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Repair: Infinity Focus Calibration

Hello, everybody! I feel like I am writing the same thing every time I write a new article on fixing lenses when it comes to the part of calibrating your lens’ infinity focusing so I am going to write a dedicated article on this subject. I hope that you’ll enjoy this.

What’s Happening:

For those of you who don’t know what I’m talking about, a manual lens’ ability to focus at infinity accurately when you turn the focusing ring all the way to infinity is important. It is very important because if your lens can’t achieve this then the focusing scale is off and is not reliable for use with manual focusing techniques like hyper focal distance focusing and the like. So long as your lens can focus on something far (more than 4-7km) and the infinity symbol is dead-center with the centerline of the scale while the lens is racked all the way in until it can’t be turned any further then you are good. This is very important as far as manual focus lenses are concerned. Some manual lenses were designed to focus past infinity to compensate for the elements physically expanding due to heat. These are usually telephoto lenses as far as my experience goes but will depend on which design or materials used on the glass. You will have to make your own research on which lens does this because I don’t have a complete list for this.

HAW_8607Manual focus lenses need to be able to focus properly all the way to infinity. The building is around 1.2km from where I took this. Your lens will need to be able to focus accurately on a subject that’s about 4km far or more. Telephoto lenses will require you to do this as accurately as you can but wider lenses can be a bit more forgiving and a subject that is only about 2km away may suffice because the DOF of wider lenses is greater.

Some people may be asking themselves how these get inaccurate to the point where you need to calibrate them. The answers are really simple:

  1. A lens that has suffered shock like being dropped or knocked.
  2. The focusing ring has become loose due to wear or damage.
  3. The lens was “serviced” but reassembled incorrectly.
  4. A lens that has been correctly serviced and calibration is part of the job.

This problem can be corrected so long as nothing is damaged beyond repair or when the lens has been reassembled again back the right way. If the damage is so severe and fixing it is impossible then you will have to replace the damaged part/s. In the case of lenses not being reassembled properly then you will have to open it up and put it back properly. I’m only going to talk about bullet points 2 and 4 so if your problem is bullet points 1 and 3, it is best to look for some other resources to correct your problem.

Getting it right is important because if you did not then the scale will not be accurate. For example if you focus on an object 5m away but the scale will say something else. This can be very frustrating for people who actually read the scales to focus their lens! This is how important this topic is so I take this thing very seriously.

Where to Adjust:

There will usually be some place where you can adjust the infinity focusing of a lens. The older lenses may not have this because they were made with tighter tolerances so this is going to be a bit different. Conventionally, you do the adjustment by moving the focusing to position you need and the focusing ring will not move past infinity. On some lenses, a separate mechanism is used to constrain your lens’ focusing range. For these lenses, you will have to adjust 2 things just to get it to work properly. It really depends on which era your lens was made and which part of the market segment it was targeted to. I will show you some samples below to help you understand what I am talking about.

IMG_2322Some lenses have a 2-step design for you to calibrate your infinity focusing. This one has an inner ring where you can set the focusing range (shown here) and a focusing ring that you can adjust for the scale (now shown) for fine tuning.

IMG_5781On this thing, adjustments can be made by loosening these grub screws so that you’ll be able to rotate the brass ring to calibrate your focus. This is for the Bronica S2 helicoid.

img_1455This is a more common way where the focusing is secured with screws and loosening the screws will allow you to move the focusing ring so you can adjust the distance scale.

IMG_0529On this lens, this stop is used to constrain your lens’ focusing range and where your lens will stop once it has been fully collapsed (infinity). Loosening these screws will allow you to adjust that brass stop left and right. This is from the Nikkor 200mm f/4K/Ai lens.

IMG_0323This is the same gimmick as the one shown before this but it’s a lot simpler. Read the post about the Nikkor 135mm f/2.8K/Ai lens here.

