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Thread: Arca Brainbox utility?

  1. #1

    Arca Brainbox utility?

    Before buying an Arca 6x9/4x5 FC, I was intrigued by the Brainbox accessory. Thi s mechanical aid offered to help measure and calculate "depth of field, extensio n and swing angle." This may represent Dumbo's Magic Feather for a LF beginner like me, but I'm curious. One dealer told me Arca has discontinued the Brainbox ; but B & H still lists it as a special order item for $235. My question is whe ther anyone has used the Brainbox, knows how it compares in convenience and accu racy to Sinar's near-far focusing system, and whether it is or is not available.

  2. #2

    Join Date
    Mar 1998
    Posts
    1,973

    Arca Brainbox utility?

    I am told by the factory that i bought the last "Brainbox" in the US. This was a couple of years ago. Supposedly the design is being revamped and updated. If you can find one then yes I think it is worth it. It is very convient: it slides onto the rail behind the rear standard/ function carrier. The way it works is l ike so: you focus on the nearest point you want in focus and slide the brainbox up to t he back of the rear function carrier. You then focus to your far point by drivin g the rear function carrier forward and push a button on the side of the brainbox. A geared arm shoots forward and makes contact with the back of the function carrier. you then look at the scale for the format you are using and decide what size circle of confusion you want to work with (there are two scales for each format 1:4 (or close-up) or infinity (general work) you read the f-stop against the marker line and that is the f-stop you'll need for the depth of field you wa nt. You then divide the distance between the two points in half (there is also a sca le in cm) and drive the function carrier back to that halfway point (let's say t he distance between the two points is 2.6cm, you then focus back till the distance is 1.3cm) (all of this is much easier done than described). it is as accurate a s the Dof scale on my Sinar C (which was a hybrid of a Sinar F front standard and a P rear standard.)

    I've never used it to determine tilt or swing angles.

  3. #3

    Join Date
    Oct 1999
    Posts
    44

    Arca Brainbox utility?

    The Brainbox has not been available for at least 4 or 5 years. Arca-Swiss also has no plans of making a new version. Sorry. Jeff

  4. #4

    Arca Brainbox utility?

    Steve, I'm one of those people who need brain.But here is worth a try.

    You could try to make a Sinar equivalent DOF scale on your rear function carrier focusing knob and tension control knob. Figure out the distance on the rail per turn of the focusing knob, or distance/turn where delta is depth of focus. Then use the equation delta = 2*c*N to get the minimum f-number N to cover the depth of field required, where c is circle of confusion you want depending on the choice of your format and how much you want to enlarge.

    <ol> <li>Tape on both the rear function carrier tension control knob for focusing and focusing knob. So you can mark on the tapes. Make sure the tension control knob right next to the focusing knob is relatively tight enough to minimize back lash (maybe not that much even when tension is loose). <li>Convert the distance on the rail to turns on the knob by simply turning the knob and looking at the calibrated scale on the rail. Mark every 1 mm delta for example on the left side of the focusing tape. <li>After you transfer the delta to turn on the focusing knob, carefully transfer the 1 mm marks on the focusing knob (angles) to the tension knob. When you do this angle transfer, make sure you look directly down to marks. You now transfered 1 mm marks on the tension knob. <li>Remove the tape on the focusing knob. <li>Mark f-numbers N's on the left side of the tape, based on N = delta/2/c for a given delta. <li>Mark a line somewhere by a marker on the left side of the focusing knob to indicate where you start focusing and to align the f-number N = 0 on the tension knob to the line on the focusing knob. <li>You now have a Sinar equivalent DOF knob. </ol> Caution: Because the size of the two knobs are different (tension control knob being bigger than focusing knob), carefully transfer the mark on the focusing knob to the tension knob at the same angle.

