Gretag 120 Tube Lens Tested With Surprising Results

[RobertOToole]

Gretag 120mm f/6 Lens Test

The Gretag 120 lens showed up at my office a couple of weeks ago, thanks Miljenko, and I was able to run it in a stacked setup with a couple of lenses. Honestly I didn't expect much but the lens turned out to be one of the biggest surprises of the year.

My timing on this test was really poor, when I started testing, the seller had almost 10 units in stock. I posted some of my early results with the lens and immediately the dealer sold 4 or 5 units by that night and by the next day the lenses sold out, all before I even finished testing!

You can find the full test on my site: https://www.closeuphotography.com/gretag-120-lens-test

3.4X TEST: GRETAG 120 VS MAKRO-SYMMAR 120
The Componon 35 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 tube lens.

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 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.



The 100% crop images below are all 1000 pixels across so make sure you click on a thumbnail to open the full size file. You can always save the files and compare them in another the app of your choice.

GRETAG 120 Center



Makro-Symmar Center



GRETAG 120 Corner



Makro-Symmar Corner



Test Results

The results out of the Gretag are amazing. Compared to the Makro-Symmar 120 images, the two are extremely close, these some of the best results I've seen from a tube lens, and I tested more than a dozen, just in October.

The Gretag lens is an excellent tube lens and is highly recommended.

When I return from the business trip I am on now I plan to test the Gretag 120 on a normal, non-stacked, setup.

Questions, comments are welcome.

Best,

Robert

[Scarodactyl]

Awesome! I had actually just bought one when I read yoir post about it, since I was looking for a tube lens for my new lomo 3.7x on aps-c. Looks like this was a good one to get!

[Lou Jost]

Great result! The corner looks better in the Makro-Symmar, but they are close. I had also bought one...

[RobertOToole]

Awesome! I had actually just bought one when I read yoir post about it, since I was looking for a tube lens for my new lomo 3.7x on aps-c. Looks like this was a good one to get!

That should be an awesome combo, the 3,7 works fantastic on a tube.

I completely forgot about that

For anyone that hasnt seen the results of the Lomo 3,7 on a tube, or had forgotten, like me:

https://www.closeuphotography.com/lomo-3-7x-and-sr120

[RobertOToole]

Great result! The corner looks better in the Makro-Symmar, but they are close. I had also bought one...

I agree Lou. I chose this corner, the upper right, since it shows the most difference, the lower left is my favorite corner with that disk but they were just about identical. Also the lower right was super close so I skipped it.

Makes me wonder who made the lens for Gretag, online some of the other Gretag mini-lab lenses are made by Rodenstock supposedly, but who knows with this lens, the CA control is really remarkable.

Best,

Robert

[kaleun96]

Glad I snapped up one of these too! Thanks for the lens test as always Robert.

[Miljenko]

Thank you Robert for this test with surprisingly positive outcome. I was watching this lens for some time and finally decided to get one due to low price = low damage in case of getting a lemon. As soon as it gets to Croatia I'll provide some MTF numbers with few well known taking lenses. But you just take a time and do whichever additional tests you want to perform.
Best regards,
Miljenko

[kaleun96]

Hey Robert,

How do you mount this lens specifically? I've read your references to the M52-M50 adapter and your SM2/M52 studio setup but I'm scratching my head about the best way to mount this lens.

I'm guessing you could either have two M52-M50 step down rings threaded over the middle part of the lens, with one having male threads facing towards the front of the lens and the other with male threads facing towards the rear. You could then have an SM2 extension adapter threaded on each M52-M50 adapter to clear the barrel of the Gretag 120. From there, on the rear you adapt to your lens mount and on the front you adapt to your stacked lens' mount.

Another option would be to have one long SM2 extension tube with the Gretag 120 sitting entirely inside the tube, meaning you'd just need one M52-M50 adapter (the no-lip ring type where the external threads are directly on the outside of the internal threads).

A third option would be using Raf's Printing Nikkor adapter for the rear and some other adapter for the front of the lens.

Is there a better way than any of the above that I've missed?

[Miljenko]

Hi Cam,
just before Robert wakes up and presents his solution, here is how I've done it. It is actually solution #1 as you described it but with a poor man's twist. Instead of SM2 I'm using cheap Chinese extension rings and two M50-M52 adapters. There are actually two extension ring diameters; those for mirrorless cameras have M52 threads. You need one 14mm and one 28mm ring to reach lens edges at both ends from the adapter rings. Since the extension ring set is so cheap, I have left the whole setup on the lens for good.
Best,
Miljenko

[kaleun96]

Hi Cam,
just before Robert wakes up and presents his solution, here is how I've done it. It is actually solution #1 as you described it but with a poor man's twist. Instead of SM2 I'm using cheap Chinese extension rings and two M50-M52 adapters. There are actually two extension ring diameters; those for mirrorless cameras have M52 threads. You need one 14mm and one 28mm ring to reach lens edges at both ends from the adapter rings. Since the extension ring set is so cheap, I have left the whole setup on the lens for good.
Best,
Miljenko

Thanks Miljenko!

