Help me choose: Tak FSQ-85 or RASA8

[Adam J]

18 minutes ago, ollypenrice said:

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.

Vlaiv is correct they are intrinsically connected. 

OP is making an argument that 200mm aperture will resolve more than a 85mm refractor..am not so sure that true, I would say that for most of Europe unless you are at significant elevation both will resolve the same due to atmospherics but if you did take the RASA up the mountain your not going to get close to 0.58 from its optics. 

Image quality is also about Signal to Noise as you cant get details with poor signal to noise to the RASA images will help in this case but the problem is that there is a point when more Signal to noise will no longer gain you detail. 

So it depends on the target. 

Adam 

 

 

[Adam J]

12 minutes ago, Icesheet said:

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 👍

Now the FRA300 has a wonderful spot diagram, one of the few scopes that by claim at least would make use of 2.3um pixel cameras. 

Adam 

[ollypenrice]

38 minutes ago, Adam J said:

Vlaiv is correct they are intrinsically connected. 

OP is making an argument that 200mm aperture will resolve more than a 85mm refractor..am not so sure that true, I would say that for most of Europe unless you are at significant elevation both will resolve the same due to atmospherics but if you did take the RASA up the mountain your not going to get close to 0.58 from its optics. 

Image quality is also about Signal to Noise as you cant get details with poor signal to noise to the RASA images will help in this case but the problem is that there is a point when more Signal to noise will no longer gain you detail. 

So it depends on the target. 

Adam 

 

 

I don't say that they are not intrinsically connected, I say that certain optics can perform relatively poorly on stars while performing well on extended objects.  I think the relationship is not simple, that's all. Two instuments come straight to mind, the Meade 10 inch ACF and the RASA.

Resolution in imaging is also intimately connected with signal because, with more signal, you can sharpen more in software.

I would not expect to get O.85" out of the RASA's optics even though I do live on a mountain. I repeat that I don't need to, I need to get respectable resolution for a 400mm FL. 

Unfortunately I cannot compare the resolution of my Tak data with my RASA because the sampling rates are so different, the Tak being under sampled. What I can say is that that I'm delighted by the extended object resolution I find in the RASA. This is a crop of the Pillars of Creation from a single frame RASA image which comfortably framed the Eagle and Swan nebulae together. Let's forget spot diagrams and look at pictures. Do you find anything to reproach in this level of visible detail from an instrument of 400mm focal length? I don't. What does the OP think?

Olly

[Icesheet]

2 hours ago, Adam J said:

OP is making an argument that 200mm aperture will resolve more than a 85mm refractor..am not so sure that true, I would say that for most of Europe unless you are at significant elevation both will resolve the same due to atmospherics

 

 

I wasn’t making an argument, I was asking a question. I was curious to know, based on my local conditions what would resolve more detail and provide a sharper image.

 

1 hour ago, ollypenrice said:

Do you find anything to reproach in this level of visible detail from an instrument of 400mm focal length? I don't. What does the OP think?

Olly

I certainly do not, and your images as well as your apparent change in stance regarding such scopes is part of the reason they interest me. However, I see the other side too. I am interested in spot diagrams and star shapes. I’m looking for the right balance of going deeper in my limited imaging time but getting the most from the optics in terms of sharpness and star shapes. It’s also about me choosing something that fits my habits. 

The sampling rates and FL of both are fairly similar so maybe there is a quasi-objective answer of what would provide the more pleasing image.

Anyway all good input, don’t know if it’s made a decision any easier for me though 😆

[Icesheet]

3 hours ago, Adam J said:

Now the FRA300 has a wonderful spot diagram, one of the few scopes that by claim at least would make use of 2.3um pixel cameras. 

Adam 

I agree the FRA300 looks great but then I’m surprised you think the FSQ has poor performance with the new flattener. Looks better corrected and smaller spots than FRA300 although can’t find any quoted RMS radius. The new reducer for the Tak does quote spot size though and it’s 1.6micron on axis, 1.9 at APSC and 3.9micron at full frame. Of course price difference aside.

