Raynox DCR-150 tube assembly with flocking

[rjlittlefield]

From time to time people ask how to mount a Raynox DCR-150 for use as a tube lens with microscope objectives.

Here is one scheme that works well and is made entirely of off-the-shelf extension tubes and adapter rings, plus some DIY flocking.



By the numbers, these parts are:

1. macro extension tube set with bayonet mount to fit camera
2. bayonet-to-M42 (42mm x 1.0mm thread) lens mount adapter
3. M42 extension tubes (two sets)
4. M42 to 52mm adapter ring
5. 52mm-52mm male-male reverse adapter ring
6. 49mm to 52mm "step up" ring (49mm male, 52mm female, used in reverse to fit the 49mm female threads on the normal front of the Raynox)
7. Raynox DCR-150 lens, reversed
8. 52mm to 43mm "step down" ring (52mm male, 43mm female, used in reverse to fit the 43mm male threads on the normal rear of the Raynox)
9. 55mm to 52mm "step down" ring with through threads, used here as a 52mm-52mm female-female reverse adapter
10. (optional) 52mm to M42 adapter ring (52mm male, M42 female)
11. (optional) M42 to 52mm adapter ring (M42 male, 52mm female)
12. 52mm to objective thread adapter (52mm male, objective thread female)

Parts #10 and 11, the two rings labeled "optional", are mainly to provide a few mm of extra separation between the objective and the Raynox DCR-150. Some tests have show that this makes a slight improvement in image quality.

Note: it is critical that you add flocking or baffles to kill reflections from the sides of the tubes and rings. Failing to do this can severely degrade image quality!

The most reliable way to see reflections is to simply point the assembly at a bright light, stick your eye where the camera sensor will be, and look for any bright rings surrounding the central aperture.

For illustration, here is a setup that uses a small camera to do the looking (with an extra set of tubes to block out external light). You can see in the live view on the back of the camera that this assembly has a lot of reflections that have to be killed.



Here is a test target to show the effect of glare. It consists of a white card with a hole poked in it, the hole exposing the interior of a closed box lined with black flocking. It's pretty safe to say that only an insignificant amount of light is actually coming out of that hole.



Shown here is the pattern of reflections, the image captured by the camera, and the histogram of that image. You can see that one set of reflections (from the M42 tubes) is responsible for overall veiling glare that would kill contrast in dark areas, while a large ring of reflections (from the bayonet mount at camera) is responsible for a bright ring around the outside of the field. (This was shot using a full-frame Nikon D800E camera. Full-frame Nikons are particularly vulnerable to the second problem because the mounting bayonet has a small diameter compared to the sensor dimensions.)



Here is the flocking used to eliminate the reflections shown above. The thin strip covers the mount ring at the camera, and the larger panel covers the entire inside of the string of M42 tubes. I used black Doodlebug cardstock . An alternative material is Protostar self adhesive fabric; there is also a newer Protostar sheet material that looks quite good but I have not worked with it yet. Both are available HERE.



In addition to these two sheets of flocking, I also added a circular sheet of flocking on the back of the objective adapter, to kill any reflections bouncing back off the Raynox. And just for completeness, I put a small dot of flocking on the end of a registration pin at the outer bayonet of the first set of tubes, which was responsible for the small isolated bright spot shown in the second row of the panel of reflections. Probably it was too small to visibly matter, but it was simple to eliminate just to be safe.

One more detail... Some extension tubes have bayonet fittings that do not fit as tightly as I would like. But in this tube assembly, it's very simple and effective to epoxy the M42 adapter (part #2) against the bayonet of the extension tubes (part #1). That leaves the entire tube assembly composed of screw threads, which are quite rigid.

As of this writing (Sept 2017), all of the parts here can be ordered from Amazon, except for the objective adapter which comes from an eBay vendor, and the flocking material. Total cost including the Raynox is about $170 plus tax, with shipping inside the U.S.

I hope this helps.

--Rik

[lolhonk]

wow very nice explanation and example. Thank you very much rik!

[mawyatt]

Rik,

Nice writeup, images and explanations!

Sometimes eBay has 52mm tube screw sections in 7, 14 & 28mm sections available cheap. These can mount directly to a Nikon BR2A for camera mounting.

Cheers,

Mike

[rjlittlefield]

Thanks, guys.

One more comment about focus...

With Canon tubes from Fotodiox on the rear, this assembly gives just about perfect infinity focus.

With Nikon tubes, as shown here, the longer flange focal distance of Nikon bodies makes the tube assembly a few mm too long, so it ends up focusing maybe 30 feet out.

Standard extension tubes are uniformly multiples of 7 mm long, so by just choosing tube combinations the focus error can be as large as 3.5 mm.

That's close enough for all but the most critical work with large NA objectives, say 100X NA 0.80 . (See the graph HERE.)

But if you want to get it dead on, then it's a simple matter to replace some of the M42 fixed tubes with an M42 focusing helicoid. Those are mechanically less rigid than fixed tubes, so they are best used in a vertical setup, or locked in place with epoxy after adjustment. (Duct tape would also work fine, if you prefer the mad-scientist look.) If you use a helicoid, remember to add flocking; some helicoids are almost like mirrors on the inside.

--Rik

[concon]

Great share! For ease of use I just grabbed the kit from MJKZZ that comes with the Variable Extension Tube (already had a sleuth of stepup/down rings and adapters for Cannon to Sony).

For flocking I cut strips from this (been using it for awhile and does the job well enough): http://a.co/f3o3EjJ


My problem with the MJKZZ VLE is that it's just a thread and doesn't actually have any sort of locking mechanism. It's supposed to help achieve that perfect/optimal working distance from sensor to Raynox; however, it isn't too reliable as a forgetful mind/hand will easily unscrew it forward/back.

I followed this post for distances and ideas:
http://www.stackrail.info/index.php/en/blogs/153-using-raynox-close-up-lens-as-tube-for-infinite-microscope-objective

[rjlittlefield]

[mawyatt]

[rjlittlefield]

[Charles Krebs]

Normally I use the Protostar product, but Rik discussed "Doodlebug 1898 Beetle Black". Not readily available as such any more, but the Hobby Lobby sells it under a different SKU.

Beetle Black Crushed Velvet Scrapbook Paper - 12" x 12"
http://www.hobbylobby.com/Scrapbook-Paper-Crafts/Paper-Cardstock/Printed-Paper-Single-Sheets/Beetle-Black-Crushed-Velvet-Scrapbook-Paper---12-x-12/p/100914
You can order it on-line as well.
My understanding (from a conversation with Doodlebug Design) is that this is the same as the Doodlebug 1898 product. (Remember this does not have an adhesive backing).


concon:

[All Ex]

Would it be a good thought to use one of this in front of the Raynox in order to reduse the number of steps that are required with wide apertures?
_________________
All--Ex
My YouTube initial video

[rjlittlefield]