Blocking Filter, Mini ERFs and Alternatives

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by Merlin66 »

Sorry,
I still prefer calling the "Mini-ERF" a "mini-ERF" than a ITF - I think an ITF could be any filter....
The ERF in the SM60 etc is basically just a red filter....blocks below 600nm or so and passes everything above.
The curve above (for the "mini-ERF" not the blocking filter -title is incorrect) shows that it effectively blocks everything above 750nm
When the two are combined you end up with a bandpass of approx 600-750nm.
The Baader D-ERF has a narrow bandwidth (600-700nm) and blocks everything else (up to 1500nm).
Hope this helps.


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by etatsolarchat »

If you want to replace the Mini-ERF(ITF) filter. I think a KG5 filter followed by a standard astro H-alpha filter would fit the bill..., right?


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by etatsolarchat »

Merlin66, For blocking filters I see 6A quoted in literature, how did you decide 6-8A? Would a spec of 7 be optimal?

Bob, what are you going to use instead of the KG5?


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by Merlin66 »

(what's your name?)
The 6-8A is based on the finesse and resonance of the various etalons used by amateurs....
The PST blocking filter(s) are very similar to the Lunt.....


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by DSobserver »

I just add a 23A red filter in front of my SM40 and now it works again using a KG5 filter!

Now I need good and clear sky to judge how much removing from filter, replacing (for the moment) with red filter and using KG5 instead of mini-ERF, it improve the picture.

"If you want to replace the Mini-ERF(ITF) filter. I think a KG5 filter followed by a standard astro H-alpha filter would fit"

Fully agree

Now regarding the BF, 6 or 7 or 8A doesn't care for the moment as the main point is to find them at a good price :whistle:


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by etatsolarchat »

Cool, I was thinking instead of an expensive H-alpha filter maybe a red 25 would work as well so let us know how the 23A red does for you!


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by DSobserver »

So this morning some quick test (before work and ...clouds :angry: )

As I said I'm using a DS PST and when removing front SM ERF and replacing the mini ERF with KG5, with red 23A filter is much better than without : I can see Ha sun. But it's still not perfect. The sun is bit orange and as soon as you tilt too much the SM it became green (again.... :X )

Most probably 23A is not enough. Could be that a 25A would be better.

I also could saw that apparently the rust on my mini ERF is affecting transmission 'cause picture is brigher with KG5 filter...

So :
1- I have to replace 23A filter with a "darker" one. I'll most probably use an Ha one and like this adding on top a KG5 I should be 100% IR/UV safe.
2- Find a solution to install my KG5 filter before BF and not after (on the eyepiece) as it is now. Any idea?


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley »

So this morning some quick test (before work and ...clouds :angry: )

As I said I'm using a DS PST and when removing front SM ERF and replacing the mini ERF with KG5, with red 23A filter is much better than without : I can see Ha sun. But it's still not perfect. The sun is bit orange and as soon as you tilt too much the SM it became green (again.... :X )

Most probably 23A is not enough. Could be that a 25A would be better.

I also could saw that apparently the rust on my mini ERF is affecting transmission 'cause picture is brigher with KG5 filter...

So :
1- I have to replace 23A filter with a "darker" one. I'll most probably use an Ha one and like this adding on top a KG5 I should be 100% IR/UV safe.
2- Find a solution to install my KG5 filter before BF and not after (on the eyepiece) as it is now. Any idea?

What are the transmission curves for a 23a and 25a?


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by DSobserver »

Maybe this is of any use to you.
When I used my PST for photographic purposes I noticed that my mini-ERF (ITF) was heavily corroded, and found that a 35 nm H-alpha filter can be a good substitute. (Although I am not sure for visual use.)

ok for photo bud not safe for visual!

here is the 23A :


and here the 25A :


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by DSobserver »

Here are some filter curves.
Go to longpass filters and scroll down a bit to find the 23a and 25a curves.

faster :lol:


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley »

You'll get absolutely no difference with the 25a over the 23a.

Look carefully at the y - axis of the scales on the different graphs for the transmission curves for the 23a, 25a and ITF filters; the 23a & 25a are % transmission graphs, the ITF filter in an OD scale - the latter is logarithmic - considerably different magnitudes of transmission...

