Shoot close with zoom or out with prime lens

daymobrew

I was recently helping shoot group class photos for my child's primary school.
I used my Canon 550D with a 50mm f1.8 lens (the cheap Canon prime) with a tripod.
I also have a Sigma 17-50mm 2.8 zoom.

Which should I have used?
I started off with auto focus but I saw that it sometimes it didn't focus well so I switched to manual focus and focussed on a child towards the outside, set aperture to 6.5 (to increase DOF) and ISO to 200.
It was a bright day. We were in the shade on the northern side of the building so that the children wouldn't be squinting.

My questions:
- Would it have made any difference (to the amount of light entering the camera) if I moved closer to the group and used the Sigma zoom at a low focal length?
- Would DOF be a bigger issue when closer?

DaireQuinlan

daymobrew wrote: »

My questions:
- Would it have made any difference (to the amount of light entering the camera) if I moved closer to the group and used the Sigma zoom at a low focal length?

No.

- Would DOF be a bigger issue when closer?

Yes.

Using a shorter focal length would have resulted in all sorts of weird distortions and perspective effects. These sort of situations you're probably best off using as long a focal length as possible and stopping down as much as you can. Ultimately your aim is to get all of the kids in focus with as little distortion as possible, that's pretty much it. Class photos should be pretty workmanlike affairs.

ED E

I'd argue that you're too tele. 35mm on FF is considered "natural" and your 50 is an 80 effective. Shooting around 25mm on the Sigma would give you less flattening (which I suppose is something you might actually want, maybe).

Heebie

daymobrew wrote:

My questions: - Would it have made any difference (to the amount of light entering the camera) if I moved closer to the group and used the Sigma zoom at a low focal length? - Would DOF be a bigger issue when closer?

You would have had more light, but you would also have had more distortion of their faces due to the closer proximity, and you might have had to stop down the aperture even tighter to get the depth of field to encompass their entire face and hair etc..
You would have been more likely to have the color of your clothes affect the color in the photos as well.

The prime was highly likely the right choice.

DaireQuinlan

Heebie wrote: »

You would have had more light

This isn't the case. Exposure would be exactly the same irrespective of the distance to the subject, assuming he didn't have a camera mounted flash, but that's a different matter altogether.

daymobrew

ED E wrote: »

I'd argue that you're too tele. 35mm on FF is considered "natural" and your 50 is an 80 effective. Shooting around 25mm on the Sigma would give you less flattening (which I suppose is something you might actually want, maybe).

The only downside with the 50mm was that I was a good bit back from the people so it was harder to direct them (my wife was closer and off to the side to issue instructions).

I was happy with the results, which always look better printed than on my laptop screen.

Thanks everyone for the reassurances.

Adrian.Sadlier

To summarise the above:

The 550D is a crop sensor with a crop factor of 1.6. This means your 50mm acts as a 80mm on a full frame camera (as mentioned above).

The distance from the subject does not affect the amount of light.

I personally would use 25mm to 30 mm on the Sigma (depending on the size of the group).

The closer you are to a subject such as a class the larger the DOF you will need.

Assuming you focus on a child in the centre of the group, the children at the edges of the group will be much further away. The smaller the focal length, the greater the distance (relatively).

The solution may be to get the children lined up in a curve, all equidistant from the camera. This will minimise the DOF required.

But if it is outdoors on a day like today, just use around f11, ISO 200 and shoot away. If you use a tripod and a remote trigger it would be better.

DaireQuinlan

Adrian.Sadlier wrote: »

The solution may be to get the children lined up in a curve, all equidistant from the camera. This will minimise the DOF required.

This probably won't do what you think it will. Most lenses nowadays are corrected so that the field curvature is as small as possible i.e. they're designed to have a flat focal plane. So for maximum DOF you'd have to line they kids up. I'd be more concerned about distortions toward the edges of a WA lens but of course that's less of an issue with a crop, the WA lens behaves more like a normal focal length.