Focus Adjustment for DSLR's
May 14, 2019 09:00:17 #
Hi all
Have you calibrated your lenses? If you use mirrorless then your focus is done by comparing contrast at the sensor and you can pretty much stop reading here, its the same in live view for DSLRs.
So if you have the time for live view that should work out very well for you.
For regular DSLR focus light from the lens is diverted from the mirror to some dedicated focus chip usually in the bottom of your dslr, when your mirror lifts your sensor should be at the same position relative to the lens and focus should be spot on.
If its not you may have a lens thats smart enough to take calibration settings and a really smart zoom lens may take settings for different focal lengths as things move in zoom lenses the correction needed may be different at different focal lengths and focus distances.
To be fair a prime lens may be more or less in focus at different focus distances too. hmm live view and focus peaking is pretty good but slow.
So lets look at calibrating a lens to your camera. You are best to calibrate with just the centre spot, it's possible that the focus chip is skewed some way but thats going to mean a trip to your manufacturers service centre if they will even do this for you. Your tolerance may be less than theirs.
Mostly you will want to concentrate on lenses f2.8 or faster. This helps ensure good light and a narrow depth of field a slower lens will have a wider depth of field and may pick a different focus point depending if its focusing in or out.
Ok my first attempt was with a steel ruler at 45 degrees against a wall with live view i could nail the 45 cm mark but when i tried with the regular focus i got the wall sharp every time. You can use a rule flat on the ground with the camera tilted at 45 degrees and that should work.
However i decided to print a target like this one. http://www.squit.co.uk/photo/files/FocusChart.pdf
basically print it out mount to foam board or a cardboard box and set the ruler part to 45 degrees. Focus on the target and take a shot and the zero line on the rule should be focused and the lines back and forward get fuzzy as they are further forward or back from the focus plain. If the target is fuzzy then the ruler should help figure out if the problem is front focus or back focus. Of course the ruler and target need to be on the same focal plane parallel to the lens to be clear.
The key thing is the sharpness of the target. With my 50mm f1.7 lens i took pictures at 0 +1 +2 +3 +4 +5 in lightroom i color coded them as red and gave 5stars for +5 4 stars for +4 and so on. i did the same for minus calibration and color coded them as blue. It is very easy to forget which adjustment was applied for each shot. You may want to use live view to create a reference shot. Using a 2 second delay should minimize vibration, you can also tether and evaluate easily on a laptop if your camera allows for that.
You are really looking for the sharpest target. The ruler helps evaluate where acceptable focus is. I found i could evaluate focus just with the target and found that my 50mm f1.7 was at best focus at zero. Which may seem like that was pointless but I didn't know before hand.
Distance:
Pentax recommend a distance of 30 - 40 x focal length for a lens e.g 1.5 - 2 meters for a 50mm, you might want to chose something closer to what you tend to shoot at. For a zoom it may be worth evaluating the best compensation at different focal lengths. For a 70 - 200mm that might be 70, 85,135,200
You may not get a consistent correction and maybe you may have to pick 1 or 2 to save for a lens or maybe none. If you evaluate a manual lens it may be best to adjust for your current session. Applying the correction takes a few seconds, finding it will take a good bit longer.
If in doubt live view with focus peaking should get the best focus, auto focus can ignore your focus spot, despite aiming dead on the ruler my k1 decided the wall behind it was the subject. Back button focus can help along with single shot af.
I hope this has been interesting and increases your keeper rate.
Have you calibrated your lenses? If you use mirrorless then your focus is done by comparing contrast at the sensor and you can pretty much stop reading here, its the same in live view for DSLRs.
So if you have the time for live view that should work out very well for you.
For regular DSLR focus light from the lens is diverted from the mirror to some dedicated focus chip usually in the bottom of your dslr, when your mirror lifts your sensor should be at the same position relative to the lens and focus should be spot on.
If its not you may have a lens thats smart enough to take calibration settings and a really smart zoom lens may take settings for different focal lengths as things move in zoom lenses the correction needed may be different at different focal lengths and focus distances.
To be fair a prime lens may be more or less in focus at different focus distances too. hmm live view and focus peaking is pretty good but slow.
So lets look at calibrating a lens to your camera. You are best to calibrate with just the centre spot, it's possible that the focus chip is skewed some way but thats going to mean a trip to your manufacturers service centre if they will even do this for you. Your tolerance may be less than theirs.
Mostly you will want to concentrate on lenses f2.8 or faster. This helps ensure good light and a narrow depth of field a slower lens will have a wider depth of field and may pick a different focus point depending if its focusing in or out.
Ok my first attempt was with a steel ruler at 45 degrees against a wall with live view i could nail the 45 cm mark but when i tried with the regular focus i got the wall sharp every time. You can use a rule flat on the ground with the camera tilted at 45 degrees and that should work.
However i decided to print a target like this one. http://www.squit.co.uk/photo/files/FocusChart.pdf
basically print it out mount to foam board or a cardboard box and set the ruler part to 45 degrees. Focus on the target and take a shot and the zero line on the rule should be focused and the lines back and forward get fuzzy as they are further forward or back from the focus plain. If the target is fuzzy then the ruler should help figure out if the problem is front focus or back focus. Of course the ruler and target need to be on the same focal plane parallel to the lens to be clear.
