Reading mode: Light Dark

How should I confirm focus?

Go to last post
fastHID

fastHID

Leading Member
Messages
811
Solutions
1
Reaction score
25
Location
Santa Clarita, CA, US
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)
 
I should have done this initially, here are 2 shots, not meant to be a direct comparison, taken a few minutes apart, at slightly different focal lengths and position, first one at F10:


at f10

second at f5.6:




f5.6

tonight, I'll do a proper comparison shot
 
fastHID said:
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
Click to expand...
Or an HDMI monitor. But even that's no substitute for experience, because you still can't tell how much detail you can pull out of the shadows and stuff. And experience lets you move fast. Not everything sits still for hours. Like sunrise, for example.
 
fastHID said:
just comparing visually on a monitor, f5.6 was soft, f10 and f13 fairly sharp looking
Click to expand...
At viewing size, 50% crop, 100% crop?
 
fastHID said:
I should have done this initially, here are 2 shots, not meant to be a direct comparison, taken a few minutes apart, at slightly different focal lengths and position, first one at F10:


at f10

second at f5.6:


f5.6

tonight, I'll do a proper comparison shot
Click to expand...
Forget the sharpness, I want to go there! 😊 where is that?





--
Sam K., NYC
“A camera is a tool for learning how to see without a camera.”
-Dorothea Lange
 
If you're shooting from a tripod, with what appears to be a static subject, you should be using LiveView. CDAF is much more accurate and repeatable than PDAF through the viewfinder.

You are focusing at wide-open aperture, which varies on this lens based on the focal length. A lens is always wide open until you press the shutter release to take the shot, or press the the DOF preview button.
 
fastHID said:
It is 'Main Beach' in Laguna Beach California, I took these just before my photo class last Thursday.
Click to expand...
The f10 looks much sharper than the f5.6, at least on my iPad. Not near a computer now. Were they both taken under exact same conditions. 5.6 should not be so far off.
 
fastHID said:
I'll go repeat it now making no changes but f-stop and using liveview and magnification to focus
Click to expand...
Also try again with OVF AF. Take at least three pics each, enabling AF each time. Use tripod and 2 sec timer.

--
Sam K., NYC
“A camera is a tool for learning how to see without a camera.”
-Dorothea Lange
 
Last edited:
This is on a tripod right? Was IS on? I know my 55-250 STM produces very blurry images if I don't turn off IS when it's on a tripod. I suggest this because I find both shots to not be very sharp although the f/5.6 one is clearly worse. The latter is indeed a weak spot on the 18-135 (~80mm and wide open) on that lens if recall correctly.
 
yes, IS was off and it was on a tripod. I did just rely on AF and a review of what spots it focused on does not really reveal anything.

I think I just happened to shoot at this lens' weakest focal length
 
fastHID said:
yes, IS was off and it was on a tripod. I did just rely on AF and a review of what spots it focused on does not really reveal anything.

I think I just happened to shoot at this lens' weakest focal length
Click to expand...
I can't believe its that bad. Did you repeat test with same result?
 
I plan to this week. last night was foggy here but will repeat with same settings and see.

In the parking lot here at work, with those same settings, I am seeing the same huge difference between f5.6 and f10, yes. The lens is very soft at 75-80mm and f5.6
 
skanter said:
skanter said:
yes, IS was off and it was on a tripod. I did just rely on AF and a review of what spots it focused on does not really reveal anything.

I think I just happened to shoot at this lens' weakest focal length
Click to expand...
I can't believe its that bad. Did you repeat test with same result?
Click to expand...
DXOmark shows a discernible drop in performance around 85mm. If it is any worse at 75-80mm then it can be that bad. I still think there is an overall softness to both images though which I'm trying to figure out. i.e. I expect the 18-135STM to be weaker wide-open at 75-80mm but it's weak even stopped down to my eyes which seems odd. f/10 is bordering on diffraction territory that's true but I'm seeing some general "haziness" to both images.
 
fastHID said:
I plan to this week. last night was foggy here but will repeat with same settings and see.

In the parking lot here at work, with those same settings, I am seeing the same huge difference between f5.6 and f10, yes. The lens is very soft at 75-80mm and f5.6
Click to expand...
is it too late to trade in for another copy?
 
I just looked again and what I thought was motion blur could be heat haze I guess. What was the temperature fastHID?
 
You must log in or register to reply here.

Keyboard shortcuts

f
Forum
m
My threads
Mobile site
About
Editorial content
Cameras & Lenses
Community
All content, design, and layout are Copyright © 1998–2025 Digital Photography Review All Rights Reserved.
Reproduction in whole or part in any form or medium without specific written permission is prohibited.
When you use DPReview links to buy products, the site may earn a commission.
©GPS Media - Guides, Products, Services.
Back
Top