Redcat 91 WIFD vs the mighty Takahashi 106EDX4 - Forums

Hello All,

I'm in the process of buying a new wider field scope and ofc my eyes were on Tak 106EDX4 based on what real world results photographers are posting on this site. But its an expensive scope so I did my research and my eyes turned to the Redcat 91 and its flawless spot diagrams. My question is that is the redcat now factually "better" than the takahashi? or do telescope manufactures exaggerate their in-house testing for marketing purposes? what I mean is that is there something I'm missing on how william optics are displaying their spot diagram data to make it look so flawless? are they displaying it in any different parameters than what's on the Takahashi official site

for my case I'm looking for the best telescope in that range of focal length money can buy and would appreciate some guidance in this matter.

I would be comparing the Redcat 91 WIFD to the Tak FSQ 85 EDX- of which I had a Baby Q and still have the Redcat. I used both in the same permanent setup with a ASI 2600mm and ZWO 7-position filter wheel, piggybacked on a C11” seated on top of an AP1100 mount. Images from both scopes were comparably the same to me in detail and color. However, I had two issues with the Baby Q that convinced me to sell it. One, on certain bright stars, you will get an hourglass like shape (I did post this as a topic on a forum here and how to fix it) that some may find annoying. Two, the bigger problem, was that the focus draw tube eventually started to sag, causing the autofocus motor to stick. Thus, it was impossible to get the scope to focus. This occurred because of the poorly designed focal tube that is essentially attached to the main body of the scope with a piece of teflon glued to it. Apparently, the glue eventually detached due to the weight of the accessories. This occurred only after having the scope for 3 years. It is also possible that heat in my observatory during the summer contributed to the glue issue.

The design of the Redcat avoids the sagging and no funky star shapes on certain bright stars. Now, I have only had this scope since it recently became available, so time will tell if it has any issues.

So, based on my experience with both scopes, I would go with the Redcat based on quality of the images and cost.

You might want to look at the Ultracat 108 that is being released soon. That would be a lot closer to an FSQ106 than the RC91.

https://williamoptics.com/products/ultra-cat-108-wifd

Personally I would love to see WO release an Ultracat 130 at f/5.

Ashraf AbuSara:
You might want to look at the Ultracat 108 that is being released soon. That would be a lot closer to an FSQ106 than the RC91.

https://williamoptics.com/products/ultra-cat-108-wifd

Personally I would love to see WO release an Ultracat 130 at f/5.

I didnt know that was actually in the pipeline - thanks for the heads up

my question still stands though on how william optics displays their spot diagrams

Bruce Donzanti:
I would be comparing the Redcat 91 WIFD to the Tak FSQ 85 EDX- of which I had a Baby Q and still have the Redcat. I used both in the same permanent setup with a ASI 2600mm and ZWO 7-position filter wheel, piggybacked on a C11” seated on top of an AP1100 mount. Images from both scopes were comparably the same to me in detail and color. However, I had two issues with the Baby Q that convinced me to sell it. One, on certain bright stars, you will get an hourglass like shape (I did post this as a topic on a forum here and how to fix it) that some may find annoying. Two, the bigger problem, was that the focus draw tube eventually started to sag, causing the autofocus motor to stick. Thus, it was impossible to get the scope to focus. This occurred because of the poorly designed focal tube that is essentially attached to the main body of the scope with a piece of teflon glued to it. Apparently, the glue eventually detached due to the weight of the accessories. This occurred only after having the scope for 3 years. It is also possible that heat in my observatory during the summer contributed to the glue issue.

The design of the Redcat avoids the sagging and no funky star shapes on certain bright stars. Now, I have only had this scope since it recently became available, so time will tell if it has any issues.

So, based on my experience with both scopes, I would go with the Redcat based on quality of the images and cost.

Redcat does seem in terms of build quality a soild purchase - in the middle east we do get extreme temperatures so its good to know how most of redcat delicate internals are relatively isolated from external weather. though another comment suggested that a redcat 108 is in the pipeline so I'm now more inclined to wait for that release.

Rabeea Alkuwari:
Ashraf AbuSara:
You might want to look at the Ultracat 108 that is being released soon. That would be a lot closer to an FSQ106 than the RC91.

https://williamoptics.com/products/ultra-cat-108-wifd

Personally I would love to see WO release an Ultracat 130 at f/5.

I didnt know that was actually in the pipeline - thanks for the heads up

my question still stands though on how william optics displays their spot diagrams

I would take spot diagrams with a grain of salt. Definitely would not use them to compare one manufacturer vs another. Just primarily that the manufacturer is promising well corrected off axis and on axis performance upto and beyond a full frame sensor.

It's gotten to be so difficult to shop for scopes these days. There has never been more out there in terms of both variety of scopes as well as images here on Astrobin to compare them, but with the advent of tools like BlurX it has become increasingly difficult to compare using the results you see here. Yes, you can still discern the differences if you spend a lot of time studying images, but it would be great if there were also a place to browse uncorrected/minimally processed images so that you could compare the optics or other equipment rather than the processing. Looking for EAA images is sometimes helpful, but there's usually a limited subset of scopes that people tend to use for EAA.

There are two things that need to be considered - optical technical quality (spot diagrams, p/v graphs, Strehl rating etc) but then there is the way optics render a target… This can be a really unquantifiable quality that no technical diagram or test will ever be able to show you.

