Summer with the Colour Deep-Sky Mintron

Colour Deep-Sky Mintron imaging

The MTV-73S85HP-EX-SW-R colour deep-sky Mintron was used at the Prime focus of an f/4.8 10 inch Newtonian to image M57 and M13 and with a 0.5 focal reducer for M51.

The Video was recorded to DVD including dark-frame video and then played back through a capture card and recorded by GStar as an AVI capturing a frame every 5.5s. The dark frame was scaled and used in Registax to correct the registered and stacked frames:

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The Ring Nebula M57

At the prime (Newtonian) focus

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The Whirlpool galaxy M51

With a 0.5 focal reducer

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M13

At the prime (Newtonian) focus

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Using a Mintron with a scope on an Altazimuth mount

De-rotating a set of Mintron images

A problem with using altazimuth mounts for imaging is that long exposures result in image rotation.

This demonstration was done with a DVD recording of M42 using an 80mm f/5 achromat refractor and an MTV-73S85HP-EX-SW-R colour deep-sky Mintron mounted on a Merlin altazimuth driven mount. Images were captured and combined so that in the resulting stacked image there was no rotation within the image. This was done by experiment and then 4 such stacked images were captured in succession. Although there was no rotation within each stacked image, the images were not derived from many integrated frames. When the 4 images were themselves stacked in Registax, the resulting image showed considerable image rotation.

Image Rotation when simply stacked in Registax

The stars have trailed out into little arcs.

Deep Sky Stacker

However, the freeware software Deep Sky Stacker will de-rotate the images with respect to each other before they are stacked. This was done with the same 4 images and the resulting stacked image showed no rotation, the detail was not motion blurred and the image had a higher signal to noise ratio.

Image produced by Deep Sky Stacker

Deep Sky Stacker does not have the sophisticated wavelet processing posessed by Registax but the de-rotation of images with respect to each other before they are stacked gives more power to an altazimuth mount as an imaging tool in combination with a Mintron or other camera.

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Scaling Mintron darkframes

Capturing an AVI of M101 with GStar
GStar is a freeware AVI capture program written by Steve Massey.

The virtue of this program when capturing AVIs from a frame-integrating camera is that it can be set to capture a frame after a set number of seconds and to concatonate the frames thus captured into an AVI file. As with HandyAVI, this allows the integrated frames to be captured without duplication. Both of these programs work with Windows Vista.

I had captured Video of M101 to DVD with a MTV-23S85HC-EX-R monochrome deep-sky Mintron, at High Quality as in the previous post.
Here I used GStar to capture 200 frames from the DVD recording and store them as an AVI.

GStar capture screen

The characteristic Amp Glow can be seen to the left and top of the image.

I also had captured Dark-frame video to DVD and I used GStar to capture 50 integrated dark-frames to AVI. I stacked the 50 frames in Registax 5 and the result is a dark -frame in which the amp glow is clearly seen as well as vertical banding.

Dark-Frame produced by Registax

If the image AVI is stacked in Registax without using dark-frame correction, the resulting image shows the amp-glow and the vertical banding artifacts

Stacked image data with no dark-frame correction

However, if the dark-frame generated by stacking the dark-frame data is used as the dark-frame in Registax, the correction can be seen to be over compensated and where the amp-glow showed, now that part of the image is too dark. This is because the 256 frame integrating Mintron camera still auto compensates when the scope is covered to produce dark-frame data even if the AGC is set to OFF.

Stacked image using the raw dark-frame

The solution is to scale the dark-frame so that it compensates exactly the correct amount.

This can be done easily if the capturing and registering is being done on the fly in AstroVideo. However, a different approach is needed if other software is used for capture. The scaling must be done by trial and error although it doesn't take long to get the correct degree of scaling.

The dark-frame must be scaled down before it is used in Registax. If it is scaled by the right amount, the resulting image will be properly corrected.

Image resulting from using a dark-frame scaled to 0.56 of its original value.

Scaling a dark-frame using Arithmetic in Paintshop Pro

In this example, the dark-frame is added to itself and then divided by 3. The resulting image is 0.666 of the brightness of the original dark-frame.

The table below shows a simple scheme starting with a dark-frame for generating variously scaled darkframes. This table can easily be extended to produce various levels of scaling:

Table for generating scaled dark-frames using Image Arithmetic

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Mintron imaging with a 10" F/4.8 Newtonian

A Mintron MTV-23S85HC-EX-R monochrome deep-sky frame-integrating camera was used with an Opticstar 0.5 focal reducer and a light-pollution filter at the Newtonian focus of a 10 inch Orion Newtonian reflector. The real-time video was recorded in high quality to DVD. Later the DVD was played back through a capture card and AstroVideo was used with an XP computer to capture 180 frames with a frame captured every 5 seconds with scaled, dark-frame subtraction, registering and summing on the fly. The darkframe was the sum with fixed alignment of 20 frames captured from DVD recorded with the scope covered. The frame was scaled to 0.03 of the summed image rather than the 0.05 as would be expected if the camera did not auto adjust when covered.
M101


I shall experiment with HandyAvi on a Vista computer to capture frames, and dark-frame scaling in other applications before the frames are stacked in Registax.

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Capturing images from a Mintron under Windows Vista

The AVI capture software HandyAvi is ideal for capturing integrated frames from a Mintron under Windows Vista. This is a low cost, high quality piece of software that does not do the on-the-fly integration into 32 bit deep fits files that AstroVideo does, but it does produce AVIs that either it can stack, or Registax can stack.
HandyAvi can be obtained from http://www.azcendant.com/download.htm
It comes with a 170 page manual available in PDF format or readable online at:
http://www.azcendant.com/ViewManual.htm

Screenshot from HandyAvi

Six frames were captured at 5 second intervals: the interval between image updates on maximum, 256 frame integration. HandyAvi can be set to capture at fractions of a second as well so for example, frames could be captured at 2.5 second intervals if required. Play the movie below and note that the second hand of the clock jumps round at 5 second intervals.

