15 replies to this topic

[RickV]

What's the best camera for my H-Alpha Telescope?  I try to provide some guidance here.

 

Let's look at some familiar H-alpha telescopes and available 2018 astro-cameras.

 

With the ZWO ASI178MM and my 350mm focal length Lunt LS50, the diameter of the sun with some space around it is about 1660 pixels... 1660 x 2.4µm = 4.0mm.  e.g.  Solar diameter at 350mm = 4.0mm.  Using this basic information, one can make a table of focal length versus solar diameter on the sensor.

 

Focal length (mm)  Solar Diameter (mm) on Sensor

  50                         0.57

  75                         0.86

100                         1.14

150                         1.17

200                         2.29

250                         2.86

300                         3.43

350                         4.0

400                         4.57

450                         5.14

500                         5.71

600                         6.86

700                         8.0

800                         9.14

900                       10.29

1000                     11.43

1100                     12.57

1200                     13.71

1500                     17.14

One can use this table to determine if a full solar disc will fit on any given sensor.

 

One can take this a step further to determine the suitability of a camera to work with an etalon on a given H-Alpha telescope.

 

IMAGE RESOLUTION

Image resolution depends upon the diameter of the Airy disc.

 

The Diameter of the Airy disc = 2.44 x wavelength x f#, where f# is called the f-number.
f# = focal length of the telescope / aperture of the telescope

The smaller the Airy disc, the smaller the details that can be resolved by the telescope,
Resolution is inversely proportional to the size of the Airy disc; high resolution requires a small Airy disc.

A small Airy disc means a small f#.  A small f# means a large aperture and/or short focal length.

 

To resolve (reasonably image) the Airy disc, how many pixels are needed across the diameter of the Airy disc?

The answer is that at least 4.5 pixels are needed across the diameter of the Airy disc.

 

Diameter of the Airy disc = 2.44 x wavelength x f#
For teal-green light of wavelength 0.527 microns, we calculate...
Diameter of the Airy disc = 2.44 x 0.527 microns x f# = 1.2859 microns x f#
Placing 4.5 pixels across the diameter of the Airy disc corresponds to a pixel size of
(1.2859 microns x f#) / 4.5 or f# / 3.5.
For good resolution in white light, the Maximum Pixel Size = f# / 3.5

 

However, here one is concerned with Hydrogen Alpha imaging.
For Ha wavelength of 6562.8 Angstroms (0.65628 microns), we calculate...
Diameter of the Airy disc = 2.44 x wavelengh x f#    
Diameter of the Airy disc = 2.44 x 0.65628um x f# = 1.601 x f#
Placing 4.5 pixels across the diameter of the Airy disc corresponds to a pixel size of
(1.601 microns x f#) / 4.5 or f# / 2.8.
For good resolution in H-Alpha light, the Maximum Pixel Size = f# / 2.8.

 

 

Some H-Alpha examples...

NOTE: Similar calculations could be performed for white light telescopes - use Maximum Pixel Size = f# / 3.5.

 

Given the available (2018) H-Alpha telescopes, what cameras are best suited to capture a full solar disc?

 

1. What's the best camera for a Coronado PST?
PST: 400mm focal length, 40mm objective lens, f/10.
Maximum Pixel Size = f# / 2.8 = 10 / 2.8 = 3.57µm.

 

ZWO ASI174  (1936x1216 pixels @ 5.86µm)
No, the large 5.86µm pixels are too big (>3.57µm required for good resolution).

 

ZWO ASI178  (3096 x 2080 pixels @ 2.4µm)
The small 2.4µm pixels would be OK (less than 3.57µm) but over-samples the image.
According to the table, at 400mm focal length, the solar disc would be 4.57mm in diameter.  This requires 4.57mm / 2.4µm = 1904 pixels.
Do we have that?  Yes, the ZWO ASI178 has 2080 pixels on the vertical.

 

ZWO ASI290  (1936x1096 @ 2.9µm)
The 2.9 µm would be OK (less than 3.57µm) but over-samples the image.
At 400mm focal length, the solar disc would be 4.57mm in diameter.  This requires 4.57mm / 2.9µm = 1576 pixels.
Do we have that?  No, the ZWO ASI290 has only 1096 pixels on the vertical.

 

ZWO ASI120 (1280 x 960 @ 3.5µm)
The 3.5µm pixels are an excellent match to the ideal 3.57µm pixel size.
At 400mm focal length, the solar disc would be 4.57mm in diameter.  This requires 4.57mm / 3.5µm = 1306 pixels.
Do we have that?  No, the ZWO ASI120 has only 960 pixels on the vertical.

 

ZWO ASI1600 Mono (4656 x 3520 @ 3.8µm)
The 3.8µm pixels are larger than the ideal 3.57µm pixel size.
At 400mm focal length, the solar disc would be 4.57mm in diameter.  This requires 4.57mm / 3.8µm = 1203 pixels.
Do we have that?  Yes, the ZWO ASI1600 has 3520 pixels on the vertical.

 

ZWO ASI183 (5496 x 3672 pixels @ 2.4 µm)
The 2.4 µm would be OK (less than 3.57µm) but over-samples the image.
At 400mm focal length, the solar disc would be 4.57mm in diameter.  This requires 4.57mm / 2.4µm = 1904 pixels.
Do we have that?  Yes, the ASI183 has 3672 pixels on the vertical.

