Infamous fast zoom for m4/3 very slight vignette

pat donnelly

http://vimeo.com/24087337

Not bad results? Rolling Eyes

Other members seek to ban all references to zoom lenses for 16mm adapted to m4/3 cameras. On the grounds that they simply are not ever to be used. Confused

rbelyell · Expire: 2014-01-31

no, thats not true. however you have posted numerous threads referring members to specific c mount zooms, without caveat or without personal knowledge about performance, that other members like myself know from experience will not work on mirrorless cams. your last thread referring to a non-vignetting zoom starting at 16mm, again not through your own personal experience, was flatly incorrect.

it is not a matter of 'banning', it is a matter of your being resposible with information you put out there that others may rely on to their detriment. in your present thread you refer to a lens with a 22.5mm minimal focal length. as a c mount zoom lens gets closer to 25mm as a minimum FL, it is much more likely to not seriously vignette. any 20mm or less at the minimum FL is almost certain to perform very poorly or not at all on mirrorless cams.

this has been explained numerous times by many members, and ignored just as many. because it has been ignored a plea was made that when referring to these specific lenses, in order to protect our members, claims as to their performance should only be made on personal knowledge. it is a simple concept that i hope can now be grasped.

pat donnelly · Posted: Thu Jun 23, 2011 2:14 pm Post subject:

I have personal knowledge!

rbelyell · Expire: 2014-01-31

with this particular lens, which as ive said may work, or with the dozen or so others you've posted that i AND OTHERS have said will most probably not?!

do you understand the difference between a zoom that starts near 25mm and those that start under 20mm? do you understand the former are likely to work properly on mirrorless cams and the latter are overwhelmingly NOT likely to work? can you make that distinction or does it somehow prove elusive?

people from all over the world consult this forum for advice and facts about lenses and cameras. please do not continue to mislead them into thinking c mount zooms with a wide side of under 20mm will work correctly on mirrorless cams unless uou personally know it will. i guarantee you that if you can find one that does, many members will want one, including me.

pat donnelly · Posted: Tue Jun 28, 2011 11:58 am Post subject:

You appear to lack personal knowledge?

Which of these zooms have you used?

LucisPictor · Expire: 2013-12-03

Please, guys, be nice. Wink

ekoe · Joined: 28 Jul 2011 Posts: 47

I've been quietly working on a solution to the c-mount zoom on m4/3 question for several months. I'm not going to take sides, other than to say there is a lot of bad info out there regarding c-mount zooms for m4/3 and as a result there are a lot of users purchasing non-viable lenses on bad advice or good intentions yet little expertise.

The 22.5-90/1.5 is in fact a very good c-mount zoom lens for m4/3, providing good coverage with a bit of vignette in 16:9. The vignetting is somewhat acceptable if you're not someone who is particularly adverse to the least bit of vignette. And, the vignette is easily removed in post by scaling your footage. Using motion keyframes, you can easily vary the scaling as the vignetting changes through the zoom. This can be done in a few minutes and requires no render.

To complicate matters, there are at least two models of Cosmicar 22.5-90. I have both.

I also have an 18-90mm/1.9 c-mount zoom that has fuller coverage of the m4/3 sensor than the 22.5-90/1.5. It's also considerably smaller than most of the viable c-mount zooms for m4/3. So the rules of thumb that a larger zoom lens, or a longer focal length zoom lens will ipso facto provide better sensor coverage are not necessarily wrong, just unreliable.

Few discuss the parfocal adjustment that will need to be performed on the adapted zoom lens, otherwise the lens will not hold sharp focus as you zoom. Without parfocal adjustment the lens will not hold sharp focus through the zoom, you will not be able to pull critical focus, and any zooms in shot will soften the focus. The further out of adjustment the lens is, the softer the focus will drift through the zoom. The tolerances for parfocal adjustment can be .001mm.