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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 05 Oct 2012 (Friday) 09:06
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Is what you see thru the viewfinder EXACTLY what the photo will be?

 
jwhittaker
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Oct 05, 2012 09:06 |  #1

I thought I knew this, the answer should be YES - that's what SLR is all about.
But I am confused now. I have a 1.4 35mm Samyang manual focus lens I just got.
If I have this set to 1.4 aperture and look at books on my bookshelf (about 4 feet away) thru viewfinder, I can clearly see the small print of the books titles.
But when I take the picture, I can't read the titles on the LCD screen, they are out of focus.
Makes no sense, the viewfinder is smaller than the LCD and I can read it, but not on the LCD - it is out of focus.
I am thinking that maybe at 1.4 aperture the field of focus is so narrow, that where the mirror sends up the image to the viewfinder is a different position to when the mirror is out of the way (eg the sensor screen).
Any one know what I mean?, or can cast any light on this?


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Sirrith
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Oct 05, 2012 09:09 |  #2

The viewfinder cannot show you true DOF at apertures wider than around f2.8 or f4. Also, unless you have a 100% viewfinder, you will get extra bits on the edges showing up on the LCD when you take the photo. Finally, the particular problem you are experiencing could be down to slight movement on your part before the photo is taken, throwing the subject out of focus, since at 1.4 and 4 feet the DOF is very shallow.


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Oct 05, 2012 09:13 |  #3

Most new SLRs aren't made with accurate MF in mind. The focusing screens aren't optimized for it and the positioning may be off. Shimming the screen may help.


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jwhittaker
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Oct 05, 2012 09:17 |  #4

I just did a little test........ Looking thru viewfinder I can see the book title clearly, if I press the liveview I can see the title is blurred, switch back to viewfinder and clear. Weird.
I really need the viewfinder to be accurate (of course!), I will look at shimming, not sure what that is.


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Sirrith
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Oct 05, 2012 09:27 |  #5

It could be your dioptre setting. Try adjusting that.


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jwhittaker
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Oct 05, 2012 09:42 |  #6

Thanks I tried the diopter but no difference. On liveview, if I get it in perfect focus, then slightly go too far to make it out of focus, then look through viewfinder it is still in OK focus (up to a point).
So the viewfinder has more tolerance for what it shows as in focus as opposed to live view/ the actual photo.
Seems to be a discrepency. I guess it may be a shim needed?


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melcat
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Oct 05, 2012 09:45 |  #7

As Sirrith says in #2, your viewfinder screen is such that you can't see f/1.4 on your camera through the finder. What you do see is exactly what you'd see if you used the depth of field preview to look through the lens stopped down to (on most Canons) around f/2.5.

Some Canon cameras allow the screen to be changed. Yours doesn't. Camera companies like to do this because they can then assemble the finder to lower accuracy. Hence the references here to "shimming", but doing so still won't make it WYISWYG.

If you want WYSIWYG you need a camera which takes a "super precision" screen (type number ends in -S).

If you *don't* have an -S screen installed, manual focus is tricky. You need to pick a midpoint between when it's just out of focus front and back, and the position of the midpoint between those two varies according to a complex formula involving distance, aperture and focal length. Shimming might help with that. Personally, I regard it as too hard to bother with and won't use such a camera with fast lenses.

For that reason, I wouldn't buy the 7D, 5D Mk III, 1DX or any Nikon.




  
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mwsilver
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Oct 05, 2012 09:47 |  #8

jwhittaker wrote in post #15082883 (external link)
I thought I knew this, the answer should be YES - that's what SLR is all about.
But I am confused now. I have a 1.4 35mm Samyang manual focus lens I just got.
If I have this set to 1.4 aperture and look at books on my bookshelf (about 4 feet away) thru viewfinder, I can clearly see the small print of the books titles.
But when I take the picture, I can't read the titles on the LCD screen, they are out of focus.
Makes no sense, the viewfinder is smaller than the LCD and I can read it, but not on the LCD - it is out of focus.
I am thinking that maybe at 1.4 aperture the field of focus is so narrow, that where the mirror sends up the image to the viewfinder is a different position to when the mirror is out of the way (eg the sensor screen).
Any one know what I mean?, or can cast any light on this?

