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2.8 vs 3.5 : Is the difference that big?

Nish Nishant , Dec 11, 2008; 02:13 p.m.

Typically, lenses like the Tamron 17-50 F/2.8 or the Nikon 17-55 F/2.8 are suggested whenever someone asks for a good lens to use in low light indoor conditions (avoiding flash). I intend to get one such lens as soon as I can afford it (most likely the Tamron).

But I was wondering how effective this would be in helping you avoid flash. My kit lens (Nikon 18-55, the non-VR one) supports 3.5 at the wider zoom end. And with 3.5 (using Aperture priority mode) the only way I can avoid flash is to use ISO 1600 which gives pretty crappy pictures using both the D40X and the D80 (the two cameras I own).

Would getting a lens that gives me an F/2.8 aperture really make that big a difference? Assuming I shoot at 800 ISO, will the 2.8 aperture setting allow me to shoot good pics without flash in indoor lighting using the kit lens?

My only other lens is the 50mm F/1.8 but that's not remotely wide enough for getting everyone in frame. Also at 1.8, it results in backgrounds that are often too washed out and it's also very hard to get everyone in focus.

Before I get the Tamron lens (400+ bucks), I was wondering if it will actually solve my problem. Or whether it'd be better to invest in an SB-600 and use bounce flash to get natural looking pictures (though I doubt they'd be as good as no-flash pictures).


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Ellis Vener , Dec 11, 2008; 02:24 p.m.

f/2.8 means you'll gain 2/3rds of a stop more light coming through the lens over f/3.5 difference between ISo 1000 and ISo 1600) but you'll also ahve shallower depth of focus when used wide open.

For family pix with young kids a flash will likely be of more use especially if you use it off camera.

William Pahnelas , Dec 11, 2008; 02:28 p.m.

relative to what you're talking about, i don't believe the difference is that "big". even with a fast lens used wide open (or close to it), you're still talking long exposures and high ISO if you aren't planning to use a flash. since you already own two bodies, i assume eventually you'll spring for a f/2.8 17-5x zoom. in the meantime, get the SB600 and use bounce to get natural looking pictures. and yes, done properly, they can be natural looking.

Edward Ingold , Dec 11, 2008; 02:49 p.m.

An f/2.8 aperture is not intrinsically that much better than an f/3.5 aperture at the same focal lengh, but faster lenses (within limits) tend to be built better and have better optics. Ultra-fast lenses (>f/1.4) tend to emphasize speed above image quality, and often extremely expensive (e.g., Leica 50/0.95).

This is especially true for zoom lenses. For example, f/2.8 lens tend to have fixed apertures throughout the zoom range, whereas f/3.5 and slower lenses tend to have variable apertures. The overall build quality is better too, especially with regard to focusing and weather-resistance.

Chris Werner , Dec 11, 2008; 03:52 p.m.

This is probably a bias developed many years ago, but my Pavlovian reaction to f2.8 is "good lens", based on the fact those lenses that I have had have been well made and pretty good. Conversely, and for the oposite reasons, f3.5 to me says "cheap". No that they can't perform well in certain circumstances, but I've found there to be a distinct difference in build and optical quality.

But viewed purely in terms of light gathering, it's a meaningful, but not huge difference.

Shuo Zhao , Dec 11, 2008; 04:07 p.m.

Essentially all f/3.5 lenses (zooms) available on the market today are variably aperture designs. They are either f/3.5-4.5 or f/3.5-5.6 or "the dreadful" f/3.5-6.3; while almost all f/2.8 lenses are constant aperture designs (save for a few f/2.8-4 lenses). If constant aperture f/3.5 lenses are ever made, they should become popular, much like those constant f/4 pro lenses Canon makes.

Dave Lee , Dec 11, 2008; 04:12 p.m.

I had a Nikon 35-70mm f3.5 AI Macro Zoom (constant f3.5 aperture) for a while, it was pretty fun to use as a walkaround lens on my F3HP. The Nikon 35-70mm f2.8 AF zoom replaced it (though I don't have one of those). I also had a Vivitar Series 1 70-210mm f3.5 constant-aperture zoom which was also pretty nice.

Albert Darmali , Dec 11, 2008; 04:57 p.m.

ISO800 and f/3.5 won't take you far in terms of available light photography.
But then again, the difference is that big only at times when you need it. When you need to take in as much light possible, the difference will pay by itself. It will be the difference between a sharp picture or a blurry picture.
Ideally I would prefer my 17-50mm range to be constant f/2 but then it will be too expensive and too big I guess...

Nish Nishant , Dec 11, 2008; 10:52 p.m.

Thanks everyone. I still do intend to get the Tamron lens but perhaps not as soon as I may have after reading all your comments.

I also realized another thing. A 2.8 aperture might give shallow DOF at 50mm but at 17mm it probably won't be as shallow.

The majority of my shots are of my 16 month old son who never stays still. So most of my shots of him (with the 50mm 1.8) end up being out of focus. What's tiring is that some of them look good on the LCD but when I transfer the pics to my laptop I see that they are soft. What I do now is take several shots, so at least a few of them come good. I realize that this is rather unprofessional an approach (bruteforcing really) but I am hoping that as I use the lens I'll get better.

Nish Nishant , Dec 11, 2008; 10:55 p.m.

in the meantime, get the SB600 and use bounce to get natural looking pictures. and yes, done properly, they can be natural looking.

Thanks William. Looks like a flash should be a bigger priority for me than a faster lens.

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