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Old 08-05-2020, 07:18 PM
Emuhead (Andrew)
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Ok - ive got analysis paralysis.. SOS! (Which OTA..)

Hi all,

Ive reached a point where i think ive read every article there is, some of them twice or three times (slow learner), watched every youtube video to the point where i think im just watching peoples videos about gear.. essentially its a home shopping channel, and im really now just at a point where im ready to just blindly hope for the best.. which is something id rather not do when spending a large sum of hard earned.. so.. this is where im at and if you are willing to listen and offer advice, id be grateful.

I want to take mind melting astro photos.. much like these wizards here and here

Ill get it said that I dont want to do any visual, nor take planetary images, or moon images, or even galaxy images... im all about nebulas, dust & clouds & colour. Ill farewell some of you there im sure.. sorry.

If youre still reading, brilliant, ill continue. So I dont have endless funds but I am willing to pay the price to get the job done once & right if possible.

Im looking at these scopes with a keen eye:
Skywatcher Esprit 100ED 550mm f/5.5 Triplet (optional x0.65 reducer)
Skywatcher Esprit 120ED 840mm f/7 Triplet (optional x0.65 reducer)
William Optics GT102 703mm f/6.9 Triplet (optional x0.8 or x0.72 reducer)
William Optics Zenithstar 103 710mm f/6.9 Doublet (optional x0.8 reducer)
William Optics Zenithstar 126 970mm f/7.7 Doublet (optional x0.8 reducer)

Anything more expensive im certain are amazing, but i cant justify the price of admission there.. Looking at you AP, SV, Takahashi..

I was also recently looking at SCT's (a third time - im seriously on loop ruling things out and then back in again) only because of the huge light gathering power they have, but they dont sound like are without their numerous downsides either. I was looking at f/4 Newtonians briefly but then saw some images and decided that id much rather round stars only, so they are out.

I purchased an EQ6-R with a payload capacity of 20kgs.. probably only usable to about 15kgs max (im guessing, happy to be corrected). Im also thinking i should probably stay somewhere between a 500mm to 1000mm focal length for now based on the things id like to shoot, but ideally 700mm to 1000mm from the telescope simulator i used.. (and that is where im at right now. Simulating a telescope - i have the passion just without the scope).

Ill be autoguiding with a 60mm guidescope and an ASIAir Pro for now. Potential move to Stellarmate, Astroberry, or a miniPC/NUC, but will see how the ASIAir goes first. Shooting with a Fuji XT2 APS-C mirrorless camera, for now, however im sure the obligatory 1600MM with all the filters wont be too far down the road.

So.. that long story cant be shortened, but long story short.. are those 5 scopes decent? Will they help get the images im chasing? Do they have downsides people dont speak of? Some better than others from your experience? Can i even shoot at f/7 (for the longer scopes) or will i have to get a focal reducer bringing it down to f/5.5 anyway. Is a Triplet really that much better than a Doublet? Is there a sweet spot for focal length, and for focal ratio for that matter? Do SCTs really lack contrast due to the secondary mirror getting in the way. Are smaller diameters better to reduce 'muddiness'. Do i need help? (yes )

Strehl, spot size, mirror flop, image shift, 3"+ focusers... this is a great hobby but pretty full-on to get ones head around at times. Especially this one.

S O S
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Old 08-05-2020, 07:25 PM
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I have seen great results from the Esprit triplet APOs. Not to say the WO scopes aren't great too. I would steer away from doublets as claims they are APO are usually marketing BS. Agema Telescopes excepted.

The bigger the better, If you have the budget the standout there to me is the Esprit 120.

I would consider:

Triplet and has an FPL53 element.

A decent focuser.

Plenty of examples of user images using these scopes. Astrobin is the best resource for that.

WO are great at machining. Their machined parts are works of art. I am not so sure about their scopes. Perhaps they are. But they also BS about APO and call FPL 53 triplets fluorite sometimes. Fluorite is a crystal and a high end lens element like Takahashi and TEC use. It is superior to FPL53 which is why they call it that. FPL53 has a lot of fluorite in it but its not fluorite.

You don't need a 3 inch focuser for an APSc camera like Fuji XT2. 2.5 inch would work.But if you plan to go full frame one day 3 inch is safer.