In a stock DS PST, I have to be honest here, not sure why or what the logic would be for removing the ITF unless it was rusted beyond use?


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by DSobserver »

Sorry but I don't follow both of your points :

Interest to replace mini ERF for a PST, a DS PST or a SM is the same I think....

Regarding transmission curve between ERF and red filter, you're right, but still don't understand why tilting the red one, the sun become greenish...


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley »

Sorry but I don't follow both of your points :

Interest to replace mini ERF for a PST, a DS PST or a SM is the same I think....

Regarding transmission curve between ERF and red filter, you're right, but still don't understand why tilting the red one, the sun become greenish...

I think the absolute minimum if you want to replace the ITF is a nighttime Ha filter, the narrower the bandpass the better and appropriate KG glass.

If you tilt any filter, you blueshift it's bandpass, which is why I suspect you seeing your greenish sun when you tilt your red filter...


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by etatsolarchat »

I can see tilting a thin film filter changing characteristics, but how is that for a basic #23 red glass filter?

Stupid question #2, what machine is used to create these nice transmission plots? Never mind, Carl Zeiss M4-QIII Lab Spectrophotometer :cheer:


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by colinsk »

We really should describe a homemade spectrophotometer. It would not be that hard if you had a nice blazed grating. The rest could be salvaged or cheap parts.


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by etatsolarchat »

Ok, I started a new thread for you :bow:


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by Bob Yoesle »

Bob, what are you going to use instead of the KG5?

Hi Etat,

First, if I had a failed ITF, I'd get it replaced with another ITF, as they are relatively cheap. And this is BY FAR the safest route to take in protecting ones eyesight from far IR... I would only consider alternatives for imaging - not visual - use. But even then, why risk a mistake in use?

Trying to replace (or in my case protect) the ITF with a optically poslished 2" KG5 has resulted in quotes of $425-$750 (uncoated) and it would cost another $100 + per filter for AR coating, and then additional funds for mounting in a tilted cell, whereas a new replacement BF30 ITF would be around $100-$200, be coated, and fit the existing tilted cell.

My reason to consider KG5 glass was to protect the ITF itself from any residual short and medium IR (thermal loading/cycling heat) passed by a sub-aperture Baader DERF in my future 152 mm scope, and to protect the CaK module's PST filters for the same purpose in my 130 mm APO. For H alpha my alternative will be a Baader Red CCD filter. It too is way cheaper than a polished KG5 (optical polishing is a neccessity IMO), and likely is a much better quality substrate.

For my CaK module (again imaging only) I'll employ the currently used Badder Blue CCD filter, with a Baader ND 3.8 film filter on the objective - I will have to see what the CaK exposures are with this set up to know if it is practical. If not, the "bare" Baader Blue CCD filter will have to do, and may have to be replaced if it fails down the road from excessive heat. Same cost issue as above - e.g. way cheaper than a polished KG5.


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by etatsolarchat »

Awesome, thanks Bob. I'll follow your lead on the 152mm so eager to hear know how it goes!

Maybe if a bunch of us start pestering Baader, they's do a polished/coated KG5 and sell it for $100 ;)

Oh, the E, is for Eric maybe I can change that...


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley »

Just as a bit of further information on this post you may be interested in...

I recently compared the ITF from my BF10 with the ITF from my PST. They are different. The view through the PST one is brighter, and comparing views holding them up to the sky and viewing with naked eye, the PST one seems to pass more shorter wavelengths. Physically they also appear to be different filters; even though they are the same size, the PST one has a black cell that it sits in (similar I have to say to some of the Omega filters I have seen). Using either in combination with my PST mod results in reflections galore that reduces contrast. The best results I am getting with my PST mod is with the ITF removed and a peice of KG3 and Baader Neodymium in place...


