A debated topic regarding the RASA 8 and the primary glass. Should the glass be removed or kept in?
We are now going to discuss this and see if it is worth removing it or keeping it.
Some pointers before going further:
We are now going to discuss this and see if it is worth removing it or keeping it.
Some pointers before going further:
- This is based on the Starizona filter drawer only!
- The filter holder, which is a separate device for the RASA requires you to remove the glass in question.
Several tests/ experiments have been completed to find out if the clear glass on the RASA is required in the back focus train when using the Starizona filter drawer. A lot of people have been debating if it should be removed or kept due to the clashing of information from Starizona and Celestron.
Celestron says to remove it, while Starizona says to keep it in.
This of course has confused people. Let’s find out if this is the case, or if it even matters.
Leaving aside all of the issues the RASA has had in the past – the requirement of the piece of glass which is no more than 1-2mm in the back focus train is a concern since the speed of the scope itself. Since it is an F2 system, the back focus is very precise and being 1-2mm out can have large effects on the picture.
Celestron says to remove it, while Starizona says to keep it in.
This of course has confused people. Let’s find out if this is the case, or if it even matters.
Leaving aside all of the issues the RASA has had in the past – the requirement of the piece of glass which is no more than 1-2mm in the back focus train is a concern since the speed of the scope itself. Since it is an F2 system, the back focus is very precise and being 1-2mm out can have large effects on the picture.
The First and second night
Since the good old British weather isn’t the most reliable for clear skies – this experiment was taken over a few weeks. The target was SH2-117 (also known as NGC 7000 and IC 5070 – North America Nebula and Pelican Nebula respectively) I aimed at these targets for several reasons. A 2-panel mosaic would show a lot of detail and I would have multiple options if it was needed to do single target comparisons. Also because this is a favourite location for me (Why not!? This is a well-known target, and the pictures are jaw-dropping)
The night was a 90% full moon which was situated on the opposite side of the sky (one of the other reasons to do a Narrowband target) and the second night, a few weeks later, was on a new moon ~1-2%.
The first night I was able to capture just over 1 hour 15 mins on each target as the night was clear all night, being springtime in the UK the nights are getting shorter, making it difficult to get a decent amount of data (not really a problem for an F2 system though). This was made worse the next time because we are getting closer to the summer solstice (the longest day of the year) each day that passes. The second night was clear till roughly 01:30 when an extremely large cloud waddled over.
By this time I knew it was time to pack up, so was packed up just before it arrived over my head, just to find out when I looked up next that the cloud dispersed, and it was clear again! By this time, the equipment was packed away in the car, and I just grumbled and drove home. The second night produced only 45 mins of data which was disappointing, but it was enough to do the comparison.
Since the good old British weather isn’t the most reliable for clear skies – this experiment was taken over a few weeks. The target was SH2-117 (also known as NGC 7000 and IC 5070 – North America Nebula and Pelican Nebula respectively) I aimed at these targets for several reasons. A 2-panel mosaic would show a lot of detail and I would have multiple options if it was needed to do single target comparisons. Also because this is a favourite location for me (Why not!? This is a well-known target, and the pictures are jaw-dropping)
The night was a 90% full moon which was situated on the opposite side of the sky (one of the other reasons to do a Narrowband target) and the second night, a few weeks later, was on a new moon ~1-2%.
The first night I was able to capture just over 1 hour 15 mins on each target as the night was clear all night, being springtime in the UK the nights are getting shorter, making it difficult to get a decent amount of data (not really a problem for an F2 system though). This was made worse the next time because we are getting closer to the summer solstice (the longest day of the year) each day that passes. The second night was clear till roughly 01:30 when an extremely large cloud waddled over.
By this time I knew it was time to pack up, so was packed up just before it arrived over my head, just to find out when I looked up next that the cloud dispersed, and it was clear again! By this time, the equipment was packed away in the car, and I just grumbled and drove home. The second night produced only 45 mins of data which was disappointing, but it was enough to do the comparison.
