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Lymax SCT Cooler
Submitted: Friday, 13th January 2006 by Paul Haese

I have owned the Lymax SCT cooler for nearly a month now and thought it prudent to review this piece of equipment. I purchased it for a little over $200 including postage from OPT in the US.

What is it?

The Lymax SCT cooler is as the name suggests designed to cool the tube and mirror of a Schmidt Cassegrain Optical assembly. SCT’s are known as closed systems. That is, the OTA is completely enclosed with a corrector plate at the front, an aluminium tube and the mirror assembly at the back. There is only one opening to the scope and that is at the rear of the scope. As a result of this design bringing the mirror and assembly to ambient temperature is nearly impossible during a nights viewing. Some pundits suggest that ambient temperature can be reached within 3 hours. However I think that six hours is closer to the mark. Tube currents during this time will badly affect imaging attempts and deceive the owner into thinking that the seeing is not good. So with this sort of design a rapid cooling system is almost a must for hi resolution photography and viewing. This is where the Lymax SCT cooler comes into play.

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Lymax SCT Cooler

The design is fairly simple: a 1” tube with four angled holes at one end and a fan assembly at the other. See image below. The fan contains a replaceable Dacron filter, which prevents dust from entering the OTA. It is powered by a 2 meter long lead, which has a male cigarette lighter plug. This lead can be plugged into a 12v power source. The tube inserts into the rear of the scope and slides all the way up the baffle until it just protrudes into open space. The design of the angled holes forces air back across and down onto the mirror. This air then is forced out of the tube and the mirror cools at a rapid rate.

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Filter

Thoughts on its use

I have to say that using this tool comes with a fair amount of trepidation. The idea of inserting something that is blowing air onto the mirror that cannot be cleaned easily and may void your warrantee is somewhat daunting. The filter prevents dust from entering the tube and can be seen in between the vanes of the fan. See image to the right.

However large the risk of dust is, the potential benefits of the coolers use is that the scope will attain peak performance long before astronomical twilight is over. This means you can get to that planet that is just transiting within the hour of set-up. It also gives the scope a fighting chance to keep pace with the change in ambient temperature all night long.

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Baffle

Also of concern is when inserting the cooler for the first time, the thought that they have sent you the wrong one goes through your mind as your inserting it into the baffle. It is a good idea to get a tape measure out and do a side-by-side comparison. You don’t want to hit the secondary. That would be disastrous and quite frankly ruin the scope. When fully inserted you should see the end just poking out of the baffle. See image to the right.

Its actual use

I used the cooler within a couple of days of receiving it. I first checked to ensure that the cooler had a filter in it. Then I checked for length. Yes I had the right one. I then did an out of focus star test. See left image below. The diffraction rings were as per usual looking very poor and moving all around. A typical signature of tube currents. I then inserted the cooler and ran it for 30 minutes. I immediately took another avi of the same star and the results were immediately noticeable. See right image below.

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Before cooling

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After cooling

While not totally cooled as evidenced by the slight tube current to the lower right, it is clear that the cooler has made a huge impact on the performance of the scope. Several nights later I used the cooler again and obtained the image below.

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Mars

While not a perfect image of Mars, it is one of the smoothest that I have obtained. I put this down to the ability of the cooler to bring the scope down to ambient.

Things to Remember

I have found there are some things to remember when using the cooler:

  1. 1. Check for dust and lint on the cooler itself. Run the cooler outside of the scope for at least 2 minutes. This will get any dust out of the holes that might be hiding. Better outside than inside.
  2. Keep an eye on the filter. Ensure that it is clean, and free from build up.
  3. Make sure you store the cooler in the box it came in and the box is closed up properly. I intend to get a big resealable plastic bag for the entire box, just to keep the dust out.
  4. When using the cooler do not smoke or have any smoke anywhere near the cooler. It will draw the smoke into the scope. The smoke will damage the coatings on the mirror.
  5. Ensure that the drawtube is at close focus. If the drawtube is not in this position then the cooler will not protrude from the baffle the correct length.
  6. When you buy the cooler ensure you buy the filter spares that are optional. This will keep you going for quite some time. I figure it is at least 12 months worth of filters. You should have 5 including the spares.
  7. Use the cooler for a minimum of 30-40 minutes. And; perhaps do a top up later in the evening for another 10 minutes.
  8. When you have finished with the cooler, put it immediately into the box. This will prevent dust from falling onto it.

Final analysis

This is a great tool, well worth the money. It has made a huge difference to the preparation of my imaging efforts. If you follow the rules and precautions with its use you are sure to obtain better results than previously. Would I buy it again? Absolutely. I think all SCT owners should have one. Thankyou Lymax for this great tool.

Review by Paul Haese (rumples riot). Discuss this review at the IceInSpace Forums.

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