Lomo 3,7x Objective stacked on the Schneider Makro-Symmar 5.6/120 line scan lens
This is a test of the Lomo 3,7x objective and Schneider Makro-Symmar 5.9/120 (SR120) in a stacked configuration. The performance of the two lenses together is really surprising and quite a bit better than the objective alone.
The Lomo 3,7x
This Lomo 3,7 was made in the 1980s in the Soviet Union and is still common the used market where today it’s one of the best values out there. This is a finite microscope objective designed for use with a 160mm tube length without any need for a tube lens. Using a tube lens with a finite objective, at least in my experience, usually results in a drop in performance but this is not the case with the Lomo 3,7.
For more specifications on the Lomo 3,7x and a test comparing it with the Canon MP-E 65 see the full review here on Closeuphotography.com: https://www.closeuphotography.com/lomo-3-7x-objective.
Stacked or Coupled Lenses
Stacking lenses, also called coupling lenses, is a technique to increase magnification where you mount a longer focal length lens on the camera and a second shorter focal length in reverse and face-to-face on the rear lens which is set to infinity focus. Together the combination has the potential to resolve more than either of the lenses setup for close-focus with extension.
You can predict the maximum possible resolution from a certain lens by using the simple fact that a wider aperture = higher potential resolution. The Lomo objective focused at 3.7x magnification by extension only would have an effective aperture of f/16.8 using the simple formula, effective aperture = nominal aperture * ( Magnification + 1 ). Now with the Lomo 3,7x mounted on the Makro Symmar 5.6/120 the effective aperture would be only f/13.2 using the formula effective aperture = nominal aperture * Magnification.
Image Quality example at 2500 pixels
Click on the image below to open the full size version in a Lightbox viewer to be sure you have the full size image right click, or two-finger press on the image and select Open in a New Tab or New Window from the menu. You can also right click, or two-finger press, and select Save Image As to save and compare the images on your computer with the image viewing app of your choice. In any case to check the URL of the full size image it should end in format=2500w.
Lomo 3,7x Objective stacked on the SR120 line scan lens at 3.67x.
Test: Extension vs Stacked with Makro-Symmar 5.9/120 at 3.7x
The Lomo 3,7x objective is designed to focus using extension so how does the lens perform in a stacked lens configuration? Looking at the effective aperture for both configurations, the stacked lens pair has nearly a full stop advantage over using extension only, so it should have a noticeable advantage in sharpness.
Front lens: Lomo 3,7 Objective normal mount
Nominal aperture: f3.57
Effective aperture stacked: f13.2
Effective aperture with extension only: f16.8
Rear lens: Schneider Kreuznach 120mm f/5.9 Makro-Symmar Line Scan Lens set to f.5.6 and normally mounted focused at infinity
This is the entire frame at 3.67x with the crop areas highlighted in blue.
Comparing the 2500 pixel Crop Images at 100% view
Click on any image below to open a larger version in a Lightbox viewer or better yet right click, or two-finger press on the image and select Open in a New Tab or New Window from the menu. You can also right click, or two-finger press, and select Save Image As to save and compare the images on your computer with the image viewing app of your choice.
100% Center Crop: Extension only vs Stacked
On extension the Lomo 3,7x has very good sharpness and excellent chromatic correction in the center. With the Lomo setup stacked with the Makro-Symmar SR120 the increase in sharpness in the center corp is pretty amazing and there is no increase in chromatic aberrations in the center. Make sure to click on the image above to view the full size 2500 pixel image.
100% Edge Crop: Extension only vs Stacked
At the edges the stacked lens pair shows better sharpness and contrast with the same great chromatic correction as the lens on extension. The difference in the two set-ups is very easy to see here with the fine lines in the center. Notice that there is not increase in CAs with the black vertical line on the right side of the image. In fact the stacked lens images looks like it might have even less CAs than the lens on extension.
Make sure to click on the image above to view the full size 2500 pixel image.
100% Corner Crop: Extension only vs Stacked
The difference in image quality is pretty strong with better sharpness, contrast and fine detail resolution in the stacked image.
Make sure to click on the image above to view the full size 2500 pixel image.
Setting up the Lomo 3,7 x and Makro Symmar for photography
Lomo 3,7x Objective stacked on the SR120 line scan lens
Setting up a lens pair in a stacked configuration is usually really simple, the longer focal length rear lens is mounted to the camera body normally and he shorter focal length front lens is mounted as close as possible to the front of the rear lens. For these two lenses all you will need is a 40.5mm to RMS step down adapter available on Ebay, Raf Camera makes a one of these and it is available on Ebay or RafCamera.com: https://www.rafcamera.com/adapter-m40-5x0-5-to-rms
Lomo 3,7x Objective stacked on the Schneider Makro-Symmar 5.9/120 line scan lens with Thorlabs SM2/52mm studio setup.
Instead of using a step-down adapter I like to use these lenses together with both lenses mounted inside Thorlabs SM2/52mm threaded tubes. The advantage of this setup is that you can set the position of each lens independently as close or as far way as needed as they are not mounted together.
Stacking Pros and Cons
The good
Better sharpness and resolution compared to same lens using extension only
Inexpensive since you can most likely use a pair of lenses that you already own
Easy to use since the magnification is set
Normal focus non-specialized lenses work well
The Bad
High performance lens pairs can be hard to find
The performance is so good it can make you want to forget about extension only setups
Each lens pair combination has a limited magnification range
Lens Stacking Notes
Mount the front lens as close to the rear lens as possible.
Control the aperture of a coupled lens pair with the front lens iris but some pairs work better with a aperture disk placed between the lenses so its best to try both methods.
Stopping down the front lens slightly seems to improve image quality slightly with most lens pairs.
Optimally both lenses are set to infinity focus although setting the rear lens set to closer focus can work well.
Even though both lenses in a stacked setup are focused at infinity lenses optimized for close up distances seem to work as well or better than normal focus lenses.
For best results the front lens should be set to infinity focus rather than close focus.
To avoid corner shading rear lenses 80mm or longer work best.
Short focal length lenses from 24-50mm work best as front lenses.
Large aperture rear lens are said to minimize vignetting with some combinations but I find that f5.6 or slower lenses seem to work fine.
Vignetting can sometimes be partially eliminated by adding an extension tube or by setting a closer focus setting to the rear lens.
If a stacked lens pair will vignettes try to move the front lens closer to the front of the rear lens, sometimes you will have to set the front lens inside the hood or shroud of rear lens.
Links for more information
More information on the 5.9/120 Makro-Symmar:
https://www.closeuphotography.com/schneider-makro-symmar-sr-120/
The HM 5.6/120 Makro-Symmar version:
https://www.closeuphotography.com/schneider-makro-symmar-120mm/
The full test of the Lomo 3,7x on this site:
https://www.closeuphotography.com/lomo-3-7x-objective