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"Imaging Newtonians"

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#1 Dave Lee

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Posted 02 July 2013 - 06:21 PM

Since somebody seems to have permanently painted our skies a wet/medium gray, I was musing on an interesting project. I am just entering AP with a DSLR (modded T3 Canon) using 50mm and 200mm prime focus lens. The next step up for me would be maybe a 0.5x focal reducer on my C11 (mounted on a G11), but I feel that I am a long way from taking on 1400 mm fl.

It occurred to me that building a 6" f4 Newtonian strictly for imaging might be an interesting project. A place called Opticast ( http://www.opticastm....com/index.html ) does cast mirrors in that size that are incredibly inexpensive (don't think that I want to become a mirror grinder). And Astro-Tech sells a complete scope for only $300 (doubt that I could build it for less).

What do folks think about this? I was looking at the more traditional 80mm ED/APO path, but this path seems more intriguing somehow. OTOH, it is wierd to think that I would probably spend as much on 'fixing' coma as I would on the whole darned scope :cool: :cool:

dave

#2 InIt4TheImaging

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Posted 02 July 2013 - 07:30 PM

Hi Dave.

1. Be prepared to buy a good(expensive) focuser as well as that sweet little coma corr.

2. Newtonians do not travel well so if you have some distance to your imaging site, be prepared to do some field collimating.

//Daniel

#3 CounterWeight

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Posted 02 July 2013 - 07:53 PM

I think it's great to think about, I always am. It's the 'free lunch' that can bite us though. Fast and flat, good stars (no bloating or coma and even spot sizes), and aperture... and inexpensive, and then for me 'low to no maintenance'. There are many approaches that get very close, though each seems to have a caveat, usually an expensive one, like the reducer/correctors for the ASA or BSPN's. You can get a lot with a fast refractor but $$ gets up there quickly if you want to get f/4 or better and large aperture out of the equation for most mortals.

Right now I'm looking at the ES 'comet hunter' but then it's not at all inexpensive for the aperture compared to the AT or Orion imaging Newt's.

There is a lot of 'activity' in this part of the hobby by the vendors and dealers so it's always interesting to look at.

#4 Raginar

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Posted 02 July 2013 - 07:55 PM

Daniel is spot on. IN are not as 'cheap' as you think they will be. You'll need a really good focuser (kindof standard with all scopes) and you'll need a coma corrector (I guess most refractors need a field flattener).

Otherwise, imaging newts are cool though and building one could be a fantastic project.

#5 Madratter

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Posted 02 July 2013 - 08:07 PM

Personally, I would be awful tempted to go with the equipment you already have. Starting at 1400 isn't easy but I've been making a go of starting at 1260.

You have a good mount and good scope. The additional pieces to make it work aren't a whole lot more than an imaging Newtonian (and you would still need to buy some of those pieces like an autoguider).

Definitely slap your camera on the C11 and try some unguided subs of 30 to 60 seconds on some bright targets (M13 would be a good one) and see what you get. Grab maybe 60 frames, stack them, and see what you have. (If you shoot without a focal reducer, then you better stick to just 30 seconds tops to start).

Even if it turns out bad, you have lost basically nothing but a bit of time spent out under the stars. And since it is a bright target, you can even do it with the moon up when you wouldn't be shooting other stuff anyway.

#6 Kendahl

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Posted 02 July 2013 - 08:19 PM

Two issues with fast Newtonians are coma and collimation. You definitely would need the Astro-Tech coma corrector that is an extra cost option for their imaging Newtonians. Collimation is difficult and must be very good in order to get decent images.

Although it would be twice the price of a 6 inch Astro-Tech and coma corrector, you might consider Explore Scientific's Comet Hunter Maksutov-Newtonian. Same aperture, a little bit slower which makes it easier to collimate, and negligible coma thanks to the corrector lens. Your G11 mount would handle it easily. There have been extensive discussion of this scope. Search Cats & Casses for "Comet Hunter" (including the quotes). Go back five years to get everything. I thought about getting a Comet Hunter but decided on a refractor with a built in field flattener so that I would not have to fight with collimation.

#7 Jeff2011

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Posted 02 July 2013 - 08:43 PM

My AT6IN arrives tomorrow. I already have a baader coma corrector and am used to collimating my Dob. Might be a while before I can image with it because of the weather.

#8 Dave Lee

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Posted 02 July 2013 - 09:05 PM

My AT6IN arrives tomorrow. I already have a baader coma corrector and am used to collimating my Dob. Might be a while before I can image with it because of the weather.


