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Herschel wedge configuration help


Victor Boesen

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I've been using my Lacerta wedge for quite a while now and enjoy it very much, however I'm not yet fully satisfied with the current configuration. Let me elaborate.

I have always had a 2" ND3.0 filter placed in a 2" to 1.25" adapter, and at one point also an OIII filter stacked behind it.

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This configuration works fine, also when I add my 1.25" continuum filter or a polarizing filter to the eyepiece. However, the problems arise when I use my 2X TeleVue barlow, which, due to its long nosepiece, will hit the ND3.0 filter, if not inserted carefully. This requires me to insert the barlow and eyepiece in the following configuration.

IMG_20220604_172937.thumb.jpg.f473f93c3276a679b284d25b40ceec13.jpg

What I have noticed though, is that, with my 18mm ortho (being the worst) there's a very annoying and bright glare from the continuum filter reflecting light to the barlow lens (I think??). With my 10mm it is not as bad but still enough to annoy me. So what then.... Today I tried removing the 2" ND3.0 filter and replace it with a 1.25" one at the nosepiece of the barlow, leading me to the following configuration.

IMG_20220604_173031.thumb.jpg.e0bcceaf01e558ed9262dfd720936de9.jpg

To my surprise this eliminated the glare, and the view was nice and sharp. However, say I don't want to use the barlow, that would lead to a lot of screwing/unscrewing of the ND filter. Another thing that worries me about this configuration is that the 1.25" filter is almost touching the prism, and I worry that the filter can not withstand the heat, despite only receiving 5% of the sunlight?

IMG_20220604_173237.thumb.jpg.cb589644efdada5056c99bdde0ae904b.jpg

So my current thoughts are the following:

  • Getting a 2" continuum filter and stacking it with the ND3.0 filter
    • Fixes the glare, no screwing/unscrewing when switching eyepieces, barlow and etc.
    • Still requires me to insert the barlow half way, leads me to next point
  • Switch out the barlow with a focal extender (Probably ES or TV)
    • Shorter nosepiece means it would hit the mounted 2" filters
    • Costs money😅

I should probably also add that I would ideally also like to use a binoviewer for white light, in which case I would need a glass path corrector somewhere (which then could end up with a nosepiece the same length as my TV barlow).

To sum up, I guess my final question is, have any of you solved a problem similar to this and how? Or do you have any ideas/suggestions to work around the problem of keeping the optical path short, without requiring me to unscrew/screw the filters from different eyepieces/barlows each time I switch?
I hope someone can figure out a smarter way around this than I'm currently able to😅

Kind regards, Victor

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I use the following setup.

The 2” ND3 and polarising filters are attached to the bottom of the rotator. Then the 1.25” continuum filter is fitted to the bottom of the 1.25” to T2 eyepiece holder using a ZWO 1.25” filter to T2 insert that screws into the bottom of the eyepiece holder.

Simple but works extremely well.

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Edited by johninderby
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10 minutes ago, johninderby said:

Correction

The nosepiece would hit the filter adaptor not the surface of the filter and is about 30 to 31mm distance.

Thanks again John:thumbright: Yes, I'm afraid that would not be of any difference than what I'm currently able to achieve :icon_scratch: My current best solution would be to switch the barlow out for a focal extender of some sort, which will have a shorter nosepiece, and then hopefully be able to mount the continuum filter on the end of that. Otherwise a 2" continuum filter could also work well, but would, in my opinion, be a lot of money spent😅 Will have to consider this problem a little further. After all I can still use my wedge while thinking :)

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