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-   -   85mm lens center above rail center spec (https://www.dvinfo.net/forum/special-mounts-applications/486062-85mm-lens-center-above-rail-center-spec.html)

Robert Rozak October 12th, 2010 11:11 PM

85mm lens center above rail center spec
15mm rails on 60mm centers ... pretty straight forward.

But, 85mm lens center above rail center spec ... how strictly is this followed in the industry?

I measured the DSLR base to lens center on a number of cams (approx):
- 44mm for 5D
- 42.3mm for 7D
- 39mm for T2i

I know zacuto has an adjustable DSLR baseplate. But, most other manufacturers offer a single baseplate which isnt adjustable (without options for different heights for different cameras).

So, is it important to be 85.00mm, or just close enough within the band of goodness ... ?


Chris Soucy October 12th, 2010 11:35 PM

Er, Robert.................
Be gentle, I'm a complete "know nothing" with this sort of setup.

I don't really understand the question (I refuse to believe I'm the only one, at least I hope not), care to enlighten us ignorant souls as to what that is all about?

What's so magical about a 85mm lens centre above the rail spec?

Er, what industry, considering you're comparing DSLR's to, er, what, exactly?

Confused and ignorant.


Robert Rozak October 13th, 2010 10:44 PM


The 85 mm is supposed to specify the distance from the center of the 15 MM rails, to the center of the lens. This is so that optics of the lens will line up with th other accessories such as matte boxes. To do this, manufacturers sell a " DSLR Baseplate" to raise up the DSLR lens up above the parallel 15 MM rail system, to align the optics with the accessories like matte boxes.

Some manufacturers have adjustable DSLR Baseplates.

However, some very well known manufacturers do not (if I'm reading their specification page correctly):
Redrock Micro - DSLR Base Plate

But, every DSLR camera positions it's lens at a slightly different height above the base of the body.

So, how can a DSLR Baseplate that is not adjustable work?

I'm guessing that the differences between the DSLR bodies is just not that big of a deal (a couple of mm)?

I can see how a couple of mm would not make much of a difference for a focus follow (who cares if the gears engage a couple of teeth lower our higher).

Matte boxes might be a different story? But then again, RedRock makes a matte box that is adjustable +/- 10mm.

So, after all this, I guess it just isn't necessary to have a DSLR Baseplate that is adjustable to get the center of the lens exactly 85mm above the center of the 15mm rails?

I'm looking for other inputs to either confirm this, or explain the problem with this thinking.


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