C11 HD Hyperstar or reducer?

[Wiu-Wiu]

I love the narrow field my C11 gives - especially for small galaxies. But having it out imaging in the open is reserved for clear nights without wind, as the long FL is hard to keep under control. 

The long time it takes to gather light is also something that has been on my mind.

I've looked into ways to reduce integration time and the focal length, but both give me a smaller imaging field of view. The hyperstar would bring it to F/2, making it a whopping 26 times faster than at f/10. But it would also reduce the FOV to about the size I get with my Esprit 120. 

The reducer makes it f/7, cutting the integration time in half, and keeping a decent "small" fov. (but keeping the wind/guiding issues in play)

What would be the better upgrade? Are objects still good quality when cropped out of the 'large' FOV (and more: are they better than in the Esprit?)  Or is it worth spending more time to gather light and just take the reducer? 

Anyone care to weigh in on this? Both solutions would be at the same cost, as with the reducer I would still need an extra focuser to keep the guiding (oag) under control.

[Xplode]

I'd say save your money, the Esprit with it's ease of use and a lack of all the problems that comes with an SCT i'd advice you to use the it instead of the C11.
Hyperstar is incredibly hard to get right, dealing with tilt, focus etc is a big problem and not for most people.

The Esprit 120 will most likely be just as sharp as the SCT during most nights and the stars will be tight instead of fuzzy looking

 

[ollypenrice]

My observations are in red.

I love the narrow field my C11 gives - especially for small galaxies. But having it out imaging in the open is reserved for clear nights without wind, as the long FL is hard to keep under control. 

There is no reason to love a narrow field of view. The tight framing of a target does not bring any more detail to the image. The detail you can theoretically resolve is measured in acrcseconds per pixel and is not affected by how big your chip is or how much empty sky you have round a galaxy. You can always crop the image. The detail you can really resolve is limited by atmospheric seeing and guiding. Getting any real detail below about 1 arcsecond per pixel is difficult.

The long time it takes to gather light is also something that has been on my mind.  The size of your aperture is the only thing which affects your telescope's light grasp. Reducers at the back can obviously have no effect on this. Light goes in at the front!

I've looked into ways to reduce integration time and the focal length, but both give me a smaller imaging field of view. No, reducing the focal length increases the field of view. With a given aperture you can reduce integration time by using a more sensitive camera, binning the capture or by using larger pixels.

The hyperstar would bring it to F/2, making it a whopping 26 times faster than at f/10. Wrong. Don't be fooled by the Hyperstar website. Exactly the same amount of light is entering the telescope with or without the Hyperstar. The Hyperstar just puts object photons onto fewer pixels which 'fill' faster. But do you want a tiny galaxy without details and surrounded by empty sky? In truth you cannot compare exposure times with and without the Hyperstar because there is no way in the world that you would use them on the same targets.

But it would also reduce the FOV to about the size I get with my Esprit 120. No, this means the Hyperstar will greatly increase the field of view. However, the Hyperstar will be faster on the same FOV than the Esprit but the Esprit will give you a much better result for several reasons. It is optically and mechanically much better and F2 is too fast to be practical.

The reducer makes it f/7, cutting the integration time in half, and keeping a decent "small" fov. (but keeping the wind/guiding issues in play) Again, no, F ratio does not work like that with reducers.

What would be the better upgrade? Are objects still good quality when cropped out of the 'large' FOV (and more: are they better than in the Esprit?)  Or is it worth spending more time to gather light and just take the reducer?  Use the reducer to widen the field of view.

Anyone care to weigh in on this? Both solutions would be at the same cost, as with the reducer I would still need an extra focuser to keep the guiding (oag) under control.

 

What has been running through my comments is a thing called The F Ratio Myth. It causes a lot of noise and disagreement. Basically the camera F ratio rule (One stop down is twice as fast) works because in a camera lens you increase the area of aperture when you open up the diaphragm. Adding a focal reducer doesn't do that. It doesn't make the objective bigger.

What you should do to speed up capture is use bigger pixels. It's the amount of light per pixel which matters. You can do this with a mono camera by binning 2x2, 3x3 etc. With colour cameras you're stuck in Bin1 so you would need a change of camera. The Sony S7 is a good match for the C11.  Your 500D in the C11 is working at 0.35 arcsecs per pixel. It is totally impossible to capture real detail at this resolution so you would do far better to have pixels at least twice as big or to use a camera which, binned 2x2 or 3x3 would give you effectively bigger pixels. This would mean switching to mono. Mono is faster for other reasons as well.

