Where's the dust.

[Simon Heffer]

Sony A77 with Sigma telephoto lens. I can see I have some dirt somewhere. I've having trouble finding it. It only shows up on the viewfinder when the telephoto is fully extended.
Does this mean it's:
a) On the fat end of the lens
b) on the camera end of the lens
c) its in the camera body
d) else where?


Any thoughts?

Ta,
Simon

 

[Coley.]

Im new to this myself but think it may be dirt on the sensor ....

 

[neil_g]

does it show on the photos?

 

[HoppyUK]

If you can see spots through the viewfinder, that's where the dirt is, usually on the underside of the focusing screen, above the mirror. Spots here, or on any other part of the lens or optical system will not be visible on the image.

If there are spots on the image, that's dirt on the sensor and that is usually only visible at high f/numbers that show them much more clearly.

A bit of dirt and dust is inevitable and unavoidable. Just need to clean the sensor now and then.

 

[Simon Heffer]

Thanks all.
I guess I should go over to the Photography forum to get SLT sensor advice?

 

[Johnd2000]

Thanks all.
I guess I should go over to the Photography forum to get SLT sensor advice?

It could be any of the options you mentioned, but my money would be on the sensor. It's certainly not on the focussing screen, because SLTs don't have them.

Try taking a shot of the sky at f22 or above. That should make the dirt on the sensor show up best.

To clean the sensor, go into cleaning mode from the menu, remove the lens, carefully flip up the mirror (small tab on bottom) without touching its surface, then use a blower or wet clean as needed. Give the mirror a few puffs of a blower while you're at it, but DO NOT use any cleaning fluid or swabs on the mirror itself. If you do, you run the risk of damaging the mirror (which is actually a very thin plastic film).

There's lots of threads here about sensor cleaning. It's nothing to be afraid of, but if you are, most camera shops will do it for you, for a fee.

 

[HoppyUK]

It could be any of the options you mentioned, but my money would be on the sensor. It's certainly not on the focussing screen, because SLTs don't have them.

Try taking a shot of the sky at f22 or above. That should make the dirt on the sensor show up best.

To clean the sensor, go into cleaning mode from the menu, remove the lens, carefully flip up the mirror (small tab on bottom) without touching its surface, then use a blower or wet clean as needed. Give the mirror a few puffs of a blower while you're at it, but DO NOT use any cleaning fluid or swabs on the mirror itself. If you do, you run the risk of damaging the mirror (which is actually a very thin plastic film).

There's lots of threads here about sensor cleaning. It's nothing to be afraid of, but if you are, most camera shops will do it for you, for a fee.

Sorry, brain fade... of course SLTs don't have focusing screens. Apologies :nuts:

 

[Johnd2000]

Sorry, brain fade... of course SLTs don't have focusing screens. Apologies :nuts:

To be fair, the way the OP explained it didn't help. It's odd to see dirt in the EVF image, unless previewing DOF at very small apertures (or reviewing a taken picture,I suppose).

 

[HoppyUK]

To be fair, the way the OP explained it didn't help. It's odd to see dirt in the EVF image, unless previewing DOF at very small apertures (or reviewing a taken picture,I suppose).

You're too kind, I have no excuses

I wonder if there's a clue in the OP though, that the dirt only shows up at the long end of the zoom.

The reason dirt is usually only visible at high f/numbers is because depth of focus (as opposed to depth of field) increases with f/number. But depth of focus is also increased by focal length (it works opposite to depth of field in that sense) so it may be that at - guessing - maybe f/5.6 on a 300mm lens will show it up.

 

[wessyfiesta]

I would say it is in your lens, i have a 18-55mm kit lens, i use it for slow shutters, the dust spots come out in photos at f16 onwards, tip for you, take both caps off and look down barrel of lens into daylight, as though it was a telescope, then zoom in and out, if you don't see any marks it has to be in your camera.

 

[HoppyUK]

I would say it is in your lens, i have a 18-55mm kit lens, i use it for slow shutters, the dust spots come out in photos at f16 onwards, tip for you, take both caps off and look down barrel of lens into daylight, as though it was a telescope, then zoom in and out, if you don't see any marks it has to be in your camera.

No, anything on or in the lens is so far out of focus to be visible. Dark marks in images are always summat on the sensor, usually they show up on areas of even tone like sky, when used with a higher f/number that pulls them into clearer focus.