Best Portable Setup for imaging (your inputs please)

[JohnH]

OK here we go again, I have been unable to come to a firm conclusion on upgrading my telescope. I mostly enjoy imaging with my 20D and I would like to work on DSOs Today I am mostly limited to widefield currently by my little ETX90. I would like any upgrade to be able to get 2-3 minutes at prime focus so I can get a decent shot of the brighter DSOs without guiding and an autoguide capable system for the fainter fuzzies later.

I also need a reasonable amount of portability as I do not have a pier or shed to house this equipment so it will get setup/taken down on each use.

My camera lenses (std canon usms) are not really useable for quality imaging so mostly I will want to image through the scope. I will also use a webcam for planetary (secondary interest at the moment).

Therefore I need two OTAs and a good mount. I live in Hornsby Heights, NSW and have reasonable dark skies (except to the south) no problem to see Mag 6 at Zenith on a clear night.

I am budgeting on approx 4k for this.

I am considering the Meade LX90 with an Orion ED80 (can the mount handle this) or equivalent (eg 8" SCT) on an EQ mount, goto is also a need for me as I am still learning the sky...

[iceman]

Moving to equip section.

[[1ponders]]

Hi John, sounds like your going through the same process I've been going through for the last 6-8 months. Yes you can get some nice shots with the LX90 and the LX200, but IMHO its a fair bit of mucking about with the wedge, which is why I've gone back to EQ mounts. Also you need to get a separate weight set for them and they still need to be modified to effectively balance the system when you have a refractor piggypacking and shooting prime focus.

There are a lot of great relatively cheap eq mounts available atm, but my recommendation would be no less than an EQ5 (preferably HEQ5) or EQ6. I've just bought a third hand Losmandy GM-8 without goto and so far I'm wrapped in it. But if you want goto (Gemini controller) you can add another $1k to the price. (round about $3500 brand new) Carrying capacity is around 30 lb so with an 8" and an Orion ($695) and your canon your looking at about 22-23 lb (the celestron 8" is about 12 lb, the 9.25 carbon fibre is 20 lb (and mucho mucho more expensive) and the Meade 8" is around 19 lb ($1600)) These weights are just over the recommended 60% weight limit for astrophotography.

If you look in this months AS&T they have a review of some of the EQs available. My preference would be either the Skyscan or the Celestron CGE, both highly recommended mounts, both goto capable.

May I ask why your limiting yourself to only 3 minute unguided when with a web cam you can autoguide quite easily, for either the bright DSOs and the faint fuzzies. It only takes a few more minutes of setting up to autoguide?

Anyway, if your looking to spend around $4k then using the prices above as a guide you will have around $1700 for mount, guiding rings ($160) maybe microfocuser ($400-$500) . Hopefully this will help you and not add more confusion to the pot :)

Cheers

[JohnH]

Thanks for that very helpful reply you are spot on - I oscillate between GEM and Fork/Wedge but have not reached a firm conclusion as yet - the EQ6 seems to be very highly recommended, can you confirm it can be auto guided though? There seems to be no computer interface for the Skyscan so to do this it needs an AUX input to the motors correct, anyone out there doing this with Guidedog? I also read that A S&T review also but it did not help me much as the details are very light...

I did not intend to imply that I would not autoguide only that I want something I can use unguided to start off with - I guess I am asking for a good mount with PEC - as I will build up/tear down each session and I am not familiar with autoguiding (yet) I want to be able to image without my laptop and more cables at least sometimes.

[[1ponders]]

Check this out John. Answers most of the questions http://www.skywatchertelescope.net/EQ6.html
Yes can be autoguided and has PEC though not neccessarily PPEC.

Also check out here http://www.telescopes-astronomy.com.au/skywatcher-pricelist.htm

[acropolite]

John, This guy uses an LX90 and autoguides and achieves good results with modest equipment. http://www.users.bigpond.com/lansma/

[gbeal]

Hi John,
firstly, why two OTA's?
I would recommend you can do "most" with one, albeit in a limited sense, but adequately.
Gary

[seeker372011]

I use a Celestron CG5 -AS G To and autoguide with GuideDog. ...works well, especially given the mount is very reasonably priced.

here's the yahoo group for more info

http://groups.yahoo.com/group/Celestron_AS/?yguid=150343216


and here's a link to some some images that Jim Solomon has taken with a 300D, an 8 inch and this mount. (IMHO Jim has been the pace setter as far as this mount and astrophotography is concerned)

http://home.comcast.net/~solospam

I have been using the same mount for imaging through my ED 80 with a 5 inch reflector as guide scope.