 

Edited February 12 by Icesheet

[ollypenrice]

42 minutes ago, Icesheet said:

I wasn’t making an argument, I was asking a question. I was curious to know, based on my local conditions what would resolve more detail and provide a sharper image.

 

I certainly do not, and your images as well as your apparent change in stance regarding such scopes is part of the reason they interest me. However, I see the other side too. I am interested in spot diagrams and star shapes. I’m looking for the right balance of going deeper in my limited imaging time but getting the most from the optics in terms of sharpness and star shapes. It’s also about me choosing something that fits my habits. 

The sampling rates and FL of both are fairly similar so maybe there is a quasi-objective answer of what would provide the more pleasing image.

Anyway all good input, don’t know if it’s made a decision any easier for me though 😆

I have changed my view on the RASA, for sure.

When time is limited, my view is that the priority has to be signal. I've come to feel that that's the case when time isn't limited as well. Obviously the signal has to be of a certain quality but in a trade off between slightly better star shapes and four times as much signal, I'll take the signal.

Olly

Edit: I entirely agree about choosing gear which suits your habits and preferences. Same with software. We need to be happy and comfortable.

Edited February 12 by ollypenrice

[Stuart1971]

4 minutes ago, ollypenrice said:

I have changed my view on the RASA, for sure.

When time is limited, my view is that the priority has to be signal. I've come to feel that that's the case when time isn't limited as well. Obviously the signal has to be of a certain quality but in a trade off between slightly better star shapes and four times as much signal, I'll take the signal.

Olly

Edit: I entirely agree about choosing gear which suits your habits and preferences. Same with software. We need to be happy and comfortable.

I agree, we can do something about the star shapes now with BXT, but there is no Xterminator tool “yet” that will add more signal….👍🏻

[Adam J]

25 minutes ago, Icesheet said:

I agree the FRA300 looks great but then I’m surprised you think the FSQ has poor performance with the new flattener. Looks better corrected and smaller spots than FRA300 although can’t find any quoted RMS radius. The new reducer for the Tak does quote spot size though and it’s 1.6micron on axis, 1.9 at APSC and 3.9micron at full frame. Of course price difference aside.

 

it is possible they have improved it.

[Adam J]

2 hours ago, ollypenrice said:

I don't say that they are not intrinsically connected, I say that certain optics can perform relatively poorly on stars while performing well on extended objects.  I think the relationship is not simple, that's all. Two instuments come straight to mind, the Meade 10 inch ACF and the RASA.

Resolution in imaging is also intimately connected with signal because, with more signal, you can sharpen more in software.

I would not expect to get O.85" out of the RASA's optics even though I do live on a mountain. I repeat that I don't need to, I need to get respectable resolution for a 400mm FL. 

Unfortunately I cannot compare the resolution of my Tak data with my RASA because the sampling rates are so different, the Tak being under sampled. What I can say is that that I'm delighted by the extended object resolution I find in the RASA. This is a crop of the Pillars of Creation from a single frame RASA image which comfortably framed the Eagle and Swan nebulae together. Let's forget spot diagrams and look at pictures. Do you find anything to reproach in this level of visible detail from an instrument of 400mm focal length? I don't. What does the OP think?

Olly

Olly is that image Duel narrow band data? 

[ollypenrice]

58 minutes ago, Adam J said:

Olly is that image Duel narrow band data? 

No, just OSC.

Olly

[gorann]

RASA any day! So much deeper and therefore you get more to show and more to find, including the occasional new finding. Will not happen with the Tak in a reasonable time. If you want refractor stars from a RASA just do BlurXT to get the shapes and then Unsharp Mask on the star layer to get the pinpoint look, although personally I am kind of soft on soft stars as they do not distract so much from the nice nebulosity you are looking for. Who are imaging to primarily image stars?

Edited February 12 by gorann

[AKB]

2 hours ago, ollypenrice said:

No, just OSC.

With any filer, may I ask?  UV/IR perchance?

Tony

[Elp]

1 hour ago, gorann said:

Who are imaging to primarily image stars?