 

Celestron NexImage Burst Monochrome  (1280 x 960 @  3.75µm)
The 3.75µm pixels are larger than the ideal 3.57µm but might be OK.
At 400mm focal length, the solar disc would be 4.57mm in diameter.  This requires 4.57mm / 3.75µm = 1219 pixels.
Do we have that?  No, the camera has only 960 pixels on the vertical.

 

Celestron Skyris 236M  (1920 x 1200 @ 2.8µm)
The 2.8 µm would be OK (less than 3.57µm) but over-samples the image.
At 400mm focal length, the solar disc would be 4.57mm in diameter.  This requires 4.57mm / 2.8µm = 1632 pixels.
Do we have that?  No, the Skyris 236M has only 1200 pixels on the vertical.

 

Mallincam SSIc  (1270 x 1030 @ 3.63µm)
The 3.63µm pixels are just over the size limit of 3.57µm but would likely be OK.
At 400mm focal length, the solar disc would be 4.57mm in diameter.  This requires 4.57mm / 3.63µm = 1259 pixels.
Do we have that?  No, the Mallincam SSIc has only 1030 pixels on the vertical.

 

For the Coronado PST to image a full solar disc, suitable cameras appear to be the low cost ZWO ASI178 or higher cost ZWO ASI1600 and the ZWO ASI183.

 

2. What's the best camera for a Lunt LS50?
Lunt LS50: 350mm focal length, 50mm objective lens, f/7.
Maximum Pixel Size = f# / 2.8 = 7 / 2.8 = 2.5µm.

 

ZWO ASI174  (1936x1216 pixels @ 5.86µm)
No, the large 5.86µm pixels are too big (>2.5µm) required for good resolution.

 

ZWO ASI178  (3096 x 2080 pixels @ 2.4µm)
The 2.4µm pixels would be excellent, a good match to the ideal 2.5µm.
At 350mm focal length, the solar disc would be 4.0mm in diameter.  This requires 4.0mm / 2.4µm = 1667 pixels.
Do we have that?  Yes, the ASI178 has 2080 pixels on the vertical.

 

ZWO ASI290  (1936x1096 @ 2.9µm)
The 2.9 µm pixels would be oversize (>2.5µm required for good resolution).
At 350mm focal length, the solar disc would be 4.0mm in diameter.  This requires 4.0mm / 2.9µm = 1380 pixels.
Do we have that?  No, the ASI178 has only 1096 pixels on the vertical.

 

ZWO ASI120 (1280 x 960 @ 3.5µm)
The 3.5 µm pixels would be too large (>2.5µm required for good resolution).

 

ZWO ASI1600 Mono (4656 x 3520 @ 3.8µm)
The 3.8µm pixels are too large (>2.5µm required for good resolution).

 

ZWO ASI183 (5496 x 3672 pixels @ 2.4 µm)
The 2.4µm pixels would be excellent, a good match to the ideal 2.5µm.
At 350mm focal length, the solar disc would be 4.0mm in diameter.  This requires 4.0mm / 2.4µm = 1667 pixels.
Do we have that?  Yes, the ASI183 has 3672 pixels on the vertical.

 

Celestron NexImage Burst Monochrome  (1280 x 960 @  3.75µm)
The 3.75µm pixels are far larger than the ideal 2.5µm.

 

Celestron Skyris 236M?  (1920 x 1200 @ 2.8µm)
The 2.8 µm pixels would be oversize (>2.5µm required for good resolution).
At 350mm focal length, the solar disc would be 4.0mm in diameter.  This requires 4.0mm / 2.8µm = 1429 pixels.
Do we have that?  No, the Skyris 236M has only 1200 pixels on the vertical.

 

Mallincam SSIc?  (1270 x 1030 @ 3.63µm)
The 3.63µm pixels are far larger than the size limit of 2.5µm,

 

For the Lunt LS50 to image a full solar disc, suitable cameras appears to be the low cost ZWO ASI178 or the higher cost ZWO ASI183.

 

3. What's the best camera for a Lunt LS60?
Lunt LS60: 500mm focal length, 60mm objective lens, f/8.3.
Maximum Pixel Size = f# / 2.8 = 8.3 / 2.8 = 3.0µm.

 

ZWO ASI174  (1936x1216 pixels @ 5.86µm)
No, the large 5.86µm pixels are too big (>3.0µm required for good resolution).

 

ZWO ASI178  (3096 x 2080 pixels @ 2.4µm)
The 2.4µm pixels would be over sampling.
At 500mm focal length, the solar disc would be 5.71mm in diameter.  This requires 5.71mm / 2.4µm = 2327 pixels.
Do we have that?  No, the ASI178 has only 2080 pixels on the vertical.

 

ZWO ASI290  (1936x1096 @ 2.9µm)
The 2.9 µm pixels would be an excellent match to the required 3.0µm.
At 500mm focal length, the solar disc would be 5.71mm in diameter.  This requires 5.71mm / 2.9µm = 1969 pixels.
Do we have that?  No, the ASI290 has only 1096 pixels on the vertical.

 

ZWO ASI120 (1280 x 960 @ 3.5µm)
The 3.5 µm pixels are oversize (>3.0µm required for good resolution).
At 500mm focal length, the solar disc would be 5.71mm in diameter.  This requires 5.71mm / 3.5µm = 1631 pixels.
Do we have that?  No, the ASI120 has only 960 pixels on the vertical.

 

ZWO ASI1600 Mono (4656 x 3520 @ 3.8µm)
The 3.8µm pixels are too large (>3.0µm required for good resolution).

