New sensors from On Semi

[Shiraz (Ray)]

Originally Posted by Slawomir

Hi Greg,

I was suggesting that ICX834 (not 814) could be a cheaper alternative to 11002.

And you are right, ICX834 would need to be put at the end of a much smaller telescope to give the same FOV as 11002, but that what I meant - maybe I did not explain it correctly.

Agreed, ICX834 has tiny pixels but read noise in only 2e- with FLI MLx834 - I really think when combined with FSQ106 (1.21"/px) it would be a very capable relatively fast narrowband imaging setup.

KAI11002 would need to be combined with 1500mm fl to give the same resolution, and both setups would have about the same FOV.
Yes, KAI11002 has much deeper wells but also significantly higher read noise and significantly lower QE making it, in theory, less suitable for narrowband imaging, in spite of being more expensive (as you pointed out- larger mount, larger filters etc).

So if someone's on a budget (relatively speaking) and has a smaller telescope, I feel that ICX834 presents an interesting and in theory quite capable option.

this is a Really Smart idea Slawomir..

Taking it a bit further, I have just done some back of the envelope calculations and a NB setup using a 180mm f3.5 lens and 834 could possibly even be more sensitive than the very popular FSQ106/11002 combination (will need to do the modelling properly to make sure that is right) and with similar field of view and resolution - nothing budget about it from a performance viewpoint, just a lot lower cost. Very very neat! Only question mark that I can think of for now would be how the camera lens handled bright stars - the FSQ produces beautiful soft fuzzy balls and a camera lens may possibly be a bit harsher (although that may not be such an issue at NB).

[gregbradley]

Originally Posted by Shiraz

this is a Really Smart idea Slawomir..

Taking it a bit further, I have just done some back of the envelope calculations and a NB setup using a 180mm f3.5 lens and 834 could possibly even be more sensitive than the very popular FSQ106/11002 combination (will need to do the modelling properly to make sure that is right) and with similar field of view and resolution - nothing budget about it from a performance viewpoint, just a lot lower cost. Very very neat! Only question mark that I can think of for now would be how the camera lens handled bright stars - the FSQ produces beautiful soft fuzzy balls and a camera lens may possibly be a bit harsher (although that may not be such an issue at NB).

Well I could test that out. I have a Nikon 180mm F2.8 ED lens and Nikon adapter for my FLI Filter wheel. My Trius 694 fits into my FLI Filter wheel so I should be able to image with it and focus manually. I have to work out a mount for the lens. Perhaps a lens foot and a Losmandy D clamp and fit it on top of the Honders. I think I may have those parts. A project for the future once I have finished current imaging projects.

A step down ring may help with the sun stars on bright stars that a lens aperture creates. I also have adapters for the very excellent Pentax 165mm 6 x 7 F2.8 which is sharp wide open.

Greg.

[Shiraz (Ray)]

Originally Posted by gregbradley

Well I could test that out. I have a Nikon 180mm F2.8 ED lens and Nikon adapter for my FLI Filter wheel. My Trius 694 fits into my FLI Filter wheel so I should be able to image with it and focus manually. I have to work out a mount for the lens. Perhaps a lens foot and a Losmandy D clamp and fit it on top of the Honders. I think I may have those parts. A project for the future once I have finished current imaging projects.

A step down ring may help with the sun stars on bright stars that a lens aperture creates. I also have adapters for the very excellent Pentax 165mm 6 x 7 F2.8 which is sharp wide open.

Greg.

sounds good Greg. Only issue may be the NB filter - 3nm is too tight for an f2.8 system and will really reduce the signal, although I suppose that it would be OK for an initial test just to see if there are any hidden gotchas.

have done some more careful modelling - results attached. Looks very promising in all respects - Slawomir's 834 + 180 system should be similar to an FSQ106/11002, provided the chosen camera lens can get close to the diffraction limit (the better ones seem to be able to do so in the centre of the field - which is all that is needed). I assumed 5nm NB for the two f2.8 systems and 3nm for the FSQ106, dark sky, seeing of 2 arcsec and RN of 11e for 11002, 5e for 694 and 3e for 834.

[Slawomir (Suavi)]

The data looks interesting, thank you Ray.

I think Alluxa can modify their filters to adapt them for given telescope, so perhaps 3nm narrowband filters with high transmission are possible for fast systems.

One possible advantage of using 3nm (or narrower) filters is that since stars have continuous spectrums, the amount of photons coming from stars gets reduced with narrower filters while the signal from a nebula at a particular emission line remains constant - I found it helps (with 3nm filters in my case) to reduce the effect of shallow pixel wells - saturation point is reached somehow later.

Would love to test such system (ICX834 at f2.8 with custom narrowband filters) - just need a few sponsors to fund the project

[Shiraz (Ray)]

Originally Posted by Slawomir

The data looks interesting, thank you Ray.

I think Alluxa can modify their filters to adapt them for given telescope, so perhaps 3nm narrowband filters with high transmission are possible for fast systems.

One possible advantage of using 3nm (or narrower) filters is that since stars have continuous spectrums, the amount of photons coming from stars gets reduced with narrower filters while the signal from a nebula at a particular emission line remains constant - I found it helps (with 3nm filters in my case) to reduce the effect of shallow pixel wells - saturation point is reached somehow later.

Would love to test such system (ICX834 at f2.8 with custom narrowband filters) - just need a few sponsors to fund the project

I think that the problem is that the outer rays at f2.8 are a fair way off the normal to the filter, so they do not even get through it (the interference stack transmission peak shifts to shorter? wavelengths as the incidence angle increases). 3nm is fairly inefficient at f3 and worse at f2.8. Broader filters are more tolerant to incidence angle and a 5nm should do OK at f2.8. For a system with high central obstruction, the passband can be shifted so that the filter works over the range of incidence angles presented by the light that gets through the input annulus, but I don't think that is a viable approach with an unobstructed system. The alternative would be a full aperture NB filter in front of the lens.....

In any case the 834 system will have more dynamic range than the 11002 system, so operating at 5nm should not be a major problem - there will be more background light to contend with, but that has been accounted for in the modelling and the 5nm 834 is still close to the sensitivity of the 3nm 11002 system.

[Slawomir (Suavi)]

Thank you for explaining that Ray; I have been recently looking at an option for going narrower that 3nm with my f5.6 system and what you wrote has perfectly clarified the concept of the issues with angle of incidence.

[gregbradley]

The narrowband filters I have are 5nm not 3nm so that should help.

Of course a Nikon 180mm ED lens or a Pentax 67 165mm F2.8 lens is not the optical equivalent of an FSQ106ED.

Greg.

[Shiraz (Ray)]

Originally Posted by gregbradley

Of course a Nikon 180mm ED lens or a Pentax 67 165mm F2.8 lens is not the optical equivalent of an FSQ106ED.

Greg.

in a heavily undersampled system and over a smallish field, that probably doesn't matter much. It will be very interesting to see how you get on - particularly keeping the focus in the 17 micron CFZ .