I cannot fault anyone for using a 15mm rail system. They’re modular and most convenient – provided you don’t run into an oddity.
But that’s what I found when I mounted a Cinematics High Riser Baseplate to my own rig. After installation, neither my Fotga DP500II follow focus block or Cordvision arms fit with ease, so I decided to look into the matter further.
From bottom to top:
Cordvision 90 degree angle arms
Generic, Chinese 15mm rail block (all over eBay and often supplied with cheese plates)
Fotga DP500/DP500II Follow Focus Q/R block
Cinematics bridge from Q/R high-riser baseplate
The industry standard center-to-center distance is – supposedly – 60mm.
But is it?
Relative center-to-center distances of the four blocks are as follows:
In short, the real standard (amongst the prosumer market, anyway) is 60.5mm – if one considers that the Fotga and generic blocks are the most common and frequently sold on eBay.
Additionally, I should note that Cordvision rails are thicker than most by 0.2-0.3mm, which accounts for the difference in the Cordvision products.
Thankfully, the Cordvision 60.7mm spacing presents no problem when running 60.5mm spacing everywhere else, but the Cinematics 60mm causes the 60.5mm equipment to bind up. Though the contracting portion of the block can take up some discrepancy (as noted with the Cordvision equipment), the inner section will not – and this is where the extra 0.5 center-to-center distance of the Cinematics’ bridge causes havoc. You can see it plainly in this photograph:
There’s the secret of my fitment issues – but how to rectify it? Grinding the 0.5mm off the inside of the block will only cause one of the clamps to fit loose – and that’s not a reassuring thought when these bridges are the only two things holding my entire rig from crashing down over the riser mount.
Luckily, the generic bridge shown earlier has a 40mm recess in it, which matches the Cinematics riser block perfectly, even without the curvature built in:
The generic bridge also has the necessary center hole, but threaded – and unusable as-is. A bit of work in the drill press changed that. A 7/32nd drill bit was used to clean out the threads, followed by a 1/4″ to make the final hole. The result?
It may have cost me the use of one of my cheese plates, but I can adjust any block (particularly the follow focus, of which its position changes with each lens used) on the bottom of the rig with no issue now.
Rule of thumb: If you’re running 60.5mm throughout, replace your Cinematics blocks with generics. It’s the best solution.
Kurt K. – “Man With the 5D”