NGC 281 Imaging Advice

[Celestron4]

I have had a go at photographing NGC 281 (Pacman Nebula) and am starting to get some results from 16, 5 minute exposures. I have posted the processed image below. I use a Celestron Nexstar 6 Schmitt-Cassegrain telescope on a Celestron AVX mount. My imaging camera is currently a Canon EOS 1100D DSLR. I realise that more image time will bring the nebula out more clearly and I am aiming to get more images when I can. Is there anything else I can do to improve my image and is my camera going to limit what I can do?

 

[Snoani]

Is your camera modified or unmodified?

[Celestron4]

My camera is unmodified. I am looking at one-shot colour CCDs at the moment if this helps.

Edited July 31, 2020 by Celestron4

[ramdom]

What is your light pollution level (Bortle scale)?

More time per exposure isn't necessarily good - it depends on your light pollution.  If you are in a light polluted area, you may be better off with shorter exposures but more of them. The PacMan is a relatively bright object so you shouldn't need to spend too much time on it total. If you are in a light polluted area five minutes may be too long and one thing to look into is a broadband filter.  Also I've seen some people use these so-called duo narrowband filters for colour cameras and they're producing really quality images with those - with most of the light pollution filtered out, these emission nebula will really shine through such filters.  

If you're imaging from a dark site then obviously your issue isn't light pollution, but I don't know much about your camera...

--Ram

Edited July 31, 2020 by ramdom

[Celestron4]

I have class 4 Bortle skies according to the ClearOutside app. Would a broadband filter work with an unmodified DSLR? I know that using narrowband filters with an unmodified DSLR is not ideal and was wondering if broadband is the same.

Edited July 31, 2020 by Celestron4

[ramdom]

Yes, both the broadband (which will let most light in, just not ALL) and the duo narrowband filters (these are not the same as regular narrow band filters) will work on a unmodded DSLR (so can real NB filters but the issue with a DSLR IMO is cooling and in your case, a slightly older model).  This is what I mean by the duo narrowband filter:

https://www.cyclopsoptics.com/astronomy-filters/stc-astro-duo-narrowband-filter-48mm-2-free-shipping-free-lenspen-set/

It's a 2" model and it's expensive (about $300+) but I don't know the prices - this is just the first link. It says on there it's suitable for DSLRs and OSC cameras. So if you do get a OSC CMOS camera that can be cooled, you can still consider this down the road.

Bortle 4 is good though - that's rural/suburban transition if I recall so you shouldn't be having that much issues with light pollution unless you're imaging with the full moon or have a light source. So it could be your processing - I'm just wondering why your images look a bit washed out. 

--Ram

[Celestron4]

It’s quite possible that my processing is the issue. I use DeepSkyStacker and bring the stacked image into photoshop. There is just over an hour worth of image time in it at the moment which might also explain the ‘washed out’ appearance. I used 5 minute exposures at ISO 1600 of that helps. Most of the images were taken when the moon was below the horizon or setting so shouldn’t be the cause. Any other ideas?

Edited August 1, 2020 by Celestron4

[michael8554]

[Celestron4]

Looks better! I will add more image time which I hope should make a difference. I have attached the .tiff file from DeepSkyStacker. I'm wondering whether it is only the way I'm processing the images or something else?

Night 1 Stack .TIF

[Celestron4]

Here's a picture of M51 taken earlier in the year. It has roughly 2-3 hrs of exposure time (mostly in 3 and 5 minute exposures at ISO 1600). It also seems to look a little bit 'washed out'. Any ideas why?

Edited August 2, 2020 by Celestron4

[Celestron4]

[alacant]

Hi

Considering you used an old camera which has not been modified this is an excellent effort. Your technique with this telescope is a lot better than i ever managed with similar.

There is some distortion around the edges which a field flattener may help with.

I had a go with a big hammer at the colour and the stars. with a bit more time, this could be a nice image, especially if you took more frames.

HTH

Edited August 2, 2020 by alacant

[MarkAR]

2 hours ago, Celestron4 said:

Here's a picture of M51 taken earlier in the year. It has roughly 2-3 hrs of exposure time (mostly in 3 and 5 minute exposures at ISO 1600). It also seems to look a little bit 'washed out'. Any ideas why?

