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Getting a solar image in focus


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I really did try a search for this info but it was beyond me!

I have been viewing some really impressive sunspots with a simple Baader (silver) solar filter. My 80ED scope gives brilliant results and the spots are really crisp even with a 4.7mm EP. However, when I try to image it with my DSLR, the live view image just burns out and I can't get a convincing focus. With a 1/200 exposure through the filter, the pictures are not bad but I needed to use a suck it and see / repetition and chose best of the possible focus settings . That's obviously not satisfactory. Is the only answer to use an even heavier filter or to stop down the 80mm aperture?

I guess you'll say I should get on my knees and focus through the viewer but it is so much easier to use my tiltable view screen.  Also, if I were to use an astro camera, I wouldn't have that option.

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I had a similar issue with Lunar, the live view worked fine for focusing but the resulting exposure was way off in brightness compared to what the screen was showing.

There are two things you can try, play with the "live view exp simulation" in the menu if you have it (might be called something different on some cameras), the other thing that worked for me was to get a chipped T adapter, this allows you foll the camera by setting a value for f/ratio which makes the live view image change in brightness (think I may have run my camera in AV mode rather than manual), you can then get the live view brightness exactly the same as the resultant shot.

Alan

P.S. Its probably worth trying AV vs Man anyway even though the reported f ratio will be 0, they do show differing live view vs exposure brightness. 

Edited by Alien 13
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The ED80 is a fixed aperture and the only way to 'underexpose' is to use the minimum ISO (100), which of course I did. A proper exposure time gives me a good saved image but it's the situation with the sensor exposed during live view that gives the problem. I would guess that I could either use another filter (I did try adding  my Moon filter, which is 13% neutral) but that was not enough. Perhaps a cardboard circle would give me a few stops down - say f16 - but then the focal depth is less critical. 

I have to 'apologise' that I want to do this without too much investment in solar imaging - it's obviously not a problem if very narrowband (and unbelievably expensive) filters are used as they only let in a smidgen of light in the first place. Perhaps stopping down would be the best way and I don't think there would be a diffraction limit at f22 or so.

23 minutes ago, Alien 13 said:

, play with the "live view exp simulation" 

 

Thanks. I will try playing with that but the displayed image really looks burned out as if it's just too much light landing on the sensor.

Needless to say, it's cloudy all day . . . . .

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14 minutes ago, sophiecentaur said:

The ED80 is a fixed aperture and the only way to 'underexpose' is to use the minimum ISO (100), which of course I did. A proper exposure time gives me a good saved image but it's the situation with the sensor exposed during live view that gives the problem. I would guess that I could either use another filter (I did try adding  my Moon filter, which is 13% neutral) but that was not enough. Perhaps a cardboard circle would give me a few stops down - say f16 - but then the focal depth is less critical. 

I have to 'apologise' that I want to do this without too much investment in solar imaging - it's obviously not a problem if very narrowband (and unbelievably expensive) filters are used as they only let in a smidgen of light in the first place. Perhaps stopping down would be the best way and I don't think there would be a diffraction limit at f22 or so.

Thanks. I will try playing with that but the displayed image really looks burned out as if it's just too much light landing on the sensor.

Needless to say, it's cloudy all day . . . . .

There is no need to stop down your scope or add extra filters, what is happening is that in manual mode your shutter is at 1/200 sec and live view probably at 1/8 second (in normal mode) so there is bound to be a big difference in perceived brightness. It also worth trying the camera in TV mode as well as AV and manual it sometimes tricks the live view to match exp, failing that a chipped adapter lets you input a fake f/ratio to fool the camera electronics.

Alan

Edited by Alien 13
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3 hours ago, Alien 13 said:

live view probably at 1/8 second

I can see some jerkiness in the live view mode so that could certainly be relevant. I will try alternative modes during focussing. 

Where would I get a "chipped adaptor"? Also how much would it be? Sounds like an expensive, one-off device to make the camera think it was using an f8 stop. The camera knows when it has no focal length info - you have to enter that in at switch on. There is also a control for lenses with no aperture control ("Aperture ring" setting) so I would imagine that one could use a false aperture lever which is what the camera uses with non-auto lenses. A clever bit of machining could be needed there. Possible, unlike the electronic solution, but beyond me, I think. I still might try a cut out temporary stop for focussing, though.

But what do astro cameras do about this problem? Is there software control, perhaps?

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To take a image I use iso 100 and exposure time of 1/250-1/500 ..

To focus I bump up the exposure to fairly high 3200 something like that and use live view until the sunspots pop..you know when you have focus because the surface with have different tones,light and dark patches..also look at the limb and it be sharp.. font forget to re-adjust the iso to 100 otherwise you just get a burned out image

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9 hours ago, sophiecentaur said:

I can see some jerkiness in the live view mode so that could certainly be relevant. I will try alternative modes during focussing. 

Where would I get a "chipped adaptor"? Also how much would it be? Sounds like an expensive, one-off device to make the camera think it was using an f8 stop. The camera knows when it has no focal length info - you have to enter that in at switch on. There is also a control for lenses with no aperture control ("Aperture ring" setting) so I would imagine that one could use a false aperture lever which is what the camera uses with non-auto lenses. A clever bit of machining could be needed there. Possible, unlike the electronic solution, but beyond me, I think. I still might try a cut out temporary stop for focussing, though.

But what do astro cameras do about this problem? Is there software control, perhaps?

The chipped adapters are called "focus confirm" but unfortunately the T variety are rare but you can buy the chips and glue them on yourself (a plastic widget for alignment comes with them) they cost around £5, I myself use an M42 version of these together with a 10 mm T piece extension and they fit together quite well even though the threads are different.  

The aperture is controlled in camera as you would with a lens fitted although physically you are not doing anything to the scope, the camera however now thinks you have an f/8 or whatever you choose to set lens fitted and meters accordingly.

Alan

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