How can I tell how big targets are going to be when planning?

[swag72]

I am doing a little database for targets to image and in it I am including the size of the target. When I want to know how big something will appear in my image, how can I work this out?

For example - A spiral galaxy that is 6.9' x 6.4' - How big will that appear in my SW120ED and Atik 314L? Is there a simple way to get an idea?

Also, with regards to size in astronomy targets - as a measurement is ' larger than " and is 180" for example larger or smaller than 300"?

[RikM]

Try this FOV estimator.

[pete_l]

You'll find lots of field of view (fov) calculators on the web. After you have used one to discover the fov of your telescope/ccd combination, it's just a case of comparing the fov with the size of the object in question.

[swag72]

Cheers Rik - I use this FOV calculator, but I am looking at a lot of more obscure NGC numbers that aren't in this.

@Pete - So I work out the FOV of my telescope / camera combo which gives me a figure, how does that then corespond to the figures on my database for example?

Does that make sense?

[steppenwolf]

Sara, if you use the FOV calculator detailed in the 'Frame' chapter in my book, you can enter this data into a planetarium program like Cartes du Ciel and produce an overlay of the sensor on top of any object thus seeing exactly how it will fit AND you can determine the best orientation for your camera to make the best of the image..

[swag72]

That works well Steve - And in my fiddling with CdC I've got the overlay of my 2 scope combo. But if I find something without a picture - Then I'll have to work it out for myself I guess

[Bizibilder]

Try "CCD Calc" (freeware) - you can enter the details of your scope and camera and it shows a picture of your object of choice within a fov box. Admittedly it only has a library of a few hundred DSO's (including all the Messiers) but you can estimate from them quite easily for less common targets.

[Parallax]

I was going to suggest New Astronomy Press CCD Calculator but I can't get the links to work.

This would have done exactly want you want. You inout your scope and camera details and it displays a real image and a border equivalent to your FOV. There are lots of IC, NGC, SH2 etc (separate d/l).

All rather academic though, if the links don't work!

Steve

[swag72]

Cheers folks - CdC seems quite good so far and I am already using New Astronomy Press CCD Calculator.

Appreciate you all taking the time to answer.

[Komet]

Cheers folks - CdC seems quite good so far and I am already using New Astronomy Press CCD Calculator.

Appreciate you all taking the time to answer.

Are you also using the extra objects pack with it - there are loads?

Fleming Astrophotography

[ianaiken]

I use Astroplanner which is pretty cool as it gives you data like transit time of the object, declination at a specific hour and draws nice graphs and stuff to show you and can show you images of the targets and how they look in you defined equipment list, you can then easily change your equipment to see what impact this has. Also you can then sync your FOV with CdC. See AstroPlanner

[swag72]

@Mick - Great link, duly downloaded!

@Ian - Ken (Merlin66) has mentioned AstroPlanner in another thread - may have a look see.

[ronin]

The prime image is the scope focal length times the subtended angle in radians.

That is an approximation as for small angles Tan (Ang) = Ang if you use radians.

That will give the image that falls on the chip assuming the chip is at the prime focus.

Andromeda is 1.5 deg, this is about 0.03 Rad, so the image is FLx0.03 millimters in size. Don't know the FL of a SW120ED.

Another approximation is that 1 deg = 1/50 rad.

[ronin]

Using the information you gave:

120ED believe this is f/7.5 so 900mm FL

The galaxy is a little smaller then 7x7 arc minutes.

This is 0.117 degrees, this is 0.0023 Rad. (I used 50 deg=1Rad not the 57 so the value above is a bit bigger then it should be, countered by me picking 7 arc minutes for the galaxy size.

This makes the image at prime focus ~= 900*0.0023mm = 2.1mm on the chip.

So you are looking something in the 2mm size image on the chip.

Depending on the pixel size depends on the resolution you get.

[ollypenrice]

I'd have thought Andromeda (M31) was a little over three degrees. Am I missing something?

Olly

[lukebl]

That works well Steve - And in my fiddling with CdC I've got the overlay of my 2 scope combo. But if I find something without a picture - Then I'll have to work it out for myself I guess

It's really easy to get a picture of the area. In CdC Just zoom into the area of interest, then click on the 'DSS' button to get an exact image of the area. Here's a screen grab from CdC showing the precise field of view of my SXVF camera:

And here it is with the DSO image downloaded:

I use this feature all the time to choose which objects to view and image. Absolutely brilliant.

[swag72]

I wondered what the DSS button did!! Cheers all!

[swag72]

Does the DSS info stay for always or just until you switch off CdC? It seems to slow the processing down rather significantly.

[lukebl]

Does the DSS info stay for always or just until you switch off CdC? It seems to slow the processing down rather significantly.

It does slow it down, and doesn't save it when you switch off CdC. It also won't attempt to display the DSS image if the field of view is too large (any larger than about 2 degrees, I think). Despite this, I find this feature really useful