Wratten W47 filter

[Merlin66]

Any ideas were to find a Wratten #47 Violet filter????

[JA]

Hi Ken,

At one stage I had a sample of various Kodak Gel Filters I don't recall if they included any blues and not sure whether I can find them, but I'll have a look.

If it's for a trial, I could loan you a HOYA 80B 52mm screw in filter. Maximum transmission is around 85% at 400 nm (more than the Wratten47), but it doesn't cut off as quickly as the W47, tapering down to about ~20% at 650 nm. Used with a suitable UV/IR filter with enough UV response for you, it might be OK. Or you could use a Neutral density filter to reduce transmission across the board to get it to "look" a little more like the Wratten 47 filter's transmission curve.

Hoya 80B ....
284145

Some other possibilities ....
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Another possibility would be to use only the Blue channel from a colour camera as the transmission for the Blue is fairly close to the Wratten 47. Take for example the ZWO183mc response....
284148


Best
JA

[astro744]

What format, 1.25”, 2”, square sheet or camera lens (size)?

[Merlin66]

Ideally a 2” (48mm) or a 1.25”
I’m looking for something to compliment the Astronomik UV-IR for better blocking around 393nm.
A couple of the HOYA curves look interesting.

[Stonius]

Agena Astro Have the Lumicon ones. Cheap too



https://agenaastro.com/lumicon-2-47-violet-filter-lf2055.html


https://agenaastro.com/lumicon-1-25-47-violet-filter-lf1055.html

[Merlin66]

Markus,
Looks good....but the US$40 postage is a killer!!!


Also - can't find any HOYA E-B390 or B370 filters anywhere......

[Stonius]

Yeah, but they're quick. A few days. Normal post is a Killer from the US. I've been waiting for something to arrive via normal USPS for over a month now.

[astro744]

I found this and the postage with Royal Mail is low. However either the photo of the filter is wrong or the filter is too light. W47 is very dark with only 3% transmission.

https://www.firstlightoptics.com/visual-oberving-rgb-filter-sets/astro-essentials-125-wratten-47-violet-filter.html

Also found https://optcorp.com/products/tpo-violet-color-filter-case-f47

Not sure of postage. You’ll have to fill in your details. If the postage is more than the filter just reverse the prices. I.e. a $40 filter with $12 postage. Sounds better that way.

Check with Telescope and Astronomy in South Aus. I bought some filters off the guy a couple of years ago off a Christmas clearance mailing list he had. They were all made in Japan Meade models. He may have some left.

[ausastronomer]

Hi Ken,

I actually thought I had a #47 Antares 1.25" filter which I would have sold to you for the postage cost, but ALAS I can't find it. I managed to find 7 x 1.25" Antares Colour Filters and 11 x 2"(48mm) Hoya Filters, but not a #47 amongst them. Every other colour known to man, but no #47.

The problem is digital photography has changed colour filter needs dramatically, to the extent that Hoya don't make that many colour filters and they don't make any with 48mm threads to fit 2" astronomy accessories. They no longer make a #47 in any size.

A couple of possible options.

1) Call Lee Andrews at Andrews Comms. He used to sell a whole range of 1.25" GSO filters. GSO definitely make, or used to make a 1.25" #47.

2) If you want to go with 2" format,which is possbly a better option, have a look at the curves on the Hoya FL-W filter (https://crkphotoimaging.com.au/products/00zhyaflwfl/hoya-fl-w-filter). I think this looks reasonably close to what you are after. You won't be able to get it in 48mm, but you can get it in 49mm and then use a 49mm to 48mm step down ring, which should cost about $10.

Cheers
John B

[ausastronomer]

Lee Andrews has a 1.25" #47 filter on his website for $15

http://www.andrewscom.com.au/optical-telescopes

Follow the link then click on "General Accessories". It's a good way down the page.

It won't be the same quality as a 2" Hoya filter, but it might be good enough for what you need.

Cheers,
John B

[Merlin66]

Contacted Lee….no more in stock.
I’ve gone for one from Amazon, 2” for $55 delivered.

[Don Pensack]

Here is a spectrum of a typical #47 filter:
https://www.cloudynights.com/topic/604995-imaging-with-an-adc/?p=8343497
Should be excellent as an inexpensive CaK filter for imaging.

[Merlin66]

Don,
Thanks. I’m familiar with the W47 transmission curve and the NIR leakage.
It’s currently used by a couple of guys with their spectroheliographs when working in CaK.
Our issue is a parasitic light “curtain” on the reconstruction image which may be caused by processing…..we don’t know.

[Merlin66]

The FL-W filter turned out not to be as successful as I hoped.
I’ve put it up for sale.
Ken

[Merlin66]

Here's a typical curve for the W47 showing the NIR leak.