What am I missing?

I have ordered the Cambo WDS 350 and the 90mm Schneider lens. I also ordered the Cambo Compact to use for long hikes where weight is an issue and need to shift/rise/fall is not likely.

To date I have received only the Cambo Compact and the 90mm lens - WDS350 is on back order currently from Phase - hoping to get it within the next two weeks.

I shoot landscape with the Phase P-45+ back.

I would like to ask a question. As many of us shoot landscape I'm hoping they'll be an answer found here. I would assume arch. work would be similar with focus/DOF issues.

Now, I've been running tests with the Compact and the 90mm lens to confirm my Hyperfocal logic that I've used for film work. What I'm finding is not making sense to me.

If I have a landscape scene with an infinity point in it, say a mountain valley with water fall in foreground and mountains in the distance, and I set my aperature at f11, putting my infinity mark on the lens focus ring exactly on the f16 mark, INFINITY IS NOT IN FOCUS. But if I set my aperature to f11 and put my infinity mark on the lens focus ring exactly on f5.6, the distance points are in focus. Two stops off???!

At first I thought this was a problem with my P45+ needing to be calibrated. Phase shipped down a P-45 loaner yesterday and I've confirmed the exact same results with it. More importantly, I've also confirmed the exact same results with BOTH Phase backs on my Hasselblad 503cw with the 100mm CFI lens!

I'm using the same logic I've shot film for the last 40 years, but finding it's not applicable to a Phase/Cambo setup.
What am I missing?

Signed,
Frustrated in GA,
Jack

PS: I did learn that I apparently have a problem with my brand new P45+ back as the images on it are wished out compared to the P45 loaner when shooting identing scenes.

It seems to me that DOF ranges are a function of resolution. The higher the resolution, the narrower DOF becomes - the circle of confusion becomes smaller. Therefore the indicators which were right for film are no longer applicable.

The res of a p45 will indeed make you percieve a narrower DOF esp if you are look at 100% on a monitor

I was taught to use one stop more than nikon marking for 'hyper focal' focusing and that was 35mm film !

I was also taught that lenses like nikon go 'beyond infinity' because the marked focus distances change with temperature and thermal expansion of the camera and therefoere are really not to be relied on (although I can see that a black 600mm is going to be more affected than 90)

I would think a cambo may be an innapropriate tool for shooting with a 90mm surely that is more SLR lenghts

I would imagine if anything is 'out of register' it is more liekly to be the cambo or the lense than the back or the mating of the two - a lot more mechanical bits

Anyway I am not sure that the mechanical tolerances are up to it - the alignment of the GG and the Sensor or the focus markings on the lense or the calibration therof or even the thickness paint of the markings

I would bracket the focus or shoot tethered so you can actually see what you are doing

How do you focus??

S

(Disclosure - I dont own cambo - I own an H1 and a sinar P2 with a flexadapter)

Hi Jack:

As others have mentioned using the DOF scales on any digital camera can take some adjustment in practice. In general if you set the lens to f11 you might set your focus to f8 at infinity rather than f11. This one stop difference is pretty standard in using distance scales on digital. Same on my M8 as well.

The best thing would be to test your lens, as you've done, and take note of what works at which settings. All of the components you have there are great tools, the lens, the camera, the back and together you will get great results.

When I first got my Cambo WDS i took some time to test the DOF scales on each lens to know where each one worked best. Now it's just intuitive and easy.

Jeffrey,

Please describy your personal technique to test the Cambo DOF.

Thanks,
Jack

You could try photographing a fence or road with bollards going away from the camera

pick a bollard focus on it and see which otheres are in focus and at what Fs

You could think about a laser tape meusure (other thread) to help you with this

I am not convinced you are actually getting bollard one sharp - let alone the others

S

found this out the hard way with my first Dback and my hasselblad set-up...when i called hasselblad, one of the techs explained to me that eh focus scales on the lenses were made for film some 30 years ago and would not even work correctly with the newest, sharpest film stock....i would say that focus isn't 2 stops off, it is 2 stops less (critical focus)...even the newest lenses still use the same old focus scales, nobody bothers to re-measure....goes for every system....

Jack,

Here's a link to dof calculator for various digital cameras (dslr, mfdb), various media (35mm, 645, etc) and various lenses lengths. P45 is one of the mfdb's shown, and the hyperfocal distance is indeed different from what is shown on focusing scale for my 35mm Digitar. I find this calculator to be fairly representative when using 35 Digitar w/ P45.
http://www.stegmann.dk/mikkel/barnack/

John

Most likely that the DOF scales on lenses are almost without exception designed with a fairly large Circle Of Confusion value left over from film days. With digital sensors, you get more resolution per square millimeter than you did with film. While that is great for increasing overall resolution and image detail, an unavoidable side effect is that DOF is much narrower than when shooting with film, at least if you define "in focus" as pixel-sharp detail when viewing the file at 100%. A 2-stop difference would sound about right. If this is your concern, read this article and download the DOF calculator spreadsheet. If you fill in the sensor size and resolution fields correctly, it will accurately calculate DOF where DOF is defined as pixel-sharp focus when viewing the file at 100%.

