Imaging The Pleiades cpc800 question

[zakkhogan]

i have a bit of a personal quest to capture The Pleiades when it back in the evening skies.

I will be using my cpc800, at F\10, as i dont have a reducer and my exposures will be limited to 10 - 15 seconds as i dont have a wedge..

I had very reasonable results with m3 last week, what results do i expect from this? will i capture any of the nebula or just the star cluster?

many thanks

Craig

[JamesF]

Do you know if you'll have a large enough field of view for the Pleiades?

James

[zakkhogan]

i'll be imaging with my dslr, so i assumed so, but i could be wrong

[JamesF]

I believe you end up with a field of view of 7.5x5 arcminutes for the 300D. I think you may need far more than that, but I will try to check my Maths in the morning.

James

[Psychobilly]

Here we go here the FOV of an APS-C sized sensor on an 8" SCT at F10 and with the F6.3 reducer... overlayed on M45

Peter...

[JamesF]

Looks like it's going to be a struggle to fit it all in...

I'm sure I got the calculations wrong doing it in my head last night. Plate scale in arcseconds per mm is about 206265 / focal length, or 101.5 arcseconds per mm. The 300D sensor is 22mm x 15mm I believe, which gives an area of sky 2233 arcseconds by 1522 arcseconds, or 37.2 arcminutes by 25.4 arcminutes. M45 must be at least a degree (60 arcminutes wide), so that tallies pretty well with Peter's image above.

You may need to look at creating a mosaic. Four panels might well do it without a reducer, two panels with.

I think you might pick up some nebulosity with a fifteen second exposure using the 300D though perhaps not much, but the best way to find out is to give it a try.

James

[zakkhogan]

Wow, thanks for all the very useful information, i had no idea how involved this stuff could get,

And i have no idea how you worked out the fov and i have no idea what an arcminute or arcsecond is for that matter (ive just been pointing and shooting)

however, i really appreciate all the in put, i think investing in a reducer is important,

Again thanks alot

[JamesF]

An arcminute is 1/60th of one degree, and an arcsecond is 1/60th of one arcminute. They're useful ways to measure distances across the sky.

The formula for plate scale comes from a bit of relatively simple trigonometry, but I'll save you the maths

James

[zakkhogan]

to ask a really noob question, how would i measure such a distance? for example, is it equal to the width of your finger?

[JamesF]

There are a number of ways you can make the measurements with your hands. The ones (I think I can remember are:

width of little finger: 1 degree

width of index, middle and ring fingers: 5 degrees

width of fist: 10 degrees

span of outstretched index and little fingers: 15 degrees

span of outstretched thumb and little fingers: 25 degrees

It's worth checking those against known distances in the sky if you want to use them relatively reliably. I struggle with the last two. I have dumpy fingers

James

[zakkhogan]

James.... you are a volt of information, thank you