A new Schmidt-Cassegrain added to the mix. I have seen no images from this but the specs are impressive. The price is not but it is premium optics, integrated focuser, heaters and It’s fast. I’m curious on the communities thoughts on this as it could be Planewave dipping their toes more into the backyard astrophotographers realm rather than mostly observatory optics/systems. One thing that stands out to me is that massive central obstruction.
📷 Screenshot 2026-06-03 184940.png
Yeah I want one BAD
Fast but with a sliver of an aperture with that comically large secondary. Looking forward to seeing results 😀
60% CO, holy cow. That's a lot of lost signal if you compare it with faster newtons with around 35-40% CO.
It will be fast but I agree with others about that central obstruction. In the normal size range (20-35 percent) it does degrade the image but it’s workable. At 60%, I would imagine that the loss of contrast would be a serious matter. The redistribution of light in the airy disk would be severe that actual resolution would be diminished rather a lot. Anyone with a refractor can do the real life experiment. Make a paper mask and do a image comparison, one with and one without.
The advert says ”At 568 mm focal length, the system offers a wide field without giving up the resolution and light-gathering capability expected from a 203.2 mm aperture.” I really doubt that…
Then again, for the job it’s designed to do it might not matter. With most pixel sizes available today you’re going to be undersampling the heck out of it anyway.
Tony Gondola · Jun 4, 2026, 01:56 PM
It will be fast but I agree with others about that central obstruction. In the normal size range (20-35 percent) it does degrade the image but it’s workable. At 60%, I would imagine that the loss of contrast would be a serious matter. The redistribution of light in the airy disk would be severe that actual resolution would be diminished rather a lot. Anyone with a refractor can do the real life experiment. Make a paper mask and do a image comparison, one with and one without.
The advert says ”At 568 mm focal length, the system offers a wide field without giving up the resolution and light-gathering capability expected from a 203.2 mm aperture.” I really doubt that…
Then again, for the job it’s designed to do it might not matter. With most pixel sizes available today you’re going to be undersampling the heck out of it anyway.
I agree the central obstruction is quit large here however the DeltaRho series also has a massive central obstruction and is quit capable of producing very nice images very fast. At the same time, I do feel a well tunes F/4 or F/3 newtonian will produce on average much better results.
Maybe Planewave needs to make a 10 inch F/3 or F/4 newtonian? I can only image if they made it with premium design, components, and it held collimation solid that it would do very well.
Does the f2.8 take into account the obstruction?
Maybe they could do a version with a smaller obstruction and do a smaller imaging circle?
I wonder how small it could be for aps c or even a 533 ? :)
If they are giving the geometric F ratio then I calculate the T-stop to be around 3.6
TiffsAndAstro · Jun 4, 2026, 02:55 PM
Does the f2.8 take into account the obstruction?
Maybe they could do a version with a smaller obstruction and do a smaller imaging circle?
I wonder how small it could be for aps c or even a 533 ? :)
I don’t think PlaneWave develops such products with aesthetic astro imaging in mind. Those telescopes are there for sky surveys and you need the biggest possible sensor coverage for that.
Hi Christian ,
the obstruction is too big and the Price is much to high ..I use a Takahashi Epsilon180 ED with f:2,8…the secondary mirror has a diameter of 79mm and it shows within a circle of 44 mm star points with 4-5 microns size…total obstruction is 22%
I would always prefer a Hyperbolic mirror design rather than a schmidt cassegrain optical Design😃
CS,
Peter
I just did the math for how much light the central obstruction blocks. Basically its the equivalent of a f 3.76 refractor with a 151.8mm aperture. This is assuming worse case scenario though with both mirrors being at 93% reflectivity which I know will not be the case.
There are 2 words that describe this telescope:
large FOV
étendue
This should be a very nice instrument for surveys with a 3.7446 deg² FOV and 1.37"x1.37" per pixel on IMX571
or 8.7846 deg² FOV on IMX455 sensor (although with 42mm imaging circle I think it will be too much… further testing is needed)
And if someone is trying hard to compare this to a RASA, keep in mind you can use a filterwheel with this one, or the DR280 and their bigger brothers..
I just asked an AI, which replied that, with its obstruction, the FSCT8's effective light-gathering power equals an unobstructed ~162 mm (6.4") aperture. That’s perfectly usable. (Heck, I used a Hyperstar on a C6 and was please with my results.) This calculation assumed, however, that the 60% obstruction was 60% by diameter, not surface area. The Planewave site was not clear on this point.
Percentage of primary diameter is the usual way to specify it. It certainly looks like 60%.
The scope looks interesting for sure. Could work very well for a remote set up.
IIRC they wont actually be released until late 2026.
Peter Knappert · Jun 4, 2026, 04:00 PM
I would always prefer a Hyperbolic mirror design
Yep. I wouldn’t trade my 150mm f/2.8 hyperbolic newt for a 8” Schmidt cassegrain design
Well, I am officially on the list for the FSCT8.
chvvkumar · Jun 8, 2026 at 09:11 PM
Well, I am officially on the list for the FSCT8.
