Schneider Betavaron 3.. .10/0.08 Test (Zoom Enlarging Lens)
This is a review of the Schneider Betavaron 3.. .10/0.08 Zoom enlarging lens made in the 80s.
The PDF file is available here ( http://www.schneiderkreuznach.com/ar...tavaron_81.pdf ).
There are things on the PDF that are not clear. Perhaps because of German to English translation.
I will go over the important points and explain what the lens does and does not do.
The flange-focal length is about 80mm, so this would mount on a lensboard that one would use for an 80mm lens (recessed, flat or extended, depending on your enlarger).
The screw mount is M39 Leica. Mine came with a retaining ring.
Focal length zooms from 50mm to 125mm. The Zoom ring is marked with MAGNIFICATION (3x to 10x) rather than focal length (see more below).
Aperture is from f4.1 to f22. The aperture ring is marked with integers 1-5. This is to aid in calculating the aperture needed to keep exposure the same as you zoom.
Weight is a massive 750g!
They made the lens in different versions with slight variation of the barrel. Some have a bayonet on the front to accept an accessory lens (-0.9 diopters) to make bigger enlargements.
Last edited by ic-racer; 01-23-2011 at 01:20 PM. Click to view previous post history.
Recommended Format = 35mm
Even though it zooms to 125mm, the image circle is only large enough for 35mm, even at the 125mm setting. So you cannot use it as a medium format enlarging lens.
In fact, the image circle (at the recommended operating distance) is a little small for 35mm.
The specs indicate the image circle is 43.3mm. I have rarely seen lenses with image circle listed to the tenth of a millimeter, but what this means is that at 43.4mm it is already getting dark. If you measure your 35mm negatives, they most likely will all have a diagonal greater than 43.3mm, so you may clip the corners (but there is a work-around, see below).
In fact the recommended format is not just listed as generic 35mm, it specifies a mask size of 23mm x 35mm. That is about the size of my glassless printing frame mask which crops the image slightly.
Because of this very tight image circle, the lens and negative have to be centered exactly. There are a myriad of ways to do this that I won't go into detail here. If it is not centered exactly, you can clearly see a dark corner.
How To Use It So It Zooms Without Refocusing:
This lens will turn your enlarge into an autofocus enlarger, but you have to have the lens set to the exact height over the paper. It is actually easy to get it into the correct position following the instructions in the PDF. I will go over the instructions here.
1) Set the lens so the lensboard is about 650mm above the paper. (We will tweak it to exactly 648mm with the following procedure).
2) ZOOM all the way to the biggest image and open the aperture. Now use the enlargers focus control (lensboard movement) to get it into focus.
3) ZOOM all the way to the smallest image and now re-frocus by moving the WHOLE HEAD up and down.
4) Repeat steps 2 and 3 to zero in on a perfect head height so that zooming requires no re-focusing.
With the lens set to 648mm like instructed above, the numbers on the ZOOM ring should correspond to the magnification of the image.
Each magnification has an optimum aperture and it turns out that this optimum aperture provides a constant exposure at each magnification. So there is a little scale on the lens that relates each zoom setting to a specific aperture. This way, if you keep the aperture number at the setting indicated in the scale for each magnification, you will both be at the best aperture AND the exposure will stay constant.
For example at 6x magnification, the optimum aperture is "3" on the scale. I actually checked this with a grain magnifier at the center and edges and indeed "3" provides the best compromise between edge sharpness and overall diffraction.
Now if you zoom to 8.5x magnification and adjust the aperture to number "2" as, indicated on the engraved scale, you will both be at the best aperture for that magnification and the exposure time should not change much.
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How Does This Lens Compare to a Fixed Focal Length Lens?
When used as indicated above, the corners are not sharp enough for most critical work (see work-around, below). They will be OK for mass produced snapshots, but even within the 43.3mm circle, the grain gets soft and oblong at the periphery.
I tested this in a number of ways (glass carrier, lens exactly centered and perpendicular with laser alignment on Omega D5500 enlarger).
I looked at the aerial image of the grain with a Peak 1 magnifier.
I did side-by-side prints with different enlarging lenses.
I scribed a 43.3mm circle on a sheet-film negative and examined the grain pattern, both with the exact focus set on the edge and at the center of the circle.
After playing with the lens for a few days I discovered a way to improve the performance so that it matches that of a fixed focal length lens at the edges.
Work-around to Improve Edge Sharpness:
Many enlarging lenses share a characteristic that as the lens gets closer to the negative, the view becomes less. The image circle gets smaller and the light rays from the edges of the negative make more of an acute angle to the lens. This all adds up to poor performance at the edges in big enlargements (when the lens needs to be focused close to the negative).
So, I thought that I could improve the Betavaron performance by increasing the distance between the lens and the negative. This is easily accomplished by lowering the enlarger head and re-focusing. I set my head to have the negative about 480mm from the paper. At this distance the biggest image is about 8x10 and it zooms smaller from there.
At this distance the ZOOM SCALE is no longer accurate and re-focusing is needed when zooming.
However, at this distance the image circle is bigger than 43.3mm and the grain maintains sharpness all the way to the edge of the 24mm x 35mm frame.
Last edited by ic-racer; 01-23-2011 at 01:25 PM. Click to view previous post history.
So, I played with the Betavaron for quite a few hours last night. I though the zoom effect would be cool. Kind of like William Klein, Candy Store 1954.
I have known of the Klein photograph for many years, and it is obvious the zoom is done in the darkroom. I figured he either did a focus shift or had a non-angled autofocus enlarger to do the effect. In his case he zooms smaller from the main exposure.
This is what I came up with last night. I think the enlarger zoom effect it is something to explore further.
After experimenting with the enlarger zoom effect, now I can pick up its subtle use, like in this one of Klein's. You can just make out the black streaks in the lower left hand from the man's leg. http://www.masters-of-photography.co...kets_full.html