What are you actually focusing on, the books, or something closer? Did you try the same test at say f/8


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jwhittaker
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Oct 05, 2012 09:50 |  #9

Yes focusing on books. No probs at say f4. I think the guys above have got it sussed, the OEM focussing screens can't deal with f1.4. thanks.


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Wilt
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Oct 05, 2012 09:55 |  #10

jwhittaker wrote in post #15083045 (external link)
Thanks I tried the diopter but no difference. On liveview, if I get it in perfect focus, then slightly go too far to make it out of focus, then look through viewfinder it is still in OK focus (up to a point).
So the viewfinder has more tolerance for what it shows as in focus as opposed to live view/ the actual photo.
Seems to be a discrepency. I guess it may be a shim needed?

The issue with dSLRs is that the focus screen has been purposefully made to be BRIGHTER and therefor less precise in its ability to show 'sharp focus'. This is because half of the light is already stolen from the viewfinder and redirected down to the AF sensor!
In film SLRs, all the light goes up to the viewfinder, so the focusing screen can be 'coarser' in its texture...which makes it more precise in depicting sharp focus. And since it gets all the light, it can be coarse-textured without the viewfinder being too dim to use.

So, with the dSLR standard focus screen, it is possible for the viewfinder to SEEM to be in focus, when it actually is not...which is when the Live View screen is a bit blurred.
When you focus first with Live View, the actual focus is sharp, and you can throw it a bit out of focus, and yet the focus screen in the viewfinder still seems to be 'in focus' (but the AF sensor is not fooled)

...And your statement in green text is verified!
That is why Canon offers option screens, like the Ex-S screens which are advised for f/2.8 and faster lenses...it is a bit coarser (like the old film SLR focus screen) and it needs to be used with faster lenses so the viewfinder is not too dim.


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Ramon-uk
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Oct 05, 2012 10:06 as a reply to  @ Wilt's post |  #11

I agree with everything said so far about the standard focus screens but you should also realise that sharpness is relative to image size. The size of the image through the viewfinder is much smaller than that of the live view screen so will not show focussing defects as easily.

If you have an unsharp image, say 2ins x 3 ins and then reduce it to a thumbnail it will look sharper.




  
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jwhittaker
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Oct 05, 2012 10:10 |  #12

Ramon, the thing is that being able to read text or not is the real test. I can read the text through the small viewfinder, but not on the larger liveview screen, that's what alerted me to the issue as I would have understood if it was the other way round.


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Wilt
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Oct 05, 2012 10:17 |  #13

jwhittaker wrote in post #15083166 (external link)
Ramon, the thing is that being able to read text or not is the real test. I can read the text through the small viewfinder, but not on the larger liveview screen, that's what alerted me to the issue as I would have understood if it was the other way round.

Effectively, the viewfinder display has more 'depth of field' preview than the Live View display. A coarser focus screen would have less 'depth of field' preview than the finer textured dSLR focusing screen. In the past, a clear screen on film SLRs presented a very bright image, but little to no perception of 'out of focus'.


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Oct 05, 2012 10:26 |  #14

If your 600d is anything like the rebel xti (400 or 450d, I forget) I use sometimes then it probably exaggerates dof quite severely. Compared to my 1d2 or the 5d3 it is quite pronounced, manual focusing with a fast lens isn't much fun. Try to pick the midpoint of the in focus range if you must.


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sebr
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Oct 05, 2012 10:36 |  #15

As others have said, the viewfinder does not display the depth of field accurately and everything outside the focal plane will be more blurred than it looks like.
Another difference between viewfinder and photos is that the viewfinder on your camera does not cover the entire image and the actual picture will be larger than what you see.

This is something that you get used to after a while...


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Is what you see thru the viewfinder EXACTLY what the photo will be?
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