Feild of veiw indicators

[libraryman]

I'm not sure if this is the correct section for this post because it relates to my Canon 550D and the field of veiw indicators in software such as Stellarium or Sky 6.

Hopefully someone can guide me with respect to the sensor size of my 550D, when i imput the appropriate telescope and camera combination i see that the sensor field of veiw is the same for my 102 Vixen f/9 and my 200mm f/4.4 reflector

This seems really odd to me, i expected to see a larger ccd sensor box for the f4.4 because of the shorter focal length and wider feild of veiw.

The effect is the same in Sky six, which must mean software is not the problem...just me or my understanding of the feild of veiw

Ray

[JamesF]

"Plate scale" or "Image scale" is the amount of "sky" you can see per unit measure of camera sensor. It can be calculated as 1/f if you want the answer in radians, or 206265/f if you want the answer in arcseconds, but clearly the scale depends only on the focal length of the telescope.

In your case based on the figures you've given, the Vixen has a focal length of 918mm and the reflector 880mm meaning the plate scales will work out as 224 and 234 arcseconds per mm respectively. It wouldn't therefore suprise me to find that the fields of view are very similar for both. I get 1.37 degrees for the Vixen and 1.43 degrees for the reflector.

Obviously the the f/9 and f/4.4 figures are approximate and your actual focal lengths are, say, 900mm and 880mm there'll be even less difference.

James

[libraryman]

Thanks James, that has helped my understanding, i'm looking to try and image the Pelican nebular but i can only just fit it into the reflector feild of veiw.

i have the option of useing my Vixen with a reducer @ f/7.2 but with less apeture and rarther slow, i'm not sure if i'm asking a lot of it! would you comment on which scope is more siuted to this subject assuming that niether is perhaps ideal.

Ray

[JamesF]

I've never used fast newts for imaging so I'm probably not the one to be answering that. I fancy it might be somewhat easier to get a result using the Vixen if you want to widen the field though. I'd have thought that increasing the FOV with the reflector and keeping coma under control might prove tricky.

Perhaps someone who knows what they're talking about can answer properly though

James

[libraryman]

Thanks James, hopefully other forum users can help with regard to my best option for this target, as it happens i don't own a coma corrector yet but it is on my wish list

Ray

[sologuitarist61]

That is a very handy feature of Stellarium isn't it? I have my cameras listed and all my EP's (with the exception of the Baader zoom which I don't think will go in) and it is really handy to be able to decided at the planning stage just which EP you are going to need to get the object to fill the EP/sensor.

[OzDave]

I'd go for the reflector. With a slower image train you are just asking for more trouble. Consider that with the reflector, you'd be able to expose for the same amount of time, but capture more light and get a smoother image as a result.