Tag Archives: 365Astronomy

Sharpstar 20032PNT F3.2 Paraboloid Astrograph Review

Having owned the Sharpstar 15028HNT, I decided I wanted a larger light bucket without really sacrificing on speed, so I opted for the big brother of the 15028HNT which is the SharpStar 20032PNT.

I picked up my 20032PNT from Zoltan at 365Astronomy, and could not wait to get it home and unbox it, so after removing it from not just one carboard box, but two, I was presented with a very large flight case, which evidently is a larger version than the one that came with the 15028HNT.

Once I had the scope unpacked and inspected everything, the first thing I noticed was the focuser, the 20032PNT has a large focuser, which is big enough to accomodate the reducer/corrector that has an M68 connector thread as well as an M54 and an M48 connector thread.

The scope is well built, as I would expect from the build quality of the 15028HNT, the red annodised alluminium tube rings just give that final touch of finese. The 3 inch focuser is very smooth, and will no doubt be able to handle quite a load of equipment.

The first thing I planned to do was ensure that the primary mirror was secure and did not rock back and forward as well as replace the stock fan. I have fed back to SharpStar that they should mount the fan externally and also mount it with shock absorbing rubber mounters, and have the airflow into the tube from the back, rather than drawing air down the tube from the secondary. Here are my images of the fan replacement:

Primary Mirror assembly removed from OTA
Fan assembly with mirror removed
Stock Fan

Stock fan removed and added in a PWM fan connector should the fan ever need to be replaced, it can be replaced without removing the mirror assembly
Anti vibration fan mounting points
External fan connected to PWM connector
How the fan looks from the outside, the image is missing the fan filter which I added afterwards

Once everything was back together, I mounted my Eagle4Pro onto the top bar, as well as added an extra long losmandy plate because I wanted the OTA as far forward as I could get it in order to have the camera in the right location without it hitting the mount at all.

And here is the scope on the mighty EQ8 Pro mount

My first set of image testing did not go so well. My previous 15028HNT did not protrude above the walls of the observatory, so despite the fact that the secondary mirrors on both scopes are right up at the top of the tube, the 20032PNT was picking up stray light from my neighbour, so I had to adopt a dew shield that would extend the OTA by around 5 inches:

Scope with dew shield attached

Flats
I first started to have issues with my flats that was taken with a flat panel, the flat frames would “Overcorrect” the images, but one thing I noticed that there was a lot of vignetting happening. Sky flats seemed to work better, but I was not happy with the vignetting. Now since I am using a full frame sensor on the ASI6200MM Pro, and the scope supports full frame, I was a little intrigued as to why I was getting so much vignetting, you can see from the master flat below that there was indeed a significant amount of vignetting.

Red Master Flat in PixInsight

I did some calculations and found what my problem was. Since my camera is full frame, it has a diameter of 44mm. The M54 connector on the telescope is 55mm away from the sensor, so a simple equation tells me that my light cone is larger than the M54 connector:

Sensor diameter + (distance from sensor / focal ratio)
44 + (55/3.2) =61.1875mm

The internal diameter of the M54 connector is around 51mm, so the light cone was being restricted by around 10mm. So I had a custom M68 to M54 adapter made which is 28.5mm in length, the reason for this is because the backfocus from the M68 connector is 61mm, so if we apply our formula:

44 + (61/3.2) = 63.06mm, this is way below the internal diameter of the M68 connector male thread, so vignetting should be minimised. Now because I do have some M54 in my image train, I know I would not completely elliminate vignetting and this is why, using the above formula, we can work out the light cone at varying part of the imaging train:

12.5mm (EFW mating to camera) = 47.9mm
18mm (50.4mm Filters distance from sensor) = 49.62mm
32.5mm (Light entrance to EFW distance from sensor) = 54.15mm

As you can see, I should expect some vignetting to occur because the light cone at the EFW M54 connector (with around 51mm internal) is 54.15mm, so I would be clipping the light cone slightly, but the result is as follows, again red filter, you can see that the vignetting is significantly reduced:

Collimation was done using the exact same process I used on the 15028HNT, you can read the guide here.

Conclusion:
SharpStar have again produced an outstanding quality astrograph, with a massive focuser to take on the largest of imaging trains, as well as finishing off the product with high quality annodised OTA rings. I am extremely happy with the performance of the telescope, below is my first image which happens to be a 2 panel mosaic:

Iris Nebula, 2 Panel Mosaic, Each Panel consists of 151x60S frames at Gain100, for L, R, G and B, for the full resolution image please use this link

Backfocus information:
M42 connector: 53mm
M54 connector: 55mm
M68 connector: 61mm

Focal Length (With Reducer/Corrector): 640mm
Focal Ratio: F3.2
Newtonian Type: Paraboloid
Focuser Size: 3″

The only complaint I have is with regards to the fan, which I have made a suggestion to SharpStar on that. Good job again SharpStar!