    Note: the above calculation does not take magnification m into account as Sinar doesn't (but supplemented by another knob). You need to use a more accurate formula: N = delta/2/c/(1+m) but notice the minimum f-stop N for the required depth of field decreases as magnification m increases. So you're guaranteed to have the required depth of field at any magnification for a given delta, using the earlier formula: N = delta/2/c. Notice this equation is the same as N = delta/2/c/(1+m) when m = 0. But of course you need to compensate exposure time for the bellows extension so use the delta/2 position of the rear frame to figure out the extra stops to be added to time. To convert the bellows extension to stops, use one of the methods described in the Be llows extension exposure compensation.

    The DOF knob is still good in approximation even when standards are tilted/swung so you can still use the DOF knob. When you use tilt/swing, the way you determine the DOF using the knob is different from the way you'd do with no tilt/swing. <ul> <li>When no tilt/swing then focus on farthest and nearest you want in focus, using rear focusing knob. (the plane of focus is vertical to optical axis) <li>When tilt/swing, then focus on the two farthest angle planes from the optimum plane of focus or two objects on the corresponding to which intersect the corresponding planes of focus. The "Farthest" anlge plane is far in angle sense.

    Let me know anyone if anything is wrong. I think actually try making one for myself this afternoon....

  5. #5

    Arca Brainbox utility?

    </ul> Did it fix the indentation? Anyway don't make your decision solely based on the lack of DOF calculator on the camera. Arca F-line is something more than that.

  6. #6

    Arca Brainbox utility?

    The procedure 5 should read

    Mark f-numbers N's on the left side on the [tension] tape, based on N = delta/2/c for a given delta. Sorry if there's any confusion arised

  7. #7

    Arca Brainbox utility?

    Steve.. there is many ways to skin a cat. For DOF and lens tilt, I do the following which is much faster. Buy a programable calculator and program in the formula for DOF... then use a range finder to determine distances in your scene, or if you are shooting in a studio use a tape measure... enter the near pt. and the far point in the equation and press compute and the calc. will provide you the answer at what distance to focus at. This works 98% of the time for me... unless you are shooting the Grand Canyon and the formula asks you to focus at dead air. Who cares about extension, if you are focussed at the right distance, you will automatically have the proper extension. As for tilt, same thing, enter the formula, or do the simple math in your head... fl/(jx5) where J equals the distance in feet under the lens in which the plane of sharp foucs intersects, so a 150mm lens at 10 ft below the lens requires a 3 Deg. tilt... from their you need to examine the gg to get it just right.... The beauty of a programable calc. is you can program anything in it, and also if you get a snazzy one that has a numeric solver like some of the TI's, you enter a formula and enter in all the variables except one, then solve for that one... without re writing the equation to solve for each variable individuly.. better than a spread sheet! Hope this helps...

  8. #8

    Arca Brainbox utility?

    Ok, I tried the procedure I described above yesterday. There are still some typos and minor improvements in the above procedure. I figured out the delta/turn to be about 4.75mm &plusmn;.25mm experimentally when a strip of standard laser paper is placed on the focusing knob and glued the ends together. One whole revolution of the knob gives about 20mm (2cm) delta on the rail.

    Method 1 <ol> <li><li>Calculate delta = 2*c*10^(1/2*log(2)*Av) where Av = {5, 5_1/3, 5_2/3, 6, 6_1/3, 6_2/3, 7, 7_1/3, 7_2/3, 8, 8_1/3, 8_2/3, 9, 10_1/3, .....}. Av = Aperture value in APEX notation. Av = {5, 6, 7, 8, 9, ...} are equivalent to N = {5.6, 8, 11, 16, 22, ...}.

