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Old 30-09-2017, 09:29 AM
glend (Glen)
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Hyperstar on Edge HD8, anyone doing this?

I am considering getting the Hyperstar lense for my Edge HD8 and i am looking for some feedback from those that might have done this before. The attractions of f2 imaging are significant. I would be purchasing a ASI non-cooled OSC camera to use with this setup for broadband, as cooling should not be required at f2, or is it?
Specific questions:

1. I assume the 0,79x reducer corrector is overkill or wrong, at f2.
2. I assume guiding is not required at this speed for broadband, but on faint targets or narrowband, i could see a need but probably a simple guidescope would suffice?
3. Do camera cables crossing the front affect image quality, or induce diffraction spikes?
4. Re narrowband, with my mono cooled camera, does the TEC exhaust heat plume affect the image, and is there an easy way to change the filter (assuming no filter wheel obviously)? I know Starzonia recommend a wide spectrum narrowband filter (like 10nm) due to shifting that occurs at very fast f ratios.
5. Given the speed, are light pollution filters required for any broadband use other than dark sites?
Any general advice?

Last edited by glend; 30-09-2017 at 09:56 AM.
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Old 30-09-2017, 10:01 AM
JA
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Quote:
Originally Posted by glend View Post
I am considering getting the Hyperstar lense for my Edge HD8 and i am looking for some feedback from those that might have done this before. The attractions of f2 imaging are significant. I would be purchasing a ASI non-cooled OSC camera to use with this setup, as cooling should not be required at f2, or is it?
Specific questions:

1. Can the 0,79x reducer corrector still be used or is this just overkill or wrong, at f2.
2. I assume guiding is not required at this speed, but on faint targets i could see a need but probably a simple guidescope would suffice?
3. Do camera cables crossing the front affect image quality, or induce diffraction spikes?
Any general advice?
Any obstruction (including the central obstruction) will reduce contrast/cause scattering and yes the cables, just like a spider will cause some degree of diffraction (spikes), BUT, it should be possible to minimize these somewhat.

If there are seperate cables for power and data, try stacking them one behind the other. You could even go all out and un-sheath the cable by removing the outer insulation and then make the multicore cable inside in to a one-behind-the-other configuration (like a flat cable) and minimize intersection with the light path by placing it on edge. Although it is a possible minor risk, as some cables (esp for data or higher frequencies) are designed to operate as twisted pair for low impedance and may not like this. You'd soon see based on any signal degradation.

Also you could experiment with how the wires cross the light path: One straight run, A pair in opposite directions, curved etc.... There are many simulations of this effect to help give some initial guidance, but for me I would try one straight run as it appears to scatter the least, with 2 "dashed line" diffraction spikes in simulations I've seen. The U shaped types are also a good contender. I will try to post one if I find it.

Best
JA

EDIT: Added link, but not the one I was thinking of/looking for....
http://www.astrosurf.com/viladrich/a...iffraction.htm

Last edited by JA; 30-09-2017 at 10:25 AM.
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Old 30-09-2017, 10:06 AM
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Atmos (Colin)
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Never used one but I have read a lot about them.

1) I really doubt that you could use a 0.79x reducer when using the hyperstar, I doubt it has enough back focus and the aberrations would drive you crazy.

2) Whether guiding is required all depends on your exposure time which will probably be quite short if you're using a CMOS. Whether you need to guide in narrowband really depends on the PE of your mount.

3) Yes! But there are ways around that. You have to bundle them into a single circular pattern across the aperture and it encompasses about 1/5th of the diameter. Google it and you'll find plenty of examples with C11/C14's.

4) Difficult one, probably but it is likely below the resolution limit of your image scale so you likely won't notice it. As for changing filters, Baader make filter changes and I think Starizona have them dedicated for the hyperstars. Even with the shorter exposures you'll still want a TEC cooled camera.

5) Light pollution is light pollution no matter the speed of the scope
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Old 30-09-2017, 10:50 AM
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multiweb (Marc)
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8" is not much aperture at all for an hyperstar so I'd say between the camera and cables you'd get too much junk in the light path. Never heard about the reducer. You don't want to have the camera too far from the corrector. The weight of the whole thing could damage the corrector IMHO.
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Old 30-09-2017, 12:38 PM
glend (Glen)
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Quote:
Originally Posted by multiweb View Post
8" is not much aperture at all for an hyperstar so I'd say between the camera and cables you'd get too much junk in the light path. Never heard about the reducer. You don't want to have the camera too far from the corrector. The weight of the whole thing could damage the corrector IMHO.
I don't see any apeture impacts at all, well maybe a few off axis rays. There are plentry of round body camera choices that have no obstruction of the light path, as long as they do not overlap the secondary ring. As to the cables, power and USB only and as indicated below, they can be stacked and curved to minimise any obstruction, certainly less than a four vane newt.
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Old 30-09-2017, 01:05 PM
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Camelopardalis (Dunk)
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Sounds like a worthy experiment to me

The reducer is only for when light is going down the baffle tube...which doesn't happen when you take the secondary out to insert the Hyperstar lens.

The obstruction on the Edge 8 is about 70mm, so a ZWO cooled camera should work fine as they're 68mm. Just curve the cables around.

f/2.1 sounds pretty interesting for narrowband...
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Old 30-09-2017, 03:09 PM
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multiweb (Marc)
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Quote:
Originally Posted by glend View Post
I don't see any apeture impacts at all, well maybe a few off axis rays. There are plentry of round body camera choices that have no obstruction of the light path, as long as they do not overlap the secondary ring. As to the cables, power and USB only and as indicated below, they can be stacked and curved to minimise any obstruction, certainly less than a four vane newt.
If you get one of those skinny cylindrical cameras with the jacks at the back then you'll likely get away with it. Get a cooled one though. Cables curved or straight will still be there and will affect the picture. My point is that the ring where the light enters the aperture is already quite thin on a C8. Just surprised they made an hyperstar for it. Looking forward to the photos. Good luck with it.
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