Weird issue w/Ext. tube + M42 lens

Started Apr 20, 2012 | Discussions
Martin Ocando
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Weird issue w/Ext. tube + M42 lens
Apr 20, 2012

If I shoot my G3 using the extension tube and my 55mm Takumar, stopped down to f:11, this is what I get. Look the bright spot in the center of the image:

But if I shoot wide open, the center is not bright, but I don't have enough DOF.

What could be causing this, and how to avoid it.
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Aleo Veuliah
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Re: Weird issue w/Ext. tube + M42 lens
In reply to Martin Ocando, Apr 20, 2012

Really strange, don't know why that happens

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Martin Ocando
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Re: Weird issue w/Ext. tube + M42 lens
In reply to Aleo Veuliah, Apr 20, 2012

Shows up on the LCD or EVF when shooting. I think it might be related to shooting stopped down. Maybe having aperture control might mitigate the effect.

Aleo Veuliah wrote:

Really strange, don't know why that happens

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MAubrey
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Re: Weird issue w/Ext. tube + M42 lens
In reply to Martin Ocando, Apr 20, 2012

I've experienced this with extension tubes and legacy glass, too. But I haven't figured out what causes it...
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MAubrey
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Re: Weird issue w/Ext. tube + M42 lens
In reply to MAubrey, Apr 20, 2012

Flare has been my best guess, but I don't know why that would be a problem only with really small apertures...
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nickoly
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Umm,, iris busted and bad glass?
In reply to Martin Ocando, Apr 20, 2012

Check that the iris is opening and closing properly, that the glass is clear, and also use another lens to determine what the proper exposure might be.

Martin Ocando wrote:

If I shoot my G3 using the extension tube and my 55mm Takumar, stopped down to f:11, this is what I get. Look the bright spot in the center of the image:

But if I shoot wide open, the center is not bright, but I don't have enough DOF.

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Lights
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Re: Weird issue w/Ext. tube + M42 lens
In reply to Martin Ocando, Apr 20, 2012

Do you get this with the extension tube off? or any indication of it? (trying to eliminate the tube, from the lens - but if it's a combination of) very odd.
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nickoly
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Re: Weird issue w/Ext. tube + M42 lens
In reply to Lights, Apr 20, 2012

Aha! good idea...

I can't see hoew it would happen, but it has just occurred to me that the tube could be fouling the iris control pin!

Lights wrote:

Do you get this with the extension tube off?

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MAubrey
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Re: Weird issue w/Ext. tube + M42 lens
In reply to nickoly, Apr 20, 2012

Well, if that's the case, then my experience of this phenomenon has a different cause. It only happens with the extension tube at small apertures and my lens doesn't have an iris control pin, just an aperture ring.
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BBbuilder467
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Re: Weird issue w/Ext. tube + M42 lens
In reply to Martin Ocando, Apr 20, 2012

I have a set of cheap extension tubes and what I and others have found is a light leak particularly around the lock/detent button near the lens. If you happen to catch the light just right you can get a terrible flare.

Take the tube and cover the opening and then shine a flashlight at the button and the joints. I covered mine with black electrical tape until I decide to just seal the button hole and leave that lens on semi-permantly. I can actually see through that hole and it reflects on the chrome clip inside.

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nickoly
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Re: Weird issue w/Ext. tube + M42 lens
In reply to MAubrey, Apr 20, 2012

Beats me, but I still think the OPs problems are bigger than the extension tube. I guess we find out when he shoots without one......

I can't see how a tube would foul the pin, and I have no idea how it would cause an aberration like this, hence I suspect the lens(!)

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Aleo Veuliah
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Re: Weird issue w/Ext. tube + M42 lens
In reply to Martin Ocando, Apr 20, 2012

Maybe it is a reflection from the white on the image, maybe the tubes are not good inside and the small aperture makes it visible , try it with different subjects

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Martin Ocando
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Re: Weird issue w/Ext. tube + M42 lens
In reply to Lights, Apr 20, 2012

No issue without the extension tube.