Be sure and let us know how this does imaging clouds in the rain :(

dave

#9 Jeff2011

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Posted 02 July 2013 - 09:21 PM

That new scope curse. :(

#10 Alex McConahay

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Posted 03 July 2013 - 02:20 AM

Just a couple of general comments from an old atmer.

As far as saving money building your own scope: you do not generally save money on your first or on small mirror scopes. You have to buy tools and books and parts for a Foucault tester and make mistakes. This adds to the cost. Later mirrors there are more savings.

Starting mirror making at f4 is a challenge. The faster he mirror the more demanding the figure.

Imaging newts should have different mirror cells than most dobs. Most ATMs go with a simple sling. Your imaging cell needs to be more stable because your mount will put the mirror in places a dob would never put it.

I know you said you were not planning your own mirror grinding, but keep these things in mind if you decide to roll your own.

Alex

#11 Jeff2011

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Posted 03 July 2013 - 10:40 AM

My AT6IN arrived in one piece, the OTA that is. Thank you Astronomics! It came with a bunch of nice accessories too. There is a glimmer of a chance it may see first light tonight.

#12 Footbag

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Posted 03 July 2013 - 10:51 AM

A few things to keep in mind. Unless you have a very small sensor, a .5 focal reducer will not work on an SCT. F6.3 is the max and running it at f7 is optimal.

As far as building a newt, it sounds like a great project, but will likely cost more then a AT6IN. Even with a focuser, and MPCC, a newt is a bargain for what it is capable of. I don't know how they do it. You can buy an AT6IN for less then the price of a mirror.

#13 rflinn68

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Posted 03 July 2013 - 11:00 AM

I image with the AT8IN, AT65EDQ, and a C8 depending on the target. Once I bought the Baader Mark III MPCC and the Moonlite focuser for my AT8IN it became my favorite scope to image with. Collimation is only a problem if I'm imaging the same target over multiple nights because I dont want to remove my camera and render my flats useless. It does need collimated before every session. Other than that, I love the scope now. But you do need to add the cost of a good coma corrector and focuser. The focuser is definitely the weak link of the AT imaging newts.

#14 Dave Lee

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Posted 03 July 2013 - 01:19 PM

A few things to keep in mind. Unless you have a very small sensor, a .5 focal reducer will not work on an SCT. F6.3 is the max and running it at f7 is optimal.

As far as building a newt, it sounds like a great project, but will likely cost more then a AT6IN. Even with a focuser, and MPCC, a newt is a bargain for what it is capable of. I don't know how they do it. You can buy an AT6IN for less then the price of a mirror.


I'm very interested in your 0.5x focal reducer comment. Your comment sounds like my understanding of the 0.33x reducers. The Optec 0.5x is advertised to support (specifically for f10 SCT's) 17mm diagonal chips (a bit under half of the chip in my DSLR). But those claims don't make them true.

I agree that I would not be able to duplicate the cost of the Astro-Tech imaging Newt (even at the 'almost free' mirror price referenced originating post in this thread.

dave

#15 Jeff2011

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Posted 04 July 2013 - 09:11 AM

First Light! I have not been able to image with it yet, but I think the scope fits the mount well.

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#16 terry59

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Posted 04 July 2013 - 09:28 AM

I'm looking forward to your first image. I've seen some excellnt images from skilled people.

BTW, thanks for the info on the centering adapter for my AT72ED. It works great.

#17 Raginar

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Posted 04 July 2013 - 10:29 AM

Jeff, looks good! Get some imaging done ;) Once the cloud clears, of course. Oh, and the rest of texas appreciates the rain you've given them.

#18 Jeff2011

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Posted 04 July 2013 - 10:41 AM

Thanks guys. Terry, I am glad that centering adapter/extender worked out for you. My AT6IN came with one. Now I have two. :)

#19 astrodog73

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Posted 08 July 2013 - 02:52 AM

I image with the AT8IN, AT65EDQ, and a C8 depending on the target. Once I bought the Baader Mark III MPCC and the Moonlite focuser for my AT8IN it became my favorite scope to image with. Collimation is only a problem if I'm imaging the same target over multiple nights because I dont want to remove my camera and render my flats useless. It does need collimated before every session. Other than that, I love the scope now. But you do need to add the cost of a good coma corrector and focuser. The focuser is definitely the weak link of the AT imaging newts.


I've done exactly the same.... $200-odd of coma corrector, $600 worth of Moonlite motorised focuser on my 8" f/4 newt, add a laser collimator and its a great imaging rig.... grabs obscene amounts of photons quickly... :)






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