What the ERF?

[Roel]

To keep the heat off the etalon I'm using a second hand front ERF on my 70mm PST mod for about a year now, sold to me as a Baader D-ERF. The diameter is 95mm and the thickness is 10mm. Works great: when I put my hand in the focused sun image I can feel no temperature rise, not even when using a 90mm objective. The color is deep red. But strangly I can not find a Baader ERF on the internet that has the same dimensions, which gives me the impression it might be something else? They all appear to be 90mm, not 95mm: http://www.teleskop-express.de/shop/pro ... htung.html

I know a 100mm Lunt ERF is actually 105mm in diameter, is this also the case with Baader filters?

[Merlin66]

The original C-ERF from Baader were different...maybe you have one of those. Does it have a highly reflective front surface or just looks a dark red?

[Roel]

It looks just dark red. It does not have that blueish coating like the ERF in my link.

[Merlin66]

I'd lay a pound to a penny is one of the old Schott glass ERF, Still works well, but doesn't have the same IR cut-off (and bandwidth) as the current D-ERF versions.

[Roel]

Two pictures of my ERF mouted in a aluminum cell: http://www.astroforum.nl/showthread.php ... post408455

By Schott, do you mean an old Baader filter which uses Schott (type of glass) or is Schott a filter brand?

[Merlin66]

Can't see the images without logging in in Dutch...
The Schott is a type of glass ie RG610

[Roel]

Update: I have just contacted the seller and I already got a reply. He says he bought the filter in Huckelhoven and the guy who sold him the filter told him it was a kind of prototype by Baader before they started the production of their C-ERF's.

Working link: http://www.roelblog.nl/wp-content/uploa ... 7/mod3.jpg
Another picture of the filter mounted in a plactic pot for my future 90mm mod: http://www.roelblog.nl/wp-content/uploa ... wasERF.jpg

[DSobserver]

we can't open them..... :unsure:

As far as I know, visually the difference between C & D-ERF from baader is that second one is both side treated when first one only one. By treatment, I mean this redish/bluish surface.

So if in you case there is no treatment I'd say that it's something else.... :dry:

[Roel]

The filter does not have any bleuish coating on either side.

[swisswalter]

Hi Roel

It is certainly not a Baader D-ERF. It may be an early C-ERF, but does it matter? Just use additionally an UV/IR block filter when using it

[swisswalter]

Hi Vincent

thank you for your email. I can't answer. It always bumps back to mee. It seems as I'm on your black list