I use a KWorld DVD Maker USB 2.0 capture card to capture data from the Mintron to a laptop computer as discussed in an earlier post.

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A Mintron, a C6 and focal reduction

A MTV-23S85HC-EX-R monochrome deep-sky Mintron was used with a C6 Schmidt Cassegrain fitted with a 6.3 Celestron focal reducer and field flattener. The Mintron was also fitted with an Opticstar 0.5 focal reducer on the standard C/CS adapter as well as a Skywatcher light-pollution filter. I could not bring this assembly to focus. However, if I used a half-length adapter, the focal reduction was not so high but The camera could be brought to focus. This was the configuration used to obtain this image of M51. 100 x 256-frame integrated frames were captured, registered and summed in Astrovideo. The resulting FITs file was processed in the Gimp and finished in Neat Image.


The Next two images were obtained using just the 6.3 focal reducer/field flattener.
This image of M57 is the sum of 95 x 256-frame integrated frames.


This image of M13 is the sum of 80 x 256-frame integrated frames

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Focal reduction and image scale with a Mintron

The standard C/CS 1.25" adapter is about 28mm long. A focal reducer lens will attach to the end of this tube and change the F/ratio of the system, producing an optically faster system with a smaller image scale and wider field of view. I have produced 1.25" adapters of various lengths to demonstrate that different image scales (via different F/ratios) are produced with different length adapters. This is important for some telescopes that are unable to focus in enough when a focal reduced lens is used with a normal length adapter.

Focal Reducer Lens

Mintrons fitted with a 12mm or a 28mm adapter, a focal reducer lens and a light pollution filter.

The MTV-23S85HC-EX-R monochrome deep-sky Mintron was used with an f/10, 6" Schmidt Cassegrain telescope.

M3 with the 0.5 focal reducer and a 28mm adapter

M3 with the 0.5 focal reducer and a 20mm adapter

M3 with the 0.5 focal reducer and a 12mm adapter

The differences in image scale can be seen in these images and can be comparted with the image below produced with no focal reducer.

M3 with no focal reducer




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A Mintron or an eyepiece ?

If it is visible in the eyepiece, a Mintron camera will produce an image on a TV screen that you will be able to share with others in real time. No waiting in line to peer into the eyepiece. Point at the image on the screen and discuss the structure of the object you are viewing. If you record the video on VCR or DVD you can revisit your observing session on a rainy night. This is an ideal setup for schools, societies, star-parties and public demonstrations as well as individual observing. It is a great way to share the 'eyepiece'.




This is a photograph taken of a CRT TV monitor screen to show what the real time view of M13 was like using a MTV-23S85HC-EX-R monochrome deep-sky Mintron, an Opticstar 0.5 focal reducer lens, a Skywatcher light-pollution filter and a 6 inch Schmidt Cassegrain f/10 telescope. I set up a compact digital camera on a tripod, pointed it at the screen, zoomed in to make the image larger, set a time delay before the shutter fired and pressed the button.




The Video was recorded in HQ onto DVD. 100 x 256-frame integrated frames were captured from DVD, registered and summed on the fly with AstroVideo using dark-frame subtraction to produce this image.









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Versatile Mintrons

The MTV-23S85HC-EX-R monochrome deep-sky Mintron is good for observing the Sun with a solar telescope such as the PST used here with a 3x Barlow. Registax was used to register and stack frames captured into AVIs for the prominences and disk separately. Andrew Sprott's Solar Layers program was used to combine the final prominence and disk images.

M13 taken with the MTV-23S85HC-EX-R monochrome deep-sky Mintron. A 6 inch f/10 Schmidt Cassegrain was used with an Opticstar 0.5 focal reducer and captured with Astrovideo using scaled dark-frame subtraction.

An MTV-73S85HP-EX-SW-R colour deep-sky Mintron was used with a 3x Barlow. Registax was used to stack and register the frames captured into AVIs.

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The MTV-73S85HP-EX-SW-R colour deep-sky Mintron Video camera for Lunar imaging

The MTV-73S85HP-EX-SW-R colour deep-sky Mintron is a good lunar and planetary imager for observing or imaging showing the versatility of the camera.

April 4th 2009 an f/10 6" Schmidt Cassegrain was used with the Deep-sky colour Mintron.
The principal settings were: integration was turned of, AGC was on, AWB was used and a
shutter speed selected to give the best exposure.

Clavius and Tycho region at the prime focus.


Crater Clavius with a x2 Barlow.


Crater Copernicus with a x2 Barlow


The region of craters Arzachel, Alphonsus and Ptolomaeus at the prime focus.


The apennine mountains at Prime focus.


Crater Plato at Prime focus

AVIs were processed in Registax.



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MTV-73S85HP-EX-SW-R colour deep-sky Mintron with a Skymax 127 Maksutov

With a Skymax 127 Maksutov Cassegrain telescope and a 0.5 focal reducer, this image of The trapezium region of the Orion nebula was obtained. Astrovideo was used to sum 50 integrated frames and dark-frame correction was used.

With a x3 Televue Barlow and the frame integration turned off, Saturn was imaged and captured to DVD. Then 5000 frame AVI was captured from the DVD playback and was used to synthsise the above Image.

With a x3 Barlow and a x1.6 focal extender lens captured a larger image of Saturn, showing the versatility of this camera.

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