This is what I don't get. Fair enough if it's an open cluster, on the target or for a mosaic or you're using a mahoosive sensor. But most of the time it's for a singular target which can be cropped.

Edited February 12 by Elp

[GalaxyGael]

17 hours ago, Icesheet said:

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. 

There's a few epsilon 160s available in Europe right now just fyi ( but off topic a bit)

[Icesheet]

11 minutes ago, GalaxyGael said:

There's a few epsilon 160s available in Europe right now just fyi ( but off topic a bit)

Not off topic at all! Where are they available? I’m on a waiting list at Kyoei in Japan, where the Tak gear is available quite a bit cheaper than Europe. Since I have to deal with customs wherever I order from it makes sense for me to order from there. 

[Icesheet]

10 hours ago, gorann said:

RASA any day! So much deeper and therefore you get more to show and more to find, including the occasional new finding. Will not happen with the Tak in a reasonable time. If you want refractor stars from a RASA just do BlurXT to get the shapes and then Unsharp Mask on the star layer to get the pinpoint look, although personally I am kind of soft on soft stars as they do not distract so much from the nice nebulosity you are looking for. Who are imaging to primarily image stars?

You certainty are prolific with it and produce cracking images! It’s not so much primarily imaging for stars. It’s the work involved getting them good enough and if the process would defeat me before I get to that point. 
 

I would love to see 6hrs on a range of targets from both scopes with comparable conditions to see what the difference in a final image would be. Maybe I should buy both and test 😂

[geeklee]

3 minutes ago, Icesheet said:

Maybe I should buy both and test 😂

Now you're talking!  This is a much better idea 🤣

[GalaxyGael]

Depends on your imaging preferences and how to tackle each night. Fsq85 is arguably easier overall if you get a good sample, but osc-only imaging as I do benefits from speed and wide-ish field. You get all the tones and colour NB does not, with the option of adding to it if you wish. But to be fair, it depends on the types or targets. For those focal lengths, are you nebulae in broadband, galaxy clusters, dust, or?

Both need setup time at the beginning. But fsq85 small star shape is fine with 2600mc with the 1.01x flattener. I know it's also perfect with 5.94um pixel full frame imx410. Extreme astigmatism comes from miscollimated fsq85 that shows more with small pixels, and that is more common than you think and takes a lot of time waiting for repair. With a good sample, assuming the focuser doesn't have slop, the fsq85 is very sharp. New reducer looks tempting, but the fsq85 with modern sensors is back focus sensitive, no way round that unless you go backwards in sensor tech and size. There are easier lens systems with in built flatteners around if that matters to you.

Now star shape....Rasa never appealed to me in that department, but it gives signal at the fl unmatched by almost nothing else. That matter to some, maybe you?

Fsq85 to me is worse. Cat eye bokeh from the virtual field stop of lens 3 in the stack that gives almond shaped out of focus stars and causes cracked stars, or inverse dark lighthouse beam effects in focus. These used to be hidden behind stumpy little 'newtonian-esque' spikes in older cc'd cameras with bigger pixels from the significant periodic texture of microlenses on the side that the light hits. With planar back side lit sensors, you'll see huge unavoidable dark beams that rotate around the frame, markedly pronounced with osc cameras in broadband where the stars are not suppressed like NB imaging. To me, it's worse than any system with diffraction, and from a scope where stars should be round. And it gets even worse if you do mosaics where they don't line up etc.....Do you need round stars? There are better apo out there for that. 

But, there are too many decent triplets with flatteners that work at f4.8 now, and even the 110mm flat field options that are almost identical to the AP 110gtx in design (can't say anything about execution). Esprit 100 is a great example of similar focal length, round stars and good sharpness tbh.

The FRA300 in a good sample is fantastic, very easy setup and the whole thing melts in to the background. Probably since it is small and tidy, but corrects 2600mc and larger.

But from my experience in bortle 6, and knowing others in bortle 4, osc imaging is better with fast optics. You're forced to use shorter subs (balancing zero gain options to use the whole full well capacity too), which takes care of stacking statistics, and you can get an image in broadband or NB in a single night.

