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Setup experiments with twin bellows and a Nikon D810

Last Updated: 3rd Oct 2014

By Stephan Wolfsried

As I promised in my last article here is a report on my recent setup changes:

The problem was that the Mitutoyo objectives which are available in 50x, 20x, 10x, 5x, 2x, 1x. left a small gap of app. 15% FOV which I cannot close with a bellows extension of 150 mm of the Novoflex bellows Balpro1. E.g. on my Sony Nex 7 with APS-C Sensor the 20x ended with 0.9 mm FOV and the 10x started with 1.05 mm FOV. I asked Novoflex to build a bellows with 180 mm extension, but they told me that would be too complicated. They recommended to build a twin bellows and they offer an adapter set to assemble this. First of all I took the two sledge version of my linear actor:

Linear actor with two sledges

The two sledges bear an adapter plate with 150 mm length.

adapter plate

Finally the twin bellows is mounted on the adapter plate

twin bellows

The lower ones ridge of the twin bellows was cut at the half, so the overall extension is now 200 mm instead of previously 150 mm. It is a compromise not to let the overall length get too large.
The whole adapter plate and the linear actor are very compact as the side view shows:

Side view

With camera and objective the whole setup is like this:

Setup with camera and Luminar objective

And here is the setup with a Mitutoyo objective on a Nikkor 180 mm MF objective as tubes lens.

Setup with camera and Mitutoyo objective

Finally here is the grand overview of my photographers working place.
Handling of the probes is done under the bino, here I define what I would like to photograph.
The system control pad shows me the FOV. With that information I choose the appropriate objective.

Photographers working place

Actually I have to learn the differences between the Nikon D810 instead of the Sony Nex 7 which I previously used.
One big difference is the Mirror, which the Nex 7 doesn't have. The stiffness of the actuation is a necessary condition and as I presume solved in a perfect way. Due to the increased overall length of the assembly the camera is causing vibrations which run through the assembly to the objective. Therefore a mirror prerelease of app 2 sec. is mandatory. Also the usage of the electronic first curtain.

Another difference is the data volume to be processed. Even a jpg Picture has now 20 Mb or more and a 200 picture stack now needs about 45 to 60 minutes to be processed with Helicon Focus with my actual Windows PC. Upgrading my computer hardware was now the next task.
With an IMac and maximum processor performance and memory available today I come down to appr. 18 minutes. Next will be to let do I/O and processing in parallel. What I also learned is that Helicon Focus doesn't work satisfying under OS-X. The retouching feature is not practicable and the mouse sensitiveness overceeds my finemotoric capabilities. I needed to install Parallels and work with my old 5.2 HF Windows Version. With this one I am really happy. The only problem is that the apple magic mouse is too sensitive, but a Logitech wired mouse works well.

The following table shows that the gap between the different objectives is now almost closed. The downside of this assembly is that the minimum length of the bellows is now doubled either. The red bar is the value for the lower bellows extension (only 50 mm) and the green one is the value for the upper bellows extension.

FOV range with different objectives in mm with twin bellows and full frame sensor

At the end I must admit that the price for closing the FOV gap definitely is too high: As the last couple of my photo uploads show the result is o.k., but the calm down time between each picture of the whole stack is by far too long and the stiffness of the actuation becomes totally irrelevant because the rest of the assembly is too weak. So I will get back to the mono bellows and overcome the FOV gap otherwise, e.g. with the same objective once on a 180 mm tubus lens ond once on a 200 mm one. Or by using spacers.

FOV range with different objectives in mm with single bellows and full frame sensor

This is the FOV Range with the Nikon D810 and the single bellows. Actually remains a gap between 2,7 mm and 3,2 mm FOV.
Maybe I will close this with a further 5x on a 200 mm Nikkor objective.

My main motivation in having a camera with full frame sensor instead of one with an an APS-C sensor was the 1.5 times larger FOV.
This is as shown above really the case, but the resolution is by far better with the Sony Nex 7 and its APS-C sensor.
I am not really sure what is the main reason for that, but in fact is so. Maybe pixel density plays a role: 6000 pixel distributed on 24 mm result in 250 pixel/mm. With the full frame sensor the corresponding value is only 204 pixel/mm. The visual difference (See the Pyrrhotite pictures as example) is much more than 20%...Click on the pictures and load the HR version to see and compare the details.

Pyrrhotite with Sony Nex7
Pyrrhotite with Nikon D810

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