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Solar Scope for Full-frame Coverage

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#1 mmalik

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Posted 08 September 2020 - 01:50 AM

I don't see much in terms of solar imaging and especially none in terms of full-fame (35mm) setups. I would like to have this discussion in the context of Lunt scopes and what kind of setup (scope/filter) would be suitable for such an adaptation.

 

Question: When it comes to solar (dedicated) scopes, I guess diagonal is referred to as the (solar) blocking filter? If this is the case, then I think all solar (dedicated scope) imaging would have to happen via the (solar) diagonal or the blocker? Corrections/elaborations welcome.

 

Note: Primarily, I am NOT referring to regular or modular scopes that get adapted to solar. Although I would like to discuss those as well, first I would like we get the (solar) dedicated scopes out of the way.

 

Let's start off by looking at as well as qualifying Lunt 50mm (dedicated) solar telescope with B600 blocking filter; my understanding is this particular setup would 'not' be full-frame/2" compatible? Also I am curious to know about the back-focus on such a scope whether or not it will be able to reach focus?

 

If Lunt 50mm may not be capable of native full-frame/2" adaption, then what would be the best starting size (or FL) in Lunt scope & blocker (diagonal) that will allow such an adaptation and be able to reach focus. Regards


Edited by mmalik, 08 September 2020 - 02:07 AM.


#2 nicknacknock

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Posted 08 September 2020 - 02:02 AM

For solar imaging, it depends on you intend to do.

 

For example, I use the Lunt 60 which is f8.33 and has a focal length of 500mm - it gives me a full solar disk with the ASI78 that has a pixel size of 2.4 micron pixels.

 

"Full frame" does not come into equation for solar imaging because:

 

1. You need to use the fastest frame rate possible

2. You will use ROI to actually limit the FOV and increase frame size

3. You will typically match the scope to the appropriate camera sensor (sampling, sensor size, pixel size) and appropriate barlow depending on what you are imaging (full Solar disk or parts of Sol) and you may need different sensors to have appropriate sampling

4. Said sensor to be mono as solar imaging is very unforgiving and you need max sensitivity and speed

 

Solar scopes are typically defined for imaging by the Blocking filter diameter. The B600, provides only 6mm diameter. My Lunt comes with the B1200. if money is no problem, there are bigger blocking filters as well!

 

The Lunt 50mm comes with a helical non-rotating focuser. That focuser is atrocious for imaging by the way. There are aftermarket focusers, the Starlight and Moonlite 1.25" focusers. The range of focusing is pretty narrow and could possibly influence what you want to do.

 

I hope the above helps a bit in terms of providing perspective.


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#3 nicknacknock

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Posted 08 September 2020 - 02:21 AM

Some more details more pertinent to your questions:

 

Solar scopes use Etalons to allow only Ha wavelength to pass and then a blocking filter at the back to block any unwanted stuff (people like their eyeballs and their camera sensors not crispy fried!). You need to use both to have a complete system in place, so you need to mount the camera at the back of the blocking filter.

 

Both the Etalon system and Blocking filter are essential to have and work as one unit to successfully and safely see or image the sun.

 

Modified solar scopes and discussion of such modified solar scopes are not a topic permitted on CN, for the safety of members who may attempt to do something and end up with adverse results (bodily injury, destruction of equipment).

 

Due to your background, you are referring to DSLR cameras. I understand the curiosity, but solar is a different ballgame because:

 

1. You have to content with thermals from the ground as you set up

2. You have to content with seeing conditions within the atmosphere

3. Other atmospheric pollution (like for example where I am, we have dust from the desert)

 

Solar imaging is full disk at a specific focal length and / or concentrating on particular features (e.g. proms on the solar limb or sunspots). I prefer full disk myself so i chose the appropriate scope and camera combo based on budget and desired outcome. Plus I matched this combo to the SkyWatcher SolarQuest mount to get the job done a bit faster. 



