Low Fstops & Crisp Photos


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Sep 23, 2015
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I keep trying to get crisp photos with very low fstops. I stand farther back, but eyes are still not crisp at 2.8, 3.2, etc. what the deal? Help? Tips? any tricks? what am I missing? and yes my shutter speed is 200 or above and ISO is decent.
How are you focusing? What lens are you using?

You still need to go to f/4 or 5.6
Understanding Depth of Field in Photography

IIRC you use a Canon 5D MK III camera.

The 5D MK III image sensor has an Anti-Aliasing (AA) filter in front of it.
The AA filter helps control moiré but it also cause photos to lose some sharpness.

Consequently, photos made with a 5D MK II will need to be sharpened to some extent. Photos destined for electronic display generally cannot be sharpened as much as photos destined for printing.
Image sharpening using Adobe Ps, LR, ACR is a book length subject:
Real World Image Sharpening with Adobe Photoshop, Camera Raw, and Lightroom (2nd Edition)

Most fast (f/1.2, 1.4, 1.8, 2, 2.8, 3.5) lenses need to be stopped down 1 to 2 stops before they start to deliver their sharpest focus.
f/2.8 is a bigger number, and a bigger more open lens aperture, than f/3.5 is.
Understanding Camera Lenses
Tutorials – Sharpness
Understanding Camera Autofocus
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I keep trying to get crisp photos with very low fstops. I stand farther back, but eyes are still not crisp at 2.8, 3.2, etc. what the deal? Help? Tips? any tricks? what am I missing? and yes my shutter speed is 200 or above and ISO is decent.

Post some samples. I shoot at between f1.6 to f2 all the time :)
Lots of things come to mind with this.

Too close to subject
Front/back focus
Not having your lens micro adjusted to your camera.

Just to name a few. Like others said, post an example. Then we can see what the issue is.
Don't Canons have the 100% crop focus button (for a lack of a better name) to check your focus?

I tend to have issues like you're describing.
I keep trying to get crisp photos with very low fstops. I stand farther back, but eyes are still not crisp at 2.8, 3.2, etc. what the deal? Help? Tips? any tricks? what am I missing? and yes my shutter speed is 200 or above and ISO is decent.
post examples as mentioned.
And your "stand farther back" ... isn't very descriptive. such as you were at 1 foot, now 200 feet ?? or 1 foot now 2 feet? 5 now 10 ?

If you use a Depth of Field calculator ==> A Flexible Depth of Field Calculator
you can determine, what many people have a problem with, is the actual depth of field based on your focus point (Do you understand the various Focus Modes and just don't allow the camera to select a focus point on it's own ?) ; in relation to aperture and distance from the subject.
I have to agree with Vteo that a few pics might help diagnose the problem...and more info about what gear you're using might help too. In lieu of that, there are a few things that could cause such a problem.

When you're using low f/stops, you are generally dealing with a very shallow DOF (Depth Of Field). Depending on your lens, your distance to the subject, etc., it may take just a slight miss with your focus point to throw something like the eyes out of focus. Likewise, how you use the focus point in your camera can have a HUGE impact on this as well...many novices for example don't know they can use a single focus point and will have ALL of them turned on. Also remember that your shutter speed should be equal to or better than your focal length. You said you're shooting at f/2.8 at 1/200 second, but you haven't provided the focal length...if your shooting at 200mm for example, that 1/200 of a sec could be too slow.

On the issue of DOF alone, my advice would be to look closely at the picture...ALL of the picture...and see if that sharp point of focus is perhaps landing somewhere else. This alone should tell you if it's actually your aim or something else.

Also, while this is a bit more subjective, I've found that sometimes the aim of the focus points aren't quite as accurate as you might expect. Both of my Canons for example used to shoot just a little low of the center focus point in the view finder. I do a lot of critter photography, particularly dogs, and with my Canons I used to have to aim the camera just a bit high...if I tried to lock the center focus point onto the eyes, the camera would usually focus on the nose instead, so I had to aim the camera a little high (say, the dog's forehead), lock the focus, then re-compose the shot a hair (or allow a bit of room for a crop).

