Herschel wedge - Upper limit on telescope size?

[iwatkins]

Hi All,

Recently got into solar in a big way. Have the PST and love that, and looking for more when funds allow.

But my first love is white light and am going to invest in a Baader Cool Ceramic Herschel Wedge for imaging.

Obviously, used carefully in a refractor, safe. But is there an upper limit to their use with regards to aperture? I cannot help thinking, the larger the telescope, the more energy the wedge has to dump?

I've had a trawl through Baader docs and no mention of a limit.

Initially will be used on a SW 80ED but looking to add a 150mm f8 refractor to my stable and use it on that.

All pointers and thoughts welcomed.

Cheers

Ian

[A McEwan]

I use a Herschel Wedge (the older Baader style) with my 6" f8 and get awesome results visually. I use the permanent ND3.0 filter and a 2" Baader Solar Continuum filter permanently installed and a single polarising filter to adjust the brightness for comfort level.

Haven't seen anything official or unofficial on maximum usable aperture though.

Ant

[iwatkins]

Thanks Ant.

Exactly how I'll use the wedge is as you describe. Baader wedge now ships with a few additional NDs to tune brightness.

Cheers

Ian

[A McEwan]

Yes, I have the additional filters as well, but prefer to fine tune using a variable polariser. The other ones are useful in other situations though.

Ant

[Merlin66]

The Herschel wedge has been successfully used on very large refractors >8" aperture.

No problems.

You need a collection of ND filters to be able to "tune" the intensity to best match your visual needs and the performance of your camera.

[iwatkins]

Thanks Ken (twice in two minutes).

Yep, Baader wedge on the way from Germany as we speak comes with four various NDs with one, the 3.0 prefitted, plus a Continuum filter. So for visual I can should be able to tune for comfortable brightness. But will look into a variable polariser if I need finer tuning as Ant suggests.

For imaging, I hope to be able to get some very fast shutter speeds, my DSLR can do 1/8000 and the DMK (if they ever finish making them and get it delivered) can do something like 1/10000.

My main concern was long term usage and build up of heat on the enclosed exhaust side of this wedge. But sounds as though that isn't really an issue.

Cheers

Ian

[Merlin66]

There's certainly no issue, short or long term with the residual heat build up!

The Baader "Cool" design is built to last a lifetime (and more!)

(My recent DIY Herschel wedge using a 30degree prism from Surplus Shed and a "heat deflector" was used on my 150/1200 ("Big Yin") continuously for a few days to see if there were any "issues" or problems - even that simplified arrangement worked 100%)

[RikM]

Does a Herschel wedge significantly beat a sheet of Baader film for detail resolved in white light?

[Merlin66]

IMHO, there's no better way of observing in white light! The clarity and quality is 100%.

The limitation however is that it can ONLY be used with simple achromatic/ APO objectives. (No secondary lens near the focus)

No good for reflectors or SCT's etc.

[iwatkins]

Thanks Ken, good to know on the heat build up.

Did you manage to get anymore of those prisms in the end?

Rik,

I've used film for years and been happy with it, both for visual and imaging. However, a month or so ago, a work colleague bought a Baader wedge so we did a side by side comparison. The difference isn't huge if I'm honest, wedge maybe 10% better? But it is what you get for that 10%. Granulation was much easier to see and certainly easier to image. Contrast overall is also improved. But when seeing settles it really then makes a huge difference, you can nearly feel the texture

Before this, because I hadn't tried a wedge, I thought the cost greatly outweighed any benefit, I was always happy with film. But now I have, I'm happy to have bought one.

When it arrives, I would be happy to meet up, have you take a look and see what you think if that would help? I know a few people in the past have said they couldn't see any difference between wedge and film, but it was clear as day to me.

Cheers

Ian

[nytecam]

... and a single polarising filter to adjust the brightness for comfort level. Haven't seen anything official or unofficial on maximum usable aperture though. Ant

I've used crossed polaroid filters as an infra-red transmitting filter [white landscapes etc] so whilst it's useful for visually dimming an over bright solar image it may not be trimming the IR component as assumed:eek:

[RikM]

Thanks for that Ian. I will take you up on that.

I have always been very happy with Baader film and when the colimation is good on my Newt I have been amazed at the detail you can see. I now have an ST80 and will be making a full aperture Baader film mask for it tomorrow (in the hope of using it at a public solar observing at Slimbridge on Sunday, but the weather doesn't look too hot!), I have always felt that I was only using the film until I decide if I like white light observing. If I do, then I will get the proper kit for it

If there is that much of an advantage, then I will go for a solar wedge when finances permit because it just seems a more 'permanent' tool for the job rather than a bit of fancy foil taped to some cardboard.

[A McEwan]

I've used crossed polaroid filters as an infra-red transmitting filter [white landscapes etc] so whilst it's useful for visually dimming an over bright solar image it may not be trimming the IR component as assumed:eek:

Is further IR filtering required? The ND3.0 and Baader Solar Continuum Filter are stacked after the prism and then the variable (single) polarising filter is eyepiece mounted.

Ant

[iwatkins]

Solar Continuum only has a narrow band pass at around 540nm so would have thought that was the IR taken care of?

Cheers

Ian

[hunterknox]

I've used crossed polaroid filters as an infra-red transmitting filter [white landscapes etc] so whilst it's useful for visually dimming an over bright solar image it may not be trimming the IR component as assumed:eek:

With a Herschel prism?

[Merlin]

Polaroid filters alone should never be used to look at the Sun! I have an APM Herschel prism, that gives nice sharp views of sunspots.

There wasn't an ND3 filter incorporated, so I fitted one, making sure it was well secured with a coil spring. With this arrangement I use the Continuum filter and a variable polariser to fine tune the brightness.

A test we can do with filters is to point the TV remote through them. If the remote is able to change channels through the filter/s, the filtering isn't enough.