What have you seen in a 5" Refractor, that you've not seen in an 8" newt?

[Flame Nebula]

3 hours ago, Stu said:

They certainly can. It is specifically emission nebulae (and planetary nebulae) which are enhanced as the emit light at specific frequencies so that filters can be produced which just allow these frequencies to pass, blocking out most of the rest. This does dim the image a bit, but increases contrast by increasing the difference in brightness between background and target. They still perform best under dark skies and with good dark adaptation but will allow views of some objects under relatively light polluted skies.

Reflection nebulae, and galaxies generally don’t benefit from filters as their light is broadband in nature so a filter just decreases the brightness of the whole image.

Don’t listen to the ‘you can only use them in 8” or larger scopes’ comments, they are not true. Yes, you do need some dark adaptation and dark skies but filtering can give amazing views of some objects like the Veil in 4” scopes, smaller even.

Actually, you haven’t talked about a 4” scope as far as I recall. If the same question was asked about 8” vs 4” you could add wider files views to the list. If you stick a 31mm Nagler in a Starfield 102mm you get a 3.5 degree field, enough for the whole Veil just about, whereas an 8” gives just over 2.1 degrees.

Hi Stu, 

Thanks for this. They do seem useful. I live in a bortle 6 area, so hopefully dark enough. Seems dark enough to me on moonless night, although nothing like sky that looks like icing sugar has been scattered across it. 😉

I did consider the starfield after Mr Spock's wonderful comparison with a tak. For similar money I could get a used Sw120 Ed, and I understand the jump between 4 and 5 " apo is significant, plus I have an 80ed already, so going from 3" to 5" seems better, with the 8" newt topping out the aperture. So, going back to your wide field comment, I could use the filters with the 80ed. Just need to make sure I get the right size for all three (potentially) scopes. Actually, thinking about that, all my eyepieces are 1.25", so I think the decision is clear on that point, as I currently haven't budgetted for any more eyepieces😊. My 8-24mm Baader zoom has proven to be multiple eyepieces in one package, at least as good as my individual ones within same range, although they are not top end ones, whereas the zoom is quality. My widest is an ES 68° 24mm, which quite a nice one, for the money. That would give me 2.7°, according to astronomy tools. Maybe I do need to get a wider eyepiece! 🤣

Edit: just checked again, and if I have my 0.85 reducer on, I could get 3.2°, so not far off. 

Edit: so having researched further, £180 would get me a quality combo of an astronomik O-III and an ES 62° 32mm,2" eyepiece,  which should give me 3.3° and with the filter, a good chance in my bortle 6 skies. What do you think? 

Edit: Mmm, a 2" O-III is £180,so £270 for the combo. I thought it seemed cheap before! 

Edit: I've read some of your past posts on using a 1.25" filter with 2 " eyepiece. Sounds interesting! Have you done this for the veil? I've asked flo if they sell an adapter that will allow this, as I have mainly 1.25" eyepieces, so for smaller objects, would use those. 

 

 

Edited April 20 by Flame Nebula

[Mr Spock]

7 hours ago, Flame Nebula said:

Do you mind me asking which brand of variable polariser you used? 

From reading other threads it also looks like having a O-III and UHC filter can enhance certain objects like nebula and planetary nebula. Do you have either of these? 

The variable polariser I use is the Astro Essentials from FLO. Not that expensive.

I have a 2" and 1.25" OIII - I sold my UHC. None work that well in my light pollution.

[Flame Nebula]

9 minutes ago, Mr Spock said:

The variable polariser I use is the Astro Essentials from FLO. Not that expensive.

I have a 2" and 1.25" OIII - I sold my UHC. None work that well in my light pollution.

Thanks Mr Spock 

If my memory serves, you're in bortle 6? Same as me, or in same ballpark. Although I can get to darker skies not far away, they'd be in some farmer's field🤣

[John]

I find good O-III and UHC filters very useful under my bortle 5-ish skies. I say good ones because I've tried a few lower cost ones that were not very effective but staying with brands such as Astronomik and Tele Vue (which are now made by Astronomik) has paid noticeable dividends. With small to medium apertures the O-III filter especially can make the difference between seeing practically nothing and having quite a nice view of targets such as the Veil and Owl nebulae. The UHC's are a bit more subtle but subtle over a slightly wider range of targets, if that makes any sense !. If possible it's worth having both in your tool kit though. I'm talking about visual use of course. Imaging filters are different although still very valuable I believe.

