Meade DSI

The DSI PRO has a sensor which is 510x492pixels in size. That is the image size that will appear on your screen. Now each pixel is 9.6x7.5microns (1/10000s mm) across.

The formula to calucluate how much of the sky each pixel sees is;

Field of View = 3438arcminutes x pixel dimension /focal lenght

Calculating this out you get for each pixel on the dsi
.9902 arcseconds x .7735 arcseconds. So each pixel will see that sized piece of sky. Now that we know that we can see that the entire chip will cover a piece of sky (510x.9902) * (492 * .7735) = 505 x 380arcseconds.

In arcminutes (1/60 degree) thats 8.41 x 6.34 arcmins. Now that is a really small piece of sky.

Could you explain the forumula one more time, i got different values. What is the "pixel dimention" ?

Hi Eirik.

According to the meade website the sensor has pixels to 9.6(width)x7.5(height) microns. Im mm thats .0096mm x .0075mm (divide by 1000 fro mms).

Now putting that into the formula

FOV in ArcMins = 3438 x pixel size / focal lenght we get (for a 2000mm focal lenght);

FOV = 3438 x .0096 / 2000 = .0165024 arcmins * 60 = .990144 arcseconds (width) and
FOV = 3438 x .0075 / 2000 = .0128925 arcmins * 60 = .77355 arcseconds (height)

So now we know the FOV of each pixel;

With that info and knowing the chip is 510 x492 pixels in size we can just multiply by the number of pixels to get the FOV of the chip itself;

.990144 x 510 = 504.97344 arcsecs /60 = 8.416224 arcmins (width)
.77355 x 492 = 380.5866arcsecs /60 = 6.34311 arcmins (height)

Does that make sense? There is a progam which will calculate the field of view of your combination called "What U See", the link is down at the moment, I'll try find it.

I forgot to multiply with 60 :oops:

".0165024 arcmins * 60...."

Thx

Hey no worries, you dont have to go back to arcseconds and then forward to arcmins if you dont want to. I just think its interesting to see the pixel FOV in arcseconds cause it means something to me. A tiny fraction of an arcmin doesnt mean much.

Hi spaceboy could you tell me is the performance of the neximage the same as the toucam and is the neximager easy to use : regards Darren

Matthew & Darren,

I have not used the toucam so I can't compare the two, I think Dave Grennan has though.

Yes the neximager is very easy to use. What I do is first take the images with it connected to the laptop in the observatrory, then when I get home transfer them onto a cd-rom and process them on the desktop computer using the supplied registax software.

The instructions for using the neximager controls such as exposure, contrast, brightness of image and shutter speed are easy to follow.

If I could figure out how to place images within these messages then I'd show you a few to help you make up your mind about purchasing one.

Spaceboy