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Solar Observation > Solar telescopes > Coronado > SolarMax III > Coronado ST 70/400 SolarMax III BF15 <0.5Å Double Stack OTA
Product no.: 59508

ST 70/400 SolarMax III BF15 <0.5Å Double Stack OTA

$ 5,900.00 incl. VAT, plus shipping costs
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Product description

More about the series SolarMax III...

Observing the sun in H-Alpha is a lot of fun using these compact SolarMax III telescopes! The integrated ‘True’ Etalon filter provides higher contrast and a sharper image than other solar telescopes with smaller filters.

SolarMax III telescopes have an improved focuser with sensitive focusing and other high-quality features. The filters can be removed from the Solarmax III, allowing the solar telescope to also be used as an achromat for observing the night sky.

The sun is observed at a wavelength of 656 nanometers - known as H-alpha - showing an ever active solar surface and prominences at the sun's edge. There is always something to see on the sun in the H-alpha!!

RichView™ tuning: The Doppler effect causes the wavelengths of interesting structures to vary around the H-alpha line of 656.3 nanometers. This effect is particularly noticeable in the change between the central solar disk and the edge (prominences). The RichView™ tuning system allows you to adjust the filter, to find the best possible contrast.

Please note: The aperture mentioned in the product name refers to the apochromat's front lens. You can find the size of the etalon filter in the technical data.

Double stack: Every SolarMax telescope also comes with double stack. This means that two etalon filters are fitted one behind the other. This reduces the half width of the light which passes through the H-alpha line to less than 0.5 Angstroms. Without double stack, the half width is less than 0.7 Angstroms. The half width is provided in the product name and in the telescope's technical information.

The smaller half width results in higher contrast. The Sun’s structures appear three-dimensional. The image is also darker and needs to be finely readjusted using the tuning system due to the filter’s smaller half width.

BF blocking filter: The deflection optics with the eyepiece receiver also accommodate the blocking filter. This filter reduces the brightness of the solar image and is therefore a very important part of the solar telescope, and which must under no circumstances be removed! For purely visual observing, a small blocking filter is sufficient, but for photography a larger one should be selected.

Sol Ranger: Pointing a telescope at the sun is more difficult than you may think and can often involve involuntary glimpses of the sun with unprotected eyes! The Sol Ranger finder scope is a special solar finder that uses a ground glass screen. This allows you to point your telescope at the sun easily, safely and quickly.

Delivery includes a Cemax eyepiece. The eyepieces of this series are specially optimized for observation in H-alpha. The optimization applies to the remuneration. The eyepieces have no 'filtering effect' and can therefore also be used at night.

It not only matters which telescope you buy but also where you buy it. Our additional services:

  • We are a leading telescope dealer and know the devices we sell. Our customer service team will gladly help you after your purchase if you have problems with assembly or operation.
  • We provide a copy of the 80-page Telescope ABC beginners handbook with every telescope.
  • We also provide an edition of the exciting astronomy magazine, “Sterne und Weltraum” with each telescope.

Our expert comment:

First light with the Coronado ST 70/400 Solarmax III DS

In October, after a waiting a while for delivery, I received the Coronado ST 70/400 Solarmax III DS telescope with a 15mm blocking filter.

Although a different set-up was already available, an old Solarmax 90/BF30 system by Coronado (the corroded blocking filter for which had been perfectly repaired by Astroshop), I wanted a smaller, lighter weight complete unit for fast, comfortable observations with minimal barriers to set-up.

It was clear to me that the resolution for a 60mm clear aperture cannot begin to compare to that of “large” systems, as this is physically limited. I had also previously had a Coronado 60mm with a 15mm blocking filter so I knew what I was letting myself in for. That was why I wanted a double stack this time.

The device comes in a sturdy aluminium case which adds a bit of weight but is not cumbersome. Its foam padding is so firm that it takes some effort to safely remove the device. Removing the eyepiece for the first time can become a real challenge! I already knew that it only came with an 18mm eyepiece and I already had a Coronado Cemax Barlow lens and other eyepieces. It’s a shame that a 12mm Cemax, which would be a sensible fit given the magnification, does not appear to be separately available at all.

After a forced break of around a quarter of a year due to the weather, I was able to use the small solar telescope in good conditions on 7th February – frost-free as Solarmax H-alpha systems should not be used in frosty conditions - and very clear skies. Aa a comparison the older Solarmax 90/BF30 on an achromatic Vixen 102/1000 refracting telescope, both placed one after the other on an azimuthal TeleVue Gibraltar mount, with a prism clamp with double clamping screws mounted on its fork. The ST 70/400 is well mounted although the Coronado prism rails have no front brakes. Admittedly, there are notches for the fixing screws on the side but they are useless when you are working with adapters with large contact surfaces. Resultantly, despite securely tightened screws, the lens tube slowly slid back by a centimetre during observation. I have since installed a brake in the dovetail rail using a nut and bolt.