The other possibility (if I'm not understanding your question correctly) is that the focus scale on your lens is not set correctly, and the infinity mark is misplaced by 2 stops on the DOF scale. If that is the case, the lens will need to have the focus scale ring adjusted so that the infinity mark corresponds to actual infinity focus.

Hey Jack,

Your lens needs to be returned. I have an Alpa with 5 lenses ranging from 24 to 100mm and all of them focus tack sharp when set to infinity with a P45. When I got my first 3 lenses one was a little off. The offending lens was .1 mm too far from the sensor. The result was an infinity setting that made pictures which were in focus about 50' out from the camera. The dealer (Fotocare) and Alpa both quickly exchanged the lens. When I bought the next two lenses, the infinity focus was the first test I made with them (and found no problems).

It is tough with these systems just starting out with one lens. You have nothing to compare that lens to. With three lenses, adjusting the shims in the H1 adapter in the Alpa, it took a little work to figure out which lens had the problem.

As everyone here seems to agree, the depth of field scales seem designed for a larger circle of confusion. The depth scales are to ignored in favor of experience using each lens and then checking the result on the screen.

--------------------

O.K. I Thought about this for two more seconds, and I'm wrong. You don't know if this is the lens, because it might be the body, or the mounting plate for the P45. The goal of course is the ability to mount the P45 on any Cambo body with any Cambo lens and and have the infinity be tack sharp. I can tell you that with 3 different Alpa bodies and 5 lenses that I don't have a problem with this (except for that one lens exchange). This problem should go in your dealers lap.

Jonathan/Eric,

If it is a Lens Focus Ring Scale "mis-alignment", I'm disappointed in Schneider. This is a brand new Digitar lens, supposedly designed to perfectly mate to a Phase type digital back! That's what we pay extra for, right?

If the person that purchases ones of these expensive lenses has to do his own personal calibration test for a lens that is two full stops off, then I think I should invoice Schneider for my time. I can see having to "tweak" a lens by say 1/4 stop, but two is very concerning to me.

Due to the historic excellence of Schneider lenses, I'm prone to discount the fact it's the lenses error - which is probably part of what I'm doing wrong. But IF I put the Phase P45+ back on my Hasselblad 503cw with the Hassie 100mm lens and run the same tests, I get the same error.

Thus, my logic at the moment is same back on different camera bodies and different lenses gives same 2 stop error must be a back issue. Couple that with the fact that images from the Loaner P45 have more saturation and color balanced indicates a faulty back.

Make sense?

Not really if one considers that we are dealing with products from engineering marvels and compenents that are prices in the Ozone!

But reality and perception frequently have little to do with each other.

Jack

All engineering is done to a tolerance

say the plane of the back =/- .05 of a mm

the back carrier =/- .05 of a mm

The thickness of the camera =/- .05 of a mm

The lens mountr =/- .05 of a mm

Pretty soon it stacks up

Thats why alpa go on about thier tolerance

And we go on about thier price

All your bits may be fine

Chuck in the fact that there are three manufactuers and you are heading for everyone saying 'my bits fine'

But if you are intedning to focus a 90 using the distance scale I think an enginner needs to calibrate the whole rig at one go

Of course manufacturing tolerances drop by a factor of 100 when you shoot tethered becuse you ignore the distance scale

Is your focus off or are you not getting the expected DOF - I dont get it

S

Make a test...

Focus in the studio using Live Video and see if the actual distance to subject is anything like what is listed on the lens.

I am more inclined to think it is back / camera rather than the lens.

Anyhoo - just a guess!

Jo S.x

Well, we're all just product testers now Jack.

I have put 8 MFDB's on my Alpa over the last 18 months, and there was one P45 that didn't focus like the rest. The other 7 were right on, both Leaf and Phase backs.

Each time I use a new back on the Alpa I test the infinity focus before taking any pictures.

Eric,
Yesterday I set a GA license plate at exactly 10 feet from the sensor plane. Took shots, Cambo Compact with 90mm Schneider, and checked results. With the focus ring set to 10 feet, all of the license plate is out of focus, not sharp. Dropping the focusing ring down to 8.75 feet and it's sharp.

What do you use for a Infinity Test logic?

The issue I'm trying to resolve is accurate focus, which I'm not getting.

Jack