Beginner Question about extenders

Jwar1976

Jwar1976

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John
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Hi all,

I recently purchased two teleconverters a Canon 1.4x MKII & a Kenko Teleplus 2x. Now the thing is that while I am happy with test shots when connecting my 70-200 2.8L II to my 7D, I am extremely puzzled on why in LR Classic, it is only showing the view as 280mm in the Metadata, where as by rights it should be 640mm at it’s longest. Part of me is thinking is because the teleconverters are EF mount so reading technical data as tho it is connected to a Full Frame, but then I could be completely wrong.

Is there anyone here that can shed light on this ?.

Many thanks
 
Two observations.....
Only the converter closest to the body will be read to adjust the reported focal length.
Your figure of 640mm would seem to be derived by using the 1.6 crop factor of the 7D......this is only a cropped image and the focal length of the attached lens/converter is exactly that, focal length, and it does not change whether the lens or combination is mounted on a crop body, full frame body or any other sensor format size.
 
Normally one teleconvertor will be reported to the camera, the one closest to the lens. This is because the teleconverter tells the lens of its presence, which it then includes in the data it sends about itself back to the body. As the second teleconverter cannot tell the first one that it exists too, the lens does not know about it to tell the body.

Also, depending on the version of Kenko one you have it will not fully report its presence. Those are DGX ones, though I am not sure what data they do report, if any. This is so that they can fool a camera's AF system into working with larger maximum apertures than they support. The Canon EOS 7D only supports autofocus up to f/5.6. Using a 2x teleconverter on an f/4 lens, for example, would make it f/8 and the camera would refuse to autofocus otherwise.

And the focal lengths of lenses are the focal length of lenses. Because of the popularity of 35mm film cameras, there is a tendency to talk about cameras with smaller sensors in terms of the equivalent focal length to get the same field of view as you would with a 35mm one.

Whilst 560mm (200 x1.4 x2) on a camera with a Canon APS-C sensor gives the same field of view as an 896mm lens on a camera with a 35mm sensor, the physics are it is still a 560mm lens. So that is what will be recorded, or at least it would if it knew about both teleconverters being present.
 
Thanks for the replies, I haven’t stacked the Teleconverters at all, either the Canon 1.4x MKII or the Kenko C-AF 2x DGX, both show as 280mm when connected to the 70-200 & 7D MKI
 
So the Kenko 2x teleconverter is only reporting itself as a 1.4x?

What do the other EXIF fields say? I have 1.4x and x Kenko ones, but they are much older DG types which properly report their presence. So in the EXIF data they show the lens name with a "+ 1.4x" of "+ 2x" appended.

Once you start using third party teleconverters, or stacking them, the whole issue of what gets reported can get messy due to software compatibilities and was of getting around restrictions.

Looking back at an old photo of mine, it seems when I have staked them the correct focal length is recorded (i.e. 560mm from my 70–200mm), even though only the presence of the one closest the lens was reported in the lens data. Presumably as the communication to the camera passed through the second one it leaves the lens data alone but applies a correction to the focal length.
 
mij said:
So the Kenko 2x teleconverter is only reporting itself as a 1.4x?

What do the other EXIF fields say? I have 1.4x and x Kenko ones, but they are much older DG types which properly report their presence. So in the EXIF data they show the lens name with a "+ 1.4x" of "+ 2x" appended.

Once you start using third party teleconverters, or stacking them, the whole issue of what gets reported can get messy due to software compatibilities and was of getting around restrictions.

Looking back at an old photo of mine, it seems when I have staked them the correct focal length is recorded (i.e. 560mm from my 70–200mm), even though only the presence of the one closest the lens was reported in the lens data. Presumably as the communication to the camera passed through the second one it leaves the lens data alone but applies a correction to the focal length.
Click to expand...

