[madbrain]

I bought a Sigma DG 28-300mm zoom a few weeks on Amazon. It was discounted to $55 because it was missing both caps. I only got to try it recently.
There is a puzzling issue : viewfinder is extremely dark. Autofocus is very slow and unreliable. Manual focus is impossible due to dark viewfinder.
Same issue in live view - dark. But CDAF seems to work a bit better, though even slower.

Here is the kicker : after pressing the shutter, the picture has the correct exposure. The issue is only before shooting.
I have set the aperture lever to A . Also tried to force it to f/3.5 . The same issue remain. I cleaned the contacts, too.

I already submitted a return request to Amazon, but not sure it will be honored as I think I'm past 30 days from order, though not 30 days from receipt. The order was shipped late.

Is there anything I can do to salvage this lens, or is it a dud ?

---------- Post added 06-11-18 at 03:48 AM ----------

Actually, it only gets correct exposure randomly, most of the times, it does not. I tried it both in my K-30 and K-1 II and same issue. Both bodies work fine with other lenses.

[Hamiltom]

It sounds like the "A" setting is not engaging on the lens.

Can you manually set aperture from the camera when the lens is in the "A" setting? There should be an indication for your f stop when use manual setting mode.

If the back screen indicates "f---", then there is no electrical connection to the lens. That means dirty contacts or the lens has internal electrical issues.

Normally dirty contacts are the problem. Try cleaning the contacts with alcohol solution 50-70% vigorously - try to get the contact points to rotate so that the entire surface is clean. They may appear to be clean, but they could be internal clogged with dirt.

Good Luck.

[LensBeginner]

Does the shape of the aperture change when you rotate the aperture ring on the lens - unmounted from the camera, looking through it against a light source e.g. a window?

[reh321]

I bought a Sigma DG 28-300mm zoom a few weeks on Amazon. It was discounted to $55 because it was missing both caps. I only got to try it recently.
There is a puzzling issue : viewfinder is extremely dark. Autofocus is very slow and unreliable. Manual focus is impossible due to dark viewfinder.
Same issue in live view - dark. But CDAF seems to work a bit better, though even slower.

Here is the kicker : after pressing the shutter, the picture has the correct exposure. The issue is only before shooting.
I have set the aperture lever to A . Also tried to force it to f/3.5 . The same issue remain. I cleaned the contacts, too.

I already submitted a return request to Amazon, but not sure it will be honored as I think I'm past 30 days from order, though not 30 days from receipt. The order was shipped late.

Is there anything I can do to salvage this lens, or is it a dud ?

Actually, it only gets correct exposure randomly, most of the times, it does not. I tried it both in my K-30 and K-1 II and same issue. Both bodies work fine with other lenses.

The lens has a mechanism which opens it fully wide regardless of the f-stop set; the camera body is supposed to use that to have maximal lens opening for focusing and composing - going to correct aperture only when taking the picture. From your words, I believe that mechanism is not working. Someone more knowledgeable than me would have to tell you a solution other than sending it in for repair.

[LensBeginner]

The lens has a mechanism which opens it fully wide regardless of the f-stop set; the camera body is supposed to use that to have maximal lens opening for focusing and composing - going to correct aperture only when taking the picture. From your words, I believe that mechanism is not working. Someone more knowledgeable than me would have to tell you a solution other than sending it in for repair.

It's not the lens, it's the camera that holds the aperture lever from the moment you twist the lens on the body to mount it: when you do it you can see that the aperture goes from completely stopped down (spring loaded) to fully open.

[madbrain]

Does the shape of the aperture change when you rotate the aperture ring on the lens - unmounted from the camera, looking through it against a light source e.g. a window?

I can tell it's changing dimensions. There is a very loud click between f8 and f11 though, needs strength to go between those 2.

[LensBeginner]

I can tell it's changing dimensions. There is a very loud click between f8 and f11 though, needs strength to go between those 2.

It shouldn't need force...

Try setting your lens at f/8 or so. On the back of the lens (the side of the mount) there should be a moveable metal tab protruding above everything else (google "lens aperture lever" if you are not sure, and check the images).
Can you move it? if you move it, does the diaphragm open?

[madbrain]

It sounds like the "A" setting is not engaging on the lens.