Maybe worth a separate thread on filters ?

 

 

[Flame Nebula]

4 minutes ago, John said:

I find good O-III and UHC filters very useful under my bortle 5-ish skies. I say good ones because I've tried a few lower cost ones that were not very effective but staying with brands such as Astronomik and Tele Vue (which are now made by Astronomik) has paid noticeable dividends. With small to medium apertures the O-III filter especially can make the difference between seeing practically nothing and having quite a nice view of targets such as the Veil and Owl nebulae. The UHC's are a bit more subtle but subtle over a slightly wider range of targets, if that makes any sense !. If possible it's worth having both in your tool kit though. I'm talking about visual use of course. Imaging filters are different although still very valuable I believe.

Maybe worth a separate thread on filters ?

 

 

Hi John, 

Indeed, I just edited a post to Stu, about my research, which matches exactly what you've said. 👍

Mmm, a new post. Not sure if I dare.. 🤣

[wesdon1]

19 hours ago, Mr Spock said:

I think there are many swings an roundabouts between a good apo and a Newtonian.

On a day of good seeing my 12" Newt can reveal the finest detail on the moon. A few nights ago it was cruising at x380. It's not the highest it can go as the seeing wasn't perfect, but high enough to see 1km craters. However, the same night, double stars were fuzzy. When seeing is excellent it shows pinpoint airy discs, and I have split 0.4" doubles, but it does require excellent seeing. Very good isn't good enough and most of the time stars can look fuzzy.

With something like Jupiter you have to use a variable polariser with the 12" to cut down brightness. When you do you can't see diffraction spikes.

The 4" apo on the other hand shows airy discs at the drop of a hat. Seeing can be just acceptable and it is good. It can never approach the 12" for detail, but its performance belies its size, especially when seeing isn't so good.

If I was going purely for double stars I'd want a large apo. 150mm+ if funds were unlimited.

There's the other issue, cost. If you include the mount, the 4" in total cost four times what the 12" cost... I'm sure you could create an offset sub aperture mask for the 12" to avoid the central obstruction and get the same mm for mm performance - without the size convenience of course.

@Mr Spock Hi, may I ask, what is that "offset sub aperture mask"? Also, and please forgive me if I sound stupid, but how is it possible to avoid a Newtonians central obstruction? Or have I misunderstood what you meant? Again please don't laugh at me if I sound dumb! 🤦‍♂️😂

Many Thanks, Wes.

[wesdon1]

19 hours ago, Flame Nebula said:

Thanks Mr Spock, 

Pulling out one particular comment, I was interested in the variable polariser. How does it affect the appearance of jupiter, wrt bands, GRS, etc? 

@Flame Nebula Hi again. I've used a variable polariser many many times of 7-8 years doing visual and in my experience they aren't much use for Sat. and Jup. in terms of reducing brightness because brightness of those planets has never been an issue for me. One planet that I would argue the VP is essential for viewing though, is Venus! It is stupendously bright! You definitely need a VP to view Venus, and you get to resolve it's phase! It's very pretty!

I must also qualify the statement, by saying I've only ever used the VP with an aperture of up to 8 inches, so it's entirely possible larger aperture 'scopes might benefit from it when viewing Jup. and Sat? I'm other much more experienced members can advise you on that!

Edited April 20 by wesdon1

[Flame Nebula]

4 minutes ago, wesdon1 said:

@Flame Nebula Hi again. I've used a variable polariser many many times of 7-8 years doing visual and in my experience they aren't much use for Sat. and Jup. in terms of reducing brightness because brightness of those planets has never been an issue for me. One planet that I would argue the VP is essential for viewing though, is Venus! It is stupendously bright! You definitely need a VP to view Venus, and you get to resolve it's phase! It's very pretty!

I must also qualify the statement, by saying I've only ever used the VP with an aperture of up to 8 inches, so it's entirely possible larger aperture 'scopes might benefit from it when viewing Jup. and Sat? I'm other much more experienced members can advise you on that!

Thanks Wes, 

I'll probably see what jupiter looks like without, and then consider it. I was more interested in if it would allow extra details to be seen. Did you not see anything extra at 8" aperture? 

[wesdon1]

17 minutes ago, Flame Nebula said:

Thanks Wes, 

I'll probably see what jupiter looks like without, and then consider it. I was more interested in if it would allow extra details to be seen. Did you not see anything extra at 8" aperture? 

