Newtonian Reflectors for Astrophotography

[Startrek (Martin)]

Would just like some feedback from IIS members who use Newtonian reflector telescopes for astrophotography imaging

As a beginner I use a 6” f6 with 900mm fl for both visual and imaging work,a great little starter scope, light, easy to collimate, easy to clean the primary mirror , clean crisp views,reasonably good imaging,only set me back $299

I notice a large number of IIS members use refractors, SCT and MN’s which are substantially more expensive than the humble old newt reflector

Interested to see any comments / views on the Newtonian reflector vs Refractor for astrophotography work

[Imme (Jon)]

Not sure if reflectors cut it???

Check out Diego's pictures......that should settle any arguements

[Benjamin (Ben)]

Looking forward to responses to this. Trying to get my 8” Newt organized for imaging (focuser alignment, collimation, elimating tilt in the heavy image train, getting the correct distance from sensor to Coma Corrector - trying the match the mechanical alignment with the optical alignment) while taming it on an HEQ5. Think the mount is okay, but the rest seems to require quite a bit of fiddling around and testing. The refractor seems to me to be a more stable system to deal with, although some similar issues. Diego’s pics are amazing so clearly it’s possible but I wonder what efforts go into making that happen, or have gone into making it happen?

[Rkonrad (Richard)]

Most newt will not focus a DSLR camera but one can move the primary mirror closer by using longer screws then you will need an extension tube for visual or just get an astrograph reflector

[Rkonrad (Richard)]

Originally Posted by Benjamin

Looking forward to responses to this. Trying to get my 8” Newt organized for imaging (focuser alignment, collimation, elimating tilt in the heavy image train, getting the correct distance from sensor to Coma Corrector - trying the match the mechanical alignment with the optical alignment) while taming it on an HEQ5. Think the mount is okay, but the rest seems to require quite a bit of fiddling around and testing. The refractor seems to me to be a more stable system to deal with, although some similar issues. Diego’s pics are amazing so clearly it’s possible but I wonder what efforts go into making that happen, or have gone into making it happen?

Your 8 Inch reflector F5 over a meter long so will have wind issues ,on the HEq5 is great for visual but close to limit for AP , but worth a try

[Benjamin (Ben)]

The 8” Newt is definitely a wind sock and on the HEQ5 a gentle breeze makes the guiding jump around a bit. Perhaps another good reason to go for a more compact refractor, particularly if you image in lots of different locations? When I head out of town to a dark site (in my smallish car) I usual take an ED80 refractor for this reason - just not sure what the wind will do and it sits great on the HEQ5. The backyard I can experiment a bit more. I wonder what impact the observatories Diego builds has on the efficiency of imaging with his Newt?

[ChrisV (Chris)]

+1. Hoping for useful advice here. I'm finding the 8" F5 newt tough after using an 80mm refractor for the past year. Same issues as Ben with tilt etc. I'm thinking of trying a better focuser - or is that overkill for ago newt ?

[doppler (Rick)]

Refractors are light and compact, have short focal lengths but can have fairly fast focal ratios, good for astro photo's but with a smaller image scale. At the other end MC's and RC's are compact, have very long focal lengths but much higher focal ratio's, long exposures needed.
The newt is the in-betweener, reasonable focal length, great light gathering and very fast focal ratio's.

Yes the big drawback of the newt is it's physical size, but the best way to handle that is to put it on a pier in a sheltered location, ideally an obs. I have a 10" f4.8 on a HEQ5, but mounted on a pier next to my shed. I have other scopes but I love the way the 10" newt gets fast results with short subs, all I need now is a cooled astro cam.