ZWO ASI6200 62mpx Full Frame Camera Review

I recently wrote a review on the ZWO ASI2400 24mpx full frame camera, so I thought I would also do the same for the big brother which is the ZWO ASI6200 full frame camera with a mammoth 62mpx which I picked up from 365astronomy when returning the ASI2400 after the review. Looking at both of the cameras, there is no obvious difference from the outside except for the model number, both cameras are exactly the same size and feel roughly the same weight and the build quality is identicallyu exceptional.

ASI6200MC Pro One Shot Colour Camera

If we compare the specifications of the ASI6200 to the ASI2400 we can see where each camera has an advantage over the other:

ASI2400ASI6200
Weight700g700g
SensorIMX410IMX455
Sensor SizeFull FrameFull Frame
Pixel Size5.94um3.76um
Resolution24mpx62mpx
Full Well Capacity at 0 Gain100ke51ke
Qe>80%91%
ADC14-Bit16-Bit
High Gain Mode140100
Full well at High Gain Mode20ke18ke

So as you can see from the comparison on specification there are some differences, the ASI2400 has the edge on full well capacity, however the ASI6200 has a much more smaller pixel size as well as a higher Qe which to me gives the ASI6200 the edge over the ASI2400.

Now since both cameras are the exact same field of view due to them both being full frame sensors, the question is how does this affect resolution, clearly the ASI6200 has the upper hand having significantly more pixels than the ASI2400, but how does this translate to an image?

Iris Nebula taken with the ASI2400MC Pro, 82x150S at Gain 26, darks, flats and BIAS frames applied
Iris Nebula taken with the ASI6200MC Pro 48x150S at Gain 100, Darks, Flats and BIAS frames applied

As you can see, both cameras offer the exact same field of view, however when you zoom in on the images you start to see where the ASI6200 excels above the ASI2400 with the higher resolution

On the left is the ASI2400MC Pro and on the right is the ASI6200MC Pro

As you can clearly see from the above two images, the 6200 offers a much better resolution which will allow a much finer level of detail, however, depending on your sky conditions and focal length the ASI6200 might not be possible due to over or under sampling

You can see here, that on my SharpStar 15028HNT which has a Focal Length of 420mm the ASI2400 would lead to Under Sampling in my “OK” seeing conditions

But the ASI6200 shows in the green area:

If I increase the focal length to around 1150 the ASI6200 no longer becomes suitable and the ASI2400 is more suited to this focal length and sky conditions:

So as you can see, both the ASI2400 and ASI6200 is not a “One Size Fits All” scenario, you have to work out the best suitability depending on your conditions and equipment to be used.

From a price perspective, the ASI6200 is only slightly more expensive than the ASI2400, but both cameras offer the full frame capability and a fantastic field of view, but for me personally the ASI6200 beats the ASI2400 when using the focal length of my SharpStar 15028HNT. Just like it’s smaller version, the looks, feels, sounds and operates exactly the same way. Here is another image taken with the ASI6200 and then my Synthetic SHO version which I will be writing a tutorial on how to acomplish with Dual Band Filters.

North America Nebula – 60x300S at Gain 100 using the Optolong L-eXtreme Filter on the SharpStar 15028HNT
Synthetic SHO using the same data as the previous image

Either way, both ZWO cameras I have tested have been of awesome quality, and I would recommend either camera if you wish to go down the full frame route, but personally my favourite is the ASI6200MC Pro, more images to come since this is now my new camera.

ZWO ASI2400MC Pro Full Frame 24mpx camera review

I was lucky enough for 365Astronomy to offer me one of the ZWO ASI2400 full frame cameras to test and write a review, so obviously I jumped at the chance, and within a couple of days I was successfully imaging and acquiring data with it, so firstly what is the ASI2400?

The ASI2400MC Pro is a full frame 24mpx camera that utilises the Sony IMX410 back illuminated sensor, ZWO produced a similar camera before which was the ASI128MC Pro (24mpx) and they also have the ASI6200 (62mpx), so what are the differences between the cameras?

ASI2400MCASI128MCASI6200MC
Image SensorIMX410IMX128IMX455
Pixel Size5.945.973.76
Full Well Capacity100ke76ke51.4ke
Cooling Delta-35C-35C-35C
Resolution6072×40426032*40329576×6388
ADC14-Bit14-Bit16-Bit
Read Noise1.1e-6.4e2.5e1.2e-3.5e
DDR Buffer256MB256MB256MB
QE >80%>53%>80%
FPS (Video)852

If we compare the ASI2400 and the ASI128 since they have similar pixel sizes and offer almost a matching resolution, but the ASI2400 clearly is a better camera, with a higher full well capacity, this means that it takes a lot more to saturate out the colours around bright stars for example, but also a big increase on the quantum efficiency going from 53% to >80%.

