Is a teleconverter superior to a crop

[enseth]

I've been mucking around with a 1.4 x teleconverter lately. It seems to produce good results but I have been unable to firmly establish whether you gain superior IQ using a teleconverter against just cropping. I'm sure there is a technical analysis of the two processes. Does anyone have the answer to which is "best"?

[ameerat42]

Yes, no, and not necessarily (=maybe, sometimes).

If a good lens and good TC, then generally yes.
If either bad, then pretty much the same.
If both not hot, give up.

What makes it good is that you end up with a larger image, but if that is bad, then...

You might not get 200% IQ with a TC, but something past, say, 180% would be WW.

You'd really have to do tests.

[mpb]

I'm not an expert in relation to TC'er ( or anything for that matter) but:-
You also need to consider the reduced light available when using a TC, from memory you lose 1 stop with a 1.4xTC and 2 stops with a 2xTC.
If you are shooting with plenty of light this may not be a problem.

Also camera shake becomes more of an issue.
May also affect focus speed or even the ability to autofocus.
(need someone with some expertise to confirm above)

[John King]

Gidday enseth

Basically, I agree with Am.

Further warnings - TCs are worth roughly what you have to pay for them.

I have two 2x TCs from my film days, both Teleplus branded. One's highest function was to donate its lens caps to a higher purpose (MC4). It was as bad as that! This was a real cheapie, <$100. The other, an MC7, is a focusing TC for macro type close up work. The MC7 cost a bomb in the early 1980s with a RRP of over $800. It is still worth using to this day.

e.g. Rosa taken with my OM1 plus f/4 200 plus MC7 TC from about 5-6m away (scanned from Agfa Vista 400 negative (print) film:



The harsh, flat light is due to the time of day (around midday/early afternoon), not due to lack of contrast in the TC or lens.

I also have an Olympus EC-14 1.4x TC for my Olympus ILCs. It also cost a bomb, with a RRP of over $700 when released. It does degrade the image quality very slightly, but not really significantly. It does exaggerate any faults in the lens it is used with, however!

It gives me an effective FL in 135 format terms of f/5 and 566mm using my f/2.8-3.5 50-200. As long as I stop the 50-200 down to at least f/5.6, this combo works very well. However, My 50-200 by itself has to be stopped down to f/5.6 to produce the goods. While usable wide open in some circumstances (e.g fairly low DR), it falls apart in others. At f/5.6 and smaller, it is excellent.

[nardes]

Here we go. Our Moon taken as follows:

400mm F5.6
400mm F5.6 digitally resampled x2 in Photoshop
400mm with x2 EF II Extender

Cheers

Dennis

[arthurking83]

I think Dennis just proved that with the right lens, a TC works pretty damned well!

One thing that we know(as in a known known) is that a TC always reduces contrast a little from the bare lens.
So in a low contrast scene, a TC may not be an ideal way to extend a lens's ability.
How much contrast is lost depends on the primary lens tho .. so imagine a lens with low contrast levels shooting in a low contrast scene situation with a TC added that further reduces contrast!

Then you have the added side effect of increased chromatic aberrations due to the TC and so on and so forth.

Personally I'd go with the TC for the most part, rather than shoot with the view to crop.

[tduell]

I have been having some trials and tribulations with my 1.4xTC and my 150-450 (see my sig for lens details).
Basically my problems have been less sharp images when using the TC and shooting birds. Usually this is with the lens at full zoom and handheld.
In my case I think some of the problem has been down to the in-body shake reduction not coping with the FL and my shakes.
In an effort to overcome this I have tried (again) to use a monopod, and my latest efforts are much better, but still not up to the quality I can get when not using the TC.
I have just had (another) look at the AF fine adjustment, but I think it is possible to convince yourself that every time you run through this test process you have made an improvement.
I have yet to see how the latest settings perform.
Quite extensive and well controlled tests of the 150-450, 1.4xTC and other long lenses were reported on PentaxForums, with the conclusion that Pentax's 1.4xTC didn't reduce the IQ of the 150-450, although I think the tests were all done using a tripod.

Cheers,
Terry

[nardes]

I have found that the localised atmospheric conditions play a huge part in IQ when using the 400mm F5.6L, either “naked” or with the x1.4 or x2 EF II Extenders.

Basically if you are looking at mirage-like conditions through the viewfinder – forget it!

Hot air rising above warm concrete, buildings, roads, etc. plays havoc with IQ. The Moon shots were taken through more stable air, over grass and pointing up.

Cheers

Dennis

[enseth]

Thank you for the comprehensive answers. Nardes moon photos illustrate the benefits of a TC under ideal conditions. I will continue with the TC where appropriate and once again thank you all for your input.