#4 nicknacknock

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Posted 08 September 2020 - 02:30 AM

If Lunt 50mm may not be capable of native full-frame/2" adaption, then what would be the best starting size (or FL) in Lunt scope & blocker (diagonal) that will allow such an adaptation and be able to reach focus. Regards

Lunt 60mm and larger, come with 2" focusers so you can use a DSLR, which I assume is your intent. And you can get a different blocking filter, a straight through for example, at a larger clear aperture. Like this one (you can change the top to 2" if you wish, although it has a T2 top) if you wish or this one which is straight through filter and should mostly illuminate a full frame DSLR.


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#5 mmalik

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Posted 08 September 2020 - 02:31 AM

Thanks; I am asking the question primarily in the context of full solar disk covering the full-frame MILC or DSLR sensor naively (i.e., without added focal reduction or extension). Regards



#6 nicknacknock

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Posted 08 September 2020 - 02:37 AM

Then the only option would be the B3400 which has 34mm diameter. You can add that to any solar scope which has a 2" visual back. Copying from Lunt website:

 

"The B3400 Blocking Filter is recommended for telescopes with focal lengths of 3400 mm when used visually, and 1800 mm when used for imaging applications.

The 34 mm blocking filter is housed in a 2″ straight-through housing."

 

Cost is $1,798.00 though. Plus you will need the solar scope itself with the Etalons, or by separate Etalons to mount (gets VERY expensive to get separate Etalons) on another scope via appropriate adapters. This is not a DIY solution with any tweaking. Any scope can do for this, but preferably something f7-ish and slower. Both front Etalon and blocking filter need to be mounted in this configuration, like any other Ha configuration.

 

There are some pre-owned configurations by the way here.



#7 mmalik

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Posted 08 September 2020 - 02:41 AM

For example, I use the Lunt 60 which is f8.33 and has a focal length of 500mm - it gives me a full solar disk

Can you post a pic of your setup; is your blocker diagonal or straight kind? Have you done full-frame MILC/DSLR imaging with your setup? Thanks for all the info. Regards

 

 

Edit: I presume yours is NOT straight through then...


Edited by mmalik, 08 September 2020 - 02:44 AM.


#8 nicknacknock

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Posted 08 September 2020 - 02:48 AM

Lunt LS60 tilt tuned single-stack (I'll start Ha imaging again when temps drop and I will use a double stack module), with 2" Moonlite Focuser and Pegasus Cube for focusing, B1200 blocking filter, Tele Vue Sol Searcher, ASI178MM, connected to laptop running Firecapture for aquisition, IMPPG for initial stretching and deconvolution and finally Photoshop. Mount is SkyWatcher SolarQuest on SW pier and SW tripod (comes as a set).

 

I couldn't be more pleased with this setup and plan to run it for many years to come. The Etalon on this one is particularly good (this ain't my first solar scope) and the views, especially with Binoviewers will knock your socks off!

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#9 nicknacknock

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Posted 08 September 2020 - 02:49 AM

I only use the ASI178MM for my purposes, no DSLR.



#10 futuneral

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Posted 08 September 2020 - 02:50 AM

I was just looking at these so here are direct answers to your question in the original post:

 

This scope produces sun's image smaller than 4mm, so it won't illuminate a full frame sensor.

 

The back focus is minuscule on the LS50THa. You won't be able to reach focus with a DSLR using the standard package. With focuser fully racked in, you get like 20mm above the diagonal (with the eyepiece holder removed).


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#11 nicknacknock

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Posted 08 September 2020 - 02:53 AM

This scope produces sun's image smaller than 4mm, so it won't illuminate a full frame sensor.

Agreed - the only benefit to a larger Blocking filter is to have more real estate space when you increase focal length. For the 50mm, there is no need for another Blocking filter. Usually the B600 is recommended for imaging so that you have some space on the side for proms and framing.



