Which would you choose 6” Newt or 4” Achro ?

[John]

6 hours ago, Louis D said:

In my experience, my 6" f/5 Newtonian runs huge circles around my 80mm (3.1") f/5 refractor.  To equate them in performance in any way is a complete insult to the Newtonian.

Maybe things were different in the UK in the 1950's though ?

I suspect Sir Patrick's advice stemmed from that era.

 

[IB20]

6” f8 all day long. Now a 4” APO v a 6” newt and I’d probably plump for the 4”.

[Louis D]

5 hours ago, John said:

Maybe things were different in the UK in the 1950's though ?

I suspect Sir Patrick's advice stemmed from that era.

 

I think the choice was biased by poorly figured, coated, and aligned Newtonians of the day.  3" slow achromats of that era tended to be of very good quality in comparison.  A 6" Newt of the day would have been very long and unwieldy.

Some old Unitron cartoons along these lines:

[F15Rules]

On 20/02/2024 at 18:44, John said:

I have enough refractors so I'd go for the F/8 6 inch newtonian I think.

I always liked the classic looks of  the TAL 2M 🙂

 

Thats the only Newt I've ever found attractive to look at. But I'd still have to stand up to view most objects and tilt my head at an awkward angle to view through it🤪!! A literal pain in the neck!😂

On 20/02/2024 at 18:27, vlaiv said:

Out of interest, what is the purpose of this inquiry?

I suspect David's original thread starter post was somewhat, er, mischievous..😉🙄.

Dave

[vlaiv]

6 minutes ago, F15Rules said:

I suspect David's original thread starter post was somewhat, er, mischievous..😉🙄.

[Saganite]

21 minutes ago, F15Rules said:

Thats the only Newt I've ever found attractive to look at.

Dave

Never thought I would hear you say that ...ever, about 'ship's funnels'  Dave....🙂

Edited February 23 by Saganite

[F15Rules]

20 minutes ago, Saganite said:

Never thought I would hear you say that ...ever, about 'ship's funnels'  Dave....🙂

Well, Steve I'm nothing if not open minded!!🤭😋

[John]

39 minutes ago, Saganite said:

Never thought I would hear you say that ...ever, about 'ship's funnels'  Dave....🙂

Antidote to a "ship's funnel" 🙂

U.K. Astronomy Buy & Sell (astrobuysell.com)

[Saganite]

There was a time when I craved a 3" brass refractor, or was it a 6" reflector?....

I ended up with a 6" reflector , homemade  in 1974, certainly couldn't afford the former.

But the brass refractors have a unique beauty all their own....

[Coco]

I have a Celestron 102mm f6.5 achro & Bresser 127L which I really like, my 6” f/8 Newtonian (sold) was better than both for colour, better than the 102 for sharpness on planets but not as sharp as the 127L, Neither are as good as my 12” Revelation dob with Hilux coatings. 
I’ll get around to mounting the 102 on my dob at some point as it has encoders + Nexus and can easily take the weight, should be easy to dig out bigger OIII targets.

[F15Rules]

36 minutes ago, John said:

Antidote to a "ship's funnel" 🙂

U.K. Astronomy Buy & Sell (astrobuysell.com)

Thats beautiful John..and with a Carton OG too! I wonder if Richard might accept a cheeky offer for the objective only, to try out versus my Vixen 80mm F15??😂

[Mr Spock]

Ship's funnel? Don't insult the Tubies like that 

[lvan]

Refractor > Reflector

[900SL]

On 22/02/2024 at 15:10, Louis D said:

In my experience, my 6" f/5 Newtonian runs huge circles around my 80mm (3.1") f/5 refractor.  To equate them in performance in any way is a complete insult to the Newtonian.

How would you rate the 6" f5 Newt against your 90mm f6 CF Apo? I've been thinking of a 150/750 newt for longer fl...

[VNA]

Hello, would think aperture would win?

Yes there is the secondary mirror, but. . .  still would go with the 6"
If it were an apochromat, then I would go with the 4",

[Louis D]

7 hours ago, 900SL said:

How would you rate the 6" f5 Newt against your 90mm f6 CF Apo? I've been thinking of a 150/750 newt for longer fl...

Funny you should mention that.  I'm going to try mounting them on either side of my DSV-2B mount the next chance I get and compare the views for aesthetics as well as for absolute sharpness, contrast, resolution, etc.  I'm curious if Sir Patrick was on to something.  I figure a 90mm f/6.9 FPL-53 triplet APO should be similar to an old 3" f/15 or longer achromat as far as color correction goes.  The focal length will obviously be completely different, though.  The Newt is probably faster than the Newts of old as well.