Processing
To make things fair, I processed both data sets equally. This had some limitations. First, some processing required independent results – BlurXTerminator is a good example – requiring star sizes to be unique to the data. Using the wrong star size would diminish the results of the data in the picture.
But stretching, curves etc. used the same processes (and stretch graphs) to try and keep them balanced. Most were like I predicted the data to be regarding results etc. but what caught me off guard was the star sizes. The sample with the optics glass installed had larger size stars (nearly double the size at 4.60 average, with the non-glass data only having 2.63).
To make things fair, I processed both data sets equally. This had some limitations. First, some processing required independent results – BlurXTerminator is a good example – requiring star sizes to be unique to the data. Using the wrong star size would diminish the results of the data in the picture.
But stretching, curves etc. used the same processes (and stretch graphs) to try and keep them balanced. Most were like I predicted the data to be regarding results etc. but what caught me off guard was the star sizes. The sample with the optics glass installed had larger size stars (nearly double the size at 4.60 average, with the non-glass data only having 2.63).
The results
The results were surprising. The expectation for them to be massively different was on the cards. But the overall result was very different to what I expected. They are quite similar regarding detail, apart from one minor thing - the data with the optical glass removed showed little to no blue (Oxygen III) data.
The details were nearly the same, the structure of the Nebula was the same, and the dust clouds between IC 5070 and NGC 7000 were the same, although the data without the optical glass did pick up more HII (red) data in the bottom corners. That doesn’t mean to say it has more HII in the regions, as other pictures will show this area in a different spectrum of light.
The difference is still very clear. The optical glass does help and is required in the optical/ back focus train. The detail in the dust lanes and structure is clearly visible. The fact Oxygen III is more predominant in the data with the Optical glass also reinforces the fact the better back focus is bringing more detail to the picture.
I was able to collect more data in one of the pictures, although I made sure they were the same number of exposures etc. but even if I did use them it would be on the data set with no optic glass. Which struggled to bring out the Oxygen III data.
Overall, the result is quite clear. Keeping the optical glass installed on your RASA 8 is recommended. And the results show this. Of course, the results, I say every time I make a video/ or write up, the results are to personal taste. The result is for your benefit primarily, and everyone else secondary. Obviously, you want people to like your picture, but the overall result of the colours etc. is personal to you. Some people may like the HII over the OIII in the picture, and that’s okay, there are methods to apply that, but I would say do it with the optical glass installed.
The results were surprising. The expectation for them to be massively different was on the cards. But the overall result was very different to what I expected. They are quite similar regarding detail, apart from one minor thing - the data with the optical glass removed showed little to no blue (Oxygen III) data.
The details were nearly the same, the structure of the Nebula was the same, and the dust clouds between IC 5070 and NGC 7000 were the same, although the data without the optical glass did pick up more HII (red) data in the bottom corners. That doesn’t mean to say it has more HII in the regions, as other pictures will show this area in a different spectrum of light.
The difference is still very clear. The optical glass does help and is required in the optical/ back focus train. The detail in the dust lanes and structure is clearly visible. The fact Oxygen III is more predominant in the data with the Optical glass also reinforces the fact the better back focus is bringing more detail to the picture.
I was able to collect more data in one of the pictures, although I made sure they were the same number of exposures etc. but even if I did use them it would be on the data set with no optic glass. Which struggled to bring out the Oxygen III data.
Overall, the result is quite clear. Keeping the optical glass installed on your RASA 8 is recommended. And the results show this. Of course, the results, I say every time I make a video/ or write up, the results are to personal taste. The result is for your benefit primarily, and everyone else secondary. Obviously, you want people to like your picture, but the overall result of the colours etc. is personal to you. Some people may like the HII over the OIII in the picture, and that’s okay, there are methods to apply that, but I would say do it with the optical glass installed.
Processed data from the data with the optical glass installed (Left-hand picture) and the data without the optical glass installed (Righthand picture). While there are minimal differences, there are key points. The lack of OIII in the Data with no optical glass, and slightly fewer details in the dark dust structures.
The differences are minimal. Which do you prefer and why?