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Old 23-07-2013, 05:48 PM
Mckechg (Grant)
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cassegrain Vs Newtonian for AP

Hi all,

i have come into a window of opportunity and I am looking to purchase one of the below.

I primarily do AP and I have a DOB for visual.

I have a HEQ5 Pro mount and I use a DSLR (canon 7D) with a long 500mm lens for my AP now.

I travel with my scope (in my car) and portability is important. hence the 800mm focal length preference.

I however wish to get a scope. (NOW :-) )

These are my two options; the Cassegrain is a late suggestion by the supplier and I have no knowledge of them as an AP platform.

OPTION 1: http://www.bintel.com.au/Telescopes/...oductview.aspx

OPTION 2:
http://www.bintel.com.au/Telescopes/...oductview.aspx

The price is not the biggest driving factor and I was settled on this
( http://www.bintel.com.au/Telescopes/...oductview.aspx ) until I was told it was no longer available.

I want to do more DSO and alike. So please suggest as needed. I want to purchase ASAP. (like before the weekend)

Thanks guys and gals.

g./
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  #2  
Old 23-07-2013, 07:13 PM
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mill (Martin)
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Grant i would take the BT200 for nebulae and the GSO for smaller stuff.
I used both and still have the GSO 8" for small stuff and a 120mm refractor for wider field.
Hope this helps.

Martin.
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Old 23-07-2013, 08:02 PM
el_draco (Rom)
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choice of scope.

My 2c worth:
- Mount is a limiting factor so you don't really want a long focal length cass; (Make sure you know what this is, none of the scopes listed is a cass.)
- A fast refractor is a good choice in terms of portability, and there are plenty on offer. UniPol has a Meade 80mm triplet in classifieds atm but you may need to change focusers for serious astrophotography. His gear is always immaculately cared for, (read "like new").
- The newts you have selected are faster, but fiddlier and bulkier and you may have issues getting back focus.

You have a few considerations to balance here but I'd make one comment.... don't rush it!

Good luck

Rom
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Old 23-07-2013, 09:12 PM
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multiweb (Marc)
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Newt before SCT any day. SCTs can be fiddly and are long FL. Harder to handle. Newt fields look better corrected than any SCT.
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Old 23-07-2013, 09:26 PM
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Shiraz (Ray)
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Both good scopes but:

The RC has a long focal length and is not very well matched to your camera (which has small pixels). Sensitivity will be low and on an HEQ5 you will have a hard job getting stable imaging.

The Newtonian will require a coma corrector and at f4 can be a real PITA to get and keep properly aligned - everything needs to be aligned within 10s of microns and the mechanical components of low cost scopes are often not really up to the job. I don't think this type of scope will do what you want out of the box - they can be made to work, but expect to be fiddling with it from day 1.

Sorry to step outside of your options list, but if you are set on a scope in the 200mm class, maybe you can save yourself a lot of headaches and have look at a Skywatcher 190mm Mak Newt. These have a fairly short fl and properly corrected optics out of the box. The downside is that they are pretty heavy - your HEQ5 would be just able to carry one, but you would need to start thinking about a heavier mount at some future time (which you will probably do anyway if you get more seriously into AP). Many astro shops have the MN scopes - they are relatively expensive, but noticed that Andrews has them on special. I have not used one, but they have some good design features, should match pretty well to your camera and reviews have been uniformly positive.

good luck

Last edited by Shiraz; 23-07-2013 at 10:09 PM.
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Old 24-07-2013, 02:37 AM
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Ditto. I was going to suggest you should look into a Maksutov Newtonian as I think f/8 is a poor choice for your choice of camera. There are a few to choose from - Skywatcher, Orion, and Intes or Intes-Micro, apertures from 125 to 203mm and focal ratios between f/4 and f/8.

You'll need to select one with resolution appropriate to the pixel spacing on your camera sensor.
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Old 24-07-2013, 09:36 AM
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Satchmo (Mark)
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For once I agree with Wavytone ( and its not F15 ! ) .The Skywatcher 190mm ( 7.8" ) F5.3 ( ?) Mak- Newtonian is one of the unsung gems in the imaging scene. Flat field , essentially no coma , and no diffraction spikes.

At $1500 at Andrews an absolute bargain . They are rebadged under a number of other brands too. Got a great write up a while back in Skya and Telescope review. Apparently an HEQ6 was straining with it so you won't get away with an Heq5 though ( Edit : just saw you have an EQ5 - well you could give it a try !)

Last edited by Satchmo; 24-07-2013 at 09:48 AM.
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Old 24-07-2013, 08:45 PM
Mckechg (Grant)
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Thanks guys - all brillant answers and as I thought, the newt or something TOTALLY diff which the Mak Cas would be.

I will do some research, read and the make an impulse decision as always

Really appreciate the responses.

g./
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Old 24-07-2013, 10:19 PM
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Shiraz (Ray)
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Quote:
Originally Posted by Mckechg View Post
Thanks guys - all brillant answers and as I thought, the newt or something TOTALLY diff which the Mak Cas would be.

