Macro tube advice

Hi all,
Firstly I'm sorry if this is in the wrong place but I couldn't work out where to post it.

I have started taking photos of my 120 film in order to digitise them, I have lit them from behind using opake acrylic and I'm getting great results however I am having issues getting close enough to the film without needing to crop, thus reducing quality.

I've heard I can use an extension tube* on a std lens to decrease the minimum form using distance?

I am using a Sony a6000 and have the choice of the 18-105 f4 G-series or Chinon 55 f1.7

Can anyone advise what tube* I would need to be able to focus close enough to fill the sensor?


(*thanks for the correction on terminology.)

I presume you might be taking a 55-56mm wide med format area and trying to capture it onto a the A6000 23.5mm wide sensor. That is 0.43x of original size, or 1:2.33 mag ratio. OTOH, if you are trying to cram a 55-56mm vertical into 15.6mm, you have to achieve 0.279x, or 1:3.58 mag ratio.

A macro photo extension tube requires that it be placed BETWEEN the usual lens and the camera body, moving the optics away from the focal plane of the camera in order to focus on the close up subject. Depending upon the FL setting of your lens, the length of extension tube to achieve 0.43x or to achieve 0.279x will be 'it depends'. I will use the Sony lens to elaborate:

• At 16mm FL setting of the lens, 0.43x needs 7mm extension tube and 0.279x needs a 4.5mm extension tube.
  
• At 32mm FL setting of the lens, 0.43x needs 14mm extension tube and 0.279x needs a 9mm extension tube.
  
• At 50mm FL setting of the lens, 0.43x needs 22mm extension tube and 0.279x needs a 14mm extension tube.
  
  

ok, i think this makes sense haha!

So.....

I take my a6k, put my 18-105 f4 G lens on and set my focus at 50mm, set it to something like f11 to get the sharpest shot.

If i want to fill the frame with the negative from top to bottom, leaving black (or white) boarders to the left & right i would use a 14mm extention tube?

Thanks.

urbanfreestyle wrote in post #17964953
ok, i think this makes sense haha!

So.....

I take my a6k, put my 18-105 f4 G lens on and set my focus at 50mm, set it to something like f11 to get the sharpest shot.

If i want to fill the frame with the negative from top to bottom, leaving black (or white) boarders to the left & right i would use a 14mm extention tube?

Thanks.

You will need an extension tube... as Wilt points out, the size will depend on the magnification you need, and also on the focal length. The problem with most modern lenses is that their actual focal length varies with the focus setting. The markings on the lens are only true at infinity focus. Most likely when you are doing your photocopying, you won't be at infinity. Actual focal lengths are usually unknown, so it is not possible to calculate the required extension reliably. So the best thing is to get an extension tube or set of tubes and do some trials.

There are a couple of other things to be mindful of when doing macro with a zoom lens. The greater the magnification, the closer the subject will be to the front element of the lens. This may or may not be an issue in your case, but sometimes the working distance can shrink so that it is a problem. At high magnifications, the subject might actually touch the glass of the lens. The other issue is the aperture. You should be OK at f/11, but at that aperture, you will probably be diffraction-limited. You will probably get better resolution at wider apertures. Again, some tests would be in order before you do tons of work.

so probably best to get a set like these from an online store and play?

urbanfreestyle wrote in post #17964974
so probably best to get a set like these from an online store and play?

Yes, but I don't know how good the Optekas are.

sorry, i just meant like a three adapter set lol.

Unlike a situation where OPTICS are involved in the add-on (e.g. teleconvertor) an extension tube does nothing optically. The difference between a 'good' vs. a 'poor' extension tube is simply how securely it mounts on the body and how securely it mounts on the lens, and whether or not it has electrical connections that retain connectivity between the lens and the body, for focus control and diaphram control. I have a $50 set of tubes that maintain the connection between body and lens even when all THREE tubes are stacked together...something that some $150-200 products will not do!

A couple more (unsolicited) comments:

Scrupulously remove dust before copying.

Will your negs lie flat? If so, that's great. Usually they would lie emulsion side (dull side) down.

If they don't lie flat, use a glassless neg holder if you have one, or maybe rig one up. Glassless is great because it avoids newton rings, and there will be 4 fewer surfaces to keep clean.

sounds like a good plan, i'll get on it in the morning