Intro to Hyperstar

[curtisca17]

I had my first encounter with hyperstar back in 2014 with my Celestron 14" SCT and was blown away with what it could do for me during live viewing with a camera (EAA, EEVA, Video Astronomy, etc.).  I had to let my 14" go as it was getting to heavy for me and replaced it with an 11" SCT with hyperstar an essential part of the package.  These days I spend more time with traditional astrophotography and have found hyperstar to be just as amazing a tool as it was for EAA.  If you have an SCT and haven't yet tried it I can highly recommend it as it provides a 25X increase in optical speed over the native f/10 (12.5X over f/7) and provides an equally larger FOV.  With the increased speed it takes a lot less time to capture the subframes I need for my final image since I need less subs.  There is a double payback with less image acquisition time and less post processing time with fewer subs needed  Also, the image scale with hyperstar is usually much smaller than the seeing warrants so 2x2 binning is an option to further speed up the system.   While most think that hyperstar is just for the larger DSOs and not the smaller ones like M27 that is not the case if you have a large sensor camera, say 20mm or larger diameter.  Even with 2x2 binning images are most often still over sampled so it is possible to zoom into the final image and get a reasonable size image of these smaller DSOs without impacting resolution.  I put together a video which gives examples of what hyperstar can do and shows everything one needs to get started with hyperstar (at least I think I covered everything).  If you have an SCT and do not already have hyperstar or are considering an SCT you might want to take a look at this.  Even if you already use hyperstar all the time I would appreciate any feedback on your experiences and inputs.  You can find the video here https://www.youtube.com/watch?v=EA2TWvnIIbU  

 

Regards,

Curtis

[Elp]

It's a good video, covers a lot of points especially why it's so faster than the default f10 configuration.

You touched upon the cable routing, I found it can significantly affect the diffraction spikes around stars especially bright ones, having a standard usb cable sticking out the side of an uncooled camera is also noticeable as a chunk taken out of any star halo. I mitigated this by using a 90 degree usb connection so it doesn't stick out so much into the clear aperture, and then wrap the remaining cable around the camera and HS and onto a custom made ring bracket I made to run the cables to the OD.

Using cooled cameras for AP it also helps to cover up all around the USB and power connections with black tape so the lights from inside the camera do not radiate out.

For taking darks, using a filter drawer and having a black dark frame filter makes it easier to do, no need to cover the front or anything, just change to the black filter and take your dark frames, this obviously only applies when using an uncooled camera for DSO.

[curtisca17]

3 hours ago, Elp said:

It's a good video, covers a lot of points especially why it's so faster than the default f10 configuration.

You touched upon the cable routing, I found it can significantly affect the diffraction spikes around stars especially bright ones, having a standard usb cable sticking out the side of an uncooled camera is also noticeable as a chunk taken out of any star halo. I mitigated this by using a 90 degree usb connection so it doesn't stick out so much into the clear aperture, and then wrap the remaining cable around the camera and HS and onto a custom made ring bracket I made to run the cables to the OD.

Using cooled cameras for AP it also helps to cover up all around the USB and power connections with black tape so the lights from inside the camera do not radiate out.

For taking darks, using a filter drawer and having a black dark frame filter makes it easier to do, no need to cover the front or anything, just change to the black filter and take your dark frames, this obviously only applies when using an uncooled camera for DSO.

Thanks.  Actually, if you look at Dave's HH Nebula image you can definitely see diffraction spikes on the bright stars, so point well taken.  Nice idea on the uncooled camera dark frames.

[ollypenrice]

Many (or maybe all) of these issues have been extensively discussed on here and I think you are reiterating a number of mistakes in your video. The most obvious is 'The F ratio myth.' Your Hyperstar does not speed up capture by 25x.  It does not speed up capture at all.  Please bear with me. Exposure time does reduce as the square of the F ratio, as you say, when the F ratio is reduced by increasing the aperture. That's why 'F ratio' and 'aperture' are used as equivalents in daytime photography but note that, in this case, the focal length of the lens has remained the same and the iris has been opened to let in more light. You are not doing this. You are lowering the F ratio by reducing the focal length. 

If you point your scope at a small galaxy which will fit on the chip at F10 and F2, you are getting exactly the same number of photons from the object either way. What changes is the number of pixels you put them on. The Hyperstar puts them on fewer pixels so those pixels 'fill' faster. However, you would get exactly the same result from using larger pixels, or binned pixels. Professional telescopes often have slow F ratios but they have cameras with huge pixels and they are, therefore, incredibly fast. However you go about it, putting your object photons onto fewer pixels simply trades resolution for speed. In an over-sampled system this trade-off may come at no cost in terms of final, real, resolution.

