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What do you recommend 8 inch or 10 inch Newtonian

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#1 sami2012

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Posted 18 September 2013 - 03:57 AM

Hi all,,,,


I am looking to buy a Newtonian for Astrophotography but I between the 8 inch or 10 inch, What do you recommend ???, about the Newtonian fast a F/4 OR F/5 .
regards
sam

#2 orlyandico

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Posted 18 September 2013 - 04:11 AM

f/4 is better than f/5, both of them would want a coma corrector.

the 8" is always going to be better than the 10" unless you have a capable mount ( = AP900 or comparable).

i have a Mach1 and I got an 8" for it. I don't like over-stressing the mount.

#3 sami2012

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Posted 18 September 2013 - 04:42 AM

i have the neq6 pro mount ,and about Collimation this f/5 hale the time of f/4

#4 orlyandico

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Posted 18 September 2013 - 05:11 AM

well of course collimation of the f/4 will be harder. but it's almost 1 stop faster for photography (1.56X so a 10-minute sub on the f/4 would be equivalent to a 16-minute sub on the f/5). Both will need a coma corrector for astrophotography.

personally, for an NEQ6 i would stay with the 8". some people put 10" or even 12" on the NEQ6 but i guess they like losing their hair...

#5 csrlice12

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Posted 18 September 2013 - 08:44 AM

Unless you already have AP experience, I'd not do this...an 8-10" newt, even on an adequate mount is a terribly huge and unweildy beast. You'll not only need a $$$$$mount, but tube rings as well, probably a ladder. AP with this type equipments calls for an observatory.....this is a very, very, expensive road you're getting ready to travel....If you're just starting out, look into the AP forums. You'll still need a good mount, but using a small APO/refractor will still provide you with beautiful images.....and it won't be cheap either, but at least it will be easier to use. You can do some limited (15-45sec) exposures with a smallish APO on a motorized CG5 (or equiv), which is probably going to be as cheap as you can go......and don't forget the camera, adapters, computer, software, and TIME, AP requires Lots and Lots and Lots of time, most of it at the computer......

#6 orlyandico

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Posted 18 September 2013 - 08:59 AM

The reason I went for the 8" is because it's f/4 compared to my current f/6.7 APO triplet.

And I also got a Keller reducer which brings it down to f/2.9 - there is no APO out there that can do f/2.9 (the fastest are the Borg 125SD with super reducer, and Tak FSQ-106 with reducer, both for $$$$$ lots of money $$$$$)

#7 csrlice12

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Posted 18 September 2013 - 09:06 AM

Yea, but you've been at this awhile....Be truthful now, would you really recommend a 10" newt for AP to a person with no astronomy or photography experience?????? Now, if I already had some experience and was looking to "upgrade"....

#8 orlyandico

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Posted 18 September 2013 - 09:12 AM

Err, no. That's why I recommended the 8" - the OP says he has an NEQ6 - that's an Atlas for the rest of us.

The 8" is about 22lb and is about 30" long, making it roughly the same footprint as an Orion 100ED. I'm pretty sure an Atlas could carry it competently.

Now the 10" is a totally different story...

#9 mpgxsvcd

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Posted 18 September 2013 - 10:16 AM

I definitely would say that a 10” Newt is probably too much for a lower end mount. However, an 8 inch is a perfectly acceptable solution even for the budget mounts like the CG-5. You just have to spend a few extra minutes getting the balance right and make sure your camera and guide scope are as light as possible.

Collimation is easy. It really isn’t as hard as everyone makes it sound.

The Carbon Fiber Newts are also a lot lighter so that can make a big difference. There is an 8 inch Carbon Fiber Newt under $900 right now.

#10 SeattleScott

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Posted 18 September 2013 - 11:43 PM

I know a couple guys who started out with AP instead of visual, and they went with an F4 Newt. They soon upgraded to an Atlas mount for it and had considerable success. Yes, they now have a 4" Apo on a Mach1 mount, but the Newt was a satisfying enough experience to launch them down the expensive path of AP.

#11 orlyandico

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Posted 19 September 2013 - 12:51 AM

This I don't get. I already have the Mach1 and 90mm APO... And I'm going in the other direction. ^_^

There's someone in the local club with an AP 130 that he used for many years. But these days he's using a Tak Epsilon...

#12 sami2012

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Posted 19 September 2013 - 05:30 AM

what do you think about Ritchey-Chretien or Newtonian?????

#13 mpgxsvcd

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Posted 19 September 2013 - 10:05 AM

I think the RCs are very nice scopes. However, they are about double what the equivalent Newtonian costs. If my budget allowed it I would have an RC. Since it doesn’t I have a Newt and I am not too upset about that.

#14 orlyandico

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Posted 19 September 2013 - 10:18 AM

The RC's are f/8 to f/9. So long focal length and slow focal ratio requiring a better mount and longer exposure times. For this reason a newtonian in my opinion is a more friendly option.

