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Blocking filter straight through or in the diagonal?

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#1 supertrucker

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Posted 12 February 2024 - 04:25 AM

Hello everyone I plan to put in a order with lunt for a 60mm modualer unit with the b1200 filter and wanted to know if there are any disadvantages to having the blocking filter straight through, I have heard from one individual on a YouTube video he wished he had chose the straight through option. For better resolution. And probably better suited for astro photography. Am I missing something here. And do you have any recommendations, something I may be over looking any common mistakes when ordering a new h-alpha unit. I would like to see if it can be shipped in a case that could accommodate the stacked unit also for sometime in the future. It looks like everything is backordered, any idea what the wait time is, thanks for your input have a great day. Jack

#2 astropgr

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Posted 12 February 2024 - 05:29 AM

The difference would be a longer focal length and another mirror that maaaay reduce brightness and add tiny amounts of distortion. Straight through would be better for astrophotography since it would be easier to mount the camera. 


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#3 supertrucker

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Posted 12 February 2024 - 05:35 AM

Would straight through be better or worse for visual? Or add any inconvenience?

#4 Helen P

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Posted 12 February 2024 - 07:53 AM

Would straight through be better or worse for visual? Or add any inconvenience?

Envision yourself trying to look into the eyepiece with the telescope pointed almost straight up.....

Yes, not having an diagonal is terrible for visual.


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#5 supertrucker

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Posted 12 February 2024 - 08:04 AM

I see your point but I do plan to use the diagonal when doing visual. It's just why offer a option if the straight through is better for visual and astrophotography I'm guessing 90% of the time I will be using it for visual

#6 PETER DREW

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Posted 12 February 2024 - 08:10 AM

Also, for visual, be aware that a blocking filter larger than the standard one just gives you more field round the solar image, it doesn't increase the "sweet" spot.


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#7 MalVeauX

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Posted 12 February 2024 - 08:22 AM

Hello everyone I plan to put in a order with lunt for a 60mm modualer unit with the b1200 filter and wanted to know if there are any disadvantages to having the blocking filter straight through, I have heard from one individual on a YouTube video he wished he had chose the straight through option. For better resolution. And probably better suited for astro photography. Am I missing something here. And do you have any recommendations, something I may be over looking any common mistakes when ordering a new h-alpha unit. I would like to see if it can be shipped in a case that could accommodate the stacked unit also for sometime in the future. It looks like everything is backordered, any idea what the wait time is, thanks for your input have a great day. Jack

It's overall better to have the straight through module, if you're ok with providing your own diagonal. It's not better optically. You end up with the same results, you're just choosing your own diagonal. It does have advantages for imaging (no mirrors, no reverse image, less dust surfaces, less focus travel need, etc). If this is strictly visual, it really won't matter much other than your preference for using your own diagonal or not. It can absolutely matter if you want to use specific binoviewers that notoriously need more focus travel. If you have a diagonal with the blocking filter, it eats up a ton of focus travel. But a straight through with another diagonal could end up with even longer focus travel needs, making some binos impossible to reach focus. So it really comes down to specific gear you want to use, and heavily depends how you will configure it. The larger blocking filter diameter is useful to have when it is farther inserted into the light cone for reaching focus with visual setups like binos, where the larger diameter is less likely to mask the light cone and effectively reduce your aperture in terms of brightness and resolution. For imaging, there's no advantage to a larger blocking filter than the disc image (based on the objective's focal length, so 5~6mm is plenty on this instrument for imaging; going 12mm or larger would be for binoviewer use needing inward focus travel, etc, and pushing this filter into the light cone more).

 

Very best,


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#8 supertrucker

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Posted 12 February 2024 - 08:26 AM

Because I do plan to put a camera on it at times plus I like the idea of a wider field of view is why I chose the b1200 I am trying to figure out if by selecting the straight through option is going to negatively effect the visual performance through the diagonal or will it visually perform the same having it installed in the diagonal. hope I'm making sense.

