Some questions about imaging newts

[pluto (Hugh)]

Hi all,

I'm having a slow day so I'm window shopping on the 'net and, as a way to speed up my imaging, I'm toying with the idea of buying a fast imaging newt.
I have no idea about newtonians so I have a couple of questions and any advice would be welcome!

I guess the first thing is that I would want to use my existing camera (STT8300 + self guiding FW + AO) which is quite heavy. If I went for something like one of the Skywatcher f4 or f5 CF imaging newts I would definitely upgrade the focuser but am I likely to suffer any tube deformation?
Are these ~$1k scopes worth it or too much hassle to get them working well? If so what are the better/more expensive alternatives?

Also I know I would need a coma corrector but I'd need quite a lot of back focus to use with my AO (From memory about 105mm, but I could be wrong there). Do coma correctors like the Baader MPCC offer that kind of back focus or would I need something more exotic?

I'd be happy to spend time collimating as even if I had to spend an hour every session I'd still be way ahead with the shorter sub lengths I'd be acquiring compared to my TSA120.

Is there anything else I'm overlooking? I know some members here produce amazing images with newts but it seems strange that more don't use them given the relatively low cost, large apertures, and fast focal ratios...?

Thanks in advance

[multiweb (Marc)]

What are you looking at? 8,10, 12"? F/4 is fast. You'll have to buy a quality if not dedicated field flattener and coma corrector. Above 8" primary mirror mounting becomes interesting. Because of the weight you'll need a good primary cell. Also keep in mind if you use an AO/FW then you're going to need a reinforced tube around the focuser area and also a solid focuser. In a nutshell if you buy "cheap" you'll have to fiddle with it a fair bit to make it work. If you want something that works out the box you'll have to spend some $$$ for it to be mechanically sound. Make sure you have all your measurements/back focus work out before you commit.

[LewisM]

I "got around" the need for aperture by using a fast refractor - the FSQ-106. If f/5 isn't fast enough, you can go to f/3.65 with the reducer (and still maintain perfect field flatness).

All that goes soon, as I traded my FSQ-106ED for an FSQ-106N, so will be "stuck" at f/5, but I am not particularly upset. f/5 to me is a nice balance between depth and FOV. f/3.65 is a little too wide for my aesthetic tastes.

Anyway, if you want a QUALITY imaging Newt that requires absolutely minimal fiddling and holds collimation for a VERY long time, consider the f/4 Vixen R200SS. Only downside to it is the thick spider vanes (which is how it maintains secondary collimation so well) but these can be milled down.

The Skywatcher Quattro's seem to be almost clones of the R200SS, though somewhat cheaper. Heard OK reports on them, but holding collimation is NOT as good as the R200SS. GSO "generic" imaging newts need SERIOUS DIY work - mirror springs, secondary pinching, focuser etc. If you are willing to fiddle, then they are a good cheap beginning.

I did own 3 R200SS, and I can wholeheartedly recommend them. The figure on the mirror is superb. Also has a proprietary flattener that seems to work as well as the Baader MPCC.

[rustigsmed (Russell)]

G'day Hugh,

Nice to be hoovering up the photons at break neck speed!

I'd recommend the baader RCCi coma corrector http://www.teleskop-express.de/shop/...-distance.html
setback is around 94mm to go longer I think you will need to go exotic. (The MPCC is only 55mm)

But then again will you need the AO in a shorter focal length scope? If finding a CC more than 100mm it might get expensive.

I think you will be pretty safe with a CF model in terms of worrying about tube deformation. I remember seeing a pic on the teleskop express website demonstrating the strength of the CF tubes think it had cement bags sitting on them not warping at all.

Collimation at f4 does take longer but nothing to worry too much about really.

The focuser upgrade is a must (but this is true of most scopes) - secondary mirror collimation screws replaced with bob's knobs (so you can adjust by hand) and you're on your way.

yep I don't know why more people don't use them, throw a barlow in and you've got good FL too for close ups.

