6" F/4 Newtonian, is it a regret?

[TareqPhoto]

Hey all,

I ordered 6" F4 Newtonian today with Bob's Knobs for secondary as i can't wait to have a good serious telescope with good colors, refractor i must buy an APO that good, or even semi APO and not sure it will be well corrected for colors as well, so i decided that the Newtonian will take away this color issue thing, and then i only have to worry about collimation, we will see how difficult it will be collimating F4 once i receive the scope.

What else i have to add with the scope beside collimator and coma corrector? Are you happy with F4 Newt or you feel it is the nail in the head to be used?

[ollypenrice]

F4 is fast and best used with expensive, well-made mechanical parts. It will need good collimation and careful coma correction. Some succeed, some don't. Once I've said that I'm no longer in the realm of hard facts and so I'll stop there. Give it your best go. You may be delighted.

Olly

[Peter Drew]

I have had one.  Never had the option of a coma corrector or modern eyepieces but it gave wide fields and bright images.  Difficult to get high magnifications convenientltly but was meant for wide field visual use anyway.  Colour correction was of course perfect.   🙂

[Skyline]

Don't use a laser collimator and be prepared you might have to invest further. 

Just the facts.

[rl]

Newtonians at F/4 have two main plusses;

They are compact for the aperture. a 12" F/4 is a reasonable portable proposition for anyone fit and healthy with a car.

They are very fast photographically. 

The minuses;

The central obstruction tends to be bigger. This need not be a dealbreaker but if the scope is for photography then the secondary will be oversize to fully illuminate the whole of a 2" circle. If the mirrors are really accurate this does not have to be a dealbreaker for visual use.

Collimation needs to be good.

You need good eyepieces; only expensive ones work well at F/4. 

I've owned several F/4 newts and been very happy with them. My current scopes are a 8" F/4.5 and a 12" f/4. 

What made you choose F/4? Slower ones are much easier for the inexperienced...

[andrew s]

For F4 you will need a good set of collimation tools. I have used Catseye tools in the past with success. 

Regards Andrew 

 

[Chris]

I'll be honest with you, if you like tinkering with things then you'll be happy, but if you want something that will just work out of the box for imaging then you are likely to have to invest a bit of time and extra money.

I've had a couple of f4's and found I was constantly tinkering with them trying to get them setup right. Good advice above about purchasing advanced collimation tools, my cheap laser wasn't accurate enough. Temperature changes also effect collimation with f4's which is something you need to take into account unless using a carbon fibre tube which is more stable. 

F5 is the sweat spot I found. Still fast but very easy to collimate compared to f4.  

I didn't get as far as worrying about coma with mine as I was stuck at the collimation stage, but I know some do get on with f4's and I hope you're one of them

[TareqPhoto]

24 minutes ago, ollypenrice said:

F4 is fast and best used with expensive, well-made mechanical parts. It will need good collimation and careful coma correction. Some succeed, some don't. Once I've said that I'm no longer in the realm of hard facts and so I'll stop there. Give it your best go. You may be delighted.

Olly

The problem is, i saw few did use this type of scope and having amazing results, so i believe that if some can do it why not us or me, i don't want to just give up and say this is an impossible to use scope, and because of the budget i felt like this is my only option now.

[TareqPhoto]

23 minutes ago, Peter Drew said:

I have had one.  Never had the option of a coma corrector or modern eyepieces but it gave wide fields and bright images.  Difficult to get high magnifications convenientltly but was meant for wide field visual use anyway.  Colour correction was of course perfect.   🙂

It will be for DSO imaging and sometimes the moon.

[TareqPhoto]

23 minutes ago, Skyline said:

Don't use a laser collimator and be prepared you might have to invest further. 

Just the facts.

I have a laser collimator and pro Cheshire collimator from FLO.

[TareqPhoto]

21 minutes ago, rl said:

Newtonians at F/4 have two main plusses;

They are compact for the aperture. a 12" F/4 is a reasonable portable proposition for anyone fit and healthy with a car.

They are very fast photographically. 

The minuses;

The central obstruction tends to be bigger. This need not be a dealbreaker but if the scope is for photography then the secondary will be oversize to fully illuminate the whole of a 2" circle. If the mirrors are really accurate this does not have to be a dealbreaker for visual use.

Collimation needs to be good.

You need good eyepieces; only expensive ones work well at F/4. 

I've owned several F/4 newts and been very happy with them. My current scopes are a 8" F/4.5 and a 12" f/4. 

What made you choose F/4? Slower ones are much easier for the inexperienced...

I didn't read this comment long time ago until i mentioned i ordered one, so it is like i buy things late and then people start to comment and mention points of pros and cons.

