Venus transit - imaging filters and exposure times

[lukebl]

Just a few thoughts regarding imaging the forthcoming Venus transit.

I'm keen to get some interesting images as the sun and Venus rise from my location on the North Norfolk coast, hopefully capturing them as they emerge in all their glory out of the North Sea. I'm aiming to do a movie of the sunrise.

However, it occurs to me that, due to the obscuring effects of haze and low altitude at the horizon, the regular Baader solar filter will make the sun far too dark to image. I've taken some nice images of sunsets myself without any filters like the one below, when a regular solar filter would have made the image far too dark.

OBVIOUSLY, I wouldn't advocate unprotected viewing of the sun, but the much reduced magnitude at sunrise due to haze and atmosphere will have a significant effect. Getting the right exposure, whilst still capturing some of the foreground landscape will be tricky. Just wondered how others were planning to deal with that issue.

[JB80]

Top pic, is that yours?

What settings did you use?

I'm still trying to work this out myself and I suspect that I wont know the answer until I've done a couple of mornings of test shoots just before the event in similar conditions.

I'll be in Santorini overlooking the sea so I'm not counting on much haze or cloud cover to help me out. I'm thinking some ND filters may just come in useful but how many and which ones I'm not certain of.

The ND400 will be total overkill so I'm thinking to have an ND4 and ND8 on hand but that's complete guess work.

So hopefully I'll get a few mornings of test shots first to nail the exp and f ratio down.

I'll also make a baader filter up for once it's risen.

My plan is to set up hopefully with settings that are right and take a timelapse as sun breaks taking a shot every 6 seconds and then once it's up to switch to a baader filter and track it with the Polarie and do the same thing, a pic every 6 secs.

Does that sound about right?

By my working that's 600 shots an hour and we get nearly 2 hours so I need enough space for nearly 1200 shots. Probably closer to 1000 due to switch over and general faffing.

[Photosbykev]

a bit of general info for the transit (based on London). Sunrise is 03:46 UTC (add an hour for BST)

During the transit, the diameter of the Sun is 1891.4 arcseconds and that of Venus is 57.8 arcseconds.

In other words, the diameter of Venus is 0.03 that of the Sun, making it look like a rapidly moving sunspot

[JamieW]

Those are some really good points you raise.

Do Baader make any solar filter film specifically for imaging that has a higher light transmission? Maybe something that could be used with an ND filter?

EDIT: Yes they do http://www.widescreen-centre.co.uk/Products/BAADER_Astro_Solar_Filter_.html . Would that be any good?

[JB80]

^ It wouldn't be any good for a dslr, infact Baader even say on their site about there photo film...

Do not use it for producing solar eclipse viewers, do not mount it onto DSLR camera lenses.

http://www.baader-planetarium.com/sofifolie/details_e.htm

Seeing as it's no good for visual it won't do your eyes any good or your sensor.

And I'd even imagine that even with the low light of a sunrise that would still be fare to dark.

[JB80]

Just curious are these along the lines of what your thinking?

http://www.pbase.com/image/111523946

http://severinghaus.org/pictures/nature/celestial/venus_transit/DSCF1067_venus_sunrise_sm.jpg

They are somewhat what I am hoping for but there seems to be a common theme of haze and atmospheric conditions running through the pics.

I've been browsing loads of sunrise pics and am about 50/50 that the type shot I imagine is possible.

I found this little article which may be of use unless anybody has anything else to add to it.

http://winjeel.com/photography/how_to_take_photos/sunrise_sunsets.htm

There seem to be a few approaches to take really.

[lukebl]

Just curious are these along the lines of what your thinking?....

Yes, that's the sort of thing I'm thinking of. I'm even wondering whether it's worth using a telescope at all and just going for, say, a 300 or 400mm telephoto. At sunrise, I doubt if any filter is needed provided the lens is stopped down sufficiently. The pic in my original post (which I took on the Plymouth-Santander ferry) didn't use any filters, although in that image the sun itself is overexposed and I doubt if Venus would have shown up.

