Light entering viewfinder during long exposure question

[matthew_lynes]

<p>I've recently purchased a B+W 10 stop filter to take long exposures during daylight on my 50D. However I understand light entering the back of camera can sometimes be an issue but the question is when is this a problem?<br>

Is it the case that when composing the shot it's an issue but once the shutter fires and the mirror flips up it prevents further light entering or is it the case that the viewfinder needs to be covered for the entirety of the shot? Does the mirror lock up mode make any difference here?<br>

Also is it the case that if I switch to live view when composing the shot, light does not enter through viewfinder.<br>

Any help and advice much appreciated.</p>

[bueh]

<p>Once the mirror is up, no light should be able to enter via the viewfinder.</p>

[test11664875106]

<p>Haven't read manual of my DSLR in details, but I remember from EOS 3 days that the manual explicitly advised to cover the viewfinder for long exposures and that's why there is built-in fixture on the neckstrap that fits tightly onto the viewfinder (need to remove eyepiece) so it's always there when you need it.</p>

[danield]

<p>It's only an issue with metering before taking the shot. When the mirror is down light entering the viewfinder joins with light entering trough the lens before reaching the meter. In most situation a lot more light enters via the lens than via the viewfinder, so this is not an issue. But with a long exposure or night-time shot there is less light entering through the lens so whatever enters through the viewfinder may have a greater impact on the meter readout.<br>

So cover the viewfinder before metering the scene. If you don't use the in-camera meter it doesn't matter. And while the shot is taken the light path trough the viewfinder is covered by the mirror so there's nothing to worry about.</p>

 

[zml]

<p>Some DSLR bodies (1D/1Ds series) have a built-in eyepiece shutter and AFAIK all other Canon DSLR bodies include a rubber thingy for that purpose. All this is for a reason, use it every time the eye is not close to the eyepiece during exposure to prevent any possibility of light entering the camera that way.</p>

[Charles_Webster]

<p>Canon provides a viewfinder eyepiece cover to deal with this. Mine is attached to the strap.</p>

<p><Chas></p>

[cabbiinc]

<p>Daniel D has it right about the metering. Typically when not taking a long exposure your eye is against the eyepiece blocking the light. When taking a long exposure usually you're on a tripod and may not have your eye against the eyepiece.</p>

[g dan mitchell]

<p>I've done daytime ND long exposures... and I haven't really found this to be a big problem, if it is a problem at all. As pointed out, it would show as a problem getting the correct automatic exposure. Light cannot get to the sensor this way during a shot since the mirror is up and blocking the path of the light.</p>

<p>If you are actually shooting such shots in Av, etc. modes, you can simply check this histogram display of the image after the first shot and adjust as necessary. </p>

[steve_dunn2]

<p>You definitely need the eyepiece covered (whether with your eye or something else) while metering.</p>

 

<p>During a long exposure, I'm not sure. Yes, the mirror flips up, but does it form a light-tight seal covering the entire focusing screen? I honestly don't know. I would err on the side of caution by assuming that there could be some light leakage, and therefore it would be wisest to cover the eyepiece. As others have pointed out, most if not all bodies either have a built-in eyepiece shutter or an attachment on the strap to perform this function.</p>

[jaydesi]

<p>I've been reading about IR photography with unconverted cameras, and most places recommend covering the eyepiece during the long exposures to prevent problems caused by light entering the eyepiece. In the OP's situation, with the light coming through the eyepiece stronger than through the lens (with the 10-stop filter in place), I suspect it would have a similar impact.</p>

<p>Night photography may not suffer the same way, since the ambient light entering the eyepiece is probably at the same level as the light coming in through the lens.</p>

[peter_langfelder]

