|
Iceman and Merlin66 are correct. The size of your image increases as you increase your effective focal length.
The formula to calculate image size is:
Size of object in arsec X Focal length of Optical System in mm all divided by 206265.
For example, if Jupiter is 50 arsec in diameter and you are imaging with a system with a focal length of 2500mm, your image of Jupiter will be 0.6mm in diameter at the focal plane. Jupiter will cover about 107 pixels in a ToUCam with 5.6 micron pixels. For an LPI (with 8 micron pixels) Jupiter will cover about 75 pixels - this demonstrates why a ToUCam has a better image scale than an LPI for the same focal length!
If you increase the focal length of the above system to 5000mm (by adding a 2x barlow, for instance) the image of Jupiter will be 1.2mm in diameter at the focal plane. The image will cover about 214 pixels on a ToUCam and about 150 pixels on an LPI.
Robert_T, I think it's quite possible that your Mewlon may give you a larger image size than your SCT. The effective focal length of a 'compound' telescope ( eg an SCT or Dall-Kirkham Cassegrain) changes as you move the mirror to focus. It is possible that, even though your Mewlon has a stated FL of 2150mm it may have a very different value depending on where the mirror is. Your SCT may well have a different FL than that stated, again, depending on where the mirror is.
|