Image scale question

[Chasm]

Hello,

I am attempting to order a camera for my telescope to begin learning imaging.  I just discovered the concept of image scale and wanted to verify something.  I have a Skywatcher 150mm/1040mm and wanted to order the ZWO ASI2600.  That camera is 26MP which, if Ive calculated correctly, gives me a 5.15 image scale.  Is that the wrong camera?  Do I need to stay around 9MP?

[Merlin66]

Chasm,

In astronomy the camera MP doesn't  mean anything..... that's for home photography.

What is important is the pixel size and the array size.

The ASI 2600 has 3,76 micron pixels and an array of 6248 x 4176 pixels.

Entering this data with your telescope (150/1040) gives a plate scale of 0.74 arcsec/ pixel. This would be a reasonable scale - depending on your local seeing conditions.

I use CCDCalc for these sort of calculations....http://www.newastro.com/book_new/camera_app.html

(the title of the camera/ lens is wrong but the data is correct)

[alacant]

16 hours ago, Chasm said:

150mm/1040mm and wanted to order the ZWO ASI2600. 

Hi

If you've a good mount and good atmospheric conditions, that should be fine. We sometimes need 0.75 as/p, so not every night is good enough to do it justice but It's always good to have a go anyway. Look at the images, not the numbers!

Cheers

[david_taurus83]

You'd be over sampling at that scale and unlikely to benefit due to seeing and loosing SNR. A focal length of 500 or less would be better for beginning. You could always bin 2x2 though.

What mount do you have?

[Chasm]

8 minutes ago, david_taurus83 said:

You'd be over sampling at that scale and unlikely to benefit due to seeing and loosing SNR. A focal length of 500 or less would be better for beginning. You could always bin 2x2 though.

What mount do you have?

It’s an eq6-r.  

[Chasm]

17 hours ago, Merlin66 said:

Chasm,

In astronomy the camera MP doesn't  mean anything..... that's for home photography.

What is important is the pixel size and the array size.

The ASI 2600 has 3,76 micron pixels and an array of 6248 x 4176 pixels.

Entering this data with your telescope (150/1040) gives a plate scale of 0.74 arcsec/ pixel. This would be a reasonable scale - depending on your local seeing conditions.

I use CCDCalc for these sort of calculations....http://www.newastro.com/book_new/camera_app.html

(the title of the camera/ lens is wrong but the data is correct)

That makes more sense.  What’s your opinion on CCD vs CMOS?  I’ve a processing learning curve ahead of me no matter what so...

[david_taurus83]

14 minutes ago, Chasm said:

It’s an eq6-r.  

You could probably get away with that focal length if you binned, just, with guiding. The other issue is field of view. It will be fairly narrow at that focal length. Good for galaxies but you won't fit large nebulae completely into view. Depends on what you want to image really. Give it a go with your current scope and see how you get on.👍

[Chasm]

1 hour ago, david_taurus83 said:

You could probably get away with that focal length if you binned, just, with guiding. The other issue is field of view. It will be fairly narrow at that focal length. Good for galaxies but you won't fit large nebulae completely into view. Depends on what you want to image really. Give it a go with your current scope and see how you get on.👍

Thanks David,

I haven’t bought the camera yet so, I can change it.  I’ll be happy with galaxies as I learn to image.  Nebulae can wait for a new scope but, in the meantime would I be challenging myself too much by getting a CCD SBIG 5.5 m/pixel mono camera with a filter wheel?  That would put my sampling at 1.1.  I’m completely new to the endeavor so it’ll be a learning curve at first in any case.   I’m thinking of going with the ASIair as well.  May even need to switch from Mac to windows depending on the processing recommendations I have yet to ask for.  I don’t mind going at this with a gear head start but, I don’t want to make it impossible.  More suggestions?

Thanks, Charles

[Merlin66]

The CMOS sensors can't be hardware binned like the old CCD chips. Any binning has to be done in the software post acquisition.

 

[alacant]

23 hours ago, Merlin66 said:

binning has to be done in the software

Hi

The latest asi cameras, one of which is listed by the op, do a pretty convincing bin in camera before it becomes a file on your storage device. It makes my own lowly 120mm super sensitive. Indeed, as if the pixels had been binned.

Cheers

[ollypenrice]

Image scale arises from pixel size and focal length as Merlin says. You have no realistic hope of resolving detail at 0.74" per pixel because, ignoring the seeing, your mount would need to deliver a guide RMS of half that, so about 0.35 arcsecs and an autoguided EQ6 is unlikely to provide that. And then the seeing will get you as well. Now with a CCD camera this would matter because this oversampling would cost you signal  in relation to noise. You could hardware bin to mitigate the problem. But with a CMOS camera is oversampling such a big deal? I would have thought not. Read noise is very low. If you over-sample, at least your results will be at the limit of your equipment and the sky. I wouldn't morry about it myself.

Olly

Edited November 2, 2020 by ollypenrice

[gorann]

13 minutes ago, ollypenrice said:

Image scale arises from pixel size and focal length as Merlin says. You have no realistic hope of resolving detail at 0.74" per pixel because, ignoring the seeing, your mount would need to deliver a guide RMS of half that, so about 0.35 arcsecs and an autoguided EQ6 is unlikely to provide that. And then the seeing will get you as well. Now with a CCD camera this would matter because this oversampling would cost you signal  in relation to noise. You could hardware bin to mitigate the problem. But with a CMOS camera is oversampling such a big deal? I would have thought not. Read noise is very low. If you over-sample, at least your results will be at the limit of your equipment and the sky. I wouldn't morry about it myself.

Olly

I completely agree with all what Olly says. You seem to be set at buying a colour camera and the ASI2600 is as good as they get - an outstanding camera with very low noise, no amp glow (so no need for dark frames) and a large field of view (APS-C). I cannot imagine that any CCD colour camera can compete with it's image quality, so forget about a CCD (especially colour CCD - I have hard to believe anyone would buy them anymore). Yes, you will probably be oversampling a little bit (except on that magic night when you are really lucky with seeing and your mount's performance) but that is no problem with this camera as Olly says.

[Chasm]

Things are starting to make a little sense but, I still have to look up new terms every time I read a reply so, I am holding off on imaging until I have researched a far, far greater amount on AP.   Haha!

thanks for the help.   I’ll be back.

charles