The drawtube makes large and find adjustments very smoothly and precisely. Remove plastic cap before use!

According to the operating instructions, the T-Max tuner is used to gently tip the outermost etalon until the double images disappear from the visual field, then the detail contrast is set using the large Rich View slewing ring. The second etalon can then be gently tilted until the illumination matches up. However, you can also do this the other way round and start with the Rich View tuner. Due to its low focal length of 400mm, the device is so short than you can comfortably adjust all tuners with the stretch of an arm without taking you eye off the eyepiece.

The Sol Ranger sun finder serves its purpose well but is not super precise, meaning that I can find my target just as quickly using the shadow method.

Now to the image... The image is very clear and high in contrast in a pleasing “natural” orange tone, the surrounding area pitch black. Filaments appear dark, flares are extremely bright. The 18mm eyepiece is perfect for quick wide-angle observations. For higher magnifications, I have tried other eyepieces - due to its transparency, a 7.2-21.5mm zoom eyepiece from Lunt proved itself to be the best. But higher magnifications in a double-stack device with a small aperture produce very dark images.

As expected, the detail resolution does not match that of the Solarmax 90, so everything seems more effortless, but the contrast is lower. The Solarmax 90 with its repaired BF30 blocking filter has such a bright image that it makes sense to use a blue-green filter or a polarising filter in order to better recognise details. Filters are not required for the smaller device. Both devices react naturally to fluctuations in seeing and it is clear that nothing amazing could be expected from the low-lying early-February sun. Amazingly, slight cloud cover made arguably no difference.

The heavily-promoted 3D effect kicks in with the Coronado if you “scan” a little using the etalon and the Rich View tuner. Dark filaments then appear as though they are hovering.

It would also be remiss not to mention that it appears initially as though it would be difficult to manage to achieve uniform lighting across the image. I suspected this after Ullrich Dittler’s test review (https://www.astroshop.de/magazin/test/teleskop-tests/coronado-solarmax-iii-70mm/i,1419) and had it confirmed by images published online. You also need to readjust occasionally using the etalon and the Rich View tuner. Meanwhile, it has been confirmed that the 1st elaton should never be tipped too heavily - at low magnifications, the double images should still be visible at the edge. At higher magnifications, the double images should be completely outside the visual field.

At first light on 7th February, I had the unbelievable luck of being able to observe a spectacular prominence in its entirety using the small Solarmax ST 70/400. I cannot remember ever having observed such a bright and large eruption, this was an M1 class flare on the rear of the Sun. Initially visible as a blindingly bright lump on the Sun’s edge and developed into a bright double loop which grew rapidly and revealed lots of bright, clearly defined and high-contrast details – an amazing experience which showed what this small device can do – and all this even though you should expect to be able to view prominences better at 0.7 angstroms than using a double stack with a bandwidth of < 5 angstroms. Its bigger brother had not even been mounted so as not to miss anything.

All in all, the ST Solarmax III 70/400 had a good debut and I am excited to see what awaits me in even better conditions. In any case, you can quickly be ready for observing using the small device. Set-up and alignment takes less than 3 minutes. It is a shame that it is too heavy for a Skywatcher Solarquest AZ mount and other small solutions – the double stack weighs around 4.4kg. So it makes sense to have a solid foundation. I am generally of the opinion that a perfect tracking system is desirable for solar observation. All in all, this purchase was worth it - the device meets my expectations and is a good addition to larger devices.

(Eva Seidenfaden)



Type of build
Solar H-Alpha
Aperture (mm)
Focal length (mm)
Aperture ratio (f/)
Resolving capacity
Limit value (mag)
Light gathering capacity
Max. useful magnification
Tube weight (kg)
< 0,5
etalon filters (mm)
Blocking Filter (mm)
Double Stack
Filter systems
Tube construction
Full tube


Connection ( to eyepiece)
Type of build
Gear rack
Free aperture (mm)
Gear reduction
1:10 Fine movement
Connecting threaded socket (camera-side)
Adjustment range (mm)


Type of build
Mounting type
no mount

Included accessories

Prism rail
Tube clamps
Finder scope
Solar finder
1.25'' eyepieces
Transport cases
Deviating optics


SolarMax III

Area of application

yes (H-alpha)

Recommended for


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*All prices include VAT plus shipping costs.

Coronado ST 70/400 SolarMax III BF15 <0.5Å Double Stack OTA

Transport cases

Coronado ST 70/400 SolarMax III BF15 <0.5Å Double Stack OTA
Example image 1

Coronado ST 70/400 SolarMax III BF15 <0.5Å Double Stack OTA

Example image 2

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