The Good, the Bad and the Ugly – a tale of 3 Coronado BF15 blocking filters

[arnedanielsen]

This story starts in 2013 when a dear astro-buddy of mine passed away. He was a good friend, eager solar observer and we had gone to see several total solar eclipses together. He owned two Coronado SolarMax scopes – one 60mm and one 90mm. I ended up buying the 90mm from his son while the 60mm was sold to someone else.

This Autumn I came across a Coronado SolarMax 60II, which I bought. However, some of you mentioned in your comments that the exposure times needed for this setup was rather high and advised me to check the BF for rust. I inspected it visually, but it did not look like it was suffering from rust.

Last week I stumbled upon another Coronado SolarMax 60 for sale. It turned out to be the 60mm from my late friend, which was put up for sale again. The owner had used it very little over the last 8 years and wanted to sell it. According to the pictures in the ad the BF was severely rusted, but the front-filter and the scope itself looked good. I contacted the seller as it was very tempting to get the front-filter to be used as DS for my setup and we came to an agreement.

Last Sunday I finally had the time (and weather) to do a test of all the BF filters. I setup my portable kit consisting of the SolarMax 60II and ZWO ASI178 camera mounted on the SkyWatcher SolarQuest. I then added the newly acquired front-filter for double-stacking. This increased the contrast and made the filaments stand out much more clearly, but there is certainly something to be learned fine-tuning this setup.

184587951_1058048494604454_7523413072332007035_n.jpg (455.45 KiB) Viewed 569 times

I started with the BF filter from my 90mm.
Using a gain of 80 this filter only needed an exposure of 9.0ms for a properly exposed image. The contrast was also good.

Sun60FD_082640_Ha_(Coronado_60mm_BF15)_20210508_ZWO ASI178MM_lapl6_ap1300_resize.jpg (136.38 KiB) Viewed 569 times

Stack of 100 best images with no flats, processing or sharpening

With the BF filter from the 60mm II I had to increase the gain to 160 and still ended up with and exposure of 20ms. The image from this setup was the least contrasty.

Sun60FD_091446_Ha_(Coronado_60mm_BF15)_20210508_ZWO ASI178MM_lapl6_ap1310_resize.jpg (141.03 KiB) Viewed 569 times

Stack of 100 best images with no flats, processing or sharpening

Finally attached the BF filter from the 60mm and keeping the gain at 160 I had to increase the exposure to a whopping 199ms :-o. The contrast, however, was quite good.

Sun60FD_092614_Ha_(Coronado_60mm_BF15)_20210508_ZWO ASI178MM_lapl6_ap1304_resize.jpg (147.01 KiB) Viewed 569 times

[Image]
Stack of 100 best images with no flats, processing or sharpening


Here’s a couple of images of the severely rusted BF.

184726782_520133329367205_8035299338529731_n.jpg (621.96 KiB) Viewed 569 times

184844300_513703056675725_5892943032177655411_n.jpg (491.66 KiB) Viewed 569 times

I’m thinking of trying to fixing/replacing at least one of the bad BF – just so that I don’t have to swap the BF from my permanent setup on the 90mm all the time. Any recommendations on this. Should I try to repair or buy a new Coronado BF? Any other options??

Best regards,
Arne

[marktownley]

Good comparison Arne, glad you found the root of the problem. You can replace the failed ITF filters quite cheaply and easily, the damaged mirror coating is a different issue though and i'm not sure is fixable.

[MalVeauX]

Hi,

You can get a new ITF from Maier or BelOptik to repair that part of your blocking filter issue.

For your diagonal, the mirror in the diagonal isn't some special mirror (maybe someone can verify this, I don't think its anything more than a cheap star diagonal mirror with an ITF/BF in the nose and some gold paint). So you can just take the 1.25" nose piece containing the blocking filter and ITF and simply thread it into a new diagonal. Or just use it straight through.

You could probably just open up the diagonal and replace the mirror with another one from a standard star diagonal I think? Again maybe someone can verify?

Very best,

[arnedanielsen]

Thanks guys!

I will try and get hold of an replacement ITF from BelOptik.

Best regards,
Arne

[rsfoto]

Hi Arne,

That is the horror story of Coronado Blciking filters. I own 3 BF30 and they have been replaced about 4 times and I got tired of sending them back in order tog et a new. I need to send them always to USA and it takes ages to get them back so after reading a few messages here I decided to take out the ITF filter and just put a 12nm H-alpha filter there and it works flawless. Thts is what I am using for my H-alpha mosaics I post here.

A 12nm 1.25" H-alpha os for sure cheaper then a new ITF ...

Look here in Germany from Astronomik alias Gerd Neumann (my preferred filter supplier)

https://www.astronomik.com/de/fotografi ... -12nm.html

https://www.astronomik.com/de/fotografi ... l?size=135

[DeepSolar64]

Arne,
That setup looks familiar for I also have a SolarMax II 60. You are using an older model stacking etalon though. Mine is 2 years old and so far no rust on my filters. I so wish that Coronado and Lunt could economically use hard coated filters to eliminate the rusting problem or give a transferable lifetime warranty on the blocking filters.

