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Fine tune your lens?

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slogen51
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Fine tune your lens?

Post by slogen51 » Fri Nov 12, 2021 10:29 am

I have noticed for a while that particularly in low light my photos appear to be slightly out of focus on the left side of the image. The blur is obviously more perceptible when shooting close-in in poor light for example when trying to picture nose art on the recently returned Panthers. I naturally assumed the fault lay in my second hand Nikon 70-200 F2.8 VRII lens which admittedly has taken a few knocks in my care!

Before consigning the lens to the bin and forking out nearly £2K! on a new F2.8 zoom I researched Google to see if this was a common problem and came across articles about Fine Tuning your Lens. I had not previously heard of this and it is something you can do your self if needed.

From my understanding DSLR ( not mirrorless*) use phase detection where some of the light is reflected away from the viewfinder down to the AF sensors. Some computing maths happens and the camera calculates the focus. One of the inputs for calculating the focus is the specified distance that the lens is from the main image sensor - in a DSLR it is not the main image sensor that is used for focus unless the camera is in Live view mode.** Essentially the AF program is trying to synchronise the AF sensors to the main Image sensor.

As mentioned above the camera ' knows' where the main image sensor is for calculating the focal plane - here is the kick! From what I understand the camera and lens are made to a specifications that include an acceptable tolerance so the camera image sensor position has a tolerance and the lens is built to a tolerance which although incredibly precise can work against you.

It is important to say that the tiny intolerances in focus will not normally be noticeable as depth of field DOF will nearly always cover off any focus miscalculations however when shooting wide open the shallow depth of field could expose focus blur when pixel peaking heavily cropped photos.

* Mirrorless cameras focus directly off the image sensor so will not have this potential issue - similar to LV mentioned below

** When in mirror up Live view the main image sensor is doing the focusing using Contrast detection which although slower than viewfinder/AF sensor phase detection means that focus is based on the actual light hitting the image sensor at the time the shutter button is released.

I noticed that on a tripod ( actually kitchen table) photos were sharper in Live view LV than when shooting through the view finder so I suspected I had the need to use fine tuning.

There is lot of stuff on the WWW to show you how to fine tune your lens to your camera and there are kits you can buy but I watched a YouTube that showed you can basically use trial and error to do the fine tuning :-

I am obviously not a professional photographer , more point and shoot on aperture priority merchant so I assume a lot of you will already know this and a lot more.

I have fine tuned my D7200 with my Nikon 70-200 F2.8 to +8.

It is easy to store the setting in the Nikon set up menu plus you can easily turn fine tune on / off.

I assume the fine tune number is a parameter used by AF to make an allowance for any manufacturers tolerance in your kit.

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xkekeith
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Re: Fine tune your lens?

Post by xkekeith » Fri Nov 12, 2021 2:07 pm

I used Reikan FoCal software to adjust the micro tuning on my Canon 7Dii and various lenses, its easy to use and I've been pleased so far .....
I have also got a mirrorless Canon RP and noticed a very small but consistent difference with the 7D sharpness on one lens.
Canon EOS RP & 7D II

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daggerfan
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Re: Fine tune your lens?

Post by daggerfan » Fri Nov 12, 2021 11:10 pm

Slogen51, you started your post by saying some of your pics looked slightly out of focus on the left side of the image. I don't see how in-camera focus adjustment can correct for just one side. Is it possible one or more of the elements in your lens could have been knocked out of alignment? Might be worth getting Nikon or an approved service agent to check the lens out.

slogen51
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Re: Fine tune your lens?

Post by slogen51 » Sun Nov 14, 2021 5:00 pm

While looking into the left hand blur I stumbled across the fine tuning stuff - I don't suppose it will fix the 'lop side' issue but I think the pictures are sharper all round. However I haven't had the chance to get out and really put it to the test - hopefully I will have a chance at Mildenhall Monday/Tuesday.

On Friday I took a couple of shots of a Quid from Folly with fine tune on/off and I think the fine tuning slightly improved the photos but I need to get to Marham or Lakenheath on a dull day - shouldn't have too long to wait!

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Richard B
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Re: Fine tune your lens?

Post by Richard B » Thu Nov 18, 2021 1:03 am

Lens fine tune as been around for a good number of years, my old canon 50D had this to fine tune your lens, using a focus card and tune each lens in, then once saved it would auto adjust when each lens you had tuned.
Soft image on one side could be a sticky petal in the lens or curtain sync in the camera..
The fine tune was really ment for front and back focus on your lens as they do tend to vary some may be out on front focus others back focus out slightly.

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daggerfan
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Re: Fine tune your lens?

Post by daggerfan » Thu Nov 18, 2021 11:17 am

Using the USB dock you can fine-tune the autofocus on, say, the Sigma 150-600 C or S lens by 16 settings (four focal lengths at four distances each). All well and good, but if I wanted to fine-tune the autofocus on my Nikon 70-200/2.8 in-camera using my D610 I could only do so for one focal length at one set distance. This might be fine if you were doing portraiture for example, but for aircraft, some taxiing, others flying, it's perhaps not so useful. And adjusting in-camera for one focal length/distance in a zoom lens, is there not the potential for knocking the focus accuracy off at other focal lengths/distances?

slogen51
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Re: Fine tune your lens?

Post by slogen51 » Wed Nov 24, 2021 7:30 am

I think fine tuning has made a slight difference but it really only applies in poor light when the depth of field is shallow. In decent light I can stop down and retain a decent shutter speed.

Lens fine tuning does not apply in this context to mirrorless cameras or in live view when your camera is focusing directly from the image sensor. I took some photos of a stationary C-17 at Lakenheath using the view finder and then again using LV live view on a Nikon - the LV pictures appear sharper in my opinion.

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