Cameras and image size

[Kevdan]

Hi All,

How do you know what your camera is capable of? They say that a SPC880/900 is similar to a 6mm eyepiece which with my 2x barlow gives me about as much as I can get from my scope,

However I got a Pentax istDL DSLR which is 6.31mp CCD and the images even with the Barlow are hundreds times smaller So how do you know what I need to use to get bigger sized images, If I used barlows I would need about 30 2x stacked and thats pretty impractical.

Kev.

[Bizibilder]

Try:

The New CCD Astronomy Home Page

It shows image size (DSO's) for all common camera/scope combination you can think of!! Plus you can add your own specific ones if they are not on the list.

[MorningMajor]

I'm no camera expert, but the webcam does 600x480 pixel images, and will do so whether it's in a Barlow or not, or if you use a focal reducer or not. At 6.1 mp the picture size will be larger, but the image itself will remain the same,

I'm sure a phtotgrapher will explain it better, but I think my theory is right

[polakovic]

Try this: FOV Simulator

Peter

[jgs001]

Whilst the Pentax sensor is only 6.3 Mp, that's not the real story. The chip dimensions are key... the webcam is about 5mm on the diagonal, whereas the SLR is 23.5 x 15.7 mm (not sure on the diagonal, but it's a lot bigger). Seen another way... converting everything to 35mm equivalent numbers for focal length... You 150 has a 750mm focal length...

With a full frame camera, that's 750mm...

With the Pentax, the FOV is equivalent of 1200mm (1.6x crop)

With the webcam, the FOV is equivalent of 6375mm (8.5x crop)

Those numbers are a little approx (not sure on the exact webcam crop factor), but it gives the right idea... You can (!!!) use an SLR with far too many magnifiers to get to a similar FOV, but... it really isn't worth it.

[Kevdan]

With a full frame camera, that's 750mm...

With the Pentax, the FOV is equivalent of 1200mm (1.6x crop)

With the webcam, the FOV is equivalent of 6375mm (8.5x crop)

Thanks but what is a crop factor ?

[jgs001]

the crop factor is the approx size difference between a 35mm frame and the size of the sensor of the camera your using.. a consumer DSLR is 1.6x (APS-C), the Pentax. The FOV of the iamge you get through a lens should be multiplied by the crop factor to show the focal length of a lens you'd need to use on a 35mm camera... it's a way of getting an idea of the scale provided...

[Kevdan]

Ok I got it now.

Cheers.