Greg.
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Old 08-05-2020, 07:35 PM
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Originally Posted by Emuhead View Post
Hi all,

Ive reached a point where i think ive read every article there is, some of them twice or three times (slow learner), watched every youtube video to the point where i think im just watching peoples videos about gear.. essentially its a home shopping channel, and im really now just at a point where im ready to just blindly hope for the best.. which is something id rather not do when spending a large sum of hard earned.. so.. this is where im at and if you are willing to listen and offer advice, id be grateful.

I want to take mind melting astro photos.. much like these wizards here and here

Ill get it said that I dont want to do any visual, nor take planetary images, or moon images, or even galaxy images... im all about nebulas, dust & clouds & colour. Ill farewell some of you there im sure.. sorry.

If youre still reading, brilliant, ill continue. So I dont have endless funds but I am willing to pay the price to get the job done once & right if possible.

Im looking at these scopes with a keen eye:
Skywatcher Esprit 100ED 550mm f/5.5 Triplet (optional x0.65 reducer)
Skywatcher Esprit 120ED 840mm f/7 Triplet (optional x0.65 reducer)
William Optics GT102 703mm f/6.9 Triplet (optional x0.8 or x0.72 reducer)
William Optics Zenithstar 103 710mm f/6.9 Doublet (optional x0.8 reducer)
William Optics Zenithstar 126 970mm f/7.7 Doublet (optional x0.8 reducer)

Anything more expensive im certain are amazing, but i cant justify the price of admission there.. Looking at you AP, SV, Takahashi..

I was also recently looking at SCT's (a third time - im seriously on loop ruling things out and then back in again) only because of the huge light gathering power they have, but they dont sound like are without their numerous downsides either. I was looking at f/4 Newtonians briefly but then saw some images and decided that id much rather round stars only, so they are out.

I purchased an EQ6-R with a payload capacity of 20kgs.. probably only usable to about 15kgs max (im guessing, happy to be corrected). Im also thinking i should probably stay somewhere between a 500mm to 1000mm focal length for now based on the things id like to shoot, but ideally 700mm to 1000mm from the telescope simulator i used.. (and that is where im at right now. Simulating a telescope - i have the passion just without the scope).

Ill be autoguiding with a 60mm guidescope and an ASIAir Pro for now. Potential move to Stellarmate, Astroberry, or a miniPC/NUC, but will see how the ASIAir goes first. Shooting with a Fuji XT2 APS-C mirrorless camera, for now, however im sure the obligatory 1600MM with all the filters wont be too far down the road.

So.. that long story cant be shortened, but long story short.. are those 5 scopes decent? Will they help get the images im chasing? Do they have downsides people dont speak of? Some better than others from your experience? Can i even shoot at f/7 (for the longer scopes) or will i have to get a focal reducer bringing it down to f/5.5 anyway. Is a Triplet really that much better than a Doublet? Is there a sweet spot for focal length, and for focal ratio for that matter? Do SCTs really lack contrast due to the secondary mirror getting in the way. Are smaller diameters better to reduce 'muddiness'. Do i need help? (yes )

Strehl, spot size, mirror flop, image shift, 3"+ focusers... this is a great hobby but pretty full-on to get ones head around at times. Especially this one.

S O S
Simple answer is a RASA 8 and a asi294mcpro, you will get heaps of nebulae in spades and tonnes of dust
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  #4  
Old 08-05-2020, 07:35 PM
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Outcast (Carlton)
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Have you looked at the size of objects you wish to image & what image circle you will require in relation to your camera sensor size?

Longer focal length will result in smaller image circle; for example, when I started my imaging journey with an 8" f10 SCT, I was unable to capture objects such as m42 & eta carina in there entirety. Even with a 0.63 reducer, I could only just squeeze them in. I now image with an f6 80mm triplet & 130mm f5 newtonian & they happily cover my interests.

Longer focal lengths also usually require longer capture times.

If you want to get a feel for fov, put your sensor specs & each scopes specs into stellarium, you can even add in the reducer. Then pic targets & get a feel for how they will frame.

Also, there are ccd calculators that will show if you are under or oversampling with particular combinations, I think there is one on the bintel site.

Double vs triplet, well I think that depends on the quality of the glass used. If choosing between two scopes of equal quality, I'd choose a triplet over the double assuming I could afford it...

I'm sure other, vastly more experienced imagers will chime in with more advice but, that's a snapshot of what I've learned over my journey that relates to your questions.

Hope it's helpful

Edit: I see they already have...
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Old 08-05-2020, 07:37 PM
Emuhead (Andrew)
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Thanks for the fast response Greg. I have spent a fair amount of time on the old astrobin checking out what these & other scopes can do, and its a great resource for sure.. even have my own little page on there.

