Help me choose: Tak FSQ-85 or RASA8

[Icesheet]

I don't have enough clear nights to justify the amount of scopes I have so I’m going to thin down, again! I currently have a number in the 250-400mm FL range and I plan to sell them and replace with one dedicated imaging scope to mate with an ASI2600MC
 

Currently, the main contenders are:

Tak FSQ-85 (1.72”/px) 450mm FL, option of 330mm at f3.9

Pro’s
• Proven performer to APS-C (assuming good sample), even better correction with new flattener

• Ease of use

• New reducer looks fantastic at f3.9 and relatively reasonably priced  

 

Con’s

• Frustrating having to deal with back focus on what’s supposed to be flat field Petzval  

• Risk of sample variation, expensive if collimation out  

• Focuser not good enough?

 

RASA8 (1.94”/ px) 400mm FL

Pro’s

• Blazing speed

• Resolve more detail with >aperture?

• Cheaper

 

Con’s

• Collimation

• Not easy to get good correction at edge of APSC?

• Limited to ASPC and will need new filters. 
 

According to MeteoBlue my local seeing is tends to be in the 1.5-2 arc sec range and I’m in Bortle 4 according to light pollution maps. Have no idea if this is the case but in either case the sampling of both scopes seems ok. 
 

More important to me is to make use of the limited clear skies I have. I  tend to not image one target over multiple nights so I want to collect as much as possible in one night! That of course favours the RASA but I need to balance that with ease of use. If there’s regular fiddling to be done I tend to give up and losing a night to issues is more of an issue than what’s gained from the extra photons on the sensor. 
 

I’ve become quite picky with star shapes and sharpness. I’ve been using a FRA400 recently which is easy to use and gives me round stars but images appear a bit soft for me. I’m curious to hear what people might think would produce the sharper cleaner image out of the RASA/ Tak? Baby Q seems tighter with spot size etc but is this offset by the extra aperture of the RASA? I realise a lot of the processing tools we have these days can negate much of the negatives of both setups but I would like the easiest data to work with to start with.  
 

Right now I’m leaning to the Tak but I would say that’s mainly because of my trepidation of dealing with collimation etc. Otherwise, I feel it’s a toss up. 
 

Will cross post this on another site so apologies if you read this twice and thanks for reading and even better if you offer an opinion!

Chris

[Elp]

I don't have a RASA but do image at F2 with a Hyperstar and I can say this, once you image at this speed and resolving capacity with the given aperture you likely won't use anything else as often because everything else will seem too slow. I took this route because of the same issue, limited image time and opportunity.

But, if you are finicky about star shapes that may be an issue. The Rasa is better than what I use, but I setup and break down mine every time and don't even have to look at collimation, the given star field looks good enough to me and the main reason to use it is for target acquisition, not star shapes, but even so it's collimation looks good and it doesn't seem to change, if I have to adjust its no issue so for me I don't see why people fuss so much about collimation on faster systems. A larger sensor may present more of an issue however.

For crisp sharp round stars you can't beat a refractor. I still use mine for star acquisition to combine with the F2 data. I also find setting up a refractor easier on the mind even though both generally take the same amount of time.

If you do look at the Rasa 8, make sure it's from the new batch which have only just come back on market from Celestron after a lengthy more than 12 month quality issue, a reputable seller will know about this and be able to advise. If buying used make sure it has proven imaging capability.

[Stuart1971]

1 hour ago, Icesheet said:

I don't have enough clear nights to justify the amount of scopes I have so I’m going to thin down, again! I currently have a number in the 250-400mm FL range and I plan to sell them and replace with one dedicated imaging scope to mate with an ASI2600MC
 

Currently, the main contenders are:

Tak FSQ-85 (1.72”/px) 450mm FL, option of 330mm at f3.9

Pro’s
• Proven performer to APS-C (assuming good sample), even better correction with new flattener

• Ease of use

• New reducer looks fantastic at f3.9 and relatively reasonably priced  

 

Con’s

• Frustrating having to deal with back focus on what’s supposed to be flat field Petzval  

• Risk of sample variation, expensive if collimation out  

• Focuser not good enough?

 

RASA8 (1.94”/ px) 400mm FL

Pro’s

• Blazing speed

• Resolve more detail with >aperture?

