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Coronado Blocking Filter BF10 BF15 Bargains

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#1 photomagica

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Posted 05 May 2021 - 06:29 PM

I noticed that Adorama has great sale prices on Coronado BF10 and BF15 blocking filter diagonals as of 2021 May 5. See: https://www.adorama.com/cdbf10.html I ordered a BF15.

Bill


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#2 briansalomon1

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Posted 06 May 2021 - 08:22 AM

Here is a link to an article about David Lunt, founder and chief optical designer of Coronado (H-alpha) equipment.

 

https://skyandtelesc...-lunt-19422005/ (I like the photo here because I used to have an old TV102)

 

The Coronado legacy equipment was manufactured with the same attention to detail and adherence to quality standards the current Lunt equipment is made with today and the Coronado legacy equipment still has a very good reputation.

 

When Coronado sold the company to Mead the quality of the product began to change and today there are myriad reported problems and QC failures with Coronado/Mead equipment.

 

I know some, and maybe most of the Coronado/Mead equipment is a fine product and the Lunt equipment may cost more, but for many reasons, the Lunt equipment is worth it's price.


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#3 vincentv

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Posted 06 May 2021 - 11:35 AM

The meade BFs can be a great value. But you need to be aware of 2 things:

-The mechanics are not as good as Lunt's. There are no threads to attach cameras or binoviewers.

-The ITF will need to be replaced eventually.

 

That being said they can work just fine. My BF15 is considerably brighter than my b1200. It makes the luntanado a joy to use. The image is just a bright as single stacked.

And the reason is not because Meade is always better. There's a *ton* a variability in the transmission of the trim filter. I needed a BF15 and got lucky with this one.


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#4 photomagica

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Posted 06 May 2021 - 12:24 PM

Here is a link to an article about David Lunt, founder and chief optical designer of Coronado (H-alpha) equipment.

Brian - I have used the Lunt solar telescopes at Lowell Observatory and the quality of the equipment is truly impressive as are the images. I'm a big Lunt fan. I may acquire a Lunt instrument or solar components in the future. I appreciate your link to the S&T article.

I recently acquired a used PST - pre-Meade I believe, and also a used 40mm double stacking etalon, which may also be used on its own - again pre-Meade or early Meade. This PST double stack setup performs in a very satisfactory manner and has exceeded my expectations. (My wife, also an amateur astronomer, loves this telescope and has decided it is now hersgrin.gif ) My plan is to experiment with the BF15 and the 40mm front filter on another telescope. Ultimately I'd like to own a solar telescope in the 80mm aperture range, however the prices when you get to that aperture range are a bit breathtaking. Therefore, my plan is to use my ATM and machining skills to assemble an instrument from components. 

Bill



#5 briansalomon1

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Posted 07 May 2021 - 10:39 AM

My Grandmother took me to visit Lowell Observatory way back in 1975. I believe we were looking at Andromeda and I'll never forget when the Astronomer explained why the distance to the galaxy made the light I was seeing through the telescope that night millions of years old.

 

Like you, an affordable H-alpha budget makes sense to me. I use an NP101 for everything and have a single 60mm etalon w/blocking filter adapted to the scope and I think that's all I need.

 

Most of the old timers store their H-alpha equipment with desiccant packets so that's what I do. Hopefully, it will help keep the budget under control.


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#6 photomagica

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Posted 07 May 2021 - 07:07 PM

My Grandmother took me to visit Lowell Observatory way back in 1975. I believe we were looking at Andromeda and I'll never forget when the Astronomer explained why the distance to the galaxy made the light I was seeing through the telescope that night millions of years old.

When you get a chance, definitely go back to Lowell. Their new Giovle Open Deck Observatory is fantastic at night and they have their Lunt solar scopes out for awhile every clear day.

Bill



#7 MalVeauX

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Posted 07 May 2021 - 08:01 PM

I recently acquired a used PST - pre-Meade I believe, and also a used 40mm double stacking etalon, which may also be used on its own - again pre-Meade or early Meade. This PST double stack setup performs in a very satisfactory manner and has exceeded my expectations. (My wife, also an amateur astronomer, loves this telescope and has decided it is now hersgrin.gif ) My plan is to experiment with the BF15 and the 40mm front filter on another telescope. Ultimately I'd like to own a solar telescope in the 80mm aperture range, however the prices when you get to that aperture range are a bit breathtaking. Therefore, my plan is to use my ATM and machining skills to assemble an instrument from components. 

