How should I confirm focus?

[fastHID]

Using my 18-135 STM 'kit' lens, I did a few shots on a tripod at ISO100, at 75mm, at f5.6, then at f10, and f13, and learned that at f5.6 and around 80mm is not a sharp combo. The images were good at f10. Later, I reviewed DXO tests on this lens and others and saw that at 80mm and f5.6 is soft.

My question is this, at the time through the viewfinder all looked ok. Should one confirm focus using live view and magnification? Will the screen show what we'll get at 5.6? or must I use DOF preview button and look through the viewfinder?

What is the best way to view what you are going to get? (not tethered to a laptop)

 

[fastHID]

and to clarify, I did reshoot tests using manual focus, then changing nothing but aperture, shot f5.6, 6.3, up to f16 then compared. this lens does best at about f9-11. I even found mirror lockup can make a difference.

so my question is how do I preview properly and see that I'm getting soft results (not necessarily out of focus) before I take the shot?

 

[TTMartin]

You have to understand focus and image sharpness are actually two different things.

Focus determines where the plane of maximum sharpness will be.

Maximum sharpness is determined by a variety of factors such as those you noted. (lens, aperture, etc).

 

[fastHID]

I do understand. That's why I ran my tests. I'm asking what is the best way to PRE-VIEW what you are going to later see in the results.

 

[TTMartin]

I do understand. That's why I ran my tests. I'm asking what is the best way to PRE-VIEW what you are going to later see in the results.

Preview what?

Focus?

Depth of field?

You can't really preview sharpness as that is impacted by things like camera shake that doesn't occur until the photo is taken.

 

[fastHID]

Sorry, I didn't word the original post perfectly.

I'm on a tripod, using mirror lockup, focusing finely, using the timer, using all I can to promote a sharp image. How would I view the image visually BEFORE I take the shot, and let's say for example that I'm mistakenly up at F32 and the result will be horrible?

Is it through the viewfinder? is it via liveview? or is it not possible, and I simply need to check the result after it's taken?

 

[TTMartin]

Sorry, I didn't word the original post perfectly.

I'm on a tripod, using mirror lockup, focusing finely, using the timer, using all I can to promote a sharp image. How would I view the image visually BEFORE I take the shot, and let's say for example that I'm mistakenly up at F32 and the result will be horrible?

Is it through the viewfinder? is it via liveview? or is it not possible, and I simply need to check the result after it's taken?

In that case I believe using LiveView, 10X zoom and the Depth of Field preview button would be your best solution. I've never tried it, but, I'm assuming it would work.

Really knowing your equipment, and what aperture is sharpest is the best for this. And it is a lot easier to check your aperture than go through all of that with the DOF preview button.

 

[fastHID]

thanks. my presumption was that I'd still be sharp enough at f5.6 but I was sorely mistaken. to me this is a vote for higher quality lenses.

who wants to memorize that at 80mm be at f10, at 50 mm be at f8, at 24mm be at f-whatever

I'd rather have a lens that I can rely on to be good at a certain aperture throughout the zoom range. I am learning though

thank you

 

[Pritzl]

That's why I bought the Sigma 18-35 and upgraded my 55-250 to the STM version. Both are sharp throughout their range at all apertures leaving me free to consider more important things like framing, composition, foreground, background and light.

 

[MarshallG]

thanks. my presumption was that I'd still be sharp enough at f5.6 but I was sorely mistaken. to me this is a vote for higher quality lenses.

who wants to memorize that at 80mm be at f10, at 50 mm be at f8, at 24mm be at f-whatever

I'd rather have a lens that I can rely on to be good at a certain aperture throughout the zoom range. I am learning though

thank you

I think the answer to your question is "experience."

Experience will let you rapidly determine the best shutter/aperture/ISO trade off for each of your lenses, at every focal length, given the motion in the photo, the amount of blur you want, and whether you have a tripod or not. Seriously, I'm not trying to be a smarty pants. Just take tons of pictures and do what you're doing; create catalogs of images and sharpness effects for different settings. The little screen will NOT show you everything you'll see on a 27" monitor or a printout. Only your experience, tests and memory will do that. Too little aperture and its soft. Too much and it's soft. But sometimes, the softness of a wide open lens is better than the blur of a slow shutter. Sometimes, too high a shutter speed makes a moving object look unnatural.

 

[elfroggio]

Sharpness is an optical illusion.

It has nothing to do with the technical specifications. Sharpness is very subjective. A 100% black photo, like a photo taken with the lens cap on, is 100% unsharp. It's the same with a 100% white photo even with the best camera/glass combination.

