About Filter Offset and Temperature Compensation

Voyager Autofocus & Robofire
#1

Increasingly, I receive requests to manage the filter offset and the focuser’s compensation of position automatically according to the temperature.
Honestly, I consider myself a good astrophotographer and the experience of many years with different setups (expensive and not) has led me to avoid both because they do not bring good results.
Most of the focus systems that we amateurs are able to have doesn’t have the precision to address the two issues. Since the philosophy of Voyager is to obtain quality data and not quantity of data
the approach on the two issues is different. Voyager uses the group by slot. A slot of X poses for filter with focus by slot which means, focus at the beginning of the slot and every X poses if set.
In this way you have the best real focus for the filter in use and for the current sky and position conditions. In the case of Voyager the focus can be on a single star or on fullfield.
The difference is substantial, the LocalField favors the obtaining of a uniform flat field and is useful for refractors or flattened systems. The RoboFire VCurve system working on one
single star in the center field prefers the quality of the focus in terms of the best possible FWHM, leaving the field flat to the goodness of the instrument. Both focus are manageable in Voyager
and it is also possible to indicate that if the LocalField is in use for some filters, the RoboFire VCurve on the single star is used and I think in particular of narrow filters.
Then comes the talk of the download speed of the camera, camera with slow downloads do not suit the LocalField. Surely with the single star and the ROI goes very fast.
The LocalField can also go into ROI, but the benefit of smoothing the field is reduced and the results going in direction of the single star focus in terms of FWHM . The best is to bin the camera and leave the field near full if you want to use LocalField in terms of flat field.

Voyager does not currently handle filters offset directly if you use the ASCOM camera control, but if you use Maxim or TSX camera controls, then you can easily manage the offset of the filters transparently to Voyager, you just have to take care to configure the focuser within the respective programs and set the offset values.

In the future I will also include the filter offset management with camera ASCOM direct in Voyager, is very simple, but I will point out that the solution is not indicated in terms of quality.

1 Like
#2

Thanks for you consideration of this issue. My system has a very stable focus.

Many times, I can focus once at the beginning of the session. I takes about 5-7 degrees F to make measurable change in focus.
The offsets are needed for my narrow band filters.
The filters sets are parafocal but the NB in 3mm verses 2mm for LRGB.

I can refocus with every filter change but it is only necessary with at least a 4 degree F decrease in temp.
I will try it your way too.

Max

#3

The problem is not temperature but when you move focuser to apply offset. If you have a focuser that can move of small steps and go in real asked position you are ok with offset. Usually this mean to have a 4000€$ focuser but also depend on gravity again… my experience is not to use but how i said i can add.

#4

I think the Optic Gemini that I use is that truly that good.

It only cost me about 3200-3500 Euros :joy::grinning:

Max

#5

If you are sure that focus is only question of focuser you can use offset … i prefer to use focus routine and lost some time. Voyager have this phylosophy … best data and offset isn’t a way to have best data!

All the best
Leo

#6

I will probably configure focus each filter as you recommend.
I think there is a need for offset distances.
The NB filters are 3mm and LRGB 2mm so filters need different starting points.

#7

I think RoboFIre can manage it without problems.

All the best
LO

#8

Leonardo
Are you still intending to provide temp and filter focus offsets ?

I don’t want to use temp offsets as I think that a few minutes using the autofocus routine (when temp changes) is the best way to get good data.

I would like to use offsets for filters becuase I like to use short exposures with regular dither. I want LUM frames to be in very good focus but I’m not so worried about R, G, B, Ha etc. I don’t really want to run an auto focus run on my Ha filters as that would take too much time (for me).

Ian

#9

temperature and offset in not managed in voyager (exception for offset in array because is not possible at now to do in different way). And this will not change in the future.

Focus with HA or narrow band filter take the same time of the broadband filter in Voyager, there is not difference. User the RoboStar focus on single star.

All the best
Leonardo

#10

Recuesive theme, make it sticky :wink:

#11

Hi! We have a remote telescope in Spain. Today we are using another software, but we are now
evaluating your Voyager demo. We have very big temperature differens the first hours in night so
we really need temperature compensation. Any plans for adding that soon?

#12

Hi, We don’t have these features and won’t add them. We prefer to let users use automatic focus.

All the best
Leonardo

#13

Ok, thanks for quick answer. Then we have to go through Maxim and Focus max for that ( as today ).
Works, but less programs = less problems (-:
We will continue the testing!

#14

Try LocalField or Robostar Autofocus in Voyager, are autofocus of next generation compared to FocusMax

All the best
L

#15

I agree with Leonardo. From my experience a temperature compensation is not necessary with Voyager. LocalField autofocus is fast and reliable. It takes about 1 minute.

There are temperature differences of 10-15 degrees in my location and the focus of the EdgeHD scope is very sensitive to the temperature. Therefore I refocus every 0.7 degrees automatically. It works very well.

Best regards,
Vitali

#16

Hi,

FWIW, I have never used temp compensation because my focusers always produced a small amount of image shift. What I’ve done is to refocus if the temperature changes more than 0.9C, it even works on a f2.2 systems.

Cheers,

José

#17

The type of offset i consider useful is the rough focus position…
I will always use autofocus
I only want the software where the rough focus position was, move there and then perform autofocus…
This is my reason, i have Lum, Red, Green Blue filters of one brand, and Ha, Oiii, Sii of another…
I would love to define an offset to tell voyager “go to this position before autofocus” … i would never replace autofocus on my system…

I hope i explained myself…

Diego.

#18

Hi Diego,

Autofocus works also if you are not at focus. In any case you can move focuser using dragscript:

If you have a different set of different brand/thickness I suggest to separate sequence between one brand and another and using a different profile.

All the best
Leonardo