Can you manually set aperture from the camera when the lens is in the "A" setting? There should be an indication for your f stop when use manual setting mode.

If the back screen indicates "f---", then there is no electrical connection to the lens. That means dirty contacts or the lens has internal electrical issues.

Normally dirty contacts are the problem. Try cleaning the contacts with alcohol solution 50-70% vigorously - try to get the contact points to rotate so that the entire surface is clean. They may appear to be clean, but they could be internal clogged with dirt.

Good Luck.

When the lens is set to A, the LCD screen shows numbers that make sense for the f stop not "f---". But the aperture does not seem to be actually changing on the lens.
When I set to other than A, I get "F---". Green button in M mode always gives the same shutter speed and ISO. However, interestingly, when I look at the resulting image file, the aperture is recorded as f3.5 .
I think it's always shooting wide open when set to non-A . But closed down to lowest aperture in viewfinder. Very weird.

[LensBeginner]

When the lens is set to A, the LCD screen shows numbers that make sense for the f stop not "f---". But the aperture does not seem to be actually changing on the lens.

It doesn't have to change when you change it on the camera, it must remain wide open to help focusing, both by hand (viewfinder) and by the autofocus sensor.
It only closes when you press the shutter

When I set to other than A, I get "F---". Green button in M mode always gives the same shutter speed and ISO. However, interestingly, when I look at the resulting image file, the aperture is recorded as f3.5 .
I think it's always shooting wide open when set to non-A . But closed down to lowest aperture in viewfinder. Very weird.

It's normal to get F--- in positions other than A.

It's also normal that the EXIF data will show the smaller aperture when setting the aperture ring by hand, since the camera has no way of knowing which aperture the lens actually is at (but knows the larger one because it's in the lens data).

The viewfinder is darker when using a lens with a smaller maximum aperture i.e. a consumer zoom opposed to a bright prime, what are you comparing it to? it should be about the same of your kit lens, but darker than a, say, 50mm f/1.8

[madbrain]

It shouldn't need force...

Agree, it shouldn't ...

Try setting your lens at f/8 or so. On the back of the lens (the side of the mount) there should be a moveable metal tab protruding above everything else (google "lens aperture lever" if you are not sure, and check the images).
Can you move it? if you move it, does the diaphragm open?

The lever works opens the diaphragm only very slightly. There is not much play in the lever, maybe only 1-2mm vs 6-8mm or so on other lenses. I think the lens is broken.

[reh321]

It's not the lens, it's the camera that holds the aperture lever from the moment you twist the lens on the body to mount it: when you do it you can see that the aperture goes from completely stopped down (spring loaded) to fully open.

The Original Post ends with the words

I tried it both in my K-30 and K-1 II and same issue. Both bodies work fine with other lenses.

This would indicate it's the lens, not the body. There is a problem within the lens, between the lever and the actual aperture. It probably needs CLA by an expert.

[UncleVanya]

Message Amazon. Explain shipment was slow and the problem. Good luck. It is likely fixable, but at what cost?

[LensBeginner]

The lever works opens the diaphragm only very slightly. There is not much play in the lever, maybe only 1-2mm vs 6-8mm or so on other lenses. I think the lens is broken.

Yup it is... sorry

The Original Post ends with the words
This would indicate it's the lens, not the body. There is a problem within the lens, between the lever and the actual aperture. It probably needs CLA by an expert.

I agree that the issue is with the lens, but it's the camera which keeps (or tries to keep) the aperture on the lens wide open, against the force of the spring.

Message Amazon. Explain shipment was slow and the problem. Good luck. It is likely fixable, but at what cost?

Agree. It's not worth it, especially since there could be bigger issues. The aperture lever not moving makes me think the lens has suffered a blow, so there's no guarantee it's not decentered eithe.

[madbrain]

Message Amazon. Explain shipment was slow and the problem. Good luck. It is likely fixable, but at what cost?

Seller denied refund already . I just filed an A to Z claim.

[SSGGeezer]

Seller denied refund already . I just filed an A to Z claim.

Good luck since it sounds like a poor seller. Was it fulfilled by Amazon or just linked through Amazon? I am very leery if it is not a fulfilled by Amazon product because of slow shipping and lousy customer service like this.