I suspect I might just take my 90mm MAK with solar filter for visual use, and use a 300mm telephoto for the images. A simple closeup detail of the sun with the black dot of Venus is fine (and there will be loads of those around!), but photogenically I'm after something a bit different.

[JB80]

There are quite a few pics taken with small scopes as well so I think if you can do it then it's worth a try, maybe have a practice run and see if it works out.

I can't take any thing like that with me but I am a snifter away from buying a teleconverter. Even though my 300mm is a bit rubbish the pics I have seen at that length give me hope.

I'm not certain what sort of foreground I'll have, ocean for sure. There'll probably be some big ship right in the way knowing my luck.

Like I mentioned I think a time lapse would look good but I'm not certain it'd be a great idea for the sensor.

[lukebl]

... There'll probably be some big ship right in the way knowing my luck...

But that's what'll make the picture look interesting! I'm really hoping there will be a ship passing. I was even looking for a viewpoint where the sun rises through a distant windfarm, but couldn't rind the right location.

[JB80]

That's true, I imagine there will be quite a few boats and cruise ships that side of the island that morning, or maybe people will be oblivious to it. Time will tell I guess.

[Photosbykev]

Yes, that's the sort of thing I'm thinking of. I'm even wondering whether it's worth using a telescope at all and just going for, say, a 300 or 400mm telephoto. At sunrise, I doubt if any filter is needed provided the lens is stopped down sufficiently. The pic in my original post (which I took on the Plymouth-Santander ferry) didn't use any filters, although in that image the sun itself is overexposed and I doubt if Venus would have shown up.

I suspect I might just take my 90mm MAK with solar filter for visual use, and use a 300mm telephoto for the images. A simple closeup detail of the sun with the black dot of Venus is fine (and there will be loads of those around!), but photogenically I'm after something a bit different.

Don't forget that the lens aperture is only stopped down for the duration of the exposure. At all other times it is wide open.

Having said that I've shot the sun using my Canon 600mm f4 prime lens at sunrise and sunset when it was hazy without any issues. I would not shoot the sunrise or sunset with the 600mm on a clear day and I certainly wouldn't shoot it once it had cleared the horizon

[Starlight 1]

May be looking at useing a 35mm film camera (no sensor)

[Andy Dodson]

Hi Luke,

I've taken lots of the photos that you're describing, see http://www.pbase.com/andy_dodson/sunsets__searching_for_the_green_flash usually with at 200mm with a 2x on a 20D, so 640mm EFL in '35mm speak'. I find that underexposing by about 3 to 5 stops usually stops the solar disk being blown out. However when it's really clear air (you're not going to have that problem in the UK are you !) then you may loose the foreground detail, so shooting in RAW and using autobracketing on the exposure might really help you later to photoshop the required result, though I can hear you groaning about doing that on a time lapse! Of course if it's nice & hazy you won't have that problem, and that's 1 reason why I wrote 3 - 5 stops above, it's just so changeable. Obviously practice beforehand, but even so you're still going to have to 'wing it' on the day. I won't have that possibility here as the transit will start at an altitude of 21°, be 26° at mid transit and end at 2°. So I suppose there might be a possibility at egress. If I shift when I loose the sun to the local horizon and get to the sea quickly. Though it'll be a miracle if the sun isn't in a bank of cloud by then. I just hope the weather is better than today, - lashing it down all day. Oh well, only 105 years to the next one.

regards

andy

[Photosbykev]

For Canon users there is plenty of software out there that will handle the HDR bracketing for you in a timelapse. Typically a camera will give +/-2 stops for bracketing, software will extend this to multiple images with very large exposure ranges.

[Psychobilly]

For sunset HDR I tend to combine EC and bracketing to offset the exposure range...

The Nikon D200 was much better for this than the Canon 7D as it had a much more flexible AEB setup covering a much wider range...

When your using AEB don't forget to set shooting Drive mode to Continous as well so you fire off the burst of exposures as quickly as possible...

Peter...