 

ZWO ASI183 (5496 x 3672 pixels @ 2.4 µm)
The 2.4µm pixels would be over sampling (ideal is 3.0µm).
At 500mm focal length, the solar disc would be 5.71mm in diameter.  This requires 5.71mm / 2.4µm = 2327 pixels.
Do we have that?  Yes, the ASI183 has 3672 pixels on the vertical.

 

Celestron NexImage Burst Monochrome  (1280 x 960 @  3.75µm)
The 3.75µm pixels are larger than the ideal 3.0µm.

 

Celestron Skyris 236M  (1920 x 1200 @ 2.8µm)
The 2.8 µm pixels would be close to the ideal 3.0µm required for good resolution.
At 500mm focal length, the solar disc would be 5.71mm in diameter.  This requires 5.71m / 2.8µm = 2039 pixels.
Do we have that?  No, the Skyris 236M has only 1200 pixels on the vertical.

 

Mallincam SSIc  (1270 x 1030 @ 3.63µm)
The 3.63µm pixels are larger than the size limit of 3.0µm,

 

For the Lunt LS60 to image a full solar disc, the only suitable camera appears to be the ZWO ASI183.

 

4. What's the best camera for a Coronado 60?
Coronado 60: 400mm focal length, 60mm objective lens, f/6.7.
Maximum Pixel Size = f# / 2.8 = 6.7 / 2.8 = 2.4µm.

 

ZWO ASI174  (1936x1216 pixels @ 5.86µm)
No, the large 5.86µm pixels are too big (>2.4µm required for good resolution).

 

ZWO ASI178  (3096 x 2080 pixels @ 2.4µm)
The 2.4µm pixels would an excellent match to the 2.4µm required for good resolution.
At 400mm focal length, the solar disc would be 4.57mm in diameter.  This requires 4.57mm / 2.4µm = 1904 pixels.
Do we have that?  Yes, the ZWO ASI178 has 2080 pixels on the vertical.

 

ZWO ASI290  (1936x1096 @ 2.9µm)
The 2.9 µm pixels are larger than the maximum size of 2.4µm.
At 400mm focal length, the solar disc would be 4.57mm in diameter.  This requires 4.57mm / 2.9µm = 1576 pixels.
Do we have that?  No, the ASI178 has only 1096 pixels on the vertical.

 

ZWO ASI120 (1280 x 960 @ 3.5µm)
The 3.5 µm pixels are too large (>2.4µm required for good resolution).

 

ZWO ASI1600 Mono (4656 x 3520 @ 3.8µm)
The 3.8µm pixels are too large (>3.0µm required for good resolution).

 

ZWO ASI183 (5496 x 3672 pixels @ 2.4 µm)
The 2.4µm pixels would be an excellent match to the ideal 2.4µm.
At 500mm focal length, the solar disc would be 5.71mm in diameter.  This requires 5.71mm / 2.4µm = 2327 pixels.
Do we have that?  Yes, the ASI183 has 3672 pixels on the vertical.

 

Celestron NexImage Burst Monochrome  (1280 x 960 @  3.75µm)
The 3.75µm pixels are larger than the ideal 2.4µm.

 

Celestron Skyris 236M  (1920 x 1200 @ 2.8µm)
The 2.8 µm pixels are larger than the maximum size of 2.4µm.
At 400mm focal length, the solar disc would be 4.57mm in diameter.  This requires 4.57m / 2.8µm = 1632 pixels.
Do we have that?  No, the Skyris 236M has only 1200 pixels on the vertical.

 

Mallincam SSIc?  (1270 x 1030 @ 3.63µm)
The 3.63µm pixels are larger than the size limit of 2.4µm.

 

For the Coronado 60 to image a full solar disc, suitable cameras appear to be the ZWO ASI178 or the ZWO ASI183.

 

5. What's the best camera for a Quark?
A Quark operates at at about f30.
Maximum Pixel Size = f# / 2.8 = 30 / 2.8 = 10.7µm

 

If one does not want to image a full solar disk, any of the above cameras will work but the ASI187 with 5.86µm pixels would be the closest match.  However, many of the cameras can be binned 2x2, 3x3 or 4x4 to achieve a larger pixel size and may be a better match.

 

ASI174 (1936x1216 pixels of 5.86µm)
- binned 2x2 becomes 968x606 pixels of 11.7µm.

 

ASI178 (3096 x 2080 pixels of 2.4µm):
- binned 2x2 becomes 1548 x 1040 pixels of 4.8µm, or
- binned 3x3 becomes 1032 x   693 pixels of 7.2µm, or
- binned 4x4 becomes   774 x   520 pixels of 9.6µm

 

ASI290 (1936x1096 @ 2.9µm)
- binned 2x2 becomes 968 x 548 pixels of 5.8µm, or
- binned 3x3 becomes 645 x 365 pixels of 8.7µm, or
- binned 4x4 becomes 484 x 274 pixels of 11.6µm

 

ZWO ASI120 (1280 x 960 @ 3.5µm)
- binned 2x2 becomes 640 x 480 pixels of 7.0µm, or
- binned 3x3 becomes 427 x 320 pixels of 10.5µm

 

ZWO ASI1600 Mono (4656 x 3520 @ 3.8µm)
- binned 2x2 becomes 2328 x 1760 pixels of 7.6µm, or
- binned 3x3 becomes 1552 x 1173 pixels of 11.4µm

 

