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October 23, 2019, 11:41:33 PM


Author Topic: Sigma 17-50mm F2.8 EX DC OS for Canon  (Read 6911 times)

Offline Scott S

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Re: Sigma 17-50mm F2.8 EX DC OS for Canon
« Reply #15 on: February 01, 2015, 07:25:10 PM »
Ok...I just checked your links. You were definitely referring to DoF. On that... I can't argue (although 2 stops?? proof?) as I agree there will always be a DoF degradation on a crop vs FF. But only DoF, not light exposure.
That is where we were not matching up our points I believe.
everything I've read says you lose a bit of everything on a cropped sensor.
that said, I would like to point out that the gist of my original post was I'd like a wide aperture zoom with a decent spread for portraits, and the 18-135 is going to be way to limited in aperture for the purpose. I can add light through ISO, or shutter speed etc, I can't get Bokeh back on that lens.
so disregard the amount of light comments if you like, but I still think you must lose something, the sensor is smaller, the issue is DOF and DOF only for me. well, not entirely true, having a stop or two before I have to grab a strobe does come in handy!  ;D

Offline Scott S

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Re: Sigma 17-50mm F2.8 EX DC OS for Canon
« Reply #16 on: February 01, 2015, 07:26:58 PM »
Using a light meter my exposure was as follows .......   400 iso, f4.0, 1/160 shutter speed.

Exposure looks the same to me
look at his gloves, the whites are a bit darker on the crop, and you have a scene with a limited depth built in, go outside and place Mickey in the yard with a tree or car a few feet behind him and see if the DOF is the same.

Offline Craig

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Re: Sigma 17-50mm F2.8 EX DC OS for Canon
« Reply #17 on: February 01, 2015, 07:33:29 PM »
Just wanted to prove that exposure is the same, crop or full frame. There might be a slight variance in each camera body but not because of sensor size.
6D, T2i, Canon 600EX, 430EXII, and some other stuff my wife doesn't know about.

Offline Ochotona

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Re: Sigma 17-50mm F2.8 EX DC OS for Canon
« Reply #18 on: February 02, 2015, 09:53:37 AM »
Interesting discussion.  Thanks all for the bit on DOF, I hadn't really ever considered the difference between formats.

Offline Scott S

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Re: Sigma 17-50mm F2.8 EX DC OS for Canon
« Reply #19 on: February 02, 2015, 06:42:33 PM »
Rather than edit (again) my last reply, let me amend it with a new post:
I re-read what you wrote about the aperture and realized it was not just about light but could also mean (for portraiture) Depth of Field, or bokeh.  If that is what you meant, then you are probably correct. I still couldn't find anything that said it was a 2 stop difference though but the main point was there IS a difference of DoF for any given length.  It won't be any DARKER, but the DoF would certainly be affected.
But, that then brings me back to the reason I suggested it (the 18-135) at all was your statement of "There just isn't the perfect walk around lens available for APS-C."  Perfect?  That's going to be highly subjective and dependent on each persons need. As a rule though: if you are wanting good portraits, you would use a good portrait lens and not a walk around "Jack of all trades, Master of none" type of lens.
Many portrait photographers prefer a prime (again- subjective as to length) over a zoom. This makes sense as you would probably get a better (sharper) image with a prime.
Walk around lens...almost exclusively...are some sort of zoom to accommodate any given scenario.
Here is a pretty informative article on General Purpose (which is a pretty good description of a walk around lens) lens and none of them were primes. Note that none of them were very long in length either but that goes back to the person's shooting style.
http://www.the-digital-picture.com/Canon-Lenses/Canon-General-Purpose-Lens.aspx
I had to laugh because my suggested walk around lens was not listed at all until the end as a budget alternative. <sigh> Shows how little I know about various lens!
I also noted that the first couple of lens they suggested as walk around lens were pretty damn nice and might actually do well for portraiture (at full zoom though, not at wide angle).
I gotta admit, that 24-70 f2.8 might be fun to try and walk around with.

I just re-read the thread and I think where we got separated is in how I phrased my sentence, I stated that there was no good portrait all around, by which I meant to say a good lens for portraits with enough range to handle most situations without having to change lenses and having a wide aperture to retain good bokeh characteristics. such a lens, for a portrait photographer would cover roughly 17-135 and be at least f2.8 if not wider. the 18-135 would be a good all around one lens option for someone not trying to specialize in any one genre of photography, but a lens that has as it's widest aperture f5.6 (f9 on a crop body) at portrait lengths would be terrible. if the 18-135 were a constant 2.8, I'd be in all day long, of course then it would be a $1500.00 lens.

Offline Scott S

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Re: Sigma 17-50mm F2.8 EX DC OS for Canon
« Reply #20 on: February 02, 2015, 06:47:25 PM »
Using a light meter my exposure was as follows .......   400 iso, f4.0, 1/160 shutter speed.

Exposure looks the same to me
Hey craig, I was wondering, the meta data has been stripped and the two photos combined, could you tell me what the focal length is on each image and if you cropped at all? if all of the parameters are the same the exposures should be the same, but then you'd have to crop one to get the subjects to match, if you shot at different focal lengths then I believe the metering would be altered to achieve the same exposure values. as stated before the crop photo has darker whites which indicates under exposure, they are not the same, and illustrates my point, to get the exact same image without manipulating in post, a crop sensor will underexpose at the same settings as a full frame.

Offline Craig

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Re: Sigma 17-50mm F2.8 EX DC OS for Canon
« Reply #21 on: February 03, 2015, 07:48:48 AM »
to get the exact same image without manipulating in post, a crop sensor will underexpose at the same settings as a full frame.


Here is a post on another forum. If you still think that sensor sizes make a difference in exposure, we have to agree to disagree.

http://photo.net/canon-eos-digital-camera-forum/00b8QQ
6D, T2i, Canon 600EX, 430EXII, and some other stuff my wife doesn't know about.

Offline Doodle

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Re: Sigma 17-50mm F2.8 EX DC OS for Canon
« Reply #22 on: February 07, 2015, 02:07:07 PM »
Well, here is an interesting blog done by BorrowLenses on this very topic.
Seems that the fstop on 3 different cameras came out the same..not underexposed or overexposed as previously thought.
They were, in fact, discussing sensor size and bokeh...which graphically showed how it affects shots and their backgrounds but NOT light issues because...there was none. Pictures explain it pretty well.
http://www.borrowlenses.com/blog/2014/05/the-bokeh-effect-how-sensor-size-affects-background-blur/
Take your camera with you dammit. You can't take your next "best photo" if your camera is sitting at home in the bag, now can you?