cheap f4 reflector: am I crazy?

[alacant]

Hi. I've been thinking about a fast reflector such as this f3.9 model . I currently have a 6" f5 -alas only on loan- by the same company and like its build quality and the images it can produce. Is it true that the fast newtonians aren't worth the hassle? I've read horrors of them going out of collimation simply by slewing to the target. Maybe I'm mad to even consider this option and should get a f5 like the one I have ATM... All POVs welcome. TIA and clear skies.

[Pieter]

I can't help you with any specific data but I was going for such a scope normally but the vendor at a local shop that sells these items told me in an honest moment he had a lot of people lately with problems and returning them.

On the contrary, I know someone that has one and he loves it but has not yet used it for astrophotography.

[laser_jock99]

The GSO F4 Newtonians are okay budget scopes (I  own the 6", 8", 10" & 12" versions).

http://www.teleskop-express.de/shop/product_info.php/info/p52_TS-Optics-GSO-8--f-4-Newtonian-Telescope---optical-tube-assembly.html

The optical quality is good and the mechanics can be easily modified to make the scope as stable as the more expensive 'tuned' F4 scopes.

 

[alacant]

8 hours ago, laser_jock99 said:

the mechanics can be easily modified

Hi. OK, thanks for the feedback. What needs to be done with the mechanics? Which do you use most? I was thinking of the 200mm which would be at the limit for my eq6. Also does the Baader cc work with your 8"? Sorry, so many questions. TIA

[laser_jock99]

15 hours ago, alacant said:

Hi. OK, thanks for the feedback. What needs to be done with the mechanics? Which do you use most? I was thinking of the 200mm which would be at the limit for my eq6. Also does the Baader cc work with your 8"? Sorry, so many questions. TIA

The main mod that can be done on most budget Newts is to improve collimation stabilty and ease of collimation is by replacing the springs and putting in some decent quality adjuster knobs:

Why manufacturers don't do this to start with beats me- it only costs a few extra pounds?

Other things I have done to improve performance and stability include using a longer, stronger Dovetail bar (e.g. replace the supplied Skywatcher bar with a longer Losmandy type bar) the wider tube ring spacing reduces tube flex. Also adding a sturdy aluminium 'top bar' to the tube helps enormously and gives you a mounting platform for your guidescope. I have also added some internal flocking to my Newts.

 

Here you can see my 8" F4 GSO (Revelation Astro branded) scope with wider spaced tube rings and a 'top bar' with an SW ED80 attached as a guide scope.

 

The scopes I use the most are the GSO 6" F4 (a delightfull little widefield instrument) and the Revalation Astro 12" F4 (large, imager's workhorse). The 10" & 8" seem to fall in between these two somewhat so are kept at a different site for occasional use.

The Baader MK3 MPCC works with all four scopes as does the rather interesting ASA Keller 0.7x Coma Corrector.

 

You also mention that a 200mm scope is the limit for your EQ6? I have been using the 12" (300mm) Newtonian on my EQ6 for a few years now purely for imaging and it seems to cope! Probably not for begginers or portable set-ups though. The 200mm is a fair 'all rounder' though and still portable. The 10" & 12" are tedious to move around and thus best suited for observatory use.

 

12" F4 & 35Kgs of counterweights (note also the custom made 80cm, 25mm thick dovetail bar).

 

Proof the EQ6 can work with a heavy (if well ballanced) scope- 1200s single sub of M78

 

 

[ollypenrice]

They're not for me. That just means what it says, I don't want to get into a fight!

Olly

[laser_jock99]

15 minutes ago, ollypenrice said:

They're not for me. That just means what it says, I don't want to get into a fight!

Olly

Not everyone the has patience or inclination to get fast Newts working properly (I don't think I have fully optimised mine yet.....). In some ways a refractor is the best plug-n-play imaging solution, but where's the fun in that!

[ollypenrice]

3 minutes ago, laser_jock99 said:

Not everyone the has patience or inclination to get fast Newts working properly (I don't think I have fully optimised mine yet.....). In some ways a refractor is the best plug-n-play imaging solution, but where's the fun in that!

Hehheh, well, the fun for me is in taking the pictures and processing them knowing I have nice clean, accurate data! I have loads of fun imaging but I also have a responsibility to our guests to provide them with rigs which work - as in work now, immediately and for the rest of the night. And for the rest of the week...