Now the first thing I noticed was that the ASI2400 was only slightly cheaper than the ASI6200, but the ASI6200 is offering a much higher resolution, so why would people not just go for the ASI6200? Well it comes down to pixel size, the ASI6200 has a pixel size of 3.76 so it would be better suited to a short focal length scope, if I attach the ASI6200 to my SharpStar 15028HNT which has a focal length of 420mm at F2.8, this will give me around 1.85 Arc-Seconds per Pixel which for UK skies is an ideal figure, the ASI2400 has a bit more flexibility with the focal length of telescopes because of the larger pixel size, so whilst the ASI6200 offers a higher resolution image sensor of 62mpx, the ASI2400 offers more flexibility of a higher focal length telescope.

When I unboxed the ASI2400 I was very impressed with the quality, this was the first ZWO Camera I have ever actually seen in the flesh, the red finish matches my SharpStar 15028HNT, but one thing that I noticed straight away was the two additional USB Ports on the top of the camera which I sat and thought to myself that it would certainly help with tidying up my cables around the scope. In the box was a couple of adapters to obtain the very common 55mm back focus, two USB Cables, and a USB 3.0 cable, and the camera arrived in a very nice case too.

I removed the camera sensor cover and revealed the massive full frame sensor and compared it to the APS-C sized camera I have and was like wow, that’s a big sensor, here’s a picture of the sensor:

Size matters, the Full Frame sensor on the ASI2400MC Pro

I noticed too that there was a special tilt plate on the camera which in my opinion is a critical point, my other camera has a tilt plate that is very cumbersome to use, so after a while of looking at the sensor, I decided to start adding my ZWO filter drawer and M48 extension tubes in order to get it connected to the mount, I am using the ZWO M54 2″ Filter drawer which has a 2mm M54 to M48 adapter too, threading the filter drawer on the camera was very smooth, but I would not expect anything less than that with ZWO kit connecting to ZWO kit, here’s a picture with the filter drawer and the Optolong L-Pro 2″ filter connected to the camera:

ZWO M54 Filter Drawer connected to the ASI2400MC Pro

Once connected to the telescope, I had to find out where the camera was facing when connected at the optimal distance of 55mm as all of my image train is threaded on, once identified which direction the top of the camera sensor was facing I could rotate the focuser and then re-check the collimation with the laser before putting the camera back on and connecting the cables.

Identifying which side of the camera the top of the sensor was is so easy on this camera, there’s what looks like a black plastic button on the side of the camera, it is obviously a cover of some sort, but this also indicates which side the top of sensior is located, something I wish all camera vendors would do.

One of the first things I do when testing out a new camera is dark frames, all vendors claim they have zero amp glow, so this is always my first test, and the ASI2400 didn’t let me down, indeed there was zero amp glow and I tested with various exposure times and gain settings, here’s a 300S exposure with Gain 26 which has had a Screen Transfer Function auto stretch applied:

After connecting it all up to the telescope, and acquiring some darks, flats, and BIAS frames, and the skies were clear, it was time to put the camera under a proper test, I had set a couple of targets up, the Cygnus Loop and the Elephant’s Trunk Nebula using the Optolong L-eXtreme Narrowband filter and here are the results:

Cygnus Loop – Eastern Veil, Western Veil and Pickerings Triangle – 29x300S at Gain 26, ASI2400MC Pro on the Sharpstar15028HNT using the Optolong L-eXtreme Dual Band Filter
Elephant’s Trunk Nebula – 19x300S at Gain 26, ASI 2400MC Pro on the SharpStar 15028HNT using the Optolong L-eXtreme Dual Band Filter

So you can see the camera performed really well, stars are almost perfect in the corners (a little fine tuning required on spacing), I am hoping to get a few more clear nights over the next few days to build on the above images and really show off the performance of the ASI2400, and I can’t wait to test it out on the Iris Nebula.

Conclusion:
The ASI2400 is in my opinion an awesome piece of kit, that massive full frame sensor has the adaptability for longer focal length telescopes due to the larger pixel size, the advantage of the USB Hub built into the camera, the adjustable tilt plate on the front of the camera is the most advantageous aspect, would have saved me so much time trying to rectify tilt instead using copper shims, but also the smaller things that are equally as important like having something to identify which way round the sensor is rather than trying to figure it out with images in my opinion is what sets this apart from other similar cameras from other vendors.

If you are looking for a full frame camera and have a short focal length telescope, the ASI2400 or the ASI6200 full frame cameras will do just the job,but any longer focal length scopes, then the ASI2400 is the right choice.

Additional image taken since writing this post:

M31 – Andromeda Galaxy – 51x90S frames at Gain 0 using the Optolong L-Pro Filter, darks and flats applied