F-ratio support for Astromechanics lens control

I’m using an Astromechanics ASCOM lens controller for a widefield setup I’m building. I’m wondering if it’s possible to add an option to select the f-ratio without having to disconnect the ASCOM driver from Voyager and change the option manually. Can we have that change on the fly?

Also, it would be great to be able to have the f-ratio and lens model recorded in the FITs header, if that’s possible as well.


I suppose is a focuser ASCOM driver.
There isnt option to change this settings in ASCOM interface, this is a driver setting.
You must ask to developer if they have some command string to send when connected, in this case I can add a send ascom string block in DragScript

All the best


is there not possibility via ALPACA (ASCOM REMOTE)
If that’s possible then you can use that comment within drag script.
even connected to voyager. I do that, but then for my mount.
Control the observatory via my OCS(node-red) via Remote ascom, while Voyager also interact directly with the ascom drivers. its a idea give a try :wink:


I’ve done some reverse engineering:


Aperture is only a variable to define the command string blind during position request !!
Cannot be changed externally.

I researched and I must say that the astromechanicsgroup solution is very interesting.
Aperture control, fire management with the optics motor and elimination of possible blur for the stabilized optics. On stabilized optics, if you do not feed the stabilizer meniscus, it remains free to move, in my case the Canon EF 200 f / 2.0, which with Canon Eos cameras is formidable, using ASI cameras that do not feed the optics I have to throw away 20-25% of shots.
However in my view the astromechanics option for my color camera, an asi2600mc, is not very practical from the point of view of changing the filters which requires opening / disassembling and closing / reassembling the adapter every time.
Since I also use different filters for color (baader uv / ir, L-Pro, L-Enhance, L-Extreme, Lumicon Deep Sky) I am evaluating the possibility of using the filter wheel as I already use for the monochrome solution (asi2600mm ) where the astromechanics option is great.
In your opinion, if in the voyager configuration I declare that the asi2600mc is monochromatic, so as to be able to configure the filter wheel, can there be contraindications / complications?
thanks a lot

Marzio why you do not set to off the stabilization ?
Anyway about your request you can set the camera like mono and use a filter wheel, a lot of users already do this.

All the best

Very well, thanks Leonardo!

Unfortunately it’s not that simple, at first I didn’t understand. I thought it was a driving problem or a fixing problem of some mechanical element. Instead the problem is that if you use a stabilized lens with an EOS camera, which powers the lens, when the stabilizer is on it does its function, when the stabilizer is off the electronics of the lens “keep the meniscus still”. Using an ASI camera that does not power the optics whether you put the stabilizer on or off it does not matter, the electronics are not powered and therefore do not work … and the meniscus is free to move. I encountered the problem with my Canon EF 200 / 2.0 but later with a friend the same problem with a Canon EF 400 / 2.8. Searching the internet we then found confirmation in those who do macro photography with extension bellows, in this case even if you use the EOS camera this is not connected to the lens which is free to move so they do bellows with contacts and connection wire to avoid it, as well as being able to control other functions of the optics. In short, a great disappointment when I discovered the phenomenon. I am attaching a 1: 1 crop of one of the many shots thrown away.

Thanks again


Thanks for explanation Marzio.

All the best

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HI Marzio,
Just for information, up until a few years ago, I regularly used Canon lenses with IS with CCD Cameras and had no problems frame after frame (apart from clouds :wink:). The vast majority of older Canon EOS EF lenses with IS all parked the IS lens elements if the lens was turned off properly (with Camera ON turn Lens IS to OFF, turn camera off, remove lens after 15 seconds) this was the case for my Canon EF 500mm IS and both the EF I and II series of the 100-400mm IS zoom. Apparently, some of the newer RF IS lenses do not park the IS element and could therefore exhibit the shift you have seen but most manufactured before 2020 can be successfully parked to work “off camera”.

Hi BigAI,
I did not know this, as soon as the sky opens I try and then I tell you !!!
Thank you :blush:

Hello BigAI,
I spoke a little while ago with the Canon assistance who confirmed what you say. The IS lock is performed mechanically when the camera is turned off whether the IS is on or off to prevent the moving part from “crashing”. It is the chamber that sends the lock command when it is turned off. However in this state (optics off) a small movement is tolerated due to mechanical tolerances which can change from optic to optic. If, on the other hand, the lens is powered (camera on) and the IS is off, then the IS is “kept” blocked by the electronics.
Thanks again