Infinity focus & extension tubes

[mmodica]

This is going to sound like an odd question, but... what is the maximum length extension tube I can use without losing infinity focus at all focal lengths on my Canon T1i/28-135mm? The reason I'm wondering is because I'd like to get an ET and leave it on all the time since I try to avoid removing my lens as much as possible.


Thanks!

[Sean Setters]

For all intensive purposes, you will lose infinity focus on all lenses when using extension tubes. I

[Fast Glass]

The only lenses in general that allow you to use a very small extension tube are super telephotos, my Minolta MD 600mm f/6.3 could use a guesstimated 8-10mm extension tube before I lose infinity focus. I have a 12mm tube and it doesn

[Dr Croubie]

once again i post something and tdp just doesn't update it.

anyway,
my 15-85 and 70-300L both focus 'past' infinity, so theoretically i can
put in 'something' in extension tubes and still get to infinity.

but
it depends if you mean 'focus at infinity' or 'focus at hyperfocal and
let DOF keep infinity in focus'. the latter is obviously more easily
achievable, but then you may have some kind of limited aperture range.

*wanders off to find his kenko tubes and experiment*


.


first test, 70-300L with 12mm extension tube.


focussing at farthest, 300mm, back fence is out of focus. longest focus distance ~ 5m


70mm, i can get my foot in focus if the sensor plane is around the height of my knee.


no way either of them can use any aperture less than f/100 to get infinity in focus using DOF.


where's my 15-85?

[Dr Croubie]

15-85 +12mm results:


85mm, farthest focussing is about waist-high to the ground.


15mm, focusses perfectly on the waterdrops on the front of my lens, put there by the dew on the grass i was trying to focus on


.


and finally, nifty fifty 1.8.


farthest focussing with a 12mm tube is about 20-30cm.


.


.


so you don't have the same lens as me, but the trend is clear: ie, it's not worth it unless you can find a 1-2mm extension tube.


just
buy yourself a good sensor cleaning kit and get used to it (or just
forego being able to take really macro shots without changing a lens)

[Dr Croubie]

I've seen some debate as to whether or not
a 12mm extension tube could be used on a very long telephoto lens and
still retain infinity focus, but I've never seen proof of it working.

and
just to spam this thread with another reply: i've got a 250mm f/3.5
soviet MF prime, and two 2x teleconverters (making 1000mm f/14). if i
could find a way to mount it on a tripod i'd give it a go when the sun
comes out...

[Sean Setters]

and just to spam this thread with another reply: i've got a 250mm f/3.5 soviet MF prime, and two 2x teleconverters (making 1000mm f/14). if i could find a way to mount it on a tripod i'd give it a go when the sun comes out...

LOL.....go for it.

[mmodica]

Thanks for all the replies everyone. Focusing off to the hyperfocal would be fine, but I calculated that the hyperfocal at 135mm with f/5.6 would be ~557 ft which is pretty close to infinity. Even stopping down to f/11 (which I almost never do) only brings the hyperfocal back to 279ft.


Judging by the distance scale on the 28-135mm it looks like at the shorter focal lengths it can focus past infinity but again I do like being able to zoom to 135mm. I guess I

[Dr Croubie]

I don't know what was worse:


the IQ i got from 2x 2x teleconverters that seem to love purple, mounted on an already not-the-best lens,


or the thought of my neighbours ringing the cops because i was
pointing a big, black, bazooka-looking thing in the vicinity of the city
centre:


[img]/photography_gear1/resized-image.ashx/__size/1200x0/__key/CommunityServer-Discussions-Components-Files/8/7608.P7112335s.JPG[/img]


.


at any rate, the farthest focussing i got was about 3-500m, even at
f/5.6 * 4 (f/21.6) my DOF was only a few meters, the branches behind
were OOF. (and the weird things at the top of the photo were a
palm-thing across the road from me, maybe 30-50m away.) the branch at
lower left seems to be the best in focus, best you can get with that
setup at ISO3200 on a 7D at any rate.


[img]/photography_gear1/resized-image.ashx/__size/1200x0/__key/CommunityServer-Discussions-Components-Files/8/7416.IMG_5F00_5958s.JPG[/img]






your mileage may vary, anyone got an 800mmL or a 1200mmL? (there's one on ebay now, only US$80000, who wants to buy it to test?)

[neuroanatomist]

@mmodica - Welcome to the TDP Forums! Nice to see another 'local' (I'm in the Boston area).


To continue the threadjack a bit:

your mileage may vary, anyone got an 800mm

No, but on an outing a couple of months ago (with Bill W.), I tried a 2x II Extender with my 100-400mm. It was a staring contest between a great horned owlet and a grackle. The owlet won, eventually (after a few dive-bombs by the aggressive grackle).


Focusing at 1280mm FF-equivalent (800mm on the 7D) was tough, even on a tripod with IS turned on (and with no IS, it would have been very, very tough!). I think the results of the 800mm combo turned out better than the equivalent shot at 400mm (from the same position) with the FoV cropped to match the 800mm shot:


[img]/cfs-file.ashx/__key/CommunityServer-Components-UserFiles/00-00-00-35-15/100_2D00_400_2B00_2x.jpg[/img]