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!
They are both great lenses, each with a different set of strengths. And the upside is there is no bad choice. These are great times for photographers for sure.
Jack:
what is your opinion on lens shimming to set infinity focus for tech cameras? alpa makes a point of it and I know the cambo has the ability to tweak the body side lens mount.
As I see it, you set focus on the infinity stop and take a series of shots, adding or subtracting shims (for the alpa) to adjust lens to sensor distance, until distant objects come into best focus.
what is your opinion on lens shimming to set infinity focus for tech cameras? alpa makes a point of it and I know the cambo has the ability to tweak the body side lens mount.
As I see it, you set focus on the infinity stop and take a series of shots, adding or subtracting shims (for the alpa) to adjust lens to sensor distance, until distant objects come into best focus.
jotloob
Subscriber Member
Question to those of you who work with the DIGARON-W 40mm .
There is a CF available but it does not say anywhere that you need to use a CF .
Looking at the ALPA pages .
Do you use a CF and if so , what is your experience ?
Is a CF required more when using a FF sensor in comparison to a 37x49 sensor ?
There is a CF available but it does not say anywhere that you need to use a CF .
Looking at the ALPA pages .
Do you use a CF and if so , what is your experience ?
Is a CF required more when using a FF sensor in comparison to a 37x49 sensor ?
Good question John, and the answer is maybe
:I think if you have an Alpa or Cambo, you definitely want to shim for infinity accuracy, and you need to make sure any tech cam/lens combo can achieve infinity focus. However with the Arca having it's helical as part of the body, and with that helical having such a huge range (4 full turns), shimming is basically "built-in" to the camera via that helical, so all you really need to do is calibrate to each specific lens.
For those unaware, the Arca helical is about 4" in diameter, has 32 distinct points with 4 hash-marks between each main graduation around the perimeter -- and you can easily interpolate half-way between each hash -- for a total of 320 distinct reference points per turn, and you have 4 full turns. Thus you can simply mark any lens for it's true infinity number on the helical, and you're done.
HOWEVER! With the new Phase IQ back technology, as long as your lens hits infinity the numbers on the scale only need to get you close. From there, you can use the Focus Mask feature in the IQ back and "see" the PoF in the image review as it pops up. So *my* current mode of operation is: 1) Compose (I estimate it with wides), focus by estimation, estimate exposure, shoot; 2) Review frame's composition, histo and FM (Focus Mask); 3) adjust exposure if necessary, move focus point in or out as needed and adjust composition as necessary; 4) shoot frame 2, repeat steps 2 and 3 as required; 5) once I have my final "perfected" composition, exposure and focus all set where I want them, I wait for the light/moment I want and take final frame, then take the LCC immediately afterward. I'm set.
In practice, this may mean I take as many as 6 or 8 "set-up" shots to get composition and exposure all perfected with shifts and tilt, but those 6 or 8 frames take maybe 2 or 3 minutes total. Then I wait for the light as needed and take my final capture. By taking the LCC frame after my final, when I'm reviewing my images in my C1 session, I know exactly where in the chain my "perfected" composition was. However, since the last few frames are all usually very minor tweaks, the single LCC is generally adequate for them too if for some reason I decide I like the one or two before the final better.
Edit post just to finish the above discussion point: I finally got out yesterday for some infinity testing with my Arca RM3D and Rodie 40HR-W. I was able to confirm infinity focus -- a series of high-tension towers at about 300, 600 and 900 meters spacing and then trees and rocks on a ridge about 5 Km distant behind them on a relatively clear Sierra morning. Result was this: 300m tower and 5Km trees all came into crisp focus at the same spot.
Point one. Interestingly, there were three of the hash points on my Arca ring that all appeared equal i sharpness, but then the hash's outside those were showing slightly softer. (Each hash mark is 1/170th of a turn on the ring, and equal roughly 14 microns of lens extension delta.) This was at f7. Anyway, I inferred the mid-point has as true infinity, and suspect that the lens is resolving enough higher than the sensor pixel pitch that the hash-marks to either side of that while less sharp, are still out-resolving the sensor. Impressive for sure.