ZWO ASI183 (5496 x 3672 pixels @ 2.4 µm)
- binned 2x2 becomes 2748 x 1836 pixels of 4.8µm, or
- binned 3x3 becomes 1832 x 1224 pixels of 7.2µm, or
- binned 4x4 becomes 1374 x   918 pixels of 9.6µm

 

Celestron NexImage Burst Monochrome (1280 x 960 @  3.75µm)
- binned 2x2 becomes 640 x 480 pixels of 7.5µm, or
- binned 3x3 becomes 427 x 320 pixels of 11.35µm

 

Celestron Skyris 236M (1920 x 1200 @ 2.8µm)
- binned 2x2 becomes 960 x 600 pixels of 5.6µm, or
- binned 3x3 becomes 640 x 400 pixels of 8.4µm, or
- binned 4x4 becomes 480 x 300 pixels of 11.2µm

 

Mallincam SSIc  (1270 x 1030 @ 3.63µm)
- binned 2x2 becomes 635 x 515 pixels of 7.26µm, or
- binned 3x3 becomes 423 x 343 pixels of 10.89µm

 

ASI183 (5496 x 3672 pixels @ 2.4µm)
- binned 2x2 becomes 2748 x 1836 pixels of 4.8µm, or
- binned 3x3 becomes 1832 x 1224 pixels of 7.2µm, or
- binned 4x4 becomes 1374 x   918 pixels of 9.6µm

 

Suppose one wants to image the full solar disc with a Quark; is that possible?  Yes, it is.
The original Quark has an internal 4.2X Barlow.  The Quark operates best at about f30.
Without additional optical devices, Maximum Pixel Size = f# / 2.8 = 30 / 2.8 = 10.7µm

 

Suppose one couples the Quark to a 100mm focal length photography lens with the iris set to f8.
From the table, at 100mm the solar disk image is 1.14mm in diameter.  Coming out of the Quark, the system is now a 4.2 x 100mm = 420mm H-Alpha telescope of f# = 4.2 x 8 = f33.6.  The diameter of the solar disc on the sensor is 4.2 x 1.14mm = 4.8mm.  Many of the above cameras, with binning, may be suitable.

 

It is also possible to place a focal reducer after the Quark.  For example, one could use a 200 mm focal length photography lens with the iris set to f8.  Coming out of the Quark, the system is a 840mm H-Alpha telescope of aperture f33.6.  The diameter of the in focus solar disc is 4.2 x 2.29 mm = 9.6mm.  Place a 0.5X focal reducer between the Quark and the camera and the system becomes a 420mm H-Alpha telescope of f# = f16.8.  The diameter of the solar disc on the sensor is 0.5 x 9.6mm = 4.8mm.  Here the Maximum Pixel Size = f# / 2.8 = 16.8 / 2.8 = 6.0µm.   Many of the above cameras may be suitable, with or without binning.

 

I hope this article may assist you in choosing the best camera for your H-Alpha Telescope.

 

V/R
Rick

[Tanglebones]

Thank you, Rick - very timely, as you know.  Let me digest this...

 

- Stu

[lorenzo italy]

Hi Rick,
the data you have collected is very interesting.
I have my doubt,
I have a Lunt60mm and the ZWO ASI178MM, and I can shoot a complete sun disk with just one shot.
And in fact I bought this camera because I knew I could do this.

I'm not questioning your calculations, but I think it's useful to inform about who wants to take this cmos camera.

 

Using an online tool,

http://www.agopax.it...rogramma.htm#p6
if I use the dimensions in mm of the sensor (7.4mmx5mm) the result is a framed field of 48'x34 'at 500mm focal length, therefore the Sun is taken up in its entirety, having on average a diameter of 30 '(as happens in reality).

 

If I do the calculation using the size and the pixel number of the sensor (3096x2080 pixels at 2.4 μm) the result gives me a field of 42.6 'x 28.6', so in this case the whole Sun does not fit.  

It's a mistery.....

 

Fortunately, to calculate the field I have always used the measurement in mm of the sensor, as is the case with reflex photography.
This avoids the problem of the number of pixels and their dimensions, but the calculations are based simply on the size of the subject on the focal plane and if the sensor is large enough to capture the whole field.

 

Lorenzo

Edited by lorenzo italy, 29 April 2018 - 02:35 AM.

[Great Attractor]

Note that pixel size larger than the “sampling optimum” is not much of a problem; you just use an appropriate Barlow lens (little to no loss of quality). The other way around is more problematic; e.g. a small pixel camera (like 3-3.75 µm) with a Quark and f/8 refractor, which gives massive oversampling. Using cheap 0.5x focal reducers may cause loss of sharpness in the outer FOV or uneven illumination.

[johnpd]

Hi Rick,

 

  I commented on your post about a month ago on this subject. I have an 80mm refractor with an 480mm F/L, thus technically @ f/6. However I forgot to realize that my H-a filter is only 60mm which I assume would make my actual F# @ f/8. This would make my optimum sensor pixel size about 2.9. Is this correct?

 

JohnD

[rigel123]

Of course there are trade-offs in any situation.  To get the full disk on my Lunt 60mm using the recommendation I would use the ZWO ASI183, however at the resolution to get the full disk I only get a frame rate of 19fps.  At the full resolution on my Skyris 236M I get 54fps but need to do a 2 panel mosaic to get the entire disk.  Really not a big deal and I can always opt to use my ScopeStuff .5 reducer if I simply want a shot that shows the entire disk and good enough to display here.   To get higher frame rate on the ZWO I would need to reduce the ROI and then the full disk would not fit the frame anymore.  Not that you couldn’t get a decent shot at 19fps but not ideal.  And the $300 difference in cost between the cameras has to be a consideration.