[sanmatt]

^ It wouldn't be any good for a dslr, infact Baader even say on their site about there photo film...

http://www.baader-planetarium.com/sofifolie/details_e.htm

Seeing as it's no good for visual it won't do your eyes any good or your sensor.

And I'd even imagine that even with the low light of a sunrise that would still be fare to dark.

Oh crumbs thats exactly what I was going to do with mine. I have read a stack of astro pages on doing this over the last few days This one for example http://www.astronomylog.co.uk/2010/06/24/how-to-make-a-digital-camera-solar-filter/

[JB80]

That warning is just for the 3.8 Photo density film, if you use the 5.0 Safety film it will be fine and you will still get a pretty good image out of it.

I plan to do the same thing as well with the Safety film so you could use that.

That said I have seen an awful lot of images lately of Sun with the sunspot with people using the 3.8 and a dslr, it's just Baader do give the warning so maybe it's nood good for dslr sensors or your eyes through the viewfinder.

I'm not going to risk it.

Thanks for the link, that's a neat way of doing it too.

edit: I actually find that warning a little odd, surely it you could use it on your scope then image with a dslr through the scope?

Maybe it's just a general warning for the visual side and they don't want people viewing it through the viewfinder.

[sanmatt]

I dont know now, the writing on the Baader solar filter itself says its for telescopes, video and camera etc...

[Stargazing_Cliff]

I will be imaging it with me various telescope cams various softwares to record some avi's so then i just frame grab.

putting some cams on test with sun sometime soon as skies clear

got me set up ready for solar viewing or imaging with Baader solar filter.

i shud get good view of transit from where i am

Middlesbrough uk northeast.

only one thing probably get telephone cables in way when sun rises to front me house

but back garden fine soon as sun sets. shud get some good views

i think it's only when sun rises if i'm correct.

probably test couple shots from window then move me telescope to front garden or me drive way which shows sun best.

people in street be woundering what heck am i doing .

[JB80]

I dont know now, the writing on the Baader solar filter itself says its for telescopes, video and camera etc...

I can't say for sure myself really I just happened to read the warning and figure it's there for a reason. It's kind of counterintuitive for a product aimed at the photographic market.

Like I said it could just be for operator safety purposes.

[sanmatt]

I can't say for sure myself really I just happened to read the warning and figure it's there for a reason. It's kind of counterintuitive for a product aimed at the photographic market.

Like I said it could just be for operator safety purposes.

There are instructions with it and it tells you 'how to make your own objective solar filter for binoculars, camera or telescope'..so I'm guessing it's ok.

[JB80]

Have you got the normal 'Safety' film or the one thats for photo imaging though? There are two different types of film they sell.

If it says Safety 5.0 then you are good to go, if it says photo film 3.8 then baader go out of their way to mention that it is not for visual use at all.

If it has the instructions for a bino cell mount then I would guess you have the 5.0 film and will be fine.

[sanmatt]

Have you got the normal 'Safety' film or the one thats for photo imaging though? There are two different types of film they sell.

If it says Safety 5.0 then you are good to go, if it says photo film 3.8 then baader go out of their way to mention that it is not for visual use at all.

If it has the instructions for a bino cell mount then I would guess you have the 5.0 film and will be fine.

I cant see any mention of which one it is anywhere on it. I'm guessing its the 5.0 safety film.

[Mr TamiyaCowboy]

two shots :

one exposes for the scene and background,

second you pop the badder film over and expose for the sunspots.

then either gimp it or photoshop, the two pictures together the background as layer 1 the sunspot exposure layer two. some tweeking and gaussian blur should have it looking like a single exposed shot

[Stewart Coulter]

If any out there are looking for a public observing event to join in W London, look at www.wolas.org.uk for details of our event at Uxbridge athletics track. The location is excellent for observing with a clear low NE horizon from the top of the stand. It is one minute from the A40 and just a few more to the M25 if you need to make a quick get-away after. The BBC might be there as we may be the only such event in the area. If you would like to come with a telescope you are welcome to email me at stewartcoulter@hotmail.com since I am co-ordinating and we could use any help offered, much appreciated, otherwise just turn up! But check our site first for weather update.