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07-13-2009, 03:09 PM   #1
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FA 28-70/f4 question

Hi guys,
The LBA is really contageous. I told myself quite firmly that I do not need any new lenses, but there was an ad on a local Craigslist for MZ-5 body with FA28-70/4 for mere $99 and I couldn't resist. I do not need the film body as I have three of my own collecting dust in the drawer. However, I wanted the lens. I met with the seller and tried the lens on my K20 at fully open aperture as I figured if it's good at f4 it will be better at smaller apertures. I took a few shots and liked the result - great optics. Lens was clean and in a good shape. I offered the guy $50 for the lens and he accepted. When I tried it at home I found that it was greatly overexposing at smaller apertures. To make it short, I discovered that the aperture blades were oily and stuck permanently at f4. The aperture lever moves but doesn't spring back. The lens is quite sharp at f4 and probably can be used as such, but I still would like to repair it. Is this costly? Can it be done at home as DIY project? I found few links to repair procedures of K lens, but nothing for FA. Another anomaly I found is that when I shoot at 28mm, the EXIF shows 31mm. Is this behavior normal for this lens? I am debating whether to fix the lens or try to ask for a refund (the guy advertised it as"excellent").
Thanks,

07-14-2009, 11:23 AM   #2
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I have never taken this lens apart, but I would say a repair is at least moderately difficult. Zooms add an extra layer of complexity, and an AF zoom has a lot of small parts. You might be able to take a shortcut and only remove the rear light shield and entire rear lens group. That would give you access to one side of the aperture blades, which may be enough to clean them. A lot depends on how the lens is constructed - sometimes it's very difficult to figure out how they put the lens together. It shouldn't require many tools, maybe only one screwdriver, but you'll need patience.

The EXIF should show 28mm. That may also be a result of migrating oil inside too. The contacts that determine focal length are usually just under the lens barrel and not too hard to access and clean.
07-14-2009, 12:19 PM - 1 Like   #3
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This is what you get when opening a 28-70/4 :



So, you are warned.

George
07-14-2009, 02:49 PM   #4
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Wow, all those parts and yet, it looks like the rear elements and aperture blades are still in one assembly!

The parts that report focal length to the camera are in the tray, upper right. Thin metal fingers brush against a pattern of electrical contacts on a part wrapped around the front element.

07-14-2009, 04:02 PM   #5
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QuoteOriginally posted by Just1MoreDave Quote
Wow, all those parts and yet, it looks like the rear elements and aperture blades are still in one assembly!

The parts that report focal length to the camera are in the tray, upper right. Thin metal fingers brush against a pattern of electrical contacts on a part wrapped around the front element.
Yeah, here I have another picture of that lens :



The contact fingers are already removed here.
This lens is not particular difficult to open, just have the right tools, and remember how it disassembled (make lots of pictures during the process to be sure).
And never use force ! Just find the place where the hidden screw is.

George
07-15-2009, 11:41 PM   #6
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Original Poster
QuoteOriginally posted by glasbak Quote
This is what you get when opening a 28-70/4 :



So, you are warned.

George
Thank you, George and everybody who answered my question. After seeing the pile of parts in your photo I have no desire to venture this way. I have very little patience and a poor eyesight so this would wreck my nervous system. I thought there was an easier way to disassemble the lens.
11-29-2009, 03:23 AM   #7
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help to mount a bejersey (smc FA 1:4.5-5.6 80-320mm)

Hello guys,
I'm new in this forum, and I have a "little problem" trying to mount a bejersey -> Pentax smc FA 1:4.5-5.6 80-320mm
Because a problem of electric contacts, prior I tried cleaning and tightening the screws does not solve anything, and then because the price to resolve will be similar to a new lens... I dismounted it even more ...
Please if someone had a diagram I would appreciate very much.
First of all, say that there are parts that are not fixed and are not disassembled and were mounted look like ...
Are not fixed (see photo): "11", "2" and especially "1" is not exactly as mounted and its function, although they were above the "8" -near number-.
If anyone would think the same thing to me, tell him to be careful with small parts, which fall easily into.
The contact pins "11" for me that did not arrive, I stretched a little the docks.
Thanks for your support
joan
PS: also in other forum Ayuda - cómo montar el objetivo 80-320 (antes: uso objetivos FA con una K7)
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