SolarChat!

My name is Alex and I'm new in this Wonderful Forum I live in the Mugello Valley, near the Appennini north of Florence, Italy, I love astronomy since I was eight year old.
I'm going to make my first Pst Mod, stage 1 , i'm planning to add a 70 or 80mm f10 acro WITHOUT FRONTAL ERF to the black box from a type II PST blue objective internal erf, and my question is:
Can I use my 1.25" Astronomik UV-IR block filter as additional internal ERF?
This setup: 80mm or less acro obj -Astronomik filter-Pst black box is safe enough for the life of my eyeballs and for etalon and internal Pst filters?
Thanks

Hi Alex, welcome to the forum!

Using the filter above will be better than using nothing, but I think you should be using something that offers a bit more protection. A 2" 7nm/35nm Ha filter would be much better.

Mark

Thank you for reply Mark!
Do you think that the default cofiguration of PST with anything between the achromat and the black box isn't enough safe? I'm confused... i'm planning to change the 40mm achro with a 70mm achro (both f10) putting and additional filter that cut the IR, about filtering nothing less than original setup.

Ah, ok.. I've read your other reply about the heat issue that change the tuning or etalon. Now all is clear, I need a full aperture Erf :-D

Hello Vicchio

I suggest you read this post (in Italian), with many apologies to all those who do not understand Italian language.

http://www.binomania.it/phpBB3/viewtopi ... 9&start=10

In this post I recommend the use in a small telescopes two photographic filters like ERF (RG630 + IR Cut, like B + W 091 + IR Cut), with a considerable saving of money. Contrary to superficial objections that I received after writing the post, the good quality photographic filters (such as the B + W) have a good enough optical quality to not degrade the image visibly. I have done many checks on twenty commercial photographic filters in my lab (universitary level) and quality of these filters (B + W, Hoya, Kenko) is normally lambda / 2, with exceptions lambda / 4 and lambda / 1.
In a small telescope, there is no big difference between photographic B + W filters and the filters to Baader astronomy (such as optical quality), so my solution is good. The best quality ERF Baader (lambda / 10) is not used with a small refractor and the picture you get with my solution is equal to that obtained with the ERF Baader. This is because I noticed that the weakest link in the optical chain of a small solar telescope (50-70 mm in diameter) is the BF (blocking Filter). For this reason, as already written, the perfect quality of an ERF Baader (lambda / 10) in a small telescope is not exploited and you get the same thing using as ERF, in front of the lens, two good filters such as those recommended by me or a B + W 091 front of the lens and an IR cut filter before the BF.

IMHO the easiest and best "sub-diameter" ERF is to add a Baader 35nm Ha CCD filter element.
Either the 2" (preferred) or at least the 1.25" version.
They do the job very well.

Hello Merlin66

Yes, the use of a Baader H-alpha 35nm as ERF is a good solution, more or less like the others on this chart attached.
The Baader H-alpha filters have quality Lambda/2 as the B + W.
I have tested (in may samples) that the standard Baader filters have quality lambda/2 as photographic filters (the quality Lambda/4 is that of the special filters Baader "Optically Polished", like my Baader Neodymium Moon & Skyglow Filter "Optically Polished").

Please note prices:

Baader 35 nm H-alpha 2" : 145 euros
Baader 35 nm H alpha 1 "1/4: 75 euros
B+W 091 2": 30 euros (new), also 10 euros (second hand, but new)

So if the price is an important element (in other words, if one has no money), the solution which I have suggested is not a bad solution.
Obviously, if one already has a Baader filter H-alpha 35 nn 2 "and is of sufficient diameter to its use, can use this with satisfaction without spending any more money (but I recommend, for safety, to add, in any case, also a filter IR Cut ... It does not hurt ).

I also own a Baader D-ERF 110 mm (475 euros), but I also bought for 12 euros (12 euros vs 475 euros), on the internet, a filter B+W 091 NEW 114 mm in diameter (!).

I tested the two filters for a long time with a Tal 100 mm telescope there is not difference in the vision of the sun images. My Baader D-ERF is correct lambda/10 (I checked this in the lab). My B+W 091 114 mm diameter filter is correct lambda/2 in 75% of the diameter (lambda/1 in the whole diameter).
Evidently, in my optical chain (Tal 100, etalon Lunt 60mm and BF Omega Optical), the great quality of the Baader D-ERF it is not exploited.

What I wanted to say ((that is also my philosophy... ) is that if one has money can buy the best. If one has little money can find solutions that also work with little money, sometimes with a small loss in quality, sometimes with no drop in quality.

This is my experience.

Thank you for reply Antonello :-D I've read all your posts, here and in the others forum, I appreciate very much your tests about photografic filters, too bad it's too late for saving my money because after a week without answer I've bought a Baader Erf filter...

Vicchio wrote:Thank you for reply Antonello :-D I've read all your posts, here and in the others forum, I appreciate very much your tests about photografic filters, too bad it's too late for saving my money because after a week without answer I've bought a Baader Erf filter...

The ERF Baader is a excellent filter, with a big optical correction and worth the money. This filter is realized with two interferential treatments, one for red and one for IR-Cut. Other filters (Beloptik, Lunt, my solution with B+W 091 plus IR-cut.), that I prefer, are made with a RG630 filter (type B + W 091) for red and a dichroic treatment as IR-Cut. I prefer the second solution because I use and prefer, as Blocking Filers, my various BF Omega Optical.
The ERF Baader filter is excellent with BF commercial Lunt, Coronado, etc.
The ERF with RG 630 are excellent with all the BF (including my Omega Optical who do not like the ERF Baader ...).

Enjoy your great ERF Baader ... your viewing quality will be at the highest level.

Really seems to be a nice piece of glass ;-) I'm going to assembly all the pieces i've collected to do my stage 1 mod, i write about it on the italian Astrofili forum too.

Interesting info, thanks!

Hi Mark, nice to meet you.
Sorry to hijack this post, but may I ask you, in you expert opinion, what would be the max aperture one can use on a f/10 OTA when using a Baader H-alfa 35nm 2" filter as ERF behind the objective?
Let's say you have a 10mm diameter OTA, would such a filter (with only 3mm glass thickness) sustain the heat without breaking, considering the concentration of light behind the objective?
Thanks a lot in advance.

Cisco

Cisco,
Welcome on board!
I use the 2" Baader 35nm filter on various solar scopes. It works well on a 100mm f11 PST mod.
I usually recommend that in the reduced ERF design it should be > 50% of the effective aperture, but I know of many set-ups where the ERF is smaller.