[Louis D]

8 hours ago, lvan said:

Refractor > Reflector

As far as price, you got that right.  My 6" f/5.9 achromat cost 3 times what my 6" f/5 Newt cost (both used).

[The60mmKid]

19 hours ago, Saganite said:

There was a time when I craved a 3" brass refractor, or was it a 6" reflector?....

I ended up with a 6" reflector , homemade  in 1974, certainly couldn't afford the former.

But the brass refractors have a unique beauty all their own....

The unique beauty of the brass refractor is that you don't have to look through it for it to blind you.

😊

[lvan]

17 hours ago, Louis D said:

As far as price, you got that right.  My 6" f/5.9 achromat cost 3 times what my 6" f/5 Newt cost (both used).

A 4” evostar costs less than a 150p

[The60mmKid]

On 23/02/2024 at 01:22, Louis D said:

I think the choice was biased by poorly figured, coated, and aligned Newtonians of the day.  3" slow achromats of that era tended to be of very good quality in comparison.  A 6" Newt of the day would have been very long and unwieldy.

Some old Unitron cartoons along these lines:

The second picture seems to show that one may use a Newtonian as a giant bong. Try that with a refractor. Another point for the Newt.

[lvan]

9 minutes ago, The60mmKid said:

The second picture seems to show that one may use a Newtonian as a giant bong. Try that with a refractor. Another point for the Newt.

Frac would make a better pipe though…

[lvan]

A pipe is less maintenance than a bong, and will get used more, so it stands to reason:

frac > newt

[Louis D]

On 23/02/2024 at 13:28, 900SL said:

How would you rate the 6" f5 Newt against your 90mm f6 CF Apo? I've been thinking of a 150/750 newt for longer fl...

Just got back in from a couple of hour comparison of the two scopea on Jupiter, Collinder 70, the moon, the Orion Nebula, and the Trapezium.

First, both make for excellent scopes.  I could see someone being quite happy with either, especially not having both to compare views.

The differences were more subtle than I expected.

Both are pretty much color free.  The atmosphere was causing a bit of red/blue fringing top to bottom on Jupiter and the moon in both.

Before it got reasonably dark when observing Jupiter, the central obstruction shadow of the Newt was really annoying.  Huge win for the unobstructed APO for daytime use.

Jupiter:

• Better image scale at the same exit pupil made it easier for me to see past my floaters at a particular magnification.  Aperture wins.
• As I increased magnification, the APO didn't really decrease much in contrast on the belts.  However, no new details were visible.  The Newtonian definitely had reducing contrast meaning lower powers were better.  Unobstructed wins.
• Perceived details seemed better on the edges of the belts in the Newt.  They appeared frayed instead of solid as in the APO, as if some detail was about to appear with a bit more aperture.  Aperture wins.

Collinder 70:

• Pretty much dead even.  The APO's stars looked a bit more pinpoint, but the Newtonian showed dimmer stars a bit better.  Tie

Moon:

• Looks great in both.  Perhaps a bit higher contrast in the APO, but a bit finer details visible in the Newt.  Tie

Orion Nebula:

• More nebula brightness, extent, details, and contrast visible at all magnifications.  APO didn't really show anything as good.  Aperture wins.

The Trapezium

• Stars were possibly a bit more pinpoint in the APO, but the Newt was no slouch.  Tie
• E component plainly visible in Newtonian, but no where to be seen in the APO.  It was not a subtle difference.  Huge win for aperture.

Overall, I preferred the larger exit pupil at a given magnification in the Newt due to my really bad floaters.  At really small exit pupils in the APO, I can even plainly see the shadow caused by my observing eye's vitreous humor detachment.  It wasn't as obvious for some reason in the Newt.  I confirmed what it was because it wasn't there in my non-observing eye which has no detachment.

Basically, the higher contrast of the APO just could not compensate for the extra aperture of the Newt.

The higher position of the focuser in the Newt was also easier to use standing instead of crouching as with the APO.  When using the APO alone, I extend the tripod legs to avoid crouching which leads to longer vibration settling times.

The APO's focuser tends to unravel with heavy eyepieces at high altitude angles unless I tighten the drag adjustment.  The Newt's focuser doesn't seem to have this issue, probably because of its angle relative to the ground.

Size wise, they're about the same length with the diagonal attached and the focuser extended to its typical position on the APO .  The Newt is obviously wider.  The Newt is also a few pounds heavier.

