Pentax F 35-70mm f3.5-4.5

JeffJS · 12-31-2010, 01:05 PM

Since you've returned the lens it doesn't matter now but it's also possible the aperture blades were dragging and you Were overexposed somewhat.

elg · 12-31-2010, 01:25 PM

Originally posted by JeffJS

Since you've returned the lens it doesn't matter now but it's also possible the aperture blades were dragging and you Were overexposed somewhat.

JeffJS,

It still matters a little bit, as kit lens sometimes demonstrates similar effect at times (though this is occurring a lot less than with SMC F 35-70). It never happened with Sigma 28-135 IF though.
What's the reason for dragging aperture blades? Does it indicate that the lens will not last long?

Thanks,
elg (Erika)

JeffJS · 12-31-2010, 02:29 PM

Originally posted by elg

JeffJS,

It still matters a little bit, as kit lens sometimes demonstrates similar effect at times (though this is occurring a lot less than with SMC F 35-70). It never happened with Sigma 28-135 IF though.
What's the reason for dragging aperture blades? Does it indicate that the lens will not last long?

Thanks,
elg (Erika)

Dragging blades can indicate oil on the blades or weak springs on the aperture mechanism. I doubt this would be the case with your kit lens but you can easily check it. Simply remove the lens from the camera and flick that little lever on the back. It should open the blades completely and snap right back when you release it. If your sigma has an A setting on the aperture ring (or no ring at all) you can compare the two and see the difference (if a ring and no A setting put it at f22 or whatever the highest number is). Except for wide open shots, a dragging aperture will not completely stop down during the exposure, causing overexposure.

Remember (or know now) that the camera does not stop the aperture down for metering unless you tell it to. It's a calculated exposure based on previous knowledge (by the designers) of how exposure metering works. That is, you tell the camera what aperture you want to use and based on that and the ISO setting, it will calculate the shutter speed.

Simple age can cause this and it's one thing to look for especially in buying used lenses (and certain types of shutters). Usually you can See the oil on the blades if you look carefully. It will typically show up as a wet looking discoloration on the edges where the rest of the blades appear dry. In many cases, it's easier and cheaper to replace the lens when it happens than to have it serviced. To do a proper cleaning job, the aperture blades must be removed from the lens and cleaned individually. My price for doing it for someone else starts at $75 and goes up depending on the lens. That's assuming I can even get it apart.

Leaving a lens in a hot closed up car exposed can also cause it.

With respect to your kit lens, I'm sure the Sigma is a quantum leap better in terms of sharpness. You nailed one possible cause for the halo effect, overexposure, which is what prompted my response.

NewTake · 04-11-2011, 08:07 AM

I also own this lens... have been very happy with the sharpness and focus. However, I have noticed that it seems to blow out highlights very easy, so I rarely use it for landscape shots. (highlights blown out while the rest of the image looks underexposed). I can only chalk it up to not having a good dynamic range. That said, it is great for controlled light and portrait applications and I wont be getting rid of it.

reeftool · 04-11-2011, 08:17 AM

I own the lens also. It's pretty sharp, sharper than the 18-55 kit imo. The macro feature works well and that's what I mostly bought it for. The lens is poorly built. The zoom broke on mine and now it's a 70mm macro. An optically good lens but buy it cheap, like under $50. It's just about all plastic. I used it in the Single in January challenge and it did not survive a month of daily use.

**Just1MoreDave** · 04-11-2011, 12:02 PM

Originally posted by reeftool

I own the lens also. It's pretty sharp, sharper than the 18-55 kit imo. The macro feature works well and that's what I mostly bought it for. The lens is poorly built. The zoom broke on mine and now it's a 70mm macro. An optically good lens but buy it cheap, like under $50. It's just about all plastic. I used it in the Single in January challenge and it did not survive a month of daily use.

You should probably demand a partial refund from the seller.

Sorry about that. It seemed fine to me.

04-11-2011, 08:07 AM	#19
NewTake Junior Member Join Date: Jun 2010 Photos: Gallery \| Albums Posts: 47	Highlight Issues I also own this lens... have been very happy with the sharpness and focus. However, I have noticed that it seems to blow out highlights very easy, so I rarely use it for landscape shots. (highlights blown out while the rest of the image looks underexposed). I can only chalk it up to not having a good dynamic range. That said, it is great for controlled light and portrait applications and I wont be getting rid of it.