The Redcat 91 and future Ultracat 108 could be technically perfect (I've not used one… I can't say) but the way a Tak FSQ106 renders an image is really something else…. I had a FSQ106N (back in the day) and it was undeniably exquisit - it had its optical flaws, lets not imagine for a second that they are without their issue… the hourglass shaped diffraction on bright stars was annoying to say the least, but it was also kind of like the calling card of the FSQ….)

There's more to a scope than spot diagrams.

Ashraf AbuSara:
Personally I would love to see WO release an Ultracat 130 at f/5.

I read there will be a Mega-Cat 130 in the future.

Alex Nicholas · Mar 11, 2025, 01:19 AM
There are two things that need to be considered - optical technical quality (spot diagrams, p/v graphs, Strehl rating etc) but then there is the way optics render a target… This can be a really unquantifiable quality that no technical diagram or test will ever be able to show you.

The Redcat 91 and future Ultracat 108 could be technically perfect (I've not used one… I can't say) but the way a Tak FSQ106 renders an image is really something else…. I had a FSQ106N (back in the day) and it was undeniably exquisit - it had its optical flaws, lets not imagine for a second that they are without their issue… the hourglass shaped diffraction on bright stars was annoying to say the least, but it was also kind of like the calling card of the FSQ….)

There's more to a scope than spot diagrams.

If you can’t quantify it, it’s probably not real.

It’s important to call out that the FSQ106 is no longer made, and didn’t exactly do well in the era of small pixel cameras in larger formats. It’s a very old design and I’m looking forward to seeing what they do next.

Been using the UltraCat 108 for 3 months now. I am really enjoying this scope. It can handle full frame well once tilt is removed. The tilt plate that they have on the scope can be a bit finnicky to use. You cannot use both an OAG and a rotator with this system out of the box. Probably need to make a custom adapter to achieve that. That being said given the focal length an OAG is not necessary anyway despite the fact I chose to use it.

I don’t have the FSQ, but I have not noticed any “hour glass” stars in the subs I am imaging. The lowest FWHM under good seeing I have seen were in the low 2.2-2.3”. The illumination drop off from the center to the corner of full frame is less than 10% based on my testing.

This was paired with the 6200mm:

📷 3Ac4S15.jpeg

Awsome star shapes Ashraf. My redcat 91 has similar star shapes coupled with 6200, however im having issues with my flats overcorrecting my O data that I have yet to resolve. May I ask if you are having similar issues with ur O data? Mine are 3nm Chroma filters

📷 a19044b4-183a-49e3-a941-3f56417306a7.jpeg

Ashraf AbuSara · Dec 17, 2025 at 02:12 PM
Been using the UltraCat 108 for 3 months now. I am really enjoying this scope. It can handle full frame well once tilt is removed. The tilt plate that they have on the scope can be a bit finnicky to use. You cannot use both an OAG and a rotator with this system out of the box. Probably need to make a custom adapter to achieve that. That being said given the focal length an OAG is not necessary anyway despite the fact I chose to use it.
I don’t have the FSQ, but I have not noticed any “hour glass” stars in the subs I am imaging. The lowest FWHM under good seeing I have seen were in the low 2.2-2.3”. The illumination drop off from the center to the corner of full frame is less than 10% based on my testing.
This was paired with the 6200mm:
📷 3Ac4S15.jpeg

Rabeea Alkuwari · Dec 17, 2025, 02:51 PM
Awsome star shapes Ashraf. My redcat 91 has similar star shapes coupled with 6200, however im having issues with my flats overcorrecting my O data that I have yet to resolve. May I ask if you are having similar issues with ur O data? Mine are 3nm Chroma filters
📷 a19044b4-183a-49e3-a941-3f56417306a7.jpeg
Ashraf AbuSara · Dec 17, 2025 at 02:12 PM
Been using the UltraCat 108 for 3 months now. I am really enjoying this scope. It can handle full frame well once tilt is removed. The tilt plate that they have on the scope can be a bit finnicky to use. You cannot use both an OAG and a rotator with this system out of the box. Probably need to make a custom adapter to achieve that. That being said given the focal length an OAG is not necessary anyway despite the fact I chose to use it.
I don’t have the FSQ, but I have not noticed any “hour glass” stars in the subs I am imaging. The lowest FWHM under good seeing I have seen were in the low 2.2-2.3”. The illumination drop off from the center to the corner of full frame is less than 10% based on my testing.
This was paired with the 6200mm:
📷 3Ac4S15.jpeg

No not at all. Flats have worked well with all my frames. Generally this is an issue with calibration not the OTA itself.

📷 Screenshot 2025-12-17 105338.png

Hi Rabeea,

I ran some OIII filter checks on my Cat 91 with 6200 Rabeea, though I’m using Antlia 50mm unmounted and not Chroma, because I usually image in LRGB and may have missed the problem if it exists for me. However, I didn’t see any issues and my flats with matching darks calibrate well. I suspect the problem isn’t with your scope my friend.

Daemon de Chaeney · Dec 17, 2025 at 08:01 PM
Hi Rabeea,
I ran some OIII filter checks on my Cat 91 with 6200 Rabeea, though I’m using Antlia 50mm unmounted and not Chroma, because I usually image in LRGB and may have missed the problem if it exists for me. However, I didn’t see any issues and my flats with matching darks calibrate well. I suspect the problem isn’t with your scope my friend.

Yea somehow my Oiii flats are not calibrating well…need to look into that since i just load my calibration frames in wbpp without any pre processing.

FYI my filters are mounted. I first suspected its the plastic obstructing it, but it doesnt make sense that it didnt effect LRGB