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Zeiss Macro Planar 120 on Sony Alpha 99 with an Arax tilt adapter

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Note: This article will be updated with more info in the coming days/weeks.

Introduction

Older Hasselblad lenses can be had very cheap. Later versions of the same lens groups are also used in the Hartblei lenses using Zeiss groups and cost many times more.

The lenses were tested by Lloyd Chambers who liked them a lot, especially the 120 Macro Planar. On the other hand the very same Macro Planar lens group got very bad rating in the Photodo test, and the MTF curves published by Zeiss are quite a bit ugly.

I have bought a decent copy of this lens, which I intend to use as a tiltable macro lens for use on my Sony Alpha SLT99. 

The MTF issues 

MTF curves don't lie. MTF curves don't say the whole truth either and always need interpretation. That said let look at the MTF curves for the Macro Planar 120/4.

Zeiss has a data sheet describing the lens, available for download here.

Below are two screendumps from that data sheet.

The first one is the normal one, at infinity:

MTF at infinity
The curves are measured MTF at 10, 20 and 40m lp/mm in white light at infinity. These curves are not very good. A decent lens for a DSLR would have above 80% MTF for 20 lp/mm across the field. The 40 lp/mm curves are good at center but drop rapidly. Not a good lens?! Note however that curves tangential and radial curves are close. This indicates that astigmatism and lateral chromatic aberration is well corrected. Could it be the lens suffers from curvature of field? 

Now we recall that this is supposed to be a macro lens so we check the MTF curves a 1:5, and the information changes.

MTF at 1:5
Now MTF at 20lp/mm is around 80%, what we would expect of a decent DSLR lens and MTF at 40 lp/mm stays around 50% across the field. This is a really good macro lens.

So what we see is that the Macro Planar 120 has a significant curvature of field at infinity but a very much better corrected field at 1:5. 

Let's check this in practice:


The image above shows two central crops taken with the Zeiss 120/4 at f/4. The image on the right is focused on the center while the left one is focused near the corner. The right hand image would be sharper and this is obviously the case.


This image shows two crops from the left top corner of the previous image, where focus was laid in the second shot. Here the left crop has the focus.


Stopping down improves performance and the Zeiss lens is very usable at f/8:


These are central crops shot with Sony 70-400/4-5.6G at f/8 and the Macro Planar at f/8. Macro planar on the right. Those images are close and I don't think that any difference in image quality would be visible in prints.




Scheimpflug

A problem in photography is that it is difficult to achieve large Depth Of Field without stopping down. Stopping down increases diffraction thus reducing fine detail contrast and ultimately also resolution.

There is a principle, called the Scheimpflug principle that allows us to tilt the plane of focus. So even if the plane of focus is thin it can cover a large area. See the image below. There are two insets at actual pixels indicating that both foreground and background is sharp, although DoF is thin. Click here for a full size image.




Mythical flare

A nasty observation I made on testing the Sonnar 150/4 was that it was very sensitive to flare. At that time I had no lens hood for that lens. I observed the same issue on the Planar 120. Lens hood did not help, nor did a compendium type lens shade, until I used the fron plate for the 250 mm lens. 

That the 250 plate help made me realize that the ghosting probably was caused by internal reflections, so I put the lens on an old SLR using "Bulb position on shutter" and looked from behind. I realized that the internals of the Arax adapater are anodized black but not painted matte black. I have some matte black paint on order, and I hope it will help dampening this internal flare.


Last Updated on Monday, 15 April 2013 00:55  

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