• Cheaper

 

Con’s

• Collimation

• Not easy to get good correction at edge of APSC?

• Limited to ASPC and will need new filters. 
 

According to MeteoBlue my local seeing is tends to be in the 1.5-2 arc sec range and I’m in Bortle 4 according to light pollution maps. Have no idea if this is the case but in either case the sampling of both scopes seems ok. 
 

More important to me is to make use of the limited clear skies I have. I  tend to not image one target over multiple nights so I want to collect as much as possible in one night! That of course favours the RASA but I need to balance that with ease of use. If there’s regular fiddling to be done I tend to give up and losing a night to issues is more of an issue than what’s gained from the extra photons on the sensor. 
 

I’ve become quite picky with star shapes and sharpness. I’ve been using a FRA400 recently which is easy to use and gives me round stars but images appear a bit soft for me. I’m curious to hear what people might think would produce the sharper cleaner image out of the RASA/ Tak? Baby Q seems tighter with spot size etc but is this offset by the extra aperture of the RASA? I realise a lot of the processing tools we have these days can negate much of the negatives of both setups but I would like the easiest data to work with to start with.  
 

Right now I’m leaning to the Tak but I would say that’s mainly because of my trepidation of dealing with collimation etc. Otherwise, I feel it’s a toss up. 
 

Will cross post this on another site so apologies if you read this twice and thanks for reading and even better if you offer an opinion!

Chris

I will give you my experience…

I owned a Tak FSQ85 and it was very poor indeed with modern small pixel cameras, even with 2 flatteners it was still pretty bad, and why should you pay a premium for a 4 element Petzval design scope with built in flattener, and then have to add a second flattener on the back, and have all the backspacing issues that you should have avoided with the Petzval design,  it’s a joke to be honest, and the extra flattener gives about a 15% increase in image quality,  at least they now supply the extra flattener in the box with it, as for using a reducer, well, I never even got that far.

If you get a poor example then you are stuck, as there is no option but for it to go back to Japan for adjustment, with approx an 18 month wait.

If you really trawl the internet this issue is very common and they are not all they are cracked up to be…

Fo me the Rasa all the way…..

I was the worst scope I ever owned, and I have had a few

if you want astigmatism in the outer 1/3rd of your images like this, then go for the Tak

 

[geeklee]

1 hour ago, Icesheet said:

Right now I’m leaning to the Tak but I would say that’s mainly because of my trepidation of dealing with collimation etc. Otherwise, I feel it’s a toss up.

It's not so much the collimation as - hopefully - that's not something you should have to do (often/at all) nor want to on an expensive F2 system!

For me, it's the margin of error for what you consider "good enough"  This is vasty subjective and no different it seems for RASA images - where speed is king.  If you do need to tweak things (whether that be collimation or some tilt etc) and have minimal clear nights like a lot of us, could you see yourself sticking it out?  How good will be good enough?

I take it size and weight aren't a factor for yourself or mount?

With two scope options ranging from F2 to F3.6 (with reducer) and a possible budget of ~£2.2K to~ £3.1K you've got a big margin there - could anything else sit in that gap?  How critical is the speed as - again - that's quite a difference in aperture/speed with the two options.

It sounds like most of these are the items you've already thought about!  

Edited February 12 by geeklee

[Elp]

If you're willing to forgo the F2, and are intending to buy new I'd also consider the Askar 103/120 triplets. Framing certain nebulae can be an issue at such FLs though.

[fwm891]

I have an 8 inch RASA and have just acquired an Askar 120 APO with 0.8x reducer flattener. I capture with an ASI 2600MC Duo on both the FoV of the RASA is larger (3.36° x 2.25° v 2.00° x 1.34°).

Personally I've had no problems with collimation with the RASA. Your biggest problem with the RASA will be fitting filters and retaining image registration if you have to remove the camera to fit a filter. There are filter drawer units for cameras with 6.5mm back focus (asi533MC) the 2600MC has a 17.5mm back focus there are filter slip-in units which means you retain image registration. Not sure where you would find them in the UK.

I have the 120 APO permanently mounted in a obsy the RASA I now use as a mobile scope so I can get the most photons in the shortest time available.

Note: your FoV with the RASA is fixed. With the 120 APO you have the 1x and 0.8x options...

