Sunspot Photography

[YT2095]

has anyone here actually Done this at all?

 

It`s a project of mine that Ive been working on for some time, in both aquiring data and apparatus, along with experimentation.

 

does anyone know what is the best color filter(s) to use and does this filter go on the Main front lens (closest to the sun) or between the telescope eyepiece and the cam lens, or both even?

 

I`ll be using color film, cross processed to B&W, so the use of red filters is fine.

the film type is 100ISO, so the image grain will take being enlarged quite nicely.

[Rev Blair]

Interesting question.

 

I've never shot through a telescope, so I'm not sure whether you'd place your filters in front of the lens or the eyepiece.

 

The first thing is to buy high quality filters, I think. Otherwise you'll get lens flare and it will hurt your images.

 

I think I'd try both a single and a double polarizing filter first. You'll likely want those in front of the lens, since they are adjustable.

 

After that, since you're cross-processing to b+w, I'd go with 25 red. That should make the surrounding sky almost black and increase contrast.

 

Then I'd work my way down to a lighter red, then through yellow and green. Yellow will also darken the sky, though not as much as red. Green is generally used for darkening foliage, but I'd try it just to see what effect it had.

 

I've never tried colour filters with colour film that was cross-processed, so I'm curious as to whether the efect will be the same.

 

I'd also shoot some with no filter at all, as a kind of control.

 

I'm also curious...is there a reason why you are shooting colour and cross-processing to black and white? Is it just for convenience or does it capture sunspots better?

[Klaynos]

As long as the filters do not alter the beam it shouldn't matter. Having said that to get a nice linear effect you really want to place the filter in collimated light, which light hitting the front the the telescope sortof is... (I say sortof because it's not really but unless you're doing some snazzy stuff you're not going to get much better as the sun isn't s point source).

 

Polarisers definitely need collimated light. Further from collimation the crapper the extinction ratio.

[swansont]

Of course, certain filters need to be on the front of the telescope so you can align it without going, "Auugghh!"

 

A colleague had a scope out recently and we saw sunspots, and then he redirected it and we saw Venus. It was just a bright dot, but I'd never seen it at lunchtime before.

[Royston]

As I'm yet to buy any filters for my telescope, I projected an image of the Sun through the eyepiece, onto some paper. This is actually standard with my telescope, but there was obviously light scattering due to the humidity on that day, and the image was pretty uninspiring.

 

However, here's some images using the same method...you'll need to scroll down to the bottom...

 

http://www.tdmodels.co.uk/cpac/gallery/solarsys.htm

 

I presume B+W would give you the sharpest contrast, and therefore clearer sunspot images, but astrophotography isn't my field...yet.

[Klaynos]

The small telescope on top of my physics building they have done the paper reflection method for transits of planets before now...

[John Cuthber]

I may be mistaken, but I think the filter you need to get pictures of the sun is a nearly black one to discard the overwhelming bulk of the light. IIRC silvered mylar is often used.

A single line filter (very narrow bandwidth) can get some beautiful images but they are not cheap.

Also, contrast with the sky behind the sun isn't an issue. If you can see the sun properly then the sky will be black.

[Jacques]

I found that link where you have the basic for Safe solar Viewing

NEVER LOOK AT THE SUN WITHOUT:

A PROPER FILTER ON THE FRONT OF YOUR TELESCOPE OR BINOCULARS

or by

PROJECTING THE SUN'S IMAGE ONTO A VIEWING SURFACE

 

 

DO NOT USE A FILTER ON THE EYEPIECE!

[YT2095]

 

I'm also curious...is there a reason why you are shooting colour and cross-processing to black and white? Is it just for convenience or does it capture sunspots better?

 

quite simple really although it`s a manyfold reasoning, 1) using color film on a roll is Very cheap it also allows me to use any color filter I want.

2) all my B&W film is more expensive and towards the orthochromatic (red filters are out the question).

3) I`m equipped for B&W chemistry and it`s also Very cheap.

4) you get a better contrast with B&W

5) color sunspots (if there is such a thing) wouldn`t be of any benefit without Mega magnification, my telescope at Best does a theoretical 520x

 

that said, the experiment for SS photography outlined here will be using binoculars to start with and a simple 35mm camera that I`v modified, I have later plans for a camera obscura design using film plates.