A few years ago I had the opportunity to photograph with a Officina Stellare Veloce RH200 f:3 with ESATTO 3,5” focus motor. This telescope was manufactured by the Italian company officine stellare and has an 55% obstruction. So the FSCT8 is not a new design. Problem at such telescopes are the starsizes and some blurring of bright stars because of the heating of the corrector plate. But every telescope has its sky 😀
I stay at that…Hyperbolic designs with perfect ED Coma correctors or classical f:4 newtons with an ASA 0.73 CC which brings the scope to f:3 are the better choice….
Peter Knappert · Jun 9, 2026, 07:59 AM
Hyperbolic designs with perfect ED Coma correctors
Hyperbolic single mirror designs do not have coma. The corrector is there for spherical aberration and field curvature (if large flat fields are required).
Peter Knappert · Jun 9, 2026, 07:59 AM
chvvkumar · Jun 8, 2026 at 09:11 PM
Well, I am officially on the list for the FSCT8.
A few years ago I had the opportunity to photograph with a Officina Stellare Veloce RH200 f:3 with ESATTO 3,5” focus motor. This telescope was manufactured by the Italian company officine stellare and has an 55% obstruction. So the FSCT8 is not a new design. Problem at such telescopes are the starsizes and some blurring of bright stars because of the heating of the corrector plate. But every telescope has its sky 😀
I stay at that…Hyperbolic designs with perfect ED Coma correctors or classical f:4 newtons with an ASA 0.73 CC which brings the scope to f:3 are the better choice….
An f4 newt or a hyperbolic astrograph of similar focal length will be much larger than the FSCT, which requires me to upgrade my mounts too. The FSCT can comfortably ride on an AM5/AM5N class of mount and is much much shorter than a newt. I was considering the Tak Epsilon 160 before but the collimation requirements and shift in collimation with focuser position and the need to upgrade to a Hercules immediately put me off it. One of my friends got a new Epsilon 180 and he still hasn’t had his up and running after a couple of months of trying as he could not get it collimated and now sending it in for adjustment. This guy owns an 12” iDK so not a beginner.
Another consideration is the closed tube design and fixed mirrors which (hopefully) means no image shift or mirror flop and more stable collimation. Dew heaters are a concern but I would think PlaneWave will have a better implementation than mass market SCTs but this is to be evaluated regardless.
For clarity on central obstruction you must take in account the total area of the telescope’s mirror for its light grasp divided by it’s total area of central obstruction. Large numbers lower contrast but for deep space objects this is less of a consideration than the light grasp. Back in the 80’s when we were designing Newtonians for deep space visual Astronomy we did not use the linear figure for figuring percentage of central obstruction as planewave is doing for this scope. We used the total surface area of both mirrors with the secondary divided into the primary. Telescope mirrors are circular objects, not linear. The linear obstruction is 55% but the circular obstruction is much less, and the circular number is the actual central obstruction. If the mirror was only 4.5 inches tall and 8 inches wide then yes the obstruction would be 55%, but it’s not. This website will clarify this for you if you are still unsure as to the actual central obstruction of this telescope, and for this scope that figure is around 31%.
https://www.bigdas.com/tool/calculators/telescope-obstruction-calculator
Well it’s the same information, just expressed differently. Percentage by diameter is what is typically used by advertisers and most amateurs, mostly because it’s easier to visualize and more intuitive.
Very simply the area reduction in fraction of the telescope aperture is the linear obstruction value (expressed as fraction of the same quantity) squared. A 55% linear obstruction is thus equal to a 30.25% loss in effective aperture (against no obstruction).
Tony Gondola · Jun 12, 2026, 03:46 PM
Well it’s the same information, just expressed differently. Percentage by diameter is what is typically used by advertisers and most amateurs, mostly because it’s easier to visualize and more intuitive.
Its very misleading as to the actual central obstruction. It may be more easier to visualize, but when you refer to the linear obstruction as the actual central obstruction, this has nothing to do with the actual “central obstruction” of a circular object, and will lead the buyer into a false sense of the telescope effective aperture. Which is its relationship between the actual aperture minus the central obstruction. To say that 55% of the primary is obstructed lowers the effective aperture from 8 inches to less than 4 inches which is not the case in this design. You should never describe the central obstruction as linear. For one its just not true, and two it is misleading as to the actual reduction in the effective aperture of the scope. This compares apples to oranges, linear vs circular, the two are not the same and should never be used like they are simply because one may be more easier to visualize. Each one describes a different outcome on the effectiveness of the telescope. Already you can read the effect that number has had on the contributors to this thread. Some saying they would never buy a scope with such a large central obstruction. It is big I’ll grant you but not as big as the number being used would imply. Math doesn’t lie, and the math in this instance says the central obstruction of the round secondary on a round primary is just 31%. That’s the actual number here not a linear one.
I don’t disagree, the math is the math and it’s simple to do. I’m just explaining that looking at it as percentage of diameter is the way it’s commonly expressed in advertising and within amateur circles. I think most people understand the difference.
On the performance side, the presence of any obstruction will reduce contrast and the final T-stop of the system. Contrast matters a lot planetary imaging, for the deep sky imaging, light loss in the system will matter more. It’s all in the MTF curve for the respective systems. A large obstruction will reduce contrast in mid to low frequency details in the image. Yes, contrast can be boosted in processing but I’m not sure that will give you the same result as not having the reduction in the first place. I would love to see a real world deep sky image comparison but I’ve not come across one.