 

Thinking even deeper, to grab say a video of 500 frames I would need to capture for 26 seconds with the ZWO and only 9 seconds with my Skyris so less time for features to change and much larger files to deal with using the ZWO.

 

I'm not arguing Rick’s math, just exploring other considerations one may need to know when looking for a camera, there are always trade-offs!  If you are willing to work with trade-offs you can end up with decent shots with most of the cameras out there, which is pretty evident when you see the shots we all post with quite the variety of equipment!  The one constant is, if you want high resolution, close-up shots of small features on the sun, be prepared to spend a boatload of $$$$$😉. (Of course a boatload to me might be a dinghy and to someone else a yacht!)

Edited by rigel123, 29 April 2018 - 08:29 AM.

[MalVeauX]

Just to add to the discussion, as this thread is really more specific to sampling, than the overall camera, there's more to "best" camera when imaging than simply matching pixel size to focal-ratio and wavelength. Sampling is important, very important, to high resolution imaging and the calculations here are a good measure to help direct towards the right pixel size on a sensor. But, it's not absolute, it really is best to match the pixel size as calculated when possible, or undersample as the compromise so the above tables help you figure out the size pixels to use to match or go bigger with nicely. But there's more to layer into the selection criteria, so here's a few more things that are relevant to the discussion.

 

FPS matters a lot. I'd rather have 60~100 FPS and decent seeing, compared to having an optimal sampling match. If I had to compromise on the camera's pixel size, I'd rather have larger pixels to under sample than small pixels to over sample. Undersampled results will handle poor seeing better than oversampled results. All of it is a factor of blur. But I'd rather capture more data with lucky imaging and undersample. For a full disc, this is not nearly as important because of scale; features do not change at that scale very quickly. But in high resolution, this matters greatly, limited by seeing and also because features change very quickly and it is noticeable which will have features unable to properly align and contribute to dropped frames from the stack exclusion and/or poor alignment and increased blur. This is why we don't image a solar feature in high res for 2 minutes straight and get 10,000 frames. We image short bursts, a few seconds.

 

Binning is not something I would rely on either, as what you gain from it is created from loss. The last thing I want to lose when imaging at high resolution, is resolution, if I can match scale and seeing supports the resolution. The type of binning matters too, software versus hardware, etc.

 

Field of view is the other major consideration. Many combinations cannot achieve a full disc with these inexpensive small sensor cameras (ZWO's and the clones). There are a lot of other cameras out there not being discussed here with larger sensors and different pixel sizes. If your goal is full disc FOV, it's a major consideration to have to look at what will work with one's particular focal length scope to achieve that, especially without a focal reducer if possible (changing sampling). If your goal is only high resolution, then this is less of an issue, and it's more important to have good seeing, good sampling (or undersampling if compromising) and high FPS. For a full disc imaging setup, a larger sensor with a wider FOV, slower FPS, and under/oversampling is less of a problem (though way oversampling is still the worst of the three options if you want fine detail), and even color sensor is ok, and also less issues with seeing conditions.

 

Sensitivity can matter a lot too, depending on the equipment. Imaging with a double stack through something F20~F30 for example is going to be a lot more difficult to achieve good stackable images in high resolution from, if the camera is not very sensitive. Most of these cameras are plenty sensitive for the job, but it's still a big part of the overall concept of the camera selection. It's not uncommon for me to be over gain 300+ doing solar in high resolution when imaging between 393nm and 540nm ranges.

 

How you process and your tools for processing matters a lot too. Gathering the data is one thing, but producing an image, be it an academically accurate image, or just a pretty picture, from that data takes work and interpretation. But if you consider the impacts in processing if your image is severely over-sampled and has too much noise, it will impact sharpening methods immediately and force you to work at a smaller scale, or much lower resolution. There are many more things that processing impacts can be involved with, but that's one of the big ones, especially at high resolution. But this is also part of camera selection because how you process reflects the kind of data you generate, and that data comes from the camera at the end of the day.

 

Very best,

Edited by MalVeauX, 29 April 2018 - 11:57 AM.

[MalVeauX]

The one constant is, if you want high resolution, close-up shots of small features on the sun, be prepared to spend a boatload of $$$$$. (Of course a boatload to me might be a dinghy and to someone else a yacht!)

You can image in high resolution for less than the cost of a mid-tier dedicated solar scope that is only 80~90mm, which isn't even really all that high of resolution (its great mind, but high res imagers are doing it at 5", 6", 8", 11", etc). $3k will get you there easily and reliably, the real limiting factor is simply seeing.

 

A basic GEM mount will run you $600~1200 that will do the job with a large instrument near 20lbs (AVX, HEQ5, iOptron 25, etc).

A 5 to 6 inch achromatic refractor can be had for $200~600 pretty commonly (so many options out there). Add another $200 for an improved focuser.

A Quark will run you $850~1000. You don't need an ERF up to 150mm. No additional blocking filter. Just a $50~100 UV/IR cut filter.

And a cheap ASI174MM will run you $400~600.

$3k or so will get you there (all inclusive). If you already have a mount and camera, you can do it for $1500.

