Shutter speeds and frame rates?

[stefski]

Hi All,

I'm currently playing with an old Toucam, but also thinking about future purchases...I'm afraid I get confused with the pros and cons of frame rates and shutter speeds.

If you have a shutter speed of say 1/2500. This means the 'shutter' opens and closes 2500 times a second (or is it a minute?). Then a frame rate of let's say, 30 fps. Does that mean that the shutter opens and closes 83 and a bit times per frame? Does anyone know what would be ideal for solar work in white light (I've got all the necessary filters). What is compression? Is there any literature that can explain all this stuff to someone who still thinks of cameras as boxes with a hole that contain a role of film!

Stef

[GazOC]

If you have 1/2500 sec shutter and 30 FPS frame rate then you'll end with 30 frames at the correct exposure. The camera just takes the next availaible 1/2500 sec exposure once it has finished processing the previous frame.

But when shutter speed is longer than the frame rate, it effectively becomes the frame rate because the camera is waiting for the next exposure after it had finished with the previous frame, rather than the other way round.

[Cornelius Varley]

Shutter speed means how long the shutter is open for, so 1/2500 would mean the shutter would be open for 1/2500th of a second. Framerate means how many images a second the camera takes, 30fps is 30 images per second. Regarding compression, webcams are fairly lo-tech devices and to achieve higher frame rates the data stream from the camera needs to be compressed, not all the information coming from the imaging sensor is converted into the signal being sent to the computer, only the differences between one frame and the next (the mpeg video format works in a similar way). If I was using a webcam for solar photography I would still use the same framerates as for lunar or planetary imaging ie 10 fps max.

Peter

[stefski]

Thanks you two for making it a little clearer:).

Gaz...

If you have 1/2500 sec shutter and 30 FPS frame rate then you'll end with 30 frames at the correct exposure. .

Forgive my stupidity:iamwithstupid:, but what do you mean by 'correct'? Do you mean the shutter speed shouldn't be any slower for the sun.

Stef

[Merlin66]

Gaz just means you'll get 30 exposures at the 1/2500 (or what ever you set)

For the Sun it depends on the total filters you have, I'd start at about 1/1000 sec and work from there.

[GazOC]

Thanks you two for making it a little clearer:).

Gaz...

Forgive my stupidity:iamwithstupid:, but what do you mean by 'correct'? Do you mean the shutter speed shouldn't be any slower for the sun.

Stef

Sorry Stef, I just mean the exposure/ shutter speed would be the 1/2500 that you had set and not 1/30 for the framerate or 1/83 as a combination of the two.

Correct wasn't really the er...correct word!!

[stefski]

Okey cokey, now I getcha.

Cheers, Ken also.

At the mo, I've got Baader solar film + Baader solar continuum + IR blocking filter on the TMB 80. I've had some success with the Toucam just set on 'auto', but I would like to use my Watec camera, which is a better quality mono. However, there aren't any 'auto' settings on the Watec so I needed to know from some of you experts about what I should be doing so I don't wreck the chip!

I'll try the 1/1000 setting and have a fiddle when the sun finally returns.

Cheers again for your help.

Stef