Solution to

Started Jun 6, 2009 | Discussions
dark goob Contributing Member • Posts: 983
Solution to

One problem using full-frame lenses on 4/3 is the issue of "ghosting"... at F1.4, for example, an image will look very hazy (but if you stop down to F2.0 then it's fine). Personally I have a Nikkor 50mm F1.4 (non-AI) and it's a great lens, but at F1.4 it ghosts really bad. (See image.)

So I've been looking for a way to solve this.

While reading Lens Work, a book by Canon, I learned that one problem with very bright lenses on digital SLRs is that light reflects off the sensor and then back to the rear lens element, and so on, causing this ghosting. They use anti-reflective coatings on some rear lens elements to reduce this. But that's not an option for me.

However I wondered if maybe just cutting a hole in a piece of paper or cloth, and placing it over the rear lens element, would suffice. The size of a standard 4/3 lens' rear opening is the size of a US dime, so I just put a dime down on a piece of paper and traced a circle around it. Then I cut out the hole, and then made a donut shape out of this piece of paper. I then placed it on the rear lens element of my Nikon 50mm F1.4, and the lens adapter helped to hold it in place.

Amazingly enough, this worked! The ghosting is gone and there is no negative impact on the brightness of the lens, from what I can tell. Woot! (See image taken with the ghostbuster on the lens, below.)

Hope this helps some of y'all.

-=DG=-

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OP dark goob Contributing Member • Posts: 983
Re: Solution to Ghosting on 4/3 using Full-Frame 1.4, 1.8 lenses

Sorry, "Solution to Ghosting on 4/3 using Full-Frame 1.4, 1.8 lenses" was supposed to be the title. Not sure how it got truncated...

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(unknown member) Veteran Member • Posts: 9,549
Re: Solution to

That's really cool, Dark Goob. I have an OM 50 1.4 I should try that with. It doesn't nearly that ghosty wide open, but if it would make it better that would be great.

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John Krumm
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knoblock Senior Member • Posts: 2,531
Re: Solution to

If you notice, with the fast lenses wide open, it is often extremely difficult to know if you achieved focus. I could just guess you focused on the far end and confirmed it by the second image. This often frustrates me on the Minolta 58mm f/1.4 wide open.

I've heard of using baffles but they usually say that it is the same as stopping down.

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Sam610 Contributing Member • Posts: 742
Re: Solution to

I wonder after the masking, do you notice the exposure metering change at all compare to the before the masking. And also how does it compare to the aperture close down to about the same size as the masking opening.

Sam H.

OP dark goob Contributing Member • Posts: 983
Re: Solution to

knoblock wrote:

If you notice, with the fast lenses wide open, it is often extremely
difficult to know if you achieved focus. I could just guess you
focused on the far end and confirmed it by the second image. This
often frustrates me on the Minolta 58mm f/1.4 wide open.

I've heard of using baffles but they usually say that it is the same
as stopping down.

Well that's why I always focus using the live view. If you focus with the optical viewfinder on adapted lenses, then yes, it is very difficult to achieve good focus on any lens with shallow DOF (like the 50mm F1.4 or 500mm F8.0).

I find that live view focusing for MF has been perfect.. I don't even use the optical viewfinder to manually focus anymore.

-=DG=-

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OP dark goob Contributing Member • Posts: 983
Re: Solution to

Sam610 wrote:

I wonder after the masking, do you notice the exposure metering
change at all compare to the before the masking. And also how does it
compare to the aperture close down to about the same size as the
masking opening.

Sam H.

No, the metering is not affected. Because the light that is coming into the sensor area is the exact same as before. It's just the excess light that bounces around and causes ghosting that we are eliminating.

Both shots the camera metered at 1/40 sec. Stopping down to F2.0 would cause it to be a slower shutter speed.

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John King
John King Forum Pro • Posts: 14,941
Re: Solution to fast lenses

Gidday DG

Brilliant, mate!

I will try this with my OM f1.4/50. I have seen this effect with it fairly often. Mine is a very early model (sn in the xxx,xxx range ...). I do not have this problem with my OM f1.8/50 (very late model - "made in Japan" version).

I can use some very dark charcoal coloured card that I use for lining telescope optical tube assemblies (OTAs). As long as one stays well away from the image circle for a 4/3rds lens (a millimetre or so) there should be no diffraction effect. The dark colour is essential, IMO, as this prevents reflections from the forward facing part of the card back on to the rear lens element. One solution would be to paint the limiting aperture material with matte black paint.

Another good material may be the aluminium seal in the top of some instant coffee tins. These come in different thicknesses, depending on the size of the can, usually. I routinely use this material for shimming.

May I suggest that if anyone does see a diffraction effect, chances are that the new "image circle" aperture is too close to this figure. I do not know if this would show visible effects, but I think that it should; specially if the artificial limiting aperture is made out of material that is thick, or rough around the edges (like me, lol).

Thanks again, DG; great idea, well done; good sample of shots, too. ;-)))

[edit] BTW, another small suggestion: once one has the aperture diameter right, one could use four dobs of silicon to hold the aluminium limiting aperture in place. Very easy to remove if one wants to, leaving no traces of glue etc; and makes it very secure (not rattling around it the mirror box ... ugh!). [end edit]

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Sam610 Contributing Member • Posts: 742
Re: Solution to

dark goob wrote:

No, the metering is not affected. Because the light that is coming
into the sensor area is the exact same as before. It's just the
excess light that bounces around and causes ghosting that we are
eliminating.

