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Author Topic: SLR parallax in viewfinder  (Read 4553 times)

eyebeam

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SLR parallax in viewfinder
« on: September 20, 2007, 03:32:09 PM »

Has anyone noticed, for lack of a better term, a parallax effect on the viewfinder for a SLR?

For example, when taking a macro-shot of a small spider. I center the spider body just inside the distant sun (at sunset) using the viewfinder.  The sun and spider combination is in the upper third of the viewfinder screen. However, when I trip the shutter, the image shows the spider is no longer centered in the sun, half of it is below the sun - as shown on the lcd on teh back of the camera.

I dont beleive this is not due to the camera moving, nor the movement of the sun. If I look through the viewfinder after the shot, the spider is still centered within the sun. I'm using mirror lock-up and a sturdy tripod.

Camera is a Canon 5D, lens is the canon macro 100mm. I have also observed the phenomena shooting macro with the canon 70-200mm (with a close up lens 500D).
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Bill in WV

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SLR parallax in viewfinder
« Reply #1 on: September 20, 2007, 07:37:46 PM »

Quote
Has anyone noticed, for lack of a better term, a parallax effect on the viewfinder for a SLR?

For example, when taking a macro-shot of a small spider. I center the spider body just inside the distant sun (at sunset) using the viewfinder.  The sun and spider combination is in the upper third of the viewfinder screen. However, when I trip the shutter, the image shows the spider is no longer centered in the sun, half of it is below the sun - as shown on the lcd on teh back of the camera.

I dont beleive this is not due to the camera moving, nor the movement of the sun. If I look through the viewfinder after the shot, the spider is still centered within the sun. I'm using mirror lock-up and a sturdy tripod.

Camera is a Canon 5D, lens is the canon macro 100mm. I have also observed the phenomena shooting macro with the canon 70-200mm (with a close up lens 500D).
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Parallax error is a misalignment with the sighting lens and the taking lens, sort of like the old twin lens relex; in a single lens reflex that is sort of impossible. And if the spider is still centered after your shot, you moved something when you looked. See below:

You missed one in counting what was or wasn't moving . . . The Earth it self is spinning along at about 1,000 miles an hour give or take. Let's see, the circumference of the Earth is about 25,000 miles, it makes a complete revolution in about 24 hours, yup that's a little more than a 1,000 miles an hour.

You have to act pretty quickly when using astronomical bodies in your photos. Check with your local astronomy club for hints or how to make a cheap clock drive.

Bill in WV
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Bill Evans

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Tim Gray

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SLR parallax in viewfinder
« Reply #2 on: September 20, 2007, 07:49:06 PM »

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Parallax error is a misalignment with the sighting lens and the taking lens, sort of like the old twin lens relex; in a single lens reflex that is sort of impossible. And if the spider is still centered after your shot, you moved something when you looked. See below:

You missed one in counting what was or wasn't moving . . . The Earth it self is spinning along at about 1,000 miles an hour give or take. Let's see, the circumference of the Earth is about 25,000 miles, it makes a complete revolution in about 24 hours, yup that's a little more than a 1,000 miles an hour.

You have to act pretty quickly when using astronomical bodies in your photos. Check with your local astronomy club for hints or how to make a cheap clock drive.

Bill in WV
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I doubt the earth suddenly went retrograde for a second to put the spider back in the sun after the shot was taken
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eyebeam

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SLR parallax in viewfinder
« Reply #3 on: September 20, 2007, 10:07:38 PM »

Thanks for your thoughts and comments. I know the earth rotates and that is why I mentioned the fact the viewfinder showed the spider and sun  still concentric after the image was captured.

However, I think I figured it out by trying to duplicate the effect at home. I should have caught it before posting this.

The effect is due to the fact that I was composing my image with the viewfinder (at F2.8) and the image was captured at F16. When looking through the viewfinder, the OOF sun is very large and therefore surrounds the in-focus image (spider). However, when the image is captured, the camera is stopping down to F16 and the OOF image of the sun is significantly smaller.
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Wayne Fox

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SLR parallax in viewfinder
« Reply #4 on: September 21, 2007, 12:21:55 AM »

It is possible for the mirror assembly to become misaligned in SLR cameras so what you see in the viewfinder isn't "exactly" what the lens is seeing.
« Last Edit: September 21, 2007, 12:22:12 AM by Wayne Fox »
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Bill in WV

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SLR parallax in viewfinder
« Reply #5 on: September 21, 2007, 11:00:11 AM »

