[bygp]

I use this K lens with my K200D and it gives very nice color, sharp photos with also great bokeh, all is right if I take short or mid range photos,
but if I want a landscape, focusing on infinity, I can't get a sharp photo, even at 1/4000 or f/22.
I know this is not due to my camera as I have no trouble with the SMC 18-55 kit lens.
The chinon lens was bought on e-bay and looks realy in mint condition, no scratches nowhere, no dust, all seem like new.
I tried with or without the cokin skykight filter I have, same results.

Any advice ?

(you can see a green plant taken at short range in my album, very sharp rendering)

[manntax]

Best would probably be to contact the seller and have it repaired or returned. It looks like your lens has got the infinity focusing not calibrated properly - unless it focuses past infinity , in which case you would need to apply caution to not over-focus past that sweet point. If it was me I would probably just return it and got another from reputable seller. These lenses are fairly popular - although I agree if your copy is particularly good optically, you might want to have it repaired instead returned (the sample variation among these lenses is very wide from rubbish to excellent).

[bygp]

Thanks for the advices, I won't send it back as I got it for a very low price and it takes very good shots at mid range. Repairing it would cost 20 times what I paid so...
What about calibrating the focus ring ? Do you need to dismount the lens for that ? Can't it be done with good tools ?

---------- Post added 08-21-15 at 02:26 PM ----------

I found this small tutorial, but unfortunatly, my lens focus ring does not have any locking screw or any type of windows when you slide the rubber away...

---------- Post added 08-21-15 at 02:27 PM ----------

Calibrate the focus ring of the Samyang 14mm F2.8 | DSLR Astrophotography

---------- Post added 08-21-15 at 02:40 PM ----------

Here is an example, this photo was taken with focus on infinity (although not using the smallest aperture) and as you may see, the door is blured, the max focus range seems to be at 10-20 meters, when seting aperture to f/22 I can get sharp focus up to about 100 meters but further it becomes blured... :/

[stevebrot]

What about calibrating the focus ring ? Do you need to dismount the lens for that ? Can't it be done with good tools ?

With appropriate tools you could disassemble your lens, though you might want to check a few things out first.

• Does the focus ring actually turn to the infinity mark?
• Does the lens focus closer than the indicated minimum focus distance?

If yes for both questions, chances are good that the focus ring was not properly indexed after a service attempt (inept reassembly). If no for both, chances are good that there is internal damage that prevents the focus mechanism from completing its full travel.


Steve

[aleonx3]

Before you do anything, check first if you have BF issue with this lens on the camera. I would try to focus on something closer (an object about 10 feet) to ensure the focus is on target. If the focus seems to land on something beyond your focus point, then you have a Back Focus situation with this lens (Note, this is by lens case as it may only happen to this lens). Looking at the picture you posted, I don't see anything in focus, so the focus could be beyond that door.

[bygp]

@stevebrot ; yes it does go to infinity mark. For your second question, I just tested this with a 500 mm ruler, when the ring is exactly on 0.45m I can focus at pprox. 0.35m (between the front lens and the subject), IDK how to calculate this distance, is it from the front lens or from the viewfinder lens ? If it's from the rear of the camera, then the focus distance seems ok at that range, if it's from the lens then it is totally de-calibrated.

@aleonX3 : no, this picture was resized via flickr and is not that sharp but the focus is approx. at the 2nd window (where wall angles are very sharp), IDK what is BF but I manualy focus and the photos are exactly as how I focused and as how I've seen the scene in the viewfinder.

---------- Post added 08-21-15 at 04:44 PM ----------

(but it's quite hard to see in the viewfinder if a 500m or more far subject is very sharp or not)

---------- Post added 08-21-15 at 05:04 PM ----------

@stevebrot ; yes it does go to infinity mark. For your second question, I just tested this with a 500 mm ruler, when the ring is exactly on 0.45m I can focus at pprox. 0.35m (between the front lens and the subject), IDK how to calculate this distance, is it from the front lens or from the viewfinder lens ? If it's from the rear of the camera, then the focus distance seems ok at that range, if it's from the lens then it is totally de-calibrated.

@aleonX3 : no, this picture was resized via flickr and is not that sharp but the focus is approx. at the 2nd window (where wall angles are very sharp), IDK what is BF but I manualy focus and the photos are exactly as how I focused and as how I've seen the scene in the viewfinder.

