Looling for a good low light indoor lens.

[Justin]

I am looking for a good indoor low light lens for my Canon 60D.  I have been using a 50mm f/1.8 lens but it seems like I am always too close and I can't always back up because I run into furniture or I am up against a wall.  I usually take pictures of kids & pets so a fast lens is preffered.

I had my eye on Canon's 17-55mm f/2.8 IS USM but it is a little on the spendy side and I'm not sure I need a zoom lens, when I can just take a step forward.

I am also looking at the EF-S 24mm f/2.8 STM and the EF 24mm f/2.8 IS USM.  Other than the Image stabilation, is there much a difference between these two lenses?  Is image stabilation worth the extra $450.00?

[cale_kat]

Justin, You're only $80 away from the 17-55mm f2.8 Canon which retails for around $880. (The 16-35mm f1.8 Sigma retails at $800.) You've come a ways from your original post and concerns about the price of the Canon lens. I wont argue the beauty of the Sigma lens or its imaging, I do believe the overall value remains with the Canon 17-55, I have spent some time with the 60D and 17-55 and I thought the two exceptionally well suited together. I don't know how you could find a more versatile lens at the price..

Just my $.02.

[TCampbell]

There is a danger in using very low focal ratios (e.g. f/1.8).  The depth of field starts to get very narrow -- so if your subjects (say it's two children) are not at the same distance, only one would be in focus and the other blurred.  If that's not the effect you'd want then you'd need to change the focal ratio to increase the depth of field OR make sure your subjects are at the same distance (and when deailing with young children... that may be quite a challenge.)

For example...

The "normal" focal length (1x zoom) for an APS-C camera is 28mm.  (A "normal" lens with 1x magnification means the diagonal measurement of the imaging chip matches the focal length of the lens.    The diagonal measurement of a Canon APS-C chip is about 27mm.  Nobody makes a 27mm lens, so 28mm is as close as you can get.)

So if we use an assumption of a 28mm lens, then a subject focus distance of say... 7'.  This gives us a dimensional field of view roughly 6' by 4' (it's actually slightly less than that... but I'm rounding to nearest whole-foot values).

Assuming 28mm with f/1.8 and a 7' focused distance, the depth of field is 1.28' (6.4' to 7.7').  That means if the heads of these two children are not at the same distance ... but vary by much more than a foot.... then one of them is going to be soft.

At f/2.8, this climbs to 2' worth of Depth-of-Field.    At f/4 it climbs to 3' worth of DoF.

This is why I seldom shoot this sort of thing at focal ratios below f/4.  You can... but you have to be very aware of the DoF.

It's usually easier to move the subjects into better lighting.

Note that I used a 28mm lens as a baseline (because that's the "normal" focal length where you'd have no wide-angle distortions.  Suppose we run that down the 18mm wide-angle limit on the lens... now the depth of field (at f/1.8) jumps back up to 3.25' (keeping that 7' distance)  and at f/2.8 it's 5.6' (keeping that 7' distance).     BUT... if we try to maintain the "roughly" 4x6' dimensional field of view, then we'd have to change the subject distance to 4.5' and now we're RIGHT BACK to the original 1.3' of DOF (so we didn't really gain anything ... other than wide-angle distortions.)

If you were shooting subjects at some distance, then sure... go ahead and shoot at low focal ratios without worrying too much. But given you are looking for a new lens BECAUSE of the close-shooting proximity to your subject and low light constraints... f/1.8 is probably not going to be easy to use.

[cale_kat]

I don't see shallow depth of field as a "danger" but rather as an "opportunity". No two photographers are exactly alike. 🙂

[ScottyP]

You are both right of course.  If you are not needing to get multiple things at different distances into the shot, the shallow DOF can be beautiful.  

At least with a wide lens like 18 - 35mm you don't get into terribly terribly thin depth of field (from the "risk" line of thinking).  The crop sensor too helps keep you out of the razor thin DOF, as compared to the DOF on FF at equal distances.  

I really enjoy my 35mm f/1.4 indoors for that reason, actually.  I can usually shoot wide open, or nearly so, without having to bump the ISO's too badly, and yet I usually still get enough DOF to get most shots.  That would be trickier to do using a longer lens like 50mm or 85mm due to shallower DOF.

[cale_kat]

It is also worth mentioning that the lenses with a 1.4 or 1.8 maximum aperature typically perform very well when stopped down once or twice. The benefit being that the higher you start, the better position you will be in to take advantage of natural light even when stopped down.

[TCampbell]

That's true... "extremes" of lenses are seldom their sweet spots of performances.

I mention the hazzard of very low aperture only because beginners may go from a kit lens with variable focal ratio, then learn that some lenses offer much lower focal ratios which collect substantially more light.  If you compare a kit 18-55mm f/3.5-5.6 lens at 50mm (which would be limited to f/5.6 at that focal length) to a "nifty fifty" 50mm f/1.8 that's 3 and 1/3rd stops (about 10x more light).  Ten times more light sounds fantastic on it's face...

Yet it's also important to consider that while the light collection goes way up... the depth of field becomes much narrower and this may become so narrow that you may not be able to get everything in focus that you actually want in focus without considering subject placement.

Commonly in cinematic photography only one "person" in the scene might be focused... deliberately de-focusing other people in the scene and drawing the viewer's attention to the person in the scene that the director wants them to see.  In traditional photography, if two children are in the same photo, more commonly the photographer probably wants both to be focused.  If that's the case... you may need to nudge the focal ratio back up to achieve that goal.

My original post was really to point out that very low focal ratios (f/2 and lower) don't necessarily solve the light problem without any side-effects so... use with care.

[ebiggs1]

"...  very low focal ratios (f/2 and lower) don't necessarily solve the light problem without any side-effects so... use with care."

There is no free lunch.  You give to get.  

[RichardD]

What about the Canon 28mm f:1.8?  It's going for $449 at Adorama after a $60 rebate.

[Justin]

Yes, the Canon 28mm f:1.8 lens is one that I am also considering as well as the EF-S 24mm
f/2.8 STM lens which is only $149.99 but I don’t think it is available yet.

Previous posters have a very good point about the dangers of a lens that can shoot at f1.8 because of the very shallow depth of field.  I often shoot using the TV mode (with exposure compensation) to avoid motion blur.  If I am using a lens that can go down to f1.8 there is a danger of accidentally shooting at too low of an f-stop.  Unfortunately there is no “lowest safe f-stop” mode in TV just like there is no “lowest safe shutter speed” option for shooting in AV mode with auto ISO.  At least not that I am aware of.  I can always shoot in Manual, but then I would lose the exposure compensation option.

[RichardD]

I noticed in your original post that you were using the 50mm f:1.8.  You stated that you objected to this lens because you had to back away from the subject a considerable amount but you did not raise an objection to the shallow depth of field provided by the 50mm f:1.8 lens.  If indeed you have no objection to the shallow depth of field on the 50mm there is no reason to beleive that you would have an objectin to the 28mm.

Just a thought!