Is it something like this that you bought?
https://www.amazon.co.uk/d/ibn/Photo-Pl ... B009VPPZYQ

IIRC, the Gretag lens measures 26mm from the rear of the lens to the threads, so does this 28mm extension only have a few mm of engagement in the (M52-M50 adapter) threads before the Gretag sticks out the back of it?

And then it's about 14mm from the front of the Gretag to the threads so the 14mm extension is just about enough as well.

Looks like a good solution though, and cheaper than Thorlabs. Hopefully I can find someone who ships it a bit faster to Europe though.

[kaleun96]

Did you also need to sand down the knurled lip on the front of the lens? My M52-M50 adapter doesn't fit over it and I can reverse thread the adapter on from the other side.

[Miljenko]

Yes, that's the piece you need, along with the 14mm version. But guess what: set consisting of 28, 14 and 7mm tubes (rings) with the end camera/lens adapters cost less: https://www.amazon.co.uk/Fotodiox-Exten ... cs&sr=1-10
And if you actually have a mirrorless camera you can use the rest. Otherwise, just discard those parts. I also used 7mm piece which I squeezed between 50-52 adapters which were a little bit wobbly.
But, there is a little catch with this solution: 14 and 7mm rings have to small internal diameter to fit onto the lens (49.0mm). Front lens edge has 49.4 diameter and if you want to fit 7mm ring as I did, it must be filed all the way to 50.1mm (as it slips over the lens thread).
To increase those dimensions you should use Dremel sandpaper drum or as I did, a friend with lathe.

[RobertOToole]

Hey Robert,

How do you mount this lens specifically? I've read your references to the M52-M50 adapter and your SM2/M52 studio setup but I'm scratching my head about the best way to mount this lens.

Yes, used a simple M52 > M50 step down and then threaded that into a SM2 tube which is internally threaded and clears the knurled step on the lens.

Cutting down the rear part of the would be a good idea also if you know someone with a lathe.

Best,

Robert

[kaleun96]

Yes, that's the piece you need, along with the 14mm version. But guess what: set consisting of 28, 14 and 7mm tubes (rings) with the end camera/lens adapters cost less: https://www.amazon.co.uk/Fotodiox-Exten ... cs&sr=1-10
And if you actually have a mirrorless camera you can use the rest. Otherwise, just discard those parts. I also used 7mm piece which I squeezed between 50-52 adapters which were a little bit wobbly.
But, there is a little catch with this solution: 14 and 7mm rings have to small internal diameter to fit onto the lens (49.0mm). Front lens edge has 49.4 diameter and if you want to fit 7mm ring as I did, it must be filed all the way to 50.1mm (as it slips over the lens thread).
To increase those dimensions you should use Dremel sandpaper drum or as I did, a friend with lathe.

Ah, I've just noticed that these extension tubes don't have an internal thread all the way through, instead they have an male and female thread on the ends and the middle "thread" looks more like concentric grooves to prevent reflections. But in your experience, the internal diameter of these extension tubes (except the 14mm and 7mm ones) is large enough to fit over the Gretag lens?

Yes, used a simple M52 > M50 step down and then threaded that into a SM2 tube which is internally threaded and clears the knurled step on the lens

Did you go for one long SM2 tube that covers the entire lens, or do you have two SM2 tubes setup in a style similar to the first mounting method I mentioned earlier? I can't find the right kind of M52-M50 adapter that would allow a single tube to house the lens inside, i.e. something like this but for M52-M50: https://www.aliexpress.com/item/32332788331.html

[Miljenko]

Ah, I've just noticed that these extension tubes don't have an internal thread all the way through, instead they have an male and female thread on the ends and the middle "thread" looks more like concentric grooves to prevent reflections.

There are two versions; one with the smooth internal surface ("28", "14" and "7" lettering on the outside) and the one with grooved surface ("1", "2" and "3" lettering). I.D. is the same in both cases.

But in your experience, the internal diameter of these extension tubes (except the 14mm and 7mm ones) is large enough to fit over the Gretag lens?

It is, except at the front side where Gretag lens has serrated wreath (49.4 diameter) and in threaded area (50mm diameter). The reason to file 14 and 7mm rings as I mentioned above.