Is it the eyepiece's fault?

[shroom]

Been lurking for a while, enjoy the forum. Fairly new to photography after inheriting a Rebel XT several months ago.

Been taking pics at night recently - XMAS displays, exposures of several secs at F8 - and I've noticed an infrequent but re-occuring problem. Sometimes a gallows-shaped row of faint green dots appears in the lower middle of the photo. Example -

http://lh4.ggpht.com/_MgTTnDDakGo/SUlByg34VoI/AAAAAAAABxM/5nDmInKDZr0/s720/IMG_2837.JPG

Is this caused by light creeping thru my eyepiece during a 5-sec exposure? Anybody seen this before? Any advice? I plan to start holding my hand over the back of the camera during these photos from now on - only thing I can think of to try for now.

[mbellot]

Is this caused by light creeping thru my eyepiece during a 5-sec exposure? Anybody seen this before? Any advice? I plan to start holding my hand over the back of the camera during these photos from now on - only thing I can think of to try for now.

It could be light coming in the viewfinder. Was there lighting behind you that looked like the ghost image?

You don't mention what camera you're using...

If you have an xxD series it should have come with an eyepiece cover (little rubber rectangle).

The 1DMkIII has a lever that actually closes a viewfinder "shutter", I would imagine the earlier 1D series do as well.

I've never owned an xxxD camera, but I would expect it would come with the same rubber cover as the xxD.

[MattMoore]

man I was way off....that makes sense now

[number six]

Nope, it's not from the viewfinder. When you're exposing a shot the mirror is up, blocking the viewfinder from the light path through the camera.

The eyepiece cover is to prevent light through the VF from reaching the metering system, thereby causing underexposure.

Strange. You're talking about the horizontal and vertical rows of dots across the door and to its left?

-js

[shroom]

Camera is a Canon EOS Rebel XT 350D from back in 2005. Here is another example - different set, different day, very similar green dot pattern -

http://lh6.ggpht.com/_MgTTnDDakGo/SULGcSYKfZI/AAAAAAAABmM/CqivVMtdwTA/s720/IMG_2784.JPG

Of the 75 night pics I've taken the last few days only 2 or 3 have these ghost dots - so I doubt it's a malfunction - fingers-crossed. It's gotta be light seeping in the viewfinder. I will say that both of these example pics are zoomed in tight with the kit lens - so maybe being at 50mm or above causes this to happen when a wider angle seems not to tend to be effected. hmmmm ...

[shroom]

Nope, it's not from the viewfinder. When you're exposing a shot the mirror is up, blocking the viewfinder from the light path through the camera.

The eyepiece cover is to prevent light through the VF from reaching the metering system, thereby causing underexposure.

Strange. You're talking about the horizontal and vertical rows of dots across the door and to its left?

-js
Okay, good to know. Yeah, the dots across the door. See my other example pic, too - similar pattern.

If it's not the viewfinder then it must be what I mentioned earlier - the kit lens picks something up when I zoom in towards the upper end of it's range - nearing 55 MM. I just gotta be careful from now on I guess.

Thx for all the help everybody.

[number six]

The kit lens is pretty bad for flare, which is my guess. Were you using a filter on it?

-js

[shroom]

The kit lens is pretty bad for flare, which is my guess. Were you using a filter on it?

-js
Just a UV filter - this "flare" sounds like the probable culprit - some sorta odd optical refraction situation at certain lens lengths. I just gotta figure out my no-go line when zooming into long-exp night shots like these - at least until I can afford a better lens. heh

[number six]

Just a UV filter

AHA! :lol:

Try it without the filter...

-js

[shroom]

AHA! :lol:

Try it without the filter...

-js
Sure, willing to try anything. I'll give it a shot. Do you think that'll help?
I don't see how changing the zoom would effect whether the filter does or doesn't flare some light. Worth a shot I suppose.
Hold it ... the more I think about the math and angles, the more I can see how it might. Good idea.

[garymercer]

AHA! :lol:

Try it without the filter...

-js

I agree. Could be a reflection off the filter!

[20droger]

It's ghosting, a form of flare. In your first picture, the "white" border around the "Music and Pawn" sign is actually an overexposed series of light bulbs. A reduced-intensity image of these light bulbs is what is causing the ghost in the center right of the image. If you look closely, you can see an image of the "M" in "Music" ghosting in the lower half of the door.

In your second image, the Christmas lights from the roof are creating the ghosts.

A ghost is caused when the light from an image bounces off a reflective surface in the lens or camera, moves away from the sensor, and bounce off a second reflective surface to utilmately reach the sensor at a greatly reduced intensity.

The first reflective surface is probably the sensor itself. The second reflective surface is probably the inside surface of the filter. I say this because the ghost is substantially the same size as the original image, which implies flat reflecting surfaces..

It is the extreme difference in luminance between the ghosting object (the lights) and the dark background where the ghost appears that causes the ghost to be visible.

[number six]

It's ghosting, a form of flare. In your first picture, the "white" border around the "Music and Pawn" sign is actually an overexposed series of light bulbs.

Aha! I didn't recognize the border as being light bulbs. Yep, that's it, all right. I see the M too, now that you point it out.

-js

[shroom]

The first reflective surface is probably the sensor itself. The second reflective surface is probably the inside surface of the filter. I say this because the ghost is substantially the same size as the original image, which implies flat reflecting surfaces..
Thanks for figuring that out. Very cleverly sussed out. I guess in daylight at "normal" shutter speeds you don't have to worry about that problem, but at night with long exposures I need to take that filter off. Thx to everyone for helping. I knew I was at the right place to find answers. Now back to lurking.

