How to focus on the sun?

StewartR

StewartR

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Stewart
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I was out yesterday trying to photograph the ISS transiting in front of the sun. I fluffed it for reasons we needn't go into here - a transit time of slightly under 1 second is challenging! - but my real issue was focusing. Can anyone give me any tips?

I'm using a Canon 100-400mm lens with a 2x extender, and a solar filter of course, on a tripod with a gimbal head. The camera is a 7D Mk II.

The lens+extender gives me a maximum aperture of f/11, so there is no hope of autofocus. Trouble is, even at 800mm the sun occupies only about half the height of the frame, so it's not very large and focusing accurately through the viewfinder is difficult.

I would prefer to use live view. Crank it up to x5 or x10, and I should be able to get the edge of the sun, or preferably a sunspot, nice and crisp. However, to use live view I need to have my eye about 30cm from the camera, and remember the camera is by definition pointing directly at the sun. It's quite hard to avoid accidentally looking at the sun. But even if I can manage that, when I'm looking at the rear screen I'm dazzled by the bright sky immediately around the sun.

Any recommendations? How do you do it?
 
Firstly, with the solar filter attached I surmise it will not cause a burn on the sensor.

Secondly and not from my own experience, for your own safety......how about a large cardboard baffle with a hole through which the lens goes. Maybe with a piece of dense blackout cloth to make sure you close off any gaps. Your eyesight cannot be replaced!!
 
Can't you flip the live view so that you can look down on it? Then you can shade it and look well away from the sun. If not, then what you need is a big black scarf you can throw over both your camera and your head, like the old wooden box photographers used to use.
 
If you use a Baader filter, you can look at the sun directly, and focus either manually or auto if you get an edge in the focus area...

I bought a film of Baader filter and cut my own out on a cardboard frame. I tack this frame to the lens with tape just in case it wants to fall off...............
 
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Mark Johnson said:
If you use a Baader filter, you can look at the sun directly, and focus either manually or auto if you get an edge in the focus area...

I bought a film of Baader filter and cut my own out on a cardboard frame. I tack this frame to the lens with tape just in case it wants to fall off...............
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As stuart says with a minimum aperture of f11 (due to the 2x extender) the camera cannot autofocus.

He also says he has a solar filter on which i guess is a baader filter.


Box Brownie idea of making a cardboard baffle sound good!
 
Mark Johnson said:
If you use a Baader filter, you can look at the sun directly, and focus either manually.....
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But that's exactly what I'm finding difficult. The sun is pretty featureless and it's quite small in the viewfinder. I don't think I can focus it particularly accurately.
 
chris malcolm said:
Can't you flip the live view so that you can look down on it? Then you can shade it and look well away from the sun.
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Not with a 7D Mk II. Perhaps I could use a different camera, but then I wouldn't have 10 frames per second.
 
StewartR said:
But that's exactly what I'm finding difficult. The sun is pretty featureless and it's quite small in the viewfinder. I don't think I can focus it particularly accurately.
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You should be able to focus on the edge of the sun, and maybe a sunspot or two............

Never had a significant problem myself...

Oly Em1 ii with a pany 100-400 at full blast...

International Space Station in full view by Mark Johnson, on Flickr
 
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You could always use the 149.6 million Km index mark of your lens scale! (Not helping am I?)

Do you want the ISS (408 Km) or Sun (149.6 million Km) in focus? Will your depth of field cover this? What is the hyperfocal distance to cover this?

Sorry, Stewart, my stupid mind wouldn't stop :)
 
Black cloth? Any coat draped over you and the camera will do (but don't forget some reading glasses if you need them for closer work!)


Of course, you might be able to borrow a Fuji 100-400 and 2x telecon along with an X-T2 body - the 100-400 with that extender does AF on the X-T2 which has a flippy screen and focus assist to boot.
 
Box Brownie said:
Do these guides help???

https://www.diyphotography.net/how-to-photograph-the-international-space-station-every-single-time/
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Thanks Laurence. It's funny how different people approach the acquisition of knowledge in different ways. When I want to learn how to do something, my revealed preference is to ask people I "know" for advice, rather than Google for advice from strangers.

Anyway this guy shoots tethered, and uses the laptop screen to adjust the manual focus. That sounds like a good idea to me, and it's something I can try.

He also uses an automated app to trigger the shutter at the correct time, which isn't something I would want to do, but amusingly there's something critical missing from his instructions. Can you see what it is?

