I've received the new gem from ZWO, the ASI 385 camera with new IMX385 Sony
sensor. It's an uncooled version. IMX385 is the big brother of IMX224,
nearly same sensitivity but a greater field of view. Resolution is 1936x1096
(2.1 Mpixels), size 3.75 microns.1- Presentation :
In the white carton box are included the classical ZWO accessories :
–2 m long ST4 guider cable
–2 m long USB3.0 cable
–Driver & Extra Software CD (Mac, PC&Linux Compatible)
My testing camera was equiped with an Ir-cut filter in front of sensor.
Cool for the classical RVB use but not adequate if we want to add the
Infra-red part of spectrum or use the sensor as a monochrome sensor
with an Ir-pass filter. So I've replaced it with the clear window coming
from my ASI 224. 2- Software :
Now only Firecapture v 2.6 Beta is able to fully support ASI 385.
During my first tests I have 1 or 2 crashes but all camera features seems
to work fine : frame rate, camera settting, SER video recording. So I guess
there's little bugs to fix for Firecapture.
SharCap 3.0 supports only the use with ASCOM protocol. Enough for autoguiding
but not complete for planetary/lunar/ DSO imaging. I hope that SharpCap
will be soon updated. 3- Compared field of view :
Here is the main strength of IMX 385 sensor compared to IMX 224 : a larger
filed of view. Here is a comparison between 3 sensor based on same technology
(3.75 micron FSI Exmor) but different generations :
IMX185 : 1945x1225 (2.4 Mpix)
IMX224 : 1305x977 (1.3 Mpix)
IMX385 : 1936x1096 (2.1 Mpix)
IMX 385 is 16/9e format size like IMX 290. You love or you hate ! Here I use
a view with Saturn and its main moons. Made with my 300 mm telescope and ASI
185. Even if "old" IMX 185 has the larger field of view, IMX385 losts
only a few part of the field compared to IMX224. So IMX385 will be a great
sensor for Jupiter/Saturn with Moons "familly pictures". Moreover for
lunar or large DSO targets, a larger field of view is always a good news,
believe me ! 4- Maximum frame rate :
Here I choose cameras with same sensors (IMX385/IMX224/IMX185) for comparison :
Even if ASI 224 keeps it's leadership for framerate, ASI 385 shows
an excellent level, a little better than ASI 185. Considering the minimum
image sampling necessary in planetary high resolution imaging applied to a
color sensor, these values are easily operable and well staged, to my opinion.
I previously use ASI 185 for Jupiter/Saturn imaging and I was satisfied
with the available framerates. Even for Mars, 267 fps with 640x480 ROI
was enough ! 5- Readout Noise :
On the paper, readout noise of IMX385 is close to IMX224.
I apologize, I tried to extract noise informations from Offset/Flats/Darks but
I do not succeed. The results are not correct, values are too low. I don't
understand, I use the great ISIS software and I previously have obtained correct
values for IMX174. But for an IMX174 monochrome sensor, not a color one...
So I guess I made a mistake when testing ASI 385 color, but I don't know what ? 6- Amp Glow :
Here is the main strength of IMX385 compared to IMX185. For IMX185, "heavy" Amp
Glow signal was impossible to manage efficiently. QHYCCD works to reduce it and
find a solution that remove a part of it. But the remainder was not enough
reduced to be easily managed for faint DSO targets imaging.
Now, on new ASI 385, an efficient anti-amp glow system is implemented. Amp Glow
is greatly reduced and the preview images are very clean. Remainder is very low,
even without using darks in short exposure DSO.
Here is a comparison with ASI 224, I have the old version, without the anti-amp
glow system. On ASI 385, the circuit is switched on at 1 second exposure.
Now a very quick test on NGC 7331 with 5 sec exposure : 7- First test :
I received the camera 3 days ago and I only have few minutes to make a test
"on sky" because clouds quickly "win the battle". Result is not up to it. I will
wait for a decent night and decent images.
My first impression is that image is very clean and that even in DSO imaging, we
may forget the darks. But I have to perform further testing to be sure, especially
for faint DSO objects.First conclusions :
This is only a quick review but in my opinion, ASI 385 is very convincing
synthesis between ASI 224 and ASI 185. For sure a great multipurpose camera :
planetary / lunar / DSO short exposure imaging. For sure I will keep ASI 385
and sell ASI 224 for my own use. It's more suitable with my 300/400 mm telescopes
and the anti-amp glow circuit is key feature for DSO imaging.
I only find too little drawbacks :
- Ir-cut window to be replaced by clear window. Easy to change.
- I'm a perfectionist but my wish would be to reduce a little bit the 1 second
threshold to activate amp glow circuit. In a perfect world, I would choose
500 ms. More adequate value for the bright planetary nebulas. I don't
know if it's possible or not and easy to implement ? a - LONG EXPOSURE DARKS AT LOW GAIN : b - SHORT/MEDIUM EXPOSURE DARKS AT HIGH GAIN :
Now I wait for clear skies... wink.gif
Now I wait for clear skies...
TO BE CONTINUED....