@Flame Nebula Assuming your question relates to the 5inch refractor vs 8inch newtonian? Oh yes definitely. Impo the views of planets like Jup. and Sat. and others is much better through my 8inch newt than my "almost" 5 inch refractor. One thing to note, your local seeing conditions can have a big effect your views, so when it's really bad seeing, I have found the views to be slightly better through the refractor/120mm. I believe the reason is when seeing is bad, the ability to resolve fine details in planets is limited, and larger aperture 'scopes simply help you "see" more of the bad seeing, if that makes sense? ( I don't know if you know already, but just incase, seeing refers to the atmospheres "steadiness". When its bad, the views of planets, particularly at higher mags, are not very pleasing. A good analogy is looking at pebbles in a stream, where they appear all wobbly n blurred ) My personal advice would be get an 8inch newtonian, they're relatively cheap, the ratio of pounds spent per mm of aperture is as good as you'll get in astronomy! They pack a heck of a punch for the money! Other members may have different opinions but this is my own personal experience! Hope this helps! 

Edited April 20 by wesdon1
needed to add some more bits!

[wesdon1]

21 minutes ago, Flame Nebula said:

Thanks Wes, 

I'll probably see what jupiter looks like without, and then consider it. I was more interested in if it would allow extra details to be seen. Did you not see anything extra at 8" aperture? 

@Flame Nebula Just a heads up, I don't know how quickly or not you seen my reply but i've just written a bit more to it, bits I forgot to mention! 

[F15Rules]

19 hours ago, Flame Nebula said:

Thanks John 

Indeed, I started saving up, on a slow trajectory from early 2021 towards planned purchase, late 2024, as I am essentially a planet person, and checked when jupiter would be high in the sky again , back in early 2021. I even have my wife's permission to buy a 'special' scope. Not exactly mentioned the mount, plus AP accessories, but given I originally intended to get a C9.25 evolution, you're already talking around 2.5K anyway. So, what's a K (ish) more, between friends. 🤔😉. Initially the cost of the mount and vanilla 200pds would be < 2.5K anyway. It's adding AP stuff that increases cost. If all goes well, I'll have saved 4k by September. So, the budget will cover most of the things I'd like. Do you think a used SW120ED will be as good as newest version? I've heard some things about different coatings? 

But, what will stop me, is if things go sideways on job front, as I can't really justify that sort of expenditure then, even though I've tried to ring fence it and keep it separate from other expenses. Fingers crossed. 🤞

In 2017 I was in the happy position, at the age of 61, to acquire my dream scope, an immaculate 1999 Takahashi FS128 Fluorite Apo complete with Takahashi equatorial mount, tripod and a few Tak accessories. It was to be my "lifetime scope", and my wife fully supported the purchase.

I owned the setup for 7 years but in the last 2-3 years began to have to accept that my deteriorating eyesight would prevent me from getting the best from the FS128 going forward. Also, the FS128 is a large, bulky scope for it's aperture (although not too heavy), and with our poor climate for astro, I reluctantly decided to slightly downsize the scope but to keep the Tak mount.

Here is where I think the point I want to make kicks in. When I sold the Tak in February, it was a 24 year old scope, albeit in superb condition. I had 3 firm offers to buy it at the asking price within 3 hours of offering it for sale: I managed to get back very close to what I paid for it in 2017, and with the proceeds I was able to buy a mint 1 year old Vixen SD115S apo (itself a superb scope), and a set of 6 high quality Vixen LVW eyepieces, with some change left over.

So the Tak depreciated very little, and I doubt that any reflector would hold it's value in the same way (although the reflector would of course cost far less to begin with).

I actually feel that your stated plan to end up with ED 80mm and120mm to 128mm refractors and an 8" reflector would give you an ideal spread of scopes that would cover all your needs for the rest of your observing life. On different objects and in different conditions, a 5" refractor and a  8" reflector can show a fantastic, wide range of objects really well, and are different enough to justify owning both if you are able to.

I hope your future work and eye health circumstances allow you to achieve this. All I would say finally, is if/when the opportunity arises, seize it!..your eyesight will likely never be better than it is now, nor your physical strength for lugging equipment around.

I have never regretted buying the Tak, and am fortunate to have found a worthy, if slightly less powerful replacement.

Good luck with achieving your astro goals.

Dave

 

Edited April 20 by F15Rules
Typo

[Mr Spock]

49 minutes ago, wesdon1 said:

Hi, may I ask, what is that "offset sub aperture mask"? Also, and please forgive me if I sound stupid, but how is it possible to avoid a Newtonians central obstruction?

