Coronado Blocking Filter Comparison

[kornfeld1]

I went from having zero solar scopes to more than I know what to do with...so I figured I'd post up some pictures and information that others might find useful.

The question has been raised before about whether or not the eyepiece holders/blocking filters can be swapped between various coronado scopes (this thread is an example), and as was mentioned in that thread, the answer is yes. Here are a bunch of pictures showing detail on that.

Here is a PST, a Solarmax 40, and a lonely diagonal.



The blocking filters have been removed from each, and here's a side by side comparison of a BF5, BF10, and BF15.



There's no question that the BF5 can screw into the PST, but here are shots of a BF10 and a BF15 threaded in as well.




All three sizes thread perfectly into the PST and all three sizes thread perfectly into the diagonal.

There is a mini-energy rejection filter (mini ERF) mounted in the front of each diagonal and directly below the blocking filter on the PST. It's the chrome piece coming out of the diagonal, and is the first section of black tube that sticks up from the PST body. This lens looks the same to me in each situation, but as you can see below, they are not interchangeable. The body of the mini-ERF from the PST is quite a bit bigger than the body of the mini-ERF from the diagonals.




This isn't anything new to the experienced people, but it took me a while to dig this information up in bits and pieces from various places, so I figured I'd compile all of the information in one spot with some pictures. Hope this is helpful for someone!

[colinsk]

The next step is to do a ray tracing through the penta prism and define the vignetting.

[kornfeld1]

Hmmmm.....I'm still just learning what the different models of scopes are, and what their parts are called...so you're way over my head.

I don't think this is what you're talking about, but I will add that even though the BF5 doesn't vignette any of the Sun's disc in the PST, it is sooo much nicer to observe through the BF10 or BF15 with the increased field of view.

[robert]

Really interesting, thanks (I have a failed BF10 and bits of a PST...)
Robert

[Merlin66]

Robert,
I assume you mean the "mini-ERF" has "rusted" or deteriorated?
If the blocking filter element is still OK, you can still use the diagonal, with the erf removed in a successful PST mod....the main ERF is up front.

[robert]

Thanks for spotting that. I did try the BF10 with the modded PST but I had started using the Lunt B1200 blocking filter and surprisingly that has better contrast than the BF10. So the plan would be to reuse the BF10 with my SM40 which is looking a bit sad/lonely since the BF10 died!

cheers

Robert

[robert]

I also tried a KG3 filter to replace the mini ERF but the definition of the image was very poor. I guess the optical quality was too low for that use?
Robert

[Merlin66]

Yes, that seems to be the case...

[marktownley]

If the blocking filter element is still OK, you can still use the diagonal, with the erf removed in a successful PST mod....the main ERF is up front.

Hmmmm, apart from there is then no blocking >1500nm. Not sure this is something I would want to do visually... But we've been through all this before :whistle:

Curious about your KG3 Robert, I found mine to be excellent

[Merlin66]

Mark, et al,
Yes it keeps coming up....the ERF does provide some filtering and the sensitivity of the eye in the far IR is minimal, likewise is the heat build up.

[kornfeld1]

Hey Phillip,

Any chance you would like to sell the 5mm blocking filter?

It would find a nice home in my tacklebox. B)

Sure, if you buy the rest of the SolarMax 40, the blocking filter is all yours.

[colinsk]

Mark, et al,
Yes it keeps coming up....the ERF does provide some filtering and the sensitivity of the eye in the far IR is minimal, likewise is the heat build up.

I have been studying your authoritative document on solar safety. While I still believe the eye is sensitive to far IR I do agree that the water in the atmosphere blocks most IR above 1500nm. IR-B and IR-C will cause cataracts in long term exposures.

Please be safe people! understand how the ND system works and realise how filter graphs show it (or don't show it). hmy:

[dashour]

Help! Ok, so if I swap out my BF5 for a BF15 on my PST, what will I notice visually? I understand I'll get a wider field of view, but what else? Brighter image? Resolution? etc.

I read on another thread someone said the 5 actually gave a better image, because the sweet spot was less noticeable or something. But my more general question is does a bigger BF normally give you a nicer, easier to see view, regardless of what scope you are using? I understand people want a bigger BF for imaging, but visually as well?

Thanks everyone.

[Merlin66]

I've got and use BF5/BF10/BF15 filters. I haven't noticed any difference in contrast or resolution. The spectroscope shows almost identical bandwidth and transmission for the BF10/Bf15 filters.
The real benefit is the increased FOV.
Remember, as you increase the focal length of your solar scope, the image of the sun at focus also increases, roughly 1/100 the focal length. ie 500mm = 5mm image, 1000mm = 10mm, and 1500mm gives 15mm.
This was the "driver" for larger BF filters.

[marktownley]

Help! Ok, so if I swap out my BF5 for a BF15 on my PST, what will I notice visually? I understand I'll get a wider field of view, but what else? Brighter image? Resolution? etc.

Probably reflections somewhere in the new wider fov with the bf15 - don't forget Ha systems generate reflections and these have to go somewhere. Having a smaller fov is one way the manufacturer 'hides' them from us.

[peter drew]

My conclusion also Mark. I currently use a BF15, I was initially disappointed that the whole of the new wider field compared to the BF5 view was not uniformly focusing on whatever tuning setting was applied, I now appreciate that the 20mm aperture PST etalon has a finite area of Ha and have now come to prefer a field of view that contains variations of detail. I exclusively now use a 8mm-24mm zoom eyepiece, at the upper end of the magnification range the sweet spot covers the whole field.