Olly

 

[gorann]

As Olly says the Sony A7s would be a good match for a C11, especially with a 0.7x reducer. Then you would be working at 0.88"/pixel. See http://astronomy.tools/calculators/field_of_view/

[wimvb]

The light gathering power of an imaging system is proportional to (p/F)^2, where p is pixelsize, and F is focal ratio, fl/D. Looks promising for F-ratio, right? Not so, because decreasing F (=going faster) by decreasing focal length puts light from a larger patch of the sky/object on each pixel. The same relationship can be rewritten as

The light gathering power of an imaging system is proportional to (rD)^2, where r is pixelscale, and D is aperture. This means that at constant pixelscale (level of detail, if you will), aperture rules.

This is basically the math behind @ollypenrice's argument. 

[gorann]

Yes, aperture rules - ESA do not put up 5" refractors on mountains in Chile.

[Xplode]

6 minutes ago, gorann said:

Yes, aperture rules - ESA do not put up 5" refractors on mountains in Chile.

Aperture rules, but there's a reason they put the telescopes on top of mountaines, better seeing...
There's also a reason professionals aren't using C14's, you might want to look at the RASA versions, the RASA14 was totally redesigned compared to EdgeHD/smaller RASA scopes because they have problems with mirror flop etc.
Please also compared the price for the Rasa 14 vs Rasa 11...

[ollypenrice]

1 minute ago, gorann said:

Yes, aperture rules - ESA do not put up 5" refractors on mountains in Chile.

Quite so, but the impressive size of their optics is easier to see from down here than the equally impressive size of their pixels!

😁lly

 

[Wiu-Wiu]

Thank you very much, everyone! Much appreciated!

I did mess up my story in decreasing and increasing FoV there. Thank you for correcting me. 

 

The RASA had crossed my mind, but having wind issues on the C11HD as it is, I'm going to leave that one on the bucketlist. 

Interesting point in investing in a new camera, but ZWO just doesn't seem to have that kind of pixel size cameras (I'm fond of the asiair so I want it to be compatible, and a cooled camera is a must)

 

Food for thought! I'll stick to the Esprit for long time imaging, and for now keep the edge for the occasional shorter time exposures at long focal length (supernovae, ...) and rethink my setup for the edge when I ever get a more permanent setup (which would make the asiair less "must have") 

 

thanks! 

 

 

 

[ollypenrice]

26 minutes ago, Wiu-Wiu said:

Thank you very much, everyone! Much appreciated!

I did mess up my story in decreasing and increasing FoV there. Thank you for correcting me. 

 

The RASA had crossed my mind, but having wind issues on the C11HD as it is, I'm going to leave that one on the bucketlist. 

Interesting point in investing in a new camera, but ZWO just doesn't seem to have that kind of pixel size cameras (I'm fond of the asiair so I want it to be compatible, and a cooled camera is a must)

 

Food for thought! I'll stick to the Esprit for long time imaging, and for now keep the edge for the occasional shorter time exposures at long focal length (supernovae, ...) and rethink my setup for the edge when I ever get a more permanent setup (which would make the asiair less "must have") 

 

thanks! 

 

 

 

You can increase effective pixel size if you choose mono and binning. There's an awful lot to be said for that.

Olly

[newbie alert]

Very well explained Olly..... 

Back to the OP, the esprit is a amazing scope, stick with it and enjoy

[ollypenrice]

There is another way to speed up capture... the dual rig. That's what we do here.

Olly

 

[DaveS]

If you really *must* have an ASI camera (And after my experiences with a 1600 I would be dubious) then the ASI 6200 will give you 135 format and with that number of pixels could certainly be binned 2x2 or even 3x3.

Else a 16200 based camera from Atik or Moravian. SX are expensive, and FLI rouinous.

[Davey-T]

2 minutes ago, DaveS said:

Else a 16200 based camera from Atik or Moravian. SX are expensive, and FLI rouinous.

QHY were boasting about their new cameras the other day.

Dave

[DaveS]

4 minutes ago, Davey-T said:

QHY were boasting about their new cameras the other day.

Dave

Is that a new 16200 camera or an IMX455? The last I saw of their IMX455 camera it had a price tag the wrong side of £5k unless you were an early adopter.

[Xplode]

10 minutes ago, DaveS said:

If you really *must* have an ASI camera (And after my experiences with a 1600 I would be dubious) then the ASI 6200 will give you 135 format and with that number of pixels could certainly be binned 2x2 or even 3x3.

Else a 16200 based camera from Atik or Moravian. SX are expensive, and FLI rouinous.

