Solar observing/imaging with small refractor. Which filter?

[Ken Mitchell]

Hi,

I've been thinking to get started as a beginner into solar observing and imaging (with imaging as a primary).

I currently have a 72mm refractor and ZWO 120 and dslr for imaging. 

Searching the internet on what filters to use I find mixed reviews when choosing glass or film/foil. 

Option are Thousand Oaks glass filter or similar

https://www.astroshop.eu/mounted-foil-filters/thousand-oaks-solarlite-solar-filter-80mm/p,58263

or

Baader sun filter/foil

https://www.astroshop.eu/filter-foils-solar-glasses/baader-sun-filter-foil-a4-210x297mm/p,2718#tab_bar_0_select

This is another one from Baader but no idea what the difference is with the other one.

https://www.astroshop.eu/filter-foils-solar-glasses/baader-astrosolar-photo-film-od-3-8/p,53792#tab_bar_0_select

(I have no issue with making a holder for the foil to fit the scope)

 

Which type will give better details? When using logic my guess would be foil as it is much thinner than glass so there is less loss in light and less affected by aberrations. Is this true?

In terms of durability I would guess glass filter as foil can easily be punctured, but than again if you drop the glass filter there won't be much left of it.

I would like to stay for the moment in that price range as it is just a subject of exploration and not sure if I'll continue this path and buy more dedicated solar imaging equipment.

What are your experiences in this? Suggestions?

 

Thank you!

Ken

 

[Cornelius Varley]

The two Baader films have different purposes. The first version (ND5.0) is suitable for both observing or imaging, the other (ND3.8) permits a greater amount of light through it and should only be using for imaging.

[johninderby]

Yes the Baader film will give you the best solar filter images. The problem with cheap glass filters is that they aren’t optically flat unlike the Baader film. Optically flat glass is VERY expensive to make and would add hundreds to the cost of even a small filter.

There are two types of the Baader film. The 3.8 for photography only and the 5.0 for visual. Never ever use the 3.8 for visual. Not safe.

The film is surprisingly tough and can take a knock that would shatter a glass filter.

Better than any of the solar filters is a solar wedge though. The TS one is not very expensive but really good and comes with the filters you have to buy at extra cost for most wedges.

https://www.astroshop.eu/eyepiece-side-filters/ts-optics-solar-prism-with-polarizing-and-narrowband-filter-1-25-/p,53753

Edited August 28, 2019 by johninderby

[Bizibilder]

I would advise you to use the Baader foil of ND5.0.  This is quite safe for both visual and photography.  The ND 3.8 foil is ONLY suitable for photography and NOT for direct visual observations.  You can make a filter holder quite easily from card and strong tape.  One sheet of A4 size should make at least two (possibly three or four if you are careful) filters.

I keep my own filter in a plastic box with a lid.  It is about five years old now and still in excellent condition - I am always careful not to touch the foil and to check the foil is in good condition before EVERY use.

[Ken Mitchell]

Thanks all. So I'll probably give the Baader ND5 a try.

Does ND also stands for Neutral Density as in photography filters? Are they made up of different materials? I have several ND photographic filters up to ND1000. I guess these won't be safe to use for solar?

Another question, Would there be any difference in revealing certain details or better different wavelengths when using a Baader filter+ Baader nebula Ha 7nm filter. I know these aren't made for solar but was just curious with this combo.

Ken

[Bizibilder]

They are most certainly NOT the same as standard photographic filters.

These foil filters are used for "white light" solar observing and photography - ie they transmit all wavelengths in the visible spectrum.  An Ha 7nm filter is NOT the same as a proper Ha solar telescope.  Unfortunately a true Ha telescope (or device like the DayStar Quark solar "eyepiece") is a very expensive piece of kit!

One safe alternative to the foil filter is the Herschel wedge diagonal - but again this is quite an expensive alternative.

(Just an afterthought - there are "Solar Filters" that can be screwed into a normal eyepiece.  These used to be sold with cheap telescopes.  They are EXTREMELY dangerous!!  They will shatter in the heat from the Sun and, should you be looking through the telescope at the time you will be blinded. Don't even think of using one!!)

[Ken Mitchell]

Thanks Bizibilder! Much appreciated! The Ha filter was just a thought. If I would go through with solar imaging I'd probably get something like this for my Nikon

https://www.astroshop.es/filtro-en-el-lado-del-ocular/daystar-filtro-solar-camera-quark-h-alpha-protuberancias-para-nikon/p,52376

So the Baader 5.0 is safe to use observing and imaging and won't burn the sensor or eyes, right?

Do you happen to have any examples of how imaging would look like with these kind of foils?

Ken

 

[Ken Mitchell]

Just finished the filter and took some images/videos.

Mounted filter. Might give it a paintjob in the future.

 

and the image taken with it. The image is a stack from a short video clip using Autostakkert. It's the first time I use this program so not sure I did everything correct.

 

If I use my guiding camera zwo 120, would I get better results?

 

Ken

 

[Davey-T]

Good job on the filter Ken, wouldn't buy a camera Quark, an "ordinary" one will be fine and much more flexible, you could use your ZWO120 no problem, you may get a higher frame rate but not sure if you'll get a full disc depending on your scope focal length.

Dave

[Ken Mitchell]

11 minutes ago, Davey-T said:

Good job on the filter Ken, wouldn't buy a camera Quark, an "ordinary" one will be fine and much more flexible, you could use your ZWO120 no problem, you may get a higher frame rate but not sure if you'll get a full disc depending on your scope focal length.

Dave

Thanks Dave,

Would there be a difference in using a modded dslr vs stock dslr for solar? 

Ken

[Davey-T]

2 hours ago, Ken Mitchell said:

Thanks Dave,

Would there be a difference in using a modded dslr vs stock dslr for solar? 

Ken

Not for white light imaging with the Baader film filter.

Dave