You don't need to convince me that imaging at F2 is great. I love it and do so with two rigs. My point is that the 8 inch F2 RASA I use cannot be compared with with an 8 inch F10 SCT because it has a focal length of 400mm. I'm not going to compare it with an 8 inch SCT with a focal length of 2000 mm. They don't take the same pictures. I'll compare it with a Takahashi Baby Q, though, with a FL of 450mm because they do take comparable pictures - and the RASA is way faster.

I strongly object to Hyperstar hype because it suggests that you can take 'the same photo' 25x faster when, very obviously, you can't.  The manufacturer is perfectly well aware of this deception and may one day fall foul of European trading standards legislation.

Olly

[Elp]

Other than the better optical corrections on the RASA, isn't HS a similar concept?

I agree on the speed thing, I've found aperture makes a greater difference all things being equal.

[ollypenrice]

2 minutes ago, Elp said:

Other than the better optical corrections on the RASA, isn't HS a similar concept?

I agree on the speed thing, I've found aperture makes a greater difference all things being equal.

Yes, it's a very similar concept and I share Curtis' enthusiasm for fast F ratios.

The RASA is designed from the ground up to work at F2 and seems to have more happy owners than the Hyperstar (just based on reading the forums). The RASA focuser, for instance, is - to my astonishment- capable of holding focus at F2 for long periods of changing temeperature. Some people get the Hyperstar collimated happily but some don't. Then again, there was a problem batch of RASAs so I don't know where we are with that.

Olly

[Elp]

I try not to fuss too much about the technicalities of stars as long as the target is okay, my HS collimation is acceptable to ME in its default closed configuration, and focusing with the default knob is fairly straightforward with computer assistance, I don't refocus and it usually holds even after multiple meridian flips. Maybe my C6 doesn't move as much as a heavier 8, 925 and above.

The RASA 8 situation is still open as far as I'm aware, it would have been my ideal size.

[curtisca17]

43 minutes ago, ollypenrice said:

Many (or maybe all) of these issues have been extensively discussed on here and I think you are reiterating a number of mistakes in your video. The most obvious is 'The F ratio myth.' Your Hyperstar does not speed up capture by 25x.  It does not speed up capture at all.  Please bear with me. Exposure time does reduce as the square of the F ratio, as you say, when the F ratio is reduced by increasing the aperture. That's why 'F ratio' and 'aperture' are used as equivalents in daytime photography but note that, in this case, the focal length of the lens has remained the same and the iris has been opened to let in more light. You are not doing this. You are lowering the F ratio by reducing the focal length. 

If you point your scope at a small galaxy which will fit on the chip at F10 and F2, you are getting exactly the same number of photons from the object either way. What changes is the number of pixels you put them on. The Hyperstar puts them on fewer pixels so those pixels 'fill' faster. However, you would get exactly the same result from using larger pixels, or binned pixels. Professional telescopes often have slow F ratios but they have cameras with huge pixels and they are, therefore, incredibly fast. However you go about it, putting your object photons onto fewer pixels simply trades resolution for speed. In an over-sampled system this trade-off may come at no cost in terms of final, real, resolution.

You don't need to convince me that imaging at F2 is great. I love it and do so with two rigs. My point is that the 8 inch F2 RASA I use cannot be compared with with an 8 inch F10 SCT because it has a focal length of 400mm. I'm not going to compare it with an 8 inch SCT with a focal length of 2000 mm. They don't take the same pictures. I'll compare it with a Takahashi Baby Q, though, with a FL of 450mm because they do take comparable pictures - and the RASA is way faster.

I strongly object to Hyperstar hype because it suggests that you can take 'the same photo' 25x faster when, very obviously, you can't.  The manufacturer is perfectly well aware of this deception and may one day fall foul of European trading standards legislation.

Olly

I think you haven't watched the video because we are saying similar things but coming to different conclusions.  I clearly state in the video that the same number of photons from the DSO are entering the camera with or without hyperstar.  And I go on to point out that it is the fact that the FOV has changed which means that those photons are concentrated on fewer pixels which is what increases the optical speed of the scope.   In a nutshell, I believe that I said exactly what you are saying here.  So, indeed, you get a 25X increase in optical speed.  But, as you say and I point out in the video, since the FOV is much larger with hyperstar than without, the two images are not the same.   Now, as I also say in the video, with the larger sensors typical on cameras these days, one can blow up the image a fair amount without significant impact to resolution since we are very likely oversampling to begin with.  You seem to get this later point but apparently did not hear me say it in the video.

As I point out hyperstar also allows one to fit much larger DSOs into the FOV of the frame which is a major advantage as well.

If one wants a dedicated fast SCT type scope the RASA is a great choice, I agree.  But an SCT is valued for its versatility in going from f/10 to f/7 (or f/6.3) and f/2.  Hyperstar is the tool that gets it to f/2 and I don't consider what I say in the video to be "hype".  But you are welcome to disagree with me.