Edited February 12 by fwm891
Text added

[Adam J]

4 hours ago, Icesheet said:

I don't have enough clear nights to justify the amount of scopes I have so I’m going to thin down, again! I currently have a number in the 250-400mm FL range and I plan to sell them and replace with one dedicated imaging scope to mate with an ASI2600MC
 

Currently, the main contenders are:

Tak FSQ-85 (1.72”/px) 450mm FL, option of 330mm at f3.9

Pro’s
• Proven performer to APS-C (assuming good sample), even better correction with new flattener

• Ease of use

• New reducer looks fantastic at f3.9 and relatively reasonably priced  

 

Con’s

• Frustrating having to deal with back focus on what’s supposed to be flat field Petzval  

• Risk of sample variation, expensive if collimation out  

• Focuser not good enough?

 

RASA8 (1.94”/ px) 400mm FL

Pro’s

• Blazing speed

• Resolve more detail with >aperture?

• Cheaper

 

Con’s

• Collimation

• Not easy to get good correction at edge of APSC?

• Limited to ASPC and will need new filters. 
 

According to MeteoBlue my local seeing is tends to be in the 1.5-2 arc sec range and I’m in Bortle 4 according to light pollution maps. Have no idea if this is the case but in either case the sampling of both scopes seems ok. 
 

More important to me is to make use of the limited clear skies I have. I  tend to not image one target over multiple nights so I want to collect as much as possible in one night! That of course favours the RASA but I need to balance that with ease of use. If there’s regular fiddling to be done I tend to give up and losing a night to issues is more of an issue than what’s gained from the extra photons on the sensor. 
 

I’ve become quite picky with star shapes and sharpness. I’ve been using a FRA400 recently which is easy to use and gives me round stars but images appear a bit soft for me. I’m curious to hear what people might think would produce the sharper cleaner image out of the RASA/ Tak? Baby Q seems tighter with spot size etc but is this offset by the extra aperture of the RASA? I realise a lot of the processing tools we have these days can negate much of the negatives of both setups but I would like the easiest data to work with to start with.  
 

Right now I’m leaning to the Tak but I would say that’s mainly because of my trepidation of dealing with collimation etc. Otherwise, I feel it’s a toss up. 
 

Will cross post this on another site so apologies if you read this twice and thanks for reading and even better if you offer an opinion!

Chris

I can honestly and whole heartedly say i would personally not buy either scope. The flat field on the 85 is disappointing for a scope of its cost and the F2 RASA has always seemed like too much compromise in other areas (filters, difficulty using mono). 

If spending that kind of money and wanted to be at 400mm focal length I would 100% without a doubt go with an Epsilon 130, no problems with filters and no problems with mono. 

 

Adam 

[Elp]

What's the issue with RASA and mono? Changing filters?

The OP has an OSC camera.

[Adam J]

5 minutes ago, Elp said:

What's the issue with RASA and mono? Changing filters?

The OP has an OSC camera.

Fitting the filter draw in for a start but yes no filter wheel. But I could also add off diffraction spikes form leads and not being even close to diffraction limited performance to that list. 

Edited February 12 by Adam J

[Icesheet]

4 hours ago, Elp said:

I don't have a RASA but do image at F2 with a Hyperstar and I can say this, once you image at this speed and resolving capacity with the given aperture you likely won't use anything else as often because everything else will seem too slow. I took this route because of the same issue, limited image time and opportunity.

But, if you are finicky about star shapes that may be an issue. The Rasa is better than what I use, but I setup and break down mine every time and don't even have to look at collimation, the given star field looks good enough to me and the main reason to use it is for target acquisition, not star shapes, but even so it's collimation looks good and it doesn't seem to change, if I have to adjust its no issue so for me I don't see why people fuss so much about collimation on faster systems. A larger sensor may present more of an issue however.

For crisp sharp round stars you can't beat a refractor. I still use mine for star acquisition to combine with the F2 data. I also find setting up a refractor easier on the mind even though both generally take the same amount of time.

If you do look at the Rasa 8, make sure it's from the new batch which have only just come back on market from Celestron after a lengthy more than 12 month quality issue, a reputable seller will know about this and be able to advise. If buying used make sure it has proven imaging capability.