All the other details are correct, regarding shutter / iso etc. Interestingly enough I checked another photo which was using my 100mm 2.8L on the 7D, but without the teleconverter and in the EXIF data, it states that the focal view was still 100mm, even tho it was on the 7D. Must admit I am puzzled as have seen people on Flickr use similar combinations, yet their EXIF data shows the extra focal range, should it be the Canon 1.4x or Kenko 2x on a crop sensor.

I have just used a EXIF viewer and it states the following in Composite

Focal Length 35efl 140mm (35 mm equivalent 872.6mm)
hyperfocal distance 726.o6m
 
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That is because it is still a 100mm lens, even on the 7D. The focal length is a characteristic of the lens regardless of the size is of the sensor of the camera. Some cameras may record an additional FocalLengthIn35mmFormat tag, but the Canon EOS 7D is not one of them.

The Composite tags returned by EXIF Viewer and ones that the software calculates for your convenience, but they are not recorded b the camera. Only the data in the EXIF (generic information) and MakerNotes (camera-specific information) information are actually stored in the image file. And without a FocalLengthIn35mmFormat I think the ScaleFactor35efl and CircleOfConfusion are read from a database to be able to calculate the 35mm equivalent focal lengths and hyperlocal distances.

If people on Flickr are able to show the 35mm equivalent focal lengths in their EXIF it could either be because they are using different camera models which record this information, or they are using editing software which inserts it.

But the debate over crop factors has been going on for well over a decade, but my take on it is that you should ignore making such comparisons. It has no relevance to your photography. That for someone with a different camera a 70mm records more information does not change what lens you need or how you compose your shots. The only time it matters is if you are sharing lenses between cameras with different sensor sizes, or if you are replacing camera with one with a different sensor size and it leaves you needing to buy longer or wider lenses

However, it is also important to remember that whilst the crop factor affects the field of view which is captured, the depth of field remains the same. And that is a just as important a photographic tool.

That is to say if you took a photo at 200mm at the same aperture from the same spot on both a 5D and 7D then the area of the image captured would be different, with the latter showing a smaller (cropped) portion of the 5D image. But if you cropped the 5D image to match the 7D one then they would be identical, because the depth of field would be the same for both cameras.

And whilst a 280mm lens on the 7D would allow you to capture the same area of image as the 5D, it would have a greater depth of field due to the longer focal length.

Or if you move closer to your subject with a 200mm lens on the 7D until you fill the frame with the same image as the 5D captured, the depth of field would now be smaller because you are focusing much more closely.

This is why I say the focal length is a matter of physics. This is why all lenses, whether EF-S ones or those for large format cameras, all record the focal length the same way even though the area of the image recorded will be different based on the frame size of the film or sensor.
 
mij said:
..........
And whilst a 280mm lens on the 7D would allow you to capture the same area of image as the 5D, it would have a greater depth of field due to the longer focal length.

Or if you move closer to your subject with a 200mm lens on the 7D until you fill the frame with the same image as the 5D captured, the depth of field would now be smaller because you are focusing much more closely.
Click to expand...
It might be that something went slightly awry with your explanation during the two quoted paragraphs?......(it may also be my reading of them and, if so, I appologise)
Bob
 
I used my 70-200mm with a 1.4X extender very recently and the EXIF is correctly reported as 280mm focal length. I happen to have a full frame camera but if I was using a half frame it would still correctly report 280mm because that it what it is. The crop factor is a crop factor and not a change of focal length. So if taking the same shot from the same position I could crop my FF image in LR and end up with exactly the same picture as captured by the crop camera.

280mm is not really long enough for nature which I have been doing recently but I have not felt justified in buying another longer lens, One thing I have discovered out taking butterflies is that the long combination is better than using my Macro lens, When I approach the insect with the Macro lens, before it is larger in the frame than the long lens, it flies away. This would not be true all the time but was certainly true at a local Butterfly conservation area.