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by colinsk »

OK
Let's walk through a PST...
The front objective is just AR coated - nothing special
The comes the tuneable PST etalon (Fabry-Perot etalon filter) - the heart of the instrument.
In the bottom of the eyepiece holder there's a small "Mini-ERF" to reduce the energy loading on the...
Blocking filter -positioned in the top eyepiece adaptor. This "sorts" the "comb" from the etalon and only allows the Ha bandwidth to pass through....
(In the Coronado BF diagonal there's also the "mini-ERF" and final blocking filter.)
Hope this helps.

This is for the new or repaired PSTs. The Gold objectives were:

ERF>Objective>Etalon>pentaprism>BF>EP

The first repair was the dark blue objectives and I don't know if the second piece of glass was added then. Then the second repair was

Objective>Etalon>Pentaprism>ITF>BF





I should note that I have seen both silvered pentaprisms and narrow band reflection coated Pentaprisms.

The narrow band reflection prism would leave green and blue out of focus suns inside the black box.


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by markthais »

KG glass is good for cutting the IR. That is what it was designed for. The problem is that it is not like BK-7, it has strains and homogenous problems. But on the other hand if you keep it near the eyepiece end it should work fine. It is not a good choice at the objective end. You would be hard pressed to find a piece that would pass 1/4 wave on transmission at 650nm larger then 2".
They also mention that the etalon has band passes across the whole spectrum. Depending on the design of the mirror the etalon may only have peaks +/- 30nm from the center wavelength of Ha then it is just transparent to the rest of the visible spectrum.
The blocker + red glass cuts the short side. The long side the filter can start transmit again around 900nm. If you only have a KG glass there will be a leak in the red.
The idea of using one of Baaders 7nm filters and the KG glass used near the eyepiece end should block any IR.

The scan of the BF15 should look the same on both sides at the base. It should go to zero(OD4-5) on both sides. Either it's the scan or they missed and thickness on the layers.

The attachment shows an etalon and a two cavity 1nm blocker,
Mark

Attached files


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by Merlin66 »

Colin, et al,
I believe when the change was made to the "blue" objective, the "mini-erf" was either added (for warranty repairs) or incorporated into new builds. I haven't come across a "blue" PST without the "mini-erf"
Interestly, I also haven't come across a version where the pentaprism is silvered....
We/I need to get organised to take a wider spectrum (ie 400- NIR) of the various elements.
The data I published previously (see library files) has a limited wavelength coverage and doesn't (similar to Mark's) show the full spectral extent. Next job on the list!
(I also think the mirror in the Coronado BF diagonal is a "cold mirror" which adds another complication.....


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley »

KG glass is good for cutting the IR. That is what it was designed for. The problem is that it is not like BK-7, it has strains and homogenous problems. But on the other hand if you keep it near the eyepiece end it should work fine. It is not a good choice at the objective end. You would be hard pressed to find a piece that would pass 1/4 wave on transmission at 650nm larger then 2".
They also mention that the etalon has band passes across the whole spectrum. Depending on the design of the mirror the etalon may only have peaks +/- 30nm from the center wavelength of Ha then it is just transparent to the rest of the visible spectrum.
The blocker + red glass cuts the short side. The long side the filter can start transmit again around 900nm. If you only have a KG glass there will be a leak in the red.
The idea of using one of Baaders 7nm filters and the KG glass used near the eyepiece end should block any IR.

The scan of the BF15 should look the same on both sides at the base. It should go to zero(OD4-5) on both sides. Either it's the scan or they missed and thickness on the layers.

The attachment shows an etalon and a two cavity 1nm blocker,
Mark

Very interesting input, thanks for that Mark :)


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by colinsk »

Depending on the design of the mirror the etalon may only have peaks +/- 30nm from the center wavelength of Ha then it is just transparent to the rest of the visible spectrum.

I found this out long ago for my PST etalon. Unless you use a broadband mirror for the etalon coatings it will peak. I used a reflection grating and looked through mine at an incandescent bulb. The dark lines were confined to red and by green it was clearly broadband transmission. The peaks also got narrower and narrower as it moved from the design wavelength. This is of course easy to model in Excel if you enter a reflectivity curve because the finesse is reflectivity dependent.


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley »

Check this out...

[ebay]150809975052[/ebay]

In particular the transmission curves - blocking out to 3000nm to ND5. This could well be an affordable and serious contender for replacing rusted ITF filters...