Binning doesn't really do anything for the IMX455 in the ASI6200, there's hardware binning, but it's meant for color cameras so it's not a 2x2 binning with adjecant pixels like for CCD.
Software binning is kinda pointless, it's better to downscale after stacking the image.

The 16200 sensor is really great, seems like the best largish CCD sensor out there at the moment that normal people can afford.
It also does great hardware binning.

[newbie alert]

14 minutes ago, DaveS said:

If you really *must* have an ASI camera (And after my experiences with a 1600 I would be dubious) then the ASI 6200 will give you 135 format and with that number of pixels could certainly be binned 2x2 or even 3x3.

Else a 16200 based camera from Atik or Moravian. SX are expensive, and FLI rouinous.

ASI  camera's are cmos so they can only do software binning, for hardware binning choose a ccd

[DaveS]

Thanks Ole.

I have a Moravian G3 16200 which is waiting to go on my ODK12, which itself is waiting on power being run to the obsy, even before the obsy is complete.

Edited April 23, 2020 by DaveS

[Rocket Stars]

Im having a hyperstar on my edge 8. Running on my avx. I can do 90sec exposure without guiding. Big benefit on F2. (short focal length) Is less problems guiding ect. 

Big field of view. Im happy. 

But you need a matching pixel scale. Small pixels is preferred. 

Had initially problems with collimation. But it was du to a not so well fitted sensor. Its now adjusted to 0.09mm flat level (measured to the cam body) As a normal fitted sensor usually is. Or way better.. 

Once I got that sorted. Collimation that was way out. took 30 min to get correct. Thats including me running back and forth to the computer. 

 

 

Edited April 23, 2020 by Rocket Stars

[DaveS]

8 minutes ago, Xplode said:

Binning doesn't really do anything for the IMX455 in the ASI6200, there's hardware binning, but it's meant for color cameras so it's not a 2x2 binning with adjecant pixels like for CCD.
Software binning is kinda pointless, it's better to downscale after stacking the image.

The 16200 sensor is really great, seems like the best largish CCD sensor out there at the moment that normal people can afford.
It also does great hardware binning.

 

5 minutes ago, newbie alert said:

ASI  camera's are cmos so they can only do software binning, for hardware binning choose a ccd

I was seeing this on the FLO site

And assumed that it applied to the mono version. Are ZWO selling porkies?

[Xplode]

Just now, newbie alert said:

ASI  camera's are cmos so they can only do software binning, for hardware binning choose a ccd

Wrong, CMOS can do hardware binning too, but so far i know of only the IMX455(ASI6200) and IMX571 (ASI2600) sensor that can do it.
The minus is that the binning is meant for color cameras, CMOS mono hardware binning would have been cool to try.

[Xplode]

4 minutes ago, DaveS said:

 

I was seeing this on the FLO site

And assumed that it applied to the mono version. Are ZWO selling porkies?

I would say it's kinda a grey area around the binning of these sensors.
Like mentioned earlier it's meant for color cameras so it bins several R, G, B pixels together.

There's also the thing with the ZWO Ascom driver only supporting software binning, for hardware binning the software has to connect in native mode like what Sharpcap and other planetary imaging softwares can do.
I haven't really tested the hardware binning on the ASI6200 mono camera i have access to.

[newbie alert]

25 minutes ago, Xplode said:

Wrong, CMOS can do hardware binning too, but so far i know of only the IMX455(ASI6200) and IMX571 (ASI2600) sensor that can do it.
The minus is that the binning is meant for color cameras, CMOS mono hardware binning would have been cool to try.

Thought that it couldn't do hardware bining as every row had it's own count rather than being counted at the end?

[ollypenrice]

1 hour ago, DaveS said:

 

I was seeing this on the FLO site

And assumed that it applied to the mono version. Are ZWO selling porkies?

Whenever the performance on paper of the KAI 11002 comes up it looks awful.

But whenever I process data from my 11002 it is just so gorgeous to work on. The stars are right. The colour is right. There's no fighting, just happy, happy processing.

Olly

[Xplode]

8 minutes ago, ollypenrice said:

Whenever the performance on paper of the KAI 11002 comes up it looks awful.

But whenever I process data from my 11002 it is just so gorgeous to work on. The stars are right. The colour is right. There's no fighting, just happy, happy processing.

Olly

You would be amazed at the low noise the IMX455 sensor has, i've compared the KAF 16200 sensor and the IMX455 sensor and the read noise is so low that images get deeper in a shorter time.
The downside is some stars have haloes, but the stars on the KAF 16200 isn't perfect either.