So all 5 of those have FPL-53 glass as it goes, and im sure all have pretty decent focusers (some rack & pinion, some not). I am ever so slightly leaning toward the 120mm but can i shoot at f/7, or will i have to spend the extra to get the x0.65 reducer which will end up netting me what could essentially be a very expensive Esprit 100ED (more or less).
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Old 08-05-2020, 07:56 PM
Emuhead (Andrew)
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Hey H0ughy, I was pretty set on the Rasa 8 and still may head down that path.. one shot colour though given the price of 2" filters and a mono camera.. I was hoping to get away with using my mirrorless Fuji for a while first, and it can be done I've read, but I was hoping to go a little deeper.. and the Rasa 11 (& 14/36)is way out of my price range.
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Old 08-05-2020, 08:02 PM
Emuhead (Andrew)
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Hi Outcast,

I didn't know that longer focal lengths need more time on target.. that is good to know.

I have played too much with telescope simulators, like Telescopius, getting an idea of the fov I'd get with my sensor & potential scope. It's actually pretty fun. I also have an impressive spreadsheet with combinations of oversampling & undersampling, which for my sensor is the reason why I was looking around about the 100mm diameter and up region.

Thanks for the points given, all good stuff to consider.
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Old 09-05-2020, 08:42 AM
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Camelopardalis (Dunk)
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So all 5 of those have FPL-53 glass as it goes, and im sure all have pretty decent focusers (some rack & pinion, some not). I am ever so slightly leaning toward the 120mm but can i shoot at f/7, or will i have to spend the extra to get the x0.65 reducer which will end up netting me what could essentially be a very expensive Esprit 100ED (more or less).
Not sure which reducer you are referring to, but Skywatcher don't make a reducer for the Esprit range. They come with their field flattener included, but that is 1.0x so doesn't change the focal length.

I've owned my Esprit 100 for 5 years now and it's an excellent scope for the money. But you really need to consider the targets you will chase as the extra aperture and focal length would come in handy for some targets.

Of course, the FOV you get depends on the camera you use too...so that's another factor to think carefully about.
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Old 09-05-2020, 09:41 AM
Emuhead (Andrew)
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It's a Starizona APEX x0.65 reducer. Which would make your f/5.5 a f/3.575 for the 100ED, or the 120ED down from f/7 to f/4.55.

So what I'm trying to understand now is how to compare the 100ED to the 120ED, as they both have different apertures and different f numbers. While the 100ED is faster at f/5.5, the 120ED has a larger aperture but its f/7. If both scopes had the same aperture this would be easy of course, but hunting for a formula now to properly compare these in assumably photons per second, or something similar (for the same light source and same camera sensor).

Last edited by Emuhead; 09-05-2020 at 10:13 AM.
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Old 09-05-2020, 09:42 AM
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It is very easy to get in to paralysis mode. I bought my Evostar 72 and reducer as a toe in the water and quickly realised I enjoyed the image scale and was going to want something better, but it took the best part of a year to settle on the Stellarvue I eventually bought (Thankfully before the exchange rate really tanked during the earlier days of the COVID 19 event)

It is a bit hard to advise anyone else as everyones wants, needs, budget and pet peeves are different. But I would say from my own experience that if you consider any moderately priced doublets, really cruise Astrobin for images produced with them and a similar or the same camera that you plan to use and look for issues like blue bloat etc.

To make an example of my Evostar 72, they were originally marketed as an Apo scope, but they really are not, for the price I could forgive it (And was not expecting miracles) but being a bit of a technical wonk and perfectionist I outgrew it and while I got some pretty decent results out of it, the less than tightly focused blue did not appeal to me. Currently it is acting as a guidescope while I wait for a new and better OAG to arrive than the old Thin OAG I had before now. I will probably look to sell it and it's reducer as an intro package once my new OAG arrives and I can retire it from that duty.

I guess the TL;DR version of that is be careful about setting a tight budget on the glass. You already have a mount that should carry an imaging scope pretty well, but I think the decision on scope has to be between toe in the water (Evostar 72 in my case), a fairly solid but moderately priced scope and a maybe lifetime scope (My Stellarvue SVX80, which cost four times as much as my Evostar while only having 8mm more aperture) I did have the advantage when I realised I wanted more of being able to borrow the little brother to the SVX80 off a friend, which in some ways was a bit of a mistake, as soon as I started shooting with it I knew I wanted one like it.