I've said this before so SGL may be entirely bored by it but 'fast' and 'cheap' don't belong in the same sentence. In fact 'fast, eye-wateringly expensive' and 'easy' dont belong in the same sentence either. I prefer 'slower and better' but I remain determined not to get into a fight. I'm only saying where I stand. Others can stand where they wish.

Olly

[alacant]

Hi and thanks for the comprehensive reply. It looks like the Bresser already has the top bar you mention and yes, compared to skywatcher models, the top bar makes a big difference; I have a bresser 6" refractor with the same tube rings. The reflector has the same excellent low (high?- you have to turn it a lot to make it move) . ratio rack and pinion stays-put focuser. It looks like it's gonna need the extra springs though. Bresser/ES have always been reliable for me. I've just asked them whether the tube will hold collimation all night. I await their -usually by return- response with intrigue.

[alacant]

7 hours ago, ollypenrice said:

I also have a responsibility

Dunno. Try a modern reflector? It's 2017 and technology moves forward. You or I may just be pleasantly surprized. 10 years ago I had an awful blue tube skywatcher. Rubbish; you just looked at it and the secondary twisted. Who knows...

[Steve Ward]

Just going to stick my oar in and point out that the photo you link to was not taken using the 8" your question relates to but the 150mm model which may alter things ... 

[alacant]

13 minutes ago, Steve Ward said:

the 150mm model

Hi. Yes. I took it; it's the same make. Unfortunately that telescope will soon have to be returned to its rightful owner. I'm looking for something similar and wondering if the 8" would be OK. Fed up of dim heavy refractors. Thanks.

[Dave In Vermont]

Iguess I should weigh in here, as I have a 200mm F/4 Newtonian...

I happen to love this scope. And yes - it does need it's collimation to be nurtured. But I also happen to enjoy the art & act of collimating telescopes. Gives me a chance to prowess with a laser-beam! UGH!! <Tarzan-yell here> There! Beat you all to saying it for me!

So if collimation is something that scares you, or strikes you as drudgery and/or distasteful - I honestly wouldn't suggest a very fast Newt. But some of us quite like these 'fast' Rich-Field scopes - now being called 'Astrographs' or such. Probably by the advertiser's who were brought in to change the name as they weren't selling as 'Rich-Field' scopes as the 'evil-word' collimate began circulating about them. But that's my own speculation.

Be honest with yourself before you purchase,

Dave

[ollypenrice]

1 hour ago, alacant said:

Dunno. Try a modern reflector? It's 2017 and technology moves forward. You or I may just be pleasantly surprized. 10 years ago I had an awful blue tube skywatcher. Rubbish; you just looked at it and the secondary twisted. Who knows...

I see plenty of modern fast reflectors. The best, for me, is Pieter Vendevelde's self-built fast corrected Newt. In our robotic shed is an Orion Optics AG12. It isn't on the mount at the moment because... etc!  I also see Maurice Toet's Tak Epsilon a couple of times a year. It's excellent but it took a while for even an imager of Maurice's ability and experience to get it running to his satisfaction.  I also have one of the GSO F4 Newts - in the loft....

Olly

[Astrosurf]

The Skywatcher 200P-DS is a good all-round scope and set up for AP. I didn't see you mention a mount. To take deep sky objects (DSOs), you will need a good tracking mount and autoguiding. The usual entry mount is the Skywatcher HEQ5 Pro, or equivalent. 

Don't be scared of collimation! The more you do it the faster you get. If the secondary needs collimation when you get the scope, that's a fiddle, but once done shouldn't need to be done again for a long while unless you accidentally clout the scope. I only do the primary now and it takes seconds. I do it at home, in daylight, pointing at a very distant object, like an aerial.

Good luck!

Alexxx

[alacant]

12 minutes ago, ollypenrice said:

in the loft....

LOL. Yes, yes. OK. I've got it. It's a 'yes I am crazy' from you!

[ollypenrice]

Just now, alacant said:

LOL. Yes, yes. OK. I've got it. It's a 'yes I am crazy' from you!

Never claimed to be otherwise!

Olly

[alacant]

5 minutes ago, Astrosurf said:

Don't be scared of collimation!

