FPS VS. QUALITY

Hello,

Does the FPS has a big affect on the image quality?
I know that the exposure time has to be increased with the FPS rate but does a 10FPS has better information then a 25FPS in it?
I use a SAC7B camera.

Kind regards,
Ido.

Hi Ido,

I'm not too familiar with the SAC7B but I suppose it's a USB1.X long exposure ToUcam family device ? If so, shooting at 25fps lowers image quality noticably. USB1.X has a maximum bandwith of 12MBit/s, transfering 640*480*8Bit*3Pixels at 25fps would in theory require 175.78 MBit/s. To achieve the framerate over the slow bus a lossy online compression is performed by cam and driver - the higher the framerate the worse image quality. Personally I don't use my ToUcams faster than 10fps.
This subject is the reason why todays planetary imagers long for cameras with USB2 or FireWire interfaces with 400MBit/s or more allowing much higher framerates without quality degradation by compression.

Best regards & clear skies,
Oliver

Hi Ido,

Actually the exposure time can not be any longer than the frame rate so faster frame rates will naturally have shorter exposures which helps a little in freezing the seeing but the biggest benefit IMO from faster frame rates(assuming uncompressed video) when imaging the moon or planets is that you are sampling the seeing more times in a given time frame and your chances of getting good frames increases.
If you take 100 seconds of video at 10fps and the seeing allows maybe 10% of the frames to be usable you will have 100 good frames but if you are imaging at 30fps and 10% then you could end up with 300 good frames I say could because it can vary a great amount but IMO on average your chances of getting good frames goes up along with the frame rate.
Something else I have noticed is that if the seeing is poor then higher frame rates will make little or no difference but with average to good seeing I have found higher frame rates to be beneficial, other factors are involved in it too such as if your scope aperture can support faster frame rates (enough light) that is one reason I chose an 18" scope.
After saying all that though the seeing is still the most important factor regardless of what frame rate you are using.

Thanks,

Wes Higgins

Ido Bareket said:

Hello,

Does the FPS has a big affect on the image quality?
I know that the exposure time has to be increased with the FPS rate but does a 10FPS has better information then a 25FPS in it?
I use a SAC7B camera.

Kind regards,
Ido.

Wes' comments are very true.

Another consideration under average seeing conditions is the benefit that can come from imaging at specific wavelengths to combat the air turbulence. In seeing conditions of 5-6/10 pickering It has been my experience that streams taken with a red filter show higher resolution than full visible spectrum streams or streams isolating the shorter wavelengths - even though the red filter required an increased exposure and 15 fps capture rate (instead of 30fps).

Alan

Hello,

Thank you all for the kind assistance.

Kind regards,
Ido.