    So Av = {5, 5_1/3, 5_2/3, 6, 6_1/3, 6_2/3, 7, 7_1/3, 7_2/3, 8, 8_1/3, 8_2/3, 9, 10_1/3, .....} is equivalent to N = {5.6, 5_1/3, 5_2/3, 8, 8_1/3, 8_2/3, 11, 11_1/3, 11_2/3, 16, 16_1/3, 16_2/3, 22, 22_1/3, 22_2/3, .....}. Check by Av = log(N^2)/log(2). You now have delta-Av-N conversion chart. <li>Tape on both the rear function carrier tension control knob for focusing and focusing knob. So you can mark on the tapes. Make sure the tension control knob right next to the focusing knob is relatively tight enough to minimize back lash (maybe not that much even when tension is loose). <li>Convert the distance delta on the rail to turns on the knob by simply turning the knob and looking at the calibrated scale on the rail. Make sure you always look at the tick you're referring in a consistent manner. For example, close one eye and look directly straight down into the tick while consistently positioning your head at the same point relative to the top of the frame. Mark the starting point, then mark deltas on the left side of the focusing tape. You don't need to label deltas by f-numbers at this point. <li>After you transfer the deltas to the focusing knob, carefully transfer the marks on the focusing knob (angles) to the tension knob. When you do this angle transfer, make sure you look directly straight down to marks towards the center (axis) of the knobs. You now transfered the marks to the tension knob. <li>Remove the tape on the focusing knob. <li>Mark corresponding f-numbers N's, using the chart you made in procedure 1 for a given delta, starting from N = 0 (equivalent to delta = 0). <li>Mark a line somewhere by a marker on the left side of the focusing knob to indicate where you start focusing. Then starting from that point, mark a line for every 90 degrees using different colors for each angle. For example, 0 degree = Red, 90 degrees = Green, 180 degrees = Blue, 270 degrees = Yellow. So one of the lines can be easily seen from you when you're taking pictures. You use different colors to remind yourself which line you focused first. Had they been all the same color, you would not remember which line on focus knob you started with when focused a far [near] object and then focused a near [far] object. <li>You now have a Sinar equivalent DOF knob. <li>You might want to protect marks from use of tension knobs by clear tape. </ol> Method 2 A better DOF knob without a use of tension knob but a bit more elaborate. Method 2 can be applied to any LF/MF cameras with geared focusing knobs: <ol> <li>Do procedure 1 in Method 1 <li>Cut out the 1/4 width of the rubber piece on the left side of focusing knob. Leave 3/4 on the knob as it is.* <li>Make or find a right size of plastic C-shaped ring (open ended ring) piece. The right dimensioned ring should rotate on the knob by hand but stays on the focusing knob so that the ring rotates together with the focusing knob otherwise. <li>Mark the starting point starting from any tick on the calibrated scale on the rail (defining where 0 is), then mark deltas on the left side of the focusing tape and corresponding f-numbers using the conversion chart you made just before. <li>Mark a line somewhere on the right corner close to you of the main body of the rear function carrier. Basically the line should be somewhere you can comfortably see at your working angle when you're actually taking a picture. This line is your reference point whenever you set the f-number N = 0 on the ring. Equivalent to every 90 degrees on focusing knob in Method 1. Think you have 4 moving zeros in Method 1 and 1 fixed zero in Method 2. <li>Cover the ring by clear tape to avoid marks and f-numbers washed away by use. <li>You now have a Sinar equivalent DOF knob. </ol> * Not recommended to cut more than 1/4 width of the rubber piece. The fraction 1/4 is based on experimentally how much fraction of the focusing knob I use to focus. When focusing, you don't want to touch on the ring so it does not rotate accidentally and screw up DOF calculation. So the further the ring away from your finger focusing, the better. I'll work out procedure 1 and post it later.

  9. #9

    Arca Brainbox utility?

    Ok, I tried the procedure I described above yesterday. There are still some typos and minor improvements in the above procedure. I figured out the delta/turn to be about 4.75mm &plusmn;.25mm experimentally when a strip of standard laser paper is placed on the focusing knob and glued the ends together. One whole revolution of the knob gives about 20mm (2cm) delta on the rail.

