Jump to content

Extension tubes for Negative scanning


Recommended Posts

Hi all,

 

I am looking to scan negatives and slides with an APS-C camera. From the reading I have done, this requires a macro lens focused on the negative on a light box.

 

To begin with I am looking at a low-cost alternative - my Canon 50mm 1.8 II lens with some extension tubes for magnification & closer focusing distance. Will this work? The closed focus distance on my lens is currently 45cm. Will extension tubes allow me to fill the frame and get focus? If so, what length tubes should I get?

Link to comment
Share on other sites

For clarity, what you are describing is Negative Copying, not Scanning.

 

Yes, in round figures, a 25mm Extension Tube will allow you to copy a 135 Format negative (or transparency) and fill the sensor area of a CANON APS-C Camera using the EF 50/1.8 MkII. Actually my calculation reckons that there will be about 0.9mm space at the edge of the frame - but that's close enough.

 

The resultant minimum focusing distance will be about 210mm (21cm).

 

I have the set of three Kenko Extension Tubes for my Canon EF / EF-S Mounts. That set comprises a12mm, 20mm and 36mm Tube. I am happy with that purchase. Canon make two Extension Tubes for EF / EF-S Mounts: a 12mm and a 25mm, I expect they will be relatively more expensive.

 

I am not sure if you can still buy the Kenko Tubes separately - if this Copying Task is the only use and cost is a consideration, then the 20mm will not quite fill the sensor frame - having about 3mm space at the edge. The 36mm tube will do the job.

 

If you are buying second hand, then be aware that some early models (of the Kenko and Canon Tubes and perhaps others too) only supported EF Mount Lenses - which is OK for your EF 50/1.8MkII, but not OK if you want to use an EF-S Mount Lens.

 

You may read advice that an extension tube is only a barrel of air, so just buy the cheapest. I suggest that you don't do that. There are other considerations, two which In consider the most important are:

 

1. Quality and robustness of the mounts and securing pins

2. Quality and robustness of the interior light baffle

 

To do this job well you'll need a rig to support the camera: either a copy stand (or an old enlarger stand will suffice, especially if you are a DYI person), if not, a tripod.

 

Probably you'll choose to shoot vertically and downward; with the negs sandwiched on the lightbox by a piece of (quality) clean glass.

 

***

 

I think that you should consider Copying vs. Scanning.

 

There may not value for money, for you, to go down this Copying route. Acquiring: a good set of Tubes; a quality Lightbox; a Copy rig - compared to buying a dedicated negative scanner is a question you should consider.

 

The answer might not be that Tubes (or buying a Macro lens) and all the other stuff, is cheaper and/or easier for similar quality results that Scanning, using a dedicated Film Scanner, could provide to you.

 

WW

Edited by William Michael
Link to comment
Share on other sites

That is exactly how I copy all my negs and slides. I use a Canon 50mm f1.8 with a 21mm extension tube. I fix the f number at f8 to give a reasonable depth of field (card mounted slides tend to have a bow). I use auto focus and shutter speed.
Link to comment
Share on other sites

The performance of normal lenses suffers at close range, say 1:4 magnification (1/4 size). You are better off using a macro lens designed to work as close as 1:1 magnification. The difference is in flatness of field and sharpness in general at close range. APS-C cameras don't need 1:1 magnification, but even 1:1.5 puts more demand on the optics.

 

If copying slides is a one-off thing, do the best you can with what you have. If you are archiving the family history, it pays to look for a better way. Start with a slide holder, like a Nikon ES-1 or ES-2. If you have to set up a light table and invert the column on a tripod, you will spend more time setting up and striking than getting results.

  • Like 1
Link to comment
Share on other sites

. . . If copying slides is a one-off thing, do the best you can with what you have. If you are archiving the family history, it pays to look for a better way. Start with a slide holder, like a Nikon ES-1 or ES-2. If you have to set up a light table and invert the column on a tripod, you will spend more time setting up and striking than getting results.

 

Agree. A slide holder is much simpler and quicker than a copy stand type setup. I have a Minolta 135 film holder, similar design to the currently available Nikon option. Also I can use the dedicated bellows with that film holder.

 

But - all this extra stuff is more cost.

 

WW

Link to comment
Share on other sites

WRT extension tubes: To get a 36mm x 24mm frame onto APS-C (DX) you need a 2:3 magnification ratio, or a little less if a slide is mounted - you need to crop out the frame edges ideally.

 

The theoretical formula to find the lens extension needed is -

Extension = f(1+m).

Where f is the lens focal length, and m is the magnification.

 

In this case the 'magnification' is less than 1. It's 0.667. So the total lens extension needed is 50 * 1.667 = 80.333. Less the 50mm of the lens itself to give us the (approximate) size of extension tube needed, which is 30mm. Remembering that the focus range of the lens will give us a built-in extension of around 6.25mm, or 1/4".

 

There's probably no need to be so precise, because extension tubes usually come in sets of 3. But it's good to know what sort of length(s) you're looking for, rather than just fumble about using trial-and-error.

 

In short, you need a tube, or combination of tubes, that give you 30mm extension, or a little under. Anywhere between 25 and 30mm would be fine.

 

In any case, the theoretical formula rarely works out exactly right in practise, since marked lens focal lengths are only approximate to start with.

  • Like 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...