Solar surface focusing

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Dave The Drummer
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Solar surface focusing

Post by Dave The Drummer »

Hi guys, noob solar personage here.
I've been shooting the sun for about a year or so with a variety of long camera lenses but recently an SW mak180 and an ASI178MC on an AZ-EQ6 mount, all white light with Baader solar film. Been getting what I think are great results but it takes a lot of getting.
The issue I have is reliable focusing. Obviously in the day I can't check focus on a star with a Bhatinov or similar focus tool. So I'm left with doing it by eye and a lot of guessing. This is unreliable and a couple of weeks ago I must have shot 40 videos of about 60 seconds each and ended up with one usable image. It was a corker, for me, but still that's a very low hit rate.
I've tried using the edge of the sun but there's so much wobbling about that I really can't tell. Also used a mask with the two holes in it but again so much wobbling about it's not at all clear. So I'm a bit frustrated with it.
Is there some way of getting some sort of measurement or indication of how well I'm focusing on the sun?
Pic of that sunspot group I mentioned.

Image


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Re: Solar surface focusing

Post by marktownley »

Hi Dave, welcome to the forum, that;s a great opening image.

Regards focusing, depending on when you are observing (first thing in the morning is by far the best) and given you are observing at 180mm aperture you're issue may well be poor seeing conditions. Best advice from me would be to use either the granulation or sunspots to focus on.

Mark


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Re: Solar surface focusing

Post by nicspenceryork »

Hi Dave,
Focusing on the granulation in WL changed everything for me.
Great image!
Nic


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Re: Solar surface focusing

Post by Carbon60 »

Nice one, Dave. As Mark mentioned, the seeing conditions may be against you with the 180 mm aperture. Try stopping down the aperture to 100mm, or 80 mm using a mask, as this will get you closer to optimal when the seeing conditions are not ideal. This should also help you focus on the solar granulation. I use the on screen zoom function to magnify the view so I can achieve the sharpest image I can and then revert to the standard view. This might help improve your success rate too.

Welcome to Solarchat :)

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Re: Solar surface focusing

Post by rigel123 »

Great image Dave! You are definitely describing poor seeing when you talk about the image wobbling. As Mark mentions, try early in the morning and focus either on the spots or granulation.


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Re: Solar surface focusing

Post by ffellah »

Welcome and great shot, Dave !

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Re: Solar surface focusing

Post by LucaR »

You might also put some gamma temporarly, just for the focus procedure: it helps having more contrast. Easy on firecapture, dont know for other sotwares.


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Re: Solar surface focusing

Post by MAURITS »

Welcome Dave, beautiful image.


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Re: Solar surface focusing

Post by Montana »

A very warm and sunny welcome, what a cracking image :bow :hamster:

I think you will find that we all take about 10-20 videos and only 1 or 2 are a keeper, the rest go in the bin. However, we don't show those ;)
Always focus using the granulation in the centre of the disc where there is most contrast, or the penumbral filaments of a spot at the centre :)

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Re: Solar surface focusing

Post by Dave The Drummer »

Hi guys, thanks for the welcome and all the replies, it is very much appreciated.
I hadn't considered that seeing might be the issue, I'd also not thought about shooting in the morning or evening when the sun is lower. I've been shooting in the hours around midday, mainly because it easier as there is nowhere on my property where I can see below about 20 degrees, and I thought that there was less atmosphere to pass through.
I did try and focus on the granulation of the surface, there is a point at which the entire surface seems to wobble in synchrony, if you will, and then I'm assuming that I'm in focus. Honestly not done any tests to validate this but from my photographic experience it seems to stack up. I'd be very interested in your views.
I'll also try stopping down the aperture a bit. I can make a mask for that no worries.
The reason I'm using such a long fl is to get right in close to the sunspots, solar physics in general is an area of special interest for me. I really want to see the details in them and my ultimate aim is to generate short animated .gif files of the changes over time. I do the same thing with Jupiter and that looks, to me, awesome.
Asking questions elsewhere also led me to realise that I'm oversampling with my camera, the pixels are too small for the focal length especially when I was using a barlow for planetary stuff. So I'm wondering if this might have an effect here too. It was suggested that lowering the barlow and binning the pixels would assist here, might work for solar too. I'll try it to see.
OK so I have a few things to try and see what I get. Unfortunately the phenomenal weather of the last two weeks has just closed in in the UK so the liklihood of me getting back out there in the day is minimal for a while. But I shall try.


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Re: Solar surface focusing

Post by DeepSolar64 »

Dave,
That image looks good. It's big!! The details in the spots show up well and the granules are easily seen. I view the image at full size on the monitor and focus on the spots. Daytime seeing is a pain where I live. I rarely can use a 102mm refractor to it's best here much less a 180mm Maksutov.

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Re: Solar surface focusing

Post by cybermayberry »

You certainly nailed the focus on that one for sure, wonderful image


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