Hey, Rainer, would the 12nm 1.25" filter be good for visual use as well as imaging? That would be a must for me.

James

[rsfoto]

Arne,
That setup looks familiar for I also have a SolarMax II 60. You are using an older model stacking etalon though. Mine is 2 years old and so far no rust on my filters. I so wish that Coronado and Lunt could economically use hard coated filters to eliminate the rusting problem or give a transferable lifetime warranty on the blocking filters.

Hey, Rainer, would the 12nm 1.25" filter be good for visual use as well as imaging? That would be a must for me.

James

Hi James,

Hey, Rainer, would the 12nm 1.25" filter be good for visual use as well as imaging? That would be a must for me.

I do not know but I guess the experts here will answer your question.

[DeepSolar64]

In theory it should be since it's bandpass is quite narrow. Little to no IR or UV should pass through it.

[rsfoto]

In theory it should be since it's bandpass is quite narrow. Little to no IR or UV should pass through it.

Hi James,

Here the diagramm of this filter from Astronomik website




https://www.astronomik.com/en/photographic-filters.html

[DeepSolar64]

Rainer,
The bandpass certainly looks safe. Do you screw the filter into the eyepiece or into the blocking filter diagonal? If diagonal which side? Eyepiece side or telescope side?

James

[rsfoto]

Rainer,
The bandpass certainly looks safe. Do you screw the filter into the eyepiece or into the blocking filter diagonal? If diagonal which side? Eyepiece side or telescope side?

James

Hi,

I have my filter on the side where the ITF was which means at the front end of the Blocking filter facing the Sun and so it should be in the diagonal facing the sun IMHO

I am not an expert ... So take it with a grain of salt ...

[DeepSolar64]

Obviously it doesn't get too hot there and damage the filter.

[rsfoto]

Obviously it doesn't get too hot there and damage the filter.

Hi James,

No. Look at the sequence of the filters.

ERF >> Etalon >> Blocking Filter >> etc.

[DeepSolar64]

Obviously it doesn't get too hot there and damage the filter.

Hi James,

No. Look at the sequence of the filters.

ERF >> Etalon >> Blocking Filter >> etc.

True that. The ERF and Etalons would take out the majority of the heat before it reached the blocking filters.

[arnedanielsen]

Hi Rainer,

Hi Arne,

That is the horror story of Coronado Blciking filters. I own 3 BF30 and they have been replaced about 4 times and I got tired of sending them back in order tog et a new. I need to send them always to USA and it takes ages to get them back so after reading a few messages here I decided to take out the ITF filter and just put a 12nm H-alpha filter there and it works flawless. Thts is what I am using for my H-alpha mosaics I post here.

A 12nm 1.25" H-alpha os for sure cheaper then a new ITF ...

Look here in Germany from Astronomik alias Gerd Neumann (my preferred filter supplier)

https://www.astronomik.com/de/fotografi ... -12nm.html

https://www.astronomik.com/de/fotografi ... l?size=135

This is very interesting.

I'm already using a Baader H-Alpha 35nm CCD before the Coronado BF to reduce the heat load.
https://www.baader-planetarium.com/en/b ... ilter.html

Baader35nmHAlpha.PNG (206.66 KiB) Viewed 424 times

Are you basically saying that I could remove the rusted ITF part (the part facing the telescope) altogether and just use a H-Alpha filter like the Astronomik or Baader filter together with the eyepiece(camera) facing part of the BF15?

Maybe loose the diagonal mirror, which has damaged mirror coating, as well and make it a straight through version more suited for imaging as well?

Best regards,
Arne

[rsfoto]

Are you basically saying that I could remove the rusted ITF part (the part facing the telescope) altogether and just use a H-Alpha filter like the Astronomik or Baader filter together with the eyepiece(camera) facing part of the BF15?

Hi Arne,

Yes, that is how I have my setup ... but I have a straight through BF30 ...

ERF >> Etalon >> H-alpha filter >> camera

[DeepSolar64]

This is certainly an easy fix if needed. Remove the ITF and screw in a Ha filter in the nosepiece ahead of where the ITF once was. Pretty smart Rainer!

The red filter on the eyepiece side, what is it for?

I'll remember this!

James

[marktownley]

What is the tripod you are using Arne?

[rsfoto]

This is certainly an easy fix if needed. Remove the ITF and screw in a Ha filter in the nosepiece ahead of where the ITF once was. Pretty smart Rainer!

The red filter on the eyepiece side, what is it for?

I'll remember this!

James

Hi James,

Pretty smart Rainer!

This did not grow on my manure. This was discussed somewhere here in the Solar chat forum but do not remember who is the author.

[pedro]

What is the tripod you are using Arne?

It looks like a Berlebach tripod

[arnedanielsen]

What is the tripod you are using Arne?

Hi Mark,

It's a Berlebach tripod. I have several different models (and love them all), but this particular model is the Report 7003.

Best regards,
Arne

[arnedanielsen]

What is the tripod you are using Arne?

It looks like a Berlebach tripod

Good eye, Pedro!

Best regards,
Arne