Next point is that 100m was 3 hash marks (~45 microns) in from that, and 30m was another 3 in from that. I take from this that extremely fine shifts on the focus ring to make relatively significant alterations to focus points that all fall within a traditional definition of photographic infinity. Stopping down would not improve DoF enough to make these irrelevant at 100% pixel view. Print resolution and normal print viewing distances however would -- IOW being a little off is probably close enough for most critical work even for larger prints. But it's nice to know we can get pretty extreme focus criticality here.
Final point is I noted no back-lash issues, at least within one single hash-mark on the Arca ring, and at least to what the IQ180 can resolve -- to me this is impressive. Clearly there is some back-lash or we would not be able to turn the ring. I've read that Arca claims 10u precision here and I have no reason to doubt that after viewing my empirical results.
I'll probably start a new thread on my experience with eh RM3D as I gather a few post-worthy images!
Point one. Interestingly, there were three of the hash points on my Arca ring that all appeared equal i sharpness, but then the hash's outside those were showing slightly softer. (Each hash mark is 1/170th of a turn on the ring, and equal roughly 14 microns of lens extension delta.) This was at f7. Anyway, I inferred the mid-point has as true infinity, and suspect that the lens is resolving enough higher than the sensor pixel pitch that the hash-marks to either side of that while less sharp, are still out-resolving the sensor. Impressive for sure.
Next point is that 100m was 3 hash marks (~45 microns) in from that, and 30m was another 3 in from that. I take from this that extremely fine shifts on the focus ring to make relatively significant alterations to focus points that all fall within a traditional definition of photographic infinity. Stopping down would not improve DoF enough to make these irrelevant at 100% pixel view. Print resolution and normal print viewing distances however would -- IOW being a little off is probably close enough for most critical work even for larger prints. But it's nice to know we can get pretty extreme focus criticality here.
Final point is I noted no back-lash issues, at least within one single hash-mark on the Arca ring, and at least to what the IQ180 can resolve -- to me this is impressive. Clearly there is some back-lash or we would not be able to turn the ring. I've read that Arca claims 10u precision here and I have no reason to doubt that after viewing my empirical results.
I'll probably start a new thread on my experience with eh RM3D as I gather a few post-worthy images!
Yes I did and yes it does. On my Phase with my Schneider LS lenses, I comfortably use a setting of 40 - 45. With the 40 HR-W, I need to crank that up to 65 - 70 to get the level of discrimination I want. I believe we will find that generally speaking our sharper, higher-contrast lenses are going to need higher FM settings to render a similar mask zone to that of our less sharp, lower contrast lenses.
Guy Mancuso
Administrator, Instructor
G
Gardenerbob
Guest
I hate to be a 'Silly Billy'
but, what does 'DF', stand for.
Bob
but, what does 'DF', stand for.
Bob
dougpeterson
Workshop Member
Phase One DF body.
Doug Peterson (e-mail Me)
__________________
Head of Technical Services, Capture Integration
Phase One Partner of the Year
Leaf, Leica, Cambo, Arca Swiss, Canon, Apple, Profoto, Broncolor, Eizo & More
National: 877.217.9870 *| *Cell: 740.707.2183
Newsletter | RSS Feed
Buy Capture One 6 at 10% off
brain wandered while i was running a machine...came up with this comparison to jack's findings. I am using Cambo lenses on I assume, Cambo helical focusing mounts
43mm lens: closest focus is 400mm with lens-to sensor calculating to 48.17mm. focus barrel rotates about 110 degrees. that works out to .047 mm (47 microns) per degree of rotation
70mm lens: closest focus is 800mm with lens-to sensor calculating to 76.7mm. focus barrel rotates about 270 degrees. that works out to .025 mm (25 microns) per degree of rotation
120mm lens: closest focus is 2,600mm with lens-to sensor calculating to 125.8mm. focus barrel rotates about 250 degrees. that works out to .023 mm (23 microns) per degree of rotation
looking at what jack posted, he was getting 170 ticks per full revolution, so each tick is about 2.11 degrees. His result of 14 microns per tick is then 7 microns per degree
so the arca is 7 microns per degree for all lenses
the cambos (and probably the alpa's) are from 47 to 23 microns of lens movement per degree of barrel rotation.
