Herschel Wedge - what else is needed?

[JamieW]

Well, after seeing Montana's latest pictures (wow) the lure of a Herschel Wedge has become too much to resist. So I was wondering what else would be needed for both visual and imaging sessions?

I would be using a TAL100RS and either a QHY5 or my eyes. Any pointers would be much appreciated.

Thanks in advance, Jamie.

@Edited to add that it's the safety aspect that I'd like to know more about.

[iwatkins]

Hi Jamie,

I have the Baader Cool-Ceramic Herschel Wedge, photographic version. Basically the visual version plus more ND filters to allow fine tuning for both visual and imaging.

Basic rule, a wedge reflects to the eyepiece around 5% of the light coming into your scope, the rest passes out of the back of the prism. So you need an ND 3.0 filter to reduce the light levels to a level that's comfortable and safe. So for visual, keep the ND 3.0 in the train at all times and you are then safe.

For imaging, you can go to the ND 1.8, 0.9 or 0.6, or combinations of to get a much brighter image to allow faster shutter speeds to give a better chance of catching good seeing. I can get DSLR shutter speeds up around 1/6000 sec. And DMK41 speeds around the 1/5000 - 1/10000 sec.

If you ensure you always check whether you have the ND 3.0 in the train before putting an EP in, you'll stay safe.

If you plan to image with a DSLR, do note the image path is quite long, so you may not have enough back focus. You'll also need the Baader T ring adaptor.

If you plan to image with a C mount camera, e.g. DMK, you'll still need the T ring adaptor plus Baaders T to C adaptor, which is very neat and has a built in IR cut filter.

Cheers

Ian

[JamieW]

Brilliant, thanks Ian.

[Merlin66]

Ian said it all!

[Montana]

I agree with Ian, apart from what is the T ring adapter to c for the DMK? I don't have one? I just slot my DMK into a 1.25" hole left by the 2" to 1.25" converter.

You may also wish to use a UV/IR cut filter depending on how good your refractor is.

Alexandra

[iwatkins]

Hi Alexandra,

Hey, using a 1.25" nose piece in the top of the wedge works too

But I have a borderline back focus issue on the 150/1200 so I needed a filter stack holder, C mount and an IR filter *and* I needed it short. As I was getting the T ring adaptor anyway for DSLR usage, was a no brainer to get the Baader T to C adaptor. You get IR cut and approx. 19mm off required back focus.

I'm also a sucker for having my imaging train screwed together, rather than push fit. I very nearly lost a DSLR to a push fit nose piece a while ago, hence my fear.

Anyway, it's not necessary, but it is a nice to have.

Cheers

Ian

[ampleamp]

Apologies to Jamie for jumping on his thread, but this may be relevent to him(?) - i was going to post a question on focusing with a wedge, in that I can't achieve focus with a wedge and my Meade 80 APO.

Various searches suggest that I need to get rid of the 2" clickstop holder and replace it with a combo T2-27 and a T2-08 adapter; this will then use a 1.25 clickstop.

Ian, are you suggesting that if imaging, I could simply dispense with this T2-27/T2-08 combo and just remove the 2" clickstop and screw my DMK straight onto the T thread using a C to T adapter?

thanks

Alistair

[Merlin66]

Alistair,

Yes, that's basically what I do with the DMK.

[ampleamp]

Good stuff. I am pretty sure I have a C/T adapter somewhere so will give it a try today. Thanks Merlin.

[JamieW]

Apologies to Jamie for jumping on his thread, but this may be relevent to him(?)

I am indeed a male of the species, and this thread has been really helpful. Thanks all.

[iwatkins]

You may find this diagram useful of all the bits you can use, its a PDF document: http://www.alpineastro.com/Solar_Observation/Ceramic_System_Chart.pdf

Cheers

Ian

[JamieW]

Ian, you're a star.