becomm Would be nice to have some sort of communication from ZWO about production/delivery delays

Did you actually order one without seeing the full engineering specs? <gulp>

The reason I ask is that I just went to Cloudy Nights and saw some photos of the two sensors of the camera. There is no way to compensate for the distance of the focal plane of one sensor relative to the other!

At the least, wait for full engineering specs to be revealed.

The SC2210 sensor used in the camera has a pixel size of 4 µm. Let's say you have an f/5 imaging system (pretty ho-hum average for deep sky work). A guide star will appear out of focus if the the sensor plane of the guide sensor is more than 20 µm (0.02mm) away from the sensor plane of the main sensor, when you have the main sensor in focus.

Assuming even that the guide sensor is mounted on a substrate that can be adjusted by a tiny M2 screw that has a 0.4 mm pitch, you will need to be able to adjust that screw by 18º (i.e., barely moving).

But I don't even see any mechanism for such adjustments in the photos of the camera.

With an f/2.5 optical train, you need even more precision, to about 10 µm.

You need to get assurances from the dealer that such accuracy is maintained (and over temperature and time) so you can return it if it does not.

Take a look at the original patent that SBIG filed for the concept of an integral guide camera that was awarded a patent by the USPTO in June 1996 (SBIG sold the camera that is based on this patent as the ST7).

https://patentimages.storage.googleapis.com/2b/3d/1f/41b03c5384d960/US5525793.pdf

Scroll down to the primary claim (Claim 1) in column 15 of the '793 patent. It says:

Notice the phrase "being rigidly supported and positioned a selected distance and adjecent to said first sensor..."
So SBIG knew the importance of the focal planes to implement a dual sensor, that they placed it in Claim 1.

If you were not in the hobby back then, here is a desciption of the ST7:

http://www.company7.com/sbig/products/st7.html

SBIG has many such inventions, the ST-4 camera not being the least. The ST-4 camera is what created the "ST-4" guiding standard. I myself still have an ST-8300 camera (based on a Kodak CCD) from perhaps 20 years ago. SBIG was bought by Diffraction Limited (you might have one of their adaptive optics products) a few years back.

Caveat Emptor.

Chen

Gert Hi, would it be possible to use special size filters i.e. dual narrow band that will cover the image sensor but keep the guide sensor free??

You cannot. (Think light cones instead of light beams.)

With an OAG, you would mount the guide camera on the side before light passes through the filter. With an integral guide sensor, both the primary and guide sensors are getting the same filtered light.

If you use any serious monochrome narrowband filter with 4nm type passbands, the guide chip will receive about 1% (about -20 dB) of the light it normally receives with a wide band filter. That is worse than OAG setups where the prism size is the limiting factor on the light cone.

If you have a current OAG setup that uses the ASI220, you can simulate what the -20 dB light drop is like by reducing the guide camera gain by 200 units (ZWO uses 0.1 dB per gain unit for their cameras) and trying to guide with that, assuming you are using a gain of more than 200 to start with. QHY uses 0.434 dB per gain unit, so you would need to reduce the gain of the QHY camera by 46 with a QHY guide camera. (The difference in gain units is because ZWO uses log base 10, while QHY uses log base e as gain factors.)

If the reduction in gain still allows you to guide, then the dual sensor camera will work. If not, the small sensor is just dead weight. Knowing what I know, I myself will not be buying this camera.

Chen

Gert Now just need a more precise solution without the Dremel.

And a way to swap that filter... :-) :-).

If the filter is mounted a distance from the surface of one sensor, at some point the filter will intercept the light cone that reaches the second sensor.

There are some good reasons that SBIG never proceeded beyond the ST-7 with this concept. They eventually sold cameras that do have separate sensors that are bult into the same body, but configured more like an OAG, and with a separate focusing for the guide sensor, than something that shares the same filtered light path (and also is not obstructed by the integrated filter wheel). Like this one:

http://www.sbig.de/sbig-history/stt-8300/STT8300_051612.pdf

Notice the small prism.

SBIG made pretty well thought out, and well engineered products that catered more to higher end hobbyists and professionals. Notice in the above camera that there is a mechanism to make sure that the filter wheel is positioned to the same exact place each time you choose it, instead of depending on stepper motor step counts and backlashes. This ensures that flats are taken with the filters at precisely the same spot as when the light frames are taken. Details like this are lost from some of today's manufacturers.

Chen

@"w7ay"
There is a small focus adjustment knob to help get focus on the guide camera. Now it may be tricky to use, time will tell. Only limitation I know of is that the scope needs to fill full frame sensors for the guiding camera to be properly exposed. I'll be starting with a wide redcat51 so it should be ok.

Also, I agree, pre ordering any new/untested tech is always a bit of a gamble. But I have seen some previews from trustworthy sources that show that the duo is working fine, event when guiding with 3nm filters.

I'm waiting to see how well this thing guides behind a 3nm dual-band filter. I suspect not very well...

hyiger 3nm dual-band filter. I suspect not very well...

That, and with ZWO's QC track history, how are they going to mass produce and ship a two-camera system with both sensors placed on the same critical focal plane (i.e., tens of microns precision instead of their usual +/- 500 microns flange focal distance specs)?

Chen

w7ay Is exact tilt really that critical for a guide camera? (I do see it's separately focusable from the main sensor)...