Its reasonably portable but warn you that it is not as easy to set up up as the SCTs...

On the other hand a GEM is probably what you want if you are serious about imaging

my 2 c

[JohnH]

Gary,

How would that work with autoguiding - are you suggesting an off axis guider? I need the second OTA for imaging, my camera lenses are not suitable for DSO work and a canon 70-200 f2.8 L or even the f4 is $>>>than the orion ED. I have read very mixed reports about off axis guiders plus it would increase the length of the tubes coming out of the OTA and cause problems with flexure and clearance (on the fork mounts anyway), the canon 20d I use is not light.

[[1ponders]]

OAGs :bashcomp: :fight: :( :mad: :doh: :doh: :juggle: :tasdevil: :tasdevil: :tasdevil: :sad: pain in the backside IMHO, can't wait for my Guidescope :love: :2thumbs: :D :cool: :cheers: :cool2: :birthday: :birthday: :party: :love2: :face:

[gbeal]

Hi John,
both Robby and I have been down the OAG road, and while some can use them we have both opted for the separate guidescope (as has our learned companion Mr Ponders it seems). More weigh, some more cost, but given a few things being right, eminently easier to use (in my opinion).
My question about one or two OTA's was more that I thought you were looking a longer focus OTA for planetary webcamming, and a shorter focal length OTA for deep sky and wider field imaging. I reckon you can do both with some scopes, for example the MakNewton (f6).
I have definite views on forks, and much prefer the GEM for all imaging. If visual is your only requirement then a dob base is where you need to be.

[JohnH]

Thanks for the replies, two OTAs seem to be the way to go, though this is going to increase both weight and setup time. I seem to be limited to a SCT for portability reasons and 8-10" by budget. The second tube a short 80mm ED refractor. Mount is not sure yet - GEM or Fork/Wedge though fork seems simpler to use and is less $$. What is the preferred method for attaching these tubes, I would want something faliry quick and easy to mount/demount?

[[1ponders]]

Problem with the fork mount John is that you will need some sort of wedge to get it into EQ mode anyway (otherwise you'll be limited to less than 60 sec 'cause of field rotation) and that can add another $400 - $800 (depending on the OTA size) on top of the cost of the fork mount. Unless you're going to build a pier, which defeats the portability requirement. Another bonus of the EQ over the fork is that in the fork orientation you have the weight of the OTA plus the fork and then the Tripod. At least with the EQ you can break it down to OTA, Mount and tripod.

Attaching the guidescope comes with Three options. 1. guiderings on a sliding rail, which allows maximum directional movement of your guidescope in selecting guidestar. 2. Standard mounting rings, which limit you to stars in the center of the field of view. You don't want to have to move your imaging scope too much to get a star to guide on in your guide scope. or 3. The same as the last but purchase some thing like the TAu Ceti XY finder which allows you to move your guide camera across the field of stars in the guidescope with out moving the imaging scope.

From what I've found out through research and chatting to people that have all three systems is that the last two are the most stable (less flexure issues) but the first one is the most versatile.

One issue that sometimes comes up is the problem of mirror shift when using a combination of SCT and refractor. If the mirror moves in the sct the refractor doesn't compensate for that. To get around this concern is to use an OAG, and I've already made my feeling known about those. To be honest though it works really well for some people and other hate them with a passion.

Hope this helps

[Stephan]

I read some things here which I think are not correct but I will give you my point of view.

The mount:
- GEM versus Fork
The big advantage of a fork mount is that it does not need counter weights. The big disadvantage is its instability. The rule of thumb is a fork mount with the same stability of GEM mount will weight twice as much!!! ...there goes the advantage of not needing counter weights. The next thing is that fork mounts are usually Alt/Az mounts. What does it mean for observation: the image will rotate! To overcome that you can either rotate the camera (Meade offered those systems for their SC-telescopes a few years ago) or you can have a wedge to make the mount equatorial. Now you brought a lot more instability in the system.

Back to the GEM mount... the downside as mentioned before is the need of counter weights. Otherwise they are more compact compared to the fork mounts.

That is why all professional deep sky photographer use GEM mounts for their portable systems.

Another important rule of thumb for photography is you spend 2/3 of your money on the mount and 1/3 on the telescope.

