Imaging Advice

[noideasteve]

How important is the per pixel when imaging? For example I image with a Nikon D810a and a WO star 71 astrograph which has a 2.89 p/pixel resolution count.  I'm looking to expand on my imaging and thought about purchasing an Atik 16200 camera to image with.... with this combination it will give me a 3.56 p/pixel resolution count. How will this effect my photographs. The reason I'm also looking into this camera, for the WO GT102 scope it will give me a 1.76 p/pixel count which would be a great combination I believe however the field of view is smaller. Would there be much difference in detail?
Another alternative would be purchase a Televue NP101is at with the Atik 16200 it will give me a 2.29 p/pixel count which will give me a field of view between the GT102 and the WO71 Astrograph. I'm just getting confused as to what my next step in imaging or setup should be.
Here is what I'm getting now with my D810a and WOstar71 astrograph.

Any advice would be great thank you.

[Droogie 2001]

Nice image. I don't have any advice but would be interested to hear what others think.

I have an WO Star 71 with a Moravian G2-8300 CCD and I am imaging at 3.17 Arc Sec P/P. I know that this is 'over' the recommended limit for the setup but having looked at others imaging with the same chip, OTA and Arc Sec P/P I was satisfied it would be okay.
I don't have any plans to change my setup but it is something I have always asked myself, what if...

 

[iapa]

In general, for UK skies, people have said something between 1 and 3 is a good value.

Less than 1 and you can suffer from ovesampling, too many pixels covered by a single star; more than 3 you can be undersampling. I found http://www.cloudynights.com/topic/300919-undersampled-oversampling-an-image/ to be useful.

Another thing which can be affected is your guiding. A target may move many pixels across the imaging 'scopes field of view but only one pixel on the guide camera leaving you will trailing. The guiding:imaging scale ratio should be under 4.

Another useful article I found was

Having said all of the that, recently I've been using a 200mm F10 SCT with a Canon 600D (image scale 0.69 wayyy over sampling), QHY6 guide camera on an 80mm f5 refractor (3.4, a little under sampled). The ratio of the two is around 5 

I find that currently guiding is OK for my amateurish attempts at present, 240-300 seconds generally, 600s on a good night. 

You may want to have a look of some images (AstroBin maybe?) taken by people with the combinations you propose.

As every, I doubt that there is any 'right' answer

[ollypenrice]

I've imaged in the last few years  between 0.66 and 4.65"PP. Even 4.46 can give 'keeper' results in widefield targets.

But it is better to keep it lower than that. Our current widefeild setup works at 3.5"PP and gives perfectly attractive stars. Indeed this combination of Kodak 11 meg chip and Tak FSQ106 probably has more APODS than any other single scope and camera combination, so 3.5"PP is absolutely not a problem in terms of pixelation. It is undersampled in terms of detail, of course.

However, if your aim is to image a small target like a galaxy which will fit entirely onto your chip with room to spare then the situation changes. You want to put lots of pixels under the projected image in order to get a good sized result on the screen later. Our TEC 140 works at 1.8"PP on a full frame chip and gives great results when the frame is filled by the target. Fine, but I would still like a small pixel camera which would allow me to work at about 1"PP. This would put nearly twice as many pixels under the projected image of the galaxy, meaning that the galaxy would be nearly 4x larger by area once presented at full size on the PC screen. (The problem is that you cannot buy a CCD camera with full frame chip size and small pixels, so you have to compromise between pixel size and chip size, unfortunately.)

Having the larger image is only useful if it actually does contain more detail, so I suspect that going below abut 1"PP is probably pushing your luck. It depends on the local seeing, the conditions on the night and the guiding of the mount.

Nutshell: I think it is only really useful to have this discussion if you factor in chip size, intended target, seeing stability and guiding precision.

Olly

Edited January 30, 2017 by ollypenrice

[noideasteve]

3 minutes ago, ollypenrice said:

I've imaged in the last few years  between 0.66 and 4.65"PP. Even 4.46 can give 'keeper' results in widefield targets.

But it is better to keep it lower than that. Our current widefeild setup works at 3.5"PP and gives perfectly attractive stars. Indeed this combination of Kodak 11 meg chip and Tak FSQ106 probably has more APODS than any other single scope and camera combination, so 3.5"PP is absolutely not a problem in terms of pixelation. It is undersampled in terms of detail, of course.

However, if your aim is to image a small target like a galaxy which will fit entirely onto your chip with room to spare then the situation changes. You want to put lots of pixels under the projected image in order to get a good sized result on the screen later. Our TEC 140 works at 1.8"PP on a full frame chip and gives great results when the frame is filled by the target. Fine, but I would still like a small pixel camera which would allow me to work at about 1"PP. This would put nearly twice as many pixels under the projected image of the galaxy, meaning that the galaxy would be nearly 4x larger by area once presented at full size on the PC screen. (The problem is that you cannot buy a CCD camera with full frame chip size and small pixels, so you have to compromise between pixel size and chip size, unfortunately.)

Having the larger image is only useful if it actually does contain more detail, so I suspect that going below abut 1"PP is probably pushing your luck. It depends on the local seeing, the conditions on the night and the guiding of the mount.

Nutshell: I think it is only really useful to have this discussion if you factor in chip size, intended target, seeing stability and guiding precision.

Olly

I like to shoot wide field targets or larger objects like Eta Carinea Nebula, Orion, Seven Sisters, Rho region etc etc. Galaxy shooting I haven't really done much of as the extreme widefield sector is what I like, hence why I've been starting to get into mosaics etc to expand the field of view. I guess what I'm trying to achieve is detailed wide field images so larger chips with the shortest focal length I can achieve hence looking at the TeleVue NP101is with the Atik 16200 as I believe that gives a good p/p ratio compared to the WO71 astrograph.

In terms of your other questions as such I shoot unguided between 5-10 minute exposures with my WO71 scope and Nikon D810a, my FWHM is usually around 2.4 if that's any help to seeing conditions... I'm really not sure how to tell at this stage what my seeing conditions are like besides..... yep it's cloudy, won't be imaging tonight lol.

Thank you for your help and knowledge