<p>I use a 6-stop B+W filter, sometimes in conjunction with a polarizer. I usually hold a lens cap close to the viewfinder for the duration of the exposure, but the few times I forgot to this on the first exposure and did it on a second one I haven't seen any difference in the photos. It is possible that in extreme situations (if the viewfinder faces the sun and very strong light enters while you take a photo of a dark cave with your filter on and aperture f/22) there could be enough light leaking in through the viewfinder to cause a problem.</p>

[philip_wilson]

<p>Matthew it is a problem with light enetering the viewfinder and canon have got cheap as now only the 1 series gets a viewfinder blind (my 5DII and 7D do not). In the old days mid range cameras like the A1, T90 and EOS3 had blinds. On the strap (at least with the 5DII and 7D) they give you a plastic plug but I have never really found out how to get it to stay on well. What I do (if I remember) is hold a cloth over the viewfinder when shooting on a tripod. If you drape one carefully and use a remote release it blocks the light well.</p>

[JeffOwen]

<p>My guess is that light can enter via the viewfinder and onto the sensor because that is why Canon provides the rubber cap. Even with the mirror up there is portion of the mirror that is not fully silvered (the bit used to focus and expose the scene when the mirror is down).</p>

[andrewg_ny]

<p>I think part of the assumption is that when shooting from a tripod you're likely to not remain behind the viewfinder, you may be triggering the shot with self-timer or remote release, etc. When you shoot with autoexposure as soon as you move your head away it may affect metering accuracy. If you lock exposure by using manual mode, this shouldn't be an issue. I would expect Live View would also prevent this problem.</p>

[matthew_lynes]

<p>Thanks for the comments everyone. The rubber thing that came with my camera doesn't actually fit the viewfinder, so not something Canon have paid a huge amount of attention to on the lower tier bodies I guess.</p>

[steve_dunn2]

<cite>The rubber thing that came with my camera doesn't actually fit the viewfinder</cite>

 

<p>That's odd. I've had four EOS bodies (admittedly, all advanced amateur or semi-pro: Elan II, Elan 7E, 20D, 7D) and the rubber thingie on the strap of each one fit its viewfinder. It doesn't seem to make sense to ship a strap with the wrong viewfinder cover on it ...</p>

[philip_wilson]

<p>Steve I know the rubber cover on my 5DII and 7D fits the viewfinder once you have removed the VF eyepiece. Unfortunately on both my 5DII and 7D the weight of the strap pulls the cover partially clear - this is especially the case in sub zero weather. I know I can remove the cover from the strap and it will stay on but the whole exercise is very messy. All my 1 series bodies and even bodies from lower down the Canon film range like the EOS3, T90 and A1 all had a built in viewfinder blind like the 1 series bodies. Unfortunately the 7D and 5D do not as Canon was being cheap. While I could stand in a freezing field and mess with the viewfinder and cover I find it much easier to hold a cloth over the eyepiece. Generally when I shoot I like to keep checking the shots and framin through the viewfinder (even if I use live view and zoom in for critical focus). Pulling the viewfinder eyepice on and off and clipping and unclipping the rubber cover are just really messy.</p>

[e_thp]

<p>Hey Matthew, Yes it matters. You won't see it in every situation but if there's a strong lightsource behind your camera it will show up in your final image. The mirror does block light but it's not 100%.</p>

<p>Especially when doing long exposures or tripod work as your eye probably won't be against the viewfinder blocking the light.</p>

<p>I nearly had a fit when I started getting bars across my IR images. No amount of calibration or service or sending it to california could fix it and then somebody here on PN explained that I should start covering the viewfinder. D'oh!</p>

<p>To use the supplied cover you have to take the rubber eyepiece off of the square bracket around the viewfinder. Since I don't keep my strap attached to the camera I just use a piece of electrical or gaffer's tape.</p>

<p>Last week I was out taking pics of a cemetery at about 10 pm with a security light directly behind me and I had nothing so I hung my baseball cap on top of the body with the bill floating backwards.</p>

<p>This isn't something you should worry about greatly. If you need it you'll know. if not. why worry :p</p>