M51

[IDM]

I recently acquired a Celestron C8 XLT with a Meade flattener and this image was taken on its first outing. I am not very confident about the Meade F6.3 reducer/flattener as the back spacing seems difficult and certainly I had very bad vignetting across the image that required a heavy crop prior to back ground extraction. Just to make my life more difficult the night I took the images I also decided to migrate from Sharpcap to Nina. Nina seems excellent but it didn't seem so intuitive as Sharpcap, though it handled the meridian flip with my Zwo AM5 perfectly (I followed Cuiv's settings from Youtube). 

So in the end I ended up with 217 90 second exposures using the C8 with Meade reducer and a Zwo ASI294 MC pro camera. Guiding was provided by Skywatcher finder-scope I converted to guidescope, focal length 185mm (approx.). It's not the best but I felt for a first outing I was pleased. Processing was done using a newly acquired Pixinsight license, so again I am at the bottom of the learning curve!!!

Since taking the image I had a look at the Collimation and with a backspacing of 105mm I noticed good collimation at the centre but put poor round the edges. So I don't things are right. I have since reduced the backspace to about 75mm and the collimation looks better across the sensor. The weather hasn't been great since the change so I haven't been able to test it by imaging properly, though I did do a plate solve and Nina (ASTAP) reported a focal length of 1336mm which seems a little long.

I would be grateful for all thoughts on the reducer and helpful feedback on the image

[AstroMuni]

Stars look quite nice & round across the whole image so I would have been very happy with this setting. Lovely image with lots of detail.👍

[ollypenrice]

First off, it's a very clean and workmanlike image of M51. Background and stars are excellent and spiral detail is well resolved. It's very good, surely.

The faint extensions are there and would show with more data. 5.5 hours has done a good job on the brighter stuff and has caught the blues in the extended tip of the 'bridge of light.'

To my eye the colour balance is a tad high in green and more significantly short on red at the brighter end, though the background looks good. I'm not suggesting it's miles out, it's just where I'd be looking if the image were mine.

SCTs tend to be very tolerant on reducer-to-chip distance but the true FL does vary considerably. Your variation from the nominal 1260mm is not remarkable and your intention to experiment has to be the right way, I think. While you are tinkering with this, bear in mind that all the arguments favour an OAG with this scope so it might be easier to fit one before agonizing over spacers.

Regarding vignetting, I think it's to be expected on this setup. The thing is to measure it. This is easily done on flats. If you measure the centre brightness in ADU you can compare it with the corners. I found that I could live with a 25% fall-off with my Tak 106 rig so, if your uncropped corners were at 75% of centre brightness you should be OK. If your corners were darker than that you could sample the flat on a line from corner to centre and find the point at which it reached 75%. That would indicate your largest workable field. (The reality of galaxy imaging is that you rarely need a large field anyway, at least in my experience.)

If I were you I'd be delighted with this as an opening result.

Olly

[tomato]

Excellent detail, and subtle processing of the colour. I'm always tempted and usually succumb to overdoing the saturation on this galaxy. I agree with Olly that there is a hint of green overall on my monitor, but it's not much. 

[900SL]

Very nice M51 IDM, and well done for a first image with pixinsight! The C8 looks like a good un!

[IDM]

On 09/04/2024 at 09:04, AstroMuni said:

Stars look quite nice & round across the whole image so I would have been very happy with this setting. Lovely image with lots of detail.👍

Thank you for the kind words.

[IDM]

@ollypenrice Thank you so much for the comprehensive and really helpful feedback I will have to spend some time digesting and learning.

Ian

[IDM]

On 09/04/2024 at 14:17, tomato said:

Excellent detail, and subtle processing of the colour. I'm always tempted and usually succumb to overdoing the saturation on this galaxy. I agree with Olly that there is a hint of green overall on my monitor, but it's not much. 

Thank you for the kind feedback. I am trying to be more subtle with my images. In planetary my enthusiasm used to get the better of  me so I am trying to be cautious to achieve less  = more.

Ian

[IDM]

9 hours ago, 900SL said:

Very nice M51 IDM, and well done for a first image with pixinsight! The C8 looks like a good un!

Thanks for the positive comments.

[IDM]

I was very excited when I first processed the image as I felt I was making some forward steps and I certainly appreciate all the feedback that will hopefully help me improve still further in the future. Though at times it feels like the more I learn the less I know 🙂 but I think its part of what makes this hobby so fascinating and possibly addictive, as there is always room for experimentation and improvement.

Thanks,

Ian