Very good start on this, more exposures might help and increasing the saturation a little should bring up colour. Also be careful of making the background too dark, clipping can lose you some detail in the fainter galaxy arms.

[Celestron4]

The image of the nebula looks really good. I will add some more exposures when I next get the chance. 

[Celestron4]

Is a field flattener or a different camera the best option for minimising the coma?

[alacant]

10 hours ago, Celestron4 said:

field flattener or a different camera

hi

The camera is fine. To get a dedicated astro-camera with the same sized sensor is gonna cost you €silly and anything more affordable will have a miserably small sensor, cutting down your field of view significantly. This one gives you the same field as your 1100.

One thing which would improve your 1100 significantly is to remove the filter on the sensor which blocks wavelengths of light such as those present in the Pacman Nebula. This guy does it for a small fee.

I don't think it's possible to flatten the field edge to edge on with a c6 but this will make things better. The disadvantage is that you lose a lot of focal length, the reducer brings it down to something like 900mm. You will also have to take very accurately calibrated flat frames whilst using it. There is also some discussion (CN I think) about using a refractor ff, but i don't have time to find it ATM. The ff should act withour reducing the focal length so you can still get close on those nebulae. Maybe borrow one from your local astro club an have a go? I think they work fine. 

HTH

Edited August 3, 2020 by alacant

[Celestron4]

The focal reducer you have suggested is already a part of my setup and has massively improved the images that I am getting, so a good suggestion! With the reducer using a smaller sensor might be ok. It should still allow some decently framed images if Stellarium is anything to go by!

[Celestron4]

Would the use of a smaller sensor minimise the coma on the edges of the images? I have been recommended this camera if it helps.

[alacant]

Ah, ok. If your image is with the reducer, already,  then probably the only way is to cut off a chunk around the edges with a smaller sensor.

Have you tried without the reducer? 

Cheers.

 

[Celestron4]

Removing the reducer would increase the focal length and drastically reduce my field of view, so not ideal. I will have a look at colour CCD cameras to see if I can get one for a decent price. 

[vlaiv]

On 31/07/2020 at 12:55, Celestron4 said:

I have had a go at photographing NGC 281 (Pacman Nebula) and am starting to get some results from 16, 5 minute exposures. I have posted the processed image below. I use a Celestron Nexstar 6 Schmitt-Cassegrain telescope on a Celestron AVX mount. My imaging camera is currently a Canon EOS 1100D DSLR. I realise that more image time will bring the nebula out more clearly and I am aiming to get more images when I can. Is there anything else I can do to improve my image and is my camera going to limit what I can do?

I have to say that I like your processing the best.

Do you use calibration frames? You should really calibrate your image if you have not done so (and it looks like you did not).

Other than that - I do object the shape of stars in the corners and overall appearance of the stars and I don't think that C6 is very good scope for what you are trying to achieve.

Have you considered using other similar scope - I can list at least two different scopes that will be better yet remarkably similar to C6.

This one: https://www.firstlightoptics.com/ioptron-telescopes/ioptron-photron-6-ritchey-chretien-telescope.html

or this one: https://www.meade.com/telescopes/acf-cassegrain/lx85-series-6-acftm-ota-only.html

 

 

[Celestron4]

Thanks very much for the advice. I am looking at what my options are and am now fairly sure that I am reaching the limits of what my setup can do. Is the camera going to become more limiting in the future or is it the other way around?

[Celestron4]

I have used some calibration frames (darks, flats and bias). I probably don’t have enough darks in particular, wondering if a cooled camera may make this easier due to there being less variation in sensor noise

[vlaiv]

2 minutes ago, Celestron4 said:

Thanks very much for the advice. I am looking at what my options are and am now fairly sure that I am reaching the limits of what my setup can do. Is the camera going to become more limiting in the future or is it the other way around?

I'm rather fond of ability to do proper calibration of subs and that requires set point cooling, so I would rank importance of gear as:

1. mount

2. cooled camera

3. telescope

 

[vlaiv]

1 minute ago, Celestron4 said:

I have used some calibration frames (darks, flats and bias). I probably don’t have enough darks in particular, wondering if a cooled camera may make this easier due to there being less variation in sensor noise

Biggest thing with set point cooling camera is not really reduction in thermal noise but rather ability to do proper darks - always on the same temperature. This makes rest of calibration work properly.