#9 MalVeauX

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Posted 12 February 2024 - 08:32 AM

Because I do plan to put a camera on it at times plus I like the idea of a wider field of view is why I chose the b1200 I am trying to figure out if by selecting the straight through option is going to negatively effect the visual performance through the diagonal or will it visually perform the same having it installed in the diagonal. hope I'm making sense.

It is not a wider FOV. It's simply more black space around the disc image which provides you nothing. The disc image size is based on the objective focal length. 420mm (focal length) divided by 110 = 3.8mm. The disc image will be about 3.8mm. The blocking filter needs to be slightly larger than this (so 4mm~5mm would be fine, 6mm is very generous for this) to pass the disc image without masking it. There's zero advantage to a larger blocking filter on this system with this focal length than this. Going to a 12mm does not increase the FOV at all. It just increases how much black space there is around the disc image which again provides you nothing, so whether it was masked physically or blocked optically the result is black space either way. The only reason to go larger on the blocking filter on this system (ie, this focal length) is to be able to push the blocking filter's location in the imaging trainer farther into the light cone where the diameter increases and so you need a larger diameter blocking filter to allow that to happen with out masking the light cone, and the only application that really would do this would be binoviewers that need lots of inward focus travel to reach focus.

 

There's zero difference between straight through and diagonal for visual, optical performance, etc, other than focus travel distances and imaging train configuration. The only difference is you provide a diagonal if you want to use one with the straight through if you want a diagonal in there and can remove the diagonal if you want to image without a reversed image (due to mirrors).

 

Very best,


Edited by MalVeauX, 12 February 2024 - 08:34 AM.

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#10 supertrucker

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Posted 12 February 2024 - 08:44 AM

That really explains a lot thank you for the in depth explanation on how the filter works and what to expect from it, I have some quality diagonals that will not be a problem. I plan to go with straight through and make it more versatile, thanks again have a great day
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#11 Skywatchr

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Posted 12 February 2024 - 08:46 AM

It is not a wider FOV. It's simply more black space around the disc image which provides you nothing. The disc image size is based on the objective focal length. 420mm (focal length) divided by 110 = 3.8mm. The disc image will be about 3.8mm. The blocking filter needs to be slightly larger than this (so 4mm~5mm would be fine, 6mm is very generous for this) to pass the disc image without masking it. There's zero advantage to a larger blocking filter on this system with this focal length than this. Going to a 12mm does not increase the FOV at all. It just increases how much black space there is around the disc image which again provides you nothing, so whether it was masked physically or blocked optically the result is black space either way. The only reason to go larger on the blocking filter on this system (ie, this focal length) is to be able to push the blocking filter's location in the imaging trainer farther into the light cone where the diameter increases and so you need a larger diameter blocking filter to allow that to happen with out masking the light cone, and the only application that really would do this would be binoviewers that need lots of inward focus travel to reach focus.

 

There's zero difference between straight through and diagonal for visual, optical performance, etc, other than focus travel distances and imaging train configuration. The only difference is you provide a diagonal if you want to use one with the straight through if you want a diagonal in there and can remove the diagonal if you want to image without a reversed image (due to mirrors).

 

Very best,

The only "possible" advantage could be catching liftoff proms (imaging), but that doesn't happen very often except on a very "lucky" day.

 

It's too bad Lunt jumps from 6mm to 12mm.  An 8mm would probably suffice most of the time for that "extra space" around the disc.


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#12 MalVeauX

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Posted 12 February 2024 - 08:53 AM

The only "possible" advantage could be catching liftoff proms (imaging), but that doesn't happen very often except on a very "lucky" day.

 

It's too bad Lunt jumps from 6mm to 12mm.  An 8mm would probably suffice most of the time for that "extra space" around the disc.