    Method 1

    Specifically for Arca <ol> <li>Calculate delta = 2*c*10^(1/2*log(2)*Av) where Av = {5, 5_1/3, 5_2/3, 6, 6_1/3, 6_2/3, 7, 7_1/3, 7_2/3, 8, 8_1/3, 8_2/3, 9, 10_1/3, .....}. Av = Aperture value in APEX notation. Av = {5, 6, 7, 8, 9, ...} are equivalent to N = {5.6, 8, 11, 16, 22, ...}. So Av = {5, 5_1/3, 5_2/3, 6, 6_1/3, 6_2/3, 7, 7_1/3, 7_2/3, 8, 8_1/3, 8_2/3, 9, 10_1/3, .....} is equivalent to N = {5.6, 5_1/3, 5_2/3, 8, 8_1/3, 8_2/3, 11, 11_1/3, 11_2/3, 16, 16_1/3, 16_2/3, 22, 22_1/3, 22_2/3, .....}. Check by Av = log(N^2)/log(2). You now have delta-Av-N conversion chart. <li>Tape on both the rear function carrier tension control knob for focusing and focusing knob. So you can mark on the tapes. Make sure the tension control knob right next to the focusing knob is relatively tight enough to minimize back lash (maybe not that much even when tension is loose). <li>Convert the distance delta on the rail to turns on the knob by simply turning the knob and looking at the calibrated scale on the rail. Make sure you always look at the tick you're referring in a consistent manner. For example, close one eye and look directly straight down into the tick while consistently positioning your head at the same point relative to the top of the frame. Mark the starting point, then mark deltas on the left side of the focusing tape. You don't need to label deltas by f-numbers at this point. <li>After you transfer the deltas to the focusing knob, carefully transfer the marks on the focusing knob (angles) to the tension knob. When you do this angle transfer, make sure you look directly straight down to marks towards the center (axis) of the knobs. You now transfered the marks to the tension knob. <li>Remove the tape on the focusing knob. <li>Mark corresponding f-numbers N's, using the chart you made in procedure 1 for a given delta, starting from N = 0 (equivalent to delta = 0). <li>Mark a line somewhere by a marker on the left side of the focusing knob to indicate where you start focusing. Then starting from that point, mark a line for every 90 degrees using different colors for each angle. For example, 0 degree = Red, 90 degrees = Green, 180 degrees = Blue, 270 degrees = Yellow. So one of the lines can be easily seen from you when you're taking pictures. You use different colors to remind yourself which line you focused first. Had they been all the same color, you would not remember which line on focus knob you started with when focused a far [near] object and then focused a near [far] object. <li>You now have a Sinar equivalent DOF knob. <li>You might want to protect marks from use of tension knobs by clear tape. </ol> Method 2

    A better DOF knob without a use of tension knob but a bit more elaborate. Method 2 can be applied to any LF/MF cameras with geared focusing knobs: <ol> <li>Do procedure 1 in Method 1 <li>Cut out the 1/4 width of the rubber piece on the left side of focusing knob. Leave 3/4 on the knob as it is.* <li>Make or find a right size of plastic C-shaped ring (open ended ring) piece. The right dimensioned ring should rotate on the knob by hand but stays on the focusing knob so that the ring rotates together with the focusing knob otherwise. <li>Mark the starting point starting from any tick on the calibrated scale on the rail (defining where 0 is), then mark deltas on the left side of the focusing tape and corresponding f-numbers using the conversion chart you made just before. <li>Mark a line somewhere on the right corner close to you of the main body of the rear function carrier. Basically the line should be somewhere you can comfortably see at your working angle when you're actually taking a picture. This line is your reference point whenever you set the f-number N = 0 on the ring. Equivalent to every 90 degrees on focusing knob in Method 1. Think you have 4 moving zeros in Method 1 and 1 fixed zero in Method 2. <li>Cover the ring by clear tape to avoid marks and f-numbers washed away by use. <li>You now have a Sinar equivalent DOF knob. </ol> * Not recommended to cut more than 1/4 width of the rubber piece. The fraction 1/4 is based on experimentally how much fraction of the focusing knob I use to focus. When focusing, you don't want to touch on the ring so it does not rotate accidentally and screw up DOF calculation. So the further the ring away from your finger focusing, the better. I'll work out procedure 1 and post it later.

  10. #10

    Arca Brainbox utility?

    For MF <table BORDER > <tr VALIGN=BOTTOM> <td ALIGN=LEFT>11.39</TD> </TR> </Table>

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