DIY Herschel Wedge -Take II

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DIY Herschel Wedge -Take II

Post by Merlin66 »

I've ordered the 60mm x 60mm 30 degree F2 prism (#10712) from Surplus Shed
http://www.surplusshed.com/pages/item/l10712.html
Hopefully this will be successful as a Herschel wedge. The 60mm size will still fit the Meade 2" diagonal "base".
Keep you posted.
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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

The flint prism arrived today.
It's still in its original 1950's packaging....
A very nice looking piece of glass. Hopefully the surface accuracy will be good enough for a Herschel solar wedge...if not, I'm 100% certain it would make an excellent object prism for spectroscopy.
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Re: DIY Herschel Wedge -Take II

Post by swisswalter »

Hi Ken

great buy for that little money. Always worth to have a try. I'm looking forward to the first WL Hires shots ;-)

good luck


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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

Did a "dry fit-up" today with the wedge. It fits nicely between the existing mirror mounting screws, so a couple of clamp straps can still be fitted. I'll post a couple of photos later.


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Re: DIY Herschel Wedge -Take II

Post by swisswalter »

Hi Ken

thank's for the update. Good luck and don't forget to take and publish pics ;-)


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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

Still trying to source suitable aluminium strips for the clamps, but these images show the size and neat fit of the wedge prism.
I have a 50 micron artificial star, so I'll do some star tests to evaluate the surface quality..it may be some time before we see the sun from Belgium!!!







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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

Well I set up my trusty 4" Genesis with the 50 micron artificial star. Checked that the "star images" were prefect (as usual!) then swapped over to the wedge prism "diagonal"
I'm pleasantly surprised!
The images under a magnification of x125 (using the nagler)looked almost perfect - inside and outside focus..under careful examination maybe just the slightest touch of astigmatism, but not worth worrying about.
Looks like this prism has all the right characteristics of success...
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Re: DIY Herschel Wedge -Take II

Post by marktownley »

Great stuff Ken! Glad this is working well :)

What are you after aluminuim wise? Maybe something I can help you with...


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Re: DIY Herschel Wedge -Take II

Post by swisswalter »

Hi Ken

thank you for the update and the pics. Looks very promissing. Please keep us updated again


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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

mark,
Thanks for the offer, but it may not be cost effective getting it to Belgium. An A4 sized sheet of 0.5 or 0.7mm thick aluminium would do the job.
BTW I should also have said...there was no ghosting of the image.


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Re: DIY Herschel Wedge -Take II

Post by marktownley »

mark,
Thanks for the offer, but it may not be cost effective getting it to Belgium. An A4 sized sheet of 0.5 or 0.7mm thick aluminium would do the job.
BTW I should also have said...there was no ghosting of the image.

I could do it in steel, but not aluminium. Not too bothered about the postage, it wouldn't be huge... if steel is any use let me know and i'll sort it.


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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

11:30am Managed to get a clear bit of sky...
Setup the prism wedge +ND3+Continuum on the ED80, only visual...
Using the 7mm TMB....
And the answer is???????
A resounding SUCCESS!!
The image is perfect!

A lot of surface granulation easily visible and many bright plage areas..The detail in the umbra/ penumbra of #1408 is surprising..even #1409 was easy...
The new AR 1410 shows tremendous activity and #1402 still seems to be very active.
All in all I'm very impressed!
Looks like this is a perfect solution to a white light solar wedge. I'd buy a SS prism while they still have stocks.


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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

Too late :( :(
I see there's no stock available of the flint prism at Surplus Shed. Hope you managed to get one while it lasted.


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Re: DIY Herschel Wedge -Take II

Post by swisswalter »

Hi Ken

I'm happy for you having success. Now please don't let us die dumb, we need very badly pics of your results ;-)


Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

if the "good" weather continues I'll get some images...
(The problem seems now to be that the prism is no longer available...bumma)


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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

OK, just a quick wrap up.
Finally got some clear skies (and clear of trees!!) to check out the flint prism Herschel wedge.
Mounted on a Vixen 80/910, ND3.8+Continuum with a TMB 7mm (x130)-very unsteady seeing, but...
Surface granulation visible, detail in and around 11438 and 11437 and a bright plage area where 11435 is dissappearing.
All in all I'd definately rate it as a success.
It's just unfortunate that Surplus Shed didn't have any more stock. Watch for a similar prism in the future. It works well.


