C&C: First attempt at Pleiades

OllieN said:

Thanks Nate and Rudy,

I had to crop to get rid of a couple of dust marks. I have some step down rings but this time out chose to generate the diffraction spikes as I thought they might work well on this target.

I'll take a look at brightening a little.

Ollie

Click to expand...

RudyPohl said:

Very good Ollie, by far your best image to-date. I'm please to see that 30 second exposures at f4 could give such nice results... you've got the rnc-color-stretch working for you too, that's excellent.

And like Nate wrote, a set of step-down rings used as an aperture mask will completely get rid of those diffraction spikes, it also gets rid of coma. Here's a brief description how they work...

Aperture Mask on the Nikon 300/f4:
The step-down rings are to solve the problem of very bad coma on this particular lens. At f4 the coma is quite bad throughout the entire frame and makes the image unusable. You have to stop down to f5.6 before you get much of the coma removed, but there's still lots around the outer parts of the of frame. However, when you stop down this lens you get huge diffraction spikes which are especially bad on the bigger stars. With an aperture mask made from a combination of step down rings going from 77mm-58mm, screwed onto the front of the lens and leaving the internal camera aperture setting at f4, the result you get is an effective aperture of f5.2 with no diffraction spikes (300mm/58mm = f5.2).

Here's the set many of us buy: https://www.amazon.co.uk/Fotodiox-F...359&sr=8-10&keywords=fotodiox+step+down+rings

Cheers,
Rudy

Click to expand...

FMelis said:

RudyPohl said:

Very good Ollie, by far your best image to-date. I'm please to see that 30 second exposures at f4 could give such nice results... you've got the rnc-color-stretch working for you too, that's excellent.

And like Nate wrote, a set of step-down rings used as an aperture mask will completely get rid of those diffraction spikes, it also gets rid of coma. Here's a brief description how they work...

Aperture Mask on the Nikon 300/f4:
The step-down rings are to solve the problem of very bad coma on this particular lens. At f4 the coma is quite bad throughout the entire frame and makes the image unusable. You have to stop down to f5.6 before you get much of the coma removed, but there's still lots around the outer parts of the of frame. However, when you stop down this lens you get huge diffraction spikes which are especially bad on the bigger stars. With an aperture mask made from a combination of step down rings going from 77mm-58mm, screwed onto the front of the lens and leaving the internal camera aperture setting at f4, the result you get is an effective aperture of f5.2 with no diffraction spikes (300mm/58mm = f5.2).

Here's the set many of us buy: https://www.amazon.co.uk/Fotodiox-F...359&sr=8-10&keywords=fotodiox+step+down+rings

Cheers,
Rudy

Click to expand...

Click to expand...

OllieN said:

I reprocessed my images again:

- I used 2x drizzle in DSS

- I chose to use an average stack due to the varying gradients in moonlight across my lights (I hadn't appreciated that the sigma clipping would reject an amount of my data)

- I used the GUI for rnc_color_stretch which makes it far quicker and easier to play with different stretch settings (oh and I read the manual properly rather than just running with the command line deafults)

I think it's an improvement. To my eyes the background is less blotchy and noisy.

Click to expand...

OllieN said:

I reprocessed my images again:

- I used 2x drizzle in DSS

- I chose to use an average stack due to the varying gradients in moonlight across my lights (I hadn't appreciated that the sigma clipping would reject an amount of my data)

- I used the GUI for rnc_color_stretch which makes it far quicker and easier to play with different stretch settings (oh and I read the manual properly rather than just running with the command line deafults)

I think it's an improvement. To my eyes the background is less blotchy and noisy.

Click to expand...