There are of course a number of other things that can contribute to such problems as well...dirty lens, dirty sensor, low quality filters, yadda, yadda. A lot of novices for example will buy a DSLR and get conned by a salesperson into buying a UV filter "to protect the lens"...cheap filters will ALWAYS degrade your images to one degree or another. I had also once gotten a used Tamron lens for dirt cheap because the seller claimed it "was really soft on the focus"...turns out someone smeared some Vaseline or something on the lens (an old portrait photographer's trick) . Once I cleaned the goo off, the lens was just fine. Then of course there's your subjects...some people just can't hold still for more than a split second, making it difficult to keep the eyes perfectly focused if the lens is wide open. Children for example (like critters), can often be REALLY hard to shoot with a super shallow depth of field, just because they always seem to be moving! LOL! There's a very good reason most portrait photographers shoot around f/8...aside from usually being the "sweet spot" of the lens, it gives you a bit more room to work with should someone flinch.

So again, without seeing some pics and having more info, it's hard to give any specific advice here, however, while these are just my own opinions, I hope it gives you something to work with.
Carefully read the post by Jim above and if still wish for better sharpness wide open I suggest Zeiss Otus lenses
FWIW - F/2.8 is a bigger number, and a bigger lens opening (aperture), than f/4 is, because they are fractions.
The f is equal to the focal length of the lens you are using, or that the lens is zoomed to if it's a zoom lens.

Set to f/2 a 100 mm lens has a lens opening that is 50 mm wide - 100mm (f) / 2 = 50 mm
Set to F/4 the same 100 mm lens has a lens opening that is 25 mm wide - 100 mm (f) /4 = 25 mm.

How shallow depth-of-field is depends on several factors;
1. Image sensor size
2. lens aperture
3. lens focal length
4. point of focus distance

Understanding Depth of Field in Photography

Many 'fast' prime lenses (say - f/1.4 to f/2.8) need to be 'stopped down' before they start to deliver their sharpest focus.
Consumer grade fast prime lenses often need to be stopped down at least 2 full stops before they deliver their sharpest focus.
What's your sharpness post processing work flow? There is sharpness and then there's apparent sharpness.
Post examples. I've shot between f1.4 and f2 all day and had no sharpness issues.

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What's your sharpness post processing work flow? There is sharpness and then there's apparent sharpness.

A -very- good point I forgot to include! A lot of people seem to be of the opinion that you should "get it right at the camera", however in most cases images shot with a DSLR can usually use a bit of USM (Unsharp Mask) or other form of sharpening...particularly if you shoot RAW (which you should). Very simply, it's not just about what you do at the camera - photography is a process and post processing should be part of your work flow.
There are a ton of factors to consider:
- what is the camera used?
- what is the lens used?
- is proper hand-holding technique being used?
- does the lens front or rear focus?
- does the camera have microadjustment capabilities?
- if it does, has it been properly calibrated?

On top of all this, it is entirely possible that the lens is out of whack and won't focus properly when "pushed", but may look better when opened up a bit.

Even then, apertures like F/2.8 are not all that hard to get good focus with, if all of the above are in line:




If one wants sharp photos, there are a few hints that could help:

- first use a single fixed focus point that is moved close to where you want it in the frame.
- use single focus, not continuous focus.
- try to avoid a lot of recomposing after attaining the focus.
- take your time, some lenses are slow to lock in focus.
- use a shutter speed that is at least 2X your focal distance (won't aid sharpness, but does eliminate motion blur which is often confused with bad focus).

If that is not working, and your camera has microadjustment capabilities, calibrate the camera to the lens. There are many free variants to attain this, but I much prefer a more accurate and faster way of doing things by using a software. I use the Reikan FoCal software and highly recommend it. Even if I thought my shots were sharp already, I was shocked at how much better all my lenses looked after calibration.

If calibration does not work, you have a hardware issue (most likely the lens needs to be sent in and calibrated with your camera.

Post processing... I shoot everything in RAW, and by the very nature of this format, every shot I take needs some sharpness added in post. Sometimes it is just a hair, sometimes I go nuts, but the one thing I will say is that if the photo is not sharp straight from camera, no amount of sharpening can take a blurry picture and make it better.

Also, it should be obvious that not all lenses are equally sharp. One of the benefits of the FoCal system is that it can not only calibrate your camera to your lens to perfection, it also comes out with many valuable reports... one of which is specific ratings of how sharp your lens is at each aperture.

How many here can say with certainty which aperture is a lens it's sharpest at? You would be surprised. Example, my Sigma 50mm F/1.4, one could say that maximum sharpness should be attained in the F/8 range, but in my case, I was wrong... it was sharpest at a surprisingly relatively wide F/4!

Just a few thoughts.
Oh wow, how awesome to see JerryPH back on TPF!!!!

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