#12 nicknacknock

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Posted 08 September 2020 - 02:54 AM

I'll move this to Solar Observing and Imaging so that it gets better exposure there and where solar crazies like us reside :)



#13 mmalik

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Posted 08 September 2020 - 02:55 AM

I only use the ASI178MM for my purposes, no DSLR.

To confirm your setup is 1.25" then (instead of 2"), correct? Looks great. Regards



#14 mmalik

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Posted 08 September 2020 - 02:59 AM

I'll move this to Solar Observing and Imaging so that it gets better exposure there and where solar crazies like us reside smile.gif

Sure; will keep asking questions as I get started on this endeavor. Thanks for your prompt support. Regards


Edited by mmalik, 08 September 2020 - 02:59 AM.

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#15 nicknacknock

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Posted 08 September 2020 - 02:59 AM

Yes, since I have no need for 2" or T2, I changed the top of the diagonal to a Baader t2 to 1.25" adapter. Forgot to mention, there is a Daystar tilt device in there to avoid Newton rings :)

 

But, if you do want to mount a DSLR, with the stock visual back, you only need a Nikon / Canon T2 adapter and you can screw the camera directly to the diagonal. Or just add a 1.25" to t2 adapter so that you can "slot" the camera as a 1.25" accessory and rotate it as you please.



#16 nicknacknock

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Posted 08 September 2020 - 03:02 AM

Or you can add a T2 to 2" adapter or Baader Clicklock adapter. This or this :) - and go straight from T2 to 2". And here is a low profile one.


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#17 mmalik

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Posted 08 September 2020 - 03:05 AM

What's the total weight of your setup as pictured? If you know. Regards


Edited by mmalik, 08 September 2020 - 03:07 AM.


#18 nicknacknock

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Posted 08 September 2020 - 03:08 AM

I have no idea, but everything excluding the scope fits into a soft padded bag (including a Celestron Lithium PowerTank) that's 800mm long - this one. Scope happily resides in this one.

 

It's fairly light, the heaviest component being the scope, considering it sports a heavy duty focuser and also a Focus Cube...



#19 noisejammer

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Posted 08 September 2020 - 05:16 AM

Like Nick, I use a 60mm dedicated solar scope. I was thus intrigued when a gent brought his 6" Lunt to Starfest. (I think this was ~2016.) It ran rings around my 60mm. :lol:

 

Going through it's specs - f/6 being the critical one - the Solar disc will project as 8.2 mm in diameter. It was quite bright so a 2x Barlow could easily be used leaving you with a ~16.5 mm disc. Even this would fit onto an APS-C frame, so I don't understand the desire to use a full frame DSLR.

 

More importantly, hydrogen-alpha light is at 628.28 nm and the filters will limit the bandwidth to 0.04 nm. Thus the light is extremely monochromatic. A DSLR has relatively few red-sensitive pixels (one in four and these are insensitive to h-alpha), the pixels are quite large leading to poor angular resolution and the frame rate is typically quite low.

 

Imaging the sun with a DSLR is thus not a particularly good way to do things, but if you're determined, the big Lunt scope could scratch that itch.


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#20 mmalik

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Posted 08 September 2020 - 08:07 AM

More importantly, hydrogen-alpha light is at 628.28 nm and the filters will limit the bandwidth to 0.04 nm. Thus the light is extremely monochromatic. A DSLR has relatively few red-sensitive pixels (one in four and these are insensitive to h-alpha), the pixels are quite large leading to poor angular resolution and the frame rate is typically quite low.

I think you are thinking of stock DSLR/MILC; I am going to use astro modified MILC, quite sensitive to h-alpha.

 

 

Frame rate; have you looked at a newer MILC lately? They can do 240 fps. Things are changing fast. Cooling is another factor. I mostly used cooled MILC and that's much reduced noise.

 

I don't want to necessarily fill the full-frame sensor with solar disc, just want to use MILC for more optimal size of the solar disc on full-frame sensor. Regards



#21 mmalik

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Posted 08 September 2020 - 08:21 AM

I have no idea...