[Lance B]

As others have said, it depends.

As a rule, I would suggest that if you need to gain 1.5 times the image size, then generally a TC will be better but it depends on the light because you are shooting at 1 stop slower and this may affect the AF speed of the lens and you may miss the shot. Your ISO will also need to go up in accordance as well. It also depends on how big you are going to display your images before any drop off in IQ is detected. The thing is with all this stuff is that it's all a compromise and you have to judge which compromise fits the situation best.

On a "fast" lens, like an f2.8 telephoto, TC's can work brilliantly and they generally work at their best. On "slower" lenses, they may not work quite as well, but the 1.4x TC's generally have little impact on most lenses as far as IQ is concerned. The other thing to consider is that AF speed and acquisition is also compromised but has less affect on a "fast" lens compared to a "slower" lens and this can be a real issue when chasing birds, wildlife etc. Again, the 1.4x TC will have less impact on AF speed and acquisition than an 2x TC but generally, they both will affect an f4 or slower lens more than an f2.8 lens.

I am speaking from my experience with my Nikon gear: On my Nikon 300 f2.8 VRII and Nikon 400 f2.8E FL VR, the Nikon 1.4x TCIII almost makes no difference to IQ and little difference to AF speed, it has a 1 stop light penalty thus an f2.8 lens "becomes" a max aperture f4 lens. The Nikon 1.7x TCII has a little more of a hit on IQ and AF speed, an f2.8 lens "becomes" a max aperture f5 lens. The Nikon 2x TCIII has about the same IQ drop off as the 1.7x TCII and a slightly more of a hit to AF speed and acquisition.

Here is a sample of my 400 f2.8E FL VR + 1.4x TCIII showing that if it has affected IQ I can't tell it from the lens bare!! These are large images:

[fillum]

Some good info already, but a couple of additional points (although not really related to IQ)...

Autofocus (AF) :- although a TC may have a negative impact on AF speed, the magnified view can make it easier to track your subject and keep the focus point on it. Probably not too applicable for moon shots but can be helpful for sport and wildlife.

Depth-of-Field (DoF) :- with a crop you are 'faking' the angle-of-view of a longer focal length (FL) but you are basically getting the DoF of the actual lens FL. This may or may not be relevant and really depends on your intent. Shooting field sports for example, you typically want to minimise DoF to separate the subject from the background. A shot taken with a 2.0x TC at 400mm and f/5.6 will show less DoF (i.e. more separation) than a shot taken at 200mm and f/2.8 which is cropped to give the same angle-of-view. [The reduced max aperture will increase the DoF, but the increase in FL decreases DoF by a larger amount, resulting in an overall decrease in DoF].

I shoot junior Aussie Rules with a 70-200/2.8 and initially used a 1.4x TC (Kenko I think). Was ok but I found that I get sharper results more consistently by not using the TC and cropping instead. I've been intending to get the Nikon 2.0x TC in order to get more field coverage.


Cheers.

[ameerat42]

...Depth-of-Field (DoF) :- with a crop you are 'faking' the angle-of-view of a longer focal length (FL) but you are basically getting the DoF of the actual lens FL. This may or may not be relevant and really depends on your intent. Shooting field sports for example, you typically want to minimise DoF to separate the subject from the background. A shot taken with a 2.0x TC at 400mm and f/5.6 will show less DoF (i.e. more separation) than a shot taken at 200mm and f/2.8 which is cropped to give the same angle-of-view. [The reduced max aperture will increase the DoF, but the increase in FL decreases DoF by a larger amount, resulting in an overall decrease in DoF]...

Fillum, this has to be clarified.

...Depth-of-Field (DoF) :- with a crop you are 'faking' the angle-of-view of a longer focal length (FL) but you are basically getting the DoF of the actual lens FL.

By "faking', do you mean only because you are getting the DOF of the original lens?
If so, it is incorrect. The crop is effectively a magnification of that part of the scene, as would the same scene rendered by a TC where the APERTURE of the original lens has not changed.

Ie, if you set f/2.8 on the lens and did not change that setting with the TC, then the TC would multiply that f-stop (let's say by 2X) to f/5.6. But the actual aperture would still be the same size as it was before you put on the TC.

So, all you have done is magnify the scene IN-camera through the same aperture as you used whether with TC or without.

To change the DOF you need to change either the Aperture or the subject distance.

[fillum]

By "faking', do you mean only because you are getting the DOF of the original lens?

