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Insulating Maksutov's

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#1 Kevin Barker

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Posted 30 September 2022 - 12:05 AM

Wet day today in Auckland, New Zealand, And a day off work which is nice. It has been wet for several days and at least two more to come. A good day to muck around with insulation. In my case car sun shade material. 

The three are all Intes Micro 6". 7" and 8" from the 2000's. IM 603, 703 and 815. They all have nice smooth optics.

 

The insulated jackets are removeable. I used duck tape to tidy them up and bands of self sticking material to hold them in. All three use Astrozap dew Shields which help to hold the jackets on in the 703 and 815. 

 

I have been experimenting with insulation with the 603 and 703 and when seeing cooperates I will try the 815. 

We get good seeing fairly regularly where 150-200 X is the limit for magnification but hardly ever great seeing conditions.

But a week or so ago I convinced myself the 703 was helped by being insulated. Jupiter and Saturn were stunning and I went to 200X and higher at times when the seeing settled. I did not have to wait long before the images seemed devoid of noticeable tube currents.

Auckland has a moist maritime climate. In a month or two we get pretty good seeing conditions. Well I hope we do.... and usually the clouds roll away.

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#2 helpwanted

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Posted 30 September 2022 - 08:51 AM

3 Intes Micro... I'm drooling over here! 

Nice work on the insulation... I bought a roll to do my Mak Newt (on a dobsonian mount) months ago but have yet to do it... this weekend hopefully! 


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#3 Jeff B

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Posted 30 September 2022 - 09:39 AM

Great posting and the stuff will have a most excellent impact on the 8".

 

Maybe consider two layers of the stuff?

 

As a side bonus, you'll find it takes much longer for the meniscus to dew up, if it ever does during the session, even without those annoying dew shields.  

 

Jeff


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#4 vahe

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Posted 30 September 2022 - 10:25 AM

My 8” TEC Mak definitely needed insulation to control its stubborn tube currents that formed no matter how mild the temperature deltas were at a given time. My first experiment with Reflectix was a TOTAL FAILURE, it made absolutely no difference in eliminating the tube currents, after many more trials and errors with Reflectix I finally figured out how insulation needs to be applied.

.

Initially I placed the insulation over the metal tube and secured them in place with masking tape, this method of insulation did not work due to many voids and air pockets in between the metal tube and the insulation.

.

For insulation to perform it needs to be held snug tight against the metal tube, any air pockets in between will compromise the results.

.

In my last trial I used Velcro straps, 1 ½” wide, this allowed me to tightly stretch the straps and obtain perfect contact with the OTA with no air pockets in between , this time it all worked, the Mak was used on the last Mars opposition at powers over 300x with absolutely no tube currents despite the fact that the OTA was mounted with rings and I had to cut and fit the insulation in between the rings, the images obtained were just as stable as a large APO with no hint of tube currents.
.

You can see the results in the attached picture, UGLY AS HELL but works like a charm.

.

Vahe

 

 

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#5 dweller25

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Posted 30 September 2022 - 10:41 AM

I found I needed two wraps of reflectix on my IM715 for best results, my “seeing” improved significantly and dew held off for much longer on the corrector.


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#6 Kevin Barker

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Posted 30 September 2022 - 12:23 PM

Great posting and the stuff will have a most excellent impact on the 8".

 

Maybe consider two layers of the stuff?

 

As a side bonus, you'll find it takes much longer for the meniscus to dew up, if it ever does during the session, even without those annoying dew shields.  

 

Jeff

For many years to combat dew I have wrapped tin foil around the dew shield or around a finder. Others have laughed at me but they will notice I never have to use a hair dryer.

 

As other have stated it is a good idea to be able to remove the jackets after dewy nights so everything can dry out. A couple of weeks back with the 603 the dew was dripping off the scope and mount.



#7 Kevin Barker

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Posted 30 September 2022 - 12:25 PM

I found I needed two wraps of reflectix on my IM715 for best results, my “seeing” improved significantly and dew held off for much longer on the corrector.

I might make a second layer which is one size fits all for the 7&8.



