Friday, January 23, 2015

Helios 44M-4 and Zhongyi Lens Turbo II comparisons

I recently caught a Camera Flu and acquired a couple new pieces of equipment.  To justify the acquisitions (guilty as charged) I wanted to see how things looked.

The first new piece of gear is a Helios 44M-4 that I traded a Takumar 50mm macro for.  I'd read where someone thought that altering the space between the first element and second lens group in a Gauss design lens could lead to more pronounced Petzval portrait lens-like effects.
[Read Jim Galli's comment here.]

The second new piece of gear is a new Zhongyi Lens Turbo II.  This takes full frame SLR lenses and acts as a reverse tele-converter.  It takes a full 35mm frame field and resizes it to fit APS-C or micro 4/3rd's, depending on the adapter.  Mine takes Nikon F-mount lenses and adapts them to the APS-C sensor'd Sony mirrorless series cameras.

This isn't really a test.  Nothing is being measured and any results are purely subjective.

Here is the image comparison setup.  It was made using a Sony A6000, Zhongyi Lens Turbo II, and a Nikon Nikkor 50mm f/1.4 pre-Ai shot wide open.

Sony A6000 Nikon Lens Turbo test setup

The first image comparison is of the Helios 58mm f/2 in various stages of lens element positions.  Starting with the lens properly and fully assembled, I then moved the entire front element group forward by unscrewing the group to the extent of the thread range (without the group falling out of the barrel body).  Next I moved the front element forward in the front group with the forward cell mount fully seated.  Finally, I tried moving both the front and rear elements in the front lens group apart and moved the cell mount to the front of the threaded range.

If you click on the image, it'll take you to my Flickr hosted image.  From there select full image size to look at this at 100% resolution.  Any differences between the various segments can be easily reviewed.

All comparison images were made with the Helios shot wide open at f/2. 

Sony A6000 Helios Disassembly Bokeh Test

My subjective observations are that there are indeed differences in how the image is rendered as the various elements are moved.  Interestingly, the out of focus rendition becomes smoother as the front element groups are separated and the front group mount is moved forward in their threads.  But, and this is to be expected, resolution suffers to varying degrees.

It appears a "dreamy" 1800's portrait lens effect is possible, though I'm not sure it's worth the effort.

Which led me to a second set of image comparisons.  I'd read that the Zhongyi Lens Turbo II full frame to APS-C field reducer rendered the out of focus regions more softly than the native lens used with a straight-thru adapter.  Here's my look at the question.

If you click on the image, it'll take you to my Flickr hosted image.  From there select full image size to look at this at 100% resolution.  Any differences between the various segments can be easily reviewed.

All comparison lenses were shot wide open.  

Sony A6000 Nikon Sigma Lens Turbo Bokeh Test

I did my best to keep the primary scene composition similar between the various lenses and focal lengths.  The Lens Turbo II knocks 0.72x off the focal length and increases the aperture by the same amount.  More on this in a moment.

Considering resolution it appears the Lens Turbo adapter does not degrade image quality in the in focus areas for the lenses I used.  I once again see how difficult it is to get something in focus with wide aperture lenses.  This is partly due to the amount of spherical aberration I see in many old 35mm film-era lenses.  I'm not always certain where the best focus is.

The Sigma 60mm DN Art f/2.8 is obviously sharp.  It's a modern design.  Manually locating the focus point was easy and simple.  But it's maximum aperture is a stop or two under most of the lenses I tried.  How the old Nikkors would perform at f/2.8 against the Sigma has been left to a future comparison.

Looking at the out of focus regions I have to agree with whomever noted the smoother image areas when using the Lens Turbo II focal length reducer.  In every case I feel the out of focus rendition is "creamier" and "smoother" when compared with a native lens used without an adapter.  I rather like what it does to the 50mm and 85mm lenses.

So how does the Zhongyi Lens Turbo II work?  It's pretty simple, actually.  It optically reduces the image size from full frame 35mm to APS-C or micro 4/3rd's dimension.  Interestingly it seems to do this at no cost to resolution.

The Lens Turbo also _increases_ the effective aperture by approximately one stop.  In the case of the Nikon 50mm f/1.4, when used with the adapter it becomes a 35mm f/1.0 lens.

How is this possible?  Remembering optical physics, a lens' focal length divided by the front element diameter will give you the aperture.  When you take a 50mm lens and reduce it's field of view to, say, 35mm _without_ changing the front element diameter, you effectively increase the aperture.  In the case of the Lens Turbo II the aperture is increased by 0.72.

If you don't follow me, tell me and I'll have another "go" at explaining what's going on here.

What's important to note is that a 50mm f/1.4 lens on a full frame 35mm system as a 35mm f/1.0 does on APS-C and there is no change in the effective depth of field.

Again, if you don't follow me on this, let me know and I'll try to explain things a little better.

So... where does this leave me?

I see it's possible to carry a two lens, two adapter kit and cover four focal lengths.  For instance, I could carry a 24mm f/2 and a 50mm f/1.4 Nikkor.  Used on the APS-C Sony A6000 I would have the effective full frame focal lengths of 24mm f/1.4 (focal length reduced 24mm f/2), 35mm f/2 (effective focal length of a 24mm lens on APS-C), 50mm f/1.0 (focal length reduced 50mm f/1.4), and 85mm f/1.4 (effective focal length of a 50mm lens on APS-C) at my disposal.

The combinations and capabilities are now seemingly endless.

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