Need advice please for tonight ( 19th July) - Comet Neowise - do you think I'll be able to image it with a Celestron NexImge 10 camera in a 5" Newtonian?

[StarGazingSiouxsie]

Hi, sorry for short notice!! 

I'm contemplating using my NexImage 10 Celestron camera to try and get some stills or video of Comet Neowise this evening. 

I've confirmed the camera does work with Cassie (my 5" Newtonian)  by experiementing with daytime terrrestrial video. I am using Sharpcap software.

I am a total novice at astroimaging and using a camera in a telescope. I have not used my camera for nightime viewing thus far but what an opportunity I have with this comet!!! 

So, do you think I'll be able to get some stills or video? I mean, do you think the comet will be too faint for the camera to pick up? I can see the comet clearly and quite bright through my eyepiece. 

I have been told and have read "If you can see it through the eyepeice you'll be able to see it (image it) through the camera". 

Do you think that's a generally true statement??   

I have been able to see the comet through Cassie on previous evenings this week, using a 23mm eyepiece. 

Will I need to use a Barlow lens, or would using one give me a better image through the camera?

Cassie is not on a goto mount, she is on an altaz mount with manual fine adjustment controls. 

So I am thinking of getting the comet in her FOV first, sighgting it with my 23mm eyepiece, enjoying a bit of visuial observing and then puting the camera in. 

I'll have my laptop running Sharpcap in real time on a table beside Cassie so I can see whatever images I get and make focus adjustments etc.

I wonder if putting the camera in will mean a massive amount of having to re-sight the comet in Cassie's FOV??

Any and all advice, tips, suggestions or ideas gratefully received, thank you.

Siouxsie 

Edited July 19, 2020 by StarGazingSiouxsie

[JamesF]

I think it will be tricky, to be honest.  I don't know what focal length your newt has, but I suspect you're not going to have much of a field of view with the Neximage camera compared to the size of the comet.  I'd expect that would also make it hard to focus and track, and perhaps even to find the comet when you switch from an eyepiece to the camera.

Don't let me stop you having a go, though.  It may well work out far better than I imagine

James

[StarGazingSiouxsie]

Just as an aside, I've got my best views of the comet thus far through my 10x50 binoculars. I'm just wanting to use the telescope tonight to be able to use my camera and hopefully get some video and / or stills. 

[StarGazingSiouxsie]

1 minute ago, JamesF said:

I think it will be tricky, to be honest.  I don't know what focal length your newt has, but I suspect you're not going to have much of a field of view with the Neximage camera compared to the size of the comet.  I'd expect that would also make it hard to focus and track, and perhaps even to find the comet when you switch from an eyepiece to the camera.

Don't let me stop you having a go, though.  It may well work out far better than I imagine

James

Thanks James, I appreciate your reply. 

Cassie has a 650mm focal length, f5 focal ratio.  

This may sound like a real stupid question - but - what sort of magnification does the camera have? I mean, is it like using a 10mm eyepiece or siomething? Or ??? Thanks

I will do my visual observing first and then give it 10 mins or so with the camera to see what it will see. I just wish my finderscope was better - totally useless so far.

[Chris]

Hi, I've been lucky enough to have imaged the comet on a couple of occasions and I honestly think it would be tricky to image at 650mm focal length and especially with a planetary camera having a narrow field of view. 

Do you have a DLSR camera plus lens, and a tripod? This would be the weapon of choice. I've got some pretty nice shots with focal lengths between 28mm and 70mm with a large full frame sensor. This is why you best visual views are with the binos you see. The comet is a large extended object so looks better with low power wide angle instruments. A camera and lens is the photographic version of your binoculars  

Edited July 19, 2020 by Lockie

[JamesF]

18 minutes ago, StarGazingSiouxsie said:

This may sound like a real stupid question - but - what sort of magnification does the camera have? I mean, is it like using a 10mm eyepiece or siomething? Or ??? Thanks

It's a very good question to ask to be honest.  And one that doesn't exactly have a simple answer

For all sorts of reasons that I'll avoid going into for the moment, cameras aren't thought of as having "magnification" at all, but instead have a property called "image scale".  It's also not easy to compare the image you get to the view through an eyepiece -- there's no such thing as a "standard" 10mm eyepiece, for instance.

Image scale basically tells you how much sky covers a given area of the camera (or vice-versa), so it might be measured in arcseconds (of sky) per mm (of sensor) or per pixel.  It's relatively easy to calculate as long as you can remember the numbers.  Dividing 206265 by the focal length in mm of your telescope gives you the number of arcseconds per mm for the camera, so in your case it would be 317-ish arcseconds per mm.  For the comet it's probably actually more useful to work in degrees, and it comes out as just under 0.1 degrees per mm.  The Neximage 10 sensor is 6.4mm x 4.6mm which means it covers an area of sky slightly smaller than 0.6 degrees by 0.4 degrees.

When various SGLers were talking about viewing the comet last week people were estimating the length of the tail to be about six degrees if I recall correctly, or twelve times the width of the full Moon.  So you can see that you're not going to be able to fit much of it on your camera sensor at once   Unfortunately it also means that you only need to be a tiny little bit off-target and you won't see it on the camera at all.

However, if you are lucky you might manage to get a view of the coma.  I can't find a figure for the angular diameter of the coma in a quick search, but it may well fit on the camera sensor.

One trick that occasionally worked for me when I started planetary imaging and didn't get the target on the sensor was to turn the gain and/or brightness right up.  Sometimes that allows you to see that the image is slightly brighter in one place than elsewhere, so you move towards that and hope it's the target that's causing it

James

[JamesF]

21 minutes ago, Lockie said:

Do you have a DLSR camera plus lens, and a tripod? This would be the weapon of choice. I've got some pretty nice shots with focal lengths between 28mm and 70mm with a large full frame sensor.

This is what I have been using too, though in my case a 200mm lens and crop sensor DSLR.

But if the Neximage is all you have, then use what you have

James

[StarGazingSiouxsie]

34 minutes ago, Lockie said:

Do you have a DLSR camera plus lens, and a tripod? This would be the weapon of choice. 

Hi Chris,

No, I haven't got one of them. Probably something I'll collect down the line  

Thanks for your insights and I'm gl;ad you managed to get some pictures of Neowise!!🤩

[StarGazingSiouxsie]

2 hours ago, JamesF said:

 

However, if you are lucky you might manage to get a view of the coma. 

Hello James

Thank you very much for your reply, I learnt quite a bit there.

I'll probably do what I normally end up doing - look for a target for a while and then start slewing around til she gets sick Then,  I'll find soemthing else to look at and pretend that's what I was looking for all along  But who knows, I might get lucky!!! Thanks again