#8 Kevin Barker

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Posted 30 September 2022 - 01:37 PM

My 8” TEC Mak definitely needed insulation to control its stubborn tube currents that formed no matter how mild the temperature deltas were at a given time. My first experiment with Reflectix was a TOTAL FAILURE, it made absolutely no difference in eliminating the tube currents, after many more trials and errors with Reflectix I finally figured out how insulation needs to be applied.

.

Initially I placed the insulation over the metal tube and secured them in place with masking tape, this method of insulation did not work due to many voids and air pockets in between the metal tube and the insulation.

.

For insulation to perform it needs to be held snug tight against the metal tube, any air pockets in between will compromise the results.

.

In my last trial I used Velcro straps, 1 ½” wide, this allowed me to tightly stretch the straps and obtain perfect contact with the OTA with no air pockets in between , this time it all worked, the Mak was used on the last Mars opposition at powers over 300x with absolutely no tube currents despite the fact that the OTA was mounted with rings and I had to cut and fit the insulation in between the rings, the images obtained were just as stable as a large APO with no hint of tube currents.
.

You can see the results in the attached picture, UGLY AS HELL but works like a charm.

.

Vahe

Hardly ugly Vahe. Looks very nice, much nicer than my efforts. As I observe alone or with my wife I am not too worried how it looks...in the dark!!

I am working on a couple of extra straps. As I have dovetails which are on the scope it will be tricky securing to avoid all air gaps.

And yes tube currents did cause delays in the 815 performing without insulation. But boy when it settles the images are impressive with this scope. 



#9 Kevin Barker

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Posted 07 October 2022 - 03:24 PM

Well the bad weather finally cleared. I was able to travel to a remote rural location to observe using the 703 all wrapped up in Reflectix. Cold and without dew the seeing was at best 6-7/10. But Saturn, Jupiter and a waxing gibbous Moon were perfectly presented
I observed for 4 hours, first hour entertaining friends and later watched the red spot come around. Best views were with a Baader V binoviewer without a glaspath. Up to 180 X in binoviewer. Up to 250 X using single eyepiece on Saturn
On the Moon I could make out 5 Plato craterlets nicely using binoviewer . Jeeps the combination of using a good binoviewer and reflectix seems to extract a lot of detail out of the planets, at times I would have struggled to draw what I could see on Jupiter. Pairs of 11 and 15 mm TV plossls and 10 mm AP SPL's mainly used.
Reflectix does seem to help the telescope settle straight away.
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#10 maroubra_boy

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Posted 07 October 2022 - 03:32 PM

Welcome to the Wrapped side... rockon.gif


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#11 Kevin Barker

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Posted 07 October 2022 - 04:47 PM

Welcome to the Wrapped side... rockon.gif

I consider myself a convert.  I have one layer of 5 mm on ota and two layers  from meniscus forward. Might add a second thin layer for mirror to start of dew shield. Looks like it will be clear again tonight and maybe with better seeing....... here's hoping......


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#12 R Botero

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Posted 08 October 2022 - 02:09 AM

Insulating with reflectix works wonders. I don’t ever need a dew shield anymore. Even in England in October. 

 

Roberto

 

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#13 Kevin Barker

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Posted 08 October 2022 - 04:09 PM

That looks like your big TEC in a nice observatory. Haven't considered not using a dew shield. I think they are good at acting as another baffle. I have a friend with I think a similar scope in the USA. It might be the 8 inch f20 TEC ??
I have an IM 815.

#14 R Botero

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Posted 09 October 2022 - 01:38 AM

Yes, TEC 10” f/20. I agree the dewshield is a good baffle but I have too much going on with a tandem setup. Insulation works very well during daytime too:

 

 

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#15 Jeff B

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Posted 09 October 2022 - 10:10 AM

Yes, TEC 10” f/20. I agree the dewshield is a good baffle but I have too much going on with a tandem setup. Insulation works very well during daytime too:

I was wondering about that.  Thanks!

 

Nice set ups BTW.