 

I have a few sheets of polarised film here and depending on the rotation angle of any of the 2 sheets can go from clear to near black (it`s closer to a Blue in reality), and that on the "black" setting in front of the first lens makes looking at the sun through binoculars quite an acceptable experience (I tested on reflections 1`st).

 

I`v already gotten through several rolls of film with prior experiments, all of which have failed to produce anything usable other than data of how Not to do it (still useful), and giving me an idea of shutter speed and film ISO for the job.

 

all I have to do now is wait for a clear sunny day again and try these new ideas

[John Cuthber]

Crossed polarisers don't block IR very reliably. You can fry your eyes perfectly well with IR.

This sort of thing

http://cgi.ebay.co.uk/Telescope-Solar-Sun-Filter-425P1-fits-Meade-ETX-90_W0QQitemZ250253918145QQihZ015QQcategoryZ74923QQrdZ1QQssPageNameZWD2VQQcmdZViewItemQQ_trksidZp1638Q2em122

is quite common on ebay.

Has anyone seen any spare pairs of eyes for sale?

[Klaynos]

It does depend on the polarisers, as ones rated for IR will cut out IR....

[John Cuthber]

The IR polariseres I have seen were on a silicon substrate and, therfore, completely opaque to visible radiation. One might expect this to be what limits their usefulness in the current discussion; then you find out the price and find that that would also be a major factor.

 

You can get proper filters at a perfectly reasonable price or you can take a risk with your eyesight.

[Klaynos]

I've got some polarisers in my old lab that are polarisers from 350 to 2500nm... with 100,000:1 extinction ratio.

[John Cuthber]

Can you post them to YT2095?

[Klaynos]

I think my old supervisor might get a bit angry if they dissapeared....

[YT2095]

Experimental update:

 

using the polarised film on the darkest "setting" and 100 ISO film I managed to get some pictures of the Sun, they appear on 35mm film as 8mm black dots, but there was a LOT of haze around them also (probably atmospherics) it was also over exposed.

this over ex was down to the shutter speed being too slow (I had it on manual).

 

So... I`v made a few modifications, the shutter speed has now been adjusted to auto again (whatever that is for a Kodak Brownie 127), and put some 200 ISO film in and used binoculars.

the Nice part is that I can have one lens array over the cam lens, and look through the other one to see what I`m shooting.

this has worked near Perfectly! and I have pictures of car reg plates well over 300 metres away, and Antenna over 4KMs away all in perfect focus

only problem is they are a little Under exposed.

so eitherway, I`m not TOO far off from a good result soon

[YT2095]

further update:

 

rather than messing about with polarised film etc and color filters (I`v used 4 rolls of film experimenting with them) a sudden flash of Genius occurred to me, I tested exposed Film, the Leader bit that gets exposed when you load a film into a cam and gets developed along with the rest of it.

it Works! you can actually look directly at the sun through it, and 2 layers of it and you can`t even See the sun!

 

I`v taken a few shots using this idea and I`m getting Much better results, the only problem is the Sunshine itself, the sky is a bit too Hazy to get a well defined image, so i may have to wait until Winter time to get the sky conditions I need.

[John Cuthber]

I told you it needed a really dark filter.

[YT2095]

I`v finally managed to get a crude image of the sun with a little bit of detail in there as well (something other than just a big Dot).

 

I used an IR digital cam and binoculars mounted on a tripod and held together with sellotape and blue-tack.

 

here`s my 1`st ever picture:

 

it was quite a small "dot" on the whole frame, so I`v had to crop the image in windows Paint and also flip the colors (the sun comes out Black otherwise).

 

it`s not brilliant, but it`s a good benchmark for me to work from

[DrP]

wow - is that distortion or can you actually see the corona there in quite some detail?

[YT2095]

there is indeed some distortion in the picture, the Pixel resolution isn`t great and will pixelate at higher magnification.

but yes, at This magnification and a little bit higher you can make out some crude detail of the corona quite nicely.

it`s certainly a step in the right direction for me