Gina

I've examined the Ha and OIII stacked images and the stars are smaller in the Ha. Maybe the focus was a bit out in the OIII. Here's the Ha image.

Thank you Carole. Here's the Ha stretched with HistogramTransformation which is PixInsight speak for Levels.

Than you Carole. Yes, these vintage ex film SLR lenses are brilliant. Guess I can use a star mask. The colour seems to originate from the OIII subs though I don't know why the Ha isn't contributing much to the stars - could be the Curves.

Great images with lots of detail. I presume your colour combination was SHO to RGB. With a predominance of Ha in most DSOs this does lead to a lot of green.

Heart and Soul Nebulae in Ha and OIII. 135mm f2.5 Asahi Super Takumar lens, 3nm Astrodon filters in ZWO EFW, ASI 1600MM-Cool camera. FoV 10° x 7.5°. EQ8 mount, no guiding. 50 Ha and 172 OIII subs of 180s (3m) exposures with gain of 300 and temperature of -25°C. Processed in PixInsight. Calibrated with darks and flats. Colour combination HOO mapped to RGB. Rotated to put north at the to[p and cropped.

Flaming Star and Tadpoles Nebulae plus other DSOs. 135mm f2.5 Asahi Super Takumar lens, 3nm Astrodon filters in ZWO EFW, ASI 1600MM-Cool camera. FoV 10° x 7.5°. EQ8 mount, no guiding. 48 Ha and 61 OIII subs of 180s (3m) exposures with gain of 300 and temperature of -25°C. Processed in PixInsight. Calibrated with darks and flats. Colour combination HOO mapped to RGB. Slightly cropped. Orientation :- North is Left. The star cluster just below the tail of the Flaming Star is M 38. Level with M 38 and half way to Tadpoles is IC 417. Middle near the bottom is M 36.

Excellent - congratulations.

Think I'll stick with 3D printing...

I have the same model and mine has + and - signs on the connections so I guess it does matter. Positive is on the left on that photo.

My screws are 1mm pitch. I plan to try with one motor and belt/pulley arrangement.

I get my angled USB cables from Amazon. They have a huge variety.

I have a 3D printed conical dew shield which fits on the lens and I drilled a series of little holes to take the resistor wires in a ring just in front of the lens. The resisters were inside with the joins in the wires on the outside. I covered the joints on the outside with hot melt glue. Power to the dew heater is controlled from the RPi.

Why 4 wires?

Need dew heater om my 135mm f2.5 lens. Thinking of about 2W and have 10Ω ¼W resistors. 13.8v supply. P=V²/R hence R=V²/P. For P=2W, R = V²/2 = 13.8²/2 = 95Ω Number of 10Ω resistors will be 10 near enough.

ADM Vixen-type Side-By-Side Mounting System : 11" (standard)

That makes sense.

Is this saying that the optimum gain is unity (139)?

I think you mean "so the higher the signal input value to the ADC, the higher the S/N coming out."

This is the way I've been thinking. Increasing the gain reduces the read noise the graph says but this is read noise converted to per electron. If the read noise is in the ADC then reducing the gain below unity can't achieve any benefit, surely?

Yes, I have studied the graphs and what you say agrees with what I thought. Although the read noise comes down at higher gain, the dynamic range is still best at zero gain. I guess the optimum gain depends on how long the subs are - you need longer subs at low gain to overcome the noise level. That determines the sensitivity. OTOH the more subs the better the S/N. But I guess some things cancel out and it all comes down to total integration time.

Thanks Wim. I'll try gains of 0 and 60 and see what, if any, the difference is. What I wondered is that the ADC is 12 bit and the data collection is 16 bit. Guess the gain adjustment must be in the amplifier before the ADC.

Where there is a very high contrast DSO such as M42, how low a gain can I use effectively? In other words, is there a limit where reducing the gain no longer gives extra dynamic range?

Starting the year with a widefield narrow band rig with 135mm f2.5 Asahi Super Takumar Lens as used on vintage SLR film cameras such as the Pentax Spotmatic. These are superb quality lenses even at full aperture and all my imaging has been with full aperture. Camera - ZWO ASI 1600MM-Cool with ZWO EFW and Astrodon 3nm filters. Rig mounted on EQ8 and without guiding at first. Capture with RPi 3 running INDI firmware and saved in Linux Mint desktop indoors running KStars/Ekos.

This Blog is to be a record of my imaging for this year including calibration data.

I use Astroberry as the starting point for my astro projects. Astroberry Focuser works well with my stepper driven focusers and I modify Astroberry Board for controlling things like dew heaters. I shall also be using it for my observatory ROR roof control.