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I am shooting with a Canon T1i, and I am fairly proficient with doing portraits, and I am fairly knowledgeable with how to use my camera.

I am tasked with shooting about a dozen sorority girls for graduation, and I am worried because my portrait strategies (with one person) might not work because I am not sure which of my lenses is better. Assume the ladies will all by pretty closely together in a square.

I have two lenses:

  1. Sigma DC 18-50mm f2.8 DC Ex macro lens
  2. Canon 28-105mm ultrasonic

I understand that the first one is wide angle, and I am guessing this is better, but I have read a lot about why it might not be the case. I use the second one for portraits usually because I get a decent bokeh effect if I am zoomed out enough.

EDIT: Yes, in retrospect, I realize that my question was very poorly worded. What I am asking, basically, is if we assume that I have direct control over: the background, subject position, my distance from the subject and all of that, IDEALLY, which lens would give me the better result? I hope that is more clear.

  • Based on the edit, it sounds like you just need to understand the differences between your two lenses. That's a pretty easy question. One is variable aperture one is constant, one covers longer focal lengths. Those are the basics. – dpollitt Dec 10 '15 at 18:26
  • Actually, I can adjust the aperture on both lenses. The sigma's lowest value is 2.8 – Roman Maksimov Dec 10 '15 at 19:10
  • Roman, the maximum aperture on you Canon lens varies over the zoom/focal range. The sigmas does not. That is a significant difference. – dpollitt Dec 10 '15 at 19:11
  • Ahh I see what you are saying, yes that is true. – Roman Maksimov Dec 10 '15 at 19:26
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There is a lot going on in your question that raises red flags. I would suggest reading up on the topics you mentioned on this site before the shoot and come back with any follow up questions. In particular:

I would like to address your comment:

I understand that the first one is wide angle, and I am guessing this is better...

The Sigma 18-50mm f/2.8 EX DC Lens is a zoom lens that has the ability to shoot at focal lengths in the range from wide angle to normal. It is not simply a wide angle lens, because it is not a prime lens that only has one focal length or falls under one range within a bucket such as wide angle.

For portraits, unless you have no other choice because the room is very small and you can't backup your body; 18mm is far too wide to shoot without significant distortion(at reasonable distances for portraits) and likely unwelcome environmental perspectives. I would back yourself up from the subjects and shoot at 50mm and you should get good results. Much more information in the above linked to answers on why 50mm on your camera makes sense.

As far as the Sigma lens vs the Canon, without much research on my end I believe the Sigma is of higher quality so I would use that if the 50mm focal length is what you end up using. If you shoot at 75mm, well then you have no choice :)

  • Focal length doesn't cause perspective distortion, subject distance does. You can get perfectly usable group portraits with an 18mm lens if the group is so large that you wind up shooting the group from the same distance with the 18mm lens as the distance you would shoot an individual person with an 85mm lens. – Michael C Dec 9 '15 at 23:07
  • You just need to keep the people out of the corners. With twelve individuals wearing the typical clothing sorority girls wear under the commencement gowns, no one is likely to be sitting on the ground. Two lines of six people staggered so the taller ones in the back can be seen in the gaps between the shorter ones in the front are going to be much wider than tall. You just need a background that won't show the distortion in the corners (e.g. a hedge or trees rather than a brick wall). – Michael C Dec 9 '15 at 23:12
  • @MichaelClark good point I clarified that. – dpollitt Dec 10 '15 at 0:30
  • Yes, in retrospect, I realize that my question was very poorly worded. What I am asking, basically, is if we assume that I have direct control over: the background, subject position, my distance from the subject and all of that, IDEALLY, which lens would give me the better result? I hope that is more clear. – Roman Maksimov Dec 10 '15 at 16:48
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I would take the 18-50mm and start with 18mm. If you realize you have enough space at the sides, you can still zoom in.

These are the reasons:

  • Often times the distance needed between group and camera is underestimated. 28mm may be okay, but if not, you have to change the lens or reposition yourself (with tripod?) while the group is waiting.
  • 18mm may show distorted proportions for close ups/portraits, but I don't think a group shot is affected too much. You can still zoom in to 50mm to avoid any distortions.

You also mentioned the bokeh. You know that a nice bokeh has the risk of having important parts out of focus. That's especially dangerous for a group shot where you may need a depth of field of a meter or more, if people are standing behind each other.

Perhaps you try a safe aperture first and then try something creative with bokeh. If that didn't work, nobody will know, because you fulfilled your duty with the safe aperture.

  • Yeah, that was exactly my point about the bokeh, I would have no idea how to make that happen in a group shot without someone coming out blurry, so that's what I was wondering. I have read that photographers will still use the lowest f possible with group shots, and Ijust cannot see that working. – Roman Maksimov Dec 10 '15 at 16:44
  • Using a Depth-of-Field calculator like dofmaster.com/dofjs.html you'll see that not all combinations have a critical depth of field, even with f/2.8. But there is a simple trick to have a blurry background: Just have a long distance between group and background. – Fred42vid Dec 10 '15 at 19:06

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