Is this noise caused by not covering the viewfinder fully?

I was trying out an idea I had for my 10 stop ND filter today and, having heard that stray light can get into the viewfinder and affect a shot I put something in front of the viewfinder in the lights path (but not completely covering).

I took the shot and its a bit underexposed...I gave up after realizing it wasn't going to work the way I had wanted it to. However, the shot I got looks like it was taken at ISO3200 or so. The camera was set to ISO200. I have a feeling this noise is caused by the viewfinder but I've honestly never seen an example of it before.

The image was a 30 min exposure so I didn't have the ability to try numerous test shots.

I would say that it was caused by the 30 minute exposure. Cool idea.

Yep. Long exposures produce noise. Did you have "long exposure noise reduction" turned on?

Brett wrote in post #9832833
Yep. Long exposures produce noise. Did you have "long exposure noise reduction" turned on?

This is straight RAW converted at defaults in LR.

I've seen that long ISO noise reduction setting for in camera JPG but I always thought it was to cover for stuck pixels.

doesn't the mirror cover up the viewfinder though?

rx7speed wrote in post #9832869
doesn't the mirror cover up the viewfinder though?

That was my initial understanding, maybe the reference was to metering? I know that canon includes the viewfinder cover on their strap.

rx7speed wrote in post #9832869
doesn't the mirror cover up the viewfinder though?

It does. The bit about covering the viewfinder is so the metering isn't thrown off by light coming through the eyepiece before the shutter trips, since that's when the camera does its metering. Once the shutter trips, the VF becomes irrelevant.

Long exposures heat up the sensor; hot sensors mean noisy pixels. It was the long exposure that made it noisy; try the Long Exposure Noise Reduction, which does a "black frame subtraction". You can do that now, in post-processing, by taking an exposure of the exact same duration with a lens cap on your lens, inverting it and masking the original photo with it.

Sdiver2489 wrote in post #9832838
This is straight RAW converted at defaults in LR.

I've seen that long ISO noise reduction setting for in camera JPG but I always thought it was to cover for stuck pixels.

It actually works with raw files as well. It uses "dark frame subtraction", taking an identical exposure with the shutter closed after the first exposure. It doubles the exposure time, but it maps out pixels caused by heat on the sensor in long exposures.

From Canon:

Noise reduction will be automatically activated when noise is detected in any exposure over one second. Noise reduction is subtractive, so after the initial exposure, a second exposure of identical length is made with the shutter closed. Noise from the second exposure is subtracted from the first image leaving a pristine, noise-free image. The only downside is the exposure takes twice as long.

Brett wrote in post #9832913
It actually works with raw files as well. It uses "dark frame subtraction", taking an identical exposure with the shutter closed after the first exposure. It doubles the exposure time, but it maps out pixels caused by heat on the sensor in long exposures.

From Canon:

Noise reduction will be automatically activated when noise is detected in any exposure over one second. Noise reduction is subtractive, so after the initial exposure, a second exposure of identical length is made with the shutter closed. Noise from the second exposure is subtracted from the first image leaving a pristine, noise-free image. The only downside is the exposure takes twice as long.

Thanks to both of you. I forgot that that was the purpose of this feature. I had it disabled thinking it was just additional "standard" noise reduction.

First time really trying an exposure this long so had never encountered this before. Thanks again!

keep in mind that long exposure noise reduction of a 30 minute exposure takes 30 minutes.

tkbslc wrote in post #9832999
keep in mind that long exposure noise reduction of a 30 minute exposure takes 30 minutes.

Yeah....luckily I just had a stopwatch running while I did other things . This is where the remote timer and/or connected laptop would come in handy.

how would you even meter a 30 min exposure though?
next question though is with the long exposure noise reduction would it have any effect under less then 1 second exposures?

tkbslc wrote in post #9832999
keep in mind that long exposure noise reduction of a 30 minute exposure takes 30 minutes.

Wow, I must have glossed over that it was a 30 minute exposure, although looking at the clock hand's movement, it should have been obvious.

Brett wrote in post #9833121
Wow, I must have missed that it was a 30 minute exposure, although looking at the clock hand's movement, it should have been obvious.

Hence the moving minute and hour hand

Sdiver2489 wrote in post #9833011
Yeah....luckily I just had a stopwatch running while I did other things . This is where the remote timer and/or connected laptop would come in handy.

What I mean is the camera does a long exposure black frame for the same duration you did the photo for. SO if you are doing a 10 minute exposure, after you are done, the camera locks up for 10 minutes and does its dark frame. So it can be annoying out in the field if you want to do multiple shots.