Low light lens, what's the point?

[Cinka]

I've been shooting a lot of weddings this year and have done most of my work on a Canon 40D using a 24-105. Consistently, I've been getting soft images and read some articles that say the 40D is notorious for soft images. This weekend, I rented a 24-70 2.8 to see if that helps.

I started thinking - if using a 2.8 f stop softens images and the 40D softens images - there's really no point. I'll be honest, while I feel I have a good understanding of shutters, apertures, etc. I'm still feeling around for sweet spots and not quite getting a harmonious blend of sharp images in low light. This past wedding, I spent most of the night around 5.6-8 (on the 24-70) using flash and 400 ISO. If that's the case, then there seems no point in using a 2.8 lens. I don't want to go too grainy and 400 seems to be my limit.

What am I missing? Help?

 

[aadhils]

Are you using a flash?

 

[Big Mike]

The 40D isn't a 'soft camera'. People who say that are likely jealous or bitter etc.

A friend of mine (very talented photographer) owns many of the best DSLR cameras for his photography business. 1Ds mk III, 1D (II or III), Nikon D700, but he will tell you that his favorite body is the 40D. He just got back from a tour of Europe, shooting models, and I think he only used a 40D.

What am I missing? Help?

You are going to have to show us some examples, preferably along with the EXIF data.

 

[Derrel]

On Canon's newer AF systems, lenses with f/2.8 or wider max apertures trigger what Canon refers to as "double-precision" autofocus capability. I own a 24-105 L Canon and a 20D and a 5D, and the AF system is all the older, mid-level Canons is "similar". Nine major AF points, clustered in the center of the frame, with some "invisible" AF points,as Canon calls them, in between the nine marked points on the viewfinder screen. I don;t know about the 40D having a history or tendency toward soft images...I've in fact seen some pretty good images shot with that body, from a lot of people.

I wish you had some sample photos for us to evaluate. Your question about a harmonious blend and sweet spot are kind of difficult to interpret/decipher. I'm not 100 percent sure what you really mean by those statements. But I will say this: although my 24-105-L is a decent zoom lens, its actual performance is not as good as the Canon primes I own: 50/1.4,85/1.8,135-L, or the 70-200 2.8-L IS first generation...the 24-105 is "okay" as a convenient zoom lens, but frankly, I think the autofocusing module of the 20D,and the 5D Canon bodies I use it on is simply NOT up to the task with an f/4 maximum aperture zoom lens.

Again, without photos, it's hard to understand exactly, fully, totally, what your issues and concerns are Cinka. As far as ISO 400 being the limit of grain/noise that you are willing to accept, well, that's where the full-frame cameras start to really,really show their advantages over the crop-sensored bodies. Perhaps a bit more information would help us understand exactly where the problems and concerns are with your current situation.

 

[clanthar]

You're not missing much.

If you're using an SLR and trying to see through the lens to compose and maybe focus then the extra speed of the fast lens in low light can be nice.

There's a basic rule (exceptions exist) that slower lenses are better optical performers than faster lenses. There are numerous famous examples; the 80mm f/2.8 Planar for the Hasselblad and the optically superior 100mm f/3.5 Planar, the 50mm f/1.4 Summilux for the Leica and the superior 50mm f/2 Summicron, The 80mm f/2.8 Planar for the Rollie and the superior 75mm f/3.5 Planar, the 50mm f/2.8 Rodagon for your enlarger and the superior 60mm f/4 Rodagan, etc. There are more hurdles to jump when designing the faster lens. Note that this fact is often rather upsetting to the Pros out there that put down the big cash for the fast glass; some denial may often follow it's pronouncement.

Regardless of what lens you've got, the performance of the lens is typically variable over it's aperture range. On the open end problems like spherical aberration degrade the image and on the closed end diffraction degrades the image -- the sweet spot you referred to then on most lenses is a couple stops down from wide open. So if you have the fast lens odds are you're not likely to want to use it wide open anyway.

There is however DOF of course and if shallow DOF is what you want and you're using a small sensor/film camera to begin with, then a fast lens wide open may be your best solution -- the extra f/stop will help you shrink that DOF.

Then there's this guy I know who specializes in taking photos without flash in bars: ISO 6400, 50mm f/1.4 and there's still not always enough light to handhold the shot: Bob Reuter: St. Louis Photographer, Musician, Writer, and DJ

Joe

 

[KmH]

What am I missing? Help?

IMO and in all sincerety, a good understanding of how photography and cameras work.

In addition to what the others have said, all dSLR's begin to have focusing problems in low light. That's because of the way auto focus systems work.

There is a technical side to doing photography that in this day and age of auto this and auto that, people tend to not take the time to learn and understand what the strengths and weakneses of those auto features are.