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It is possible for the mirror assembly to become misaligned in SLR cameras so what you see in the viewfinder isn't "exactly" what the lens is seeing.
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First, let me apologize if my first reply seemed sarcastic, but sometimes the solution is that simple and people do forget about relative motions between objects. I have both telescopes and binoculars and the telescopes have clock drives with four different speeds for the different objects observed, sun, moon, and two different rates for deep sky objects (either one can be used(?)), and you care share the view with others for several minutes. On the other hand, I mount the binoculars on a tripod and move them with the object, if you turn away to call someone else to take a peek, at the moon for instance, it may be gone when you get back. Oh, and be extremely careful looking at the Sun.
Here is a shot through an astronomical solar filter on an 8" telescope, I forget now which eyepiece or magnification I was using:
[a href=\"http://www.pbase.com/bill_in_wv/image/30977842.jpg]http://www.pbase.com/bill_in_wv/image/30977842.jpg[/url]

Now to your last question, anything is possible but I personally would consider highly unlikely if everything is still working and you are not hearing unusual noises coming from the mirror housing, but here I am not an expert by any means. It just seems like the tolerences would be too close for that to be happening. I would guess it more likely, because I wear glasses and do this to myself all the time, is not aligning the eye with the finder the same way each time. I find that sometimes I get involved with composition, looking at some particular item in the finder but when I check the LCD after the shot, it's off to one side or the other or the alignment has changed from what I thought it was when I pressed the release. I also find it doesn't happen as often if I remove my glasses and get closer to the finder. Maybe that's why so many people try to use the LCD for composing with P&Ss and forego the optical viewfinder, I still prefer to look through my camera instead of at it.
That's enough of a ramble for today, again, my apologies if my first reply sounded smarta$$ed, it was not my intent.

Bill in WV
« Last Edit: September 21, 2007, 11:05:59 AM by Bill in WV »
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Bill Evans

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AndyF2

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SLR parallax in viewfinder
« Reply #6 on: September 21, 2007, 12:30:44 PM »

Quote
Has anyone noticed, for lack of a better term, a parallax effect on the viewfinder for a SLR?

For example, when taking a macro-shot of a small spider. I center the spider body just inside the distant sun (at sunset) using the viewfinder.  The sun and spider combination is in the upper third of the viewfinder screen. However, when I trip the shutter, the image shows the spider is no longer centered in the sun, half of it is below the sun - as shown on the lcd on teh back of the camera.

I dont beleive this is not due to the camera moving, nor the movement of the sun. If I look through the viewfinder after the shot, the spider is still centered within the sun. I'm using mirror lock-up and a sturdy tripod.

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Are you using a cable release?  If you're squeezing the shutter release button directly on the camera even if it's on a tripod with the head clamped down, you could be deflecting the camera slightly, and it returns to it's proper position once you relax your grip on the camera.  A cable release will avoid this.
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Jonathan Wienke

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SLR parallax in viewfinder
« Reply #7 on: September 21, 2007, 01:30:12 PM »

It's not possible for an SLR to have a parallax difference between viewfinder and image where objects are in different positions relative to one another in the image. But variations in the viewfinder mirror alignment and other factors mentioned can result in slightly different crops of the lens' image circle being recorded vs. viewed.

eyebeam

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SLR parallax in viewfinder
« Reply #8 on: September 21, 2007, 01:42:18 PM »

To Bill in WV - nope, I'm not offended. Underestimating the effect of earth's rotation is a common mistake - I've made it before - but it wasn't a problem in this case.

To ANDYF2 - I'm using mirror lockup with a timed release, so my hands are not touching the camera when the shutter releases.

Last night I reproduced the effect at home. The cause appears to be, for the most part, the size of the out-of-focus sun. When looking through the viewfinder, the OOF sun is quite large and easily surrounds the in-focus object (spider). The composition was arranged through the viewfinder with the lens (automatically) at F2.8. The image was captured at F16. I described this (error) in post #4 of this topic.

So, if I look through the viewfinder while stopping down the lens, then I see exactly the image captured. There is no difference.

However, there may be something else going on. I think the relationship between the position of the close object and the OOF distant object may change with Fstop. I dont know this for sure, but I will check it out when I get home.
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eyebeam

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SLR parallax in viewfinder
« Reply #9 on: September 21, 2007, 11:54:04 PM »

Confirmed it. The secondary effect is that the center of the out-of-focus distant object changes with F-stop. This effect is greatest at the corners of the viewfinder and is nil when the OOF object is positioned at the center of the viewfinder. This effect is minor, but its there.
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