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12-31-2010, 01:05 PM	#16
JeffJS Inactive Account Join Date: Aug 2008 Location: Michigan, USA Photos: Gallery \| Albums Posts: 7,484	Since you've returned the lens it doesn't matter now but it's also possible the aperture blades were dragging and you Were overexposed somewhat.

12-31-2010, 01:25 PM	#17
elg Forum Member Join Date: Nov 2010 Location: Dublin Posts: 73 Original Poster	Originally posted by JeffJS Since you've returned the lens it doesn't matter now but it's also possible the aperture blades were dragging and you Were overexposed somewhat. JeffJS, It still matters a little bit, as kit lens sometimes demonstrates similar effect at times (though this is occurring a lot less than with SMC F 35-70). It never happened with Sigma 28-135 IF though. What's the reason for dragging aperture blades? Does it indicate that the lens will not last long? Thanks, elg (Erika)

12-31-2010, 02:29 PM	#18
JeffJS Inactive Account Join Date: Aug 2008 Location: Michigan, USA Photos: Gallery \| Albums Posts: 7,484	Originally posted by elg JeffJS, It still matters a little bit, as kit lens sometimes demonstrates similar effect at times (though this is occurring a lot less than with SMC F 35-70). It never happened with Sigma 28-135 IF though. What's the reason for dragging aperture blades? Does it indicate that the lens will not last long? Thanks, elg (Erika) Dragging blades can indicate oil on the blades or weak springs on the aperture mechanism. I doubt this would be the case with your kit lens but you can easily check it. Simply remove the lens from the camera and flick that little lever on the back. It should open the blades completely and snap right back when you release it. If your sigma has an A setting on the aperture ring (or no ring at all) you can compare the two and see the difference (if a ring and no A setting put it at f22 or whatever the highest number is). Except for wide open shots, a dragging aperture will not completely stop down during the exposure, causing overexposure. Remember (or know now) that the camera does not stop the aperture down for metering unless you tell it to. It's a calculated exposure based on previous knowledge (by the designers) of how exposure metering works. That is, you tell the camera what aperture you want to use and based on that and the ISO setting, it will calculate the shutter speed. Simple age can cause this and it's one thing to look for especially in buying used lenses (and certain types of shutters). Usually you can See the oil on the blades if you look carefully. It will typically show up as a wet looking discoloration on the edges where the rest of the blades appear dry. In many cases, it's easier and cheaper to replace the lens when it happens than to have it serviced. To do a proper cleaning job, the aperture blades must be removed from the lens and cleaned individually. My price for doing it for someone else starts at $75 and goes up depending on the lens. That's assuming I can even get it apart. Leaving a lens in a hot closed up car exposed can also cause it. With respect to your kit lens, I'm sure the Sigma is a quantum leap better in terms of sharpness. You nailed one possible cause for the halo effect, overexposure, which is what prompted my response.

04-11-2011, 08:17 AM	#20
reeftool Pentaxian Join Date: Dec 2007 Location: Upstate New York Photos: Gallery \| Albums Posts: 9,553	I own the lens also. It's pretty sharp, sharper than the 18-55 kit imo. The macro feature works well and that's what I mostly bought it for. The lens is poorly built. The zoom broke on mine and now it's a 70mm macro. An optically good lens but buy it cheap, like under $50. It's just about all plastic. I used it in the Single in January challenge and it did not survive a month of daily use.

04-11-2011, 12:02 PM	#21
Just1MoreDave Site Supporter Join Date: Feb 2007 Location: Aurora, CO Photos: Gallery \| Albums Posts: 6,340	Originally posted by reeftool I own the lens also. It's pretty sharp, sharper than the 18-55 kit imo. The macro feature works well and that's what I mostly bought it for. The lens is poorly built. The zoom broke on mine and now it's a 70mm macro. An optically good lens but buy it cheap, like under $50. It's just about all plastic. I used it in the Single in January challenge and it did not survive a month of daily use. You should probably demand a partial refund from the seller. Sorry about that. It seemed fine to me.

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