Do teleconverters cost you depth of field?

[Texas Dave]

I have a 1.4x teleconverter ordered and read that it will cost me 1 stop of light.

I was wondering if it reduces the len's depth of field?

I obviously haven't got to my "understanding lens" section yet.

[Inkanyezi]

Your depth of field should be calculated for the longer focal length that results and for the reduction of aperture as well, if you use a DOF calculator. That means that if you take a photo with f/8 and the shorter focal length without extender and take another one with f/5.6 set on the lens with the extender, you will have f/8 in both instances, but your focal length will be 1.4 times as long and your DOF will be more shallow. Your subject will also be larger in the image, so actual DOF would correspond to DOF at f/4 without the extender at the same distance.

But I think it is nigh to impossible to visualise how this would work in practise. Many people even misunderstand what DOF really stands for; the region of distances within which the circle of confusion is not objectionably large. I think it causes a lot of confusion.

So the answer to your question is Yes, you get a shallower depth of field, mainly because your image is enlarged, compared to the image without the extender. The circle of confusion is also enlarged.

In essence, it is not related to the DOF of the lens without converter, but what you do when you attach the converter is creating a lens that has a longer focal length, another lens, with one stop smaller apertures than the ones marked on it, and with 1.4 times the focal length.

This means, that if you have a lens that is 70-200, if you set it to its longest focal length, you will have a 280 mm lens with one stop lower brightness. If you set this lens to 100 mm and f/5.6, you will get exactly the same depth of field as when the original one is set to 140 mm and f/8, because that is exactly what it is. However, with the original lens at 100 mm f/5.6 its DOF will be somewhat larger, because the circle of confusion and all elements in the image thus are smaller compared to the image size.

[MrB]

Trying to keep it as simple as possible, when compared with the depth of field when using the lens without the converter...
...if the camera to subject distance is the same, using the converter to give a 1.4x enlarged image on the sensor, the depth of field will decrease,
...if you move away from the subject, until the image size on the sensor is the same as it was without the converter, the depth of field will increase,
and, of course, many other possibilities between these examples.

Cheers.
Philip

[JR1]

Interesting thread

[Texas Dave]

Thank you!

[William W]

Previously, I have seen this question become a quagmire of very technical answers.

I'd like to comment that I think this is the quintessential answer to the question from someone who seeking to get their head around the practical stuff of Photography -

. . . So the answer to your question is Yes, you get a shallower depth of field, mainly because your image is enlarged, compared to the image without the extender. . .

. . . because the point is: in mostly all circumstances, one would be going to the trouble of using a teleconverter in the first place to make the subject appear larger in the frame using.

WW

[MrB]

I would have thought it helpful to know that adding e.g. a 1.4x converter allows the photographer to be 1.4x further away from the subject to get the same size image as would be seen without having the converter, and that the combination would then also give a greater depth of field.

This should be useful practical knowledge, e.g. for those taking pictures of flora and fauna, particularly of timid or dangerous species of animals.

Cheers.
Philip

[NorthernFocus]

Others trying to explain will likely only confuse the issue and get others arguing with each other. Best to go on the on-line DOF calculator and play with some numbers for yourself.

[William W]

I think that it is important to grasp two practical concepts:

Concept 1.> A tele-converter (tele-extender) when added to a lens, can be thought of and for practical purposes can be treated as ‘a lens’

Example 1: x1.4 Extender + 200mm F/2.8 prime Lens ≡ 280mm F/4 prime lens.
Example 2: x 2.0 Extender + 70 to 200 F/2.8 zoom lens ≡ 140 to 400 F/5.6 zoom lens
Example 3: x1.4 Extender + 100 to 400 F/4.5~5.6 zoom lens ≡ 140 to 560 F/6.3~8 zoom lens

Concept 2. > if the FRAMING of a scene; the APERTURE used; the Camera FORMAT are all kept CONSTANT -
then the DoF for all practical purposes will be the same, (That is in general photography not macro.)

So, considering the above to concepts, it is worthwhile noting that if a tele-converter is used, (for example) to move the camera further away from a timid or dangerous subject and the desire is to keep the FRAMING of the Subject the same as if a tele-converter had not been used, then:

It is essentially a question of what APERTURE is used for each shot to effect any difference in the DoF between the two shots - and it is not the fact that the camera was moved back farther away from the Subject.

WW

[NorthernFocus]

Well put, Bill. It is conceptually simple. Forget about the extender even being there. Add a 1.4x to a 300 2.8, now you're shooting a 420mm f4. Period. Behaves as if it was made that way at the factory.

[Glenn NK]

There is another cost associated with extenders - image quality.

One thing for sure is that they never improve image quality.

Someone claimed that if they shot without the 2X and cropped down to the size that they got with the 2.0 extender - the IQ was better on the cropped image - that's bad.

And they all cost about $450. I have the Canon 2X Mark III and frankly I wish I had the money instead.

Glenn

[William W]

. . .they all cost about $450. I have the Canon 2X Mark III and frankly I wish I had the money instead. . .

Much of the outcome depends upon with what lenses the Canon EF Extenders are used.

This image below was made with the EF70 to 200F/2.8L USM + 2.0MkII EF Extender.
Lens used at 200mm (400mm equiv)
F/6.3 @ 1/1600s @ ISO250 Head-On Motion - Hand Held.

Note this is the lens stopped down only 1/3 stop

IMO the x2.0MkII (or MkIII) is a pretty handy device to have in the kit as for this shot my alternative was lugging the 400F/2.8L all day - and that is quite heavy for just a few shots - and it is not a zoom.




*


Below is made with the EF70 to 200F/2.8L USM + 2.0MkII (used at equiv 400mm)
F/6.3 @ 1/640s @ ISO250 Transverse Motion - Hand Held.

Again, the lens stopped down only 1/3 stop



***

. . .Someone claimed that if they shot without the 2X and cropped down to the size that they got with the 2.0 extender - the IQ was better on the cropped image - that's bad.

Also as well as considering what lens is used - to the ‘someone’ who made the claim about extenders vs. cropping - I would mention that reasonably targeted tests have to be performed to make any practical evaluation.

Reference in this link is part of the results of one such field test.

WW

[NorthernFocus]

Teleconverters are funny things. They can work fine on one lens and terrible on another. Do they improve or degrade image quality? I'd argue they can do both depending on context. Using a 2x converter on a lens puts four times as many pixels on target as if you cropped down to the same perspective with the bare lens. The IQ has to be grossly degraded for that to be a bad trade. However it's hard to argue that the IQ would be better with the same lens if you cut the distance in half rather than use the 2x. Unfortunately sometimes that's not an option.

This is one of those topics that is ripe for discussion/disagreement because there is no right answer. Fortunately the question posed in the OP is not subjective.

[Texas Dave]

Just for the record, I want to say, I really appreciate you folks!

[jcuknz]

Tangitally relevant to the discussion ... years ago I did a test between cropping from the image to using 'digital zoom' and could see no difference in results .... these days I have a 2.2 [Raynox] and x1.7 [Olympus] tele adaptors.... I prefer the Oly becuase it is dreadful to be 'too close' and not be able to zoom out without vignetting. With my rig and it is bound to be different with others I cannot zoom back with the 2.2 but can come back to nearly halfway with the 1.7. The camera is an FZ 20/30/50 over the years.

[chauncey]

I have the Canon 2X Mark III and frankly I wish I had the money instead.

I was going to suggest to Glenn that something was amiss as I have had stellar results from mine,
until Bill provided his link.
Cropping an image to the FOV of an image without using the TC might very well work for internet display
but hopes for a decent size print would prove improbable at best.