Ignore the laser sight on the Newt.  I forgot to take it off for the picture.

Yes, the APO is more svelte looking.  My grown son says it looks "legit".  The Newt looks kind of chunky in comparison.

As for Sir Patrick's assertion about the 3" refractor versus the 6" Newtonian as applied to modern scopes, I'd say "it depends".  Does slightly higher contrast and daytime use matter most?  Does light gathering and resolution matter most?  Size-wise, there's not a lot to distinguish between them.

[josefk]

Nice write up @Louis D - these side by side comparisons are always useful datapoints. 

[The60mmKid]

5 hours ago, Louis D said:

Just got back in from a couple of hour comparison of the two scopea on Jupiter, Collinder 70, the moon, the Orion Nebula, and the Trapezium.

First, both make for excellent scopes.  I could see someone being quite happy with either, especially not having both to compare views.

The differences were more subtle than I expected.

Both are pretty much color free.  The atmosphere was causing a bit of red/blue fringing top to bottom on Jupiter and the moon in both.

Before it got reasonably dark when observing Jupiter, the central obstruction shadow of the Newt was really annoying.  Huge win for the unobstructed APO for daytime use.

Jupiter:

• Better image scale at the same exit pupil made it easier for me to see past my floaters at a particular magnification.  Aperture wins.
• As I increased magnification, the APO didn't really decrease much in contrast on the belts.  However, no new details were visible.  The Newtonian definitely had reducing contrast meaning lower powers were better.  Unobstructed wins.
• Perceived details seemed better on the edges of the belts in the Newt.  They appeared frayed instead of solid as in the APO, as if some detail was about to appear with a bit more aperture.  Aperture wins.

Collinder 70:

• Pretty much dead even.  The APO's stars looked a bit more pinpoint, but the Newtonian showed dimmer stars a bit better.  Tie

Moon:

• Looks great in both.  Perhaps a bit higher contrast in the APO, but a bit finer details visible in the Newt.  Tie

Orion Nebula:

• More nebula brightness, extent, details, and contrast visible at all magnifications.  APO didn't really show anything as good.  Aperture wins.

The Trapezium

• Stars were possibly a bit more pinpoint in the APO, but the Newt was no slouch.  Tie
• E component plainly visible in Newtonian, but no where to be seen in the APO.  It was not a subtle difference.  Huge win for aperture.

Overall, I preferred the larger exit pupil at a given magnification in the Newt due to my really bad floaters.  At really small exit pupils in the APO, I can even plainly see the shadow caused by my observing eye's vitreous humor detachment.  It wasn't as obvious for some reason in the Newt.  I confirmed what it was because it wasn't there in my non-observing eye which has no detachment.

Basically, the higher contrast of the APO just could not compensate for the extra aperture of the Newt.

The higher position of the focuser in the Newt was also easier to use standing instead of crouching as with the APO.  When using the APO alone, I extend the tripod legs to avoid crouching which leads to longer vibration settling times.

The APO's focuser tends to unravel with heavy eyepieces at high altitude angles unless I tighten the drag adjustment.  The Newt's focuser doesn't seem to have this issue, probably because of its angle relative to the ground.

Size wise, they're about the same length with the diagonal attached and the focuser extended to its typical position on the APO .  The Newt is obviously wider.  The Newt is also a few pounds heavier.

Ignore the laser sight on the Newt.  I forgot to take it off for the picture.

Yes, the APO is more svelte looking.  My grown son says it looks "legit".  The Newt looks kind of chunky in comparison.

As for Sir Patrick's assertion about the 3" refractor versus the 6" Newtonian as applied to modern scopes, I'd say "it depends".  Does slightly higher contrast and daytime use matter most?  Does light gathering and resolution matter most?  Size-wise, there's not a lot to distinguish between them.

This was an enjoyable read. Thanks!

Good to keep in mind that a 6" f/8 newt designed for visual observing would probably have a ~20% CO. Those don't give up much (if any) contrast to refractors. If we changed that variable, I think all of the points you mentioned would be either "tie," or a "win" for the newt 😊

I enjoy the unbridled enthusiasm that some of the refractor fans express for their instruments. But, at the eyepiece, I've never seen a smaller refractor (whether APO or long-focus achro) outperform a larger reflector as long as the latter:

- has good optics,

- is collimated,

- is thermally acclimated,

- and isn't being pushed to do things that the seeing won't realistically allow for the given aperture.

This won't help me win any popularity contests, but my suspicion is that those who are stunned by refractor superiority have ignored one of more of those points!