[hollis_f]

Thanks for figuring that out. Very cleverly sussed out. I guess in daylight at "normal" shutter speeds you don't have to worry about that problem,
Yes, you do. Whenever you use a filter the same sort of thing will happen.

You'll still have bright areas being reflected onto parts of the image where they don't belong. But because thos bits of the image are already fairly bright they won't be so obvious. But all those bright bits being reflected all over the place will decrease overall contrast in your images.

[neilwood32]

It may sound daft but try to use something to shade the lens to try to eliminate any additional light.That is in addition to removing any filter you may have.

[shroom]

Yes, you do. Whenever you use a filter the same sort of thing will happen.

You'll still have bright areas being reflected onto parts of the image where they don't belong. But because thos bits of the image are already fairly bright they won't be so obvious. But all those bright bits being reflected all over the place will decrease overall contrast in your images.
See, that's why I said that - knew somebody would set me straight if I'm wrong. The only reason the UV lens is on there is because it was on there when the camera was given to me and I've never taken it off. My research showed it to be protection again lens breakage more than anything. So I've left it on with the understanding that dropping is inevitable and the UV filter might sacrifice itself for the good of my kit lens someday. I'm a little more confident now about dropping prevention. Should I just 86 the UV filter from now on? Would it improve my photos?

[Tixeon]

Yes, you do. Whenever you use a filter the same sort of thing will happen.

You'll still have bright areas being reflected onto parts of the image where they don't belong. But because thos bits of the image are already fairly bright they won't be so obvious. But all those bright bits being reflected all over the place will decrease overall contrast in your images.

That's exactly why it's very important that any filter be multi-coated just like the lens surfaces. A proper sized lens shade will help eliminate many reflections outdoors too.

[number six]

Should I just 86 the UV filter from now on? Would it improve my photos?

I would. It'll make a difference when you have bright light sources in the picture, as in your posted shot.

-js

[SkipD]

My research showed it to be protection again lens breakage more than anything. So I've left it on with the understanding that dropping is inevitable and the UV filter might sacrifice itself for the good of my kit lens someday. I'm a little more confident now about dropping prevention. Should I just 86 the UV filter from now on? Would it improve my photos?NO screw-on photographic filter can provide any protection against dropping a lens. In order to provide protection, the filter would have to be able to crush. Crushing slows the impact time, and slowing the impact time reduces the peak impact forces. The solid rings used for screw-on filter just cannot crush and thus won't do a thing to prevent damage to anything but (possibly) the female filter threads in the front of a lens.

Time and time again we read about folks who dropped a filter-adorned lens - even with the lens within a camera case and with a lens cap on top of the flter - and smashed the filter glass. Shards of glass get blasted all over the surface of the lens and can even get jammed into tiny crevices around the front end of the lens.

The only kind of "protection" that a filter can provide for a lens is as a barrier to very light mass flying projectiles or water drops or keeping things from touching the lens (kids' fingers, dogs tongues, etc.).

[René Damkot]

Ditch the filter (at least in a case like this), use a hood for protection.

[20droger]

Just to set things straight, a protection filter protects a lens against things such as flying sand, salt spray, blown ice, or fingers, which can damage the front element (or its coatings) and, to some degree against moisture (rain and dog tongues). A filter cannot and does not protect a lens against impact with the ground, a door jamb, etc.

There is an exception to this. A glancing blow to the front edge of a lens, as by swinging from a neck strap and banging into a door jamb, can damage the filter threads on a lens. Even a very slight ding in the filter threads can render them useless. A filter does protect against this somewhat by having its own threads damaged instead, with or without breaking the filter glass.

A lens hood does protect against impact to some degree. A good hood is designed with this in mind, and Canon makes very good hoods. A hood is definitely better overall protection than any filter for any kind of impact, including the above-mention filter threads.

A hood also somewhat protects against flare from light approaching the lens at an angle. However, a hood cannot protect against ghosting. This is because, in order to produce a ghost, the offending light must enter the lens relatively close to the optical axis. Think about it. A ghost is the result of a double reflection within the lens-camera system. If the light were at any significant angle, it would not reach the sensor on the bounce.

Here is a fairly good but simple article on flaring and ghosting: http://www.vanwalree.com/optics/flare.html

[shroom]

Here is a fairly good but simple article on flaring and ghosting: http://www.vanwalree.com/optics/flare.html
Okay I read that ... and the lens hood page it links to. I also read this POTN thread (http://photography-on-the.net/forum/showthread.php?t=615467&highlight=uv+filter) and the faq linked a few posts into it. I agree with everybody that the filter isn't likely to save a dropped lens, but also realize that it might ease the damage if you bump it into something while swinging from the strap.

After all this I sorta feel it's best to ditch the filter except in "danger" situations when sticks and stones might be flying at me while I'm trying to shoot. I'd like to get a lens hood, but the one for this lens only extends 3/4 of an inch and most of the reviews I read thought it was generally useless for protecting against light, but handy against most bumps and bruises. So, I'm just gonna go filterless and hoodless and hope a dog doesn't lick my lens. Thx for all the help. I learned a ton and appreciate the responses.

[number six]

So, I'm just gonna go filterless and hoodless and hope a dog doesn't lick my lens.

:lol:

Yeah, the hood for the kit lens isn't good for much. It's a tiny thing.

Bear in mind that a hood won't help at all if the source of the flare/ghosting is actually in the picture, as in your example.

-js