[Nass]

Baader's solar filter foil is the best quality you can get. It is great for visual observation at high magnifications and photography is much less demanding. The only problem may be mounting it to your lenses. You cannot simply put it into your filter holder (Cokin and other have gel holders for their filter systems), because the foil is highly reflective. You need to put it really light tight into the fornt of your lens. You could simply type it, as some crinkles won't degrade the IQ!

I have been using that foil for years on my telescopes. They are available in two different densities, so the choice is yours.

Ben

Yeah - I went for the 3.8 because 5 seemed just a little toooooooo dense. My quest for a suitable filter construction is nearly complete after visiting the local hardware store and finding a universal clothes dryer adapter, which is basically a tube with a flange. I should be able to cut this and flatmount the foil onto the flange, then glue that onto a 77mm UV filter base with the UV bit smashed away. That'd give me an ND 3.8 which I can use across the board with stepdowns. Obviously vignetting is likely because I'd want to use a polariser and/or IR cut out too - which makes 3 stacked filters, problematic for my new Sigma 10-20. I'll cross that bridge when I get to it though, right now I'm excited about having this foil stuff

ps. Falconeye is a God amongst men.

[Nass]

Baader's solar filter foil is the best quality you can get. It is great for visual observation at high magnifications and photography is much less demanding. The only problem may be mounting it to your lenses. You cannot simply put it into your filter holder (Cokin and other have gel holders for their filter systems), because the foil is highly reflective. You need to put it really light tight into the fornt of your lens. You could simply type it, as some crinkles won't degrade the IQ!

I have been using that foil for years on my telescopes. They are available in two different densities, so the choice is yours.

Ben

Yay! It's arrived! Ben, it comes with a sticky white paper back, some sort of protector I suspect. I take it that I need to peel that off before using it?

Thanks!

[Ben_Edict]

Yay! It's arrived! Ben, it comes with a sticky white paper back, some sort of protector I suspect. I take it that I need to peel that off before using it?

Thanks!

Yes, take it off AFTER you have cut the foil to size. Without the paper, cutting the foil is a nightmare.

Ben

[Nass]

Ben you're a gentleman and a scholar, thank you =)

Yes, take it off AFTER you have cut the foil to size. Without the paper, cutting the foil is a nightmare.
Ben

[Ben_Edict]

Ben you're a gentleman and a scholar, thank you =)

This info comes from experience (I have ruined a lot of that foil...)

Ben

[Nass]

So, I made a Baader Solar Film 3.8 filter today, and shot some test frames. And I thought I'd just post the results back, perhaps for some informed observations from people who are knowledgable about this sort of thing.

Now it is a dark, dreary, overcast day here today so I set the ISO high. I used sigma 10-20 for testing because that's the lens I want to use this on. This one is at 10mm, with no hood, 25s f11:



Then with a hood (and another filter stacked on it, I was testing light leak possibilities): 25s f11:



By this time I concluded that this circle in the image (2 actually if you look closely at the top one) must be some sort of flaring/internal reflection/ambient light thing. So I went inside and shot out the window, where there's less stray light etc: 30s f7.1:



It takes a -45 tint change magenta -> green and +60 contrast to get it looking like it should



This is a normal shot not using the filter as reference, I don't think these two are worlds apart:



Curious, what do you guys make of all this?

[Ben_Edict]

So, I made a Baader Solar Film 3.8 filter today, and shot some test frames. And I thought I'd just post the results back, perhaps for some informed observations from people who are knowledgable about this sort of thing.

Now it is a dark, dreary, overcast day here today so I set the ISO high. I used sigma 10-20 for testing because that's the lens I want to use this on. This one is at 10mm, with no hood, 25s f11:

Then with a hood (and another filter stacked on it, I was testing light leak possibilities): 25s f11:

By this time I concluded that this circle in the image (2 actually if you look closely at the top one) must be some sort of flaring/internal reflection/ambient light thing. So I went inside and shot out the window, where there's less stray light etc: 30s f7.1:

It takes a -45 tint change magenta -> green and +60 contrast to get it looking like it should

This is a normal shot not using the filter as reference, I don't think these two are worlds apart:

Curious, what do you guys make of all this?

First the easy part: the colour shift is normal for most solar filters, may it be made of foil or coated glass. Inconvenient, but your colour correction, shows, that it is manageable. WB will probably not work in camera, as the light level is too low, I guess.

The reflection is something new. I have never seen that when using the Baader foil. It is probably due to the extreme wide angle of the Sigma. I think, it is a reflection between the foil and the front lens of the Sigma and not stray light from outside. Though ofcourse your interior shot doesn't show the reflection. It may well be dependent on the focal length or the curvatore of the front element..

One way to get rid of that kind of reflection would be to mount the foil at an oblique angle and not parallel to the front lens. The foil will not show the typical astigmatism a glass filter would produce if mounted at an angle. The foil is too thin and has no refractive power.

Ben

[falconeye]

So, I made a Baader Solar Film 3.8 filter today, and shot some test frames.
[...]
Now it is a dark, dreary, overcast day here today so I set the ISO high.
[... private communication ...]
it looks like there is still a lot of purple in there! I wonder if this is evidence for this idea that Pentax dslrs let in more IR?

Nass,

some very interesting tests!

So, it looks as if the Baader filter isn't perfectly neutral in spectral sensitivity. One should probably shoot a gray card to have a good calibration target. However, I wouldn't have suspected that an increase in contrast is necessary. Any stray light still in?