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by poita »

I may need to try this out for my B600 that has a horrible film and destroyed coatings on the itf at the from of the B600.


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by Bob Yoesle »

As noted earlier in this thread, I have had a number of issues with blocking filter / ITF failures, and most recently have noted possible deterioration of my PST-based CaK filter module. One possible solution that presented itself is to both reduce thermal cycling via the use of additional filtering (i.e. “mini” ERF’s) and elimination of atmospheric moisture.

So I designed a pair of identical modules that incorporate an additional Baader CCD filter to serve as a mini-ERF, and an optical window sealed chamber that is purged and sealed with Argon gas:





H alpha unit with Baader’s Red CCD filter:





Module in place and requires only 12 mm (½ inch) of back focus (much less than the OEM BF30 itself):





Preliminary views and imaging from yesterday reveal no contrast anomalies or spurious reflections:





Next hurdle will be assembling the “glove box” for the Argon purging - will report as soon as a few issues are solved. But so far so good.


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by colinsk »

Very nice work! :bow:


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley »

Damned impressive Bob! :bow:


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by GreatAttractor »

Excuse my slightly off-topic question: DSobserver, does your KG5 filter from stockoptics.com have any negative impact on image sharpness (beside the red leakage problem you have to solve)? I'm considering it for my own build.


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by DSobserver »

well, to be honest I could found a new ITF to replace the original PST one so my KG5 stay in its box...

What scared me to replace PST ITF is that using an ITF like KG5+night Ha filter or a IF UV/IR cut on KG3 from bel optik+night Ha filter, BF will not be anymore IR protected.

Could that deteriorate it?

Any idea?

Otherwise we can use 2" filters to screw on front PST...

By the way I recently test a Lumicon Ha filter and I feel that it slightly improve contrast. Could it be that it reduce bandwidth or it's only a question of %transmission?


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by Merlin66 »

Oliver's UV-IR/KG3 filter will block all the IR.
Combined with a narrow band Ha filter ( either up front as an ERF) or combined with the UV-IR will work very well, and protected both you and the BF.
Which Lumicon Ha filter? The one I have is just a red filter - not a narrow band like the Baader.


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by DSobserver »

Oliver's UV-IR/KG3 filter will block all the IR.
Combined with a narrow band Ha filter ( either up front as an ERF) or combined with the UV-IR will work very well, and protected both you and the BF.

except that for PST I don't think you can screw them is the ITF tube, so you'll screw them on the eyepiece : BF will not be protected anymore...

I don't think that for PST, UV/IR block filter is good enough as you also need to block light bellow 650nm. For SM filter it should work 'cause there is a ERF/deep red filter on front.


Which Lumicon Ha filter? The one I have is just a red filter - not a narrow band like the Baader.

I know that it's a deep deep red filter, but visually there's a slight improvement...
Could it be that it reduce bandwidth or it's only a question of %transmission?


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by Merlin66 »

I wasn't thinking of screwing them into the eyepeiece...
I was thinking about removing the spacer/ retaining ring at the existing "mini-erf" and using a dab of hot glue to hold the 1.25" filter(s) in place.
The OD of a 1.25" filter cell is 30.97mm and the retainer is 29.47- the thread to the back box is 32.89mm - these figures (could) allow a standard filter to be placed in the "recess" available after removal of the ITF surround, and the filter would sit just inside the black box. (there's sufficient clearance to the top of the prism.) The BF section would fit as normal.

Re the Lumicon - it can only be due to the increased transmission at Ha wavelength...


