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Buying a Canon 8-64 S16, but advice on CA needed please. Samples

Canon lens CA 8-64mm

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#1 Simon Lucas

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Posted 09 June 2013 - 05:48 PM

Hi

 

my friend is thinking of buying a Canon 8-64  S16 lens for his Ikonoskop at a reasonable price. 

 

He did some test shots at the seller's premise. We saw chromatic aberration. What do you think of the CA in these, please?

 

Is this to be expected from this lens in general? Or is it this particular lens, perhaps?

 

Any input or advice welcome.

 

Thank-you

 

canon8%3F64t2_400000007.jpg

 

 

canon8%3F64t_200002096.jpg

 

canon8%3F64t_200002192.jpg

 

 


canon8%3F64t_200002968.jpg

 

 

 

 


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#2 Dom Jaeger

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Posted 10 June 2013 - 04:10 AM

Looks excessive to me, and noticeably worse on one side, which indicates a decentration issue (lens elements not perfectly aligned). I'm pretty sure you could find a better one.

 

It would help to know the focal lengths and T stops. Are these all wide open?

 

I just had an Ikonoskop A-Cam in the workshop for sensor cleaning, pity it's been sent back I could've checked one of our 8-64s on it for comparison. Some digital camera sensors seem to bring out colour fringing more than you see just projecting a lens, probably also depends on its degree of telecentricity, which wasn't an issue when used with the film cameras the lens was originally designed for. 


Edited by Dom Jaeger, 10 June 2013 - 04:12 AM.

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#3 Simon Lucas

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Posted 10 June 2013 - 08:02 AM

Hi Dom,

 

thanks the feedback. They were all shot at 64mm. They were shot at around 2 stops closed. He only had 15 minutes to do the test so they are a limited test. he will do some more tests tomorrow when they have more time. I suggested he shoot at full wide and full zoom.

 

I understand your comment about digital sensors showing up more problems than 16mm would have. 

 

This Canon lens is around £2000. My friend is an artist and cannot really afford a brand new lens like a Zeiss at the moment.  But I wonder - do you have any other suggestions?

 

Cheers

 

Simon


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#4 Dom Jaeger

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Posted 10 June 2013 - 11:01 PM

At the long end of a zoom the centering alignment of the front element to the zooming elements and rear group is crucial, or you get an edge flare/softness off to one side. Pretty common for old zooms to end up with this kind of aberration.

 

At the long end the image circle is also at its largest, so the light exiting the rear of the lens is coning out and hitting the sensor at an angle at the edges (non-telecentric). Different sensors handle it differently, but it usually causes a bit of colour spread.

 

Out of curiosity I put an 8-64 on an Alexa and at 64mm there was noticeable colour fringing towards the edges of what would be a S16 frame. It shows up more if the centering/edge flare issue is also present. The fringing disappeared pretty quickly as I zoomed out. On projection the lens didn't show much CA at all.

 

There are plenty of good S16 zoom recommendations if you search the archives here, but the Canons (this one and 7-63) are often rated near the top of the pile. 


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#5 Simon Lucas

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Posted 12 June 2013 - 04:11 AM

Dom, thank-you for the explanation of what is happening, and confirming that this is happening with another 8-64.

 

He looked at other Canons (6.6-66, 10-180) yesterday and they all exhibit this behaviour to some extent. They worked best in the middle of the range.

 

I think for the price and as an interim lens that is versatile it is still a good buy. He has three projects this year and it will stand us in good stead. Maybe he can also afford a single s/h Zeiss s16 standard prime when one comes up.

 

Thank-you for the advice, much appreciated.


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