sensor displacement in casing

[gerald.d]

Hi Dan -

Thanks for that shot. Always love to see things like that

Perhaps the question wasn't so relevant to this thread as your subject matter is very close and on the focal plane - and I can see why the distance to the sensor plane needs to be known to such a level of accuracy.

Kind regards,


Gerald.

 

[gazwas]

At such close distances would it be scoffed at to just use a good old fashioned tape measure or ruler?

 

[danlindberg]

At such close distances would it be scoffed at to just use a good old fashioned tape measure or ruler?

Still needed to know about the 7mm to know where to take the reading

 

[gazwas]

Still needed to know about the 7mm to know where to take the reading

Very true and good work Alpa for such a quick response to your tech question. :thumbup:

 

[dchew]

I've gone back and forth on the D5 now on keep it or take it out and I always seem to come back to focus mask than 100 percent viewing with a 3x Hoodman lupe. Worst case I'll use live view but I just don't use the D5 anymore. I guess here is where a IQ makes the difference since I'm pretty confident I nailed it with those techniques. But sometimes I admit it's nice to know a starting point instead of hmmm looks like 15ft

Guy,
I'd basically agree. I tend to use all the tools though, focus mask, zoom and the D5. Focus mask is my ultimate judge. I have the focus mask set very tight (maybe too tight?); there are times when there is not enough contrast in the subject for focus mask to work. Then I rely on the D5 and zoom.

Dave

 

[GrahamWelland]

So Dave, do you ever use the 'live view' of the IQ as well?

I confess that it's probably the least used part of my IQ160 ... as in almost all situations I go through the similar set of tools as you, supplemented by my rangefinder more often than the D5.

 

[dchew]

Graham,
Yeah I do once in a while, but the fact that I forgot to mention it...
I moved up from a Canon 5DII, which has the best damn live view ever. When the focus is dialed in on that camera it is like you see moire. So that is what I was used to, and I struggle with minor adjustments using the IQ live view. I use it as "another source of information" sometimes but do not rely on it.

I admit I haven't given it a robust try. There may be a learning curve I haven't jumped over.

Dave

 

[gazwas]

The fact that many don't use the live view feature on the IQ backs makes me feel a little better being a P65+ user. For me it was upgrade to an IQ back and stick with the ML2 or stick with the P65+ and get an Rm3di for exterior shoots. My Rm3di arrived at the weekend and having previously always shot tethered with my ML2 I've not had much experience shooting without a computer in tow. Will take some getting used to but just using a o) tape measure the focusing seems so accurate and I'm amazed at how easy it is to get very sharp results.

I'm not a big fan of the focus mask in C1 and just don't trust it so as a P back user the D5 seems like the way to go....

 

[Guy Mancuso]

I kind of waited to buy the tech cam until I got the IQ with the focus mask. In the field on the back itself it certainly is a better tool. For me also live view is a last ditch effort. I also shoot zero latency so I watch for heat and battery drain which live is the worst at. Battery drain I really don't care as much but heat I keep a close handle on that one.

 

[gazwas]

I kind of waited to buy the tech cam until I got the IQ with the focus mask.

Yes, I thought the same. Tech cameras need IQ backs but while I agree the added features of focus mask and amazing 100% screen are excellent shooting accessories to have in the field, following my initial tests with my Rm3di and a tape measure, the focusing of the Arca is amazingly accurate and nothing else is really required to get very sharp focus.

IMO any additional feature in a digital back above that in the P backs is a massive bonus but not a necessity any longer. With the possible addition of a Disto to remove the physical measuring problems in combination with hyperfocal focus I don't feel inadequate for not sporting an IQ or new Credo any longer.

 

[Guy Mancuso]

Gareth a Disto 5 might be of great help here for you or some folks use a Leopold range finder as well. One used for hunting

 

[greygrad]

Just wondering if the distance of 22.2mm quoted by Alpa would hold true for DBs besides the Credo and Aptus ? i.e. the distance of 7.2mm in the drawing is maintained for all DBs by varying the depth of the adapter (2) in order to account for differing sensor depths used by different manufacturers (unless they all use the same sensor depth, which would seem the sensible thing to do).

On a direct question to Alpa, I received this drawing within 4 hours. Thank you Alpa! Amazing service :thumbs:

 

[f8orbust]

The curious thing about that drawing is that it says the distance from the mounting plane on the front of the camera body, to the mounting plane on the rear, is 22.2 - 7.2 = 15mm.

Well, having just taken a set of callipers to my STC, I can tell you it's 11mm exactly.

 

[GrahamWelland]

Actually it is showing 7.2mm from the rear lip of the body vs rear face of the sensor adapter mount. Maybe there's your 4mm.

Regarding the sensor distance - it should be the same for all makes of backs. The back adapter is sized (with shims if necessary) to ensure that distance is as exact as possible regardless of make or even instance of backs.

The lens helicoid is the same (only one) for each lens for any back otherwise you'd have different adjustment there for each back if the 22.2mm wasn't common.

 

[f8orbust]

Let's get callipers out again ... yup there's the missing 4mm ... thanks Graham.

Personally, even though it's a (very useful) sketch, I think it would have been better to indicate the measurement from the plane where (1) and (2) meet, which is consistent throughout all Alpa models of camera, rather than a point on the body of the camera.

So that distance would be, um, 7.2 + 4 = 11.2mm.

 

[GrahamWelland]

I would agree in principle, but if you want to determine the sensor position relative to the body as seen from the outside then only the external face of the body would be visible when the back is on it. The internal face is, err, internal

 

[satybhat]

I find this inaccuracy confounding.
Unless the D5 is set to measure exactly from the dead centre of the sensor, there is bound to be an error which depends on the radius of the arc that the disto has to travel from the sensor's centre to it's hooked position. That is unless the object plane is exactly parallel to the sensor plane.
Here, the arc of error would be x + Delta.

Now normally, I would think it doesn't matter, the error being = delta, for larger distances to objects, but for close distances, it would have to be taken into account ?

[/IMG]

 

[stephengilbert]

Really, is this a problem? If the Disto is offset by 3 inches, at the minimum focus distance of a typical MF lens, focus at the center point of the view would be off by about .15 inches. If that is too imprecise for you, I guess you could develop a program to correct for the offset.

 

[satybhat]

Actually, I'm not even sure if this is a problem. But if we are using HPF rings and shimming to the level of micrometers, then yes, an offset of 0.15 inches does matter. Otherwise all the hoopla about precision and tolerances goes out the window. Or so I think. Really, the only way ahead then would be to develop phase-detect autofocus for Alpagon lenses :ROTFL:
But hey, disclaimer: my MF kit and back is still 4 weeks away.:watch:

 

[miska]

I think the Disto can also measure inclinations. So in principle, it's possible, knowing the inclination angle between of the Disto and the optical axis (read from the Disto) and x + \Delta (the distance measured with the disto) to calculate x. I think Jae_Moon's software for tech cam focusing does just that (and many other things):
http://www.getdpi.com/forum/medium-...s/45017-talking-technical-tech-cameras-2.html