---------- Post added 08-21-15 at 04:44 PM ----------

(but it's quite hard to see in the viewfinder if a 500m or more far subject is very sharp or not)

According to what I've read here : Nikon | Imaging Products | DSLR Camera Basics | Minimum Focus Distance on how to calculate minimal focus distance, all seems right, 0.45 on the ring = 0.45m distance. Anyway, I'm quite used to repair electronics and precision equipments, I just need to find a technician manual in order to do things right, I'm pretty sure you don't have to fully disassemble the lens to calibrate the ring, as these lens need to be assembled before calibration. The question is : how to unlock and lock the focus ring as I'm pretty sure it's stoping 1° or less before the right infinity position.

---------- Post added 08-21-15 at 05:09 PM ----------

here is the exact model I have, all made of steel : Chinon 50mm f/1.7 Auto MC, Overview, Tech Specs, Sample Photos | Photo Lenses Database

[stevebrot]

IDK how to calculate this distance, is it from the front lens or from the viewfinder lens ?

From subject to focal plane (45.5mm behind the lens mount face). If you have a bonus 5cm close focus, that is good indication that the ring and/or the focus helicoid threads themselves may be offset enough to account for the shortened focus you are experiencing.

Access to the adjustment is probably through the front. You would need to remove the lens face plate and probably the filter thread as well to gain access to the retainer screws. This is generally done using a chunk of soft rubber. Both the face plate and filter thread should simply unscrew. The screws below are NOT Phillips head. They are JIS cross-point and require a special screwdriver.

You might want to send a private message to forum user dcshooter. He has broad experience on lens disassembly and may be able to provide pointers.


Steve

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Last edited by stevebrot; 08-21-2015 at 05:51 PM.

[bygp]

From subject to focal plane (45.5mm behind the lens mount face). If you have a bonus 5cm close focus, that is good indication that the ring and/or the focus helicoid threads themselves may be offset enough to account for the shortened focus you are experiencing.

Access to the adjustment is probably through the front. You would need to remove the lens face plate and probably the filter thread as well to gain access to the retainer screws. This is generally done using a chunk of soft rubber. Both the face plate and filter thread should simply unscrew. The screws below are NOT Phillips head. They are JIS cross-point and require a special screwdriver.

You might want to send a private message to forum user dcshooter. He has broad experience on lens disassembly and may be able to provide pointers.


Steve

thank you very much for your pro answer, I have very good small PH screw drivers and I will buy the needed JIS once I can see the screw heads. Will do a last test shoot this morning at min. aperture and start "surgery". I would like to keep this lense as the lenses and the body are all in realy mint condition.

[bygp]

I found this small guide on how to remove the front plastic ring but mine realy seems to be stucked or to have been force-screwed, not able to move it at all atm :/

[bygp]

Thanks to you steve, I finally fixed it and now have a perfect infinity focus !

It was not so easy though, for those who have the Auto MC 50mm 1.7 with the orange and green front plastic ring :

- this ring is not screwed but glued with neopren, you need a tiny flat screwdriver to remove it and you'll easily scratch a little the filters holder
- once removed, you have to remove another metal protecting part that has 3 philips screws
- once this done, you can access 3 not headed locking screws, you must unscrew them enough to let the focus ring move alone
- what I did is I went further than infinity in a first step (when ring is on infinity stop), and then turned the ring while pressing on it towards me until I got the sharpness background I could get (with camera LCD zooming). Once found, I turned gently the ring avoiding it to change focus (free rotation) until reaching the infinity stop. Then screwed back the 3 lockers and mounted all covers, done

These are the pictures taken before and after the repair, both with focus on infinity :



---------- Post added 08-22-15 at 02:24 AM ----------

of course these are centerd crops of about 10% of the whole photo, both are taken at f/4 for sharper rendering

---------- Post added 08-22-15 at 02:50 AM ----------

NB : the screws I found were all philips, so the repair costed me nothing except time

[stevebrot]

Thanks to you steve, I finally fixed it and now have a perfect infinity focus !

I just provided hints. You did the work!


Steve

[bygp]

maybe i'll have to re-open it, it seems I srewed back the lockers a bit too hard, ring gets harder to turn around 1 meter focus, but that's a minor issue compared to infinity targeting 10-15m range