BTW, why do you set ISO 1000 and f/11 at the same time? I would always stay at lowest ISO to keep the latitude for post processing.

Then, I don't think that the purple cast is evidence for IR. It may just be that it isn't perfect gray (as not that important for solar observations). IR leads to blur due to a different focal length. So maybe, you compare the sharpness with and w/o the filter using full aperture with a nearby subject (small depth of field). If you see a blur/shift in focus then indeed, there may be traces of IR passing thru.

[Ben_Edict]

Nass,

some very interesting tests!

So, it looks as if the Baader filter isn't perfectly neutral in spectral sensitivity. One should probably shoot a gray card to have a good calibration target. However, I wouldn't have suspected that an increase in contrast is necessary. Any stray light still in?

BTW, why do you set ISO 1000 and f/11 at the same time? I would always stay at lowest ISO to keep the latitude for post processing.

Then, I don't think that the purple cast is evidence for IR. It may just be that it isn't perfect gray (as not that important for solar observations). IR leads to blur due to a different focal length. So maybe, you compare the sharpness with and w/o the filter using full aperture with a nearby subject (small depth of field). If you see a blur/shift in focus then indeed, there may be traces of IR passing thru.

I have searched the web for some info on the AstroSolar foil's spectral transmission. The curves are not yet on Baader's website. I have found one curve, which shows, that the foil has a slightly higher transmission in the blue part of the spectrum (about 2x the transmission in the visible part of the spectrum) and there is a transmission peak around 950nm, where it blocks much less effectively (30x its average blocking in the visual part). So, there is a slight IR excess, but on a very low level, if you look at it in absolute numbers (Gerhard Dangl's Astronomie Ausrüstung) That should not be enough IR to cause noticeable image degradation, as there is the IR filter in front of the sensor.

Ben

[Nass]

Thanks Ben, fascinating.

I wish I knew someone in my local area who had say some other brand camera with M42 adapter. Then I could test this and take both the filter and lens out of the variables - that might be interesting. Lots of good insights here, I think I have a fair bit of testing to do to work out how to get the best out of this. I shot one inside last night and the colour of that looks almost perfect compared to a regular exposure. So I'm not really sure what's going on

Real bummer about that circle though, which appears at 10-14mm (by 15mm the circle is bigger than the shot so makes no difference). Interesting that it's much more prominent on the outside ones than the inside ones (they're all 10mm). I'll give sloping the material a shot but constructing a light-tight filter at an angle with a 10mm lens might prove a challenge. It might very well be that since is such a mirror like material it's somewhat inevitable.. or it's an as yet undiscovered light leak... or it needs a custom hood... who knows, plenty of opportunity for testing though.

The next stage of this journey is actually to marry this filter into a home-made camera cover. This is a cover, made out of 1 sq metre or so of dark black butyl pond liner that would extend beyond the filter for a cm or so (ie act like a mini lens hood) and basically cover the camera etc on the way that those rain hood things do. I've got a gadget that'll put rivets into stuff so with a few of those and a drawstring I should be able to eliminate stray light from the equation at least. Will post any further progress once I get there...

[Ben_Edict]

Thanks Ben, fascinating.

I wish I knew someone in my local area who had say some other brand camera with M42 adapter. Then I could test this and take both the filter and lens out of the variables - that might be interesting. Lots of good insights here, I think I have a fair bit of testing to do to work out how to get the best out of this. I shot one inside last night and the colour of that looks almost perfect compared to a regular exposure. So I'm not really sure what's going on

Real bummer about that circle though, which appears at 10-14mm (by 15mm the circle is bigger than the shot so makes no difference). Interesting that it's much more prominent on the outside ones than the inside ones (they're all 10mm). I'll give sloping the material a shot but constructing a light-tight filter at an angle with a 10mm lens might prove a challenge. It might very well be that since is such a mirror like material it's somewhat inevitable.. or it's an as yet undiscovered light leak... or it needs a custom hood... who knows, plenty of opportunity for testing though.

The next stage of this journey is actually to marry this filter into a home-made camera cover. This is a cover, made out of 1 sq metre or so of dark black butyl pond liner that would extend beyond the filter for a cm or so (ie act like a mini lens hood) and basically cover the camera etc on the way that those rain hood things do. I've got a gadget that'll put rivets into stuff so with a few of those and a drawstring I should be able to eliminate stray light from the equation at least. Will post any further progress once I get there...

Sounds as whether you'll have a lot of homework to do. Let us know about your results and post some pics of your assembly, please.

Ben

[falconeye]

Let us know about your results and post some pics of your assembly, please.

I am actually most curious about what Nass is trying to achieve

BTW, here is the spectral curve you mentioned:

((c) Gerhard Dangl)

[darrenleow]

Some photos I took recently with welder's glass taped onto a step-up ring.

[Ben_Edict]

I am actually most curious about what Nass is trying to achieve

BTW, here is the spectral curve you mentioned:

((c) Gerhard Dangl)

Thanks for including the curve here. I am always a bit hesitant, when it comes to use third party material, prefer to simply provide the link for copyright reasons. But I am probably overly cautios.

Ben

[Ben_Edict]

Some photos I took recently with welder's glass taped onto a step-up ring.

Very nice images. I really like the mood und near monochrome tonality.

Ben