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by markthais »

All this talk about removing the IFT and replacing it with KG glass is fine if the bandpass is designed to be blocked to 1200nm.
A 2 cavity standard 6 ang filter will turn on again for a peak bandpass at about 850-900nm on the long side. The KG-3 needs to be blocked to at least 1100nm before it gets down to a low transmission level. So on the long side you have a leak or some energy between 900-1100nm. This is why you use the ITF, to block from 700nm-FIR
On the short side the 6 ang filter turn back on around 560nm with a narrow bandpass then in the blue green it really doesn't block much. This is what the red glass is for.The closer your cut wavelength to Ha the better. That is why we use RG610 or RG630.
The ITF will look silver and the bandpass will look gold.
But all this depends on how the filter is made.
When the ITF fails it get what is called rusted of foggy. When the bandpass fails it shifts the center wavelength from center to edge. So if you scan the center it will be at a different wavelength then the edge. The problem with looking at the bandpass is it can look fine and still have shifted. Usually you will find a loss in contrast or the filter will be dimmer. Two main thing are happening, it is letting the next peak leak through or has moved off the the peak it was designed for.
Just to review because there are a mixture of terms.
The ERF is to keep the heat out of the scope. If you put the ERF just in front of the etalon it is to keep the etalon cooler.
The blocking of the inter-order peaks of the etalon are blocked with filter glass(red), ITF and bandpass or a combination of bandpass, filter glass(red) and IR glass as long as the bandpass is blocked to 1200nm.
You can also have the ITF coated on top of the bandpass and red glass. This is also used.
Now, for just the ITF replacement.
The idea of using a Baader 7nm and the KG-3 is still not a bad idea to replace the ITF. The Baader 35nm all depends on the bandpass. It may or may not work. If you have a spectrometer then it's easy to tell.
The Baader filters are hard coated and are blocked passed 1200nm in the red. The red glass of the filter will take care of the short side.
The KG glass is not the best IR glass out there, but it is probably the easiest to find for the amateur.
All this is for standard filters. Hard coated bandpass filters can be different depending on the design.
But don't take a chance with the IR blocking. If your not sure then send it back to be repaired.
Mark W.


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley »

Great summary and very insightful, thanks Mark :)

You know then, picking up on your very last point; I know the KG glass isn't the best option in terms of quality, but have to ask the question, if were going for something better what would it be?

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by DSobserver »


Re the Lumicon - it can only be due to the increased transmission at Ha wavelength...

increased transmission at Ha wavelength? How can it be 'cause I simply screw this filter in front of the PST including ITF filter?


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by Merlin66 »

Sorry, I misunderstood...I thought you were using it as a part replacement for the ITF...
I can only assume then that there's an improvement in contrast? It doesn't act in any way (that I know of) to reduce the bandwidth.

Mark,
The transmission curves of the Baader 35nm filter are given at the front of this thread, the UV-IR/KG3 filter curves (above) show good blocking up into the IR....


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by markthais »

OK, stand corrected, the Baader 35nm filter looks good. It gets down before 700nm and stays down pass 1200nm. Depending how the bandpass was made. There should not be a leak before 700nm.

The KG glass has a problem with water vapor. And don't be fooled in thinking that coating the glass will keep in out.
Water vapor is a tricky thing. Is it important to the amateur market, probably not. If it starts to fail just get another one.
The better glass would be the Hoya HA30. This glass is made for them by Isuzu Glass. I was told that Isuzu will soon have all the military market for this type of IR glass. It holds up better then the KG series to weather and other requirements.
But for us,if you can get the KG already in the size you need go for it. Just use it at the eyepiece end of the scope because it will not work well at the objective end.
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Re: Blocking Filter, Mini ERFs and Alternatives

Post by DSobserver »

here are the hoya info

At 656nm transmission is around 68% and the KG3 was 60%....not so bad!

price around 65$ here but not easy to find

What about HA50 with 75% transmission?


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by markthais »

The HA-50 would probably be fine. It just turns back on in the IR, but it is out there at 1500nm. I really don't think that less then 1% transmission out there at 1500nm matters. The blocking of the IR depends on the thickness of the glass. The thicker the glass the better blocking but it also drops the transmission of the visible. Most of the glass is 2 to 3mm thick.
The use of IR glass is old school. But it still a good way to block unwanted light.
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Re: Blocking Filter, Mini ERFs and Alternatives

Post by ronatu »

Excuse me, but does anyone try to replace blocking filter?
Please share.
PS Would like to change size of it. From BF 5mm to 10-15mm.


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by MalVeauX »

Sorry to maybe dig up something old, but some filters mentioned already in this thread could hold interest.

