The GetDPI Photography Forum

Great to see you here. Join our insightful photographic forum today and start tapping into a huge wealth of photographic knowledge. Completing our simple registration process will allow you to gain access to exclusive content, add your own topics and posts, share your work and connect with other members through your own private inbox! And don’t forget to say hi!

Rm3d

jlm

Workshop Member
seems like a beauty, looks like arca got way into your pockets!
no matter how many revs you have for the helicoid, isn't the gg focusing still limited by the registration of the back compared to the gg? how well is that done?
 
seems like a beauty, looks like arca got way into your pockets!
No argument there.

no matter how many revs you have for the helicoid, isn't the gg focusing still limited by the registration of the back compared to the gg? how well is that done?
Absolutely and I've heard about hit and miss results with various manufacturers. My stuff seems to line up pretty nicely.
 

celina20

Member
Hi Chris. 1) In your experience..which method works best for focusing with this camera : tape measure, focus with the GG and a loupe or "live view" with a laptop ? Maybe this is not clear in your reviw or I dont understand it very well. ( I am a non English speaker )

2 ) In what scenarios do you prefer to use the R or M-2 camera ?

Thanks a lot

Luis
 
Last edited:
John, I asked Arca to fabricate that for me, it slides into the mount for the Vario Finder, which I don't use.

Luis, I usually focus by ground glass and then fine tune that via captures on the laptop. Live View on the P65 still sucks. I'm using the M2 more for long lens work. I don't have the 90, 135 or 180 mounted for the R (so those only go on the M2). I often find that when I'm shooting with those long lenses that I am also employing more movement than the Rm3d has, so the M2 is perfect in those applications.
 

delled

New member
Chris --

Please elaborate on the focusing mechanism and lens calibration you mention in your report.

Thanks,

Dave.

"... The focus ring on the R makes nearly 5 full rotations, that’s about 1720° of focus adjustment from infinity to closeup… much, much more adjustment than the other style or my view camera have. The ring is indexed and all the lenses come with a cheat sheet that tells you what index number to set the focus at for a given distance. I have tried this method using a tape measure and it is extremely accurate. ..."
 

David Klepacki

New member
Please elaborate on the focusing mechanism and lens calibration you mention in your report.
I do not mean to hijack Chris' thread, but I can help answer your question. I use the RM3D on occasion and am very familiar with using it.

Each lens is calibrated by Arca-Swiss in order to compensate for (very) small variations in their registration distance to the sensor plane. Unlike other camera systems where the focusing helicoid is part of the lens, on the RM3d the focusing helicoid is part of the camera body. This allows the helicoid ring to be much larger in diameter than on the lens. The larger the helicoid diameter, the finer the sensitivity you have in focusing. (As a side note, a larger diameter helicoid also minimizes internal flare, resulting in greater realized contrast.)

For example, on a standard lens helicoid for a wide angle lens the amount of focusing between 10 meters and infinity is about 15 degrees of angular movement on the lens helicoid. With the RM3d helicoid, there is close to 600 degrees of angular movement, which is a huge difference in focusing sensitivity. With this much sensitivity, it is possible to achieve "perfect" focus (in the sense that your eyes cannot perceive any better on the GG) by simply measuring the distance to your focus point, for example with a good laser measurement tool. Arca-Swiss provides a small laminated "focus table" for each lens that shows the helicoid setting as a function of distance from the sensor.

It is a very strange feeling to get extremely sharp images without focusing with your eyes ... but it works. Insecure beings that we are, we always choose to shoot tethered with live preview just to make sure we get the shot. However, if for whatever reason you cannot do this, you can safely rely on the distance method. Composing the shot can be done either with an external viewfinder or on the GG.
 

delled

New member
David --

So Arca have already done the calibration for each individual lens -- very nice. Took a bit to sink in.

Thanks,

Dave.
 

archivue

Active member
"It is a very strange feeling to get extremely sharp images without focusing with your eyes ... but it works. "

+1

and at the end of the day, your eyes aren't tired !

I'm in love with my RM3D also !
 
Top