Aperture won't stop down past ~5.6 Sigma Macro 90mm 2.8

fireforsave · 04-17-2020, 11:18 AM

I recently acquired a K Mount Sigma 90mm Macro lens. The aperture won't stop down past about 5.6 if turning the ring at a normal speed. I can get it to close a stop or two extra if I turn it a bit more rapidly. Could this be an issue with spring tension? There isn't any oil on the blades but might be further inside where I have not investigated. I've taken the mount off and it seems the aperture control arm isnt receiving enough pressure.

Last edited by fireforsave; 04-17-2020 at 11:25 AM.

**pepperberry farm** · 04-17-2020, 11:24 AM - **1 Like**

was the issue with the aperture ring explained before you bought the lens?

fireforsave · 04-17-2020, 11:33 AM

Originally posted by pepperberry farm

was the issue with the aperture ring explained before you bought the lens?

No, but I bought it from an individual along with a bundle of other stuff (maybe selling off family estate) at a steal of a price. I suspected some underlying issues, so I don't want to nickel and dime them.

Ontarian50 · 04-17-2020, 11:51 AM - **1 Like**

Nine times out of ten, such issues are due to oil getting onto the mechanism somewhere - it doesn't have to be visible on the blades to see a mechanism get sluggish or sticky. Chances are there's enough spring pressure to close the aperture, if it were bone dry.

It's a nice lens, and well worth getting serviced.

fireforsave · 04-17-2020, 12:21 PM

Originally posted by Ontarian50

Nine times out of ten, such issues are due to oil getting onto the mechanism somewhere - it doesn't have to be visible on the blades to see a mechanism get sluggish or sticky. Chances are there's enough spring pressure to close the aperture, if it were bone dry.

It's a nice lens, and well worth getting serviced.

Thank yall for the replies. This might be that 1/10th time. Controlling the aperture with a linkage further inside lens results in zero 'sluggishness' (red circle and arrow in pic). Also shown in the picture, It seems the lenses default state is F22, so what would not allow it to shut when completely assembled? Again thank you for any help.

Ontarian50 · 04-18-2020, 10:41 AM - **1 Like**

My standard operating procedure is to remove all the linkages, clean them and check them for bends or damage, and put them back in. Oil gets in all odd places and makes it sluggish.

Even then, I've had lenses that seemed to have clean apertures, but when all else was eliminated, taking the blades and plates out revealed oil residue around the edges - enough to bring things to a halt under light spring pressure.

**Just1MoreDave** · 04-19-2020, 08:29 AM

Originally posted by fireforsave

Thank yall for the replies. This might be that 1/10th time. Controlling the aperture with a linkage further inside lens results in zero 'sluggishness' (red circle and arrow in pic). Also shown in the picture, It seems the lenses default state is F22, so what would not allow it to shut when completely assembled? Again thank you for any help.

Maybe missing a spring? If a spring broke and the pieces fell off, not much evidence will remain, only some extra holes or notches. Finding a replacement is another challenge.

04-17-2020, 11:18 AM	#1
fireforsave Junior Member Join Date: Feb 2020 Location: Houston, Texas Photos: Gallery \| Albums Posts: 31	Aperture won't stop down past ~5.6 Sigma Macro 90mm 2.8 I recently acquired a K Mount Sigma 90mm Macro lens. The aperture won't stop down past about 5.6 if turning the ring at a normal speed. I can get it to close a stop or two extra if I turn it a bit more rapidly. Could this be an issue with spring tension? There isn't any oil on the blades but might be further inside where I have not investigated. I've taken the mount off and it seems the aperture control arm isnt receiving enough pressure. Last edited by fireforsave; 04-17-2020 at 11:25 AM.

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04-17-2020, 11:24 AM - 1 Like	#2
pepperberry farm amateur dirt farmer Join Date: Dec 2014 Location: probably out in a field somewhere... Photos: Gallery \| Albums Posts: 41,679	was the issue with the aperture ring explained before you bought the lens?

04-17-2020, 11:33 AM	#3
fireforsave Junior Member Join Date: Feb 2020 Location: Houston, Texas Photos: Gallery \| Albums Posts: 31 Original Poster	Originally posted by pepperberry farm was the issue with the aperture ring explained before you bought the lens? No, but I bought it from an individual along with a bundle of other stuff (maybe selling off family estate) at a steal of a price. I suspected some underlying issues, so I don't want to nickel and dime them.

04-17-2020, 11:51 AM - 1 Like	#4
Ontarian50 Veteran Member Join Date: Mar 2015 Posts: 530	Nine times out of ten, such issues are due to oil getting onto the mechanism somewhere - it doesn't have to be visible on the blades to see a mechanism get sluggish or sticky. Chances are there's enough spring pressure to close the aperture, if it were bone dry. It's a nice lens, and well worth getting serviced.

04-17-2020, 12:21 PM	#5
fireforsave Junior Member Join Date: Feb 2020 Location: Houston, Texas Photos: Gallery \| Albums Posts: 31 Original Poster	Originally posted by Ontarian50 Nine times out of ten, such issues are due to oil getting onto the mechanism somewhere - it doesn't have to be visible on the blades to see a mechanism get sluggish or sticky. Chances are there's enough spring pressure to close the aperture, if it were bone dry. It's a nice lens, and well worth getting serviced. Thank yall for the replies. This might be that 1/10th time. Controlling the aperture with a linkage further inside lens results in zero 'sluggishness' (red circle and arrow in pic). Also shown in the picture, It seems the lenses default state is F22, so what would not allow it to shut when completely assembled? Again thank you for any help.

04-18-2020, 10:41 AM - 1 Like	#6
Ontarian50 Veteran Member Join Date: Mar 2015 Posts: 530	My standard operating procedure is to remove all the linkages, clean them and check them for bends or damage, and put them back in. Oil gets in all odd places and makes it sluggish. Even then, I've had lenses that seemed to have clean apertures, but when all else was eliminated, taking the blades and plates out revealed oil residue around the edges - enough to bring things to a halt under light spring pressure.

04-19-2020, 08:29 AM	#7
Just1MoreDave Site Supporter Join Date: Feb 2007 Location: Aurora, CO Photos: Gallery \| Albums Posts: 6,340	Originally posted by fireforsave Thank yall for the replies. This might be that 1/10th time. Controlling the aperture with a linkage further inside lens results in zero 'sluggishness' (red circle and arrow in pic). Also shown in the picture, It seems the lenses default state is F22, so what would not allow it to shut when completely assembled? Again thank you for any help. Maybe missing a spring? If a spring broke and the pieces fell off, not much evidence will remain, only some extra holes or notches. Finding a replacement is another challenge.