IMG_0296Some lenses have a separate scale for you to adjust. On this lens, the scale can be moved after loosening these grub screws.

img_1644While the previous example has grub screws to secure the scale in-place, this one uses a strip of cheap cellophane tape. This is common on the Ai-S era where cutting corners is the norm. Ironically. this is from the expensive Noct-Nikkor 58mm f/1.2 Ai-S lens!

IMG_4819Older lenses were usually hand-made so you don’t really have any adjustment points. It’s mainly done by a copper shim and while I won’t consider this as an adjustment point, it’s the only way you can fine-tune this lens’ (Nikkor-H.C 5cm f/2 RF) infinity focusing.

So long as something will allow you to alter how the focusing ring works and how much it moves then this is where you should be adjusting your infinity focusing. What I said is only true for the majority of Nikkor F-mount lenses and you will encounter lenses that’s using a different scheme to achieve this like using shims and other gimmicks.

Tools:

The best way to check if your lens is focusing all the way to infinity is by mounting it to a camera body and checking it from there.  Just make sure that the camera is to spec and it hasn’t been damaged. If your camera cannot be relied on then using it for calibration is a waste of time. I will only discuss here the tools that I use and those that are accessible to the almost everyone. I will come back to this section and edit this as I build more tools to update you guys on what you can use to calibrate your lens.

Thankfully, the most accessible tool for everyone is built-in to all autofocus Nikon bodies. It’s accurate enough and gets the job done. There is a dot that lights up when your focus is correct and on some models, the dot even has arrows beside it that will indicate which direction you should turn your focusing ring so you’ll get “perfect” focus and the dot will light up. This is very clever and this is one of the reason why I love Nikon. This is handy for people who use manual focus lenses and because the F-mount is generally considered to be backwards-compatible, photographers who use manual focus Nikkors can still use the most out of their lenses with their autofocus bodies. It is basically like having the best of both worlds. For people with poorer eyesight, this is a big help as I can attest.

viewfinderThis is the focus confirmation dot found on all of Nikon’s cameras that can autofocus. It is basically a “digital rangefinder” that will light up once your subject is in focus. The older cameras only have 1 focus point at the center so it will only work on that. Selecting other focus points will allow you to check your focus on the areas these points are in.

There’s another method that I use for lenses that cannot be mounted on a Nikon F-mount camera body and this involves using a focusing screen with a prism at the middle and a magnifier loupe. What you do is remove the back cover and then set the shutter to T and then fire it. The shutter will remain open and the mirror will remain in the up position. I then use this device to look through the film plane and check my focus from there. I also use this to calibrate the flange distance because this technique doesn’t rely on the prism and mirror assembly. So long as your matte screen and loupe contraption is laying flat on the film plane then you should be OK. I’m sorry if I’m just leaving all this to your brain to process because I don’t have a picture to illustrate how this is done but I will update this as soon as I can so just wait!

The most fancy way for DIY tinkerers is to use 2 sets of camera bodies facing each other. I will show you how to do this once I have the time but the above mentioned methods are more than enough for most things. Mirrorless cameras are also useful but you’ll have to be very careful with choosing the adapters. Majority of the adapters sold online are from the cheap no-name brands and they aren’t really accurate to say the least. For example, I got a cheap adapter for my Sony A7 so I can use F-mount lenses with it. While I am sure I calibrated the lens’ infinity focusing properly and it works perfectly on Nikon cameras, I can’t achieve the same thing using my Sony A7 and cheap adapter combo. Caveat emptor! I am sure that there are better adapter that were made to higher spec but they will cost a lot considering that this is just a dumb metal tube. You are paying for quality control.

Methodology:

Now that I have mentioned why this thing happens, where it can be adjusted, what you need to fix this and when it’s OK to do it I will now show you how it can be done. You will need access to window if you’re indoor and it will helpful if the sun still shines because it will enable you to use faster shutter speeds to cancel-out vibration or shaky arms. It’s not necessary to use a tripod unless the lens you are testing is too heavy.

