Дальномер

Качайте сервис-мануал, пока ссылка жива. И пост о корректировке фокуса.


Diagnosing Contax G2 Focus Issues

Hey everyone! I’ve seen some people having focus issues and I thought I’d share a bit of what I’ve learned while trying to figure out some of my own. Hope this is helpful. Ive included a link to download the G2 repair manual. As fewer and fewer people are working on them I feel like it’s important to get the manual in as many hands as possible. Hopefully some of you are more technical than I am and can help figure some stuff out

(Note: I originally posted this on a Contax G1/G2 group, so please don’t feel like I’m talking down to you all if it seems like I’m explaining too much)

So, yeah, focus issues with the G2 can be really frustrating. It's hard to diagnose the problem because there are so many variables that can affect focus. In order to figure out what's wrong you have to understand how the camera focus system works.

The G2 is an auto-focus rangefinder, meaning that it uses sensors to determine the distance to the subject and then drives the lens to the position where a subject at that distance should be in focus. Focus errors arise if:

1. The subject distance is measured incorrectly
2. The point where the lens is focused correctly and the point where the camera thinks it *should* be focused correctly do not match.
3. The lens is not driven precisely due to mechanical issues with the lens and/or camera body AF motors.

There are actually two completely separate distance measuring ("rangefinding") systems on the G2. The phase detect rangefinder system (called the "passive" AF system in the manual), which calculates distance by measuring the overlap between images seen by the two middle sensor windows on the front of the camera, and the "active" infrared system which projects and measures an invisible infrared beam using the two outer sensors. The IR system is "actively" monitoring subject distance repeatedly while the camera metering is active to estimate the distance and then when the shutter (or back button) is half pressed to focus the phase detect (PD) system kicks in and fine tunes the focus position. If it's too dark or your subject lacks contrast and the PD system can't lock on then the camera relies entirely on the IR reading, which works with subjects that reflect IR light to a distance of about 3 meters.

To check the distance accuracy of each system put a piece of black tape over the other system's windows and see if the AF reading on top of the camera matches the measured distance. Check a few different distances. Switch the tape and check the other system. If the distances are off it could be that impact has knocked the sensors out of alignment. If it's not too bad this can possibly be fixed with software calibration without opening the camera body. The process is not simple or intuitive, but theoretically it can be done without sending the camera away. If you want to try, I've included a link to download the G2 service manual and a spreadsheet that I made to handle the calculations.

**WARNING!**If you are not meticulous in following the instructions it's possible to really screw up your camera. Always write down the previous values before you change anything so you can roll it back if necessary. Personally, I haven't had very much success with AF calibration. There are a couple vague points in the calibration instructions (handwritten modifications in my copy of manual that I'm not sure are correct) but I think that the main problem with mine was related to this next point:

- The AF systems rely on temperature sensors (thermistors) to adjust for the expansion/compression of components in different ambient temperatures. As I understand it, thermistor response can drift over time and the severity of the drifting is accelerated by moisture/humidity. If there is a lot of humidity damage the board will need to be replaced. If the drift is minor the thermistor can, theoretically, be recalibrated and restored to accuracy by comparing the actual temperature to the reported temperature and adjusting the calibration coefficient. There are settings related to this in the camera’s “manual adjustment mode” UI menu and data read-outs for the temperature, but there are no instructions and it's very confusing. I'm really not sure if I understand it properly. If anyone is an electrical engineer and figures it out let me know.

Anyway, If the AF distances do match then the problem could be the lens. Sometimes people have issues with focus and try to fix it by adding or removing shim rings in the lens. This might work in some cases, but if the lens is used with another body of course the focus will be off. If you aren't afraid to monkey with your lens you can take the front off without too much trouble and add/remove shims (using bits of brass shim material with holes drilled). If you do this and it doesn't work though, please don't sell your lens on eBay afterwards.

Here's the G2 Service Manual. Please ignore any notes I've added to the PDF. Some of them might be helpful, but I'm pretty sure others are straight up wrong. Notes written in pencil were there when I first received the manual.

And for the brave souls who want to try their hand at focus calibration here's the spreadsheet I made to automate the complex hex/decimal data calculations. It's still not a simple process, but hopefully this is helpful:

https://www.dropbox.com/s/hkc20ugmzd7bk ... Manual.pdf

https://www.dropbox.com/s/f8t7fo71638sb ... or.numbers

Сталкивались с проблемой фронтфокуса на G2 с объективами Sonnar 2,8/90?

какие были неисправности и что было сделано и сколько денег взяли?

я вам кстати вопрос задавал на который вы мне не ответили

зы.
вообще вам нужно конкретизировать проблему.
потому что на данный момент вы обозначили проблему так:
на всех камерах г2 возникает фронтфокус с любым 90мм.
читается так потому что вы назвали это "проблемой" а это слово обычно применяется к общеизвестным массовым поломкам. и сказав во множественном числе "объективы" вы обозначили что дело не в одном экземпляре а со всеми.


а автофокус как работает в этих камерах описано выше по-английски.
и вы должны понимать что если речь идет о любых 90мм на конкретной тушке то это нужно через сервисное меню поправлять настройки фокуса для 90мм.
в камере эти настройки применяются к любому 90мм. к каждому объективу свои настройки по фокусу в зависимости от дистанции.
либо это может быть сбит рабочий отрезок у камеры и нужно шайбами юстировать рабочий отрезок. но тогда это будет с любым объективом.
просто на 90мм сильнее всего будет заметно малейшее смещение.

если речь идет о том что ваш 90мм на нескольких камерах промахивается, то это щетка либостирается в энкодере либо я не знаю что, удар может быть был.
и это исправляется юстировкой рабочего отрезка линзблока.

а если речь о том что на любых г2 с любыми 90мм есть проблема фронтфокуса то это остается только гадать какая из перечисленных причин может быть в конкретном случае.

видите сколько вариантов мне пришлось перебрать в голове чтобы понять что вы имеете ввиду и как важно точно указывать на проблему?

если речь о том что у вас мажет 90мм, то так и нужно писать - "у меня фронт фокус на 90мм".

и вы должны понимать что если речь идет о любых 90мм на конкретной тушке то это нужно через сервисное меню поправлять настройки фокуса для 90мм.