Cheers

Russ

ps if considering gso you will need to replace secondary springs as well and maybe the spidervane. The skywatcher in my opinion is a higher quality build. if I had my time again I would pay for the SW over the gso (although they didn't have 12" f4 options so I didn't have much choice).

[pluto (Hugh)]

Thanks Marc that's good info.
I was thinking just an 8", I don't think the EQ6 is up for anything bigger than that.

Definitely still at the day-dreaming stage at the moment but I've got the SBIG backfocus table saved somewhere so I'll get exact distances if I get serious.

Is reinforcing the focuser area on the tube something that people do often or is it nessesary to buy an OTA with the focuser reinforced already?

[pluto (Hugh)]

Originally Posted by LewisM

I "got around" the need for aperture by using a fast refractor - the FSQ-106. If f/5 isn't fast enough, you can go to f/3.65 with the reducer (and still maintain perfect field flatness).

All that goes soon, as I traded my FSQ-106ED for an FSQ-106N, so will be "stuck" at f/5, but I am not particularly upset. f/5 to me is a nice balance between depth and FOV. f/3.65 is a little too wide for my aesthetic tastes.

Anyway, if you want a QUALITY imaging Newt that requires absolutely minimal fiddling and holds collimation for a VERY long time, consider the f/4 Vixen R200SS. Only downside to it is the thick spider vanes (which is how it maintains secondary collimation so well) but these can be milled down.

The Skywatcher Quattro's seem to be almost clones of the R200SS, though somewhat cheaper. Heard OK reports on them, but holding collimation is NOT as good as the R200SS. GSO "generic" imaging newts need SERIOUS DIY work - mirror springs, secondary pinching, focuser etc. If you are willing to fiddle, then they are a good cheap beginning.

I did own 3 R200SS, and I can wholeheartedly recommend them. The figure on the mirror is superb. Also has a proprietary flattener that seems to work as well as the Baader MPCC.

Thanks for the info Lewis, much appreciated. That Vixen looks very nice!
Yeah those FSQs are the way to go fast but I'm pretty happy with the FL on my TSA120 - just wish it was 8"!!

Originally Posted by rustigsmed

G'day Hugh,

Nice to be hoovering up the photons at break neck speed!

I'd recommend the baader RCCi coma corrector http://www.teleskop-express.de/shop/...-distance.html
setback is around 94mm to go longer I think you will need to go exotic. (The MPCC is only 55mm)

But then again will you need the AO in a shorter focal length scope? If finding a CC more than 100mm it might get expensive.

I think you will be pretty safe with a CF model in terms of worrying about tube formation.

Collimation at f4 does take longer but nothing to worry too much about really.

The focuser upgrade is a must (but this is true of most scopes) - secondary mirror collimation screws replaced with bob's knobs (so you can adjust by hand) and you're on your way.

yep I don't know why more people don't use them, throw a barlow in and you've got good FL too for close ups.

Cheers

Russ

ps if considering gso you will need to replace secondary springs as well.

Thanks Russ.
I'm pretty keen to keep using the AO, life has been immeasurably easier since I got it. I'll calculate exact distances and see what I can find.

[glend (Glen)]

I run a 10" f5 imaging newt (carbon fibre tube struts) that I built myself. I used easily sourced GSO mirrors and rack and pinion focuser. It holds my cold finger cooled Canon which is pretty heavy. I had a GSO 8" imaging newt prior to the build and it seemed solid enough with no obvious weaknesses. I can also recommend having a look at the Skywatcher MN190 Mak-Newt, a seriously good scope with ( I kid you not) large ED APO type performance at a faster f ratio. It is in my opinion the equivalent of a 6" APO at one-third the price. I woukd not go above 10" of aperture on a NEQ6, and the MN190 weighs about the same as the 10" newt. Don't be put off my the low entry price for newts, they are the best value aperture tgat you can buy - and refractors are the most expensive at comparative f and focal length. You can have a lot of fun with a budget newt and not worry so much about it.