 

2 hours ago, Elp said:

If you're willing to forgo the F2, and are intending to buy new I'd also consider the Askar 103/120 triplets. Framing certain nebulae can be an issue at such FLs though.

Thanks. It does seem a common theme that people don’t look back when they go F2. Also, from comments I’ve seen it seems issues are more related to tilt and back focus rather than collimation. If these are one time problems I’m willing to work with it as likely is have similar hurdles setting up a refractor initially, although maybe not as challenging. Yeah, my plan if I both would be to get new batch and somewhere that accepts returns if I realise it’s not for me. I have no issues with Askar scopes. I have two and they do what they are supposed to but to achieve the round stars they sacrifice sharpness and I’ve found that it’s bothering me a bit. Maybe I’m asking too much though. 

[Elp]

4 minutes ago, Adam J said:

Fitting the filter draw in for a start but yes no filter wheel. But I could also add off diffraction spikes form leads and not being even close to diffraction limited performance to that list. 

You can plan like I do and image one filter per night. Granted it's kind of defeating the purpose but you're gathering quality deep data per session. For OSC you won't have this issue unless they're planning on using the latest ha/o3 and S2/o3 filters.

Regarding diffraction patterns, you can mitigate this somewhat by designing a complete circle from the edge of the centre obstruction to the edge of the aperture (so it looks like a full circle is above the corrector plate if looking front on), this gave me the best pattern rather than a semi circle and you definitely don't want to run the cables across straight like a Newtonian. But yes, smaller round stars requires a refractor.

[Icesheet]

3 hours ago, Stuart1971 said:

I will give you my experience…

I owned a Tak FSQ85 and it was very poor indeed with modern small pixel cameras, even with 2 flatteners it was still pretty bad, and why should you pay a premium for a 4 element Petzval design scope with built in flattener, and then have to add a second flattener on the back, and have all the backspacing issues that you should have avoided with the Petzval design,  it’s a joke to be honest, and the extra flattener gives about a 15% increase in image quality,  at least they now supply the extra flattener in the box with it, as for using a reducer, well, I never even got that far.

If you get a poor example then you are stuck, as there is no option but for it to go back to Japan for adjustment, with approx an 18 month wait.

If you really trawl the internet this issue is very common and they are not all they are cracked up to be…

Fo me the Rasa all the way…..

I was the worst scope I ever owned, and I have had a few

if you want astigmatism in the outer 1/3rd of your images like this, then go for the Tak

 

Thanks for the reply.  think I maybe came across your case when I was looking into the FSQ-85. A nightmare scenario for you and one I would hope to avoid. It does seem it may have been a collimation issue though? I’d hope if I bought new I would be able to return rather wait for a lengthy repair. I’m aware I could end up in a similar scenario though, but as @Elp mentioned, the RASA’s have had their fair share of issues as well. I guess any scope is a little bit of a lottery, even the supposed premium offerings. I do agree it’s frustrating that they had to add a flattener to correct issues exposed by small pixel cameras. It negates the benefit of the native design.

[Icesheet]

1 hour ago, fwm891 said:

I have an 8 inch RASA and have just acquired an Askar 120 APO with 0.8x reducer flattener. I capture with an ASI 2600MC Duo on both the FoV of the RASA is larger (3.36° x 2.25° v 2.00° x 1.34°).

Personally I've had no problems with collimation with the RASA. Your biggest problem with the RASA will be fitting filters and retaining image registration if you have to remove the camera to fit a filter. There are filter drawer units for cameras with 6.5mm back focus (asi533MC) the 2600MC has a 17.5mm back focus there are filter slip-in units which means you retain image registration. Not sure where you would find them in the UK.

I have the 120 APO permanently mounted in a obsy the RASA I now use as a mobile scope so I can get the most photons in the shortest time available.

Note: your FoV with the RASA is fixed. With the 120 APO you have the 1x and 0.8x options...

Thanks for the opinion. Seems like yours is like most. If you can work with the quirks and deficiencies of the RASA it seems most are happy. I’m maybe just a bit too apprehensive of leaving my refractor comfort zone. 

[Elp]

If you want the sample the speed and you don't already have one consider a Samyang 135mm F2 lens. Don't think because it's a camera lens it's no good, it's one of the best AP pieces of equipment I've ever used, better than a lot of scopes for raw speed, size etc. You do get tilt issues and perhaps lottery in quality, I've got two used and both are fine. I'm actually thinking of a third...