Here's how it works:

With a 300mm scope you should be able to get around 125mm without obstruction. So around f12 and completely CA free.

[wesdon1]

14 minutes ago, F15Rules said:

In 2017 I was in the happy position, at the age of 61, to acquire my dream scope, an immaculate 1999 Takahashi FS128 Fluorite Apo complete with Takahashi equatorial mount, tripod and a few Tak accessories. It was to be my "lifetime scope", and my wife fully supported the purchase.

I owned the setup for 7 years but in the last 2-3 years began to have to accept that my deteriorating eyesight would prevent me from getting the best from the FS128 going forward. Also, the FS128 is a large, bulky scope for it's aperture (although not too heavy), and with our poor climate for astro I.l.reluctantly decided to slightly downsize the scope but to keep the Tak mount.

Here is where i think the point I want to make kicks in. When I sold the Tak in February, it was a 24 year old scope, albeit in superb condition. I had 3 firm offers to buy it at the asking price within 3 hours of offering it for sale: I managed to get back very close to what I paid for it in 2017, and with the proceeds I was able to buy a mint 1 year old Vixen SD115S apo (itself a superb scope), and a set of 6 high quality Vixen LVW eyepieces, with some change left over.

So the Tak depreciated very little, and I doubt that any reflector would hold it's value in the same way (although the reflector would of course cost far less to begin with).

I actually feel that your stated plan to end up with ED 80mm and120mm to 128mm refractors and an 8" reflector would give you an ideal spread of scopes that would cover all your needs for the rest of your observing life. On different objects and in different conditions, a 5" refractor and a  8" reflector can show a fantastic, wide range of objects really well, and are different enough to justify owning both if you are able to.

I hope your future work and eye health circumstances allow you to achieve this. All I would say finally, is if/when the opportunity arises, seize it!..your eyesight will likely never be better than it is now, nor your physical strength for lugging equipment around.

I have never regretted buying the Tak, and am fortunate to have found a worthy, if slightly less powerful replacement.

Good luck with achieving your astro goals.

Dave

 

@F15Rules Awww that's a lovely post! And very wise! 🙂👏

[wesdon1]

3 minutes ago, Mr Spock said:

Here's how it works:

With a 300mm scope you should be able to get around 125mm without obstruction. So around f12 and completely CA free.

@Mr Spock Oohh my goodness yes!! I always wondered what exactly those capped holes in my newts' front plastic covers were for! Thank You for educating me Mr Spock! ☺️👍

Edited April 20 by wesdon1
missed a bit

[Flame Nebula]

55 minutes ago, wesdon1 said:

@Flame Nebula Assuming your question relates to the 5inch refractor vs 8inch newtonian? Oh yes definitely. Impo the views of planets like Jup. and Sat. and others is much better through my 8inch newt than my "almost" 5 inch refractor. One thing to note, your local seeing conditions can have a big effect your views, so when it's really bad seeing, I have found the views to be slightly better through the refractor/120mm. I believe the reason is when seeing is bad, the ability to resolve fine details in planets is limited, and larger aperture 'scopes simply help you "see" more of the bad seeing, if that makes sense? ( I don't know if you know already, but just incase, seeing refers to the atmospheres "steadiness". When its bad, the views of planets, particularly at higher mags, are not very pleasing. A good analogy is looking at pebbles in a stream, where they appear all wobbly n blurred ) My personal advice would be get an 8inch newtonian, they're relatively cheap, the ratio of pounds spent per mm of aperture is as good as you'll get in astronomy! They pack a heck of a punch for the money! Other members may have different opinions but this is my own personal experience! Hope this helps! 

Thanks Wes, 

A very good analogy using the stream and pebbles. 👍

It seems from all I've read so far, that the logical path is via the 200pds, which is now 100% probable, up from 95% last month. 🤣

I think part of me would also like a used SW 120ed, as I think it may have the potential to complement the newt, and I have a suspicion that for some targets like Sirius , it might be easier to pull out the pup. But, it would make sense to make every effort with the 8" first. 

 

[wesdon1]

13 minutes ago, Flame Nebula said:

Thanks Wes, 

A very good analogy using the stream and pebbles. 👍

It seems from all I've read so far, that the logical path is via the 200pds, which is now 100% probable, up from 95% last month. 🤣

I think part of me would also like a used SW 120ed, as I think it may have the potential to complement the newt, and I have a suspicion that for some targets like Sirius , it might be easier to pull out the pup. But, it would make sense to make every effort with the 8" first. 