T minus 10 minutes: I always check the script one last time and set the camera to live view to cut down on mirror slap. Now is just a matter of sitting back and hoping that the clouds don’t roll in at the last second and your calculations were correct.
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Answer: After 10 minutes of sitting back and waiting for the app to trigger, the sun has drifted out of the frame!
 
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Box Brownie said:
Do these guides help???

http://www.astropix.com/html/planetary/iss_solar_transit.html
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This one is interesting. Here's what he says about focusing.

Focusing was accomplished by using the Canon right-angle finder at 2.5x magnification and focusing on the Sunspot group. This actually ended up being my biggest worry because it was extremely difficult to focus on the groundglass at f/11... I considered using the live focus on my Canon 20Da, but I couldn't see the screen well enough to judge the focus on the Sunspots because of the brilliant sunshine, even with a Hoodman on the laptop. Thankfully the seeing was decent or I would never have been able to focus on the Sunspot group.
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It sounds like he has exactly the same experience as me, and his solution is a right-angle finder with 2.5x magnification. Interestingly he said using a laptop was difficult too. Still, I can test that on sunny days when there isn't a transit, so I'll be better prepared next time.
 
Mark Johnson said:
You should be able to focus on the edge of the sun, and maybe a sunspot or two............

Never had a significant problem myself...

Oly Em1 ii with a pany 100-400 at full blast...

International Space Station in full view by Mark Johnson, on Flickr
Click to expand...
Wow. Brilliant, well done.

Maybe there's an inherent difference between using an optical viewfinder and an electronic one, or maybe my eyesight just isn't as good, or maybe wearing varifocal glasses doesn't help. But I just can't get it consistently accurate.

Actually, I could take my glasses off, tweak the viewfinder dioptric correction, and try like that. It's one fewer potential source of difficulty to contend with.

But thanks for posting the photo. Absolutely inspirational!
 
StewartR said:
Not with a 7D Mk II. Perhaps I could use a different camera, but then I wouldn't have 10 frames per second.
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True. With my ancient Sony A77 and fully articulated live view screen I can only do 5 or 8 or 12, no 10. :)
 
If you're looking at anything on the camera a baffle of some sort will help. Stiff card (large enough to do the job) would be best as cloth may flop where you don't want it or lead to moving the camera as you fight your way out of it. We used to do that with our old refractor we used for viewing the Sun by projection (before the days when I could photograph it). I've only ever used AF to focus, so not much help there. Having said that, I know it can be tricky trying to judge focus by eye. I can get stars spot on (checked by bahtinov mask) but once trying to image a lunar eclipse I couldn't convince myself the AF was getting it right, tried using the VF and live view and just couldn't do it. I'm long sighted which may not help. I do some sketching at the scope and use an old pair of reading glasses - varifocals are great but have their limitations.
 
chris malcolm said:
True. With my ancient Sony A77 and fully articulated live view screen I can only do 5 or 8 or 12, no 10. :)
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Sure. But with your ancient Sony A77 you can't use a Canon 100-400mm Mk II.

I mean, I could use a Nikon D500. That has an articulating screen and I think it shoots at 10 fps. But I wouldn't be able to use a lens as good as the Canon 100-400 on it.
 
Mark Johnson said:
Infinity comes to mind................
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Sorry, it might work for you but it doesn't for me. On Canon USM lenses, the focus scale goes beyond the infinity mark. This is to allow the autofocus to iterate towards the correct focus. It means there isn't a hard end stop on the focus scale, and the actual infinity position has to be judged by eye,
 
chuckles said:
Do you want the ISS (408 Km) or Sun (149.6 million Km) in focus? Will your depth of field cover this? What is the hyperfocal distance to cover this?
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With a focal length of 800mm on a Canon crop sensor, and making all the usual assumptions about final image size etc, the hyperfocal distance is about 3km. So I guess if I can find an object that's more than 3km away and focus on that, I should have both the ISS and the sun within the depth of field. Net time I'm doing this, I might try to choose my location so that there's something like a building or TV tower visible on the skyline.

But if I can't do that, the huge DOF doesn't actually help much. The problem is that on the focus scale there's barely a whisker of difference between 3km and infinity. So although I technically don't have to be very accurate in terms of the focus distance, I do need to be accurate in terms of rotating the focus ring to the correct position.
 
Focus on something else at infinity and then tape it down, or note the exact position so you can re-set? Try it, see if it's accurate enough.

Another idea that I've used when I can't see the LCD is to use a little handbag mirror and hold it at an angle over the screen. It's a bit of a fiddle and the image is reversed of course, but it does work :)
 
I'm imagining Richard with a handbag...
 