Yeah. What is this thing with collimation? As a refractor only person for over a year now, the 150/750 reflector I have ATM took only a few minutes. Even a loose-secondary-pointing-the-wrong-way-when-you-first-get-it isn't the rocket science the articles make it out to be. I must be missing something. There's even an article somewhere here asking if a f4 can be collimated at all. I must be missing something or a 200mm f4 really is a nightmare. If I can collimate an f5, why wouldn't I be able to collimate an f4? Or f3.9? Is it when you go below f4 maybe that something changes? Confused...

May I ask another question? I took the monkey's head nebula with the f5. It took me over 3 hours. The first frame is just as good as the last. Each time I check the collimation, it hasn't changed. Are we saying that if I used an f4, I'd have to keep stopping, remove the camera and put in the cheshire? Or refocus? Or is it something else? More confused...

[alacant]

1 hour ago, Dave In Vermont said:

it does need it's collimation to be nurtured

Hi Dave and thanks for the input. What actually are you collimating? Is it necessary to do both secondary and primary with the f4? I rarely need to touch anything on the f5 I have ATM. If at all, the primary; but hardy anything... TIA

[Dave In Vermont]

I have a telescope that Orion-USA was selling, for a very short time, that turned out to be a GSO 200mm F/4 Newt for cheap in about 2000. Orion had thought these were the, at the time, their usual cheap Synta - but they goofed! These were the much more expensive, hand-figured (back then) GSO F/4's. They pulled them off the market as soon as they realized their goof. I happened to be lucky - and bagged one.

 It doesn't really need anything other than a minor 'tweak' to the Secondary, and a similar 'tweak' to the Primary-Mirror - after taking and setting-up - once ready for a night. Often it needs nothing. And that's about usual.

Perhaps the best, simple guide to collimation was written by a member here - Astro_Baby. I usually provide a link to her website for folks to retrieve a copy, but her site is down for now. So I'll deposit a copy into this link. I made it into a Pdf. so simply SAVE to your computer, etc:

Astro Baby's Collimation Guide.pdf

Stash that for future use, or to pass on to others.

Dave

[Adam J]

I am tempted to get one and have a go. Its not a huge amount of cash to have a look see. 

My F5 130PDS is so easy to collimate its trivial....if F4 is twice as hard? What is twice as hard as trivial anyway?

Maybe its more than twice as hard? I might be willing to live with it being a tiny bit out in exchange for faster imaging on a tight budget. 

Also I love DIY astronomy and so if its not perfect out of the box ill make it better. 

[alacant]

55 minutes ago, Adam J said:

tempted to get one and have a go

That's the spirit. Even though they're impossible to collimate, I'm gonna have a go too. There's an offer: Explore scientific PN208 208mm primary 85mm secondary. They confirmed that it works with the Baader MPCC. Madness. Insanity. Thankfully, I have a big loft...

[ollypenrice]

Collimation can be dead easy. Our F4.1 20 inch Dob is a doddle, likewise the SCTs. They do what they oought to do when you adjust 'x.'  The problems arise when the scope doesn't behave according to the book. We've battled with a few of those here over the years.

Olly

[alacant]

5 hours ago, ollypenrice said:

Collimation can be dead easy

Hi. can being operative, I wonder if it's the over documentation of the procedure which dictates its perceived difficulty? There seem a myriad of contradicting guides. Some advocate the 1 minute laser fix whilst others use nothing but eyesight. Yet others implore the use of a Cheshire, whereas there are others which use a 'phone to take photos via a cap with a hole in its centre. The more one reads, the worse it gets. Dunno. Best to just look at it and do it perhaps.

[ollypenrice]

10 hours ago, alacant said:

Hi. can being operative, I wonder if it's the over documentation of the procedure which dictates its perceived difficulty? There seem a myriad of contradicting guides. Some advocate the 1 minute laser fix whilst others use nothing but eyesight. Yet others implore the use of a Cheshire, whereas there are others which use a 'phone to take photos via a cap with a hole in its centre. The more one reads, the worse it gets. Dunno. Best to just look at it and do it perhaps.

The ones that have been difficult for me (difficult to the point of being impossible) have been the ones in which changing one parameter changes another when it shouldn't. This usually arises from inadequate maechanical integrritiy somewhere in the system. Somewhere - but where? The GSO residing in our loft, for instance, has an insufficiently rigid tube. Short of changing that, I don't see it working. 

Olly