F4 in Newt was because i wanted something as 500-600mm FL, even 600 is a bit long but i can fit some targets perfectly, so didn't want to get 650mm or 750mm, 150mm[6"] F5 is 750mm, too much, 130PDS is 650mm, i was thinkin about 150mm [6"] vs. 130mm [5"] aperture and i decided the larger one even 1" difference, and because i wanted 600mm or faster so i decided why not give this F4 a try, i already have 8" F5, so at 1000mm, with 0.9x i can go wider a bit to 900mm and f4.5, and with ASA 0.73 and i am at ~730mm F/3.65, so i felt like 750mm won't be a good FL if in future i reduce my 8", and i should think about 130mm F5 with a reducer to go to ~585mm using 0.9x, but then if i reduce it it means it will be faster and then i will have same F4 collimation situation almost.

I asked about getting two or THREE same exactly Achromatic refractor for DSO imaging and all answers said it is not a good idea even with narrowbanding because they will never focus at same point for all filters of RGB and NB, so the Newt is the only cheapest option there for me, i can't spend anything over $400-500 anyway, i could never find any triplet brand new anywhere, and a doublet that good and quality isn't cheap as well so it will be closer to a triplet, it means i won't buy anything and wait longer, and my plan is to add Tak FSQ one way or another after 1 or 2 years, so an affordable APO refr is out of the plan completely because of that Tak FSQ simply, and waiting that to happen means i will waste so many targets and months without imaging, can you recommend something for my plan?

[TareqPhoto]

30 minutes ago, andrew s said:

For F4 you will need a good set of collimation tools. I have used Catseye tools in the past with success. 

Regards Andrew 

 

Honestly speaking, i was requesting 20" Dob last year but my situations changed to very worse, so i delayed or suspended the plan, if it was happening then i will simply buy Howie Glatter collimator, this is as people said the best, i still can but not now, i just have to try the collimators i have first then later i will see if i need to upgrade that.

Regards, Tareq

[andrew s]

You can't full collimate a Newtonian with a Laser.  A key requirement with a fast Newt is to position the secondary under the focuse as it does not have a unique optic axis. This is best done with a sight tube. 

Final positioning of the secondary is best done with an autocollimator. It will also reveal minute shifts as you slow the scope. 

This may not matter to you.

Regards Andrew 

[TareqPhoto]

24 minutes ago, Lockie said:

I'll be honest with you, if you like tinkering with things then you'll be happy, but if you want something that will just work out of the box for imaging then you are likely to have to invest a bit of time and extra money.

I've had a couple of f4's and found I was constantly tinkering with them trying to get them setup right. Good advice above about purchasing advanced collimation tools, my cheap laser wasn't accurate enough. Temperature changes also effect collimation with f4's which is something you need to take into account unless using a carbon fibre tube which is more stable. 

F5 is the sweat spot I found. Still fast but very easy to collimate compared to f4.  

I didn't get as far as worrying about coma with mine as I was stuck at the collimation stage, but I know some do get on with f4's and I hope you're one of them

Ok.

I have 8" F5, so i already did it.

My laser collimator isn't accurate, i figured that out, not stupid to not know, so i watched videos and read articles about how to collimate that laser collimator itself, so i did, i do have two, and both aren't, i collimated one, not sure about the other one, so i ignored it and keep using the one i collimated, it may not be that perfect accurate collimated yet, i have to give it a try with F4 later, and i still didn't test my F5, but as all said, F5 is easier, so i can't judge yet, by the way, i bought my 8" F5 in 2018 got it by Feb, i never tested it maybe until 2019 i think, and i didn't use it yet much, only twice or three times, so i tried to modify it first, what i did is to replace the stock focuser to dual speed, i replaced the screws of secondary to Bob's knobs and now it is a breeze, what else i need to do, later i will buy an advanced collimator to give it a try, in a video someone referred it to me he said i can use a Barlow with my laser collimator, i do have 2x and 3x and 5x, so the bottom line is, i must experiment or give it a try then i see if i give up or not.

[TareqPhoto]

1 minute ago, andrew s said:

You can't full collimate a Newtonian with a Laser.  A key requirement with a fast Newt is to position the secondary under the focuse as it does not have a unique optic axis. This is best done with a sight tube. 

Final positioning of the secondary is best done with an autocollimator. It will also reveal minute shifts as you slow the scope. 

This may not matter to you.

Regards Andrew 

Do you mean using a Cheshire collimator?

[TareqPhoto]

This is what i have, i use it for secondary precisely, and the laser is for primary.

https://www.firstlightoptics.com/other-collimation-tools/premium-cheshire-collimating-eyepiece/action/reviews/

[alacant]

Hi

I'm sure you'll be fine. Your colour worries will be a thing of the past and you'll like how quickly you can build up an image expecially if you're used to a smaller refractor.

I believe some years ago, f4 reflectors earned themselves a poor reputation; bendy tubes, badly corrected mirrors, focusers, spiders...

But it's not years ago any longer. I must admit I was initially put off by all the tales of woe I had read but hey, you use, set up and adjust an f4 just like you would any other Newtonian reflector.

