering using it for? I can get very very very good results on my 300 f2.8 and 500 f4.

Steve

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OP billslatteryjr Contributing Member • Posts: 544
Re: Teleconverter question

Minnesota_Steve wrote:

What lens are you considering using it for? I can get very very very good results on my 300 f2.8 and 500 f4.

Steve

I'm thinking of using a 1.4 tele on a Nikon 105mm Micro and a 180mm Tamron Macro for butterflies, dragonflies... and maybe on the newer 80-400mm for birds. Heck if it works OK on the 80-400mm I may use it for daylight sports.

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Minnesota_Steve Contributing Member • Posts: 512
Re: Teleconverter question

I use the 1.4 teleconverter on the Tamron 180 macro. It works great!

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Steve

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NikonManSoCal Regular Member • Posts: 205
Re: Teleconverter question

Any news on the putative TC1.4 III?

Leonard Shepherd
Leonard Shepherd Forum Pro • Posts: 13,366
Re: This is not quite a complete answer

Bob GB wrote:

Adding a TC to a lens is similar to magnifying the image formed by the lens in this case by a factor of 1.4. Doing so, you reduce the resulting sharpness (resolution) of the lens by the same factor (1.4) which is a reduction of 29%. r preference. I strongly suggest you try it out with the lens in question.

Sorry this is incomplete.

The first thing is image resolution is made up from sensor resolution and lens resolution. If the lens combination and sensor each measured independently have equal resolution you 29% is reduced to 14.5%.

Some sources indicate the best sensors now have about twice the resolution of good lenses at optimum aperture.

If this is true the image resolution loss becomes less than 10%. Test sites (Canon MTF stats in particular) and my own experience with a 36 MP body indicate the loss is about 10% - providing I keep my long lens technique high.

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We all aspire to take great photos but may always achieve this perhaps due to a lack of application, a lack of knowledge, or even a lack of talent.
The best photographers probably work quite hard at their photography.

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Minnesota_Steve Contributing Member • Posts: 512
Re: Teleconverter question

No.  

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Steve

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