35mm f2 IS maximum magnification with tubes

[bluenoser1993]

I'm a little confused as to why Canon's specs for prime lenses show a "range" for max magnification when using extension tubes. For example, the 35mm f2 IS has a MM of 0.24X alone, when paired with the 25mm extension tube the spec sheet states a range of 1.04 - 0.79X.

With the additional magnification to be gained calculated by dividing the tube mm by the focal length mm, I understand how there could be a range for a zoom lens, but for a prime?

Can someone please explain this? I'm gearing up a rig to photograph slides and film of some old family photos and would like to avoid the purchase of a dedicated macro lens, as macro isn't something I tend to do. I'm using a 7D II, so don't need a full 1:1 result, just want to know if Im in the ball park.

Thanks

 

[scyrene]

I'm a little confused as to why Canon's specs for prime lenses show a "range" for max magnification when using extension tubes. For example, the 35mm f2 IS has a MM of 0.24X alone, when paired with the 25mm extension tube the spec sheet states a range of 1.04 - 0.79X.

With the additional magnification to be gained calculated by dividing the tube mm by the focal length mm, I understand how there could be a range for a zoom lens, but for a prime?

Can someone please explain this? I'm gearing up a rig to photograph slides and film of some old family photos and would like to avoid the purchase of a dedicated macro lens, as macro isn't something I tend to do. I'm using a 7D II, so don't need a full 1:1 result, just want to know if Im in the ball park.

Thanks

If I recall correctly, the range of magnifications relates to the fact you can focus at a range of distances. With extension tubes, you lose infinity focus, so the magnification range would be highest at minimum focus distance (closest focus), and highest at the furthest distance you can still focus with the tube attached. That is true for each focal length, so a prime lens still has a range of magnification values.

 

[bluenoser1993]

Thanks, that makes good sense. I didn't think about the loss of infinity focus causing such a drastic loss of focus range.

Maybe I'm looking at this too mathematically, but it still doesn't add up. With a 25mm tube, 25/35=0.71; 0.71+0.24=0.95, which is the calculated max magnification, as apposed to the spec of 1.04X at the long end of the range. Even if you assume everything was rounded off in a way to have max affect, i.e. MM = 0.244 and spec of 1.035, in order for the math to work out the lens focal length would have to be 31.6mm. I realize focal lengths get rounded off for marketing purposes, but is the 35 f2 IS really only a 31.6mm lens?

Is the math only an approximation and there are other thing at play here?

 

[ajfotofilmagem]

Thanks, that makes good sense. I didn't think about the loss of infinity focus causing such a drastic loss of focus range.

Maybe I'm looking at this too mathematically, but it still doesn't add up. With a 25mm tube, 25/35=0.71; 0.71+0.24=0.95, which is the calculated max magnification, as apposed to the spec of 1.04X at the long end of the range. Even if you assume everything was rounded off in a way to have max affect, i.e. MM = 0.244 and spec of 1.035, in order for the math to work out the lens focal length would have to be 31.6mm. I realize focal lengths get rounded off for marketing purposes, but is the 35 f2 IS really only a 31.6mm lens?

Is the math only an approximation and there are other thing at play here?

The focal length (200mm for example) is measured with the lens focused on the infinite distance. When using a 200mm lens focused on a nearby object, it is actually shorter as 170mm for example.

It is expected that a lens labeled 35mm, when focused on a nearby object is effectively 31mm about.

 

[bluenoser1993]

Great, thanks, that explains it. Looks like I'll end up getting both extension tubes, as I have Advantix (APS) sized film requiring a 1X MM and 35mm film & slides for which I'll need 0.6X MM while shooting it on an APS-C camera. Had hoped one would do the job.

 

[d]

Don't forget there are a few third-party options for extension tubes that can save you some money over purchasing the Canon ones. The Kenko tubes are supposed to be decent (though I've never used them).

d.

 

[scyrene]

Don't forget there are a few third-party options for extension tubes that can save you some money over purchasing the Canon ones. The Kenko tubes are supposed to be decent (though I've never used them).

d.

Kenko tubes are excellent if you're not intending to mount a big, heavy lens on the front. For the 35mm lens, I wouldn't pay the extra for Canon own brand. However a word of warning to others - I had a Kenko 12mm tube shear off when mounted with my 500mm lens. I believe the Canon ones are built more solidly.

 

[bluenoser1993]

The Aputure brand, set of 3, 13, 21, 31mm look appealing for less than what the Canon 25mm cost. They seem to be reviewed favourably when compared to the Keno. They are even in stock in my local camera store, where as the Canon are not.

 

[bluenoser1993]

Well, that was all for nothing. I expected the loss of focus at infinity, but I didn't expect the subject to have to almost touch the lens before it could focus. My slide/film duplicator has a fixed barrel length of about 90mm, so way outside the range of usability of the 35mm lens and tubes. Guess the tubes are going back and the EFS 60 macro stays in my bag.