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 Post subject: Cropped vs Aperture
PostPosted: Tue Apr 24, 2012 11:59 am 
Hi, I've had various SLR s since the mid 70's,(the first being a { hide your eyes} Zenit E) and after that had a few different Canon SLRs.
Went away a little from photography for some time apart from two or three Canon Digi Ixus'. My last one has just kicked off and will most likely be replaced with the S100.
However, the point of this is a dumb question I have about lenses. No, not which is the best lens for this or that, I still have a grasp on reality. But a little confusion about the cropped sensor bit. I have an exc. cond 400D, ('cos I've not used it much and am beginning to dabble again), and have used only the kit lens it came with EF-S 18-55 3.5-5.6II, and the kit lens from the 50E I had EF 28-80 3.5-5.6 II ultrasonic.(still have the 50E, but tucked away somewhere). I see that with my 400D a 50mm lens becomes an approx 80mm in slr terms, an 85 approx. 135mm.
The question being, does the aperture "go with it". e.g. if I bought an EF50mmf 1.4--> 80mm 1.4 ? an EF85 f1.8--> ~135mm f1.8 ? Meaning will the 1.4 50mm become a fast 1.4 80mm on a cropped sensor camera, likewise the 85?
I understand the difference when using an extender, and f stop etc, but does the same happen with these camera/lens combos? I'd like a faster 50 or 85 or so lens, my early Canons came with 50mm f 1.8s on 'em, changed the A1 to a 50 mm f1.4mm FD lens .. a world of difference. A short affair with an F1 and accompanying lenses...the owner came back.. :cry:
Yeah, I'm getting older.. 8)
Cheers.
Oh, I still have a 380EX Canon flash from the 50E, I assume it'll be all good with the 400D- still to put batteries in it, don't use the "big" flash anymore...


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 Post subject: Re: Cropped vs Aperture
PostPosted: Tue Apr 24, 2012 1:58 pm 
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Joined: Mon Aug 17, 2009 9:46 pm
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Location: Norway
First of all, to be precise: a 50mm lens does not become 80mm on crop. A 50mm lens is always 50mm. But in terms of coverage it behaves on a crop camera like an 80mm lens would on a full frame or film camera.
Since the f-number is related to two physical properties (focal length and pupil diameter), this is the same for crop and FF. But the DoF is not the same. At a given distance a full framer needs higher focal length to fill the frame. Higher focal length gives shallower DoF. The difference is about 1 1/3 stops. That means that in terms of DoF an 85mm f/1.8 on FF behaves like a 53mm f/1.1 on crop, and a 50mm f/1.8 on crop behaves like an 80mm f/2.8 on FF. When you move from FF/film to crop you get larger DoF, which is both a positive and a negative. However, in terms of light catching abilities they are equal

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 Post subject: Re: Cropped vs Aperture
PostPosted: Tue Apr 24, 2012 1:58 pm 
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Joined: Mon Aug 17, 2009 9:46 pm
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Location: Norway
Oh, and welcome onboard! xD

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 Post subject: Re: Cropped vs Aperture
PostPosted: Tue Apr 24, 2012 2:37 pm 
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Joined: Mon Dec 11, 2006 7:01 am
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Location: bit east of Melbourne
that is a very good explanation Janern :)

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Canon Powershot S95, Canon 6D,7D, Canon 40 2.8 STM, Tamron 24-70 2.8 VC, Canon 17-40 L, Canon 15-85, Canon 85 1.8, Sigma 30 1.4, 50mm 1.8, Canon 100 2.8L Macro, Canon 70-300L +Kenko 1.4 Pro 300DGX, Canon 430EX II and RS 4 Classic


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 Post subject: Re: Cropped vs Aperture
PostPosted: Tue Apr 24, 2012 7:08 pm 
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Joined: Tue Oct 26, 2010 8:22 pm
Posts: 498
Location: 1 AU from the nearest star
Or in other words...
Take a picture using whatever lens you want on a 35mm film camera or Full Frame digital camera.
Print out exactly what you take with no editing.
Then take the picture and just cut off part of the top/bottom/sides.
That is what you get with a crop sensor camera.

What is in focus, in proportion to what is taken on a crop sensor is greater than a full frame, but that is only because the crop already discarded the edges of the shot.

While Janern was correct in what he described, I do not think I fully understood this concept until I realized the above.

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Canon 5DIII, Rebel XTi/400D
Canon EF 16-35mm f/2.8L II, 24-105mm f/4L, 50mm f/1.4, 70-300mm f/4-5.6 DO, 85mm f/1.8
Sigma 150mm F2.8 EX Macro

Sigma 10-20mm f/4-5.6 EX, Canon EF-S 18-55mm f/3.5-5.6 II
Canon 430EX II
Opteka 13mm, 21mm, and 31mm extension tubes
Vivitar 50mm f/1.8 for OM System


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