How to Repair a Zoom Telephoto Lens and Mount It on Your DSLR Camera

by tholopotami

51K5414

Intro: How to Repair a Zoom Telephoto Lens and Mount It on Your DSLR Camera


Telephoto lenses are expensive  and if you have  one intended for an older SLR camera, you may consider  using it with with your DSLR. My experience is that this is doable but there are a few critical issues that you have to deal with.

Contemporary DSLR cameras are rather unfriendly  to older lenses for different reasons such as the lens-sensor distance , the mounting mechanism or even the camera software.

It is important  to mount the old lens on the camera at the precise distance without damaging the internal parts..

In this instructable I'll show you how this can be done by a specific example using common tools and materials.

I picked this used and damaged telephoto from a street market.  It was a zoom 80-200mm F/4.5, ~400gr weight, with the  JCPenney  (an American multistore) brand on it  and the sign "made in Japan" . Even at its own time it would be inferior compared to those made by Yashica, Nikon or Vivitar with similar specifications.

It was practically separated in two and full of dust, but the external lenses did not seem to have any scratches. Initially I intended to remove the lenses for other uses but looking at it more carefully I realized that the mechanical problems could be fixed.

The challenge was to repair it and mount it on my Olympus E-420.


STEP 1: Preliminary Steps

Regardless if your lens needs repair or not,  this is what you have to do first:

Find out the camera-lens distance
  1. Attach the camera on a tripod and remove its own lens. Holding the telephoto with both hands in front of your camera with the setting of the telephoto at infinity, try to focus a very distant object. If you have a problem to keep the lens to the correct position use a paper inner tube but do not touch the internal parts of your camera.
  2. Rotate the focusing ring a few degrees and focus again. In the final construction it is better to set the infinite point a few degrees before the rotation limit. This will allow sharp focusing by leaving some space around the correct point.
  3. Focus on close objects. Try to find the minimum focusing distance available. In my case the distance  measured  was 1.7 meters at 200mm and 1.5 at 80mm.
Find/purchase the appropriate adaptor

A T-ring is the best type of adaptor for this work. It offers two possibilities for mounting a lens, either by using the 42M threading of the internal ring  or by removing the ring and fitting the tube on the main connector directly. The one shown here is the Olympus Four-Thirds T-ring for DSLRs which has a bayonette type mounting.

STEP 2: How a Zoom Telephoto Works

  • A zooming system transforms a parallel beam to another parallel beam of different diameter depending on its position (afocal operation).

  • A simple method to visualize this, is to think of the zooming system + the objective lens as a composite "objective". The effective focal distance decreases when  the components come closer.

  • Thus when we approach the zoom to the objective the focal distance decreases (ZOOM OUT) while when we retract the zooming system backwards, it increases (ZOOM IN). In the case of my lens the limits are 80-200mm.

  • Contemporary lens systems do not have a sliding tube as this one , they work mostly by turning a ring and move the objective lens away from the zooming system. An independent lens system is used for focusing (see the next design in this page).

STEP 3: Take It Apart ! (if Necessary)


Reasons for doing this:

  1. Repair mechanisms.
  2. It was exposed to dust for long and needs Internal cleaning.
  3. You want to see how it works.
  4. It is fun!
All the above were valid in this case. Primarily the objective lens part was separated by the main body. As I found out this happened because the  nylon washers connecting the lens to the  focusing tube were  broken and the tube  internally  was full of metal dust from bad contact.

Caution:

I do not recommend taking lenses apart in general. There are systems with 25 optical components , better not touch them. In this case the lens had about 5 optical components and the connecting screws where all 1.5mm and could be manipulated with medium difficulty. 

How to do it:


No violence and avoid coffee. Just use your hands and appropriate screw drivers. Do not force any other kind of tools (knives, pliers, screwdrivers) on the lens body.

Start disassembling the most obvious external parts and proceed with care as far as it is needed.

In the case described here it was only necessary to separate the three lens systems in order to clean them. However following arguments (3) and (4)  I went all the way down.

Do everything in a tray in order to avoid searching for 1.5mm screws on the floor.

Use gloves and fine tissue paper to handle the lenses.

Use toothpicks to align  tiny holes on different tubes.

If you cannot put it back together don't panic, leave it for another time.

STEP 4: Repair Work

Sliding mechanism

I had to make new nylon washers for two delicate screws that serve as guides to the external focusing/zooming tube. These have dimensions 2.5mm external diameter and 1.5mm internal and thickness 1mm. Fortunately an ink pen filling has a similar size and it fitted nicely. The tolerance was ~0.2mm.

Sanding

Some parts of the thin metal tubes were rough so they had to be sanded gently on a table with a 200 sand paper.