To balance that, I quickly realised that fast optics tempted me to image the same duration as I used to, but get what F5/6/7 refractors could not in a sensible amount of time - depth. I'll caveat that by saying its not general, and big aperture, long focal length, big pixel systems are not so f-stop dependent. So a tak epsilon takes the same imaging time for me over a few nights after owning it for a while, but I see more because it can do that at a decent pixel scale with high snr. That's what happened with me, though...

Fsq85 is fantastic in NB, but you may get such good data that you realise you want more to complete an image given it's relative speed. For osc targets only your image quality preferences will dictate whether one winter night will be sufficient. It can be from f3.3 down to f2 though.

The fast mirror scopes have their limitations as you know, and paying for the stable collimation options is a hurt-once problem, but takes that nightly concern away. and some of the concerns you read about online are sample variation, but an OSC camera setup are a little less taxing on a focuser compared to the mono setup with additional components. Aperture resolution benefits at short FL are in the weeds, and I doubt you will see night and day differences sufficient to be swayed by that criterion alone.

Edited February 13 by GalaxyGael
typos

[GalaxyGael]

47 minutes ago, Icesheet said:

Not off topic at all! Where are they available? I’m on a waiting list at Kyoei in Japan, where the Tak gear is available quite a bit cheaper than Europe. Since I have to deal with customs wherever I order from it makes sense for me to order from there. 

Pm sent

[ollypenrice]

Today a new dataset fell into my lap, Paul having captured 116x3 minutes on little Sh2-257, mostly to enhance our Orion-Monoceros widefield. It gave me a chance to study RASA resolution rather nicely, though. Here's the full field just given a basic stretch.

Now let's have a look at the Sharpless object itself in a very close crop to see what's there. I hope you'll be able to see this at full size, which is how I've posted it.

Olly

Edited February 13 by ollypenrice
typo

[fwm891]

Superb. Simply Superb!

[gorann]

2 hours ago, ollypenrice said:

Now let's have a look at the Sharpless object itself in a very close crop to see what's there. I hope you'll be able to see this at full size, which is how I've posted it.

Olly

Here is what the RASA 8 makes of the same nebula through an IDAS NBZ filter:

Göran

[Icesheet]

3 hours ago, GalaxyGael said:

Depends on your imaging preferences and how to tackle each night. Fsq85 is arguably easier overall if you get a good sample, but osc-only imaging as I do benefits from speed and wide-ish field. You get all the tones and colour NB does not, with the option of adding to it if you wish. But to be fair, it depends on the types or targets. For those focal lengths, are you nebulae in broadband, galaxy clusters, dust, or?

Both need setup time at the beginning. But fsq85 small star shape is fine with 2600mc with the 1.01x flattener. I know it's also perfect with 5.94um pixel full frame imx410. Extreme astigmatism comes from miscollimated fsq85 that shows more with small pixels, and that is more common than you think and takes a lot of time waiting for repair. With a good sample, assuming the focuser doesn't have slop, the fsq85 is very sharp. New reducer looks tempting, but the fsq85 with modern sensors is back focus sensitive, no way round that unless you go backwards in sensor tech and size. There are easier lens systems with in built flatteners around if that matters to you.

Now star shape....Rasa never appealed to me in that department, but it gives signal at the fl unmatched by almost nothing else. That matter to some, maybe you?

Fsq85 to me is worse. Cat eye bokeh from the virtual field stop of lens 3 in the stack that gives almond shaped out of focus stars and causes cracked stars, or inverse dark lighthouse beam effects in focus. These used to be hidden behind stumpy little 'newtonian-esque' spikes in older cc'd cameras with bigger pixels from the significant periodic texture of microlenses on the side that the light hits. With planar back side lit sensors, you'll see huge unavoidable dark beams that rotate around the frame, markedly pronounced with osc cameras in broadband where the stars are not suppressed like NB imaging. To me, it's worse than any system with diffraction, and from a scope where stars should be round. And it gets even worse if you do mosaics where they don't line up etc.....Do you need round stars? There are better apo out there for that. 

