- Thread starter Celsius
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Celsius said:

I have seen some of you guys use a zoom lens lik 70-200mm lens with a 25mm extension tube for macro work. However I read somewhere that such combi can reach only reach a magnification of 1/8X at 200mm. How is it possible for you guys to have such good magnification? Please enlighten. Thanks.

Celsius said:

Magnification = extension tube length / focal length ?

Or did I get the formula wrong?

Or did I get the formula wrong?

If i dun get wrong

Total extension = tube length + lens extension

Magnification = Total extension / Focal length of lens

Assuming the lens has ard 25mm extension by itself, this gives u total 50mm with a tube and ard 50/200 = 1/4 X.

Correct me if im wrong abt this.

xdivider said:

I think u have to take into consideration the minimum focussing distance of a lens. The lens has a built-in extension.

If i dun get wrong

Total extension = tube length + lens extension

Magnification = Total extension / Focal length of lens

Assuming the lens has ard 25mm extension by itself, this gives u total 50mm with a tube and ard 50/200 = 1/4 X.

Correct me if im wrong abt this.

If i dun get wrong

Total extension = tube length + lens extension

Magnification = Total extension / Focal length of lens

Assuming the lens has ard 25mm extension by itself, this gives u total 50mm with a tube and ard 50/200 = 1/4 X.

Correct me if im wrong abt this.

Celsius said:

You might be right. Still 1/4x seems quite far from life size magnifcation. But judging from some of the closeup/macro shots posted here with such a setup seems quite near 1:1 magnification.

Celsius said:

I assume you’re referring to my Thread .

The magnification you gain from Extension tube is dependent on both focal length and extension tube length. For subject below 20cm size, I normally stays at 70mm-100mm focal length, unless I want more working distance then I’ll use 150mm-200mm of course magnification will be lesser.

Like what xdivider said, crop factor of 1.6X for DLSR plays an important role to increase the magnification as well. But, I always based my calculation using the standard formula we all know. (ExTube length / focal length)

For my above thread, it was shot at around 100mm, 150mm and 75mm repectively (with 10-20% cropping)

One of the best way to increase magnification is to use an Extender between the cam and the extension tube. In this matter, the extender will multiply your extension tube strength leaving the minimum focusing distance the same.

This was shot using 70-200mm + 25mm ext tube + 1.4X TC at 70mm focal length. (cropped about 5% only) Your 25mm now becomes 35mm giving you around 1/2X at 70mm focal length.

Sgt. Pepper said:

Hi Celsius,

I assume youre referring to my Thread .

The magnification you gain from Extension tube is dependent on both focal length and extension tube length. For subject below 20cm size, I normally stays at 70mm-100mm focal length, unless I want more working distance then Ill use 150mm-200mm of course magnification will be lesser.

Like what xdivider said, crop factor of 1.6X for DLSR plays an important role to increase the magnification as well. But, I always based my calculation using the standard formula we all know. (ExTube length / focal length)

For my above thread, it was shot at around 100mm, 150mm and 75mm repectively (with 10-20% cropping)

One of the best way to increase magnification is to use an Extender between the cam and the extension tube. In this matter, the extender will multiply your extension tube strength leaving the minimum focusing distance the same.

This was shot using 70-200mm + 25mm ext tube + 1.4X TC at 70mm focal length. (cropped about 5% only) Your 25mm now becomes 35mm giving you around 1/2X at 70mm focal length.

I assume youre referring to my Thread .

The magnification you gain from Extension tube is dependent on both focal length and extension tube length. For subject below 20cm size, I normally stays at 70mm-100mm focal length, unless I want more working distance then Ill use 150mm-200mm of course magnification will be lesser.

Like what xdivider said, crop factor of 1.6X for DLSR plays an important role to increase the magnification as well. But, I always based my calculation using the standard formula we all know. (ExTube length / focal length)

For my above thread, it was shot at around 100mm, 150mm and 75mm repectively (with 10-20% cropping)

One of the best way to increase magnification is to use an Extender between the cam and the extension tube. In this matter, the extender will multiply your extension tube strength leaving the minimum focusing distance the same.

This was shot using 70-200mm + 25mm ext tube + 1.4X TC at 70mm focal length. (cropped about 5% only) Your 25mm now becomes 35mm giving you around 1/2X at 70mm focal length.

70-200mm + 25mm ext tube + 1.4X TC

how close can i get to?

Sgt. Pepper said:

@70mm + 25mm ext tube, the min focusing distance is about 4-5 inches. If you add 1.4X TC, the min focusing distance should not change but the magnification will be higher by 1.4 times.

Kelvin^Newbie said:

i seem so blur :bsmilie: wanted to buy and try it out ... how much is 25mm ext tube and 1.4X TC . . .

Uniplus 25mm is around 90$ at CP.

1.4X Kenko pro300 is around 320$ @TCW.

you may call them and check the latest price:

CP: 63374274

TCW: 63361956

Sgt. Pepper said:

Kenko extension tube ... It comes with 3 sizes: 12mm, 25mm and 36mm.

megaweb said:

The KENKO AUTO EXTENSION TUBE SET contains three tubes of different length, a 12 mm, 20 mm, and 36 mm.

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