Kjeld Olesen
Senior Member
Just to initiate those who have not followed this debate, the issue is that in order to stack two Canon teleconverters (extenders) one has to insert a 12 mm extension ring between them due to the protruding front elements. Logically this assembly should not be able to focus at infinity due to the inserted extension tube, but on the other hand especially longer tele photo lenses has the ability to focus "past" infinity. So, the question is whether the inherent ability to focus past infinity is enough to overcome the inserted 12 mm extension. Obviously, you will need a rather long tele lens before this would become a reality.
This issue has been debated regularly, and while I have generally been advocating the point infinity focus could be retained I recently erroneously reported that it was not retained with my 400/2.8 L mkI. The reason for that was that I had assembled my 2x and 1.4x extenders in the wrong order - the 2x extender (at least with this lens) needs to go on the lens while the 1.4x goes on the camera. This makes perhaps some sense since it makes the lens effectively a 800 mm lens before the 12 mm extension is added.
In any case, just last week I went to Jaegerborg Dyrehave to photograph the fallow deer (Dama dama) rutting and decided that this time I'd go far maximum reach and stack both converters onto the 400/2.8 L mkI. This time I did stack the converters in the correct order. The effective aperture becomes f/8.0 and since I was using a D5 I had to use manual focusing. Infinity focus turned out to be JUST retained with this combination. When focused at infinity the focus mark is now on the right end of the laying L rather than at the bend. There is still about 2 mm of turning ability left.
To document this, below is a scaled down picture of the Eremitage Slot taken at distance of about 700 meters (from Det Flade Vandhul)
And here are a few of the best result of the day, all taken with the stacked converters (1120 mm effectively) at ISO800 (5D) and stopped down 1/2 f-stop.
Yes, this was when I wished that I had NOT stacked the extenders :-(
--
Kjeld Olesen
http://www.acapixus.dk
This issue has been debated regularly, and while I have generally been advocating the point infinity focus could be retained I recently erroneously reported that it was not retained with my 400/2.8 L mkI. The reason for that was that I had assembled my 2x and 1.4x extenders in the wrong order - the 2x extender (at least with this lens) needs to go on the lens while the 1.4x goes on the camera. This makes perhaps some sense since it makes the lens effectively a 800 mm lens before the 12 mm extension is added.
In any case, just last week I went to Jaegerborg Dyrehave to photograph the fallow deer (Dama dama) rutting and decided that this time I'd go far maximum reach and stack both converters onto the 400/2.8 L mkI. This time I did stack the converters in the correct order. The effective aperture becomes f/8.0 and since I was using a D5 I had to use manual focusing. Infinity focus turned out to be JUST retained with this combination. When focused at infinity the focus mark is now on the right end of the laying L rather than at the bend. There is still about 2 mm of turning ability left.
To document this, below is a scaled down picture of the Eremitage Slot taken at distance of about 700 meters (from Det Flade Vandhul)
And here are a few of the best result of the day, all taken with the stacked converters (1120 mm effectively) at ISO800 (5D) and stopped down 1/2 f-stop.
Yes, this was when I wished that I had NOT stacked the extenders :-(
--
Kjeld Olesen
http://www.acapixus.dk
