PZ 16-50 - what's the real focal length of the wide end?

Started Oct 28, 2012 | Discussions thread
Keit ll
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Re: PZ 16-50 - what's the real focal length of the wide end?
In reply to Laurie Wilson, Oct 28, 2012

This is a very interesting question & it always surprises me that it doesn`t get asked more often. As someone who urged Sony to exploit the power of software correction & to combine lens design & software correction into an integrated approach I feel that I have a continuing responsibility to defend this approach.

It is relevant to query how this approach effectively alters & ` increases ` the effective focal length of any given lens. Perhaps a similar covention to describing FL in "35" Equivalence should b adopted to draw attention to the alteration in effective FL encountered by the use of barrel distortion correction. Many users do not realise that diiffering opinions over the edge performance of the kit lenes may arise because some reviewers use the in-camera correction facilities whereas others do not.

Jpeg users employing correction have a perceived advantage over RAW users who may not have access to the lateat software which has distortion correction. Some blured edges can be cropped away which entails the effective increase in FL but some residual barrel distortion may visibly remain .

It is open to arguement as to how important this change in effective FL actually is but perhaps it would be useful if technically inclined reviewers were anle to express the difference in numerical terms. So that the new 10-18mm would be described as , say , 12-20mm EFFECTIVE after software correction.( these figures are guessed & not based on actual measurements )

This software approach will be dismissed as invalid by strict purists who will see it as cheating & an attempt by manufacturers to  disguise inferior optics however I see it as a valid means of optimising relatively  inexpensive lenses. It would not be valid however if it was used to " improve "inferior lenses & use this as an excuse to charge much hgiher prices.

A good in-depth review  would look at the performance of the 10-18m in a corrected & uncorrected state & to comment on value for money issues in the light of any findings. I have chosen this lens for comment as it is not  particularly inexpensive . Ideally the degree of necessary correction should be less in high quality lenses than in cheaper counterparts. Perfect lenses would require no correction but realistically they would also be very expensive.

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Keith C

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