Sharpness depends on the contrast between the light and the dark. The higher the contrast between the pixels, the higher the impression of sharpness. Everything else being equal, a bright, side lighting will be significantly sharper than front flat lighting. Bright sunset vs fog... The higher the sharpness, the bigger the prints.

Lighting and technique is far more important than the quality of a lens. But then again, a great technique with a fantastic camera and a great lens is even better.

 

[fastHID]

yes, I have the 55-250 STM and it is very nice, quite sharp,

thanks

 

[fastHID]

Sharpness depends on the contrast between the light and the dark. The higher the contrast between the pixels, the higher the impression of sharpness. Everything else being equal, a bright, side lighting will be significantly sharper than front flat lighting. Bright sunset vs fog...

Indeed. I am learning, and probably learning more by reviewing results very carefully, and asking, why was this one sharp, and this one not. And by asking questions here. I took a shot nearing sunset, still vey bright, and the subject side-lighted, and the details in her face were amazing.

 

[fastHID]

thanks. I suspected that only on my desktop monitor would I see some of these differences I'm asking about. now I'm wondering if you can make use of a tablet to review your results while still there at the scene you are trying to capture

 

[davel33]

Not sure why no one here ask but did you MFA the lens to the body? If not then do it, the 18-135 STM is sharp over its total range. You have the 70D, it has the new Near and Far FMA adjustments. My 18-135 STM had difference of 5-6 from near to far on the zoom range on both my 70D and 7Dm2 (plus the 7D I did have).

To confirm focus use live view at 10X.

Good Luck and stay away from f11 and higher if you can

Dave

 

[skanter]

Sharpness is an optical illusion.

It has nothing to do with the technical specifications. Sharpness is very subjective. A 100% black photo, like a photo taken with the lens cap on, is 100% unsharp. It's the same with a 100% white photo even with the best camera/glass combination.

Sharpness depends on the contrast between the light and the dark. The higher the contrast between the pixels, the higher the impression of sharpness. Everything else being equal, a bright, side lighting will be significantly sharper than front flat lighting. Bright sunset vs fog... The higher the sharpness, the bigger the prints.

Lighting and technique is far more important than the quality of a lens. But then again, a great technique with a fantastic camera and a great lens is even better.

--
Thanks
http://www.sritch.com
The Dogs of Vancouver, BC

As I've said before, I think "sharpness" is overrated and unnecessarily obsessed over. If people could not look at 100% crops, and just printed on paper or looked at normal viewing sizes, there would be little concern about sharpness with almost all modern cameras and lenses. In addition, tack sharpness is not always appropriate, i.e. on portraits where you don't want to see every pore or imperfection on a woman's face. Lighting, composition and an experienced visual eye are far more important than sharpness. Of course, I'm not talking about newbies who do not know how to focus properly.

Canon will not complain, however, about people buying L lenses so they can see every hair on their cat at 100% crop!

--
Sam K., NYC
“A camera is a tool for learning how to see without a camera.”
-Dorothea Lange

 

[skanter]

Sharpness depends on the contrast between the light and the dark. The higher the contrast between the pixels, the higher the impression of sharpness. Everything else being equal, a bright, side lighting will be significantly sharper than front flat lighting. Bright sunset vs fog...

Indeed. I am learning, and probably learning more by reviewing results very carefully, and asking, why was this one sharp, and this one not. And by asking questions here. I took a shot nearing sunset, still vey bright, and the subject side-lighted, and the details in her face were amazing.

How do you determine that your shots were sharp or not sharp?

 

[fastHID]

thanks Dave, I'll read up on the procedure in the manual.

I see no change when I press DOF preview so am trying to figure that out right now.

I did nothing to attempt matching this lens to this body though.

 

[fastHID]

just comparing visually on a monitor, f5.6 was soft, f10 and f13 fairly sharp looking

 

[TTMartin]

thanks. my presumption was that I'd still be sharp enough at f5.6 but I was sorely mistaken. to me this is a vote for higher quality lenses.

who wants to memorize that at 80mm be at f10, at 50 mm be at f8, at 24mm be at f-whatever

I'd rather have a lens that I can rely on to be good at a certain aperture throughout the zoom range. I am learning though

thank you

Generally you don't have to make it that complected.

On an APS-C camera f/5.6 or f/8 AND at least one stop down from full open will normally be sharpest. i.e. a lens whose maximum aperture is f/2.8 will be sharpest at either f/5.6 or f/8 and lens whose maximum aperture is f/5.6 will be sharpest at f/8.

Stop a lens down on an APS-C camera smaller than f/8 and diffraction starts to impact sharpness, though it isn't really visible till you stop down smaller than f/11.

--

All statements in my posts represent my interpretation of data, research opinion or viewpoints.
The opinions expressed are not representations of fact, and are subject to change without notice.
All images are used for educational purposes.