 

@Flame Nebula I honestly think you wont be disappointed by getting the cheaper Newtonian first! Then definitely when funds allow get a Skywatcher 120ED, they're brilliant refractors, my best friend Colin owns one and they're such great 'scopes! 

I recall earlier seeing you ask another member was it worth buying used? My personal opinion is nearly always buy used! I'll explain. This hobby, as you know, can get very expensive indeed! So buying used is practically a must for most people! You can get save so much money plus the majority of expensive astronomy gear will have been well taken care of by their respective owners for the very reasons i'm telling you to buy used in the first place! lol. Why spend £1000 on something when you can spend £500-£700 and get an instrument that will do EXACTLY the same thing as a brand new one, save for a few scratches on it's paintwork, or some dust here and there?? Telescopes, atlleast the decent ones, are built to endure, tthey have to deal with the elements, with cold/heat etc so they're generally very hardy and with proper care and maintenance will last a lifetime! If i tell you nothing else, please consider buying quality used telescope/gear! Obviously be diligent when buying from a stranger but that's common sense for buying anything as you well know my friend! 

Edited April 20 by wesdon1
missed a bit

[Flame Nebula]

51 minutes ago, F15Rules said:

In 2017 I was in the happy position, at the age of 61, to acquire my dream scope, an immaculate 1999 Takahashi FS128 Fluorite Apo complete with Takahashi equatorial mount, tripod and a few Tak accessories. It was to be my "lifetime scope", and my wife fully supported the purchase.

I owned the setup for 7 years but in the last 2-3 years began to have to accept that my deteriorating eyesight would prevent me from getting the best from the FS128 going forward. Also, the FS128 is a large, bulky scope for it's aperture (although not too heavy), and with our poor climate for astro I.l.reluctantly decided to slightly downsize the scope but to keep the Tak mount.

Here is where i think the point I want to make kicks in. When I sold the Tak in February, it was a 24 year old scope, albeit in superb condition. I had 3 firm offers to buy it at the asking price within 3 hours of offering it for sale: I managed to get back very close to what I paid for it in 2017, and with the proceeds I was able to buy a mint 1 year old Vixen SD115S apo (itself a superb scope), and a set of 6 high quality Vixen LVW eyepieces, with some change left over.

So the Tak depreciated very little, and I doubt that any reflector would hold it's value in the same way (although the reflector would of course cost far less to begin with).

I actually feel that your stated plan to end up with ED 80mm and120mm to 128mm refractors and an 8" reflector would give you an ideal spread of scopes that would cover all your needs for the rest of your observing life. On different objects and in different conditions, a 5" refractor and a  8" reflector can show a fantastic, wide range of objects really well, and are different enough to justify owning both if you are able to.

I hope your future work and eye health circumstances allow you to achieve this. All I would say finally, is if/when the opportunity arises, seize it!..your eyesight will likely never be better than it is now, nor your physical strength for lugging equipment around.

I have never regretted buying the Tak, and am fortunate to have found a worthy, if slightly less powerful replacement.

Good luck with achieving your astro goals.

Dave

 

Hi Dave, 

I'm not sure why, but your post has had a very emotional effect on me (in a nice way! ☺️). 

I'm going to be 60 later this year, and I have no idea where the last 20 went! 

So, I feel the passage of time  very acutely now. It was a bit of a shock when I was told a year ago (or was it two?) that I had early signs of cataracts in both eyes, although I understand it's not a barrier to visual observation after you have lenses replaced. I hope not anyway. 

And regarding the job security, well, I have set a date of 15 September to start purchasing, if I've not been given any bad news by then. Bad = being told more redundancies are inevitable and soon. Otherwise, one can keep putting things off, waiting for 0% risk, which does not exist, until you realise you've run out of time. Worst case scenario, I could get probably 2/3 back on the cost of a new az-eq6, I'm sure. The newt will cost £430, so not much risk there. I'm planning to get various AP accessories. A used sw120ed around £700-900, and I probably get most of that back, if I had to resell. So, it's not like it's all irreversible one way cost. But I wouldn't sell anything unless my finances were near point of collapse, before which time I'd hope to get another job. 60 is not that old these days! 😉 It's the new 50.🤣 So, as long as I can get the zimmer frame through the door for the job interview, I'll be fine (🤣🤣). 

But seriously , thanks Dave for one of the nicest posts I've had on the forum! 

