Wow.. what a scope!

[Rob]

Saw this, and thought wow!

The images it produced are staggering

Clear Skies

Rob

 

[SamAndrew]

Yes I watched that as well, shame he glosses over the results at the end with short clips of spinning photos, have to go to astrobin for some more representative examples. Would seriously consider it if there was a way to automate the filter changes; i think it's a little too complicated for a DIY solution.

[vlaiv]

For anyone looking into getting one of these, this thread might be worth reading first:

 

[George Gearless]

Cables in front of the telescopes aperture? That doesn't make sense to me.

What am I missing?

[SamAndrew]

4 minutes ago, George Gearless said:

Cables in front of the telescopes aperture? That doesn't make sense to me.

What am I missing?

Has always been the way for Hyperstar or a secondary mirror heater.

[Knight of Clear Skies]

17 minutes ago, George Gearless said:

Cables in front of the telescopes aperture? That doesn't make sense to me.

What am I missing?

Here's a diagram of the optics which should help.

It has a short focal length for the aperture, making it a very fast system. However, I believe they have a reputation for being difficult to set up.

[ollypenrice]

3 hours ago, Rob said:

Saw this, and thought wow!

The images it produced are staggering

Clear Skies

Rob

 

If it were the scope of scopes it would have a huge following. Astrophotographers are not stupid and if F2 were the way to go they would be going that way. I would go that way if it were consistently possible to produce images of our 'house standard' that way. As it is, for this kind of focal length we use F5 and an old Takahashi FSQ106N. This example does include refinements from a TEC140 but the effect of this was essentially minor.

https://www.astrobin.com/321869/0/?nc=user

This image was entirely shot with the old fluorite F5 Tak 106N. I haven't trawled the net for RASA equivalents but, if you do, look at the star sizes.

https://www.astrobin.com/301531/?nc=user

When choosing a telescope don't glaze over when you see a load of marvelous numbers. It isn't as simple as that.

Olly

 

 

[Knight of Clear Skies]

Imaging at F2 can be completely painless - with a Samyang lens at a mere 135mm focal length (still enough to show good detail on a fair number of targets but not much of a galaxy hunter).

(The above is just 22 minutes of data. Shame about the big flare on Deneb which I think is caused by the ZWO 7nm Ha filter not being able to cope with the steep light cone, I returned it after this shot and must look at getting a more suitable one.)

[ollypenrice]

5 minutes ago, Knight of Clear Skies said:

Imaging at F2 can be completely painless - with a Samyang lens at a mere 135mm focal length (still enough to show good detail on a fair number of targets but not much of a galaxy hunter).

(The above is just 22 minutes of data. Shame about the big flare on Deneb which I think is caused by the ZWO 7nm Ha filter not being able to cope with the steep light cone, I returned it after this shot and must look at getting a more suitable one.)

This is narrowband which is vastly easier at the capture stage than broadband, certainly form the point of view of the optics. Could you show us this field in luminance or OSC?

When discussing the RASA I think we need to look at comparable focal lengths and decide whether the conversation is about broadband or narrowband. They really are different conversations.

Olly

[Knight of Clear Skies]

On 28/03/2019 at 19:39, ollypenrice said:

This is narrowband which is vastly easier at the capture stage than broadband, certainly form the point of view of the optics. Could you show us this field in luminance or OSC?

When discussing the RASA I think we need to look at comparable focal lengths and decide whether the conversation is about broadband or narrowband. They really are different conversations.

Olly

That's a good point - the Ha filter reduces the size of the stars and any abberritions. I don't have OSC samples to hand as I'm locked out of my Flickr account, but looking at this thread the Samyang produces decent stars. However, starfields can appear very crowded due to the large field of view. If I understand it correctly, airy disk size is a function of aperture (77mm for the Samyang), in theory an ED80 would produce similar size stars but they would be more widely spaced due to the smaller field of view. As a result the stars would be less intrusive in an ED80 mosaic of the same field.

So yes, I should say imaging at F2 is painless with a Samyang lens and narrowband filter, I've had trouble stacking OSC data from the Samyang in DSS and may need to look at other software. Perhaps that's the best way to use the RASA too? Fast optics are very appealing in UK weather, but I'd be wary of anything that is difficult to set up.

[Knight of Clear Skies]

On 28/03/2019 at 19:39, ollypenrice said:

Could you show us this field in luminance or OSC?

Had a quick look on Astrobin, there are some very impressive images with the Samyang on there. Here's a good NA and Pelican, decent stars but nowhere near the gorgeous field in your Tak mosaic.

https://astrob.in/363836/0/

I think the starfield is better in this 2-hour DSLR image of Rho-Ophuchi, it's hard to gauge how good equipment really is when so much is down to processing:

https://www.astrobin.com/386263/0/

This 8-panel mosaic of Orion really shows where the Samyang can shine, but we can't pixel-peep as it has been posted at low resolution:

https://www.astrobin.com/386273/0/

(Weirdly, Rigel is showing diffraction spikes but the other bright stars aren't, looks like the lens was stopped down at some point.)

My experience of the Samyang is that it produces much tighter stars than my Canon 200mm f2.8 L. The focuser is also miles better as it isn't an auto-focus lens, I can focus by eye on liveview and when I check with a bahtinov it's usually spot on.