First, locate a far-away subject that is ideally 4-7km or more. The subject can be a pylon, a building or a billboard. Anything is OK so long as it has clear and definable features on it such as hard lines or text in the case of billboards. The subject should be static, clouds or trees will be useless because they are either moving or they don’t have clear defined silhouettes and details. I guess this is just commonsense but I will just warn you anyway.

Second, with your lens attached to your camera focus on that far-away subject until it is focused. Make sure that the lens is wide-open and not stopped-down because you do not want DOF to alter your tests. If you are using a digital camera, take a test picture with a reasonably fast shutter speed like 1/250s or more so movement isn’t taken into account. Check your picture and see if that far-away subject is perfectly in-focus. Repeat until you are satisfied with your results. While doing this, you’ll want to rely on the tiny dot on the viewfinder for focus confirmation. If you are using the prism and loupe method then you would want the prism to be clear. You will have to do this a couple of times so be patient. Just to be safe, focus on something that is exactly 2m away from you and make sure that the scale points to about 2m. Do this test on objects that are 1m, 5m or whatever distance you are using as reference and it should be very close if not spot-on. If you’re not using metric then just use feet for your measurement. I know it sounds rigorous but that’s how I do it. I am not a collector and I use my lenses so they’ll have to perform properly.

Next, mark where it should be using a Sharpie marker. I usually draw a line as a guide so I will know where things should be when I achieved “perfect” infinity focus. After doing this, move your focusing scale or distance scale (assuming they are loosened) until they are lined-up properly with the infinity symbol squarely in the middle of the centerline. I am very careful while doing this step because there is a chance that you will accidentally nudge things by just a little bit and your infinity focusing can be thrown off-position. Do this carefully and then tighten or secure the scales properly. Do a series of tests again to see if the focusing is still OK and if it’s off then you should go back a step and repeat. This is a very tedious job and it can take me several minutes to do this. A pair of steady hands is essential so go about doing this carefully. You’ll be rewarded after all the frustration!

Finally, after confirming that everything is working to your satisfaction, use a bit of nail polish or lacquer to secure the screws or tape the scales in the case of lenses that use this method to secure it. Reassemble your lens completely and you are done. Good job!

Conclusion:

That’s it for this post. I know this sounds technical but this is the easiest way that I know. Of course, factories and workshops use higher-end ways to do this but we are just doing this out of our kitchens or living rooms so these methods will suffice. I am confident that the methods I mentioned are good enough for many people and I hope that this answers many things. I should have wrote this earlier on but I never felt that this required a post of its own until now. I will be updating this continuously so please come back and check if there’s anything new or just follow me on facebook to get updates. Thank you again for reading this and I hope that you learned from this. I am now hitting closer to 20K views a month! My aim is to hit that by the end of the year as a goal for this blog so if you liked it, be sure to share this on social media! I am also considering making a twitter page for this blog. My personal twitter account only contains tweets and pictures of women so I want to use twitter for something more productive. I will update you when I made an account. Thank you again and please don’t get tired of supporting my page. There are things like this that people don’t really talk about online and you can only find it here. See you, Ric.

Help Support this Blog:

Maintaining this blog requires money to operate. If you think that this site has helped you or you want to show your support by helping with the upkeep of this site, you can simple make a small donation to my paypal.com account (richardHaw888@gmail.com). Money is not my prime motivation for this blog and I believe that I have enough to run this but you can help me make this site (and the companion facebook page) grow.

Helping support this site will ensure that this will be kept going as long as I have the time and energy for this. I would appreciate it if you just leave out your name or details like your country and other information so that the donations will totally be anonymous it is at all possible. This is a labor of love and I intend to keep it that way for as long as I can. Ric.

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2 Comments (+add yours?)

  1. Trackback: Repair: Nikkor 105mm f/2.5K | Richard Haw's Nikon Maintenance Site
  2. Trackback: Repair: Nikkor-N 24mm f/2.8 Auto | Richard Haw's Nikon Maintenance Site

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