Beware; bad copy lens

[JD Winata]

Sharing info , kadang dalam perakitan lensa , semua membutuhkan presisi yg luar biasa toleransi nya , kadang tidak semua lensa equal dalam performance nya . Lensa mahal lbh aman krn quality control yg lbh ketat .
Contoh andaikan ada lensa dgn 7 group lensa dan 11 elements dimana 1 element lensa aja missed terpasang 0,5mm ,efeknya udah parah utk ketepatan AF hasil fotonya nanti.

Utk mengetest lensa good copy atau tidak adalah dgn cara menyetel di focal length terjauh (utk zoom lens) dan di aperture di f terbesar (angka f terkecil) semisal 24-70f2.8L ,set di f2.8 dan jarak 70mm.
Objeknya taruh 3 pensil berjajar dgn jarak 2cm antar pensil berbaris ke belakang , focus ke masing2 pensil dari jarak terdekat , dan shot 3X (1 shot utk masing2 pensil ) kalo perlu pakai tripod agar yakin.
Kalo bad copy maka akan terlihat missed focusnya deh.

Lensa L yg sering dijumpai ada bad copynya :
17-40f4L , 24-70f2.8L dan 16-35f2.8L dan EF100-400L

Lensa third party hampir dipastikan sering ditemui badcopy kayak gini

[sigitsay]

Bro JD, sebenarnya yang disebut badcopy apa cuma masalah focus aja?, ada yang lain ga. misalnya masalah kontras, dll. Thanks masukannya bos

[JD Winata]

So far sich bisa juga sampai separah itu ya ,dalam batch manufakturing ,proses pembuatan lensa per elements pasti dah system mesin , cuma proses pasang nya aja yg bisa gak precise maka terjadi distorsi chromatic aberration krn bias warna2 dari spektrum cahaya jatuhnya gak pas krn pemasangan tdk presisi.
Badcopy umumnya hanya krn AF nya missed aja ,cuma kalo mau di manual focus bisa tajam focusnya , kadang hanya missed dikit cuma bisa keliatan beda antara agak tajam dgn sangat tajam

[hengky]

Thks for the tips pak hans. useful tips this is...

[pethouq]

wah.. banyak juga hal2 yng mesti diperhatikan dan dipelajari oleh para yunior.. thanks for sharing..

[dony]

kalo lensa back/front fokus bisa diperbaiki gak boss ? apa cukup dikalibrasi saja ?

[JD Winata]

Kalo kamera kadang ada bad copy krn dudukan sensornya gak pas ketinggiannya ,bisa dgn mudah diadjust oleh teknisi Datascript atau Interdelta .
Cuma kalo lensa dudukan salah satu elementnya gak pas maka kudu dikirim balik ke manufaktur

[dhlee]

Pak hans, balikin ke manufacturer gimana caranya? hehe apa perlu kita mengeluarkan biaya tambahan lagi untuk hal tsb? mending jual aja ya kalo sampe dapat bad copy

[newb4ev3r]

Baru baca review terbaru Canon 1D MKIII. Ini ada feature yang menarik:

Back Focus Adjustment

Then there's the till-now controversial issue of back focus. It seems that over the past couple of years whenever a newbe has a focusing problem he blames it on backfocus – best described as a fault where the camera focuses slightly in front of or behind the point that it should. Is back focus a real issue? Yes, it is, though likely nowhere near as common as reading some discussion boards would have you believe.

It's actual cause has been described to me this way. All cameras and lenses are built to be within a certain tolerance range when it comes to the accuracy of production alignment. Let's say that the range is an arbitrary scale is +/- 5. If the stars are in their proper alignment you'll end up with a camera that is +1 and a lens that is -1, for a perfect match. You might even have a camera that is +3 and a lens that is -2, and still be within the manufacturer's tolerance.

But, what happens if you have a camera that is -4 and a lens that is -3? Both items are within the manufacturer's tolerances, yet when used together combine to produce a focusing error. This is what is widely known as back focus.

With the 1D MKIII Canon recognizes this issue, and has come up with a solution. They call it AF Microadjustment, and it's available under Custom Function III-7. This allows setting focus adjustment by +/- 20 points (arbitrary units). A good way to do this is to try focusing using center single spot on a ruler at 45 degrees to the camera plane. This will allow you to easily see any focus shift and also in which direction it is occurring.

Doing the adjustment is a trial and error processes, but once done it can be saved in the camera's nonvolatile memory and assigned to a particular lens. A maximum of 20 lenses can be calibrated this way and stored in camera. Just the project for a rainy afternoon.

Note though that only one instance of any particular lens can be saved in memory. So, for example, if for some reason you have two 50mm f.1.4 lenses, the setting for only one of them can be saved.

http://www.luminous-landscape.com/re...II-Field.shtml