SGPro focusing and FWHM output

[alcol620]

Simple question. When focusing using SGPro is there a way of getting a FWHM output from each image as the focuser is manually adjusted, rather than rely on eyeballing the image?

Thanks

[PhotoGav]

You can calculate the HFR for an image. If you click the star icon (top red arrow is pointing to it!), the HFR is calculated and displayed in the Images Statistics panel (bottom red arrow).

[Barry-Wilson]

Alan

You can also enable the Image History module which gives a graphical display of the HFR statistic that Gav has referenced.

Barry

[Uplooker]

Interested in this as well, thanks to Alan for posing the question and to Gav & Barry for their informative answers.

Thank you all again ?

[Barry-Wilson]

32 minutes ago, Uplooker said:

Interested in this as well, thanks to Alan for posing the question and to Gav & Barry for their informative answers.

Thank you all again ?

If you haven't already started a trial of SGP, I would encourage you to do so: it is a superb capture suite.

There are a large number of users now so plenty of folk to help irrespective of the stage of your automation.

[alcol620]

Extremely helpful guys, so what you are saying is that every time I manually move the focuser I can take a quick image and click the star icon to see whether I have improved or worsened the focus??

[PhotoGav]

2 minutes ago, alcol620 said:

Extremely helpful guys, so what you are saying is that every time I manually move the focuser I can take a quick image and click the star icon to see whether I have improved or worsened the focus??

Yes, exactly. In fact, when you take a photo with the frame and focus module (bottom left in the earlier screen grab), the image opens in the single frame & focus image tab, replacing what was there, so if the star icon is on for the HFR details, it happens automatically. So, you alter the focus, take a sub and hey presto the HFR value is there.

Even better, get a stepper motor system attached to the focus knob and run the autofocus routine in SGP and, hey presto, sharper focus than I've ever managed manually! You can even do it in your sleep, literally!!

[alcol620]

1 hour ago, PhotoGav said:

Yes, exactly. In fact, when you take a photo with the frame and focus module (bottom left in the earlier screen grab), the image opens in the single frame & focus image tab, replacing what was there, so if the star icon is on for the HFR details, it happens automatically. So, you alter the focus, take a sub and hey presto the HFR value is there.

Even better, get a stepper motor system attached to the focus knob and run the autofocus routine in SGP and, hey presto, sharper focus than I've ever managed manually! You can even do it in your sleep, literally!!

Great news, won't be straining my eyes in the dark tonight looking for small changes in the image.

 

Thanks for your inputs, very helpful

[alcol620]

Me again. I just had a further thought. Building on the information provided if I want to get my spacing on my TS60/ASI1600 combination could I use the same star icon to measure the HFR value for the whole image and watch it vary while I change the variable spacer that I have in the image train?? With the 0.79X reducer, I need camera/filter wheel and spacers to total 70mm. I'm thinking that as I vary the space the HFR will come down as I get nearer and nearer to the optimum value with my set up. I realise that I could use CCD Inspector or CCDCalc - will SGPro do the job for me?

[PhotoGav]

34 minutes ago, alcol620 said:

Me again. I just had a further thought. Building on the information provided if I want to get my spacing on my TS60/ASI1600 combination could I use the same star icon to measure the HFR value for the whole image and watch it vary while I change the variable spacer that I have in the image train?? With the 0.79X reducer, I need camera/filter wheel and spacers to total 70mm. I'm thinking that as I vary the space the HFR will come down as I get nearer and nearer to the optimum value with my set up. I realise that I could use CCD Inspector or CCDCalc - will SGPro do the job for me?

As far as I understand it, while focus (and consequently HFR) will change as you change the spacing, you cannot tell when the spacing is at the optimum by focus. The effect of spacing being out is visible in the corners and edges of the image, the stars will be elongated when spacing is out. I'm interested to hear Barry's thoughts about this one as I think he is far more experienced in this area.

[Barry-Wilson]

When you adjust spacing between reducer and CCD you will need to refocus to establish star profiles across the frame. As Gav said, the star shape/elongation in the corners of the frame are an indicator of whether the spacing is accurate. Star shape elongation across the frame may indicate other problems that result in tilt, e.g. Slop in the focuser.

Trial and error being methodical with incremental spacing and then focussing and assessing the field flatness is exhausting but necessary I'm afraid. Your eye is a very good instrument and will be the best bet. 

Use frame and focus to loop a 1s shot bin x2 to focus reading the graph in Image History module. When focussed take a 10s frame bin X1 with scope pointing directly upwards at the zenith (to eliminate any play in the focuser) and you can then assess flatness.

HTH

 

[alcol620]

Many thanks to you both

[Uplooker]

7 hours ago, Barry-Wilson said:

If you haven't already started a trial of SGP, I would encourage you to do so: it is a superb capture suite.

There are a large number of users now so plenty of folk to help irrespective of the stage of your automation.

Hi Barry,

I already have SGP with the addition of Framing & Mosaic. I have had it a few months now but I am still at the learning stage ?

[alcol620]

Update: Spent about 3 hours last night and this morning. Result: not there yet. Although the focus is close the stars still have some elongation in the corners. A painful process in the dark and only having to consistently adjust the spacers a small amount. Hopefully some clear spells tonight for more of the same.

Despite being difficult, I appreciate that it has to be got right, or somewhere near.

[iapa]

6 hours ago, alcol620 said:

Update: Spent about 3 hours last night and this morning. Result: not there yet. Although the focus is close the stars still have some elongation in the corners. A painful process in the dark and only having to consistently adjust the spacers a small amount. Hopefully some clear spells tonight for more of the same.

Despite being difficult, I appreciate that it has to be got right, or somewhere near.

if the elongation is in all the corners, could be that you might need a field flattener?

Your OTAs are designed to place light on a curved surge e.g. eyeball MK I, and the camera sensor is flat.

If not all corners, possible the focuser is not completely square to the optical path?

[alcol620]

2 hours ago, iapa said:

if the elongation is in all the corners, could be that you might need a field flattener?

Your OTAs are designed to place light on a curved surge e.g. eyeball MK I, and the camera sensor is flat.

If not all corners, possible the focuser is not completely square to the optical path?

I have the 0.79X reducer/corrector this should sort some of the elongation out??

[iapa]

47 minutes ago, alcol620 said:

I have the 0.79X reducer/corrector this should sort some of the elongation out??

Best answer: possible.

It's a 'thing' with many OTAs, that when imaging the focus is not even across the sensor.

Often, they are optically matched/specific to a particular OTA - on FLO's ff/fr pager there are different listings for different OTAs e.g for the SW Evostar 80 they've got a 0.85x, and for the Equinox 120 doesn't mention an fr factor. They are also usually M48 at camera side, so, may also need an adapter.

Who says this hobby is a money pit?

The FF for my Equinox 80 is non reducing so font's affect my field of view.

My newt's is 0.9x and the SCT is 0.63x so, i need to make sure I've to the right numbers in imaging software etc for focal length.