a bit more data: comparing lens movement between focusing at 10 meters and 10.5 meters for the different lenses above:
43mm: 10M vs 10.5M = 9 microns half a tick, or one degree, for the arca, about 1/5 degree for the cambo
70mm: 10M vs 10.5M = 23 microns 1.5 ticks for the arca, about 1 degree for the cambo
120mm: 10M vs 10.5M = 70 microns five ticks for the arca, about 3 degrees for the cambo
last thing: the cambo lens barrel dia gives about 1/2mm per degree on the circumference
all arithmetic subject to error, of course
43mm lens: closest focus is 400mm with lens-to sensor calculating to 48.17mm. focus barrel rotates about 110 degrees. that works out to .047 mm (47 microns) per degree of rotation
70mm lens: closest focus is 800mm with lens-to sensor calculating to 76.7mm. focus barrel rotates about 270 degrees. that works out to .025 mm (25 microns) per degree of rotation
120mm lens: closest focus is 2,600mm with lens-to sensor calculating to 125.8mm. focus barrel rotates about 250 degrees. that works out to .023 mm (23 microns) per degree of rotation
looking at what jack posted, he was getting 170 ticks per full revolution, so each tick is about 2.11 degrees. His result of 14 microns per tick is then 7 microns per degree
so the arca is 7 microns per degree for all lenses
the cambos (and probably the alpa's) are from 47 to 23 microns of lens movement per degree of barrel rotation.
a bit more data: comparing lens movement between focusing at 10 meters and 10.5 meters for the different lenses above:
43mm: 10M vs 10.5M = 9 microns half a tick, or one degree, for the arca, about 1/5 degree for the cambo
70mm: 10M vs 10.5M = 23 microns 1.5 ticks for the arca, about 1 degree for the cambo
120mm: 10M vs 10.5M = 70 microns five ticks for the arca, about 3 degrees for the cambo
last thing: the cambo lens barrel dia gives about 1/2mm per degree on the circumference
all arithmetic subject to error, of course
stephengilbert
Active member
Perhaps a new thread: Tech cameras and GQ, as in Geek Quotient.
As they say, if the shoe fits...
Speaking of GQ, I posted the following on Lulu earlier today --
The Arca R focus helix is approximately 110mm in diameter, has 172 tick marks (numbered every 5 ticks, from 0 to 34), and moves the lens in or out 2.5mm per revolution -- i.e., 2500/360 = 6.94 microns/degree, or 2500/172 = 14.53 microns/tick mark. Lacking a vernier scale, about the best that could be achieved in terms of repeatability is 1/2 a tick mark, or 7.27 microns. Arca claims 10 micron repeatability for the Rm3di <http://www.rodklukas.com/resources/Arca-Swiss_NewProducts_2010.pdf>, which coincides with the minimum shim increment from Alpa.
The scale that Arca uses appears to be based on the circumference of the focusing mount: 110 x pi = 345.6, which, when truncated to an even integer, yields 172 ticks and a final diameter of 109.50mm.
This afternoon I worked out the theoretical extension table (in Arca units) for the SK 43XL. Plugging in Schneider's published focal length for this lens: 44.6mm, I can almost but not quite duplicate the table that Arca sent with my lens. At distances beyond 10 ft, the differences are 1/2 tick or less. At closer distances, the differences increase, but are still less than one tick up to 6 ft. However, if I use 44.95mm as the focal length, I can precisely duplicate the Arca-Swiss table.
So, in my case, has Arca-Swiss measured the actual focal length of my lens and used that to generate the table? What else do they take into account in generating focus tables?
On a related point, infinity focus is stipulated as an extension of 0mm. What if the sensor is a little farther back? How does one compensate?
Dave.
[As I noted on Lulu, I'm still lacking a mount for my back, so I'm reduced to admiring Arca-Swiss engineering as opposed to using the camera.]