I looked long and hard at a RASA 8 as well and very nearly pulled the trigger but I could not find many images from one that would have convinced me at the time. H0ughy's images in this thread would have made the decision harder again! They are even taken with my current camera. Many images you see from a RASA 8 seem to exhibit loads of reflection issues. The huge advantage of the RASA if you can tame the reflections is F2! On a good night you could shoot enough subs to produce a pretty handy image of any less than insanely dim target!
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Old 09-05-2020, 10:59 AM
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Nebula don't really care about aperture. Aperture is for faint stella objects. Nebula pics come faster with low F ratio, though you can get them with any F ratio, if you have the time. Scope quality is probably the biggest issue, as we all like to push process our images until imperfections show. The better the scope, the less imperfections.

You WILL want a good mono camera. The camera is half the optical train. No OSC ever comes close to a mono. You will also eventually want narrow band for nebula, and filters... There goes the bank account.

I would probably go with a refractor with a little longer focal length, and use a reducer for wider stuff. That way you get the best of both worlds in one scope.

I was looking at the Starizona 065x reducer also for my F9 refractor to get it to f5.85. Would love to know what the quality is like, and the effective corrected image circle.
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Old 09-05-2020, 11:09 AM
Emuhead (Andrew)
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Ok Im probably realistically going Esprit 100ED or 120ED.

I really am trying to now understand how to compare the 100ED to the 120ED, as they both have different apertures and different f numbers.

While the 100ED is faster at f/5.5, the 120ED has a larger aperture but its f/7.

Of course if both scopes had the same aperture this would be easy but hunting for a formula is not as easy as you would think.. Id like to boil these down to a comparable unit of measure, like photons per second or similar (for the same sensor & target).

Given Mono is down the track.. im sticking with a mirrorless for now, the time it takes to capture the image is a concern given the longer exposure time, the more noise.. want to keep the SNR down. If only i could boil these 2 scopes down to comparable units.
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Old 09-05-2020, 11:15 AM
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Comparing without running them side by side is hard

The 100 will appear roughly 1 f-stop faster, so at the same camera settings, so exposures about half the time of the 120.

The flip side is, that for the extra time, the 120 is going to give you more zoom from the focal length.

I'd be sceptical about those reducers...the included flattener sets the bar pretty high, and again it depends on the camera you will use. Starizona specifies an imaging circle of 30mm, which is far from the native, and I'd be concerned how my stars are going to look in even an APS-C sized sensor like that. It's a case of buyer beware...unless you track down some info that demonstrates how well it works...in which case post here

The mono (and cooled) camera really brings the noise under control, and you a calibrate with darks. It really would get the best of either scope.
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Old 09-05-2020, 11:36 AM
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Originally Posted by Emuhead View Post
Thanks for the fast response Greg. I have spent a fair amount of time on the old astrobin checking out what these & other scopes can do, and its a great resource for sure.. even have my own little page on there.

So all 5 of those have FPL-53 glass as it goes, and im sure all have pretty decent focusers (some rack & pinion, some not). I am ever so slightly leaning toward the 120mm but can i shoot at f/7, or will i have to spend the extra to get the x0.65 reducer which will end up netting me what could essentially be a very expensive Esprit 100ED (more or less).
FPL53 doublet probably is quite good but really in my experience you really want the triplet. Doublets are really non APO but are called APO for marketing.
Even Tak doublets are going to fall short for imaging. I had a high end Tak FS152 fluorite doublet and it was superb visually but for imaging it tended to get false colour on brighter stars - a blue ring, which is the usual thing you see with non APO scopes.

The Esprits though seem pretty good for imaging.

Greg.
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Old 09-05-2020, 11:38 AM
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Personally, in addition to being faster and giving a wider field of view, the 100 is going to be smaller, lighter, easier to mount, easier to guide, cheaper. So long as the focusers were comparable if I were buying I would probably go with the 100.
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Old 09-05-2020, 11:46 AM
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Starizona Apex 0.65 Reducer for Esprit scopes
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Old 09-05-2020, 12:01 PM
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You can easily get bogged down with all the different numbers and specifications - I remember buying my first scope and it's a bit overwhelming. You've picked some great scopes there, any of them would do the job, but which would do it best? Well, that comes down to what you want to get out of it.