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Re: DIY Herschel Wedge -Take II

Post by colinsk »

One can polish their own prism...


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Re: DIY Herschel Wedge -Take II

Post by Spectral Joe »

You have no idea how happy I am to see this thread, and to see it go on enfettered. I am a big Herschel wedge fan (I still have the one I bought unmounted from Edmund for $3.50 in 1968), and seeing a DIY version gives me hope (and a little tingle in my ATM nerve). Too bad they're out for now, with luck they'll get more.


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Re: DIY Herschel Wedge -Take II

Post by MapleRidge »

Hi Ken...

Glad to see the DIY wedge is working well for you. Congratulations on putting the project together!

Brian


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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

Guys,
Did any of the forum members manage to buy one of these F2 flint wedges from Surplus Shed???
If so, could they contact me.


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Re: DIY Herschel Wedge -Take II

Post by Pablito »



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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

Thanks guys!
The last time I checked they were out of stock.....
I want to use one as an objective prism on my ED80 for wide field survey spectroscopy....


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Re: DIY Herschel Wedge -Take II

Post by Spectral Joe »

Pablito's link shows it in stock but I can't find it in the site search. This one: http://www.surplusshed.com/pages/item/l2102d.html might work if you strip the paint and aluminum off.


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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

Joe,
It's the F2 flint I needed for the spectroscopy....let's hope there are some left...somewhere...


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Re: DIY Herschel Wedge -Take II

Post by Spectral Joe »

OK, that makes sense. Maybe they'll get some more, you never know. I got to visit the "Shed" last year when I was driving through Pennsylvania, it's quite a place.


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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

Surplus Shed have just confirmed they're out of stock!
Did anyone buy this prism???

SS sounds like a great place to visit. Jan/ Fred have looked after me for many years.
BTW does anyone know of a cheap source of adjustable slits? I'm always in need of some for spectroscopes.....


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Re: DIY Herschel Wedge -Take II

Post by colinsk »

Thorlabs has 100 tpi taps and screws for making fine adjustments. I use them for spatial filters. They would make great adjusters for slits.


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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

Thanks for that, Colin.
The hard part seems to be getting good quality high reflective slit plates.
Lennox Laser etc want an arm and two legs for their plates...Shelyak for their chromed glass version are asking 220 euro!!!


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Re: DIY Herschel Wedge -Take II

Post by Pablito »

Ken, does it matter that it is F2 flint glass? Can I use other glass like BK7?


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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

Pablito,
No the glass is not as critical as the quality of the surface finish. If you can find a good BK7 prism it would do the job very well.


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Re: DIY Herschel Wedge -Take II

Post by Pablito »

Ok, thanks :)


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Re: DIY Herschel Wedge -Take II

Post by thakursam »

Thanks for the link Ken,

Got one on SS, waiting for shipping confirmation.

Do you have any photos taken through this DIY Wedge ?

Regards,
Sameer


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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

Sameer,
Which prism did you get?
No images, sorry. I was using it for visual with great results then converted it to an objective prism for the spectroscope when I was lucky enough to "aquire" a Baader Herschel wedge.


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Re: DIY Herschel Wedge -Take II

Post by thakursam »

Got the exact same one you posted link : http://www.surplusshed.com/pages/item/l10712.html "SPECIAL F2 FLINT GLASS 30/75/75 DEGREE PRISM" :D

After i ordered it the status changed to "Sorry - this item is currently unavailable" !!!


Bratislav

Re: DIY Herschel Wedge -Take II

Post by Bratislav »

It looks like lot of those items are single quantities at SurplusShed. I bought a similar prism for my own DIY wedge, and it also turns out it was the last one!
I'll post some photos of my DIY effort later ...