The key thing is the sharpness of the target. With my 50mm f1.7 lens i took pictures at 0 +1 +2 +3 +4 +5 in lightroom i color coded them as red and gave 5stars for +5 4 stars for +4 and so on. i did the same for minus calibration and color coded them as blue. It is very easy to forget which adjustment was applied for each shot. You may want to use live view to create a reference shot. Using a 2 second delay should minimize vibration, you can also tether and evaluate easily on a laptop if your camera allows for that.
You are really looking for the sharpest target. The ruler helps evaluate where acceptable focus is. I found i could evaluate focus just with the target and found that my 50mm f1.7 was at best focus at zero. Which may seem like that was pointless but I didn't know before hand.
Distance:
Pentax recommend a distance of 30 - 40 x focal length for a lens e.g 1.5 - 2 meters for a 50mm, you might want to chose something closer to what you tend to shoot at. For a zoom it may be worth evaluating the best compensation at different focal lengths. For a 70 - 200mm that might be 70, 85,135,200
You may not get a consistent correction and maybe you may have to pick 1 or 2 to save for a lens or maybe none. If you evaluate a manual lens it may be best to adjust for your current session. Applying the correction takes a few seconds, finding it will take a good bit longer.
If in doubt live view with focus peaking should get the best focus, auto focus can ignore your focus spot, despite aiming dead on the ruler my k1 decided the wall behind it was the subject. Back button focus can help along with single shot af.
I hope this has been interesting and increases your keeper rate.
May 14, 2019 10:42:23 #
https://www.diyphotography.net/nail-focus-every-single-time-diy-lens-calibration-solution/
A couple of videos on construction and use of a diy calibrator
A couple of videos on construction and use of a diy calibrator
May 14, 2019 14:18:58 #
juan_uy
Loc: Uruguay
I bookmarked earlier today, but I was on a rush and forgot to thank you.
Very good post that will have bookmarked for near future. I have a lens I am suspecting has a slight focusing issue (it may be the lens is just soft) so will try this when I have some time.
Thanks, again :)
Very good post that will have bookmarked for near future. I have a lens I am suspecting has a slight focusing issue (it may be the lens is just soft) so will try this when I have some time.
Thanks, again :)
May 14, 2019 14:48:45 #
juan_uy wrote:
I bookmarked earlier today, but I was on a rush and forgot to thank you.
Very good post that will have bookmarked for near future. I have a lens I am suspecting has a slight focusing issue (it may be the lens is just soft) so will try this when I have some time.
Thanks, again :)
Very good post that will have bookmarked for near future. I have a lens I am suspecting has a slight focusing issue (it may be the lens is just soft) so will try this when I have some time.
Thanks, again :)
No worries, i've tried a couple more lenses a 28-200mm Tamron and a 70-210 pentax both quite slow lenses. They don't seem to have focus correction issues but they are not as sharp as my 50mm f1.7 at least not wide open. There is some software for Nikon and Canon called Focal that automates testing to some degree and goes more in depth. I think its around $70 to buy
May 14, 2019 16:11:59 #
juan_uy
Loc: Uruguay
blackest wrote:
No worries, i've tried a couple more lenses a 28-200mm Tamron and a 70-210 pentax both quite slow lenses. They don't seem to have focus correction issues but they are not as sharp as my 50mm f1.7 at least not wide open. There is some software for Nikon and Canon called Focal that automates testing to some degree and goes more in depth. I think its around $70 to buy
The issues I am having is with my Nikon 55-300 (at 300mm). Initially I thought the lens was just soft. After seeing good comments and great examples of sharp pictures, I started thinking it was poor technique and lack of knowledge from my side.
Now, after making some tests, I am again leaning to the lens fault. Trying to micro adjust focus could be a good option.
I am planning to replace with a Tamron 70-200 2.8 G2 in short/mid term so the software option won't worth it for me.
Again thanks for sharing all this information and taking your time to explain it.
May 14, 2019 16:30:53 #
juan_uy wrote:
The issues I am having is with my Nikon 55-300 (at... (show quote)
No worries I should have a Tamron f2.8 70- 200 hopefully by friday. It doesnt have VC and the focus is a screw drive from the camera so not silent and not quite so fast. Its a warehouse return in "Like new condition" and after checking prices on various Amazon Sites i found it for €380 on Amazon.fr the UK site had the exact same lens listed at about €474. It is the exact same lens just 94 euro cheaper (Amazon and Google translate is a wonderful thing).
once you find something you like changing the domain from .co.uk to .de or .fr .es or .it can save a lot.
May 14, 2019 20:17:43 #
juan_uy
Loc: Uruguay
blackest wrote:
No worries I should have a Tamron f2.8 70- 200 hop... (show quote)
Thanks for the tip, although I live in South America, and usually can only purchase from .com if I travel there. Want to travel to Europe next year, so will keep that in mind
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