 

Jeff


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#16 planedriver

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Posted 09 October 2022 - 04:08 PM

After an extremly dry and hot Summer in Europe the last two weeks of September was suprisingly wet and cold resulting in heavy dew appearing on the first clear days pretty early into the nights. Not only did the insulation helped to fight the temperature drop but also helped to protect the scope from the direct soaking wetness. The scope has two layers while the dewshield has one - even though I very rarely use it some heat was added to the heatable dewshield so heavy was the dew - you can see the area remaining free of dew on the dewshield. Andras

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#17 Kevin Barker

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Posted 15 October 2022 - 03:03 PM

Well I had a pleasant evening with our insulated Intes 815. Two layers. This is a hefty scope about 13 kg with FT focuser.

 

A warm spring evening, the double reflectix wrap did seem to stabilise tube currents. The scope went from a 20 deg C house into a 12 deg C and dropping outdoors. I observed on our driveway.

 

Seeing up high and from buildings was a problem viewing a rising Jupiter above houses that were radiating probably the culprits. 

There were times however when the seeing was better and the planet came alive with detail and I was able to use 200 X. But mostly it looked like Jupiter was in a swimming pool. There was a shadow transit (Io??) which was very easy to see. Saturn was sharper (about 80 deg Altitude!!) and I was able to use 250-300 X. Bands of high cloud were rolling through and I packed up after 2.5 hours when a dark cloud band arrived in case it had a shower in it.

 

I have been using our Intes 703 quite a bit. I was definitely able to see the 815 delivers a fair bit more contrast and detail. The 815 has a low central obstruction around 24% versus 32% for the 703. The 815 supposedly has Sitall glass as well although I doubt that makes much of a difference.

 

I guess as much as reflectix helps settle the telescope's tube currents the reality is you need steady air. No surprises there. 

 

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Edited by Kevin Barker, 15 October 2022 - 03:42 PM.

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#18 Stopforths

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Posted 16 October 2022 - 12:48 AM

Well I had a pleasant evening with our insulated Intes 815. Two layers. This is a hefty scope about 13 kg with FT focuser.

 

A warm spring evening, the double reflectix wrap did seem to stabilise tube currents. The scope went from a 20 deg C house into a 12 deg C and dropping outdoors. I observed on our driveway.

 

Seeing up high and from buildings was a problem viewing a rising Jupiter above houses that were radiating probably the culprits. 

There were times however when the seeing was better and the planet came alive with detail and I was able to use 200 X. But mostly it looked like Jupiter was in a swimming pool. There was a shadow transit (Io??) which was very easy to see. Saturn was sharper (about 80 deg Altitude!!) and I was able to use 250-300 X. Bands of high cloud were rolling through and I packed up after 2.5 hours when a dark cloud band arrived in case it had a shower in it.

 

I have been using our Intes 703 quite a bit. I was definitely able to see the 815 delivers a fair bit more contrast and detail. The 815 has a low central obstruction around 24% versus 32% for the 703. The 815 supposedly has Sitall glass as well although I doubt that makes much of a difference.

 

I guess as much as reflectix helps settle the telescope's tube currents the reality is you need steady air. No surprises there. 

 

attachicon.gifP1080037.JPG

Good to see you using that fine instrument Kevin.    Hope you get a night with good seeing.


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#19 Kevin Barker

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Posted 16 October 2022 - 02:01 AM

Good to see you using that fine instrument Kevin.    Hope you get a night with good seeing.

Here's hoping Phil. It is clear now but rather breezy.  Usually in November we get some still air. Early start at work tomorrow so might give a wee refractor some light.


Edited by Kevin Barker, 16 October 2022 - 02:04 AM.

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#20 Dave Hederich

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Posted 23 November 2022 - 12:07 PM

Just wondering how much insulation value there might be from applying felt to the inside of a Mak tube? My understanding is that there's only a small stray light control value to applying black felt to the inside of a Mak tube. But since I already have a supply of black felt and already have experience disassembling my 4" Mak I was thinking it would be nice if there was at least some small additional value relating to insulation properties. If smaller Maks don't require insulation as much as larger ones then hopefully the interior felt might be adequate for mine.



#21 maroubra_boy

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Posted 23 November 2022 - 04:12 PM

Dave,

There is no value in it. The issue here is the heat loss of the metal tube - insulation is there to slow it, on the outside. Put the insulation on the inside does not stop this from happening and will actually keep the heat differential/heat plume for longer.

