[DSLRnovice]

My FA35 is not focussing on infinity as well as it did a year ago. I am not sure why. Today I went downtown and tested it on some buildings at a distance with fine details. In live view with high magnification I noticed that if I pushed the front element lightly towards the camera things came in sharper. Is there a way this can be tightened without spending more than the lens is worth?

Dan

[stevebrot]

Is there a way this can be tightened without spending more than the lens is worth?

Dial in a mild fine adjustment for front focus (-1 from current position).


Steve

[Fenwoodian]

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Sounds like your front element needs to be tightened. Easy if one has the right tools.

[DSLRnovice]

Dial in a mild fine adjustment for front focus (-1 from current position).


Steve

That is worth a try, but I am talking about the physical distance of the front element. Even in manual focusing it cannot achieve sharp focus on infinity without holding the front focusing element tight. Some modern lenses do not stop at infinity like this one.

Dan

[stevebrot]

Even in manual focusing it cannot achieve sharp focus on infinity without holding the front focusing element tight. Some modern lenses do not stop at infinity like this one.

Are you saying that the front element is loose in the optical group (wiggles within its setting) or that the front of the lens (filter threads included) is wobbly. A certain amount of play (very, very slight) is normal for the FA 35/2 and ability to attain focus on a distant object is typically limited by the infinity (hard) stop on the focus mechanism set at the factory. In contrast, a front element loose from the rest of the lens is not normal, would result in generally inconsistent performance, and might require professional attention.

Concerns about infinity focus performance are fairly common on this site and the reasons range from a damaged or poorly aligned lens to unavoidable side effects from evaluating distant objects with a high resolution sensor. Things get messy fast* and answers are seldom easy. Your live view experience under manual focus is a good example. If you feel that your lens has something broken inside or has fallen out of spec due to wear, your best option may be to consult a competent service facility where infinity focus can be evaluated on an optical bench and adjustments made, if needed.


Steve


* For example, my FA 35/2 comes up against its factory stop at about 70 meters distance and my FA 77/1.8 has a hard limit of about 150 meters (both evaluated in magnified live view on my K-3)? Both provide acceptable results at those distances and f/5.6 (or even f/4) since DOF covers to infinity and beyond, but then the discussion get messier still.

[DSLRnovice]

Are you saying that the front element is loose in the optical group (wiggles within its setting) or that the front of the lens (filter threads included) is wobbly. A certain amount of play (very, very slight) is normal for the FA 35/2 and ability to attain focus on a distant object is typically limited by the infinity (hard) stop on the focus mechanism set at the factory. In contrast, a front element loose from the rest of the lens is not normal, would result in generally inconsistent performance, and might require professional attention.

Concerns about infinity focus performance are fairly common on this site and the reasons range from a damaged or poorly aligned lens to unavoidable side effects from evaluating distant objects with a high resolution sensor. Things get messy fast* and answers are seldom easy. Your live view experience under manual focus is a good example. If you feel that your lens has something broken inside or has fallen out of spec due to wear, your best option may be to consult a competent service facility where infinity focus can be evaluated on an optical bench and adjustments made, if needed.


Steve


* For example, my FA 35/2 comes up against its factory stop at about 70 meters distance and my FA 77/1.8 has a hard limit of about 150 meters (both evaluated in magnified live view on my K-3)? Both provide acceptable results at those distances and f/5.6 (or even f/4) since DOF covers to infinity and beyond, but then the discussion get messier still.

Thanks for the answer. To clarify, the front section where the filters and lens hood attach has some play both wobble and in and out. When I first tested it on the K-1 infinity focus was excellent, but I have to admit I only tested from f5.6 to f16.

When I purchased the DFA 28-105 I wanted to see it compared at 35mm with the FA35. It was then that I found that it had trouble locking in at infinity, and that distant details were soft. Yesterday i went back and did the LV test. Actually I think the pressure from installing and removing the click on lens hood is to blame for the wobble.

Seeing that the 28-105 is so sharp I will probably save the FA35 for low light scenes which normally do not require infinity focus. I was hoping that there was a DIY method of tightening the front assembly, however.

---------- Post added 05-23-2018 at 07:18 AM ----------

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Sounds like your front element needs to be tightened. Easy if one has the right tools.

The element is tight within the front assembly that moves in and out when focusing. Even if that was so, I cannot find a way to tighten anything there. Unlike my older lenses, there is not notch in front where a spanner could be inserted to turn the ring. What tools would I need to tighten this one?

[stevebrot]

When I first tested it on the K-1 infinity focus was excellent, but I have to admit I only tested from f5.6 to f16.

At f/5.6 the hyperfocal for 35mm focal length occurs at 7.2 meters, so DOF covers nicely at moderate apertures, even when pixel peeking. Infinity calibration is traditionally done to a distance of about 2000x the focal length for the 24x36mm frame. That sounds short, but parallel rays entering the lens from that distance will render as a point at the sensor or film (cannot be told from an actual point).

Most modern zooms and traditional long lenses will focus slightly past infinity and adapted primes may also do so on mirrorless cameras when paired with some adapters. In both cases, it appears to be beneficial to detail capture at distance with modern sensors. Adjusting your FA 35/2 to allow greater inward travel would require a partial disassembly at best. I am doubtful that the focus mechanism can be tightened up (less play/lash), though I have been wrong before.


Steve

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Last edited by stevebrot; 05-23-2018 at 09:33 AM. Reason: corrected arithmetic error

[DSLRnovice]

At f/5.6 the hyperfocal for 35mm focal length occurs at 7.2 meters, so DOF covers nicely at moderate apertures, even when pixel peeking. Infinity calibration is traditionally done to a distance of about 2000x the focal length for the 24x36mm frame. That sounds short, but parallel rays entering the lens from that distance will render as a point at the sensor or film (cannot be told from an actual point).

Most modern zooms and traditional long lenses will focus slightly past infinity and adapted primes may also do so on mirrorless cameras when paired with some adapters. In both cases, it appears to be beneficial to detail capture at distance with modern sensors. Adjusting your FA 35/2 to allow greater inward travel would require a partial disassembly at best. I am doubtful that the focus mechanism can be tightened up (less play/lash), though I have been wrong before.


Steve

Since a moderate wide angle like this one will most likely be used in scenes either up close or with details in the foreground, I agree that the problem is not that great. Smaller apertures will be required for landscapes, and low light situations which require larger apertures will not usually be at a distance.

But It was important for me to know what was going on, since at first the DFA 28-105 looked sharper in my first comparisons.

[DSLRnovice]

Since a moderate wide angle like this one will most likely be used in scenes either up close or with details in the foreground, I agree that the problem is not that great. Smaller apertures will be required for landscapes, and low light situations which require larger apertures will not usually be at a distance.

But It was important for me to know what was going on, since at first the DFA 28-105 looked sharper in my first comparisons.

This might sound crazy to some, but I cut a narrow strip of black electrical tape, extended the focusing barrel, and wrapped the tape around it. When focused on a distant object, now the barrel has less wobble. The focus seems to be more consistent at all distances.

[Just1MoreDave]

I got a chance to look at mine. The way the filter threads disappear makes it look like the trim ring around the front element unscrews. But mine didn't budge when I tried. Recent lenses have a glued on trim ring so it might pry off, but you'd need a thin plastic tool because the front element is so close.

There are a few threads on the DA Limited primes where the focus barrel is loose, then wobbly, with AF trouble. Then the barrel falls off unexpectedly. It's rare so I suspect only a handful of lenses had trouble. With that in mind, I'd be careful with your lens, though who knows if it's the same issue.