M45, Depunked version

[wimvb]

Some time ago I managed to capture faint nebulosity around the Pleiades. But my stopped down 135 mm lens creates less than flattering diffraction spikes, which I don't like. To get rid of these, I cut an aperture mask out of black paper, which I sandwiched between the lens and a UV filter. Yesterday was an unusual clear night at my dark site, but I couldn't start imaging until about 9 pm. I managed 7 usable subs at the same settings as before, and here's a quick result, and a side by side comparison of the previous and new data. (old data was 35 x 7 miutes, new data is only 7 x 7 minutes). The mask has an aperture that stops down the lens to approximately f/5.2, while the unmasked version had the lens stopped down to f/5.6.

No elaborate processing, only simple stretches applied in PixInsight. Both images are cropped to roughly the same field of view.

Without mask

With mask

[grimble61]

WoW big difference with the spikes , i much prefer it with the stop down mask...!!!

What 135mm lens are you using..? Im looking to get the samyang 135mm for use with my asi 1600 osc. just set up with my 24-105 usml lens on asi 1600 osc

Regards

Graham

[wimvb]

It's just a regular pentax 135 mm f/3.5 lens, not the takumar. It has optical defects, such as chromatic aberration and coma, both visible in the full size image. I'm also considering upgrading, but first on my wish list is a new camera.

[Devon_Demon]

Cool, after attaching my lens to the zwo lens to camera adapter i notice a lot of play between them. unfortunately wasted an hour tonite as my subs show a large dark area were i think i have a lot of tilt as lens is not supported very well in adapter. so me thinks im going to have to make a shim. i will get it right

below is a crop. png  

Regards

Graham

de-stack-1.fit

[wimvb]

While zwo produce great cameras, I don't think they put the same effort in providing accessories. The adaptors they provide are probably cheap versions. For optical accessories, I have used this supplier in the past

http://srb-photographic.co.uk

They provided good service at an affordable price. A local vendor may also be easier to deal with in case you need to return stuff.

[Knight of Clear Skies]

M45 definitely benefits from a front-aperture mask as the diffraction spikes can end up obliterating the detail in the nebulosity.

[wimvb]

12 hours ago, Knight of Clear Skies said:

M45 definitely benefits from a front-aperture mask as the diffraction spikes can end up obliterating the detail in the nebulosity.

I agree. I like diffraction spikes sometimes, but more than four is a crowd. It's also hard to keep the delicate diffraction pattern when trying to pull out the faint dust. Masking is a pain in the lower back.

[swag72]

Wow, what a great visual difference..... the one with the mask on is many hundred times nice in my view  Who would have thought something so simple would make such a huge difference. Shame you can't do the same on those damn reflecting telescope things  

[wimvb]

1 hour ago, swag72 said:

Wow, what a great visual difference..... the one with the mask on is many hundred times nice in my view  Who would have thought something so simple would make such a huge difference. Shame you can't do the same on those damn reflecting telescope things  

Thanks. I had planned to recapture the data last weekend with the mask. But despite being a clear night, seeing was really bad, all the brighter start were fogged over. And tracking wasn't as good either this time. I probably have to find a guiding solution for my light mount. I had hoped to manage without it, as I only use it for wide field imaging.

Now, M45 is starting to go out of view at my dark site (trees obscuring), so it may have to wait until next season.

[Knight of Clear Skies]

9 hours ago, wimvb said:

I agree. I like diffraction spikes sometimes, but more than four is a crowd. It's also hard to keep the delicate diffraction pattern when trying to pull out the faint dust. Masking is a pain in the lower back.

Personally, I think (tight) diffraction spikes can help highlight asterisms in a widefield. It often works out that the naked-eye visible stars are the ones that end up with spikes, for example I like how Cassiopeia stands out in this shot:

...but they can be distracting and are somewhat detrimental to image quality. They don't offend me, stars are point sources after all and an airy disc is just as much as an optical artifact, but I prefer circular stars in most images.

[gorann]

Sorry for being a bit late into this. Just one comment (apart from the obvious that the second image is much better): For those that are not very good at cutting out cardboard rings, there is a very cheap and easy solution using step-down filter rings that can be put in front of the lens/filter. I bought a great set on e-bay for less than 10 pounds. Just put this line into the search line on e-bay:

Step-Up-Down-Lens-Filter-Ring-Adapter-Set