What I'm saying is that the (appropriately) cropped view with the native lens will show the same amount of the scene as the TC version - I used the word 'faking' (in quotes) as the reduced angle-of-view is achieved in post rather than on-camera.

I also stated that there would be a variation in the DoF between the two scenarios due to the change in FL and effective aperture. HOWEVER, something I thought of but didn't mention, as I considered it to be negligible (and confusing), is the effect on the circle-of-confusion on the cropped image which will affect the DoF on the final output (similar to shooting with a smaller sensor - oh no, not that again ). At the moment (Friday arvo ) I can't get my head around how much cropping you would need to do to match the lens with TC. If it's considerable then the DoF may be the same / similar between the two scenarios. I've always felt that a TC on a lens at max aperture and FL gives reduced DoF compared to the lens alone, but I've never done any testing into it so could be way wrong.

To change the DOF you need to change either the Aperture or the subject distance.

Or focal length - which is what the TC is doing.


Cheers.

[ameerat42]

(I wasn't worried about any "fakery" at all.)
The last part is what I disagree with - changing focal length.

Have a look at the CIC Reference here and scroll down to the part
"CLARIFICATION: FOCAL LENGTH AND DEPTH OF FIELD".

This is what I mean. In have seen many times when they try to implicate focal length (incorrectly AFAIK) as a DOF factor.

A simple test would be to try it. I'm up and down ladders (escaping snakes?) today, but ASAP I will give it a whirl.

- - - Updated - - -

Note: If anyone else wants to try, make sure your subject distance is fairly large, because if only across, say, a few
to 50 m, then there will be some effect from the movement towards the subject of the lens itself. Mmm!, maybe not
less than 20 m.

[William W]

Apropos DoF and Extenders or Tele-converters:

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

Concept 1.

> A tele-converter (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: x2.0 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.

(This is the Axiom of DoF and applies for general photography at typical Subject Distances: not Macro-photography and not at SD when approaching infinity).

*

Concept 3.

> DoF when it is in discussion about or comparisons of FINAL IMAGE(S) - must assume that the Final Images are all Viewed at the SAME distance and are all of the SAME enlargement.

(This point is critical to this conversation, where commentators want to COMPARE the DoF between FINAL IMAGES of differing ENLARGEMENTS).

***

So, if one wants to compare the DoF between the image made with a native lens and then that image is cropped - to that lens used with a tele-converter and when both images are the SAME SIZE and are to be viewed at the SAME Viewing Distance - then one needs to:

> firstly reckon the DoF of the native lens at the Aperture used

> secondly reckon the DoF for the "lens assembly" comprising lens and the tele-converter at the Resulting Aperture used

> thirdly adjust the computation for the DoF for the ENLARGEMENT of the cropped image (i.e. so it appears the SAME SIZE for viewing, as the SIZE of the other image) - this can be done by adjusting the CoC - or - by using a factor for the enlargement.


WW

[ameerat42]

A most erudite exemplification and exposition, WW.

I have eluded the serpents and descended from the ladder, but I won't be up to running a test until,
hopefully, tomorrow.

[William W]

Ta. I appreciate that comment.

WW

[William W]

I've been mucking around with a 1.4 x teleconverter lately. It seems to produce good results but I have been unable to firmly establish whether you gain superior IQ using a teleconverter against just cropping. I'm sure there is a technical analysis of the two processes. Does anyone have the answer to which is "best"?

- and -

Thank you for the comprehensive answers. Nardes moon photos illustrate the benefits of a TC under ideal conditions. I will continue with the TC where appropriate and once again thank you all for your input.

But there is the unanswered question still remaining . . . (referencing Post #2)

Will you make the time to do the various tests to get closer to an answer for the gear that you are using under different conditions?

REF Post #2:

. . . You'd really have to do tests.

Here is an example of a simple Field Test. - After you open each image, you can click on that image to view it LARGE.

WW

[arthurking83]

......


The crop is effectively a magnification of that part of the scene, as would the same scene rendered by a TC where the APERTURE of the original lens has not changed.

.....

This is a common mythconception!

You don't ACTUALLY magnify anything .. you're only cropping.

Magnification actually has a standardised definition .. and cropping isn't part of that definition.

Of course in every day lingo, we do tend to use the term 'magnify' (incorrectly) .. but this is exactly what is NOT happening when you crop, or use a cropped sensor!

OTOH: when adding a TC between a camera and lens, and keeping all other relevant variables the same .. then you are in fact magnifying the scene.

[ameerat42]

AK. It is used in the sense that the thread is about, viz:
"Do I enlarge using a teleconverter, or by cropping and [something that means magnifying but which is enlarging in PP]..."