[pluto (Hugh)]

Originally Posted by glend

I can also recommend having a look at the Skywatcher MN190 Mak-Newt, a seriously good scope with ( I kid you not) large ED APO type performance at a faster f ratio. It is in my opinion the equivalent of a 6" APO at one-third the price. I woukd not go above 10" of aperture on a NEQ6, and the MN190 weighs about the same as the 10" newt. Don't be put off my the low entry price for newts, they are the best value aperture tgat you can buy - and refractors are the most expensive at comparative f and focal length. You can have a lot of fun with a budget newt and not worry so much about it.

Ooooo, that looks good!
Just reading Lewis's thread here: http://www.iceinspace.com.au/forum/s...d.php?t=111471
And it's not that much more expensive than adding the cost of a CC/flattener to a Skywatcher newt - plus I don't have to worry about backfocus with my AO...


As with everything in this hobby what started off as "oh I can get an 8" imaging newt for $500 from Bintel", becomes a multi thousand dollar shopping spree...

[multiweb (Marc)]

Originally Posted by pluto

Is reinforcing the focuser area on the tube something that people do often or is it nessesary to buy an OTA with the focuser reinforced already?

Ideally get a CF tube thick enough. Otherwise I reckon you could mount the focuser assembly on additional tube rings if it's going to be too heavy. At f/4 any flexure will kill your collimation. It's a world of pain.

[rustigsmed (Russell)]

Originally Posted by pluto

Ooooo, that looks good!
As with everything in this hobby what started off as "oh I can get an 8" imaging newt for $500 from Bintel", becomes a multi thousand dollar shopping spree...

[pluto (Hugh)]

Originally Posted by multiweb

Ideally get a CF tube thick enough. Otherwise I reckon you could mount the focuser assembly on additional tube rings if it's going to be too heavy. At f/4 any flexure will kill your collimation. It's a world of pain.

Thanks Marc.

[Shiraz (Ray)]

I have 2x GSO Newts and a CF 250f4 Skywatcher. The GSOs have great optics but are mechanically a bit dodgy without a lot of modification. The SW CF has much better designed mechanicals and has been a real pleasure to use - even the standard focuser was OK with a 1kg imaging train load. Fitted with a Moonlite focuser and in a permanent setup, it comfortably holds collimation (and focus) for months. It has well designed baffling + excellent optics + a stiff tube + thin spider vanes and is (just) light enough to put on an EQ6. Not sure how the tube stiffness will stand up under the weight of an SBIG imaging train though - it is fine at (1kg + SX AO), but the SBIG setup is a lot heavier than that.

I got an RCC1 coma corrector so that back focus would not be a problem if I wanted to go for AO (it has been temporarily fitted with an SX AO with no issues). The RCC1 works well with the 694, so should be fine with an 8300 (it will vignette, but probably not excessively so - I have used mine with an APSc and it was acceptable).

Downsides of the SW are:
- the interior black paint in mine turned out to be water soluble - which was interesting when it dewed up.
- collimation is stable provided that nothing is bumped. I accidentally brushed against my camera the other night and had to stop and re-collimate everything. It was nowhere near as nice to use when I was breaking the system down each night, since occasional bumps were inevitable.
- the black CF looks great, but is a dew magnet. I needed to cover mine with reflective Al tape - made a huge difference, but looks pedestrian.
- even with the CF tube, it needs regular refocusing as the temperature changes (a big disadvantage of f4) - digital focus (automatic or temp compensating) is pretty much essential.

these scopes are not "point at the sky and press the button" easy to use, but they are not too demanding and the rate at which you can get images is impressive.

[LewisM]

Yes Ray, i have seen many cf tubes painted white or silver to alleviate the dew issue.

