Calculate ext tubes needed to 'extend' macro lens.

[JoolsW]

I've setup my DSLR with macro zoom lens to digitise trannies and negs. I'm very pleased with the results with 120 medium format origials.
BUT, the enlargement isn't enough for 35mm. I've seen the info for calculating size of extension tube /lens size/magnification. But because I'm using a macro lens I'm not sure how that applies.
My 28-105 Nikon lens sets to about 70mm when I do a 120 film. It's a zoom macro. Would I use that 70mm figure to do the sum? or what. I'd need approx 30% more enlargement to get a 35mm to the right size.
Any ideas?
Cheers.

 

[RAZKY]

I've setup my DSLR with macro zoom lens to digitise trannies and negs. I'm very pleased with the results with 120 medium format origials. BUT, the enlargement isn't enough for 35mm. I've seen the info for calculating size of extension tube /lens size/magnification. But because I'm using a macro lens I'm not sure how that applies. My 28-105 Nikon lens sets to about 70mm when I do a 120 film. It's a zoom macro. Would I use that 70mm figure to do the sum? or what. I'd need approx 30% more enlargement to get a 35mm to the right size. Any ideas? Cheers.

Yes, normally you would use the 70mm figure to do the sum. However, many zoom lenses, especially variable-aperture, low-cost, lightweight lenses, suffer from focus-breathing, which means that when focused close the actual focal length could be less than marked - sometimes much less. I'm not familiar with the 28-105 Nikkor, but you can check it against a prime lens of the same focal length as one of those marked on the zoom - with both focused at the same distance (rom the focal plane), the reproduction ratio will be the same if there is no focus breathing.

 

[Thiophilos]

@JoolsW , your Nikon lens is not a macro lens, even if it says macro or micro on it. It's because it is unable to shoot at a magnification of 1x. The definition of macro is reproduction at 1x.

But lens makers don't care, and say their lenses are macro when they aren't. It's only partly their fault - it's what the buyers want to hear.

If you have the Nikon 28-105mm f/3.5-4.5, it will get you a magnification of 0.5x at 105mm. That will create an image of 18x12mm on the sensor from a 35mm original. That's not too bad, depending on the pixel count of your sensor. Crop the image and you're done.

You could do better by using an extension tube. A tube of 60mm will get you around 0.67x at a nominal 105mm with the lens focused at infinity. That gives an image of 24x16mm, which might correspond to your sensor dimensions depending on what kind of sensor your camera has. With that tube, you could focus even closer too by working the focus adjustment of the lens, or go to a shorter focal length if it has better performance.

You could also probably get to 0.67x with a shorter tube + lens focusing. I don't know how to calculate the length (but guessing around 30mm).

 

[snowbear]

There is a calculator here: Macro Extension Tubes & Close-up Lenses

Because they don’t magnify to 1:1 is why Nikon calls their lenses Micro.

 

[JoolsW]

That's very good info thanks Thiophilos. Just what I was hoping for.
I have bought a set of tubes which will arrive soon. I'll try them and report back, as someone else might benefit from the info too.
My camera is an ol' Nikon D90 so it's only 12mp, though it's excellent for most purposes. (I'm not a 'newer is better' kind of a guy. E.G. when I did what I consider to be the best work of my life, -a catalogue of sculpture works in a Japanese sculpture park, I chucked on my ancient brassy old 180/2.8 mm Nikon lens and did it by hand!).

Thanks also Snowbear I'll check that link.
(BTW Nikon called mine MACRO with a A not an I).

 

[Thiophilos]

Tubes give a much stronger result with shorter focal lengths. Put a 20 or 30mm tube on and with the zoom, see what you get.

 

[Golem]

That's very good info thanks Thiophilos. Just what I was hoping for.
I have bought a set of tubes which will arrive soon. I'll try them and report back, as someone else might benefit from the info too.
My camera is an ol' Nikon D90 so it's only 12mp, though it's excellent for most purposes. (I'm not a 'newer is better' kind of a guy. E.G. when I did what I consider to be the best work of my life, -a catalogue of sculpture works in a Japanese sculpture park, I chucked on my ancient brassy old 180/2.8 mm Nikon lens and did it by hand!).