Dave
 
Way back I bought the non-USM version of the Canon 70–200mm f/2.8 over the then new f/4 IS model specifically so I could use it with a 2x teleconvertor to cheaply get the extra reach. Both because the lens quality meant it should work well with a teleconvertor (I think it does) and it would still be able to autofocus on my camera. And being a heavy lens I assumed I would mostly use it on a monopod, if not a tripod, anyway.

Canon Bob said:
It might be that something went slightly awry with your explanation during the two quoted paragraphs?......(it may also be my reading of them and, if so, I appologise)
Bob
Click to expand...

No, you are right and that did get rather garbled! Firstly I got confused with the teleconverter factor of 1.4x when obviously the lens in the example should be 320mm because of the 1.6x factor for Canon's APS-C sensors. And obviously you need to move backwards from a 5D with the same focal length lens to increase the ares being captured to take the same image. Which of course flips the depth of field effects from he way I described them. I even got it right for the second one but then changed it because it had to be the opposite of changing position, which it is but not in that reason. And to think I was trying to keep it simple without mention the compression of perspective too. Instead it is a total mess! I am very sorry about that.

Just so anyone reading does not get confused, here it is again hopefully described properly.

Assuming a shot taken at 200mm with a Canon 5D, there are three ways you can use a 7D to capture the same image area:

a) you take a shot in the same location using a 200mm lens then crop the 5D image,
b) you take a shot in the same location using a 320mm lens, or
c) you use the 200mm lens but move further back from the subject so the same area is covered in the 7D viewfinder.

However if you use the second method (b) then although the same image area will be covered they will not be identical. The depth of field is a factor of focus distance, aperture, and focal length. By increasing the focal length of a lens whilst keeping the other two the same you reduce the depth of field. Also longer lenses have a narrower angle of view, so whilst the subject will fill the frame on the 7D the same way it did on the 5D, the background will be more compressed. It will make it seem closer to the subject whilst losing background objects to the left and right of the subject. To be more technical, although perspective is only affected by the distance from the subject so does not actually change, but it is the smaller angle of view that is effectively cropping how much of the background is captured.

The third method (c) has the opposite effect. By increasing the focus distance in being farther from the subject, while keeping the focal length (and aperture) the same as the 5D shot, you increase the depth of field. And although you are using a lens of the same focal length, so it has the same angle of view as the 5D, the greater distance from the subject will widen the perspective. This will make the background appear to stretch farther back and capture more of what is to the left and right of the subject.

Only the first option (a) will produce two identical images, with the same background perspective, and the same depth of field.

This is why a 70–200mm lens is the same regardless of the size of the sensor in the camera, and why it should to be recorded that way. Because a 112–320mm lens will not give the same images on a 7D as a 70–200mm lens on a 5D. In identical shooting positions the 7D will have less depth of field and a more compressed background.

A crop factor is simply that, it relates to the amount of and image that has been effectively cropped from what would have been captured in a 35mm frame. It has does not have any relevance to the lens itself.

And to keep this to the topic, none of this applies to teleconverters as they do effectively change the focal length of the lens. So the 2x factor of a teleconverter on a 70–200mm lens will give the same image as using a 140–400mm lens all other things being the same.

I hope that is better. I have the Vertigo dolly zoom effect on a loop in my head trying to make sure I got it all straight this time!
 
I have just read the thread and have found the debate very interesting as I have just purchased a 2x converter for my Nikon D750. I have just upgraded to full frame from a crop sensor and have obviously lost the reach I gained via the crop so purchased the Kenko (test shots) it seem excellent on my old D90 with my 70-300G f3.5 - 5.6 and superb on the 80-200 D F2.8, hope that my D750 will be just as good with this as I want\need the reach for nature shots at our local bird reserve.
 
Interesting enough as Kenko use reverse engineering on their extenders, they do fit on my Tamron 100-400. However the conditions need to be perfect as at it’s longest, it goes from F6.3 to F9 but still get centre point AF as third party extenders trick the camera into thinking it is F8. I haven’t fully tried it yet as when extended it just keeps hunting, so am hoping to find a way around that without having to buy the official Tamron TC.
 
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