 

Alternatively, the next cheapest way to real high resolution is with an SCT C8 telescope (200mm F10) ($450 all day long around here), with a full aperture D-ERF ($1200~1500), PST etalon ($400ish all day long), and a decent Coronado blocking filter, say a 15mm, around $600ish. Then add the camera and you're set. Around $4~5k total if you add a camera & mount to match. If you already have a camera and mount, you could make this happen for $3k.

 

I agree, it is a lot of money for someone who's struggling with the idea of buying a telescope in general. But for someone who's already imaging, and simply wants to get into high resolution solar imaging, it's quite affordable from the perspective of imaging in general. We don't need costly Taks and monster aperture instruments. We can do it, really well, with common cheap small achromats and small SCT's that are commonly available. The only real cost is the etalon and the DERF (if applicable).

 

It's cheaper than a high resolution DSO platform. And cheaper than a high resolution planetary platform. And you get to do it any time the clouds are hiding, and it's different every day, and it's not seasonal.

 

Very best,

Edited by MalVeauX, 29 April 2018 - 10:02 AM.

[RickV]

OK Marty, you sold me; where do I sign up?

[RickV]

Hi Rick,

 

  I commented on your post about a month ago on this subject. I have an 80mm refractor with an 480mm F/L, thus technically @ f/6. However I forgot to realize that my H-a filter is only 60mm which I assume would make my actual F# @ f/8. This would make my optimum sensor pixel size about 2.9. Is this correct?

 

JohnD

Hi John,

If you have a front mounted 60mm etalon on an 80mm objective lens, then the aperture is really 60mm.  Since no lenses were changed the focal length remains at 480mm.  Then, as you say, the f# = focal length / objective size = 480mm / 60mm = 8.

For H-alpha, Maximum Pixel Size = f# / 2.8 = 8 / 2.8 = 2.9

John, you mathematical skills are spot on!

[twjs]

What's the best camera for my H-Alpha Telescope?  I try to provide some guidance here.

 

Let's look at some familiar H-alpha telescopes and available 2018 astro-cameras.

 

With the ZWO ASI178MM and my 350mm focal length Lunt LS50, the diameter of the sun with some space around it is about 1660 pixels... 1660 x 2.4µm = 4.0mm.  e.g.  Solar diameter at 350mm = 4.0mm.  Using this basic information, one can make a table of focal length versus solar diameter on the sensor.

 

Focal length (mm)  Solar Diameter (mm) on Sensor

  50                         0.57

  75                         0.86

100                         1.14

150                         1.17

200                         2.29

250                         2.86

300                         3.43

350                         4.0

400                         4.57

450                         5.14

500                         5.71

600                         6.86

700                         8.0

800                         9.14

900                       10.29

1000                     11.43

1100                     12.57

1200                     13.71

1500                     17.14

One can use this table to determine if a full solar disc will fit on any given sensor.

 

One can take this a step further to determine the suitability of a camera to work with an etalon on a given H-Alpha telescope.

 

IMAGE RESOLUTION

Image resolution depends upon the diameter of the Airy disc.

Airy Disk.jpg

 

The Diameter of the Airy disc = 2.44 x wavelength x f#, where f# is called the f-number.
f# = focal length of the telescope / aperture of the telescope

The smaller the Airy disc, the smaller the details that can be resolved by the telescope,
Resolution is inversely proportional to the size of the Airy disc; high resolution requires a small Airy disc.

A small Airy disc means a small f#.  A small f# means a large aperture and/or short focal length.

 

To resolve (reasonably image) the Airy disc, how many pixels are needed across the diameter of the Airy disc?

The answer is that at least 4.5 pixels are needed across the diameter of the Airy disc.

 

Diameter of the Airy disc = 2.44 x wavelength x f#
For teal-green light of wavelength 0.527 microns, we calculate...
Diameter of the Airy disc = 2.44 x 0.527 microns x f# = 1.2859 microns x f#
Placing 4.5 pixels across the diameter of the Airy disc corresponds to a pixel size of
(1.2859 microns x f#) / 4.5 or f# / 3.5.
For good resolution in white light, the Maximum Pixel Size = f# / 3.5

 

However, here one is concerned with Hydrogen Alpha imaging.
For Ha wavelength of 6562.8 Angstroms (0.65628 microns), we calculate...
Diameter of the Airy disc = 2.44 x wavelengh x f#    
Diameter of the Airy disc = 2.44 x 0.65628um x f# = 1.601 x f#
Placing 4.5 pixels across the diameter of the Airy disc corresponds to a pixel size of
(1.601 microns x f#) / 4.5 or f# / 2.8.
For good resolution in H-Alpha light, the Maximum Pixel Size = f# / 2.8.

 

 

Some H-Alpha examples...

NOTE: Similar calculations could be performed for white light telescopes - use Maximum Pixel Size = f# / 3.5.

 

Given the available (2018) H-Alpha telescopes, what cameras are best suited to capture a full solar disc?

 

 

.

 

2. What's the best camera for a Lunt LS50?
Lunt LS50: 350mm focal length, 50mm objective lens, f/7.
Maximum Pixel Size = f# / 2.8 = 7 / 2.8 = 2.5µm.

 

ZWO ASI174  (1936x1216 pixels @ 5.86µm)
No, the large 5.86µm pixels are too big (>2.5µm) required for good resolution.

 

ZWO ASI178  (3096 x 2080 pixels @ 2.4µm)
The 2.4µm pixels would be excellent, a good match to the ideal 2.5µm.
At 350mm focal length, the solar disc would be 4.0mm in diameter.  This requires 4.0mm / 2.4µm = 1667 pixels.
Do we have that?  Yes, the ASI178 has 2080 pixels on the vertical.

