What to do for low light

Fortunately, I have both the 15-85 and the Sigma 30. They work beautifully to complement each other and solved the problem for me that you are contemplating now.

As far as the focusing problems attributed to the Sigma are concerned, I ran across something interesting. When I got the Sigma, I took a bunch of general shots and they were all sharp.

I was concerned about the front focusing people talk about, so I took some closeups at f/1.4 and f/2.0 and they came out focused where I aimed. I then took some photos using one of those focus charts and the Sigma seemed to be front focusing a bit. Then I took some additional shots using 5 AA batteries lined up a bit offset. Perfect focusing.

I'm not sure what to make of the above, but I'm wondering if the razor thin DOF at f/1.4 might have been the culprit on the focus chart test. Or it might have been my technique.

Anyhow, the Sigma can always be calibrated if need be, but I gotta tell you, I am really please with the lens for inside use and/or low light w/o flash.

I did not find 2.8 fast enough for the night parades or inside rides. I also have tried a 50mm 1.4 and the 30mm 1.4, the 30mm turned out to be the right lens for me a night and indoors at Disney and is the reason I still have it.

Earwax69 wrote in post #14907324
The IS do the job nicely. I would say that a f4 lens with IS is roughly equivalent to a f1.8 prime.

I don't agree with that, unless what you are shooting does not move at all.

As others have commented, fast lenses will limit your depth of field, but that's not the whole story. You can think of each pixel as a photodetector at the end of an opaque straw. If light doesn't enter the straw at the right angle, it can't get to the photodetector.

After quite a lot of experimentation, DxO Labs published resultsthat showed this behavior applies to all cameras. In the case of the 7D / 60D / T3i / T4i sensor, it was found that the sensor looses about a stop when the lens has an aperture of f/1.4. This means that even with f/1.4 lenses your camera cannot detect light that is coming from faster than f/2.

A second issue is that fast lenses often exhibit focus shift when they stop down. This leads to images that are softer than they need to be. Whether you like it or not, this problem happens during night shooting as much as it does during the day.

It seems reasonable then to look for a lens that is sharp at f/2 and which will not exhibit much focus shift. These are available but (not unpredictably) they're often expensive. I use the Zeiss 28/2, 35/2 and 50/2MP when low light performance is essential. Manual focus is not a problem - it turns out that manually focusing using live view and a loupe will outperform most autofocus systems in good light and almost all autofocus systems in weak light.

My recipe when I must shoot in low light is therefore

1. Open up the aperture bearing in mind the subject and the depth of field I need.

2. Crank up the ISO so that I can use a sensible exposure (with a 28mm lens on your camera it would be 1/60 sec if you practice reasonably good technique.) I find a monopod lets me get at least an extra stop here without having the bulk of a tripod. It pays to have looked at the best sensitivity / noise trade off for your camera - I can't speak for the T4i but the 5D2 has optima at 125, 250, 500 and 1000 ISO. Knowing this can win you a third of a stop for free.

3. Fix the resulting noise using Define, Noiseware or Denoise plug-ins. The denoising algorithms in Lightroom are pretty good but the aftermarket products are considerably better.

4. If I must, I will bin the image 2x2, 3x3 or 4x4 (which improves the noise by about 1, 1.5 or 2 stops respectively.) This is fine when you can live with a 5x7 print but you need to take care to frame the subject well - you can't crop the image and do this too.

Binning also hides some camera shake, so with 4x4 binning, you can easily use 1/f (seconds) hand held and 2/f (seconds) with a monopod.

Wait wait wait, what's that binning thing? Please explain "idiot proof" as this is new for me!

Thanks noisejammer for the details !! very interesting...

So having seen that maybe the Canon 35mm f2 is a good choice?
I just saw some pretty good reviews of it and its a lot cheaper then the Sigma 30mm f1.4.

Anyone tried Canon 35mm f2 that can give feedback on how sharp it is wide open at f2?

From what I've seen the 35 F2 is pretty sharp wide open but the sigma is a full stop faster and equally sharp at F2

Sigma 30 > 28 1.8 > 35 2

Earwax69 wrote in post #14910070
Wait wait wait, what's that binning thing? Please explain "idiot proof" as this is new for me!

This is a trick from astrophotography.

Say you had an image that was 4096x2048 pixels. If you were to bin it 2x2, you would add the values in pixels (0,0) (0,1) (1,0) and (1,1). The result would be the pixel in position (0,0) of your new image. Doing this, you end up with an image that is 2048x1024 pixels in scale. The blur is halved but most importantly, so is the noise. This means going to 2x2 improves noise by 1 stop.

4x4 sums 16 pixels and since noise goes with the square root of the number of photons, the noise is improved 4x (or two stops.) ... sorry, I did the calc in my head so I'll correct the original post.

Of course, binning 4x4 would convert the original 4096x2048 to 1024x512 image. Although the common wisdom is ~300 dpi, I find that this could still be printed at 7x5 (inches) and give acceptable resolution. As I indicated, it's what I'll do if the camera is operating in extremely low light.

Talley wrote in post #14910459
From what I've seen the 35 F2 is pretty sharp wide open but the sigma is a full stop faster and equally sharp at F2

Yes, the Sigma is a stop faster BUT the light from that extra stop cannot get into the photo-detectors. Maybe if you were using a 30D it would be fine, but the high resolution cameras being offered today cannot accept light from faster than f/2.

Secondly, you should also be very wary of focus shift.... something that is almost guaranteed if you have a lens that is faster than f/2. The significance varies from lens to lens and also with distance but almost all fast glass suffers from it. The singular exceptions I'm aware of are the 35L and 85L and perhaps the Zeiss 35/1.4 (I haven't tested mine that thoroughly yet.) As before, the extra stop is of very limited value - few cameras can work with it.

Even if you can't get more light, you get shallower DOF and better bokeh. So it has its purposes. You are getting more than f2, just maybe not all the way to f1.4.

The phenomenon you are describing is at the sensor level, so no, L lenses aren't exceptions to a condition at the sensor level.

Are you telling me that the shutter speed will not increase when going from f1.8 to f1.4? I believe it does...

Earwax69 wrote in post #14911548
Are you telling me that the shutter speed will not increase when going from f1.8 to f1.4? I believe it does...

What he means is that the sensor itself cannot see light beyond a certain Fstop. Similar to lenses being rated for F stop vs. T stop. the Sigma 30mm 1.4 is actually only T stop rating of around 1.7. So what happens is the camera is programmed to mearly "boost" iso to "mimic" a brighter image found with a lower f stop lens. ya it's kinda crap but again like the other guy said you still get DOF and Bokeh with the 1.4 lens.

Wow so what you are saying is that I wont seem much low light improvement under f2?

I am looking now that the Canon 35mm f/2 since its a lot smaller and lighter (this will not be my primary lens and I will use it for travel so that is a big consideration) and also half the price.

Can someone post a picture in low light of f1.4 and f2 in all the same conditions (iso, shutter speed)
I would like to see if there is much difference??

Interesting discussion! I was planning for Sigma 1.4 vs Canon 28 1.8. Since I have a 17-50 2.8, therefore spending for a stop does not make sence to me. I was inclined for Sigma 30mm 1.4. Now you forced me to think again. Can anyone please post two pics. 550D + Canon 28 1.8 and 550D + Sigma 30 f1.4. Everything else being same.
Keep the discussion alive! Thank you!