[raymo]

Firstly, all Skywatcher Newts come to focus with a DSLR, and I think they
are the world's biggest selling brand of Newt. Obviously all astrographic
Newts do too. I think many GSO models don't.
I used my 8" Newt on my HEQ5 for visual and AP without any weight or
bulk related problems for seven years until age got the better of me. Occasionally a bit too much wind of course.
With my $5 D.I.Y. mod I could rotate the scope, and therefore always
have a comfortable focuser position, which you can't do with a refractor.
It has always puzzled me that people get so hung up on collimation; it
can be quite a way off before any signs will appear on your images. I
checked and adjusted if necessary my 8" two or three times per year.
My 10" collapsible was amazing, requiring only a tweak every six months
or so,[visual only].
Tilt can crop up on refractors too, so nothing to choose there.
raymo

[Startrek (Martin)]

Hi Raymo,

I'm looking at upgrading some time next year to an 8" reflector for astrophotography work

I am currently using a 6" f6 reflector with a 900mm FL on a HEQ5 pro mount for both visual and imaging. Its a great visual scope but has its limitations for imaging

I like the Skywatcher brand too

With your experience and background what kit would you suggest at this early stage ( approx mid 2019 purchase )

SW Black Diamond 200mm F5 focal length 1000mm

SW Quattros 200mm F4 focal length 800mm

SW NEQ6Pro mount or SW EQ6R mount

I welcome any comments / advice

Thanks in advance

PS: I have read a large number of posts on various forums stating that f4's are difficult to collimate

Do you believe that to be the case ??

[Imme (Jon)]

Anything F4....get ready for coma and collimation struggles. The sweet spot on an F5 is something like 2.5mm wide, on an F4 it goes down to under a mm (something like that anyway)

They are a little like that girlfriend you had in your 20's.....they are short, look pretty, they make things happen really quick but they're pretty high maintenance.

I've just moved from an F4 to and F5 because I got sick of playing with it.

Also if using an F4 you will need a coma corrector without doubt....another thing to play with and get right in respect to proper spacing

[raymo]

I've never had an f/4, but everything I've heard suggests that they are harder to collimate, and more sensitive to miscollimation, and harder to focus accurately. Actually, the physics of optics points to those things being right.
The SW coma corrector necessary for imaging with the f/5 is much cheaper
than the one for the f/4 scope.
The EQ6R is definitely superior to the NEQ6, if only for its belt drive which
hugely reduces drive train backlash, which should give better guiding.
The more secure power connection is also a plus. Using a 6 over the 5
will also allow you to go up a scope size in the future.
If your budget allows the EQ6R, I would opt for that and the 200mm f/5
and the SW f/5 coma corrector. If you need to save $500 or so, the NEQ6
will do a perfectly adequate job.
Having said all that, if you are certain that the 200mm is as big as you
will ever want to go, the HEQ5 will carry it easily, and is quite a lot lighter, and $500 cheaper than the NEQ6. I don't know whether this will help or confuse you.
You will need a coma corrector for imaging with the f/5, but you don't have to fiddle with spacing if you get SWs f/5 coma corrector, just fit it and use it.
raymo

[astro_nutt]

I remade my 10" f5 Saxon Newt for imaging/viewing. The secondary section can be adjusted to suit either one and can re-positioned four ways for comfort. Still learning but happy with the results.

[ChrisV (Chris)]

I've used a dslr on my GSO newt. No problem focusing - used 35mm extension. Same with my cameras listed below

[raymo]

That's very weird, Newts that won't come to focus, normally are lacking
back focus, meaning that you can't rack the focuser in far enough.
raymo

[Startrek (Martin)]

Thanks one and all for the replies

Sounds like I should avoid the f4 astrographs and stick with f5's reflectors

I assume you then need a coma corrector for the f5 in any case for the DSLR

I have no problem achieving focus with my DSLR on the 6" f6

When I use various powermates for planetary and DSO imaging with my DSLR I have to use a 35mm and 50mm extension adaptor to achieve focus

Not taking cost into consideration would the Televue parracor type 2 have the edge over the Skywatcher f5 coma corrector both for visual and Astrophotography use with respect to quality of view and images

[diegocolonnello (Diego)]

Can i be part of this one?????

I have mainly imaged with newts, first an 8 inch F5 and then a 10 Inch f4...

I did try with an 80mm Explore scientific refractor but collimation issues made me love my NEWTS a lot!!!

refractor are great for AP but they are more expensive if you increase aperture and/or specs, like triplets or cuadruplets!!!!

Newts are less expensive, you can buy more aperture, you will need a heavier more stable mount and it comes with the need for colimation skills.... (a good refractor does not need to be touched).