Grease

The Objective lens system stayed on a threaded part of the main body and a silicon grease was necessary there. This was done at the final stage of assembly after cleaning and mounting the lenses.

STEP 5: The Iris

If the iris is working then fine. In the case discussed here , the iris was in place and it is operational but it was obviously handled by a ring close to the camera which was missing. Although there was a way to do something similar I selected to immobilize the iris in the open position, by placing a plastic tube through an opening in the focusing lens compartment.

STEP 6: Build a Proper Mounting for Your Camera

  • The mounting combines the last component of the lens with the T-ring. These are connected by a brass inner ring using 2M and 3M screws. Since the part of the lens is thick enough (2.5mm) I selected to drill holes on thread them for 3M. The screws are placed from inside.

    • The internal diameters of these tubes are not equal , so I used 1mm steel collars to match them.

    If one has access to a lathe this kind of modification can be done in a better way. I think an inner tube is still the best method to connect the two parts but one could eventually use the M42 thread on the T-ring.

    The mounting shown here is rigid enough to support the weight of the telephoto (400gr). In fact I trust it more in terms of robustness  than I trust the rest of the lens!

STEP 7: Assembly and Focusing Range


Before the final assembly I mounted the lens to the camera a few times  in order to adjust the correct distance for focusing. I had to shorten  the lens part of the connector by precisly 1.3mm in order to get a focusing from 1.7m to infinity for the 200mm focal length. I also needed some space for fine focusing at the 200mm limit.

Before mounting, all parts were cleaned with alcohol and cotton. I used a special liquid and tissue paper for the lenses.

When placed on the camera, the measuring ring was adjusted in order to read  the  correct distance.

STEP 8: Measure the Field Size and Estimate the Magnification


Measure the field size

  • This can be easily done even indoors. Focus on a surface distant a few meters and shoot. Then measure with a tape the object distance and the length of the surface spanned in the photo. The lens I am describing has a field size of 5o x 3.7o

  • If you prefer to think of the field size as a distance, in the case of 5o , the length spanned when you are focusing on an object at 1000m is 175m.

  • Another simple method is to shoot the moon , which extends ~0.5o and then measure on the photo the relative size of the moon. This was done in the photos shown below. The moon was photographed a cloudy night, rain followed. I wanted to catch the seek and hide of the moon behind the clouds.

Estimate the magnification

  • This term is not very precise for cameras. The "magnification" of a 200mm lens on a DSLR can be estimated taking into account two facts. (a) 1x magnification in a conventional SLR corresponds roughly to 50mm focal length and (b) the sensor length of the DSLR is about 1/2 the 35mm film. Therefore in this case we have 8x magnification.

STEP 9: Estimate the Resolution Limit



What the resolution limit is
  • Think of a car coming to your direction on the highway with the lights on. When it is far away both lights are merged in one. You need to now what the maximum distance is for the two lights to be separated by an optical instrument (e.g. your eyes). This depends mostly on the size of the objective lens and is usually expressed as an angle.

Estimate the resolution limit
  • .My house in Athens is facing mount Ymittos on the top of which there is a group of telecommunication towers (see photo). The tallest one has two red lights  0.6m apart (measured with a telescope of known field size) while the distance to the tower is 7000m (measured from Google Earth). It is a perfect calibration target!

  • The angle of 0.6/7000 radians expressed in arcsec is ~18arcsec. The size of one pixel in a 10Mpxl sensor when this  lens is used,  corresponds to  5 arcsec and this means that the distance between the lights spans 18/5=3.6 pixels, quite a small number.

  • The theoretical resolution limit for such a lens (44mm diameter) is about 2.5 arcsec much smaller that what was estimated here. I don't think that this can be reached because there are other factors involved (complexity and quality of the lenses, atmospheric conditions) .



STEP 10: What You Can Do With It

  • In terms of magnification using this lens you have a viewing field through the camera as that through a set of  8x44 binoculars. Thus it is great for shooting distant objects. The moon is also an interesting target. Try also to shoot Jupiter with its satellites.

  • Besides long distance a telephoto is ideal for medium distances e.g. portraits or nature,  because of this nice blurring effect on the background. All the examples  shown here  were  shot at 2-4m.

  • Overall you can add one valuable piece of  equipment in your photo bag at a minimal cost.

14 Comments

ax89 13 years ago

Good instructable, and something to think about. I spent over $4k in 1980 dollars buying Nikon lenses and now they are useless with dSLRs. I was so angry with Nikon that I bought a Canon.

