Velmex is a company which produce very good quality « slide » which can be used for macro and micro photography as these slide are allowing very tiny movement of the camera. For example, some of these stage needs 40 turns for a displacement of one inch. In the metric field each turn move the camera of 0.635 mm or 635 µm. For 1/12° of turn we go down to 53 micrometer of movement. The Velmex Unislide can be found in 2.5, 5, 10, 20 & 40 turns per inch and in the metric series in 5 or 10 turns per cm..
I’ve discovered that it’s used by the famous Charles Krebs (I would be very happy to be able to get half as good pictures as him).
I’ve found a Velmex Unislide A25 6,5 » and 40 turns par inch on eBay. Reference Velmex Manual Screw Drive A2509C-S2.5.
How to choose the right turn per inch.
When I put my auction on my first Velmex slider, I haven’t realised that they exist with different setting. At least 10, 20 or 40 turn per inch. My seller told me that he had made a mistake in his item description and that his Velmex was 10 turn per inch instead of 40 advertised. As I didn’t knew what to reply to his refund proposal, I had to run a small enquiry.
In one of his message Charles Krebs said that he prefers 20 turns per inch to the 40 turn per inch as it’s more easy to use (less turn between each shot at low magnification) but no mention of the 10 turns per inch.
For the water mites I think I won’t use a lot a bigger magnification than 10x and I wondered what is the depth of field of such an objective.
I’ve found the reply on this Nikon site :
Depth of Field and Image Depth
| Magnification | Numerical Aperture | Depth of Field (µm) |
Image Depth (mm) |
| 4x | 0.10 | 55.5 | 0.13 |
| 10x | 0.25 | 8.5 | 0.80 |
| 20x | 0.40 | 5.8 | 3.8 |
| 40x | 0.65 | 1.0 | 12.8 |
| 60x | 0.85 | 0.40 | 29.8 |
| 100x | 0.95 | 0.19 | 80.0 |
According to this chart I need a slide which allow a control of 8.5µm to use a 10x magnification objective (and I don’t understand what is Image Depth in this chart)
- A Velmex with 10 turn per inch give 2.54 mm (2540 µm) of displacement for each turn. So 8.5µm is reached at roughly 1/300 of turn.
- A Velmex with 40 turn per inch give 0.635 mm (635 µm) of displacement for each turn. So 8.5µm is reached at roughly 1/75 of turn.
Conclusion : It seems better to try to get a 40 turn per inch Velmex for doing good focus stacking with a 10x objective. But with a 4X objective as my Leica C Plan, the 10 turn by inch may be OK.
Other options than the Velmex Slide
There are many other possibilities like the OptoSigma linear stage I’ve finally purchased. Here are some request to run on ebay to find them.
Request for ebay : linear stage, single axis translation stage, Linear Stage Table Positioning, Linear Translation Stage Sub-Micron, X-Axis Linear Translation Stage Slide, precision optical stage, Linearführung, Präzisionsführung, Micrometer Positioning Stages, dovetail slide, leadscrew slide, queue d’aronde, vernier, micrometer slide
Brands : Schneeberger , Mitutoyo, Newport, Oriel, LineTool, Del-tron, Micro Slides Inc, CHUO SEIKI, Melles Griot, Velmex, Gaertner scientific, Daedal, Parker, Sigma Koki, Suruga Seiki, LG motion, OptoSigma, Setco, Axmo, Giroud, New focus, Starrett, Data optics,
Adding a quick release clamp on the Velmex focusing rail.
As this slider is not design for photographic purpose one have to adapt it to hold a camera bellow and to fix it on a tripod or other fixed support.
As my wife had just bought a Manfrotto tripod (modo or digi or 785B) I think it can be a good idea to use the same quick release system for my Velmex. The reference of the quick release plate for her tripod is 785PL. Unfortunately, there is no way to buy only a system with the plate and the corresponding clamp to fix to the slider. I have to find another way.
Request to run on ebay : quick release or quick release system
Links.
- Charles Krebbs on photomacrography.net with the presentation a custom knob.
- The same Krebbs in Case study: « Portable » stacking set-up
- Dmillard had screwn clamps on his Velmex Unislide.
- Craig Gerard had run another Velmex A25 modification for a Canon MP-E 65
- The Bratcam from chris S
- A thread about the « non Velmex » slide.
- Hejnar Photo on eBay.
- The specifications of the Velmex Unislide (pdf)
Annexe
Extract from the Velmex documentation on the Unislides.
Velmex Unislide specification