I will do some research, read and the make an impulse decision as always

Really appreciate the responses.

g./
Definitely not a "Mak Cas" - you got 3 posts recommending a Maksutov Newtonian. It is a corrected Newtonian, which is actually very similar to the Newtonian you originally considered but a bit slower, better image quality over the APS-c field and much easier to use - but heavier.

A Maksutov Cassegrain would be about the worst possible choice.

good Mak Newt review at http://myastroshop.com.au/guides/swdm190.asp

Last edited by Shiraz; 25-07-2013 at 04:28 PM.
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Old 25-07-2013, 11:52 AM
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naskies (Dave)
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Grant, have you looked into / thought about auto guiding?
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Old 18-12-2019, 07:01 AM
Wavytone
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Quote:
Originally Posted by Shiraz View Post
A Maksutov Cassegrain would be about the worst possible choice.

Not so sure about that https://www.astrobin.com/search/?q=Onoprienko&d=i&t=all
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Old 18-12-2019, 09:50 AM
rzgp33 (Brian)
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Quote:
Originally Posted by Wavytone View Post



Hmmm not bad dust and gas, but fluffy cotton ball stars. That scope is not sharp.


I'm having the same issue with my C8 EdgeHD... these are great for visual, but just make cotton wool.
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  #13  
Old 18-12-2019, 02:27 PM
Startrek (Martin)
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I image with a 6” f6 newt in Sydney and an 8” f5 newt at my weekender on the south coast
The 6” f6 Bintel newt sits on my HEQ5. Imaging camera is a Canon 600D which is used for DSO and Planetary under Bortle 8 skies
Can’t beat a Bintel newt , cheap, simple to collimate, easy to maintain and does everything I want it to do plus more....
The only mod I did was change the focuser to dual speed
Here’s a few images I captured this year with the 6” f6 in Sydney .....
Cheers
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Old 18-12-2019, 04:35 PM
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ChrisV (Chris)
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I'll echo what was said below. Your limiting factor is the mount, so I couldn't recommend an SCT. First, the mount would handle the shorter focal length of the newt better. Secondly, that focal length would be a better start for DSOs (800 - 1000mm, or even shorter).

Martin below gets really nice stuff with his 6" F5. Or an 8" F5 or even an F4 if you are prepared to battle with collimation more. You will need to factor in a coma corrector - I have a Baader MkIII which I like (bought from TS Express - much cheaper than buying locally), but there's a range of opinions on what's best.

Have you considered a 4" APO ? The HEQ5 would handle it much better, plus no collimation, no coma corrector (although would need a field flattener). And way more portable !!

My disclosure - I use a 4" APO and an 8" F5 newt - and like both for different reasons. The newt is nice and fast with better resolving power, but the APO is much easier to use
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Old 18-12-2019, 06:02 PM
glend (Glen)
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While i agree that the Mak-Newt is great choice, I owned one for years and miss it now. Be aware that there are a few variations in the product line. The newest ones being sold now have a larger secondary mirror than the originals, I believe the current crop use a 64mm secondary. This change was made to facilitate larger format cameras, which would experience vingeting with the original small secondary (52mm). The consequence is less resolution with the larger secondary due to greater central obstruction. The small secondary model is fine for up to APS-C sized sensors, and in my opinion the one to buy. The originals are tightly held by owners so you may have to wait to find one.
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Old 18-12-2019, 08:19 PM
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Harpage (Danh)
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Quote:
Originally Posted by Startrek View Post
I image with a 6” f6 newt in Sydney and an 8” f5 newt at my weekender on the south coast
The 6” f6 Bintel newt sits on my HEQ5. Imaging camera is a Canon 600D which is used for DSO and Planetary under Bortle 8 skies
Can’t beat a Bintel newt , cheap, simple to collimate, easy to maintain and does everything I want it to do plus more....
The only mod I did was change the focuser to dual speed
Here’s a few images I captured this year with the 6” f6 in Sydney .....
Cheers
How did you find the Bintel newt regarding back focus? Their 6" reflector OTA is only $300, which is a steal considering a Saxon 6" dual speed reflector costs $450-$500. Paired with a $300 coma corrector and HEQ5, you could get a new AP setup for about $2000 (if you already have a camera of course).
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Old 18-12-2019, 09:38 PM
Startrek (Martin)
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The focus on my Bintel 6” f6 newt was just enough with my Canon 600D except I wanted more play in and out with focus so the guys at Bintel fitted 3 x 4mm thick cork spacer pads to the underside of the primary mirror and that gave me an extra half a turn in or out which was perfect ( no charge )
I bought mine for $299 about 3 years ago and they are still $299 today ( I chose GSO Bintel in lieu of the Skywatcher 6” f5 not because of price but because I prefer the GSO Bintel focusers to the Skywatcher focusers - better design and quality barrel and thumb screws )
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