images overexposed with a100 and minolta af50 f1.7

[starvy]

today was the first time i had ventured out in broad daylight with my new sony alpha a100 and the second hand

minolta af50 f1.7 lens. i had taken some shots over the weekend at a local festival. this was after dark and the

results in jpeg were quite impressive. however, today i found the lens to be struggling in such good light. i set

the camera at lo80 iso, aperture priority, dr turned to standars and was shooting around f8 to f16. however, each

shot was wildly overexposed. i could only get properly exposed pictures at f2 and maybe upto 3.2. but then the

picture quality was not good at all. i tried many variations, tried the camera on full manual mode, shuitter

priroty, different type of metering but no excuse. all the shots were over exposed.

 

i have not tried the kit lens closed down as yet. perhaps i ought to try that. is the minolta lens faulty,

perhaps the alpha 100 is doing something wrong?

[michael_hohner]

The aperture blades of the lens are sticky, and they do not close quickly enough or not at all. This is typically caused by oil seeping onto the aperture blades, a very common problem with the 50/1.7. If you have the courage you can disassemble the lens, clean the aperture and re-assemble the lens. The exact procedure is on the net (use Google).

[starvy]

mike,

thanks for that. i had been going through the manual for alpha a100 and the only thing i found that might be attributed a camera related setting problem was the iso setting. the manual says i should be using hi200 in good light conditions and low80 in bad night. hi200 apparently stops overexposure and low80 stops underexposure. i think i need to take out the camera again and see how it performs with this lens in good light. it might well be a case of sticky shutter blades, in which case i am quite annoyed :(

[ricardovaste]

Starvy,

 

Michael is right. It will almost certainly be sticky aperture blades. Where are you based? If you're in the UK I would fix it for free for you no problem. Otherwise, any good camera shop would fix it for you for nothing too expensive.

 

Best of luck,

 

Rich

[michael_hohner]

That's an easy test. Take off the lens, pull open the aperture on the lens (use fingernail or matchstick to move aperture lever), then let go. The aperture should snap fully closed immediately. If it's any slower, the aperture is sticky.

[paul_de_ley]

Would a simple test of the sticky blade explanation be to take some long exposure shots at night with f8 or higher?

[ricardovaste]

The depth of preview button is also useful for testing this on the A100 - save potentially getting dust inside the a100 if you don't have a body cap spare too.

[peterblaise]

The original lens rear cap closes the aperture when the lens is stored, and gives it a bit of exercise when putting the lens rear cap on and off.

 

I've not played with Sony-logo's rear-lens caps yet - do they also have the tab that operates the lens aperture?

[starvy]

hello richard

i am based in uk! i did the test that michael had suggested above with regards to pulling the blades back. guess what, it does not revert back to its original position at all unless i manually move it back! it appears that i can use the lens wide open or close to wide open but anything above 2.8 it struggles.

 

richard thanks for your kind offer. any help would definitely be appreciated!

 

thanks

[ricardovaste]

Hi Starvy,

 

Please email me: pasta_football_ilford@yahoo.co.uk. And we can talk about getting this lens fixed for you. I would be more than happy to help out a fellow a-mount photographer :), your other options are (a) doing it yourself or (b) paying a qualified technician to do it for you. I'm not qualified, but I'm confident with cleaning and reassembling lenses.

 

Rich

[starvy]

hi richard,

i sent you an email a few days ago. i wonder if you have received it as yet.

best regards