Thanks also Snowbear I'll check that link.
(BTW Nikon called mine MACRO with a A not an I).

Since youre getting a set of 3 tubes, you will find your 1:1 copy magnification in there somewhere.

Altho in normal use zooming to a longer FL makes for a bigger image, with tubes involved, its the shorter FL that can provide more magnification by fucusing closer than the longer FLs. Thaz how extension works. Look up and learn the simple formula for that.

With a zoom at a given FL you sometimes cannot focus as close as a prime of that same given FL cuz the extra bulk of the zoom gets in the way.

 

[Thiophilos]

Since youre getting a set of 3 tubes, you will find your 1:1 copy magnification in there somewhere.

Altho in normal use zooming to a longer FL makes for a bigger image, with tubes involved, its the shorter FL that can provide more magnification by fucusing closer than the longer FLs. Thaz how extension works. Look up and learn the simple formula for that.

Shorter focal lengths give a stronger magnification with extension tubes.

 

[JoolsW]

Just to comeback on this. I got my tubes... very good quality, Meika brand, about $70 Aussie. All auto with my Nikon zoom macro.
The 20mm section is perfect for 35mm. So good! I'll be interested to try them as tele-converters too. Meanwhile having a bit of fun shooting film on my M645pro and skungy (but lovable!) ol' Nikon EM.

 

[Thiophilos]

Just to comeback on this. I got my tubes... very good quality, Meika brand, about $70 Aussie. All auto with my Nikon zoom macro.
The 20mm section is perfect for 35mm. So good! I'll be interested to try them as tele-converters too. Meanwhile having a bit of fun shooting film on my M645pro and skungy (but lovable!) ol' Nikon EM.

Good stuff. Your working distance will be greater with the longer focal lengths. That matters if you are shooting bugs or if the lens gets in the way of lighting. With the tube set, you can experiment and have some fun.

 

[RAZKY]

Just to comeback on this. I got my tubes... very good quality, Meika brand, about $70 Aussie. All auto with my Nikon zoom macro.
The 20mm section is perfect for 35mm. So good! I'll be interested to try them as tele-converters too. Meanwhile having a bit of fun shooting film on my M645pro and skungy (but lovable!) ol' Nikon EM.

We all appreciate the comeback - have you determined whether the focal lengths of your 28-105 are as marked when you focus close? By the way, that is not a macro lens, it's a zoom that can focus into the macro range. A dedicated Nikon macro lens would be labelled "Micro-Nikkor" and be corrected to produce a flat field. And it doesn't matter if it focuses at 1:2 or 1:1.

 

[480sparky]

.. I'll be interested to try them as tele-converters too. ...

Extension tubes and teleconverters are not the same. The former has no optics, while the latter does.

Back in the pre-digital days, I had a 2-in-1 that did both... the optics were removable via a bayonet mount within the tube.

 

[JoolsW]

We all appreciate the comeback - have you determined whether the focal lengths of your 28-105 are as marked when you focus close? By the way, that is not a macro lens, it's a zoom that can focus into the macro range. A dedicated Nikon macro lens would be labelled "Micro-Nikkor" and be corrected to produce a flat field. And it doesn't matter if it focuses at 1:2 or 1:1.

I'm sure you're correct Razky, but my Nikon AF Nikkor lens is clearly marked MACRO on the barrel.

 

[RAZKY]

I'm sure you're correct Razky, but my Nikon AF Nikkor lens is clearly marked MACRO on the barrel.

Right - that's to indicate it focuses into the macro range. Most lenses only focus down to 1:10 or so. By the way, not everyone agrees on exactly what the macro range is. Many consider it to be from 1:1 to 10:1 or so. The Nikon Compendium defines it at 1:10 to 1:1.

 

[JoolsW]

Extension tubes and teleconverters are not the same. The former has no optics, while the latter does.

Back in the pre-digital days, I had a 2-in-1 that did both... the optics were removable via a bayonet mount within the tube.

Doh! - as you say mate!