Why do people recommend f2.8/f2.0 etc

Barks

Barks

Barks

Soldato
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20 Jul 2008
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Time and time again I've read review of f2.8 lenses where they're 'great for indoor/low-light photography' etc.

I've got a 550D and a Tamron f2.8 17-50mm. I've also owned a Sigma f2.8 Sigma 24-70mm.

So both were fantastic lenses in bright conditions and outdoors. Both were utterly hopeless at family events/parties etc where I really wanted to take decent shots.

Left in Auto mode, the camera automatically jumps straight to f2.8. Due to the depth of field it virtually almost always focuses on the wrong thing leaving the rest of the image blurred (yes I've tried different focusing options) and usually if there's a portrait where one person is even half a metre out from everyone else, they will be completely out of focus.

If I put the camera in AV and select, say, f4.0 - which is safer - it puts the shutter time to about 1second even with flash on. If I put the shutter time to 1/60 - it puts the aperture to f2.8 and we're back to square one.

In these situations you just want to hand people the camera so they can quickly and easily take photos. I shouldn't have to goto manual mode and set aperture/ISO and shutter.

Is there anyway of telling my 550d in automatic mode to AVOID going below f4.0? This is the sole reason my next lens will be an L f4.0 and not an L f2.8.

Cheers
 
Don't shoot in auto.
Line up group shots in a single file.
2.8 is shallow, it's meant to be.

You are just used to everything in focus from years of P&S, the point of wide aperture has many uses and the only negative is the price or weight (hit the gym!).
 
Biggest problem is that your using Auto mode. If your going to be using Auto your better off buying and learning to use a Flash then shelling out on a f/2.8 lens.

Indeed - your point about the group shot, with one person even being a small fraction behind resulting in them being out of focus is another situation where buying and learning to use a flash would be beneficial.
 
In answer to your question - no.

I don't want to sound harsh but its fairly apparent that you need to learn the basics of aperture / shutter speed and ISO control and how they all control and manipulate the light entering the lens.

Another thing I would say is that if you only want to use auto mode why did you buy SLR? You simply are not going to get anything like the best out of it until you get it into at least Av or Tv.
 
One good factor about the OP's post is that he's identified and understands the problems in which he's getting. He has some concept of the DOF and shutter / aperture. Just needs to learn now how they work along side each other.

EDIT: Just read your final line on your post and advise not to get the 17-40L F4 till you know what your doing. I just dont want someone to spend £400 + to get this lens and magically make them take awesome photos.
 
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Best thing to do would be to get a flash to shoot at smaller apertures, next best thing would be to get a small sensor compact with a fast lens like a Sony RX100 or a Fuji X10. That way you get the high shutter speeds, big apertures and lots of DOF to keep everyone in focus.
 
AV mode is a useful way of shooting, but doesn't work on all occasions, especially if you are wanting to shoot something in low light that might move.

The best mode to use is Manual and for low light, don't fear the ISO being upped. Once you learn to shoot Manual and use the light meter, you will wonder how you ever took photos without it.

Large apertures are useful in low light, but obviously the bigger you get, the more razor thin the sharpness becomes and so you need to be spot on with what you are focusing on. For something still life, or well posed its ideal. However, there is a misconception that you need a big aperture for low light, when using higher ISO is likely the better thing to do.
 
Again at teh risk of sounding harsh, you dont have a full understanding of controlling exposure.

Photography is about controlling light. You have 3 main options. Aperture, Shutter Speed, ISO. Increasing each one comes with 1 benefit, and 1 disadvantage. The benefit is more light in teh sensor. The disadvantage for each each:

Shutter Speed - Blurred Movement
Aperture - Smaller depth of field
ISO - Grainy images.

Photography is the art, or science, of getting the balance correct. For each image, or session, you have to decide which disadvantage you can turn to your advantage.
 
Don't forget that for each given focal length and focusing distance, the amount of depth of field you get changes. Old lenses used to have all of the information marked on the barrel so you could work it out.

See on this old Tamron zoom lens that the lines that converge towards the centre represent depth of field based on the focus distance on the focus ring. The longer the focal length, the shallower the depth of field. Also notice how the distance between the focussing distances changes the closer you focus. (the lines colours are shown under the apertures on the aperture ring) The yellow bit on the left is old magnification factors. (which tells you the ratio of an object to its size on the film. 1:1 meaning that its the same size. The arrow that follows these lines appears at minimum focussing distance and it also shows how a 2x converter affects the ratio)
TamronZoom.jpg


On a prime lens its more simple, but exactly the same.
NikonPrime.jpg
 
Thanks for the replies.