 

[ollypenrice]

19 hours ago, curtisca17 said:

I think you haven't watched the video because we are saying similar things but coming to different conclusions.  I clearly state in the video that the same number of photons from the DSO are entering the camera with or without hyperstar.  And I go on to point out that it is the fact that the FOV has changed which means that those photons are concentrated on fewer pixels which is what increases the optical speed of the scope.   In a nutshell, I believe that I said exactly what you are saying here.  So, indeed, you get a 25X increase in optical speed.  But, as you say and I point out in the video, since the FOV is much larger with hyperstar than without, the two images are not the same.   Now, as I also say in the video, with the larger sensors typical on cameras these days, one can blow up the image a fair amount without significant impact to resolution since we are very likely oversampling to begin with.  You seem to get this later point but apparently did not hear me say it in the video.

As I point out hyperstar also allows one to fit much larger DSOs into the FOV of the frame which is a major advantage as well.

If one wants a dedicated fast SCT type scope the RASA is a great choice, I agree.  But an SCT is valued for its versatility in going from f/10 to f/7 (or f/6.3) and f/2.  Hyperstar is the tool that gets it to f/2 and I don't consider what I say in the video to be "hype".  But you are welcome to disagree with me.

 

Yes, but my question is, '25x faster than what?'

Edit: With a bit more free time I can now answer that question: it's 25x faster than a telescope with an aperture of 55.8mm and the same FL.

Olly

Edited August 21, 2023 by ollypenrice

[Elp]

Isn't the 25x blurb used in comparison to the SCT at its native F10? But that's like comparing apples to oranges.

[ollypenrice]

36 minutes ago, Elp said:

Isn't the 25x blurb used in comparison to the SCT at its native F10? But that's like comparing apples to oranges.

It is, as you suggest, used to make a totally meaningless comparison. Where is the 55.8 mm telescope in this discussion? It needs to be there at F2 in comparing the Hyperstar with something meaningful, or there at F10 comparing the native SCT with something meaningful. Why? Because the 55.8mm scope has a light collecting area 25x less than the C11. 

This topic always produces more heat than light, to quote MartinB, and I'm guilty of perpetuating this!

lly

[michael.h.f.wilkinson]

Actually, in this comparison, you have to be very careful what you mean. If for a given aperture you image at  F/2 and have a smaller chip, so you have the same area on the sky as with F/10 and a 5x bigger chip, all things are essentially equal. However, if you use the same chip in both configurations, you are capturing a larger area on the sky, and therefore capturing more photons. In practice, if I have a 22 mm diagonal chip (matched to the RASA 8 image circle), and use the same chip at normal F/10 focus of a Celestron C8, you are gathering 25x more light on the chip. You are sacrificing resolution to do so, but with modern small pixel devices this might not be an issue. If you have a chip of 48mm (which is pushing the C8 beyond its limits, but could work on bigger SCTs) you gain a factor of 4.76 in area on the sky, but still lag well behind the RASA (by a factor of 5.25). The number of photons for any object fitting in the FOV provided by the chip used only depends on the aperture, not on the speed, of course, but using the same chip, you do gather more photons in total, because you are imaging more objects.

[ollypenrice]

42 minutes ago, michael.h.f.wilkinson said:

Actually, in this comparison, you have to be very careful what you mean. If for a given aperture you image at  F/2 and have a smaller chip, so you have the same area on the sky as with F/10 and a 5x bigger chip, all things are essentially equal. However, if you use the same chip in both configurations, you are capturing a larger area on the sky, and therefore capturing more photons. In practice, if I have a 22 mm diagonal chip (matched to the RASA 8 image circle), and use the same chip at normal F/10 focus of a Celestron C8, you are gathering 25x more light on the chip. You are sacrificing resolution to do so, but with modern small pixel devices this might not be an issue. If you have a chip of 48mm (which is pushing the C8 beyond its limits, but could work on bigger SCTs) you gain a factor of 4.76 in area on the sky, but still lag well behind the RASA (by a factor of 5.25). The number of photons for any object fitting in the FOV provided by the chip used only depends on the aperture, not on the speed, of course, but using the same chip, you do gather more photons in total, because you are imaging more objects.

This is certainly the key distinction. We can call the photons 'object photons' or, alternatively, 'wanted photons.' If you don't want them, there is no time gain in capturing them. My thinking is that there is no point in talking about speed until you have decided what picture you want to take, and my beef with Starizona is that they ignore this. And I think they do so intentionally as a piece of marketing hype. I might just as well say, 'I can make your car ten times faster by reducing your journey length by a factor of 10. '

Olly

[dph1nm]

One should really think of short F-ratio telescopes as a way of covering more area of sky to the same depth in a given exposure time than a scope of the same aperture with a large F-ratio. So an 8" RASA will not get you any deeper than e.g. an  8" F6 Newt, but it will be much faster at covering a large area of sky.

NigelM