IMX174 mono sensor cameras - why not?

[JayPea]

Hi,  I'll planning to pull the trigger on an IMX174 based camera, probably the £650 Altair Hypercam IMX174 mono camera (the one with fan cooling). That's my budget for just a mono camera, I decided I couldn't justify a ASI1600 and all the extras that follow on. I'm happy with the FoV and 2.3MP. I'll add a filter wheel, LRGB and Halpha.

I'd be pointing it at most things up there using focal lengths up to 600mm f6.3/f5 (the shorter faster glass will be Nikon lenses). But it's unlikely I'll use it for planetary or solar. I'll be limited by light pollution to relatively short exposures if that's still a significant issue with LRGB, so maybe the amp glow issues if real won't be a big problem.

Does anyone have any experience with this particular mono sensor on these kind of subjects (nebulae, galaxies) and lenses or scopes? Do you have any images you could share?

Thanks, John

[D4N]

The cooling on it is only fan assisted there is no peltier or temperature control so the level of cooling will depend on the ambient temperature.  If you plan to use it somewhere cold it will be quite effective but if it is too warm it won't do much.

The 174 chip is just 12bit, that shouldn't be too limiting (the asi1600 is also 12bit) but you should be aware of it as a 12bit adc can provide ~4000 shades whereas 14bit is ~16000 and 16bit is ~66000.  The human eye can only differentiate around 500 shades of grey but in Astro imaging most of the data is at the dark end of the histogram and requires stretching, if the data has higher fidelity to start with this helps prevent obvious gradients when you stretch.  This is most obvious if you stretch an 8 bit image you will see the data break up immediately.

I don't know how well the amp glow is handled on these chips as I don't have one.  I know the amp glow on my 178 was cut right off when I fitted a peltier cooler to it though, if it is sufficiently cold out the fan and heat sink could achieve this alone.

[ChrisLX200]

The ZWO ASI174 is probably the worst offender for amp glow, the QHY version is better but by how much I can't say. Dark frames will generally correct for the ZWO amp glow at shorter exposures (~20sec) at moderate gain (~200) but if you turn it max gain (250) and use 30sec exposures you get this: (master dark x10 frames). And because it's temperature dependant you'll be lucky to take all of it out..

 

 

[JayPea]

That amp glow at 30 seconds looks more than I expected. Some of the cameras allow 5 to 15 minute exposures. Would that be unusable even if kept down to a few minutes?

The only other camera I considered was the cooled 178 (pushing the budget at £700) but I thought you need top class optics for the small 2.4um pixels and obviously with much a smaller pixel area you need much longer exposure (x6?). But then again it's a small sensor so you use the sweet center spot of the lens and you can use smaller filters.

Maybe I should just flip a coin to decide...

[ChrisLX200]

The 178 is a different animal and amp glow is nowhere near as apparent. I don't have a good comparitor to show but 20sec @ gain 200 shows nothing other than a few hot pixels.

ChrisH

[Adam J]

What I dont get is why these chips have amp glow at all its like going backwards 7 years in CMOS technology.