-Tracking accuracy
First you start of with a mount which tracks accurate without any correction electronics (namely: all Losmandy mounts, all Takahashi mounts, Vixen: GP-DX and New Atlux and perhaps the Sphinx).
Now it is a big advantage if you have PEC system. People might say a PEC system makes every mount accurate but that is not the case. PEC systems are limited by magnitude of the worm error and its gradient. PEC systems don't work if the worm error is too large or occurs suddenly. This is the case with 80% of Chinese mounts like EQ-1to5, HEQ-5, EQ-6. Some dealer (very few) actually test the worm error of those Chinese mounts and sort them for visual use and photographic use. The once for photographic use are more expensive but still cheaper than equivalent mounts from Losmandy or Takahashi). So if you know a dealer who does that test buy your mount there even if you pay more money!!!
Once you have a stabile, accurate mount with a PEC system you can do auto guiding and you do very long exposures without any trouble. For auto guiding you need a port on your mount drive controller. Most are standardized to process signals from an ST-4. The ST-4 auto guiders are nice because you do not need a pc or notebook. Losmandy mounts have this port already. The Vixen Sphinx mount has this port too and is very compact. For the Chinese EQ mounts you need to alter your controller or get a different one. You will get this from the US. There are many other ways of auto guiding but most of them will require a computer.

The telescope:
- F ratio
Here an important rule, as smaller the F ratio as shorter the exposure time and as larger the field of view. A raw rule of thumb is one F number down shortens the exposure time by half. Also the light gathering increases with aperture. If you want to do deep sky photography you need a telescope with a small F number.
- Telescope choice
Newton telescopes are a good choice because they are cheap for the aperture you get. From F7 or F6 down you will need a coma corrector and they are not cheap.

Refractor telescopes are suitable from F7 and down but you definitely need a field flattener. The field flattener come often as flattener/reducer what brings the F number down again. If you want to do one shot colour imaging you need an apochromatic refractor but if you work with colour filters and do a composite (RGB) a simple achromatic telescope will do the job. In this case focus will differ for each colour.
SC telescopes need a reducer or some of them offer the possibility to attach the camera where normally the secondary mirror is. In this case the SC is actually a Schmidt camera. But for this the camera should not be too big (and the D20 is big).

For SC’s and Newton’s you will find that bright stars on long exposure times appear as discs rather than points (due to the central obstruction of the secondary mirror). Also with the Newton you will have spices around bright stars in the image.

For planetary photography you should have a long focal length and at least 8” aperture.

The guiding
Guiding with a second telescope is much easier than off axis guiding. For the guiding scope you will not need much aperture but you need focal length. At least the same as the telescope you use for the camera but preferably more (twice as much is a good number)

Equipment wise I suggest a Losmandy G8 or a Vixen GP-DX with Skysensor 2000 or a Vixen Sphinx for a mount. For DS photography an Orion 80ED (or Sky Watcher or Saxon) with a Televue 0.8 Reducer/Flattener should do for a start. For planetary photography a second hand Celestron C8. As guiding scope a second hand 60 F15 achromatic scope will do the job perfectly. If you shop around you might even have some spare money towards a ST-4 auto guider…

So now you can think about what you want to do…

[[1ponders]]

I agree Stephen if all someone wants to do is visual work (though those big naglers can put a lot of weight on the back end), but if a guidescope and camera is added to the standard configuration then a weight set will almost certainly be needed to balance the setup, to reduce the strain on the gear and drive components. (Ie I'm taking about the standard meade LX90 LX200 and celestron fork mount setup)

[JohnH]

Steven,

Thanks for that analysis - it has helped me greatly. I am convinced GEM is the way for me to go, an I am still flirting with the EQ6 it seems very capable and good value however by the time it is tuned up and goto upgraded perhaps the Vixen Sphinx is a better choice. On top will ride an ED80, still uncertain about the rest at this time.

[atalas]

Hi John,honestly you won't get two or three minutes unguided out of the lower end gear! you will need from Vixen and up like losmandy or Tak mounts. The biggest enemys would be periodic error and under mounting your setup. The highest quality purchase should be your mount!

Louie :cool3:

[gbeal]

The advice to date is all good, and I am happier that you have elected a GEM. While I have no experience whatsoever with either the EQ6, nor the Sphinx, don't rush a mount. Additionally, my first thought with the Sphinx is that while it will be happy with the ED80, it probably won't be happy with much more than that, so if you are looking bigger/heavier later on, you/we will all have to go down this road again.
While not the most accurate or well built mount, (by all accounts), the EQ6 seems more suited to a heavier load than the Sphinx.
You may think and ED80 is all you will have, but as soon as you mention "Imaging" the weight seems to double, and the cost quadruple. Sorry.
Lastly, at the expense of sounding snobby, buy the best you can, not that the two you mention won't work, but there are better, but at a price. You normally get what you pay for.
Gary

[gbeal]

Louie, that is sort of what I am trying to say, in a subtle manner. Thanks