Lunt Blocking Filter - Check yours, you won't regret it!

[AdeKing]

On 31/05/2019 at 22:43, symmetal said:

After getting a replacement blue glass filter from Bresser, I thought I'd have a go at possibly cleaning the old cloudy one. The CN thread said some people had success with CLR (calcium, lime, rust) cleaner. I had some Viakal limescale remover spray, so I thought I'd give it a try. I sprayed some into a small glass and dropped the filter in to soak. Came back half an hour later, rinsed it off, wiped it dry and was surprised that it now looks like new and is very clear (but still blue ). So worth keeping now as a backup in case the replacement shows signs of deposits appearing.

If you were going to just throw your cloudy filter away it's worth giving it a try (but at your own risk). 

Alan 

I tried this today and it does indeed work, my filter looks as goos as new and will be kept as a spare. 

Thanks for the tip Alan. 

[Altocumulus]

6 hours ago, Nigella Bryant said:

I had the same problem with the blue filter going cloudy. TH replaced it for £30 and took only 7 days. I thought, really great service. 

"Replaced it for £30?" - On a Lunt ? If so it should be covered under warranty. :chinscratch:

[Nigella Bryant]

56 minutes ago, Altocumulus said:

"Replaced it for £30?" - On a Lunt ? If so it should be covered under warranty. :chinscratch:

I bought it second hand and was supposed to be in good condition. Wasn't under warranty. 

[nigelg]

Just received my replacement Blocking filter from Bresser. So others should be getting theirs shortly, if not email a reminder.

 

Nigel

[AdeKing]

I dealt directly with Bresser Europe who supplied mine FOC and I fitted it myself. I just supplied Bresser with the serial number, I'm not the original owner but the question wasn't even asked by them, I was just asked for a shipping address and it was delivered 3 days later. 

Very pleased by the service. 

Edited June 21, 2019 by AdeKing
Spelling

[IanL]

Just to add another data point, once I had a free replacement posted from Bresser, I got a friend to clean the original one using an ultrasonic cleaner.

It worked a treat - 30 minutes in the water bath and good as new without the use of any chemicals or razor blades. I think the only other point to note is that the bath has a plastic basket rather than a metal one, so no risk of scratching the filter. Cheap ones go for about £30 on Amazon; not worth it for this one job but useful if you already have one or know a friend who does.

[tooth_dr]

On 21/05/2019 at 10:17, tooth_dr said:

I took photos of mine this morning, is it worth contacting Lunt?

 

One year later look at my filter 😮

I just replaced it a couple of days ago, before I did the solar prominence time lapse. The footage from the day before lacks contrast in comparison.

 

Edited April 17, 2020 by tooth_dr

[tooth_dr]

@symmetal Alan thanks for the cleaning tip in the thread. I used some bathroom limescale spray, let it soak for a bit, and washed in soap and cleaned with Baader wonderfluid.  Looks as good as new.

 

[symmetal]

11 minutes ago, tooth_dr said:

@symmetal Alan thanks for the cleaning tip in the thread. I used some bathroom limescale spray, let it soak for a bit, and washed in soap and cleaned with Baader wonderfluid.  Looks as good as new.

Yes, it seems to do the trick nicely. 

Alan

[Peter Drew]

Just to recap.  The blue filter is not the blocking filter, it is the ITF (induced transference filter).  True, it does have a blocking action but only to reduce the thermal load on the actual blocking filter which is a completely different component.     🙂

[jonathan]

I have been pointed to this thread as I have experienced the 'lack of contrast' in my LS60 (in my signature), upon checking the blue front filter glass I found that it was covered in a thin layer of some sort of hard deposit, I tried to remove it using Eclipse Optical Cleaning Fluid and a Pec Pad but this didn't do much, Baader Wonder Fluid took a lot of it off but not all, and this only made it more obvious that there was even more on the other side of the glass than on the outside.  Seeing as it's limescale remover that seems to do the trick to remove it, I wonder if it's some property of the glass that attracts minerals from moisture in the air and ends up growing on the glass surface like some sort of stalectite.  Ho hum!

As with others, my scope has been kept in clean dry conditions in the house, always in it's original foam-lined case, and only comes out on bright sunny days so the chance of it being condensation as might happen with a night time telescope are practically nil, although the idea of storing the diagonal in a plastic tub with some dessicant might help in as much as the atmosphere in the tub should be very dry, giving any airbourne minerals much less chance to deposit on the glass.

It could also be an effect similar to superglue, that can leave a white deposit on surfaces near where the glue is applied (no doubt it's the vapour), perhaps the deposit comes from some other component, paint, or glue used during the manufacturing process.

I have emailed Lunt to see what their advice is, and how to proceed.

[jonathan]

On 17/04/2020 at 17:08, tooth_dr said:

@symmetal Alan thanks for the cleaning tip in the thread. I used some bathroom limescale spray, let it soak for a bit, and washed in soap and cleaned with Baader wonderfluid.  Looks as good as new.

Could I ask what brand / type of limescale remover you used please?  I might go down the cleaning route for my own blue glass filter.