The Arca R focus helix is approximately 110mm in diameter, has 172 tick marks (numbered every 5 ticks, from 0 to 34), and moves the lens in or out 2.5mm per revolution -- i.e., 2500/360 = 6.94 microns/degree, or 2500/172 = 14.53 microns/tick mark. Lacking a vernier scale, about the best that could be achieved in terms of repeatability is 1/2 a tick mark, or 7.27 microns. Arca claims 10 micron repeatability for the Rm3di <http://www.rodklukas.com/resources/Arca-Swiss_NewProducts_2010.pdf>, which coincides with the minimum shim increment from Alpa.
The scale that Arca uses appears to be based on the circumference of the focusing mount: 110 x pi = 345.6, which, when truncated to an even integer, yields 172 ticks and a final diameter of 109.50mm.
This afternoon I worked out the theoretical extension table (in Arca units) for the SK 43XL. Plugging in Schneider's published focal length for this lens: 44.6mm, I can almost but not quite duplicate the table that Arca sent with my lens. At distances beyond 10 ft, the differences are 1/2 tick or less. At closer distances, the differences increase, but are still less than one tick up to 6 ft. However, if I use 44.95mm as the focal length, I can precisely duplicate the Arca-Swiss table.
So, in my case, has Arca-Swiss measured the actual focal length of my lens and used that to generate the table? What else do they take into account in generating focus tables?
On a related point, infinity focus is stipulated as an extension of 0mm. What if the sensor is a little farther back? How does one compensate?
Dave.
[As I noted on Lulu, I'm still lacking a mount for my back, so I'm reduced to admiring Arca-Swiss engineering as opposed to using the camera.]
P
Porpoise
Guest
With these experiments, Jack proves physics is right. Traditionally, like for the markings on most lenses, DoF calculations are done with a CoC value of .030mm. Discussions are mostly ended with the statement that your acceptable CoC is subjective. Meaning that you decide which resolution you need. But if .030mm is enough, why did I buy the IQ180 that was just delivered? Fmor DR and color tonality, the IQ140 won't be far behind. For maximum resolution, it makes more sense to me to start with the pixel size as the CoC value. We don't want to confuse all those pixels! For the IQ180 that means .0052mm.
A 40mm lens at f/4 then has a hyperfocal point at 77m, meaning that even with a perfect lens, you won't achieve better than pixel resolution nearer than 36.5m. But beyond that point, all the way to infinity, a good lens outresolves the IQ180. If perfectly focused at 900m, the nearest point where your lens still outresolves the IQ180 is 70.9m.
A better way to calibrate the focus, might be to determine the point at which you don't get maximum resolution when focused on "infinity". If you want resolution at 300m or anywhere else beyond 70.9m to be less than resolution at infinity, you should in fact focus beyond infinity. Your camera would be a bit farsighted, as the minimum point of focus will suffer.
On the other hand if you want a maximum range of maximum resolution, your "infinity" focus could in fact be the hyperfocal point at 77m. Any nearer focusing would start to degrade resolution at infinity. A bit of nearsightedness might be a good thing.
So we have reached a point where calibrating the focus doesn't mean to look for resolution at infinity, but rather to decide on the range where maximum resolution can be reached.
Hans (who isn't a geek at all) ;-)
A 40mm lens at f/4 then has a hyperfocal point at 77m, meaning that even with a perfect lens, you won't achieve better than pixel resolution nearer than 36.5m. But beyond that point, all the way to infinity, a good lens outresolves the IQ180. If perfectly focused at 900m, the nearest point where your lens still outresolves the IQ180 is 70.9m.
A better way to calibrate the focus, might be to determine the point at which you don't get maximum resolution when focused on "infinity". If you want resolution at 300m or anywhere else beyond 70.9m to be less than resolution at infinity, you should in fact focus beyond infinity. Your camera would be a bit farsighted, as the minimum point of focus will suffer.
On the other hand if you want a maximum range of maximum resolution, your "infinity" focus could in fact be the hyperfocal point at 77m. Any nearer focusing would start to degrade resolution at infinity. A bit of nearsightedness might be a good thing.
So we have reached a point where calibrating the focus doesn't mean to look for resolution at infinity, but rather to decide on the range where maximum resolution can be reached.
Hans (who isn't a geek at all) ;-)