I was looking at Baader's Red CCD filter (IR block) as an ERF. Seems Bob has used one already for HA.

I'm currently using the Blue CCD filter (IR block) as an ERF with a white light & calcium setup, and it works very well with a 150mm aperture refractor to reflect the heat back out. I use a 395nm +/-20nm filter as a 2nd ERF in the train and most of the heat is eliminated to the point where I can put my hand behind the system and not get melted.

I'm curious about maybe using a Daystar yellow ERF (passes IR, but blocks UV) that is full aperture (150mm in this case) in conjunction with a Baader Red CCD filter (IR block). I'm only considering it because I can get ahold of a 150mm Daystar yellow ERF for a very low price and if I combine it with the Baader Red filter, it seems like it would block most of the thermal load from UV & IR and still have high transmission. Comparison would be a 150mm Baader D-ERF in a cell, which is greater than $1500+ on its own.

Just curious as I'm looking to cut out more heat in my 150mm refractor with a budget solution, while saving for a good 200mm filter for the future.

Very best,


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by christian viladrich »

Hi Marty,
The Daystar ERF are now a bit outdated. There are not dielectric filters. This means that they aborb light and heat. In other words you will have a piece of very warm glass in front of your refractor. Not good for HR ;-)
Further more, there is a huge gap in optical quality beteween the Daystar ERF and the Baader ERF.


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley »

Personally I wouldn't bother with the yellow daystar erf. I don't see any gain in using the sub erf you are using already. Save your money!


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by MalVeauX »

Thanks, very appreciated, I was thinking about that and wondered. It makes a lot of sense that absorption filters are just going to keep heat in the line of the optics versus filters that reflect everything.

Do you guys think a Baader Red CCD Filter (IR block) would be ok with a 6 inch refractor? I have used the Blue CCD filter this way, with the 6 inch refractor for white light & calcium light, and the thermal load seems fine. I'm curious if the Baader Red CCD filter would be much improvement over just using an UV/IR block filter with my Quark with my 6 inch refractor.

Very best,


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by krakatoa1883 »

MalVeauX wrote: Sun Sep 30, 2018 12:25 amDo you guys think a Baader Red CCD Filter (IR block) would be ok with a 6 inch refractor?
I broke one just few months ago. Probably the fault is mine, may be the filter was too close to focus, however since then I make use of a H alpha CCD filter instead, no problems at all.


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by christian viladrich »

Thanks for the feeback Raf. Can you confirm it was a Baader Red CCD filter ?

Which Ha filter are you using now ? With what instrument, diameter, F/D ratio and filter diameter ?

We should make a list of the success / failed attempts ;-)


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by krakatoa1883 »

Yes, Christian, it was a red CCD filter, I removed the telecentric from my Quark and was experimenting some different solutions (which all proved to work better...) the filter was mounted just before an amplifier with my 150 mm achromat reduced to 110 mm i,e, @ f/6.8. The mistake was to mount the filter before the negative lens, I think, where heat is more concentrated. Or it may be (it was during winter) the glass broke when suddenly exposed to the ambient air, anyway I do not intend to repeat the experiment in summer :lol:

Since then I purchased a Baader D-ERF however its cell fits only my 150 mm, for my other scopes I am using a 35nm H-alpha filter as internal ERF with apertures not greater than 90 mm from f/5 (Taka Sky 90) to f/11.7 (TMB). Not tried greater apertures yet.

Based on what I read here I am tempted to purchase a 3.5nm....


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Re: Blocking Filter, Mini ERFs and Alternatives

Post by MalVeauX »

krakatoa1883 wrote: Sun Sep 30, 2018 6:53 am
MalVeauX wrote: Sun Sep 30, 2018 12:25 amDo you guys think a Baader Red CCD Filter (IR block) would be ok with a 6 inch refractor?
I broke one just few months ago. Probably the fault is mine, may be the filter was too close to focus, however since then I make use of a H alpha CCD filter instead, no problems at all.
Interesting, is that with a 6 inch refractor? Was that in the focuser or some where else? Mind sharing a link to the H Alpha CCD filter you're using?

Appreciate it!

Very best,


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