Also, there is no gain in putting felt on the inside of the OTA for the sake of "contrast". The problems of reduced contrast are 99% due to the materials used and design of the baffle tubes of the secondary and primary mirrors. Sure these are "black", but the problem is not them being black but how these surfaces reflect light at the shallow angles that light is coming on to them. Black anodised aluminium is actually very reflective and has a very high scattering ability when the incident light is at a very shallow angle. Shiny black plastic or even a matt finish plastic surface is equally reflective and has a very high scattering ability. The surfaces of the washers and bushings used to hold the central baffle tube to the primary mirror are also problematic. And not just on the outside, but on the baffle surfaces of these features - have a look up the rear of the scope without a diagonal and notice how reflective the inside of the central baffle tube actually is & how scattered this light is.

The inside of the OTA actually has next to no influence on contrast. Placing felt here needlessly risks the optics for nil gain and you also run the risk of having this felt material shedding these fibres and outgasing as this petro-chemical based product vents over time. This was a problem that plagued the 7" Intes Mak I had that a previous owner had stupidly done this and the felt was shedding fibres like a black labrador sheds hair in summer! Ironic too as Intes Maks have superior contrast to other mass production Maks and SCT's because these are designed and made very differently from these other scopes.

This is the main reason why refractors have better contrast compared to SCT's and most Maks, not because these reflectors have a central obstruction, but because of the poor design and manufacture of these internal baffle surfaces. Most people THINK it is because the reduced contrast is because of there being a secondary obstruction - NOPE! Eliminate these internal reflections from a scope and the influence of the secondary mirror on contrast you will find is actually bugger all!

Any doubts? Have a look at the two pics below. They show the inside of an SCT and an Intes Mak, both with a very similar angle of incidence of light into the OTA as this is the ONLY way to legitimately compare the two OTAs. Here you will see ALL the differences between these two scopes and why Intes Maks have so much better contrast than SCT's and Skywatcher Maks. These Intes Maks are not perfect either. There are some bespoke Maks that have refractor-like contrast because the internal baffle surfaces are designed and made even more differently, and they don't have baffle rings on the inside of the tube either!! My own 9" Santel Mak has no baffle rings on the inside of the OTA, but the baffle tube is made differently from Intes Maks, and its quality of contrast is just as good as Intes Maks.

If you want to improve contrast on your SCT and/or Mak, forget the felt. Use a high quality matt black paint, such as Black 2.0 or even better Black 3.0, on these internal reflective surfaces. THEN you will start to improve things.

Alex.

Attached Thumbnails

  • reflections inside sct.jpg
  • reflections inside Intes Mak.jpg

Edited by maroubra_boy, 23 November 2022 - 04:40 PM.


#22 luxo II

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Posted 23 November 2022 - 07:01 PM

Just wondering how much insulation value there might be from applying felt to the inside of a Mak tube?

None. Felt is not an effective insulator.

The other issue is contrast - or the lack of it due to scattered light and as Alex points out the inside of the OTA is not the usual source.

Set up on a full moon night and point your scope at the moon, then go round the front and take a look inside the corrector to see what is lit up by stray light. These surfaces are the ones where it matters - most importantly the central baffle and around the secondary cell/baffle, if that’s shiny.

Felt won’t do much apart from littering your mirrors with lint.

Edited by luxo II, 23 November 2022 - 07:03 PM.

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#23 SteveThornton1

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Posted 24 November 2022 - 12:19 AM

I’ve insulated two scopes and unfortunately it doesn’t help poor seeing.  I’ve found that refractors are better with poor 

seeing due to better contrast with being unobstructed. 



#24 luxo II

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Posted 24 November 2022 - 01:32 AM

no-one is suggesting insulation would fix poor seeing.

#25 Dave Hederich

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Posted 24 November 2022 - 10:23 AM

Good to know about felt in general and where to focus on reducing internal reflections. The only other place I've used black felt is to line the dew shield of my ST80 where it's outside the optical tube and any shedding could be easily dealt with.

 

I'm not confident about being able to paint the insides of my Mak's narrow baffle tubes unless there is a risk-free method of which I'm not aware. If felt is not appropriate then is there some other readily available thin, reflection-free black material that could be rolled up and inserted into the narrow baffle tubes?




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