Lights wrote:

Do you get this with the extension tube off? or any indication of it? (trying to eliminate the tube, from the lens - but if it's a combination of) very odd.
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Jeremy_T
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Re: Weird issue w/Ext. tube + M42 lens
In reply to BBbuilder467, Apr 20, 2012

BBbuilder467 wrote:

I have a set of cheap extension tubes and what I and others have found is a light leak particularly around the lock/detent button near the lens. If you happen to catch the light just right you can get a terrible flare.

Take the tube and cover the opening and then shine a flashlight at the button and the joints. I covered mine with black electrical tape until I decide to just seal the button hole and leave that lens on semi-permantly. I can actually see through that hole and it reflects on the chrome clip inside.

This is what I immediately thought of too.

At wide apertures the light leak might be invisible, since more light is hitting the sensor from your subject the leaked light is not of enough quantity to impact the result in a meaningful way. At small apertures with relatively longer exposures the light leak would effectively be amplified.

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Jeremy_T
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Re: Weird issue w/Ext. tube + M42 lens
In reply to Jeremy_T, Apr 20, 2012

Jeremy_T wrote:

This is what I immediately thought of too.

At wide apertures the light leak might be invisible, since more light is hitting the sensor from your subject the leaked light is not of enough quantity to impact the result in a meaningful way. At small apertures with relatively longer exposures the light leak would effectively be amplified.

Oh also - the light leak might be illuminating the aperture blades themselves.

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nickoly
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Re: Weird issue w/Ext. tube + M42 lens
In reply to Martin Ocando, Apr 20, 2012

OK, if it is kosher without the tube, maybe the tube is the villain. I assumed the lens was M42 mount, but if it is a PK Mount then maybe Jeremy is right about the light leak, and the problem is between the tube and the adapter. This might be verifiable by holding the mounted lens against your eye and keeping the front cap on.

If no leak is evident, a close check that the tube is not fouling the stop down is in order. Indeed I think you need to do that anyway, because it is pretty clear that things are not too good in the exposure department, even though it may not be a direct cause of your problem.

I suspect the focussing isn't to hot either, but I can't see how it would cause this.

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Martin Ocando
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Re: Weird issue w/Ext. tube + M42 lens
In reply to nickoly, Apr 20, 2012

Actually focusing is very hard, because the light spot is visible on the viewfinder or LCD, and I have to keep moving the subject to the sides to check focus, and then I snap the picture. Very odd indeed.

I'll check the light leak in a few. I keep you posted.

nickoly wrote:

OK, if it is kosher without the tube, maybe the tube is the villain. I assumed the lens was M42 mount, but if it is a PK Mount then maybe Jeremy is right about the light leak, and the problem is between the tube and the adapter. This might be verifiable by holding the mounted lens against your eye and keeping the front cap on.

If no leak is evident, a close check that the tube is not fouling the stop down is in order. Indeed I think you need to do that anyway, because it is pretty clear that things are not too good in the exposure department, even though it may not be a direct cause of your problem.

I suspect the focussing isn't to hot either, but I can't see how it would cause this.

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Martin Ocando
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+ UPDATE
In reply to Martin Ocando, Apr 20, 2012

There is no apparent light leak. I covered the whole structure of tube + adapter + lens, and I saw no change in the shape or intensity of the bright spot.

Now: It does get a bit larger and softer (less evident) with the longer tube, 28mm, and noticeable smaller and brighter (way more annoying) using the small tube (7mm).

I'll try to shoot with the 28mm tube later, but definitively the 14mm (middle tube) is annoying, and I must do some selective adjustments in LR4 to darken the center area. For what I saw, the 7mm is much much worse, so no point in using that one.

Back home I have a couple more m42 lenses, and I will test them out and report my results.

BTW, I did used the tubes with my 14-42mm and 20mm Pannys, and there was no bright spot. But, they were wide open, and since there is no way to stop down, I can't tell for sure it won't show up.

Any more ideas?
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LincolnB
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looks like some sort of lens flare
In reply to Martin Ocando, Apr 20, 2012

Looks exactly like the lens flare I get with my Fujian CCTV lens, with no extension tube, which also changes according to the aperture. It's possible that the lighting you use when doing macros is different than in other types of shots, which might explain why you see it with the extension tubes only.

Just a thought.

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Agitprop
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Re: Weird issue w/Ext. tube + M42 lens
In reply to Martin Ocando, Apr 20, 2012

try a shorter extension tube or a lens with a shorter FL.

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