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02-10-2009, 06:45 PM   #1
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Need help with A 100mm f/2.8 Macro

I just got the smc Pentax-A Macro 1:2.8 100mm.

The diaphragm is not snappy, but takes perhaps a third of a second or so to open up from a small aperture like f/22 to 2.8. It closes down faster but not swiftly.

I have not been able to take test photos in full daylight yet with a fast shutterspeed to see if the aperture closes down fast enough.

Anyone having experience with this lens? Is this behavior normal for this type of lens?

My D FA is snappy - the diaphragm opens up from f/22 in an instant.

02-10-2009, 06:53 PM   #2
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Sorry, I don't think it's "normal" for any lens. Needs a tune up, I'd say.

Regards,
Mike
QuoteOriginally posted by Ole Quote
I just got the smc Pentax-A Macro 1:2.8 100mm.

The diaphragm is not snappy, but takes perhaps a third of a second or so to open up from a small aperture like f/22 to 2.8. It closes down faster but not swiftly.

Is this behavior normal for this type of lens?
02-10-2009, 06:55 PM   #3
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QuoteOriginally posted by Ole Quote
I just got the smc Pentax-A Macro 1:2.8 100mm.

The diaphragm is not snappy, but takes perhaps a third of a second or so to open up from a small aperture like f/22 to 2.8. It closes down faster but not swiftly.

I have not been able to take test photos in full daylight yet with a fast shutterspeed to see if the aperture closes down fast enough.

Anyone having experience with this lens? Is this behavior normal for this type of lens?

My D FA is snappy - the diaphragm opens up from f/22 in an instant.
Congrats on the new lens! It's a great performer, probably the best 100mm macro lens by any lens/camera manufacturer (rated by a Japanese site ).

Seems your lens got sticky aperture blades problem. It's not common but does happen on some old Pentax lenses (it's very common on some Carl Zeiss Jena lenses like the 135/3.5, 35/2.4 and etc.). If you look carefully at the aperture blades, you might see some oily spots on them. I had several lenses w/ similar problem (including one A100/2.8 macro lens which I passed to my friend), but it's an easy fix by my experience. As a matter of fact, I just got an A24/2.8 from a forum friend a month ago which had the same problem. Only took less than an hour to open up, clean the blades, then put it back

Good luck.

Last edited by frank; 02-10-2009 at 07:40 PM.
02-10-2009, 07:18 PM   #4
Ole
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Thanks for the replies. I will bring it to my local camera repair guy then and have it fixed.

02-10-2009, 08:02 PM   #5
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QuoteOriginally posted by Ole Quote
I just got the smc Pentax-A Macro 1:2.8 100mm.

The diaphragm is not snappy, but takes perhaps a third of a second or so to open up from a small aperture like f/22 to 2.8. It closes down faster but not swiftly.

I have not been able to take test photos in full daylight yet with a fast shutterspeed to see if the aperture closes down fast enough.

Anyone having experience with this lens? Is this behavior normal for this type of lens?

My D FA is snappy - the diaphragm opens up from f/22 in an instant.
Ole, the same thing happened to my A100/2.8 Macro. Pentax fixed it, I believe they had to replace the spring, as well as CLA it for me.
02-11-2009, 03:12 PM   #6
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Ole. Once you get it fixed I think you will be well pleased with the A 100mm macro.

Tom G
02-11-2009, 03:25 PM   #7
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It's an inconvenience, but should not affect your photos at all.
Send it to Eric Hendrickson for repair and it will be good as new.

Chris
02-11-2009, 04:37 PM   #8
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QuoteOriginally posted by ChrisPlatt Quote
It's an inconvenience, but should not affect your photos at all.
Send it to Eric Hendrickson for repair and it will be good as new.

Chris
Actually, it is way more than an inconvenience. The aperture blades close lazily, causing over exposure.
It is a repair required issue before the lens is usable off maximum aperture.

02-11-2009, 08:57 PM   #9
Ole
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Exactly! The photo will be taken before the blades make it all the way down to f/22, so the result is overexposure!

The lens has been sent in - I'm looking forward to getting it back. It is a nice piece of glass!
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