Calculating mag when imaging?

[Ramjo]

Hi

I'm fairly new to this been observing for 7 months, now want to try some imaging

I've got a SW 80ED pro and a 250pds with a EQ6, someone told me best to use the 80 for imaging and the 250 for observing??

Anyway my main question is if I connect my DSLR onto the 80 ED scope with a t adaptor and a 2x power mate how do I calculate what magnification I'm getting to the camera?

Is it as simple as the focal ratio 7.5 multiplied by 2=15mag?

[rfdesigner]

Working from resolution:

My 30D on my 1500mm fl scope gives me a shade under 1 arc second per pixel.

The human eye gives very roughly 1mm resolution at 1m = 200 arc seconds per 'pixel'. So my 30D on my scope will give me ~200x magnification.

All very roughly.

Derek

[hemihaggis]

hmm ,i would image with the pds , as you do not need to take as long exposures with it .

a camera body attatched to your 200pds will give about x20 mag

[hemihaggis]

Working from resolution:

So my 30D on my scope will give me ~200x magnification.

All very roughly.

Derek

ehh ?? 200x mag ... i would think it more like 20x mag ,

if you had 200x mag with a dslr attatched to your scope you would be able to get great pics of jupiter ..filling the picture ...so i suggest you go and take a pic of jupiter with your 30d and look at the tiny white ball on the image ...20x

[rfdesigner]

hmmm....

something's at odds here... quick look up on the ED80.. : 3" f5..

OMG.. that's one short scope.

I've been thinking in terms of my 1500mm fl scope (can't manage to image the full moon into 2500 pixels), rather than a 375mm fl ED80.

So 200x would reduce to 50x.

apologies for any confusion.

Derek

[Ramjo]

"something's at odds here... quick look up on the ED80.. : 3" f5.."

The ED80 is f7.5

[rfdesigner]

I'm not having a good day am I?

[rfdesigner]

Right.. After a lot more reading I think I have a decent definition; firstly.. just how good is the human eye?

Visual acuity - Wikipedia, the free encyclopedia

Well it would seem that unaided 20/20 vision gives about 60"arc resolution.

How good is a 600mm fl scope with a DSLR hanging off it?.. that's down to pixel size and will vary from camera to camera, but for sake of argument let's say we have 6.4u pixels (as in my 30D). This works out as 2.2"arc / pixel, some 27 times more sensitive than 20/20 vision.

Derek

[Ramjo]

I admire your perseverance with this, thanks

I was looking at your astro pics, how did you achieve those if you don't mind me asking?

[Helen]

Certainly use the ED80 for imaging and you'll have much more fun and much less pain than trying to image with a 10inch scope! ED80/EQ6 is a classic combination that can deliver outstanding results.

Helen

[rfdesigner]

I admire your perseverance with this, thanks

I was looking at your astro pics, how did you achieve those if you don't mind me asking?

me?

I used my lodestar autoguider on the 12" @ F5... unguided so lots of short (5~10 seconds) frames stacked. Being a monochrome CCD it's very sensitive. Processed in IRIS (which is free)

Once I get guided images (off axis guider turned up last week) then I can look to much longer frames (or subs) which will give much better images.

The big advantage of a shorter focal length scope is that the mount inaccuracies aren't magnified as much so you can image longer without guiding. The ED80 will get you a quite a long way justing using it with the DSLR and no auto-guiding. (I'd start trying for a moon shot, then have a go at M42)

Derek

[Ramjo]

Was having a go tonight until the EQ6 ground to a halt, those power tanks don't last long when you get the dew heaters out, I wonder if there is a way to run everything off the mains?

Was trying m31 but my DSLR only goes up to 30" exposures and that didn't seem to get much, was using the 250pds, also my alignment might be out as I was getting ever so slightly elongated stars