But, there are too many decent triplets with flatteners that work at f4.8 now, and even the 110mm flat field options that are almost identical to the AP 110gtx in design (can't say anything about execution). Esprit 100 is a great example of similar focal length, round stars and good sharpness tbh.

The FRA300 in a good sample is fantastic, very easy setup and the whole thing melts in to the background. Probably since it is small and tidy, but corrects 2600mc and larger.

But from my experience in bortle 6, and knowing others in bortle 4, osc imaging is better with fast optics. You're forced to use shorter subs (balancing zero gain options to use the whole full well capacity too), which takes care of stacking statistics, and you can get an image in broadband or NB in a single night.

To balance that, I quickly realised that fast optics tempted me to image the same duration as I used to, but get what F5/6/7 refractors could not in a sensible amount of time - depth. I'll caveat that by saying its not general, and big aperture, long focal length, big pixel systems are not so f-stop dependent. So a tak epsilon takes the same imaging time for me over a few nights after owning it for a while, but I see more because it can do that at a decent pixel scale with high snr. That's what happened with me, though...

Fsq85 is fantastic in NB, but you may get such good data that you realise you want more to complete an image given it's relative speed. For osc targets only your image quality preferences will dictate whether one winter night will be sufficient. It can be from f3.3 down to f2 though.

The fast mirror scopes have their limitations as you know, and paying for the stable collimation options is a hurt-once problem, but takes that nightly concern away. and some of the concerns you read about online are sample variation, but an OSC camera setup are a little less taxing on a focuser compared to the mono setup with additional components. Aperture resolution benefits at short FL are in the weeds, and I doubt you will see night and day differences sufficient to be swayed by that criterion alone.

Thanks for the informative, detailed reply. I guess my main interests at this focal length are nebulae, both in broadband and with a dual narrowband filter, and the dark dusty nebulae that have become more popular recently. As I write that, it’s  obvious I should prioritise signal over everything else. Especially, since I’m rarely collecting more than 4-6 hours on one target. Also, I notice I’m pushing my images too far when processing. The remedy to that is likely more integration time or something that collects signal faster. 
 

Interesting comments on the Tak star shapes. I was aware of the reverse lighthouse effect and it’s not something that bothers me in terms of an aberration or artefact (halos are my pet peeve). Hadn’t heard about cats eye bokeh though. Had a look online and see its inherent of the Petzval design. Is that what the new flattener was/is trying to correct?
 

I’m curious to hear of the other refractors that operate at f4.8 that you think are better than the FSQ-85. And those designed like the AP 110? (I’m in that lottery!).

 

I’ve learned that I’ll likely be a OSC man with dual narrowband filters. Tried the mono route and had so many unfinished images. I’ve also learned that weight and complexity of set up hinder me. Had an EQ6R and could never be bothered to take it out. Now have a Rainbow RST and with the Askar FRA400 I’ve never been so productive, albeit I feel I’m lacking something in my images.  

The comments here are largely pro RASA, or fast reflector of sorts. I think my main worry is that if the set up ends up being a nuisance I’ll give up. However, won’t know until I try. I think I’ll probably just sit on this until later in the year as come April the night will already be short. That gives me a chance to keep an eye on the market for a deal. 

 

 

[Icesheet]

2 hours ago, ollypenrice said:

Today a new dataset fell into my lap, Paul having captured 116x3 minutes on little Sh2-257, mostly to enhance our Orion-Monoceros widefield. It gave me a chance to study RASA resolution rather nicely, though. Here's the full field just given a basic stretch.

Now let's have a look at the Sharpless object itself in a very close crop to see what's there. I hope you'll be able to see this at full size, which is how I've posted it.

Olly

Quite amazing detail given how close the crop is! I suppose this is pre BlurXT too?

[ollypenrice]

4 minutes ago, Icesheet said:

Quite amazing detail given how close the crop is! I suppose this is pre BlurXT too?

No, that had been through Blur X in Correct Only mode at the linear stage.

One note on ease: the RASA holds focus for much longer than my FSQs did.

Olly