Bill

Hi Bill,

 

Keep in mind, the focal length determines the disc size and the disc size is what is most relevant for blocking filter size needs. So a 400mm focal length PST produces a 4mm disc image approximately (this is why the BF on the PST is 5mm, as that's enough to get the full disc, more blocking filter diameter would not do anything because the disc image itself is only 4mm and it doesn't get larger before the blocking filter, only after, so there's no benefit to larger blocking filters on the PST). That said, if you do in the future move your SM40 module to another telescope, that new focal length is going to determine your disc image size. A 15mm blocking filter will allow an unvignetted 14-point-something mm size disc image pass, which is going to come from a 1400 +/- mm focal length. I doubt you're going to use a focal length like that. More realistically would be something 600mm~1,000mm depending on what host scope you choose to use, and that will produce a 6mm to 10mm disc image. Just wanted to make sure you realized what you were getting into, with a 15mm blocking filter, as it has no inherent advantage over a 10mm blocking filter, unless you are using longer than 1,000mm focal length scopes that produce greater than 9~10mm disc image sizes. Larger blocking filters are ideal for binoviewing, but again, it doesn't need to be tremendously bigger to allow the light cone to pass without vignetting with max back focus.

 

$700 is a lot for a blocking filter when you're not going to benefit from it when your disc image is only 4mm. Not trying to be negative at all, just putting it into perspective.

 

For example, $700 towards a better etalon and/or larger overall clear aperture etalon system with more resolution would be a significant upgrade, compared to no net gain with a new blocking filter.

 

https://luntsolarsys...uned-telescope/

 

https://luntsolarsys...a-solar-filter/

 

Or even you could do another SM40 with adapter and double stack them together on any donor scope with a great focuser and whatever size blocking filter is appropriate based on focal length with room to spare for binoviewer use.

 

I would suggest, for anyone, when shopping solar equipment always be careful and prudent about the return policy from where you're buying from. There's no telling if the items are in good shape or will survive shipping and if the quality is unacceptable if you'll be able to return it and how much hassle that would entail to do so. Buying solar equipment blind (as in without testing yourself) is always a gamble. Always beware a bargain or good sale. Doesn't matter if it's a store that is reputable or a used item from a classified.

 

Also, to be considered, is that blocking filters (all of them frankly), just like etalons, have no standard. There's nothing to say what transmission is acceptable or not, or how tight the bandpass of the blocking filter is (6 Angstrom? More? Less? What's the transmission profile look like?). So there's high amounts of variability, some are brighter than others, etc. Also, not all blocking filters are made equally, such as Coronado ones that use an ITF that often is not sealed completely and so it eventually degrades due to exposure to atmosphere and reactions occur (often called rusting, but its not traditional rust) which involves then replacing the ITF (which is 100% on you; and bigger ITF filters cost more).

 

Again, not trying to be negative or a downer, just wanted to point out some information about these things, especially from the perspective of a 400mm focal length PST and SM40 etalon setup point of view. If you are going to use the SM40 on a longer focal length with a new blocking filter, then sure, its appropriate. It just depends on the focal length in terms of what disc image size will be generated, and that determines what size blocking filter you need. So if you're not using a 1 meter focal length, you don't need more than a 10mm blocking filter in almost all circumstances and uses in this situation. But again, I don't know what plans you ultimately have for the next scope you plan to use with the SM40 in the future. But, just something to know!

 

flowerred.gif

 

Very best,


Edited by MalVeauX, 07 May 2021 - 08:17 PM.

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#8 briansalomon1

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Posted 08 May 2021 - 09:03 AM

"Also, not all blocking filters are made equally, such as Coronado ones that use an ITF that often is not sealed completely and so it eventually degrades due to exposure to atmosphere and reactions occur (often called rusting, but its not traditional rust) which involves then replacing the ITF (which is 100% on you; and bigger ITF filters cost more)"

 

 

I think the smartest design feature of the Lunt blocking filters is the component that absorbs most of the unwanted energy (and consequently requires periodic replacement) is a simple $7 blue glass filter.


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#9 MalVeauX

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Posted 08 May 2021 - 09:52 AM


I think the smartest design feature of the Lunt blocking filters is the component that absorbs most of the unwanted energy (and consequently requires periodic replacement) is a simple $7 blue glass filter.

Absolutely!

 

Very best,


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#10 photomagica

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Posted 09 May 2021 - 02:34 AM

Marty - Thanks. Very much appreciate your wisdom and advice. Yes - I realize the BF15 is excessive for my current purposes, however, it provides me with lots of room to upgrade the system focal length later. At Adorama right now the BF15 was $200 over the BF10 and I thought that was a reasonable premium for a future upgrade path. I'd started out looking for a BF10 since I have a 952mm focal length refractor I could try with a blocking filter and the 40mm etalon. I'm curious to see how the BF15 and the 40mm will work on this telescope. I will start with using the 40mm as a front etalon and evaluate how I like that before deciding what to do next. I'd welcome your thoughts on this.

