Grainy viewfinder

Shadwell59 · 10-12-2020, 03:52 AM

I'm hoping this is a daft question with a simple answer.
I recently purchased a second hand Sigma 28-300 lens whilst everything appears to operate correctly the view through the viewfinder is very grainy, I have other lenses through which everything is clear so it's not the camera it must be something to do with the lens. If I switch to Liveview it appears to be OK & there's no noticeable differences between similar shots taken with different lenses when printed.

Any ideas?

Unregistered User · 10-12-2020, 04:52 AM

At what focal lengths? I remember from long time ago that enlarged pictures through a viewfinder can look grainy. If you use 300mm that is quite an "enlargement" so to speak, I saw this with a 135mm.

Shadwell59 · 10-12-2020, 07:12 AM

It seems to be at all lengths. The grainy appearance doesn't vary, it's consistent as I zoom in and out. I tried focusing on a plain surface and there is no variation. It's as if it's on the mirror or prism but it's only there on this one lens. It's not a biggy, I bought the lens 2nd hand really to see whether I would use the extra range sufficiently to warrant treating myself.
Most peculiar.

lister6520 · 10-12-2020, 07:32 AM - **1 Like**

The graininess is due to the narrow aperture. You will see the same also on shorter lenses if you stop down the aperture (with the DOF preview lever), but to a lesser extent. What happens is the light strikes the focus screen more parallel at narrow apertures and this brings out the grains of the 'ground glass' focusing screen.
Normally it is not very visible at wide open but super zooms are narrow even wide open. Also make sure the aperture blades are actually opening fully as they could be jammed.

Not a Number · 10-12-2020, 07:38 AM

The rule of thumb is the slower the lens the darker the viewfinder at wide open. Thus the "graininess" becomes more apparent.

Shadwell59 · 10-12-2020, 08:26 AM

Thanks people. Are you saying that even on a high quality lens I'm still going to see this and the answer is not to use a longer length than I actually need if I want to use the viewfinder?

**stevebrot** · 10-12-2020, 10:04 AM - **1 Like**

Originally posted by Not a Number

The rule of thumb is the slower the lens the darker the viewfinder at wide open. Thus the "graininess" becomes more apparent.

This ^ ^ ^

Originally posted by Shadwell59

Thanks people. Are you saying that even on a high quality lens I'm still going to see this and the answer is not to use a longer length than I actually need if I want to use the viewfinder?

See answer above. With lenses having a narrower maximum aperture, the amount of light to the viewfinder is decreased and the view is dimmed. A side-effect of that dimming is that the matte field appears grainy. At f/3.5 (the wide end for your lens) the view should usually be fairly bright, but f/6.3 at the long end is quite a bit dimmer (almost 1/4 the light).

Steve

10-12-2020, 03:52 AM	#1
Shadwell59 New Member Join Date: Aug 2020 Location: Portsmouth Posts: 4	Grainy viewfinder I'm hoping this is a daft question with a simple answer. I recently purchased a second hand Sigma 28-300 lens whilst everything appears to operate correctly the view through the viewfinder is very grainy, I have other lenses through which everything is clear so it's not the camera it must be something to do with the lens. If I switch to Liveview it appears to be OK & there's no noticeable differences between similar shots taken with different lenses when printed. Any ideas?

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10-12-2020, 04:52 AM	#2
Unregistered User Guest	At what focal lengths? I remember from long time ago that enlarged pictures through a viewfinder can look grainy. If you use 300mm that is quite an "enlargement" so to speak, I saw this with a 135mm.

10-12-2020, 07:12 AM	#3
Shadwell59 New Member Join Date: Aug 2020 Location: Portsmouth Posts: 4 Original Poster	It seems to be at all lengths. The grainy appearance doesn't vary, it's consistent as I zoom in and out. I tried focusing on a plain surface and there is no variation. It's as if it's on the mirror or prism but it's only there on this one lens. It's not a biggy, I bought the lens 2nd hand really to see whether I would use the extra range sufficiently to warrant treating myself. Most peculiar.

10-12-2020, 07:32 AM - 1 Like	#4
lister6520 Veteran Member Join Date: May 2012 Posts: 733	The graininess is due to the narrow aperture. You will see the same also on shorter lenses if you stop down the aperture (with the DOF preview lever), but to a lesser extent. What happens is the light strikes the focus screen more parallel at narrow apertures and this brings out the grains of the 'ground glass' focusing screen. Normally it is not very visible at wide open but super zooms are narrow even wide open. Also make sure the aperture blades are actually opening fully as they could be jammed.

10-12-2020, 07:38 AM	#5
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 7,679	The rule of thumb is the slower the lens the darker the viewfinder at wide open. Thus the "graininess" becomes more apparent.

10-12-2020, 08:26 AM	#6
Shadwell59 New Member Join Date: Aug 2020 Location: Portsmouth Posts: 4 Original Poster	Thanks people. Are you saying that even on a high quality lens I'm still going to see this and the answer is not to use a longer length than I actually need if I want to use the viewfinder?

10-12-2020, 10:04 AM - 1 Like	#7
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 38,824	Originally posted by Not a Number The rule of thumb is the slower the lens the darker the viewfinder at wide open. Thus the "graininess" becomes more apparent. This ^ ^ ^ Originally posted by Shadwell59 Thanks people. Are you saying that even on a high quality lens I'm still going to see this and the answer is not to use a longer length than I actually need if I want to use the viewfinder? See answer above. With lenses having a narrower maximum aperture, the amount of light to the viewfinder is decreased and the view is dimmed. A side-effect of that dimming is that the matte field appears grainy. At f/3.5 (the wide end for your lens) the view should usually be fairly bright, but f/6.3 at the long end is quite a bit dimmer (almost 1/4 the light). Steve

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