StewartR said:
With a focal length of 800mm on a Canon crop sensor, and making all the usual assumptions about final image size etc, the hyperfocal distance is about 3km. So I guess if I can find an object that's more than 3km away and focus on that, I should have both the ISS and the sun within the depth of field. Net time I'm doing this, I might try to choose my location so that there's something like a building or TV tower visible on the skyline.

But if I can't do that, the huge DOF doesn't actually help much. The problem is that on the focus scale there's barely a whisker of difference between 3km and infinity. So although I technically don't have to be very accurate in terms of the focus distance, I do need to be accurate in terms of rotating the focus ring to the correct position.
Click to expand...

You're right of course Stewart - I was being less than helpful (perhaps tongue planted firmly in cheek) I'm with hoppy on this one.... something I've done myself (not the handbag bit though :) )
 
StewartR said:
Wow. Brilliant, well done.

Maybe there's an inherent difference between using an optical viewfinder and an electronic one, or maybe my eyesight just isn't as good, or maybe wearing varifocal glasses doesn't help. But I just can't get it consistently accurate.

Actually, I could take my glasses off, tweak the viewfinder dioptric correction, and try like that. It's one fewer potential source of difficulty to contend with.

But thanks for posting the photo. Absolutely inspirational!
Click to expand...
I'd go with this. My experience with telescopic sights on firearms is that varifocals do not help at all and need to be removed.
 
Does the 7d II have the ability to have exposure preview on the LCD? Maybe in video mode? If so you could cut the exposure enough that you could focus on what you want and then back out of that mode.
 
I'm not sure if this will work with your setup or focusing screen Stewart, but there are plenty of masks used in astronomy to help improve focus. One of these is a Scheiner Disk, which is essentially just something with 2 holes in that project slightly different images into your eyes with a telescope, or the sensor with a camera. When you've got perfect focus the images snap together and increase in brightness http://www.astro-nut.com/SolarPrimer.pdf#page=27

Might be worth a try?
 
sk66 said:
Does the 7d II have the ability to have exposure preview on the LCD? Maybe in video mode? If so you could cut the exposure enough that you could focus on what you want and then back out of that mode.
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That's not the issue. I have a Baader solar filter on the front of the lens, which is effective a 16½ stop ND filter. So the sun as seen through the viewfinder and on the live view screen really isn't very bright. The problem is the very bright sky adjacent to the sun.
 
Jannyfox said:
If you're looking at anything on the camera a baffle of some sort will help. Stiff card (large enough to do the job) would be best as cloth may flop where you don't want it or lead to moving the camera as you fight your way out of it. We used to do that with our old refractor we used for viewing the Sun by projection (before the days when I could photograph it).
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Thanks. I think I might try that.
 
For the USA Total Eclipse last year, I found that LiveView didn't actually get the best focus - the viewfinder was better. Not sure why. Once I had a good focus I taped the focus ring with a bit of insulation tape to stop it drifting.

I used a fleece zipped up and placed round the camera to allow me to see the Screen and viewfinder. I thought I had a photo to hand I could put here. Sadly not, but suffice to say that when Mum saw it she said I looked like a sad elephant. :)
 
raathistle said:
I'm not sure if this will work with your setup or focusing screen Stewart, but there are plenty of masks used in astronomy to help improve focus. One of these is a Scheiner Disk, which is essentially just something with 2 holes in that project slightly different images into your eyes with a telescope, or the sensor with a camera. When you've got perfect focus the images snap together and increase in brightness http://www.astro-nut.com/SolarPrimer.pdf#page=27

Might be worth a try?
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Mmmm, might be worth a try. Thanks.

I Googled Scheiner Disk images, and it seems the template needs to look something like this:
upload_2018-2-19_12-3-41.png
I estimate that will cause an additional 3-stop reduction in the light entering the lens, on top of the 16½-stop solar filter, which might make the mage a bit dim. I guess I can remove the mask after focusing the lens. But if it makes it too dim to focus readily, I could switch to the lighter grade of Baader filter, which is about 12½ stops, and I'll be roughly back where I was.

I imagine this can also be used with other approaches. For example, shoot tethered, magnify and brighten the mage on a laptop, and use his mask - with a bit of a luck it might be quite easy.
 
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If it's your lens (Stewart) rather than a stock one, how about prefocussing on the Moon the night before (other heavenly bodies exist and will do as well but I would suggest planets rather than more distant objects) and taping the focus ring? Or using a metallic Sharpie pen to make a semi permanent mark at the focus point rather than taping it up - that way you should be able to simply set it next time you use the lens for that purpose.
 
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