Hi
I think I have mentioned this before somewhere before but
For various reasons like not having a fully flat field or slightly tilted field etc , it is desirable to focus
is a desired area of the chip i.e to the left or right --or ignore the central area to get off centre focusing
I know we can crop the focus frame , but can we select the focus area further
Many thanks for all your work , keep it up chaps
Harry
+1 I have a Baby FSQ that needs to focus nearer the lower right corner in order to be closer to over all sharp. Alternatively I could move x number of focuser steps from the autofocus mark to achieve better focus. Could this be automated? Thanks!
I also support this request : being able to offset the AF result by a given number of steps (positive or negative)
+1
I also support this request. I haven’t tested my new scope (FSQ85) until now. But the vendor told me to focus on stars which are half on the way from the center to the edge. I think this advice is applicable for many scopes.
Reinhard
I also run into problem with autofocus with my FSQ85. The best focus as achieved by SGPro is about 10 click out from optimal focus where the corner stars are round. I think it is an unfortunate trait of the baby-Q and the usual advice is to focus between centre and edge. Unfortunately that rules out automated focusing. I wonder if there are plans to add selective focus area or manual offset options to SGPro?
For example, To achieve a nice V curve with my Feathertouch focuser paired with a starizona motor and a Rigel nstep controller, I need a step size of 25. Once autofocus finishes I need to move the focuser in by 10 clicks to get roundness across the field.
I know there is a per filter focuser offset function in SGPro. I wonder if I can try focusing with a blank filter and then rotate to the filter I need to make use of the focuser offset function as a workaround.
Hi Henry.
I thought through this issue a couple of months ago but ultimatley never followed it through as I bought the 3"FT focuser for my FSQ85 and have had really flat fields since.
My idea was to use the Red filter for AF for Lum, enabling an offset to be calculated with whatever extra +/- ‘bias’ you need for your corner stars. Then use Lum set for all of the other filters with a +/- bias for the corners. This way every filter has a proxy for AF with whatever bias you need to set. The filter for offsets is chosen in the Filter setup option within the Tool Box and Equipment Profile as I’m sure you know.
Just to repeat thought, I never actually experimented with this so don’t know how effective/ineffective it might be ;-).
HTH.
Barry
Thanks Barry
Unfortunately I am still having this problem even with a Feathertouch. Before the Feathertouch the baby Q is not usable with asymmetric stars at the corners. I bit the bullet and bought a Feathertouch and it has made good the scope now, so I can get round stars at the corners. However this requires semi manual focusing as I outlined as the best focus by HFR is not the best focus for flatness.
How do you motorise your Feathertouch? May be I need something with finer control.
I use a LakesideAstro Motor Focus system, here.
Filter offsets work well when you have sorted the settings for a consistent and repeatable V-curve if you haven’t used them already.
Which camera and filter wheel do you have? If you have an 8 filter position FW for example (such as the QSI wsg8 ones), you could put an LP filter in the 8th slot for example and set that as the default to use for AF with your bias added/subtracted from the V-curve differential to suit your corners.
I have run some experiments which I have detailed in the feature request forum recently. But basically I found that best focus by HFR with SGPro was about 1/3 to 1 step size different from best focus for overall round stars. However the difference was not consistent and I had one out of three runs where the offset was actually 0 I.e. Autofocus produced round stars to the corners. I also failed to reproduce the problem with colour and NB filters although this might have to do with the fact that the stars at the corners using filters were very much dimmer and did not necessarily show elongation with the short test subs.
As the offset is not constant it would seem that the best option remains focusing between centre and edge with selectable focus. I wonder if dropping the step size may help as well but last time I tried dropped the step size failed to produce a V curve.
I am wondering if the developer has any update on this feature? It would be very useful. I have finally solved the tilt issue with my Baby Q with a FT, but I can only get all over round stars by focusing using the corner stars. If I focus with the central area the corners are always elongated but the difference in focuser position is not consistent enough to use the focus offset feature. It would be a very welcomed feature. Pretty please?
Most APOs have enough field curvature to make full frame focusing virtually impossible. I corrected my problem by adding a field flattener in front of the camera. This resulted in pin point stars across the entire frame and the auto focus routine works perfectly.
I can highly recommend the TSFlat2,5 from Teleskop-Express:
An auto focus selectable area is not going to solve your problem.
Charlie
Thank you Charles for your well-meant advice but it is not applicable to the Takahashi FSQ85. FSQ85 has built in flattener and the flattening is supposed to be “best” when it is in focus (i.e. one does not need to worry about spacing). But this is a wild claim which applies to some sample but not others. For mine, when the centre is in best focus the stars are not round at the corners. However if I focus using off axis stars I can get all the stars to be round, up to a crop size DSLR sensor. I believe this problem is made more obvious with newer CCD / DSLR with smaller pixels which are more capable of showing the elongation due to the inherent higher resolution. I can “manually” fine tune the focus once the best focus is achieved by focusing in the centre or after autofocus routine by watching the corner stars, but this is a pain in the behind. I am obviously not the only one with the problem hence his request has popped up from time to time.
Last night I was able to get a 20 minute sub with my FSQ85 with round stars (eccentricity of 0.4) but ONLY after manual focus optimisation. I am really hoping that SGPro can have this feature so I can use autofocus with my FSQ85.
To illustrate the problem, I have attached two AberrationInspector images. The first one is a 1200 second sub via an Ha filter which shows elongation at the lower left. The elongation is not that bad but this is because it has been partly adjusted out (I took this sub thinking that the elongation has been adjusted out but it has not fully). I then adjusted focus some more and took another 1200 second sub. The corner elongation is now gone. The amount of adjustment needed is not constant, so I cannot use the offset feature.
Left lower corner elongated (half way through adjustment):
Elongated mostly gone:
The problem with autofocus is that, if you look at the centre panel the stars are very similar. I suspect as far as the autofocus routine is concerned, the two focuser positions produce similar quality stars. Because most stars are in the centre, the centre is therefore more heavily weighed and the corner stars do not contribute much to the star quality measurement. For autofocus to work with the FSQ85, one needs to exclude the centre so only the corner and edge stars are evaluated by the autofocus routine.
I would like this function added. Glad I caught this thread, as I was considering a BabyQ as my next purchase.
I see this with my BabyQ as well, I’d like to be able to exclude the centre third, or some user definable area, of the frame from the AF calculations.
Hi Ken, Jared,
can we expect this feature being implemented in near future? As another Tak user this would be really helpful feature, to be able to exclude the central (selectable) area during autofocus.
During all this time there were additional threads with basically same request, so many will benefit this feature.
Thank you!
