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Why is Canon "glass" considered slow?


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#1 George Ebersole

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Posted 07 September 2016 - 08:50 PM

So they guys at Mike's Camera, all ex-professionals, were telling me that most top brands are pretty much just as good as the next, and that "Canon glass" is not "slow".

 

So, I'm wondering why the opposite opinion seems to be held on these forums.  What experience has made the Cinematography.Com crowd say that Canon lenses to grab as much light?

 

Thanks much for any reply.


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#2 Tyler Purcell

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Posted 07 September 2016 - 10:19 PM

Depends on your definition of slow. A lot of people consider two stops to be the difference between fast and slow. An F1.5 prime vs F3.5 zoom for instance.

Most of the Canon zoom lenses are between F3 and F4, so they're not exactly "fast". Also, most of the longer zooms, get slower as you zoom. So full wide they maybe F3, but zoomed in, they're more like F4.5.

Also, Canon DSLR zooms are not parfocal. If you zoom all the way in on a subject, get focus and zoom out, they won't retain that focus. This is one many character traits that make DSLR glass more tricky to use with video.
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#3 Stuart Brereton

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Posted 07 September 2016 - 10:49 PM

Kit lens EF zooms from any manufacturer tend to be in the f3.5 - 5.6 range. Canon L series are mostly f2.8, as are the more expensive offerings from Tokina, Tamron and Sigma. Primes are faster, in the f1.4 - f2 range for EF primes and faster for L series.

 

Remember, an F stop is a mathematical value; the actual amount of light transmitted (t-stop) can vary according to the glass, coatings, and construction of the lens, so it's likely that more expensive lenses will perform better in this regard.


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#4 George Ebersole

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Posted 08 September 2016 - 03:14 AM

So there's no backfocus on DSLRs.  Great.  

 

I've got a 120 and 15-30 from one of my old kits .... but what you see is what you get. 

 

Thanks.


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#5 Robin R Probyn

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Posted 08 September 2016 - 05:54 AM

There,s no back focus on most Cine lenses either.. have to be shimmed.. I was quite happy to see that my Canon CN7 have one like the 2/3 ENG lenses.. although basically I don't touch it.. glad to know its there if needed..


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#6 George Ebersole

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Posted 08 September 2016 - 06:37 AM

You're kidding ... I feel I should have known that ... but it's like if Fujinon makes their stuff with back focus for ENG, why not prosumer gear?  I never thought to wonder about Panaflex or Arri.  

 

Oh well.  I'll live with it.  I guess part of the fun of camera work if finding a work around ... sometimes.


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#7 Phil Rhodes

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Posted 08 September 2016 - 06:45 AM

Back focus tweaks mean the distance marks can't be precise, which makes cinema people moan. Personally, I'm with Robin. Shimming something that costs as much as a car should not be a thing.
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#8 Robin R Probyn

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Posted 08 September 2016 - 08:49 AM

I think its only the CN7 and the Fujinon Cabrio,s .. that are both ENG style servo zooms that has BF adjustments.. in the "higher" end Cine zoom level.. and yes the CN7 focus marks are not up to focus puller level really or the Cab,s.. although their literature will tell you otherwise.... but really they are not for that market..and more owner users than those $80K full on Cine zooms that are from rental houses..


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#9 George Ebersole

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Posted 09 September 2016 - 03:45 AM

Thanks for the replies.  Always a learning experience here.


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