Paul Butzi Photography

ZBE Sentinel Enlarger

Jump ahead to:

Summary

ZBE Sentinel enlarger is highly automated and a very precise enlarger. While not marketed to hobbits like me, I am very pleased with this and expect to enjoy using it for many years. The features I like are:

1. Auto-focus with any lens (50-150mm). This includes floor projection as well as any easel. 2. Closed loop illumination system that delivers precisely repeatable color and intensity of light. 3. Ability to make prints of any size at one optimum f-stop for the lens and one convenient exposure time of my choice. I was pleased with an 8x10 print from a negative and to make a 20x24 print, all I did was to raise the head and not change any other settings . 4. Ability to save the settings used for printing a negative and recalling the settings at any time for reprints.

Installation

I had very frustrating several weeks just to install my new toy. After paying a small fortune for the new ZBE Sentinel enlarger, I was anxious to get working on it. But the low ceiling and the cabinets designed around my Leica V35 enlarger just would not accommodate my wall mounted ZBE. And getting the cabinet maker to come and make changes to the cabinets took forever. At last, about two weeks ago, the enlarger was installed. And so was my new Fujimoto CP51 processor and Rollma 31" roll paper dispenser. I decided that since purchase of enlarger was making a big hole in my bank account, I might as well make the hole bigger by getting a print processor that can handle 20inch wide paper and a roll paper dispenser to save (BG) money on paper. Besides Fuji does not sell 20x30 inch cut sheets.

The ZBE Sentinel is very different than any other enlarger I have owned. But for the difference in quality of workmanship and materials, there is not much difference among Durst M301(?), Omega 760(?), Beseler 23 CII and Leica Focomat V35 enlargers. Mounting 120lbs column very precisely on wall aside, installing the ZBE colorhead, auto-focus computer and various smaller parts was quite easy. Installing three lenses, in my case APO Rodagon 50, 80 and 150mm, on turret was a little tricky. Only the opening for the 150mm lens is threaded, the other two lenses are held in place by jam rings. This means that you have to lift the bellows and exercise a lot of care not to kink the delicate looking cables inside the bellows. These are for the auto-focus system.

Once all the hardware is installed, you need to calibrate lenses, easels, carriers, master color balance and offsets for each paper emulsion. This took me a whole long day. Once everything was calibrated, I made my first print - a 13.5"x20" enlargement of a 35mm negative of a pair of King Penguins. To my amazement the print was perfect in all respect except for dark bands about every inch along the 20" dimension. A call to Ken Owen at Jobo quickly resolved the problem. I learned that while Fujimoto CP31 wants paper with emulsion side up, with the Fujimoto CP51 processor you have to feed the paper emulsion side down. Next print, a 20"x30" enlargement of a Grand Canyon scene came out perfect on the first try.

Details

The last two weeks I have been busy learning how to use the Sentinel enlarger. I do not know if the Sentinel is the best enlarger as claimed by ZBE. What I do know is that it is a very sophisticated and feature laden enlarger that is very well made. Just looking at the carriers will tell you that ZBE has not cut any corners to save money. These are machined from heavy aluminum with magnets to gently but firmly hold the negative as you slide the carrier in the colorhead. It is not a perfect enlarger. IMHO ZBE should have color coded the keys on the keyboard instead of making them all green. And it would be nice to have a filter holder under the lens. The following are my observations to date:

Light Source

The Starlight 55 Light Source consists of three 360W halogen bulbs, dichroic filters, a shutter, a 5"x5" mixing chamber, a cooling fan and a closed loop controller. It is this controller that is amazing to me. Working in cooperation with the auto-focus computer, more about that later, it changes voltage to the halogen bulbs and the filters so that the light delivered to the easel is of constant intensity and color. This is true regardless of the positions of the colorhead on the column, the drop table or the height of the easel. To insure consistent color and exposure the bulbs are kept warm with small current and the shutter opens half a second after you push the expose button. This design of the light source allows me to set the lens at its optimum f-stop for the lens and convenient exposure time of my choice and never need to change them. For each print I just key in the desired filtration and print density. I am using my Jobo Colorline 5100 color analyzer to determine filtration and print density. Sentinel has an optional fully integrated color analyzer (Color-Pro), that would be more convenient. But I am not sure that I want to spend $2,000 for that extra convenience.

Enlarger Chassis

The Sentinel enlarger chassis has the usual column with negative and lens stages. The lens stage has a turret with openings for three lenses. One is dedicated to 135/150mm and the other two can be used for any lens with 39mm Leica threads. Actually they are not threaded. You need to hold these two lenses with jam rings. I have installed 50, 80 and 150mm Rodagon APO lenses. The best part of the column is the auto-focus system. The encoder in the negative stage precisely determines the position of the colorhead on the column and the encoder in the lens stage precisely determines the distance between the lens and the negative.

Calibration

Calibrating a lens is nothing but focusing at both ends of the column and entering actual magnification. The enlarger comes with a calibration negative to aid this. From this data, the computer calculates the actual focal length of the lens and uses it for auto-focus.

Carriers are calibrated to compensate for the small variations in the exact position of negative relative to the negative stage in each carrier.

The system allows for 10 easels. Any one position can be defined as "no easel" and all other positions can be at any height relative to this "no easel". This includes below the column (floor projection).

Carriers and easels are calibrated using the same calibration negative used for lenses.

Offsets

Sentinel has offsets for paper emulsions (up to 25) and processes. Filtration and density for a balanced print using most frequently used paper is recorded for the master color channel. You can assign any arbitrary CC numbers to each of the three colors and density. I used the suggested values (C=0, M=30, Y=30, D=64). Then each of the other paper emulsions I made a balanced print and entered the offsets relative to the master color channel. Again I used my Jobo Colorline 5100 and X-Rite densitometer to save time. After this, the filtration values for a negative are the same regardless of the paper to be used for printing. I have only one process but I assume that the same procedure applies to offsets for processes.

Operation

All of the above is done only once. After the setup is complete, Sentinel is a pure joy to work with. Just tell the machine which carrier, easel, paper and process to be used, enter the filtration and desired print density (this is very easy with a Jobo Colorline 5100 color analyzer), and expose the paper. Sentinel maintains sharp focus and balanced color through any change in lens or magnification. As an experiment I printed one negative at three different magnifications and on four different paper emulsions and all the prints nearly identical. All I had to do is let the system know which paper I was using. If you change lens, carrier or easel, the enlarger will automatically refocus. The image stays in focus as the head is raised or lowered. BTW, you can raise or lower the head by pressing appropriate button on the keyboard or enter the desired print size or magnification and the head will move automatically to correct height. The AF computer communicates with the light source so the light output and color are adjusted at the same time.

Another feature I found very useful is "Loading Position". You can set the loading position at any convenient height. Then on command the head will move to this position to ease loading removing carriers. Pressing any button will result in the head going back to it original position.

Lastly the system has a few computer related features.

1. I can save settings used for printing about 250 negatives under a job number of my choice (up to 5 digits). This allows me to make nearly identical reprints very quickly. 2. I can connect the enlarger to my PC and download the settings to hard disk on the PC. I have not done this yet but expect to try it in coming weeks.