Low light lenses tend to have better optics and better corrected optical aberrations, allowing the camera's AF module to function more accurately, particularly when it is using phase detection.
Plus with low light lenses, the intent isn't to use them exclusively with the maximum wide open aperture, but to stop them down so that only the middle portion of the lens is being used to insure the sharpest focus that lens can provide.

Most of today's AF systems use phase detection, backed up by contrast detection. Autofocus - Wikipedia, the free encyclopedia

 

[Cinka]

I guess I don't really know. I have a lot of images - I'd have to filter through them at some point. I suppose I can't figure out if it's me or the camera. I' m guessing it's me. Just not sure how to approach this.

I suppose, the question is: I've found that a wider f stop gives soft images, therefore, what's the point of using a 2.8? You'd want to stick to a middle range or smaller 5.6 and up to get sharper images. Am I right?

 

[Studio7Four]

Since you're using Canon lenses, one thing you can do if you're concerned about how soft (or, conversely, how sharp) you images are is to view the MTF charts for each lens. (I say Canon because I know that the MTF charts are easily found on their website for each lens; I don't know how easy they are to find for other brands.)

Each MTF chart will have a series of lines. There used to be a good explanation on Canon's website which I couldn't find now doing a quick search, but the gist of it is this: the higher the line the sharper the image. The lens is used to image a resolution pattern; the vertical axis of the chart represents the proportion of patterns correctly resolved, the horizontal axis represents the distance (along the image diagonal) from the center of the lens/image. There may be a number of lines on one chart, one for test patterns parallel to the scan axis and one for test patterns perpendicular to the scan axis at several apertures. I believe one set is usually with the aperture wide open. I don't recall if the other is necessarily with the aperture at its minimum or if it's at the lens' sweet spot.

Anyway, most MTF charts will have their highest values to the left and then fall off (at various rates) as you move to the right. This means that the lens is sharpest towards the center than at the extremities of the shot, which you'd expect. How high that initial value is, and how quickly it falls off, will give you a feel for its relative sharpness.

Note: these MTF charts are good for getting a feel for relative sharpness but should not be used to strictly compare one lens to another. For instance, the lines shown are likely at different f/#s. And since you're more than likely to be working at some f/# in the range between the plots shown (or at a focal distance other than what is shown), it's your best guess how the lens behaves in there.

 

[gsgary]

Are you sure it's not down to using too slow a shutter speed ?

 

[Big Mike]

A wider aperture give you a shallower DOF, so the chances of missed focus are more likely.

But yes, most lenses aren't at their best when wide open, stopping down to a smaller aperture does usually improve the image quality. Each lens is different, but I'd guess that most 'pro quality' lenses are still fairly good wide open.

Again, it's hard to diagnose the problem without seeing the images (and the EXIF)

 

[djacobox372]

There is no such thing as a modern DSLR that takes "soft" images, they all take razor sharp images.

If you're only getting soft images in low light, then three things could be to blame:

1) missed focus: wider apertures create a narrow FOV making focus far more critical
2) high iso's which increase the need for noise reduction, creating soft images
3) low shutter speed which doesn't freeze subject motion or camera shake
4) a poor lens, only the highest quality glass is tack-sharp at it's maximum aperture. However I suspect it's one of the other four, as the 24-20mm f2.8 should be very sharp at f2.8.

 

[RauschPhotography]

What am I missing? Help?

IMO and in all sincerety, a good understanding of how photography and cameras work.

In addition to what the others have said, all dSLR's begin to have focusing problems in low light. That's because of the way auto focus systems work.

There is a technical side to doing photography that in this day and age of auto this and auto that, people tend to not take the time to learn and understand what the strengths and weakneses of those auto features are.

Low light lenses tend to have better optics and better corrected optical aberrations, allowing the camera's AF module to function more accurately, particularly when it is using phase detection.
Plus with low light lenses, the intent isn't to use them exclusively with the maximum wide open aperture, but to stop them down so that only the middle portion of the lens is being used to insure the sharpest focus that lens can provide.

Most of today's AF systems use phase detection, backed up by contrast detection. Autofocus - Wikipedia, the free encyclopedia

Operator error seems to the be issue. I've worked with a 40D with both the Canon and Sigma 24-70 2.8s and have gotten sharp images consistently. If you want better feedback on your work, listen the crowd--post images. It'll be a lot easier to see what you're doing.

 

[Garbz]

There is no such thing as a modern DSLR that takes "soft" images, they all take razor sharp images.

The 40D is 3 and a half years old and was actually notorious for a very crappy sharpening algorithm.

 

[CNCO]

Well theres your problem - canon :lmao:

 

[KmH]

There is no such thing as a modern DSLR that takes "soft" images, they all take razor sharp images.

Sorry but that is just not true, and the main reason is the low-pass (anti-aliasing) filter in front of most image sensors.

Any amount of low-pass filtering is going to soften an image. The amount of low-pass filtering varies.