M5 The Rose Cluster

[WolfieGlos]

Been a while since I posted any images despite a lot of clear nights as of late. This one was captured a month ago, but such is life now that I struggle to find the time to process any images! In fact, I find I have time for collecting data but stacking and processing is another story.

So thought I'd start off my backlog with a simple star cluster. I dare say this cluster is probably overlooked in Virgo in favour of the countless galaxies at our disposal, this image is only an hour of data collected on 16th June with a 66% Moon in the sky and some high level cloud. I framed this one off centre to pick up the bright 5 Serpentis, and looking at the data I have managed to split this binary system but stretching shows the large halo created. I decided to leave the halo alone to give an idea of the brightness of the system compared to M5.

The target is not really visible to me now until next year, but I definitely think a bit more time would have enhanced it a little.

ASI 585mc + Starfield 102ED w/ 0.8 Reducer + Astronomik L2 UV/IR Filter, on HEQ5.

120 x 30s at Gain 252.

Stacked in Siril, processed in Pixinsight, Blur & Noise XT and GraXpert, and border added in GIMP.

Comments welcome as always.

[Sunshine]

I love cluster images,  they always take a back seat to other DSO’s, for some reason. This is a wonderful cluster image!.

[alacant]

7 hours ago, WolfieGlos said:

the bright 5 Serpentis,

Lovely image.
Here's my way of dealing with that star (!).
CS

[WolfieGlos]

19 hours ago, Sunshine said:

I love cluster images,  they always take a back seat to other DSO’s, for some reason. This is a wonderful cluster image!.

 

Thanks Sunshine, they certainly do take a backseat! It's nice to capture clusters every now and again, I generally reserve them for the brightest parts of the Moon phase when the inevitable clear skies come along 🙄

15 hours ago, alacant said:

Lovely image.
Here's my way of dealing with that star (!).
CS

Thanks alacant, that's certainly one way of dealing with it 🤣

I like how you've managed to pull out a lot of the fainter stars in that one around the perimeter of the glob. What were your capture details, was it more time or a faster scope?

[alacant]

9 hours ago, WolfieGlos said:

more time

Hi.
It was 45x2min with a gso203. But I don't think that's the difference.
Perhaps best to keep the processing simple. Lose the reducer and -especially- the AI and I'm certain that the fainer stuff will appear.
Cheers and HTH

 

Edited July 21 by alacant

[WolfieGlos]

3 hours ago, alacant said:

Hi.
It was 45x2min with a gso203. But I don't think that's the difference.
Perhaps best to keep the processing simple. Lose the reducer and -especially- the AI and I'm certain that the fainer stuff will appear.
Cheers and HTH

 

Hmm, 50% more exposure time and at f/4 rather than 5.6 is probably the difference. Without the reducer I’m at f7, although for clusters that’s not really an issue other than dismantling the imaging train. The target was also in my most light polluted portion of sky, so all working against me! 

I didn’t notice the AI losing the fainter stuff (I always undo/redo to check), I just couldn’t stretch much more due to the background. I didn’t bother with processing stars separately, so I might take a look at that when I find some time again and see if I can neutralise and desaturate the background to enable a bit more of a stretch. Work and a newborn make processing more of a chore at the moment! 

[alacant]

15 minutes ago, WolfieGlos said:

Without the reducer I’m at f7

F7 collects the same amount of light as f5.6, with the advantage that the cluster will be a bit bigger.

I agree though that as always, more time would definitely help. 

Cheers 

 

[Stuart1971]

5 minutes ago, alacant said:

F7 collects the same amount of light as f5.6, with the advantage that the cluster will be a bit bigger.

I agree though that as always, more time would definitely help. 

Cheers 

 

Hmmm, I’m not sure that is correct, the f5.6 will be faster than the f7, and collect more light in the same given time…

[alacant]

It will only be faster if you create the f5.6 by increasing the aperture of your telescope. The cluster collects less light at F5.6.

Edited July 21 by alacant

[Stuart1971]

57 minutes ago, alacant said:

It will only be faster if you create the f5.6 by increasing the aperture of your telescope. The cluster collects less light at F5.6.

Well the reducer does effectively increase the aperture of the telescope and allow more light in, as it widens the FOV, the same as a changing f stop on a camera lens does… unless I am missing something here, which is very possible 😂

Edited July 21 by Stuart1971

[alacant]

1 hour ago, Stuart1971 said:

the same as a changing f stop on a camera lens does…

On a camera lens, you change f-ratio by changing the aperture. On a telescope,  you change the f-ratio by changing the focal length. Usually to a shorter value.

That's fine if you simply want to increase the field of view. It will however do nothing to the speed of the telescope. In fact in this case, as the cluster will appear smaller, it will reduce the amount of light from the object falling on the camera.

Search: f ratio myth

Cheers 

[Gfamily]

I think the resolution to the difference of opinion is that...

What the reducer does is make the image on the sensor smaller - the same amount of light is received, but it's concentrated onto fewer pixels, so each pixel gets more. Therefore the effect is the same as having a wider initial aperture's light spread onto the original number of pixels. 

I think that's right. 

Edited Sunday at 16:32 by Gfamily

[Stuart1971]

55 minutes ago, Gfamily said:

I think the resolution to the difference of opinion is that...

What the reducer does is make the image on the sensor smaller - the same amount of light is received, but it's concentrated onto fewer pixels, so each pixel gets more. Therefore the effect is the same as having a wider initial aperture's light spread onto the original number of pixels. 

I think that's right. 

Ok, I stand corrected, thanks 👍🏻

[WolfieGlos]

4 hours ago, alacant said:

On a camera lens, you change f-ratio by changing the aperture. On a telescope,  you change the f-ratio by changing the focal length. Usually to a shorter value.

Never thought of it in that way, but yeah that makes sense. 

It’s been a good test with the 585mc this year, that I originally got for planetary imaging. Using the reducer I’m imaging DSOs at 1.05”/p , which I’m not achieving with my guiding (assuming guiding at half the image scale). But it’s still pumping out good results, perhaps some fine detail is being lost though. Without the reducer it’s 0.84”/p.

It’s definitely an upgrade from the DSLR with noise, QE, etc, but it’s a stopgap until I go to a proper camera later this year - either a 533mm or 2600mc is the plan, but I think I’m going to stick with OSC.

[alacant]

12 hours ago, WolfieGlos said:

Without the reducer it’s 0.84”/p

Hi
Yeah, so this puts more light on the cluster; f7 is faster than f5.6. 
At 5.6 you would have to enlarge the image to make it match the size at  f7, losing both resolution and brightness in doing so. Hence my original suggestion. I think it will help bring the fainter stuff forward.
 

20 hours ago, WolfieGlos said:

a newborn

Had to ask. I didn't know what it meant in this context, so congratulations!

Cheers and CS

Edited Monday at 09:26 by alacant