 

ZWO ASI290  (1936x1096 @ 2.9µm)
The 2.9 µm pixels would be oversize (>2.5µm required for good resolution).
At 350mm focal length, the solar disc would be 4.0mm in diameter.  This requires 4.0mm / 2.9µm = 1380 pixels.
Do we have that?  No, the ASI178 has only 1096 pixels on the vertical.

 

ZWO ASI120 (1280 x 960 @ 3.5µm)
The 3.5 µm pixels would be too large (>2.5µm required for good resolution).

 

ZWO ASI1600 Mono (4656 x 3520 @ 3.8µm)
The 3.8µm pixels are too large (>2.5µm required for good resolution).

 

ZWO ASI183 (5496 x 3672 pixels @ 2.4 µm)
The 2.4µm pixels would be excellent, a good match to the ideal 2.5µm.
At 350mm focal length, the solar disc would be 4.0mm in diameter.  This requires 4.0mm / 2.4µm = 1667 pixels.
Do we have that?  Yes, the ASI183 has 3672 pixels on the vertical.

 

Celestron NexImage Burst Monochrome  (1280 x 960 @  3.75µm)
The 3.75µm pixels are far larger than the ideal 2.5µm.

 

Celestron Skyris 236M?  (1920 x 1200 @ 2.8µm)
The 2.8 µm pixels would be oversize (>2.5µm required for good resolution).
At 350mm focal length, the solar disc would be 4.0mm in diameter.  This requires 4.0mm / 2.8µm = 1429 pixels.
Do we have that?  No, the Skyris 236M has only 1200 pixels on the vertical.

 

Mallincam SSIc?  (1270 x 1030 @ 3.63µm)
The 3.63µm pixels are far larger than the size limit of 2.5µm,

 

For the Lunt LS50 to image a full solar disc, suitable cameras appears to be the low cost ZWO ASI178 or the higher cost ZWO ASI183.

 

3. What's the best camera for a Lunt LS60?
Lunt LS60: 500mm focal length, 60mm objective lens, f/8.3.
Maximum Pixel Size = f# / 2.8 = 8.3 / 2.8 = 3.0µm.

 

ZWO ASI174  (1936x1216 pixels @ 5.86µm)
No, the large 5.86µm pixels are too big (>3.0µm required for good resolution).

 

ZWO ASI178  (3096 x 2080 pixels @ 2.4µm)
The 2.4µm pixels would be over sampling.
At 500mm focal length, the solar disc would be 5.71mm in diameter.  This requires 5.71mm / 2.4µm = 2327 pixels.
Do we have that?  No, the ASI178 has only 2080 pixels on the vertical.

 

ZWO ASI290  (1936x1096 @ 2.9µm)
The 2.9 µm pixels would be an excellent match to the required 3.0µm.
At 500mm focal length, the solar disc would be 5.71mm in diameter.  This requires 5.71mm / 2.9µm = 1969 pixels.
Do we have that?  No, the ASI290 has only 1096 pixels on the vertical.

 

ZWO ASI120 (1280 x 960 @ 3.5µm)
The 3.5 µm pixels are oversize (>3.0µm required for good resolution).
At 500mm focal length, the solar disc would be 5.71mm in diameter.  This requires 5.71mm / 3.5µm = 1631 pixels.
Do we have that?  No, the ASI120 has only 960 pixels on the vertical.

 

ZWO ASI1600 Mono (4656 x 3520 @ 3.8µm)
The 3.8µm pixels are too large (>3.0µm required for good resolution).

 

ZWO ASI183 (5496 x 3672 pixels @ 2.4 µm)
The 2.4µm pixels would be over sampling (ideal is 3.0µm).
At 500mm focal length, the solar disc would be 5.71mm in diameter.  This requires 5.71mm / 2.4µm = 2327 pixels.
Do we have that?  Yes, the ASI183 has 3672 pixels on the vertical.

 

Celestron NexImage Burst Monochrome  (1280 x 960 @  3.75µm)
The 3.75µm pixels are larger than the ideal 3.0µm.

 

Celestron Skyris 236M  (1920 x 1200 @ 2.8µm)
The 2.8 µm pixels would be close to the ideal 3.0µm required for good resolution.
At 500mm focal length, the solar disc would be 5.71mm in diameter.  This requires 5.71m / 2.8µm = 2039 pixels.
Do we have that?  No, the Skyris 236M has only 1200 pixels on the vertical.

 

Mallincam SSIc  (1270 x 1030 @ 3.63µm)
The 3.63µm pixels are larger than the size limit of 3.0µm,

 

For the Lunt LS60 to image a full solar disc, the only suitable camera appears to be the ZWO ASI183.

 

 

 

ASI174 (1936x1216 pixels of 5.86µm)
- binned 2x2 becomes 968x606 pixels of 11.7µm.