Bratislav

Re: DIY Herschel Wedge -Take II

Post by Bratislav »

I also started with a commercial star diagonal and did some heavy mods. My prism was round, so I had to machine proper seating (which in turn was good as it is held very secure).
I've used both photographic ND3 and a polarising filter (just one works well because light gets heavily polarised on prism reflection anyway). ND3 sits at the bottom of the 2" adapter, polariser is at the bottom of 1-1/4" adapter, which can be rotated.
Front contains a stop to reduce glare and increase contrast. At the back there is a chunky heatsink. No fans seem necessary so far.











thakursam

Re: DIY Herschel Wedge -Take II

Post by thakursam »

Thanks Wonderful :thumbsup:

TFS


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Re: DIY Herschel Wedge -Take II

Post by swisswalter »

Hi Bratislav

that is a wonderful mod


Only stardust in the wind, some fine and some less fine scopes, filters and adapters as well. Switzerland 47 N, 9 E, in the heart of EUROPE :)

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Re: DIY Herschel Wedge -Take II

Post by marktownley »

Top mod! Great stuff! 8)


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Bratislav

Re: DIY Herschel Wedge -Take II

Post by Bratislav »

Still trying to source suitable aluminium strips for the clamps, but these images show the size and neat fit of the wedge prism.


Ken,

it may sound crude, but I would simply use four dabs of silicon on far corners of the prism to keep it in place. It will never fall off! Just make sure you rough the aluminium where silicon will set (I would even drill small shallow holes to increase grab area). If you ever need to remove it, thin wire or even dental floss will neatly slice it off.
If any doubts, silicon was used to hold 8m mirror at Roger Angel Lab during figuring and testing....


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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

Bratislav,
It's a well known fact in Australia, that 99.9% of everything can be fixed with silcon, gaffa tape or fencing wire....just ask my wife ;-)
(I did end up using gaffa tape.. I just wish there were more of those F2 prism available - I really need one for an objective prism spectroscope...
BTW the etalon in the SM40 is held in place with dabs of RTV!!!)


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Re: DIY Herschel Wedge -Take II

Post by marktownley »

There's silicon inside the lunt wedge (i'm fairly certain!) to fix the prism in place - i'm with you on this one Ken, i'd include expanding spray foam into my repertoire of fix-it material too :P


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Re: DIY Herschel Wedge -Take II

Post by thakursam »

The prism i ordered was not in stock :( SS mailed me saying it was mistake !!!

However i ordered another from ebay, which is bit smaller but i hope it will work for 1.25"

http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0887229647


Bratislav

Re: DIY Herschel Wedge -Take II

Post by Bratislav »


It's a well known fact in Australia, that 99.9% of everything can be fixed with silcon, gaffa tape or fencing wire....just ask my wife ;-)


:) :) :)
Need I say that my prism, ND3 filter and even glare stop are all held by RTV ? ;)
One thing I can definitely add, there is a noticeable jump in contrast once the prism is totally enclosed (and I used plenty of flocking material in there to suppress last bit of unwanted reflection, I even blackened the edges of my prism with permanent black marker). The back plate is etched matt black, so even Sun's in-focus image is quite dim. Every bit helps, and result is staggeringly obvious - direct comparison between the wedge and standard Baader solar film is literally night and day. In Baader there is quite obvious halo everywhere, with the wedge the contrast between Sun's edge and the blackness around it has to be seen to be believed. And the color is 'right' - warm yellow to neutral white (depending on polariser angle - my prism is BBAR coated), which is very pleasing visually.


colinsk

Re: DIY Herschel Wedge -Take II

Post by colinsk »

Bratislav,
It's a well known fact in Australia, that 99.9% of everything can be fixed with silcon, gaffa tape or fencing wire....just ask my wife ;-)
(I did end up using gaffa tape.. I just wish there were more of those F2 prism available - I really need one for an objective prism spectroscope...
BTW the etalon in the SM40 is held in place with dabs of RTV!!!)

You forgot Blu tac!


colinsk

Re: DIY Herschel Wedge -Take II

Post by colinsk »

So if we trace the ray a Hershel wedge I believe that we find that a 15 deg prism is optimal and easy to grind from a 1/2" thick blank.


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Re: DIY Herschel Wedge -Take II

Post by alex »

Hi there!

Any ideas about this one?Would it be a nice candidate for a wedge?

Cheers
Alex


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Re: DIY Herschel Wedge -Take II

Post by swisswalter »

Hi Alex

I can't see a pic nor a link :oops:


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Re: DIY Herschel Wedge -Take II

Post by uplooker »

I know this thread is a bit of a zombie but it appears that the F2 Flint glass prisms are available again:-

http://www.surplusshed.com/detail.cfm?I ... ory=Prisms

Ian


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Re: DIY Herschel Wedge -Take II

Post by Merlin66 »

Ian,
You may have to refresh your Surplus Shed page....nothing shows on the current listing.....


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