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Old May 18, 2006, 3:51 AM   #1
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Hi guys,

I have a cross X version 50mm f1.7 from ebay a while ago. I notice any picture that shot over f2.8 is badly overexpose. Anyone beyond f2.8 is fine.

What's wrong with this lens? Thanks..
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Old May 18, 2006, 2:47 PM   #2
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What settings are you on? ISO, EV, exposure mode, ect. Could be pilot error.
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Old May 18, 2006, 2:54 PM   #3
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Your aperture blades may be stuck open. It's a common problem with older 50mm lenses. Sometimes, you'll see oil on the aperture blades (a telltale sign that something is wrong).

If that's the case, and you use smaller apertures (higher f/stop numbers), the photos will be overexposed at the shutter speeds selected by the camera (since longer shutter speeds are needed for smaller apertures and the camera thinks the aperture is stopping down).

Try setting the aperture smaller (for example, f/22) in Av mode and use Depth of Field preview and see if you can hear the aperture stopping down with your viewfinder getting darker. If not, your aperture blades are probably stuck open.

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Old May 18, 2006, 3:31 PM   #4
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Jim: Speaking of the aperture blades being stuck brings up another point of interest. Repairing them.

Whats involved?

Whould you be skeptical of buying that used lens?
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Old May 18, 2006, 3:49 PM   #5
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I've never attempted repairing a lens. I have enough trouble replacing a watch battery. ;-)

Here are some diagrams that may be helpful.

http://www.pbase.com/pganzel/disasse...xxum_50mm_lens

If you scroll down below the photos to the forum area, you'll also see some comments from users that cleaned oily aperture blades.

As for used lenses, I've never had any problems (knock on wood)

Most of mylenses were purchased used, including a Minolta 50mm f/1.7 that I got for $49 on Ebay as part of a package that also had a working Minolta Maxxum 7000 and a Minolta1800AF flash.

But, I have seen more reported problems with sticky aperture blades with the 50mm lenses. If you buy from one of the larger vendors of used gear (for example, KEH), they'll usually check lenses for oily aperture blades and note those kinds of problems in the item's listing. A larger vendor usually includes a warranty on used gear, too (KEH has a 60 day warranty on used gear).




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Old May 18, 2006, 4:03 PM   #6
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adeleide

I wouldn't automatically assume that you've got sticking aperture blades. But, it is a problem I'd check for (see my first post in the thread).

As lomitamikementioned, it could be a settings issue, too. If light is too bright and you are shooting at wider apertures at higher ISO speed settings,you can reach the fastest shutter speed the camera is capable of. At that point, you'll get overexposed photos until you either lower the ISO speed or stop down to smaller apertures (higher f/stop numbers).

You should see a flashing shutter speed indication in the viewfinder when taking a photo if that's the case (when your ISO speed and aperture settings would needa faster shutter speed than the camera is capable of). If you check the EXIF in an overexposed image, you'd probably see 1/4000 second, too (the fastest shutter speed the camera is capable of).

My guess from your description is that you mean apertures smallerthan f/2.8 (higher f/stop numbers)were overexposed. If that's the case, it's more likely sticky aperture blades if wider apertures (smaller f/stop numbers) are correctly exposed.






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Old May 18, 2006, 4:46 PM   #7
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Having the aperture cleaned of oil and the lens reassembled is a fairly cheap repair for a camera shop (called a CLA). For a prime lens, it should cost you $50-60 U.S. You can get a used 50mm prime for just a bit more but you never really know how long you'll have it before it also needs to be serviced. If that is your issue, I would take it down to the local camera shop and have them fix it.

I have heard that leaving a lens in a hot car can cause this (the oil used to lubricate the focus mechanism bleeds onto the aperture) and that newer lenses use better synthetic oils that aren't as likely to bleed when hot. I've never personally taken one ot these autofocus lenses apart, though I'd love to just to see how things are put together.

I use a differentway to check the aperture than mentioned above. You need a genuine Minolta rear cap for the lens (it has a tab that opens the aperture when it is properly installed). Looking through the front of the lens, install the rear cap and back it off a few times, the aperture (iris) in the lens should move freely througout its range and appear free of oil. This moves a bit slower, and gives you the benefit of moving the aperture through its whole range, which it may not depending on your settings on camera. The apreture should be very responsive, "snappy". If you aren't sure it's responsive enough, put it into the fridge (not the freezer) for a couple hours and repeat the test. Cold oil is stickier that warm oil and makes a sticking aperture easier to spot. A dry (good) aperture will not slow down at all when cold but an oily one will.

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Old May 18, 2006, 10:57 PM   #8
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Hi guys, thanks for your valuable opinion & suggestions. I use Av mode all the time, and I was shooting an indoor wedding with ISO1600, focal range f1.7-2.8 with built in flash. Exposure compensation -1 & +1 accordingly to suite indoor lighting. When I use f3.0 onwards, its overexpose...

However, when I put on my friend's 50mm on my camera, it didn't happen. :?


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Old May 18, 2006, 11:27 PM   #9
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Well, with my 5D, the built in flash seems to throttle down well enough to use wider apertures with ISO 1600 at relatively close ranges. But, I wouldn't expect superb flash accuracy at ISO 1600.

Have you got the flash mode set to Pre-Flash TTL versus ADI? I haven't noticed much difference in them. But, you're supposed to set it to Pre-Flash TTL with an older non D lens (the camera defaults to ADI).

It's more likely the aperture blades sticking. I'd try it in better light using lower ISO speeds withouta flash and see if you get the same symptoms (more overexposure as you stop down theaperture). If so, it's probably the lens.


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Old May 23, 2006, 6:51 AM   #10
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Hi guys,

After getting advise and help from your input, its confirm that my 50mm f1.7 aperture blade full of grease and causing it open wide even with small aperture. I have gone through the repair menu but I'm not experienced enough to handle that.. :lol:

So, I will be sending it for repair to my friend's shop instead.

Thanks again. Have a nice day

Cheers,
Adeleide
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