[Icesheet]

47 minutes ago, Adam J said:

I can honestly and whole heartedly say i would personally not buy either scope. The flat field on the 85 is disappointing for a scope of its cost and the F2 RASA has always seemed like too much compromise in other areas (filters, difficulty using mono). 

If spending that kind of money and wanted to be at 400mm focal length I would 100% without a doubt go with an Epsilon 130, no problems with filters and no problems with mono. 

 

Adam 

I’m actually on a waiting list for the Epsilon 160ED but have been told it will likely be years before it materialises. The 130D seems as scarce these days. I’m not sure it would be any easier getting dialling in an Epsilon over the RASA. Although image circle and field correction should be better. Not quite as fast though. 
 

Are you saying the flat field on the FSQ is not good even with the new flattener? When I look at the spots and some examples I’ve seen on forums it seems pretty much as good as it gets at this FL with a refractor and the IMX571. The new reducer looks fantastic too. That being said, you are paying a premium and not guaranteed the performance. The Vixen VSD90 looks like it may have the best correction and performance but it’s more than I want to spend. 
 

I’m not ruling out ever going back to mono but I plan to stick with  OSC at the moment so the filter issue doesn’t affect me. 

[Icesheet]

1 minute ago, Elp said:

If you want the sample the speed and you don't already have one consider a Samyang 135mm F2 lens. Don't think because it's a camera lens it's no good, it's one of the best AP pieces of equipment I've ever used, better than a lot of scopes for raw speed, size etc. You do get tilt issues and perhaps lottery in quality, I've got two used and both are fine. I'm actually thinking of a third...

I have one. That will be my super wide field and travel rig. 

[Elp]

I'm actually contemplating going all in with the SYs and replacing my refractors fully. Too few opportunities imaging is the main reason, it's getting to the point I have to spread projects over a few seasons as a result of the inconsistent weather. This hobby isn't really for the impatient.

Edited February 12 by Elp

[iantaylor2uk]

I would recommend the FRA 300. I know you have the FRA 400 and could use a reducer, but from my point of view the whole idea of these short focal length refractors is not to introduce any more glass, so I deliberately chose the FRA 300. I have matched it with a ZWO 071 MC Pro camera - although this is not the latest tech it does have quite large pixels for a CMOS camera (4.78 microns). I have found this to be a pretty good combination, and I consider f/5 to be fast for a refractor (my other one, a Tak TSA 102 is f/8!). I have also had some great results from this combination too. 

Edited February 12 by iantaylor2uk
typo

[Icesheet]

4 hours ago, geeklee said:

It's not so much the collimation as - hopefully - that's not something you should have to do (often/at all) nor want to on an expensive F2 system!

For me, it's the margin of error for what you consider "good enough"  This is vasty subjective and no different it seems for RASA images - where speed is king.  If you do need to tweak things (whether that be collimation or some tilt etc) and have minimal clear nights like a lot of us, could you see yourself sticking it out?  How good will be good enough?

I take it size and weight aren't a factor for yourself or mount?

With two scope options ranging from F2 to F3.6 (with reducer) and a possible budget of ~£2.2K to~ £3.1K you've got a big margin there - could anything else sit in that gap?  How critical is the speed as - again - that's quite a difference in aperture/speed with the two options.

It sounds like most of these are the items you've already thought about!  

Yeah it seems like the RASA will give you back what you’re willing to put in and that may be where I fall down. I would absolutely set out with the right intentions but I know if it starts needing more fiddling than the initial set up I will give up. I’m definitely open to more suggestions if you have any. For instance the aforementioned Epsilons are interesting but may present similar problems as the RASA. The new WO Pleiades look interesting but I’m not sure I’m ready to be an early adopter. Maybe a used FSQ106 could be an option?

 

In terms of size and weight it has to go on an RST135 so RASA8 size and weight is probably max. It doesn’t have to be the fastest but I see on average that I collect 4-6hrs data per night (from Bortle 4) and as I rarely get consecutive clear nights that’s usually all I’ll collect on one target. So, it doesn’t necessarily need to be F2 but the faster the better.

[Elp]

Would an Esprit be of interest?