[pluto (Hugh)]

Originally Posted by Shiraz

I have 2x GSO Newts and a CF 250f4 Skywatcher. The GSOs have great optics but are mechanically a bit dodgy without a lot of modification. The SW CF has much better designed mechanicals and has been a real pleasure to use - even the standard focuser was OK with a 1kg imaging train load. Fitted with a Moonlite focuser and in a permanent setup, it comfortably holds collimation for months. It has well designed baffling + excellent optics + a stiff tube + thin spider vanes and is (just) light enough to put on an EQ6. Not sure how the tube stiffness will stand up under the weight of your imaging train though - it is fine at (1kg + SX AO), but the SBIG setup is a lot heavier than that.

I got an RCC1 coma corrector so that back focus would not be a problem if I wanted to go for AO (well over 100mm is available and it has been temporarily fitted with an SX AO with no issues). The RCC1 works well with the 694, so should be fine with an 8300 (it will vignette, but probably not excessively so - I have used mine with an APSc and it was acceptable).

Thanks for the info Ray.

Originally Posted by Shiraz

Downsides of the SW are:
- the interior black paint in mine turned out to be water soluble - which was interesting when it dewed up.
- collimation holds provided that nothing is bumped. I accidentally brushed against my camera the other night and had to stop and re-collimate everything. It was nowhere near as nice to use when I was breaking the system down each night, since occasional bumps were inevitable.
- the black CF looks great, but is a dew magnet. I needed to cover mine with reflective tape - made a huge difference, but looks pedestrian.

Wow that's a bit worrying about the paint!!

Also I don't have a permanent obs, I leave the mount set up and aligned but I have to pack away the OTA and camera each session. But as I said before I'll still be way ahead time wise even if I have to collimate every session.

[Shiraz (Ray)]

correction - just checked on the back focus and it is 90+mm not 100+ In any case, the SX AO fitted OK

Should have checked earlier rather than relying on memory - sorry about that.

[RobF (Rob)]

I agree you can't beat bank for buck with a newt, but Hugh you're going to be spoilt with quality with your TSA. Have you thought about getting a reducer for it perhaps? f/5.6 would be about 70-80% "faster" than f/7.5, although the extra light is getting spread over a bigger FOV so some people argue with that logic.

[pluto (Hugh)]

Originally Posted by Shiraz

correction - just checked on the back focus and it is 90+mm not 100+ In any case, the SX AO fitted OK

Should have checked earlier rather than relying on memory - sorry about that.

No worries, it does seem that the CC could be a showstopper for me as I'm unwilling to give up my AO until I get a better mount. I'm really impressed with the MN190 but I'm a fair way off parting with money for either at the moment.
Thanks for the advice

[pluto (Hugh)]

Originally Posted by RobF

I agree you can't beat bank for buck with a newt, but Hugh you're going to be spoilt with quality with your TSA. Have you thought about getting a reducer for it perhaps? f/5.6 would be about 70-80% "faster" than f/7.5, although the extra light is getting spread over a bigger FOV so some people argue with that logic.

Haha yeah I do love my Tak
I had considered a reducer but I haven't looked into it too far. I'm pretty happy with the FOV I get from 900mm with the STT8300 and I'd be happier going a bit longer rather than wider. All options are on the table though, thanks for the advice!

[DJT (David)]

Hugh,I seem to recall you are in a heavily light polluted area in Sydney. Are there any issues with a fast newt for LRGB? I would imagine its not a problem for NB. I had heard though that with heavy LP there are more issues around dealing with gradients etc when imaging with faster scopes?

[pluto (Hugh)]

Originally Posted by DJT

Hugh,I seem to recall you are in a heavily light polluted area in Sydney. Are there any issues with a fast newt for LRGB? I would imagine its not a problem for NB. I had heard though that with heavy LP there are more issues around dealing with gradients etc when imaging with faster scopes?

Hi David,
Yes I do my NB imaging from the middle of Sydney but I only ever do LRGB when I get well out of the city - at least to the mountains or further.
Thanks for the info though, I hadn't considered gradient issues on a fast scope.