Pancake 25/2.8 goes beyond infinity

[ruslan]

<p>I shot a firework, and set the lens to infinity manually. After seeing the photos I found them blurred - all of them. Examining the lens I found that if I set it in MF to infinity it is really slightly beyond, - if AF - all works like a charm. Why? <br />Who uses this pancake often? </p>

[charles_stobbs3]

Never used one but for a guess the auto focus system is too fragile to risk having it bump up against a hard stop so the manufacturer built in some over travel.

[eric merrill]

<p>Most lenses are designed to allow for thermal expansion and contraction. If not, you wouldn't be able to focus at infinity at temperatures in the extremes of the operating range. </p>

<p>This is entirely normal.</p>

[qalam]

An implementation, no doubt, of Buzz Lightyear's motto: TO INFINITY AND BEYOND!

[mukul_dube]

<p>I have the ZD 25/2.8 and have had no focus trouble. I do not understand how the lens can manually be set to infinity without a target to focus on.</p>

[john_robison3]

<p>If you used the focusing screen to manually focus the 25mm it could be hard to determine if you are really at infinity. For best manual focus on my E-410 I often resort to live view, with 10X magnified engaged to set manual focus. Naturally this would apply to a static subject where you have the time to do so. The screens in most of the auto focus DSLR's are optimized for brightness and not manual focus. I also find that, with my eyes, nearsighted with a slight astigmatism, that the adjustable diopter feature cannot be adjusted close enough to correct my view of the screen but even when I use my glasses it is still hard to accurately and consistently hit correct focus. You didn't mention what camera body you are using or if you have been able to successfully use manual focus on other lenses used with your camera.</p>

[ruslan]

<p><strong>John</strong>, I use E-420. I am not a novice. I also use LV but shooting firework there was absolute darkness near me so I could not choose a far distant object to focus presicely on. <br /><strong>Mukul,</strong> the lens can be set manually to infinity like this: set camera to MF and after you do several very long turns of focus ring to infinity (360 degrees or more) - the lens <em>must be</em> at infinity. </p>

[wharridge]

<p>"set camera to MF and after you do several very long turns of focus ring to infinity (360 degrees or more) - the lens <em>must be</em> at infinity" - obviously not and NOT what I'd expect from a lens where the focus ring is not mechanically operating the focus.</p>

<p>...Wayne</p>

 

[mukul_dube]

<p>Ruslan, I agree with Wayne. There is no physical stop at the infinity end, and it should not be assumed that there is anything else that halts further movement.</p>

[wayne_murphy8]

<p>It is unusual for a manual focus wide angle or standard lens to focus "beyond infinity", but with autofocus lenses, the auto focus system does not care. Unfortunately, if you focus manually, you need to judge the focus yourself and cannot rely on the focus stop to be at actual infinity. Plenty of zoom and telephoto lenses allow the focus ring to rotate beyond infinity, generally to compensate for thermal expansion of the lens system. This is not a sign of second rate design or quality - some Nikon, Leica and Hasselblad lenses do it.<br>

Similarly, in the old days, manual focus zoom lenses (generally) kept a constant focus during zooming. This was very difficult(and expensive) for lens designers to achieve so when auto focus became standard, this correction went out the door and now, focus shift during zooming is very common. <br>

So with modern auto focus lenses, if you focus manually, you need to focus by eye and at the actual focal length you are shooting at. Unfortunately, the old rule of focussing at the longest focal length and then zooming out, no longer applies. The focus will shift when you zoom.<br>

I would guess that most auto focus systems can focus a standard or wide angle lens more accurately than by eye but if you have no reference point or contrast difference for autofocus, then focussing by visual judgement is the go. Alternatively, focus just inside infinity and allow the depth of field to carry the focus to infinity.</p>

 

[john_robison3]

<p>Olympus uses a "fly by wire" manual focusing ring. It is not physically connected to the focusing at all but sends electrical signals to the focusing motor to move the lens. As far as I know the ring can be rotated indefinitely with no stop at all. On the E-410 I have used my 24mm f2.8 Zuiko OM lens with some success but even with that set up the cheap adapter I bought on E-bay had to be shimmed so that the lens would come to infinity at the marked indicator on the lens.The adapter was too short front to back and allowed my legacy lenses to focus beyond infinity.</p>

<p>Just last month I shot some fireworks at out local annual fair. I used the 14~42 kit lens set to manual focus and the best framing was at about 20mm on the zoom ring. I used a tripod and set up in advance while there was still some daylight, this allowed me to set MF to a distant object using live view, magnified. I manually set shutter speed to 10 sec and aperture to f11 and ISO to 200. I set the shutter to 2 sec delay to suppress vibration when releasing the shutter, I don't have a remote release. I'd say that out of 40+ exposures I came away with 2 or 3 I thought were acceptable for color of the burst and appearance of the streamers. I've photographed fireworks perhaps four times in my life and have been mostly underwhelmed by the results. I think that, like a lot of photographic pursuits you have to do it a lot to get good results.</p>

[ruslan]

<p>Thank all of you. </p>