#15 Zad

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Posted 19 September 2013 - 01:32 PM

I run the Orion version of the AT8IN on an Orion Atlas EQ-G mount, and have no issues with the mount handling the scope, a DSLR with Coma Corrector, and a 50mm finder with the SSAG for autogiding. The oversized secondary fully illuminates the APS-C sized chip in my Canon 450D. A 10" may be pushing things a bit, but I have never tried to image with that big a payload. Imaging at f/4 makes for short subs, which I love. I get more data per imaging session. The Orion version of this scope has a plate that reinforces the focuser, and you can collimate the focuser. I get nice round stars from edge to edge.

As far as collimating the scope goes, it isn't any harder than any other Newt to collimate, just slightly more important. I think this issue gets a little overblown. I think this comes more into play for visual work. For visual, if you are using an f/5 newt, you don't have to be exactly spot-on, but at f/4 it becomes more important. But anytime I image, I want to be spot-on regardless if I am f/5 or f/4, so there was really no change for me going from f/5 to f/4 as far as collimation goes.

#16 Dakota1

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Posted 19 September 2013 - 01:55 PM

I have the Orion Atlas mount. I had a 10in newt on it. It was fine till any breeze at all came up and then forget it. You could not stop the vibration from the wind. Its gone!!

Bill

#17 Zad

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Posted 19 September 2013 - 01:58 PM

The question regarding RC vs. Newt is a seperate issue. Assuming the OP would be looking at an 8" scope either way, you are talking about 1600mm f.l. @ f/8 for the RC vs. 800mm f.l. @ f/4 as one possible example.

1. The RC would require subs that are 4 times longer to get the same level of exposure than the Newt.

2. The image scale would be different for the two scopes with the RC being better suited for smaller targets. I think galaxies and planetary nebula, whereas the Newt can handle larger objects.

3. Matching the focal length to the pixel size comes into play here as well. The RC matches better with cameras with bigger pixels, and the Newt mathces better with smaller. I usually want about 1-2 arc.sec./pixel.

4. The newt is a little trickier to balance the scope with due to the focuser sticking out of the side of the tube rather than the back. I turn the scope in the rings so the focuser is pointing down towards the mount to help with balance.

5. The Newt definately needs a coma corrector for nice round stars in the corners of the image. I use the MPCC with great results. The RC benifits from a field flattener from what I understand, but I have no experience in this area. The Newt has a nice flat field already, so no field flattener is necessary.

6. The RC would require more accurate tracking due to the longer focal length and longer exposures.

So, it really comes down to what kind of targets the OP is interested in, what kind of camera (and pixel size) will the OP use, and how much effort does the OP want to put into accurate tracking (will the OP be autoguiding, manual guiding, unguided).

Either scope would work very well, just a matter of preference.

#18 gdd

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Posted 19 September 2013 - 02:46 PM

You can use a reducer on the RC to get you down to f/5.6, the CCDT67 is a popular choice.

Or you can use a barlow on the Newt to get you up to F/8 for galaxies, though I have not heard of people doing so.


Gale

#19 Kendahl

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Posted 19 September 2013 - 06:39 PM

Have you considered the Vixen R200SS? It's an 8 inch f/4 Newtonian. Because it is made of aluminum, the bare tube weighs only 11.7 pounds. That means you can get away with a mount suitable for a 4 inch refractor.

#20 orlyandico

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Posted 19 September 2013 - 09:05 PM

Gale,

Now that I'm waiting for my AT8IN, I am slightly concerned about losing long focal length for those pesky little PNs.

While I wish a barlow would work, since I have a 2" lying around, I suspect it doesn't. Otherwise ASA wouldn't be selling this super-pricey 1.8X barlow corrector -

http://www.optcorp.c...tor-2korrb.html

(I already have the 0.73X reducer, which I thought was pretty expensive, but the barlow corrector costs nearly double!)

I guess the bottom line is you really have to keep a separate OTA around for those tiny planetaries.

As for the R200SS - yes it's a nice f/4 newtonian, but it is rather expensive ($1500+) compared to the Orion, Astro-Tech, etc. versions.

#21 gdd

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Posted 20 September 2013 - 12:23 AM

I did find a case where a person used a cheaper barlow with a at8in and was satisfied with results for m51. Maybe not quite as good as the ASA, but worth trying since you already have one.

Gale

#22 Zad

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Posted 20 September 2013 - 12:35 PM

I have been wanting to try out a 1.5x 2" barlow that I have on my Orion 8" f/3.9 Newt, but I haven't gotten around to it. My main concern is CA, since it was not designed for AP, and it was relatively inexpensive.

But I have been wanting to pick up a 2" 2x Televue Powermate because I think that would work well, but funds are tight right now. Has anyone tried one of these on a newt for imaging?

#23 orlyandico

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Posted 20 September 2013 - 01:31 PM

not sure if CA is an issue. The usual refractor flatteners are just achromatic doublets.

The CA becomes much less of an issue closer to the focal plane.

#24 csrlice12

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Posted 20 September 2013 - 01:53 PM

It's a newt, newt's shouldn't have CA....that's a refractor abberation....newts have coma instead......

#25 Zad

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Posted 20 September 2013 - 02:23 PM

Barlows can produce CA. In fact some barlows are advertiezed as "ED" or "Apochromatic". Astro Tech has a " 2X achromatic Barlow" AND a "2X apochromatic ED Barlow" on their site right now.






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