So, the good part, i love using a Newtonian, at the moment i am on the sweet spot of 10 inches F4... (thinking of 12 F4).... in the future...

Mount!!!!

A nicely tuned and mantained eq6 or AzEq6 can handle a 100mm refractor and get awesome results, but, no matter what someone says, they can't deal with a 10 inch telescope, mo matter what i did, my EQ6 worked hard with an 8 inch F5 Carbon Fiber scope.... lightest setup possible, cables ran inside the mount, nothing dragging and it was hard work....

I needed a bigger mount and a EQ8 was on my mind, then lucky me, i made a deal and found a nice OLD Takahashi NJP..... this mount is from 2004 and still going.... part of the payment was a nice QHY9M that i had with filter wheel and OAG................. by then i already had a ZWO 1600.

From this moment on i started to see with my own eyes what you can do with the right equipment, i moved to 10 inches and the combination worked, i have shot and processed more than 150 photos in less than 2 years, do the numbers, mostly all of them RGB or HST so multiply by the number of filters and number of subs....... only 1 out of 100 subs goes to the bin.......

Having that working ok, i started to improve my telescope:

Carbon Fiber tube
Wide Dovetail
Big, quality Focuser (with stepper motor)
Got rid of the primary mirror clips and glued the mirror
Adjusted the size of the secondary to illuminate the entire sensor with the 100% zone.
Learned how to colimate the entire thing, Focuser tilt, proper offset, etc....
Spider Vanes fixed to get clean nice sharp difrraction spikes and then, the best and most important part of all:::::

I HAVE BEEN STUDYING A LOT ABOUT MY MOUNT MY CAMERA SENSOR AND THE SWEET SPOT BETWEEN SUB NUMBERS AND EXPOSURE.

Read about GAIN and how your sensor WORKS, then learn how to use the histogram and test the right settings.....

The result?

1 hour integration time

15 x 80 sec R
15 x 80 sec G
15 x 80 sec B



Not the best photo, but shows what a 10 inch F4 does in one hour...

[diegocolonnello (Diego)]

About the use of observatories....

Is the best thing you can do (if you have the sky for it) doesn't need to be a dark site, but not like the place i lived before, between 2 airports!!!! really bad....

Before the observatories, Every time i did set up i was introducing errors, something was not the same, and then, like it happens a lot, the clouds came earlier....

I have had a dome and now a roll off, and both options are GREAT, the dome is more expensive but it is quick to get it going ( we put a NEXdome together in 2 hours)

The roll off roof is WAY CHEAPER, but took me 3 days of work.... and by cheaper i mean less than 1000 bucks including Motor...

Result?

your equipment is always there waiting for you to flip the switch, you only do one good guider calibration and that stays like that for a long time until you change something.

In my case i already had a cloud watcher, you can easily connect the cloudwatcher to the motor and have it close the roof when clouds come....

Same thing can be done with the Rain sensor from hydreon...

You can start imaging in 5 minutes get one or two hours of data, close it because clouds are coming and spend a couple more hours processing to enjoy your new photo.

[Startrek (Martin)]

Hi Diego,

Hope you don't mind me asking a few questions -

Do you use a coma corrector with your 10" f4 and if so what brand/ type ?

What type of imaging camera do you use ? Stock DSLR, modded DSLR or CCD

Is your 10" f4 difficult to collimate ?

What is your auto guiding set up ?

What method do you use to locate objects with your big telescope ?

Very impressive photo !!!!

Thanks in advance

[diegocolonnello (Diego)]

Hi Diego,

Hope you don't mind me asking a few questions -

That's ok...

Do you use a coma corrector with your 10" f4 and if so what brand/ type ?

Teleview Paracorr

What type of imaging camera do you use ? Stock DSLR, modded DSLR or CCD

CMOS cooled mono

Is your 10" f4 difficult to collimate ?

Nope, but i check it every time i shoot.

What is your auto guiding set up ?

Off axis guider. PHD2 with predictive PEC

What method do you use to locate objects with your big telescope ?

Forget about star alignment, use plate solving/SGP frame and mosaic.

Very impressive photo !!!!

Thanks...

Thanks in advance