ASI CCDs for long FL

[pmrid (Peter)]

I’m looking to match an ASI CCD to my C11 ( with .63 reducer) - with FL around 1700mm (depending on how much backfocus you use). And I want to use a OSC CCD. So binning is not an option. The answer seems to be to go for larger pixels. I have an old SXVR-H9 with pixels of 6.75 but even that is getting close to being over-sampled. But I want to stick with ASI if I can and therefore I am Looking around the ASI range and haven’t come across any obvious candidates.

Does anyone have any suggestions?

[Camelopardalis (Dunk)]

Peter, ASI071MC? Pixel size is 4.78 microns. That’s about as large as they get these days

[pmrid (Peter)]

Originally Posted by Camelopardalis

Peter, ASI071MC? Pixel size is 4.78 microns. That’s about as large as they get these days

G’day Dunk. It sounds like a fairly good unit but even at 4.78 microns, it would still be way oversampled with my C11. With the .63 reducer, it still works out at a scale of 0.56 arcsec/pixel.

And because of the Bayer matrix, Binning would not be a good option.

I suppose the only other choice would be to abandon my ZWO-centric fixation and go back to cable clutter and MaximDL with an old SBIG8300C - not my favoured choice.

[Camelopardalis (Dunk)]

8300 has 5.4 micron pixels vs 4.78 for the 071…it’s not a big difference.

What is a big difference is the noise… the 8300 can’t compete on that front. I’ve forgotten to plug the power in to my 071 and not noticed it until packing away time.

[Startrek (Martin)]

Peter,
In regards to my Obs set up down south
My 10” CF newt 1280mm fl with the ZWO2600MC OSC ( 3.76 pixel size ) has an image scale of around 0.60 arc sec per pixel
So I’m way oversampled which suits the Startools Bin module perfectly as it’s a scalable bin
It’s a win win as you can improve your SNR at the expense of some negligible loss in resolution ( which may or may not be noticeable anyway )

Oversampled data also works really well with the SV Decon module ( once Binned appropriately)

https://www.startools.org/modules/bin

Hope the above is useful ?

Cheers
Martin

[Atmos (Colin)]

I’ve used an ASI094 for a number of years at 600mm, 1450mm and 2500mm focal lengths and been happy with all 3. It has 4.88 micron pixels, full frame sensor and low noise.

[AdamJL]

+1 to Martin's point.

Get the biggest pixels you can/want, then bin.

There are trade-offs of course, but nothing that can't be removed in post these days anyway.

[pmrid (Peter)]

Thanks guys. I see the Manual recommends software binning also. So I’ve put my ASI533MC Pro on the C11 and will follow their (and your) advice. I doubt the skies will cooperate for a while though. Some things never change.

[Camelopardalis (Dunk)]

Yeah the C11 was never going to be a wide field scope

The beauty of your 533 (or pretty much any modern camera really) is that you can experiment with EAA using software such as SharpCap. To some extent, it gets around the problem of guiding such a long focal length scope… I mean, it doesn’t really, but with such a combo you’d probably only need to take 15-30 second exposures, which will likely reduce the number of frames you throw away because of tracking/guiding errors.

Agree on the weather. It’s shocking again this week…

[Rerouter (Ryan)]

Pixel scale is going to be your main limiting factor, if your at 0.25 arcseconds per pixel, your guiding has to be better than that to take good images (the guy with a ASI2600MC at 2700mm for small DSO objects)

[xthestreams (Paul)]

I'll join the "stop worrying, get a CMOS and bin" chorus.

When starting out (only a few years ago) I was super confused by the warnings regarding oversampling and the need to have crazy good mount tracking to support it. After agonising over trying to find the "correct" sensor (at a price that left me with at least one kidney), I have since done all my imaging (2400mm++) at 0.3 arcsecs native (ASI16000s, 2600s and 6200s). I then almost always usually downsample (bin) through the driver (not hardware - it's CMOS, there's really no difference, except the REDUCTION in bit depth when binned on camera to 12-bits (14?)) to 0.6, which despite still being oversampled slightly, allows for happy moments of great seeing.

The main, coherent, counterargument I'd heard against oversampling tended to be when working on low SNR use-cases - spectroscopy & photometry where the combination of older CMOS sensors non-linearity, low well depths & linear summing of noise (versus CCDs) made CMOS a poor choice especially when oversampled.

Even the CCD stalwarts at the AAVSO seem to have reached the conclusion that modern CMOS like the IMX455 addresses the photometry use case having greater well depth per square micron than the 09000 and 4240 CCDs, near zero noise (by comparison) and high QE.

Spectroscopy is a different ball-game, here the photons for a given frequency are smeared vertically. The ability to perform columnar binning across the spectrum without incurring a noise penalty is a win that I suspect CMOS quite possibly cant match even with its natively lower SNR - but I'll hastily add, I'm not even close to an expert in this field and am probably wildly wrong on all counts!

YMMV

We really do live in a golden age for the hobby, it's almost too easy.

[pmrid (Peter)]

Originally Posted by Atmos

I’ve used an ASI094 for a number of years at 600mm, 1450mm and 2500mm focal lengths and been happy with all 3. It has 4.88 micron pixels, full frame sensor and low noise.

G’day Colin.
I’ve bitten the proverbial bullet with an ASI071MC Pro with 4.78 micron pixels. The helpful advice in this thread about software binning won me over. Now we wait, and wait some more.

[Camelopardalis (Dunk)]

Aaaaarrrgggghhhh Peter…you made the clouds come back

[pmrid (Peter)]

Originally Posted by Camelopardalis

Aaaaarrrgggghhhh Peter…you made the clouds come back

The bleedin’ clouds never left up this way. Nothing but mush for at least the last couple of months and not much to look forward to. The “new normal”.

[Camelopardalis (Dunk)]

Yeah it’s been miserable this year for imaging

Here’s hoping next year is better!