My intention asking that (wight) question and considering 50mm dedicated was to possibly put it on SkyGuider Pro. 50mm comes with Feather Tough focuser while 60mm would need to be upgraded. My point being if I am limited to 1.25" setup (instead of 2") with 60mm and am NOT able to go straight through at 60mm, then why not go to a dedicated 50mm? 50mm feather touch comes with B600 blocking filter. I think 60mm with Feather Touch will be too much for SkyGuider Pro whose pay load capacity is 5Kg. 50mm with Feather Touch is 4Kg, and will be around 5Kg with camera and all else. Your thoughts. Regards


Edited by mmalik, 08 September 2020 - 09:49 AM.


#22 noisejammer

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Posted 08 September 2020 - 08:28 AM

I think you are thinking of stock DSLR/MILC; I am going to use astro modified MILC, quite sensitive to h-alpha.

 

 

Frame rate; have you looked at a newer MILC lately? They can do 240 fps. Things are changing fast. Cooling is another factor. I mostly used cooled MILC and that's much reduced noise.

 

I don't want to necessarily fill the full-frame sensor with solar disc, just want to use MILC for more optimal size of the solar disc on full-frame sensor. Regards

Yep, I'm familiar with a lot of modern camera tech. :) Having an h-alpha modified camera will not remove the resolution limit because only one pixel in four is going to work. The others may have some sensitivity owing to Bayer filter leakage but this is likely to be quite noisy in comparison to the (modified) red channel. You may be able to partially recover the resolution if you split the channels and process them separately.

 

There's no need for cooling - the sun is bright enough and atmospheric turbulence requires high frame rates == short exposures. There's no time for noise to accumulate on a photo detector. It is worthwhile that you mount a sunshade to keep your camera out of direct sunlight.

 

On the image scale - a 1000mm (40") focal length produces a solar disc of 9.0 mm (11/32"). This should help you select a useful focal length.


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#23 nicknacknock

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Posted 08 September 2020 - 08:32 AM

mmalik,

 

With a 50mm solar scope, you get a full disk with a small chip, so using a DSLR or MILC is an overkill - if it makes you happy though smile.gif

 

Cooling is wholly unnecessary for Solar Ha imaging due to very short exposures. I typically take 1,000 frames in a few seconds and that's just about it. So, you can save funds by using a non-cooled version.

 

As for the MILC, really, the size of Sol is the sole determinant and that is related to focal length and unless you go for ultra long focal length and a massive Blocking Filter AND want  a massive full disk image, I hardly see the point shrug.gif

 

Also, since DSLR / MILC cameras are not monochrome, filtration alone does not restore sensitivity of the camera. There's only one in four pixels that is truly sensitive so you lose data. Still, it doesn't mean it will not work, but perhaps sub-optimal.



#24 nicknacknock

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Posted 08 September 2020 - 08:33 AM

And I see noisejammer chimed in with some similar points while I was typing my response.

 

I would say, de gustibus non est disputandum! Give it a try and let us know!



#25 mmalik

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Posted 08 September 2020 - 09:35 AM

With a 50mm solar scope, you get a full disk with a small chip, so using a DSLR or MILC is an overkill

I understand but my goals are bit varied; I am coming up with somewhat of a universal setup, where you can do all of the following from same underlying (mount/camera) infrastructure, but without making much compromises, at least not in imaging quality as you may have surmised in my quest for Lunt solar dedicated setup. Latest MILC camera enhancements are partially the driving force. And avoiding tiny chips is part of the goal behind multi-purposing.

 

 

Note: Scopes of course will be varied and dedicated to DSO, Solar or Visual

 

 

1. Solar imaging

 

2. DSO imaging

 

3. Solar observing

 

4. Visual astronomy

 

5. Possible EAA

 

6. Etc.

 

 

Most of the goals have been achieved; solar is the last one. Will elaborate in coming posts; it is quite interesting. Regards


Edited by mmalik, 08 September 2020 - 09:55 AM.



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