Mark 

 

[Flame Nebula]

1 hour ago, Mr Spock said:

Here's how it works:

With a 300mm scope you should be able to get around 125mm without obstruction. So around f12 and completely CA free.

Mmm, that is interesting! 

So, let's see if I can generate enough brain power to work it out for a 200mm. Would it be (2/3)*125  = 80mm? F ratio, about 1000/80 = 12.5? That would give me something interesting for jupiter, like a long focal length achromat, but better? 

[Flame Nebula]

1 hour ago, Mr Spock said:

Here's how it works:

With a 300mm scope you should be able to get around 125mm without obstruction. So around f12 and completely CA free.

So, you just place a cover over the end of the newt, with a circle cut out of it? 

[Mr Spock]

6 minutes ago, Flame Nebula said:

So, let's see if I can generate enough brain power to work it out for a 200mm. Would it be (2/3)*125  = 80mm? F ratio, about 1000/80 = 12.5? That would give me something interesting for jupiter, like a long focal length achromat, but better?

About that. What you would do is measure from the edge of the secondary to the edge of the mirror. Or just subtract half the secondary size from half the mirror size.

4 minutes ago, Flame Nebula said:

So, you just place a cover over the end of the newt, with a circle cut out of it? 

It works much better if next to the mirror due to diffraction.

[Flame Nebula]

28 minutes ago, wesdon1 said:

@Flame Nebula I honestly think you wont be disappointed by getting the cheaper Newtonian first! Then definitely when funds allow get a Skywatcher 120ED, they're brilliant refractors, my best friend Colin owns one and they're such great 'scopes! 

I recall earlier seeing you ask another member was it worth buying used? My personal opinion is nearly always buy used! I'll explain. This hobby, as you know, can get very expensive indeed! So buying used is practically a must for most people! You can get save so much money plus the majority of expensive astronomy gear will have been well taken care of by their respective owners for the very reasons i'm telling you to buy used in the first place! lol. Why spend £1000 on something when you can spend £500-£700 and get an instrument that will do EXACTLY the same thing as a brand new one, save for a few scratches on it's paintwork, or some dust here and there?? Telescopes, atlleast the decent ones, are built to endure, tthey have to deal with the elements, with cold/heat etc so they're generally very hardy and with proper care and maintenance will last a lifetime! If i tell you nothing else, please consider buying quality used telescope/gear! Obviously be diligent when buying from a stranger but that's common sense for buying anything as you well know my friend! 

Thanks Wes, 

I'll probably get the mount new, as it really is critically important there are no issues with it, as I intend to also do DSO AP, which will need very accurate tracking, especially if I move up from frac to newt. But, if I see a used 200pds which has been modded, and I know many people do, and it's cheaper than new, it would be hard to resist. The only pain is travelling several hundred miles, only to find the mirror has, shall we say, seen better days. 

However, I think for the frac, you're totally right. In fact I bought my 80ed for £330 off Ebay and it's perfect! Same with the 127mm mak, £120 off Ebay. Nothing wrong with it. However, I would not buy more expensive stuff from there. I did see a £700 frac being sold near where my parents live in Wales, but not ready to buy yet. But, it shows they're out there at that price. 

With gear like the asiair, being electronic and again absolutely critical part of dso AP, I'd probably buy new. 

But, case by case I think. 👍

[Flame Nebula]

13 minutes ago, Mr Spock said:

About that. What you would do is measure from the edge of the secondary to the edge of the mirror. Or just subtract half the secondary size from half the mirror size.

It works much better if next to the mirror due to diffraction.

OK, so I think 200pds has a 58mm secondary, so that's 29. 100-29=71mm, F14 approx., assuming 1000mm focal length. So nearly a 3" frac with long focal length. I wonder how that would appear on say jupiter, compared to my 80ed. An experiment, I must conduct! 

Edited April 20 by Flame Nebula

[Mr Spock]

Don't forget your mirror is probably 203mm 

[Flame Nebula]

1 minute ago, Mr Spock said:

Don't forget your mirror is probably 203mm 

101.5-29=72.5mm. 

Definitely nearly 3" frac 😉

[Flame Nebula]

1 minute ago, Flame Nebula said:

101.5-29=72.5mm. 

Definitely nearly 3" frac 😉

So, here's a question, which is now so far off my original post, I've forgotten what started it. 🤣

But, I'm here so may as well ask. 

Do you think a very a long focal length pseudo frac using this approach, and avoiding diffraction spikes, could facilitate seeing the pup, more easily?