Some of you have inferred that I don't have an understanding of Shutter/Iso/Aperture. I don't think this is fair, I have a solid understanding of these and I never usually shoot in Auto mode. My point was more to do with the fact that you can't just hand an SLR over to a family member and expect a decent photo in the same way you can with a P&S. I think the answer to this question is you can depending on the lens but you certainly can't with an f2.8. If you think how many people buy SLRs and shoot in Auto the whole time - because they're fashionable or whatever (I have loads of female friends around my age group 20-25 who have SLRs and no clue about photography including my misses).

I'm fully aware that:

- As you increase the ISO the sensor becomes more sensitive at the sacrifice of image quality.
- The shutter speed is essentially how long you expose an image for. So 1/500 would be suitable for an action shot, 1/60 suitable for a portrait, and long 10-15second exposures for experimental shots in different lighting conditions.
- A larger aperture (f2.8 for example) results in a smaller area of the image being in focus. Using a smaller aperture you can expect more of the image to be in focus.
 
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Its not always a disaster, my other half has taken wonderful pictures on Auto with a f/1.8 prime before, although the conditions weren't all that challenging and its usually just of a single subject.

Usually, if I'm going to pass the camera around, ill set the settings myself in aperture mode first.
For ex - with average indoor conditions with okay light ill set A to f/2.8 or f/4 (with a 35mm f/1.8) and set auto ISO to a max of 3200 and min shutter speed of 1/100 (could go lower with proper technique, but set a bit higher to account for poor random technique ;) ) and it tends to do the trick.
 
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Well, put it in AV mode, dial in F/18 (Eighteen). Flash ETTL, point it directly forward. Focus point evaluative or matrix.

That should work.
 
The point i was trying to make is that it isn't only the aperture you select that affects the depth of field. The focal length and the distance to your subject both have a big effect. If you want to maximise depth of field whilst maintaining a wide aperture, you need to use a short focal length (wide angle) and the distance to your subject needs to be high. Large focal lengths and close focus increase the fall off of depth of field.

The main reason why compact cameras have plenty of depth of field is to do with the focal length. (usually around 6mm at the wide end and 30mm or so at the long end) It's the same story in reverse for medium format. (for example a super wide is about 35mm and normal is 80mm)
 
scott212 said:
I'm fully aware that:

- As you increase the ISO the sensor becomes more sensitive at the sacrifice of image quality.
- The shutter speed is essentially how long you expose an image for. So 1/500 would be suitable for an action shot, 1/60 suitable for a portrait, and long 10-15second exposures for experimental shots in different lighting conditions.
- A larger aperture (f2.8 for example) results in a smaller area of the image being in focus. Using a smaller aperture you can expect more of the image to be in focus.
Click to expand...

Then you should be aware of that when shooting, also that focal length has a big impact on the DOF. In a situation like yours I would suggest trying to shoot fairly wide to maximise the DOF available whilst also allowing for a suitable shutter speed.

Personally, when I'm doing this kind of thing I tend to shoot in manual mode but have ISO on auto (but limited to 3200-5000ish). That way the shutter speed and aperture are a constant with only the ISO changing.

I also use a single focus point to remove the issue of the camera misfocussing.
 
Hang on a minute...Am i reading this right...

You're complaining about things being out of focus yet you're not even focusing correctly...

lolwhut?

Set the camera to AV. Use 2.8 and focus recompose off the center point making sure to lock exposure. DSLRs aren't and shouldn't be for anyone also. Maybe you should grab a compact if you stick to green box idiot mode.
 
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Logsi said:
Hang on a minute...Am i reading this right...

You're complaining about things being out of focus yet you're not even focusing correctly...

lolwhut?

Set the camera to AV. Use 2.8 and focus recompose off the center point making sure to lock exposure.
Click to expand...

No, I believe the complaint is that if you gave a person who has a DSLR but doesn't really know how to use one, or even just handed it to a family member at christmas so they could take a photo, then it wouldn't get as good results on auto as a point and shoot would if you're using a f2.8 because in low lights the camera will automatically shove it down to f2.8 and have a very shallow DoF.

I think that's roughly what you've clarified with?

If so, then that's one of the inherent problems of a DSLR, and in fact any incredible tool. If you don't know how to use it properly, the chances are you won't get a good photo.

Your average joe also probably won't invest massively in lenses, and will happily stick with their kit lens as well. Something that likely won't create these issues as much, because they won't go as wide.

kd
 
I think that is also one of the things that demonstrates what being a Photographer is. If you could put it in Auto mode, give it to anyone and always come out with great photos, then it would be a bit depressing!

Also, I've setup my camera before for people to take photos, but even then, people don't know composition or how to make it pleasing.
 
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