Spaghetti Nebula with the Samyang 135mm

[JimFox]

For those in the Astrophotography circles, you know that there is a subculture in Astro that has adopted the Samyang/Rokinon 135mm f2.0 lens for Astrophotography. There are several people that make 3D printed parts to cradle the 135mm in and provide a way to attach the ZWO EAF to it so it's an AF lens when connected to the ZWO ASIAir's.

I had bought the 135mm actually about 2 years ago on sale for Black Friday, and finally I bought the 3D kit maybe 6 months ago. Finally after quite a bit of procrastination, I assembled it all a few days ago. And so when there was a clear night at my Daughters house in Northern Colorado that evening I gave it a test on my ZWO AM5 mount along with my ASI2600mc Pro astro camera.

While the lens is a f2.0 lens, so it's fast, there are 2 sets of Astro Filters you can get. One for regular astro cameras that are about f4.0 and above and those that are faster like below f4.0. My telescope is f5.6 so all of my filters are for the slower lenses. So I set the Samyang at f4.0 to get a little speed but to still be able to use my filters, in this case the Antlia ALP-T 5nm filter.

I still got a lot of vignetting at f4.0, but I ran a Flat and Dark/Flat calibration frames for it. The Flats will remove the affects of the vignetting. It's Bortle 5 to 6 at my daughters house, so that's why I for sure need a filter to help with the light pollution. When I get back out to Joshua Tree NP in California in a few weeks, I might try the lens at f2.0 without any filter just to see what it looks like.

Anyway, the Spaghetti Nebula is really faint. I have captured it before with 10 minute exposures on my regular telescope with a reducer installed which takes the 500mm down to about 360mm. And at 360mm I was cutting off the edges of the nebula. So while doing a Mosaic is an option, I had been looking forward to trying it with the 135mm so I could get it all in with a single frame.

This has less then 5 hours integration, with it being so faint, this is one that really needs at least 10 to 12 hours, and perhaps as much as 20 hours of integration to really look good.

So this is unfinished, but I wanted to share at least the FOV that the 135mm provides. When I get a change later I will take a photo of the assembled 135mm.

38 Lights @ 300 secs with Antlia ALP-T filter
30 Flats
30 Dark Flats
30 Darks

ASI2600mc Pro - Astro Camera
Samyang 135mm - Scope
ZWO AM5 - Mount
ZWO EAF
ASIAir Plus - Astro Controller
Processed in Pixinsight
BlurXterminator
NoiseXterminator
StarXterminator
NarrowbandNormalization
Finished in Photoshop

All comments are welcome,

Jim

 

[AlanLichty]

Interesting starting point. Looking forward to how it looks when finished.

 

[JimFox]

Interesting starting point. Looking forward to how it looks when finished.

Thanks Alan. It probably looks better cropped closer around the Spaghetti, but I wanted to show roughly what the 135mm will get someone if they are interested in getting the 135mm Samyang.

 

[Comet Hunter]

tough capture, well done

 

[JimFox]

tough capture, well done

Thanks so much Ed!

 

[Mike Lewis]

Ok Jim, this is a REALLY good start on this amazing but oh so faint target. The framing is excellent with that 135 IMHO. I have not checked what I would get with the Reccat 51 at 250mm, guessing from seeing this that it would still be clipping off some of the fun stuff.

I do notice that what I would have expected to by a blue contribution form OIII signal is coming out maybe more purple looking in this image? Or perhaps that is the 2 channels mixed together that you have so far brought out?

Have you considered going back to 10 minute subs on this? With star removal (and potentially very little extra data to take for separate stars) you might get a little more out of it, assuming your setup is stable enough for subs that long.

In any case a great result, and from CO light polluted skies too. Amazing! I will have to see about trying this on my wider FOV portable setup.

ML

 

[JimFox]

Ok Jim, this is a REALLY good start on this amazing but oh so faint target. The framing is excellent with that 135 IMHO. I have not checked what I would get with the Reccat 51 at 250mm, guessing from seeing this that it would still be clipping off some of the fun stuff.

I do notice that what I would have expected to by a blue contribution form OIII signal is coming out maybe more purple looking in this image? Or perhaps that is the 2 channels mixed together that you have so far brought out?

Have you considered going back to 10 minute subs on this? With star removal (and potentially very little extra data to take for separate stars) you might get a little more out of it, assuming your setup is stable enough for subs that long.

In any case a great result, and from CO light polluted skies too. Amazing! I will have to see about trying this on my wider FOV portable setup.

ML

Thanks Mike. Good points.

I have shot this at 360mm and it clipped the edges. I am thinking that at 250mm you will actually get it all to fit in the frame without clipping. But it would be great to see.

The color did get a bit wonky I think, the lack of blue could be from the 5 min subs?

I think I will do just as you say, I will go back to 10 min subs and run some separate exposures for the stars. I will be able to go to either Joshua Tree, or run up into the Eastern Sierra now that I am back in California. It just will depend on where the best clear skies will be. I want to do a full night on this guy, so maybe I can get 8 hours on it?

 

[Andy Elliott]

A great start Jim! This has been on my wish list for quite a while, but doesn't really suit my setup; I would need several panels to cover the fov. I think I need to look in to joining the Rokinon club

 

[JimFox]

A great start Jim! This has been on my wish list for quite a while, but doesn't really suit my setup; I would need several panels to cover the fov. I think I need to look in to joining the Rokinon club

Hey Andy! Yeah, it was on a list for me for quite a while so I get that.

The Samyang 135mm is a great way to setup a really wide scope.

 

[Bill Richards]

Hi Jim,

Just FYI - if you stop down a camera lens, the blades will often generate diffraction spikes on bright stars. I'm not sure if you have encountered that or not (or care about it). If you want to stop down your lens without diffraction spikes, use a filter adapter instead. I have the Canon EF 135mm f/2L USM lens which has a 72mm thread. If I want to stop it down from F/2 to F/2.8, I screw in a 72mm-to-52mm step-down filter adapter, which reduces the aperture area by ~50%. Doing this also limits the light intake to the central region of the lens, which will result in less distortion.

 

[JimFox]

Hi Jim,

Just FYI - if you stop down a camera lens, the blades will often generate diffraction spikes on bright stars. I'm not sure if you have encountered that or not (or care about it). If you want to stop down your lens without diffraction spikes, use a filter adapter instead. I have the Canon EF 135mm f/2L USM lens which has a 72mm thread. If I want to stop it down from F/2 to F/2.8, I screw in a 72mm-to-52mm step-down filter adapter, which reduces the aperture area by ~50%. Doing this also limits the light intake to the central region of the lens, which will result in less distortion.

Thanks Bill. This was my first time using it, so I hadn't even thought about the diffraction spikes. That's something I might play with in the future.

With the Samyang it has an aperture ring that I can turn from f2.0 to f16 or maybe it's f22. I need to go back and look. I had it turned to f4 for this. I think next time I will have it at f5.6.