Given your enthusiasm and the examples given I think the Esprit 100 won't have enough focal length for you. My old ED102 had a focal length of 714mm and for me it wasn't quite enough - sure, you could fit the majority of eta Carina in but other nebula appeared a bit small for my liking. At 550mm I think you will quickly outgrow the Esprit 100. The 120 at 840mm is a much better choice I think.

Yes, you will have to image for longer with the Esprit 120 at f/7 - but really so what? If it's going to give you the kind of photos you want then that's what matters. I understand you're concerned about SNR but again, that's just one of the things you'll have to account for to get the photos you want. With proper cooling the noise can be kept under control quite well.

One other thing - this hobby takes an incredible amount of patience. Those amazing images you see - you probably won't be able to get that kind of quality until you have a lot of practice. I too am chasing the ability to take those breathtaking shots, be patient with it otherwise it's easy to get frustrated along the way
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Old 09-05-2020, 12:27 PM
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Sensor size will give a certain field of view also. Small sensors like the 183 won't fit in as much as the larger 1600 or the full frame versions. Pixel size matters too.

Just buy 2 of everything and you will have it all.

Last edited by cometcatcher; 09-05-2020 at 12:38 PM.
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Old 10-05-2020, 08:48 AM
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You can easily get bogged down with all the different numbers and specifications - I remember buying my first scope and it's a bit overwhelming. You've picked some great scopes there, any of them would do the job, but which would do it best? Well, that comes down to what you want to get out of it.

Given your enthusiasm and the examples given I think the Esprit 100 won't have enough focal length for you. My old ED102 had a focal length of 714mm and for me it wasn't quite enough - sure, you could fit the majority of eta Carina in but other nebula appeared a bit small for my liking. At 550mm I think you will quickly outgrow the Esprit 100. The 120 at 840mm is a much better choice I think.

Yes, you will have to image for longer with the Esprit 120 at f/7 - but really so what? If it's going to give you the kind of photos you want then that's what matters. I understand you're concerned about SNR but again, that's just one of the things you'll have to account for to get the photos you want. With proper cooling the noise can be kept under control quite well.

One other thing - this hobby takes an incredible amount of patience. Those amazing images you see - you probably won't be able to get that kind of quality until you have a lot of practice. I too am chasing the ability to take those breathtaking shots, be patient with it otherwise it's easy to get frustrated along the way
Its aperture not F ratio that determines exposure time.
So the 120 should need less exposure time than a 100 as its got 20% plus larger aperture = more light collected.

F ratio is more the field of view (its not quite intuitive because of how camera lenses get rated often by F ratio).

Everything is easier with a 100m scope and there are lots of widefield objects. the 120 840mm focal length opens up a lot of targets. These smallish sensor ASI183mm or ASI1600 also means you can get a lot of objects as well.

I must say though that 100mm scopes provide images I find most people like the best.

Greg.
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Old 10-05-2020, 09:35 AM
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Originally Posted by gregbradley View Post
Its aperture not F ratio that determines exposure time.
So the 120 should need less exposure time than a 100 as its got 20% plus larger aperture = more light collected.

F ratio is more the field of view (its not quite intuitive because of how camera lenses get rated often by F ratio).

Everything is easier with a 100m scope and there are lots of widefield objects. the 120 840mm focal length opens up a lot of targets. These smallish sensor ASI183mm or ASI1600 also means you can get a lot of objects as well.

I must say though that 100mm scopes provide images I find most people like the best.

Greg.
Not quite right there Greg, its the interplay between f/ratio and pixel size that determines exposure time.
A perfect example of this would be with what I get from my backyard. Using the same sensor on two telescopes that have similar aperture but vastly different focal lengths. A 10” F/10 and 8” F/3. One is as 0.4”/pixel while the other is at 1.67”/pixel.

In the first instance I can do 120s exposures under full moon and bortle 7 skies and still not quite be getting close to covering read noise; this is with a OSC mind you so it picks up a lot of light pollution.
Alternatively I can do 100s exposures under Bortle 2 moonless skies and be 10x read noise with the 8” F/3.

Another example would be between your 12” Honders and a 50mm lens both at F/3.8. Your Honders captures some 390x the amount of light (with a 50% obstruction) but they require the same exposure time with the same sensor. You wouldn’t expect a 50mm lens to take nearly 400x the amount of exposure.

This is of course for extended objects like galaxies, IFN and nebula, point light sources like stars are determined purely by aperture.
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