Canon 550D video crop mode

[Tommohawk]

I've been using video crop mode for some time quite happily for planets and lunar. but now a question occurs - how much of the sensor am I using?

If the sensor is 5184 x 3456 pixels, and each pixel is 4.3 microns, that makes 22.3 x 14.9 mm.

But if only using 640 x 480 pixels in crop mode, am I really only using 640 x 4.3 by 480 x 4.3 = 2.75 x 1.48mm ????

TIA

[spaceman_spiff]

Hi Tommohawk,

I thought that for each displayed pixel in an 640X480 RGB image, a 4-pixel Bayer matrix was required on the sensor. Meaning the area on the sensor would be 4x larger. I could be wrong here.

I use movie crop mode all the time and its quite amazing that my old eq5 mount can keep a target in this small region of the sensor for hours at a time even with my scope having an effective focal length of 3.2m!

Dan

[Tommohawk]

1 hour ago, spaceman_spiff said:

Hi Tommohawk,

I thought that for each displayed pixel in an 640X480 RGB image, a 4-pixel Bayer matrix was required on the sensor. Meaning the area on the sensor would be 4x larger. I could be wrong here.

 

Take your point about the Bayer matrix, but I think the 640x480 images display as 640x480. For sure when you take a normal image it displays as 5184 x 3456 - it doesn't reduce by a factor of 4. 

The Bayer matrix RGB information from each of the 4 pixels in a cluster is converted and then outputted on each pixel I think.

[spaceman_spiff]

Ok, that sounds more plausible.

It goes to show the precision required in getting anything in that 2.75mm X 1.48mm rectangle!

Dan