SolarChat!

This is what you need https://beloptik.de/en/itf-replacement-filter/

I had a look at that already and also been reading 'a lot' about these 'trap' filters - trap in the sense Astronomy sellers 'cartel' try always to push you buying more than you really need.

That above was my input in general with filters and prices and - do I really need that? Type of thing!

About this filter, maybe just taking it out and get a Baader 35nm RED CCD and fit it on the front as some people do - also Merlin66 mentioned it.

It will be even better being on the front safe-guarding the whole optics and re-usable if one buys a Quark and fit it before the Diagonal [if used]!

I am getting quite a culture here now!

Hi M,

I would not be too disregarding and suspicious - I doubt there are astronomy "cartels" trying to push more than you need when it comes to solar filters and safety. Indeed, my experience has been that the filter makers and suppliers have at times overestimated the blocking ability of their filters, and additional filtering is needed for filter longevity and/or safety.

Here's a slide from my powerpoint presentation on solar filters related to safety:


Note that the Sun has considerable output in the IR. Most of the typical filters for blocking IR only block IR A - there is little IR blocking beyond 1400 nm, even though the Sun can put out significant IR to IR B and even beyond. The amount of IR reaching your eye is completely dependent on aperture (total irradiance of 1.05 mW per mm^2), and the telescopes f ratio, which concentrates this output to the focus and can multiply its intensity greatly - for example, a magnifying glass collects only ~ 5 W, but this concentrated near focus, as occurs near your eye with a telescope, is enough to ignite paper and burn wood.


IR A will penetrate the eye all the way to the retina, IR B will penetrate to the lens (causing cataracts and corneal keratitis long-term), and IR C will affect only the cornea. So I would recommend IR blocking out to IR B (2500 nm +), and for this (in lue of an ITF) the BelOptik ITF replacement filter or the UV/IR on KG3 in conjunction with the red 35 nm H alpha filter would be ideal.

It's your eye(s) so do as you want, and know that opthamologist and eye surgeons will always appreciate the business if you choose poorly... but as with most things a little prevention is worth a bunch of cure.

Thank you very much for the info - appreciated.

Just got the replacement ITF from Maier.

Which way should be fit? Just to be sure - I guess the Maier O-ring goes over the marked edge of the new ITF, but which way is the SUN side?
Another guess: since the O-ring 'seems' to go on 'one' side only - as above, that must be the side where the screwed on filter ring goes, but is it?

Not sure

Ha ha ha ha ha ...
Finally done it - with the O-ring too!

The locking ring thread is NOT perfectly manufactured straight - it is slightly angled!

I have taken filter + O-ring out, cleaned the threads using thin tweezers and then tried it without anything and found out the thread was not straight from factory.

I also pressed the O-ring a bit using flat part of tweezers - thrown it in and managed to catch thread using middle + annular fingers + finger nails ... just to catch it then managed to tighten it without forcing it by holding it and turn the whole structure.

What a difference this filter is - it is also has clearer coating.

I might have to reduce Exposure time or gain or both.

Looking forward for next time I manage to match when The Sun is out and I am at home !

The angled thread is to give a slight tilt to the ITF filter.....

>I have a few questions for the experts here, please.

>1. I believe it is probably worth getting the ITF from Maier [out of stock] - not just for the price, but because it does not have the second protective glass 'glued'. Would the glue be a problem?

>2. where exactly should I fit the 2" Baader Red CCD filter?
Is there an image to understand it? Glued on?

>Please be nice, I am a newbie on Solar.

>Thanks in advance
>M

Hi, if you have an old style PST with front ERF as merely a coating on the objective lens, then there is no way that I know of, of replacing the ITF filter, because there is no ITF filter to replace. These old style PST's had a light blue metallic looking "opaque" coating on the objective lens or gold colored coating on the objective lens.

If you have a later style PST with dark blue coated, clear objective lens, then you can replace the ITF with the Beloptik or Maier replacement ITF filter.

I never heard of the use of any 2" Baader red CCD filter with a PST.

I don't know what you mean by "second protective glass" or the reference to "glue". The eyepiece end of the later style PST has 2 filters, one is the 5mm Blocking Filter that you see when you look down the barrel where the eyepiece goes, the second filter is the ITF filter and is in a separate barrel UNDER the one with the 5mm Blocking Filter.

You have to remove the second barrel (and first one of course also by default as a result) by unscrewing it from the black body of the PST. They seem to have thread lock on the threads and generally need a strong strap wrench and a heat gun to get it off. Our local club has repaired 3 PST's in this way that all had oxidised and useless ITF filters.

The ITF filter is for blocking the Infra Red and takes a large heat load, apparently. Expansion and contraction makes the filter edges fail at the seal on the original Meade made filters.

Best Regards,
Alistair G.

Whoops there was a page 2 that I didn't read before replying... must be too early in the morning and I didn't notice page 2...

Best Regards
AG