I'm also aware of possible incompatibility between the blocking filter and etalons, however it is reported that Coronado blocking filters have worked well with Lunt etalons in some cases. Unless buying a complete package this whole solar thing is a bit experimental and involves risks of things not working as well as one might want. I'm OK with those risks. Also, if I need an ITF down the line, I'll deal with that when I get there.

BTW - just got word from Adorama that my BF15 is backordered. I'm OK with that as I have other projects in the queue before I get to setting things up on my refractor. In the meantime the little double stacked PST is a real delight.

Thanks again,

Bill

 

(PS. Let anyone has concerns, I'm very much aware of eyesight risks and the need to rigorously control the energy coming though across the entire spectrum from UV to IR. Some risks I will happily accept - others - no.)


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#11 MalVeauX

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Posted 09 May 2021 - 07:13 AM

Marty - Thanks. Very much appreciate your wisdom and advice. Yes - I realize the BF15 is excessive for my current purposes, however, it provides me with lots of room to upgrade the system focal length later. At Adorama right now the BF15 was $200 over the BF10 and I thought that was a reasonable premium for a future upgrade path. I'd started out looking for a BF10 since I have a 952mm focal length refractor I could try with a blocking filter and the 40mm etalon. I'm curious to see how the BF15 and the 40mm will work on this telescope. I will start with using the 40mm as a front etalon and evaluate how I like that before deciding what to do next. I'd welcome your thoughts on this.

I'm also aware of possible incompatibility between the blocking filter and etalons, however it is reported that Coronado blocking filters have worked well with Lunt etalons in some cases. Unless buying a complete package this whole solar thing is a bit experimental and involves risks of things not working as well as one might want. I'm OK with those risks. Also, if I need an ITF down the line, I'll deal with that when I get there.

BTW - just got word from Adorama that my BF15 is backordered. I'm OK with that as I have other projects in the queue before I get to setting things up on my refractor. In the meantime the little double stacked PST is a real delight.

Thanks again,

Bill

 

(PS. Let anyone has concerns, I'm very much aware of eyesight risks and the need to rigorously control the energy coming though across the entire spectrum from UV to IR. Some risks I will happily accept - others - no.)

Hi,

 

The SM40 module on the end of a long scope can be good. Not sure I would put it on a 1 meter telescope focal length though (F23~F24) because there's no benefit to this as your filter is front mounted, relative to something like a 600mm focal length. This of course generates a 9.5mm disc image at your blocking filter (with that near 1 meter scope). If you routinely spend a lot of time at medium to high power viewing, sure, it will help with allowing you to use more common and simple longer focal length eyepieces that are more comfortable and especially easier with binoviewers. The other profound issue is tuning. On a 1 meter scope with the etalon up front, and you at the eyepiece, how do you tune it? People do this and they have to rig up turn/pulley systems to remotely tune their etalon as its just so far away. And if you ever wanted to double stack it with another SM40, well, you compound that even more. Something to keep in mind; on a small system like a SM40, I would probably keep them on a focal length at arm's length so you can actually tune them without much fuss, but I favor convenience on this.

 

Personally with what you're putting into this so far, I would put more efforts into bigger aperture etalons and focus on etalon quality at this point and hunt towards the double stack of whatever that is for you. Front mounted will have the challenges mentioned above, but they will have the best jacquinot spot too for full disc viewing. Maybe another SM40 is the way to go for you. Or maybe stop with single stack and save towards a bigger aperture 60mm option in the future. It's easy to spend a ton on accessories and peripheral parts of a solar setup but you get the most noticeable difference with a higher quality high uniformity high finesse etalon than anything and double stacking it is just taking it to level 10 essentially. But that's the challenge... finding a good etalon these days? Very hard.

 

Very best,


Edited by MalVeauX, 09 May 2021 - 07:31 AM.

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#12 photomagica

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Posted 09 May 2021 - 04:35 PM

Yes - I indeed anticipated that my one-meter focal length telescope would have a reach problem for tuning the etalon and f20 something might yield a pretty dim image. Still, it is an easy experiment to perform. And we are a two amateur astronomer household so one of us can tune while the other looks.

 

I guess I'm fortunate that the etalons we have in the PST and the 40mm appear to be just fine, with the little telescope showing great detail.  I'm also pondering the merits of finding an 80mm achromat OTA that I can cut down and use the 40mm internally. I expect I'd need an energy rejection filter on the front end.

 

When there isn't a pandemic on, I'm frequently in Tucson so will definitely visit Lunt Engineering when I next get back there.

Best regards,

Bill


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#13 MalVeauX

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Posted 09 May 2021 - 04:50 PM

and f20 something might yield a pretty dim image.

That only applies to imaging. For visual, F20 is not dimmer inherently. :)

 

Very best,
 




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