[tooth_dr]

56 minutes ago, jonathan said:

Could I ask what brand / type of limescale remover you used please?  I might go down the cleaning route for my own blue glass filter.

Lol mr muscle - stuff used for cleaning bath and shower. Obviously do so at your own risk but it didn’t do any harm to mine 

[Merlin66]

The glass Lunt use is  Schott BG38, this glass (surface) can deteriorate in the atmosphere and is prone to moisture..... the surface can appear cloudy..

I've used CLR (Calcium,Lime,Rust) cleaner to give life back to a cloudy filter.

[jonathan]

I gave this my best shot...  Removed my blue filter today, started off with lens cleaner, didn't actually shift anything except perhaps some powder residue on the outside surface, then I moved on to bathroom shower soap scum and limescale remover (spray bottle), soaked the filter in some of that for a few minutes at a time to see if there was any change, leaving it longer each time, couldn't see much change.  So then I went all in, Harpic Toilet Cleaner with Limescale Remover (contains hydrochloric acid!)... I left a thin layer of it on the worst side but it didn't seem to have any effect at all after 30 minutes or so.

I cleaned the lens off and in the end I think all that was going to come off did come off, I'm left with what looks like an etched-on stain on one side (the inside), the outside surface almost looks clear except for two faint patches.  It's certainly far better than it was, the stain is more like a watermark on a piece of paper than a fungus so doesn't interfere all that much, but doubtless it has a small effect.

I have put the lens back in place (carefully, and including the blob of silicon sealant), gave it a go - wow what a difference!  The orangey red background is mostly gone, prominences can now be clearly seen against a 90-95% black background.  Thinking about it, the surface contaminant must have been dispersing the red light from the sun across the filter surface, resulting in low contrast and a redish background.

The filter still needs to be replaced (I didn't have any white vinegar to try, other than that I don't think there's anything further I can do to clean it, unless there's some nasty chemical I don't know about) so one way or another I'll do that soon enough.  I am a little concerned that the inside surfaces of the diagonal seemed to have the same sort of mineral deposits, I do wonder if fitting a new filter will only be a temporary solution and the real problem lies with the diagonal itself.  The red filter and mirror appeared to be fine though.

Oh and just incidentally I confirmed that the original case does contain a sachet of desiccant, has done since new, so I don't actually think keeping the diagonal in a separate tub with it's own desiccant would help that much (probably just end up getting damaged).

Edited April 22, 2020 by jonathan

[Altocumulus]

Drop a line to Lunt, or Bresser.de and see what they reckon on the diagonal....

[Peter Drew]

I've been aware of this issue for ages, along with methods owners have used to clean the blue filter.  What has always puzzled me is that I would have assumed that the outer faces of the filter would need to be optically polished and flat to a good tolerance.  Attacking the filter with all sorts of chemicals and abrasives I would have thought might well spoil this.      🤔 

[Rusted]

Did I read somewhere, probably on a forum, that the Lunt blue filter is actually a plastic?

Could be a completely false memory.

[Ibbo!]

Just for info on the Lunt site

 

https://luntsolarsystems.com/shop/solar-products/hydrogen-alpha/lunt-replacement-parts/blue-glass-for-lunt-blocking-filters/

 

Not exactly expensive if you have to buy one.

 

[AdeKing]

1 hour ago, Peter Drew said:

I've been aware of this issue for ages, along with methods owners have used to clean the blue filter.  What has always puzzled me is that I would have assumed that the outer faces of the filter would need to be optically polished and flat to a good tolerance.  Attacking the filter with all sorts of chemicals and abrasives I would have thought might well spoil this.      🤔 

Descalers like Viakal contain weak Hydrochloric acid which dissolves carbonates.  As glass is a silicate, HCl shouldn't cause any etching.

To dissolve silicates you need Hydrofluoric acid (HF), which is extremely nasty stuff and should only ever be handled when in head to toe waterproof PPE.  Horrible stuff, I used it by the 5l bottle load for my PhD and was so happy when I no longer needed to handle it.

[Merlin66]

Russ,

The Lunt "blue" filter is Schott BG38 glass.

CLR cleaner (Calcium, Lime, Rust) does a very good job of cleaning this filter.

 

[Altocumulus]

I * *coughs* * just used spectacle fluid .... * * coughs * * ... It cleaned 99% of mine...

Although that was after I'd gotten a replacement.

[jonathan]

12 hours ago, Merlin66 said:

Russ,

The Lunt "blue" filter is Schott BG38 glass.

CLR cleaner (Calcium, Lime, Rust) does a very good job of cleaning this filter.

 

I don't think that CLR cleaner is available in the UK.  Does anyone know of an equivalent?  There are various limescale removers, kettle de-scalers, that sort of thing, but as to which one would do a good job on a piece of blue glass is anyone's guess.

[jonathan]

3 hours ago, Altocumulus said:

I * *coughs* * just used spectacle fluid .... * * coughs * * ... It cleaned 99% of mine...

Although that was after I'd gotten a replacement.

I wonder if it depends on where you live as to what mineral deposits appear on the blue glass.  I live in an area with lots of limestone and chalk geology under the fields.

[Altocumulus]

If it were that simple....We're granite with some sandstone.