Tamron 18-250, accuracy of the distance dial

Started 3 months ago | Discussions thread
OP JahnG Senior Member • Posts: 1,979
Re: Tamron 18-250, accuracy of the distance dial

Alberto Tanikawa wrote:

Most, if not all photographic lenses do not have calibrated focus distance scales. Real cinema lenses do, and you pay a lot for it. Consumer photographic lenses have to deal with temperature differentials which affect the length of the components inside. Infinity may be at point A on a cold day, and be at B on a hot day. I suggest you use liveview, magnifying the focus area for more accurate results when manually focusing any lens.

Hello Alberto, and thank you for your comments.

(I understand your point of the temperature differences. However on this specific lens, that I used on a normal day (of about 20 degrees Celsius) the real infinitive point on the scale was just above the 7m mark, at about 60% of the distance between the low end mark and the infinite mark of the scale.I can't imagine that the scale of this lens would be usable in any existing terrestrial temperature, as normal material is not expanding / contracting very much inside a temperature range of just a few degrees.)

You idea about liveview is good, and I think that would be the way to use for MF.

Another way might be that I myself make some own marks on the scale of the lens. The whole scale is about 30 mm long, and own marks, with an accuracy of ie +/- 1mm, should give a reasonable accuracy, at least used inside a temperature range of a few degrees.



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