After my initial ghastly focus results using my old Hasselblad 500s with a CFV-39 DB, and posting the topic here on LL, I had to take stock of my shooting technique. What, exactly, was going on?
Well, we had all the technical explanations for the cause of Focus Anguish in that thread, and they all seemed to make good sense. The question was, what to DO about it. After all, when you have just paid out the most money for anything you have ever purchased in your entire life (my house excepted) for a little black box with some buttons on it, used up your entire savings and had to sell a vintage guitar in the process – and when you are producing worse pictures with it than you were with a three-quid roll of HP5, that tends to be pretty depressing.
So I did some serious thinking, and testing. The curious thing was that some of my shots were perfectly in focus, so obviously I was doing something right, some of the time, without realising it. The other piece of evidence came from focus testing on a tripod. Using my 120mm S-Planar lens at close range (say between 6 and 3 feet) I could in fact get perfect focus every time. For example, with the leaf of a fern outside my door, where the leaf was coming from the roots towards me at an angle of 45 degrees, I could focus on the tip, or half-way down the leaf, or at the base and I would be bang-on for each shot. This, I reasoned, was because in this case I had something big and clear to focus on which filled most of the screen, and I was in the area of lens helicoid movement with the most sensitivity and finesse. So then I knew that there was nothing intrinsically wrong with the focus screen position, the mirror plane, or the alignment of the DB to the body. A good start.
At the opposite end of the spectrum, distant shots with the 150mm or the 80mm focused at infinity were also perfectly crisp. It was the shots where the subject was between say 20 to 60 feet away which were the big problem, with any lens. This, of course, is just the area where the lens focusing movement is very small (and pretty stiff on the old Zeiss ‘C’ lenses) and has the least finesse. Fair enough, so what goes wrong in practice?
There we are, out for the afternoon, and the perfect subject lies before us. A splendid tombstone, aged and weathered, with fine lettering and the light slanting just so. Framing it perfectly and about 20 feet behind are the mellow 16th century church porch and an ancient yew tree (yes, my middle name is cliché). So we frame up in the viewfinder and, using the WLF magnifier (or a prism), wind the focus ring until the subject appears to be sharp. Now this is where we encounter a problem which I shall term the Area Of Uncertainty (or AOU). We can stop as soon as the subject appears to be sharp, but we find that we can move the focus ring even further, back again, and we can see no change. This is the AOU, and it exists because we do not have enough magnification on the focus screen to judge the tiny changes in focus within this critical area. A 6x or 8x loupe would probably help, but with the standard finder we cannot judge focus correctly inside the AOU, which is the range of helicoid movement within which we can see no change.
We humans may not be able to judge focus within this zone, but the sensor in the MF DB most certainly can. This malignant little rectangle of silicon will mercilessly throw the results back in your face at 100% or even 50% when you download your cherished results that evening. And the typical scenario goes like this –
We raised the camera to our eye, with the lens focused at infinity. We rotated the focus ring out, focusing to the near field until the tombstone appeared to be sharp. We hit the AOU and stopped, and tripped the shutter. On screen, we can see the awful truth about what really happened. Fooled by the AOU, we had stopped too soon and we were actually focused behind the subject. Consequently we have an image where the subject itself is soft and everything immediately behind it is pin-sharp, highlighting the fault even more. And because there is less depth of field in front of the plane of focus than behind, the grass and flowers in front of the tombstone are totally OOF, making things even worse.
So what can we do? The answer is to make use of the AOU to our own advantage, accept that there will be a focus error, but make it work for us rather than against us. We must make use of the fact that there is more DOF behind the subject than in front of it. Here is the simple rule – focus the other way around – not from infinity to the subject, but from close-up to the subject. So again we raise the camera to our eye, but this time the lens is set not to infinity (as I always used to do) but to the near field, perhaps 3 or 5 feet. This time we rotate the focus ring in, not out, and stop when we hit the AOU and the subject appears to be sharp. On the PC screen, although the plane of focus is still in error and this time slightly in front of the tombstone, the subject appears sharp because there is sufficient depth of field behind the focus point to keep it in. Even better, the grass and flowers in front are also pin-sharp. Behind the subject, DOF fades away gracefully, and though the porch and yew tree are slightly soft our eye accepts this as they are in the background.
So there is the simple trick which has really improved my manual focusing on the old ‘Blads. Perhaps I should coin another acronym – Focus From The Front, FFTF, a bit like ETTR, perhaps. It may be that loads of you chaps already do this, or it may be that you think it is a load of pants. Fair enough. But it might be worth a try.
John