BigAndRed 7 years ago

You should of bought a Pentax then, same mount since the bayonet K-mount was brought out and with an M42 to K mount (another Pentax inovation) even the older screw mount lenses can be used on the latest Pentax DSLR bodies. I have a K3, K20, K10 and several old film cameras and all share the same lenses.

amclaussen 13 years ago

I say the Same... but for Canon!!!

My old Canon "New FD" lenses of the 80's, were made UNUSABLE in 90's Canon cameras, BY DESIGN! (INTENTIONALLY). They say it was made for technical reasons and blah blah blah, but the truth is other.

It is called "Planned Obsolescence" and is responsible for much of the waste and pollution damage caused to the planet, not to say the damage to our purse!

One thing is clear: Managers and engineers were not only good, but somewhat perverse: by redesigning the mount, they made the older lens unusable in newer cameras, just to keep people buying and throwing away perfectly good lenses, just to keep "updated with the latest model". It is the business model... I wonder how long that situation will be sustainable. But thanks to clever people at INSTRUCTABLES, we can have old things working again instead of making the trash mountain bigger!

tholopotami 13 years ago

I also have an SLR Canon and I have mounted several odd lenses on it through an M42 adaptor. I one case I had to remove the final ring of the lens (unscrewing) to gain some distance. If you have a nikon lense that is worth to be mounted on your Canon it may be possible through a T-ring adaptor because Canon has a smaller camera - lens distance. If I were you I would first google " nikon lenses to canon".

crazyg 12 years ago

just reassembled a lens of that type from a camcorder,want to make a shift tilt lens for slr,so far no focus on near or far,any dismantling the handycam was fun,i like your diagram

tholopotami 12 years ago

Sorry that you did not manage it yet. Let it aside for a while and think again. These things need patience!

craighanson 13 years ago

Vary Impressive As A action Photographer I enjoyed This article

tholopotami 13 years ago

I am glad you did. As you see this lens results on soft photos compared to the crystal clear result of the new lenses intended for DSLR. However I enjoyed remaking this lens and at the end you have a nice feeling that you know this equipment inside out!

amclaussen 13 years ago

Good Instructable...
your comment on the softness of your old Zoom lens is quite logical: in those old days a Zoom was very difficult to design and manufacture.

But NOT ALL old SLR lenses were soft; the best lenses of those years were even more detailed and precise than recent designs, no joke. You would be surprised to see better older lenses compared side to side to latest ones, unless, that is, you are comparing the VERY best of today lenses (like SOME but not all of the Canon "L" series) to old "L" series SLR lenses of around 1980's vintage.

Even when today Canon "L" lenses have Autofocus and some of them motion compensation, OPTICAL quality is NOT much improved, and in some cases, today some "L" series lenses are not up to the resolution and correction of older ones.
Now, compare the price of the better modern ones... you can purchase a new car for that kind of money! Another consideration is about the SPEED of today lenses: Young people think the 50 mm F 1:1.8 normal lens is very "fast" and good lens, (at least much better than the piece of junk of the "kit lens" sold with the Canon cameras, the cheaply made 18-55).

But older people like me know for shure the 50mm F1.8 was the cheap one in the 80's, because the 50mm F 1.4 was better built and better overall... and the
expensive 50mm F 1.2 L was a really extraordinary one, competing and slightly surpassing even the best German Leica 1.2 Noctilux, no less!

Now the surprise: Professionals have found the OLDER lens is not only much better built, more precise and has better materials than the actual 1.2 L; which has dissapointed some owners with Autofocus issues.

The plain truth is that both Nikon and Canon (and others) are now producing LESS than the best lenses possible, maybe because they want to have some "room for improvement", but they are concentrating their efforts more towards the electronics and sofware, than on the Optical quality of their lenses.

Soon, the sensors will continue getting better and better, and then the industry will be forced again to concentrate on Optical quality, but I seriously doubt they will return to the precise and durable construction of the 80's.

tholopotami 13 years ago

Thank you for the fruitful comment. I have also understood that contemporary lenses although they have more functionalities are not as clear as some older lenses. I have an example. I had CANON 1000F SLR with a 35-80/4-5.6 lens. Sometimes I substituted this with a LEICA 58/2 which was far superior. Speaking about this specific zoom 200of the instructable, I think its worse feature is the sooming part. It has two lenses that move independently on different paths and when you change the zooming , it slightly defocuses.

LittlestWorkshop 13 years ago

I like your little organiser. I often use ice cube trays for the same purpose, I number them so that I can create a simple index if I need to when dismantling complex things.

tholopotami 13 years ago

This small tray has the advantage that you can cover it with a tape and store it , something I did often during the repair. However it should be made a little larger and with more compartments.

twoherbs 13 years ago

Good use of older lenses and without breaking the bank account