 

ASI178 (3096 x 2080 pixels of 2.4µm):
- binned 2x2 becomes 1548 x 1040 pixels of 4.8µm, or
- binned 3x3 becomes 1032 x   693 pixels of 7.2µm, or
- binned 4x4 becomes   774 x   520 pixels of 9.6µm

 

ASI290 (1936x1096 @ 2.9µm)
- binned 2x2 becomes 968 x 548 pixels of 5.8µm, or
- binned 3x3 becomes 645 x 365 pixels of 8.7µm, or
- binned 4x4 becomes 484 x 274 pixels of 11.6µm

 

ZWO ASI120 (1280 x 960 @ 3.5µm)
- binned 2x2 becomes 640 x 480 pixels of 7.0µm, or
- binned 3x3 becomes 427 x 320 pixels of 10.5µm

 

ZWO ASI1600 Mono (4656 x 3520 @ 3.8µm)
- binned 2x2 becomes 2328 x 1760 pixels of 7.6µm, or
- binned 3x3 becomes 1552 x 1173 pixels of 11.4µm

 

ZWO ASI183 (5496 x 3672 pixels @ 2.4 µm)
- binned 2x2 becomes 2748 x 1836 pixels of 4.8µm, or
- binned 3x3 becomes 1832 x 1224 pixels of 7.2µm, or
- binned 4x4 becomes 1374 x   918 pixels of 9.6µm

 

Celestron NexImage Burst Monochrome (1280 x 960 @  3.75µm)
- binned 2x2 becomes 640 x 480 pixels of 7.5µm, or
- binned 3x3 becomes 427 x 320 pixels of 11.35µm

 

Celestron Skyris 236M (1920 x 1200 @ 2.8µm)
- binned 2x2 becomes 960 x 600 pixels of 5.6µm, or
- binned 3x3 becomes 640 x 400 pixels of 8.4µm, or
- binned 4x4 becomes 480 x 300 pixels of 11.2µm

 

Mallincam SSIc  (1270 x 1030 @ 3.63µm)
- binned 2x2 becomes 635 x 515 pixels of 7.26µm, or
- binned 3x3 becomes 423 x 343 pixels of 10.89µm

 

ASI183 (5496 x 3672 pixels @ 2.4µm)
- binned 2x2 becomes 2748 x 1836 pixels of 4.8µm, or
- binned 3x3 becomes 1832 x 1224 pixels of 7.2µm, or
- binned 4x4 becomes 1374 x   918 pixels of 9.6µm

 

 

Rick

The LS80 has  a FL of 560 mm and an image size of 5.6 mm, so at f7 we get 7/2.8 = 2.5. So the -178 or the -183 would work?

Edited by twjs, 26 October 2019 - 06:29 PM.

[RickV]

Lunt describes the LS80 as 80mm aperture at f/7; that makes the focal length 80 x 7 mm = 560mm.

Maximum pixel size of Ha would be f/7 / 2.8 = 2.5 microns.

The 2.4 micron pixels of the 178 or 183 are 2.4 microns - a good match.

 

Can it do a full solar disc?

A focal length of 560mm would produce a solar image diameter of 6.4mm.

 

Let's try the ZWO ASI178  camera with (3096 x 2080 pixels @ 2.4µm)

Pixels needed = 6.4mm / 2.4 microns = 2,667 pixels

We have that horizontally (3096) but not vertically (2080).

 

On the other hand, the ZWO ASI183 (5496 x 3672 pixels @ 2.4 µm) has enough pixels both horizontally and vertically.

 

Best,

Rick

[twjs]

one more question, color or mono? Mono is $$$$ color is $$$

 

many thanks

Edited by twjs, 26 October 2019 - 08:29 PM.

[BYoesle]

Mono definitely - gives you 3 x more sensitivity and twice the resolution.

 

[RickV]

Hi twjs,

 

There are other options available to you at low cost... tweaking your LS80.

 

Your LS80 is 80mm in aperture, f/7 with a focal length of 560mm.  You could modify that a mite to work with the ASI178MM.

 

The ASI178MM has 3096 x 2080 pixels @ 2.4µm

You would like the image of the sun to fit within a circle of 2080 pixels of size 2.4µm.  i.e. 2080 x 2.4µm = 5.0mm

Recall from the chart that a focal length of 350mm gave a solar disc size of 4.0mm.

We want a solar disc size of about 5mm or 25% bigger than 4mm.  This means a focal length of 25% larger than 350mm or 350 x 1.25 = ~437mm.  Thus we would need to reduce your focal length from 560mm to about 437mm.  437/560 = 0.78x

You'd need a focal reducer of 0.78x.  What's available are focal reducers of 0.7x and 0.63x (for SCTs).

 

Suppose you used a 0.7x focal reducer.  You scope would now have a new focal length of 0.7 x 560mm = 392mm and a new f# of f/7 x 0.7x = f/5.  To get the f# back to the original f/7, you would need to reduce the aperture from 80mm to 392/7 = 56mm.  You could do that with anything from a cardboard annulus ring to a stack of photographic step up/down rings placed in front of your objective lens.

 

You end up with a 56mm, f/7 of focal length 392mm that can easily capture full solar disc images with the ASI178MM camera.  The only caveat will be... does the LS80 have enough inward focus to work with a 0.7x focal reducer?

 

Best,

Rick

[dhkaiser]

At the risk of raising an old thread I must note that in fact the sun does fit in the image of my LS60 and ASI178.

 

 

 

3. What's the best camera for a Lunt LS60?
Lunt LS60: 500mm focal length, 60mm objective lens, f/8.3.
Maximum Pixel Size = f# / 2.8 = 8.3 / 2.8 = 3.0µm.

 

 

ZWO ASI178  (3096 x 2080 pixels @ 2.4µm)
The 2.4µm pixels would be over sampling.
At 500mm focal length, the solar disc would be 5.71mm in diameter.  This requires 5.71mm / 2.4µm = 2327 pixels.
Do we have that?  No, the ASI178 has only 2080 pixels on the vertical.