This lens might not look like anything special but under the industrial exterior there are some of the finest optics I’ve tested in a tube lens. Comparing this lens to my standard tube lenses, this lens has turned out to be one of the biggest surprises of the year. A large batch of these lenses has been quietly selling on eBay for several months, and within a day or two after sharing some of my initial test findings online, the eBay seller sold out their remaining stock before I could get this test posted.

Special thanks to my friend Miljenko for the use of a loaner lens, and encouragement, to make this test possible.

3.4x TEST: gretag 120 vs Makro-symmar 120

The Componon was mounted in reverse and stopped down to f/3.5 using a paper disk between the two lenses. The Schneider Makro-Symmar is a special apochromatic (APO) 8 element lens, one of my personal favorites, and a fantastic performer as a tube lens. For more information on the Makro-Symmar, see the links section at the bottom of this page.

Front lens: Schneider Kreuznach Componon 35mm f/2.8 lens reverse mounted
Rear lens: Gretag 120mm lens normally mounted focused at infinity
Nominal aperture: f3.5
Effective aperture at 3.4x: f/11.9

Front lens: Schneider Kreuznach Componon 35mm f/2.8 lens reverse mounted
Rear lens: Schneider Kreuznach Makro-Symmar 120mm lens normally mounted focused at infinity
Nominal aperture: f3.5
Effective aperture at 3.4x: f/11.9

Camera: Sony α6300, model # ILCE-6300, also known as: A6300
Sensor size: APS-C. 23.5 × 15.6 mm. 28.21 mm diagonal. 3.92 micron sensor pitch
Flash: Godox TT350s wireless flash x 2 with one Godox X1s 2.4G wireless flash transmitter
Vertical stand: Nikon MM-11 with a Nikon focus block

For this test a stack of images was made with 4 micron steps, and was repeated for each aperture. The sharpest frame was then chosen using Photoshop at 100% actual pixel view. Separate images were selected for center, and corner if needed. Each image was processed in PS CC with identical settings with all noise reduction and lens correction turned off, all settings were zeroed out (true zero) and the same settings were used for all of the images. All of the images shown here are single files.

To see the full 2500px image below in a new browser tab, right click, or two-finger press, 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 view the image full size.

3.4x 100% view center crops

Click on the image below to view a larger version in a Lightbox viewer. To see an image in a new browser tab, right click, or two-finger press, 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 view the image full size.

Seeing the output of the Gretag next to the Makro-Symmar, the two are almost identical, lots of sharp detail without a trace of CAs or red fringing, even around highlights. These two crops are so close, they really look like two samples of the same lens!

3.4x 100% view corner crops

The sharpness and detail from both lenses is very good and extremely close between the two. The upper right corner was chosen for display here since there are some slight differences between the two crops. At the lower left corner the differences were too close to call.

The final verdict

The Gretag is an excellent tube lens and gets my highest recommendation. I’m impressed by the performance image quality generally and the chromatic correction specifically. Hopefully the eBay seller will get a new supply of lenses so more people can have a chance to try this lens. Over the last month I’ve tested over a dozen tube lenses between 100 and 180mm and the Gretag 120 is one of the best.

Before I could test the Gretag 120 on extension (not stacked) at macro distances I ran out of time but I will update this post once I get a chance.

TECHNICAL DETAILS

Gretag 120mm f/6 Lens
Type: Scanner lens, or photo lab printing machine?
Filter threads: none
Focal length: 120mm
Mounting threads: M50 x 0.75. Easy-to-find M52 to M50 step-down ring-type adapters will fit this lens.
Iris: none
Aperture: preset, f/6 forwards, and f/6.67 in reverse.
Forward or Reverse Mount: Forward for stacked configuration.
Current Retail Price: Available for $17 on eBay as of October 2019. Sold-out as of November, 2019.

Gretag was a photo imaging company based in Switzerland that had been around since the 1940s, in the optics and photo-laboratory business before going bankrupt in the early 2000s (not to be confused with the GretagMacbeth, the software and color-management company that is still around). That’s about all the background information I have on the lens unfortunately.

WHAT IS A TUBE LENS?

To use an infinity-corrected objective for photography, you will need a tube lens in addition to the main objective, or the system will not focus, since the tube lens is a required part of a infinity-corrected optical system. The tube lens can be a telephoto lens, a close-up diopter, or a tube lenses designed for a microscope. To find out if you need to use a tube lens with an objective, it's easy to check, infinity-corrected objectives are identified with the infinite mark (∞) on the side of the lens barrel.

The magnification obtained by an infinity-corrected objective is the ratio between the focal length of the tube Lens and the objective. The most common tube lens focal length used by Mitutoyo and most other manufacturers is 200mm, Qioptiq uses a 250mm tube lens. With infinity-corrected objectives you can change the tube lens focal length to create different magnification ratios at the camera sensor, without compromising the color correction. To calculate the system magnification for different tube lens and objective combinations, you can use this simple formula: Effective magnification = Marked magnification X the new tube lens focal length / the system tube lens focal length.

Tube lenses can also be used in a stacked lens configuration (also called coupling lenses). This is a technique where you mount a lens in reverse on a second lens, usually a telephoto lens mounted normally, that can deliver excellent results. With the rear lens set to infinity focus and with the front lens reverse mounted there is no loss of light due to extension so you have the potential to resolve more than a since a wider aperture has the potential for higher resolution. Ideally the tube lens will not add any chromatic aberrations to the image from the front lens. Some tube lenses, when stacked, can eliminate or greatly reduce chromatic aberrations.

1x test: gretag 120 vs Makro-symmar 120

Coming soon.

For more information

For more about the Makro-Symmar here on closeuphotography.com see the links below.

The Makro-Symmar 120 HM test:
https://www.closeuphotography.com/schneider-makro-symmar-120mm

Makro-Symmar 120 machine vision lens test:
https://www.closeuphotography.com/schneider-makro-symmar-sr-120

Test results with the Makro-Symmar 120 Machine vision lens and the Lomo 3,7:
https://www.closeuphotography.com/lomo-3-7x-and-sr120

Makro-Symmar 120 stacked with the SK Xenon:
https://www.closeuphotography.com/makro-symmar-xenon

Lens Test: Gretag 120mm Lens