This also looks like a Pleiades 68 alternative:

https://stargazerslounge.com/topic/418797-new-telescope-founder-optics-draco-62mm-refractor/

Edited February 12 by Elp

[geeklee]

4 minutes ago, Icesheet said:

I would absolutely set out with the right intentions but I know if it starts needing more fiddling than the initial set up I will give up.

Perfectly understandable, more so with our infrequent clear nights.

5 minutes ago, Icesheet said:

I’m definitely open to more suggestions if you have any. For instance the aforementioned Epsilons are interesting but may present similar problems as the RASA.

The suggestions all have a familiar look about them - fast reflectors!  The Epsilons are at least designed to be collimated on the bench.  I hadn't realised the long lead times on new ones at the moment - your pre-order for the 160ED could have been the only scope you'll ever need/want if you can go a bit slower (relatively )

Perhaps locate/request some full size raw RASA subs from similar skies and judge the quality and signal.

[fwm891]

38 minutes ago, Icesheet said:

Thanks for the opinion. Seems like yours is like most. If you can work with the quirks and deficiencies of the RASA it seems most are happy. I’m maybe just a bit too apprehensive of leaving my refractor comfort zone. 

https://www.firstlightoptics.com/starizona/starizona-rasa-8-filter-holder-for-larger-sensors.html

FLO it seems do a filter holder for the RASA that fits the 2600MC....

At present I'm happy having the two set-ups. this is my second RASA 8, I regreted selling the first the second it went out the door.

[ollypenrice]

1 hour ago, Adam J said:

Fitting the filter draw in for a start but yes no filter wheel. But I could also add off diffraction spikes form leads and not being even close to diffraction limited performance to that list. 

I can't see that the diffraction limit has anything to do with this comparison because the OP is looking at common focal lengths, not at common apertures. The RASA can quite possibly out resolve a diffraction limited 85mm mm scope without, itself, being diffraction limited.  The diffraction limit of 85mm is 1.36 arcsecs while that of 200mm is 0.58.   The Epsilon gives good numbers but produces star spikes and, in the case of stars of a certain size, small square stars. You have to be sure you want this on a widefield instrument.

Although I know that Vlaiv does not agree with me, I do not believe that quality of stellar image necessarily equates to quality of extended object image.

5 hours ago, Elp said:

I don't have a RASA but do image at F2 with a Hyperstar and I can say this, once you image at this speed and resolving capacity with the given aperture you likely won't use anything else as often because everything else will seem too slow.

This is my experience.  I imaged for several years with a Baby Q (and a pair of FSQ106 scopes after that.)  I've also been imaging with a RASA 8 for two years. They are all good options, but would I go back to a Baby Q after using a RASA?  Never in a million years.  And bear in mind that I don't lack clear nights. I expect around 250 per year.

A 3 to 4 hour image from the RASA usually shows me things I have never seen before. This is the Pacman in OSC.  This front of dust is new to me, though I can't speak for anyone else. 

Anyone determined to ruin their own astrophotography experience by pixel peeping should probably go for a Baby Q, hoping they'll get a good one. But if you want signal, which is what I do want, go for the RASA.

I could not possibly go back. RASA data are too exciting.

Olly

 

Edited February 12 by ollypenrice
False click

[Elp]

I also acquired S2 signal in one hour on NGC2359, something a lot of people only do in HOO. I wouldn't even attempt it with my refractors because I can only usually image it 45m-1h per session Jan-Feb.

[Icesheet]

13 minutes ago, iantaylor2uk said:

I would recommend the FRA 300. I know you have the FRA 400 and could use a reducer, but from my point of view the whole idea of these short focal length refractors is not to introduce any more glass, so I deliberately chose the FRA 300. I have matched it with a ZWO 071 MC Pro camera - although this is not the latest tech it does have quite large pixels for a CMOS camera (4.78 microns). I have found this to be a pretty good combination, and I consider f/5 to be fast for a refractor (my other one, a Tak TSA 102 is f/8!). I have also had some great results from this combination too. 

Very nearly bought the FRA300 when I ended up with the FRA400. Probably should have tbh as it seems to have tighter stars than the 400. Still, I think I would prefer 400-500 now as I’ll use the Samyang 135 and have a Tak TSA120 at nearly 900mm FL. Seems like a nice set up, I’ve seen some of your images 👍