One bit of advice: get the 4 element GPU cc, also available re-badged by SW as 'aplanatic'. Corner to corner, even over aps-c. 

Cheers

 

 

 

Edited April 16, 2020 by alacant

[Craney]

Blimey..... reading all of the above  I would have never bought one !!!!

I love my Orion Optics (UK) 6" F4.   

It will be out again after galaxy season.   Needs collimation for each session but doesn't take too long.   I invested in a Aplanatic corrector

https://www.firstlightoptics.com/coma-correctors/skywatcher-f4-aplanatic-coma-corrector.html

Expensive but very useful if you have a bigger sensor when imaging.

Here's mine. 

Edited April 16, 2020 by Craney

[andrew s]

39 minutes ago, TareqPhoto said:

Do you mean using a Cheshire collimator?

No. Some Cheshire earpieces include a sight tube.

Regards Andrew 

[TareqPhoto]

1 hour ago, alacant said:

Hi

I'm sure you'll be fine. Your colour worries will be a thing of the past and you'll like how quickly you can build up an image expecially if you're used to a smaller refractor.

I believe some years ago, f4 reflectors earned themselves a poor reputation; bendy tubes, badly corrected mirrors, focusers, spiders...

But it's not years ago any longer. I must admit I was initially put off by all the tales of woe I had read but hey, you use, set up and adjust an f4 just like you would any other Newtonian reflector.

One bit of advice: get the 4 element GPU cc, also available re-badged by SW as 'aplanatic'. Corner to corner, even over aps-c. 

Cheers

 

 

 

I just answer your last line, I HAVE "Skywatcher F4 Aplanatic Coma Corrector", anything else? 😉😂

[TareqPhoto]

1 hour ago, Craney said:

Blimey..... reading all of the above  I would have never bought one !!!!

I love my Orion Optics (UK) 6" F4.   

It will be out again after galaxy season.   Needs collimation for each session but doesn't take too long.   I invested in a Aplanatic corrector

https://www.firstlightoptics.com/coma-correctors/skywatcher-f4-aplanatic-coma-corrector.html

Expensive but very useful if you have a bigger sensor when imaging.

Here's mine. 

Lucky you, Orion Optics are nice optics brand.

I have exactly this same coma corrector, i bought it for my 8" F5, i will use it for my F4 simply.

[TareqPhoto]

1 hour ago, andrew s said:

No. Some Cheshire earpieces include a sight tube.

Regards Andrew 

Ah ok.

[laser_jock99]

These fast Newts are 'interesting' scopes and capable of good results but probably not 'out of the box'. Be prepared to modify & fettle the scope to get the best results.

A good laser collimator is a must and these are not cheap. A good coma corrector is also required for best results.

Think about the following mods- stronger primary collimation springs, longer top & bottom dovetail bars.

Be prepared to re-check the focus and collimation of the scope as it cools during a session- at F4 small changes in teperature can have big effects in the focus position with metal tube Newts.

Now- if you're a complete nutter add one of these 0.73x coma corrector reducers to your scope to make it F2.9!

NGC7000 in 159 seconds with a 6" F2.9 Newtonian

[TareqPhoto]

10 hours ago, laser_jock99 said:

These fast Newts are 'interesting' scopes and capable of good results but probably not 'out of the box'. Be prepared to modify & fettle the scope to get the best results.

A good laser collimator is a must and these are not cheap. A good coma corrector is also required for best results.

Think about the following mods- stronger primary collimation springs, longer top & bottom dovetail bars.

Be prepared to re-check the focus and collimation of the scope as it cools during a session- at F4 small changes in teperature can have big effects in the focus position with metal tube Newts.

Now- if you're a complete nutter add one of these 0.73x coma corrector reducers to your scope to make it F2.9!

NGC7000 in 159 seconds with a 6" F2.9 Newtonian

I feel like i will never make collimation right then, because everywhere all people talk about collimation, so it means i have to wait until i can afford Howie Glatter collimator or Catseye for example then i can make it right.

This reducer corrector is definitely in my list, but i don't know if i will use it for my 8" F5 or 6" F4, it will do good in both, but i was thinking about trying 0.9x reducer first maybe so i can reduce only little or it is not worthy and i just go direct to 0.73x?

I don't know what to expect with this 6" F4, but i bought now because i want to get busy with "Cygnus" constellation that is already nearby, it is still late for it to be high at good time, so until next month i will practice with the scope once i receive it and then i hope i will be ready, if it is that good really i may buy another one so i can do dual rig imaging.

[alacant]

12 hours ago, TareqPhoto said:

i will never make collimation right

Hi

Do you have a Cheshire sight tube with cross hairs? Do exactly as you do with your other Newtonian. The only difference you'll see is a greater (at first quite alarming) secondary offset.

Cheers.

Edited April 18, 2020 by alacant