If the disc image is 3.8mm on this instrument and you have a 6mm blocking filter, how much distance will a prom be for a 1.1mm advantage (half of the 2.2mm difference from 6mm up from the disc image size, if the disc image is centered). That's quite a large distance out from the disc's limb. Going to something larger diameter that shows even more than 25% of a solar diameter would require the prom to be so far away from the disc that you wouldn't see it because it would have already dissipated. Lift off and floating proms are right at the immediate disc limb. I would agree with what you're saying if the disc image was 5mm and the blocking filter was 6mm, but 3.8mm to 6mm allows a huge distance out from the disc limb to still see anything on-band. Going to a 12mm wouldn't help this, it's already plenty, on this system. The 12mm or larger would matter on something with a much longer focal length (over 1000mm) for this purpose (or again for use with binos).

 

BTW there's a big prom explosion and lift off and material arcing back down far away, going way off the limb right now if you guys want to see a prime example of what was just talked about. Check GONG/SDO if you cannot go view! (Edit: its over now, just go back and look at the time from 0900~1015 Eastern Time).

 

The solar disc radius here is about 600 pixels, 1200 pixels diameter. That CME is well over 300 pixels, or just over 1/4th of a solar diameter. Only someone viewing at low mag, full disc, would have seen the whole event with the disc in view. So if you simulated this image as your FOV, based on mag from eyepiece and disc image from focal length, you'd miss the CME here regardless of the blocking filter. But at lower mag you would have seen it completely. Just stressing, you don't need a huge blocking filter even for this, you just need to move the event to center of your FOV and/or use lower magnification to see such a HUGE event that is over 25% of the solar diameter or more.

 

solar_cme_today.jpg

 

Very best,


Edited by MalVeauX, 12 February 2024 - 10:14 AM.

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#13 Skywatchr

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Posted 12 February 2024 - 09:07 AM

If the disc image is 3.8mm on this instrument and you have a 6mm blocking filter, how much distance will a prom be for a 1.1mm advantage (half of the 2.2mm difference from 6mm up from the disc image size, if the disc image is centered). That's quite a large distance out from the disc's limb. Going to something larger diameter that shows even more than 25% of a solar diameter would require the prom to be so far away from the disc that you wouldn't see it because it would have already dissipated. Lift off and floating proms are right at the immediate disc limb. I would agree with what you're saying if the disc image was 5mm and the blocking filter was 6mm, but 3.8mm to 6mm allows a huge distance out from the disc limb to still see anything on-band. Going to a 12mm wouldn't help this, it's already plenty, on this system. The 12mm or larger would matter on something with a much longer focal length (over 1000mm) for this purpose (or again for use with binos).

 

Very best,

Yes, for this particular instrument a B1200 is too big.  I have seen some animations that seem to have "enough" space around the disc, but also had proms lift off and go out of the FOV still glowing. How far is anybody's guess before cooling.  I do not remember the particulars though as far as what instruments were used at those times.

Your advice is always sound Marty. waytogo.gif


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#14 rigel123

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Posted 12 February 2024 - 09:49 PM



Yes, for this particular instrument a B1200 is too big.  I have seen some animations that seem to have "enough" space around the disc, but also had proms lift off and go out of the FOV still glowing. How far is anybody's guess before cooling.  I do not remember the particulars though as far as what instruments were used at those times.

Your advice is always sound Marty. waytogo.gif

This was the furthest out I caught of a prom lifting off the sun and have the BF1200 simply because when I bought my 60mm Lunt in 2012 that was recommended by them for imaging.  This one was WAY out there!  Back in 2015

 

IMG_0109.jpeg

 

The actual lift off (link to Astrobin)

get.jpg?insecure


Edited by rigel123, 12 February 2024 - 09:52 PM.

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#15 Skywatchr

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Posted 12 February 2024 - 10:29 PM

This was the furthest out I caught of a prom lifting off the sun and have the BF1200 simply because when I bought my 60mm Lunt in 2012 that was recommended by them for imaging.  This one was WAY out there!  Back in 2015

 

attachicon.gif IMG_0109.jpeg

 

The actual lift off (link to Astrobin)

get.jpg?insecure

There it is! bow.gif  That's awesome Warren!


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#16 rigel123

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Posted 12 February 2024 - 11:15 PM

There it is! bow.gif  That's awesome Warren!

I still wonder how much further I might have been able to track that one.  I haven’t seen a prom to match the size of that one since.


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