Both shots the camera metered at 1/40 sec. Stopping down to F2.0
would cause it to be a slower shutter speed.

Thanks for posting. The reason I asked this, is because I though by blocking the light by the masking, the amount of light goes through is the same amount of light as aperture stop down. I was thinking about the whole image circle, not from 4/3 circle metering correspond to the sensor.
Thanks again, I will try your tip later.

Sam H

OP dark goob Contributing Member • Posts: 983
Re: Solution to

Thanks for posting. The reason I asked this, is because I though by
blocking the light by the masking, the amount of light goes through
is the same amount of light as aperture stop down. I was thinking
about the whole image circle, not from 4/3 circle metering correspond
to the sensor.
Thanks again, I will try your tip later.

Sam H

Yeah, I kind of wondered about that too. But remember, F-stop is a per-unit-of-area measurement of brightness. So as long as we're not cutting the light that would be hitting the sensor directly then we're OK, I think.

Though I could be making a terrible miscalculation here. ;p

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Sam610 Contributing Member • Posts: 742
Re: Solution to

dark goob wrote:

Yeah, I kind of wondered about that too. But remember, F-stop is a
per-unit-of-area measurement of brightness. So as long as we're not
cutting the light that would be hitting the sensor directly then
we're OK, I think.

Though I could be making a terrible miscalculation here. ;p

I think the light still being blocked by the same amount of masking as stopping down, but the camera meter off the sensor surface thus the meter still read the same.

chuckielpn Senior Member • Posts: 1,594
Re: Solution to

H-Oly cow!

I just tried it with my Konica 57mm 1.4, haziness is gone.

You sir, are a genius!

OP dark goob Contributing Member • Posts: 983
Re: Solution to

chuckielpn wrote:

H-Oly cow!

I just tried it with my Konica 57mm 1.4, haziness is gone.

You sir, are a genius!

How is it affecting your metering?

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chuckielpn Senior Member • Posts: 1,594
Re: Solution to

metering seems to be fine. some samples here shot with e-3. A mode.

and for amusement, at iso1600 with just refrigerator light. crappy banding.

took the same shots with the 50-200 swd. the $5 konica lens is not as sharp, but results were acceptable. the konica lens, however, gave me form half to a stop over the 50-200.

dark goob wrote:

chuckielpn wrote:

H-Oly cow!

I just tried it with my Konica 57mm 1.4, haziness is gone.

You sir, are a genius!

How is it affecting your metering?

Kirasir Senior Member • Posts: 1,037
Re: Solution to

Great!

The only thing - I'd do it, using a black pape, something like what was used for envelopes for photosensitive materials.
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chuckielpn Senior Member • Posts: 1,594
Re: Solution to

Yeh... i have to redo how the paper stays on there. this lens and adapter combination doesn't give me much to work with.

Kirasir wrote:

Great!

The only thing - I'd do it, using a black pape, something like what
was used for envelopes for photosensitive materials.
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Big Ga Forum Pro • Posts: 18,624
Re: Solution to

dark goob wrote:

Though I could be making a terrible miscalculation here. ;p

Yup

If you're using a normal SLR, the metering is not done off the sensor (excluding live view of course). Its normally done in a separate measuring unit normally somewhere up in the viewfinder hump.

But whatever, the point is that many old fast lenses used in the way you have can somehow fool the normal camera metering. Its possible that doing what you have done might very well improve matters, as there is less stray light bouncing around the mirror box and going where it shouldn't. Hence why it would be good to compare how well it meters (wide open) with and without your baffle.

Cheers
G.

efrench Senior Member • Posts: 1,116
Re: Solution to

On my OM 50mm f/1.8, the aperture at F/4 is about the size of a dime. How do you know you're blocking reflections and not just stopping the lens down?

Can you post the same image at f/4 (without using the baffle)?
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Kurt Petersen Senior Member • Posts: 2,572
Re: Solution to

Certainly a dramatic improvement in sharpness when adding your baffle dark goob. There has been some discussion of baffles in legacy lenses here before, particularly in regards to conversion of Hexanon lenses.

http://forums.dpreview.com/forums/readflat.asp?forum=1022&message=24713754&q=hexanon+conversion+baffle&qf=m

http://forums.dpreview.com/forums/readflat.asp?forum=1022&message=30947267&q=hexanon+conversion+baffle&qf=m

http://forums.dpreview.com/forums/readflat.asp?forum=1022&message=30503777&q=hexanon+conversion+baffle&qf=m

http://forums.dpreview.com/forums/readflat.asp?forum=1022&message=18745889&q=hexanon+conversion+baffle&qf=m

I'm not sure if any concensus was reached as to whether the baffle improved results due to cutting out off-angle light, or if it is merely an enforced stopping down of the lens.

I wouldn't rely on the cameras metering to say that adding the baffle hasn't effectively created a smaller aperture lens. It has been widely reported by users of legacy lenses on 4/3rds that metering is inconsistent at apertures wider than f/2 and you need to create a "calibration table" for each individual lens. This isn't neccesary with fast 4/3rds lenses as the calibration is built into the firmware.

I would suggest that if you want to definitively discover if the baffle is reducing your effective aperture you would need to do test shots with manual exposure, keeping shutter speed constant and varying aperture, and examine image brightness and depth of field at different aperture settings.

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Simon Cowell Senior Member • Posts: 2,543
Very good!

What's the equivalent (in size) British coin to US dime?

Can't wait to try it out.

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