Imaging with 8" lx90

[Skyver]

Hi. This is my first  post so forgive me still being in the early learning centre.

I have a Meade lx 90 8" tele. Optically it's proved a good scope and I have no problems with go to operation. I want to try some imagery. I don't own a DSLR. There is a website that can supply various bodies with infra red filter already removed.

My question is, should I go straight to DSLR for this size scope or straight to a ZWO camera and use it with an ASIair box .

Has anybody used this method yet. I'm hooked on watching Trevor Jones at astrobackyard who's presentation is first class, ( in my opinion ).

Also would it be wise to invest in a 0.63 focal reducer to speed the scope up.

This is the old uhtc lx90 not the newer acf.

I do also have a Celestron neximage 5 . Just after buying this my laptop died and i'm now back to a desktop so neximage has not been used and is wasted. Can this be used as a guider.

Thanks in anticipation for some guidance in which direction.

[Davey-T]

Welcome to SGL

A DSLR with LX90 will give you an imaging resolution of less than .5 arc seconds per pixel when you really need somewhere around 2 , you may be better off with a dedicated CMOS camera of some sort with bigger pixels.

A .63 focal reducer will still be below 1 arc second per pixel.

Dave

Edited March 29, 2020 by Davey-T

[Pankaj]

Investment in a cooled camera will give you an advantage in years to come without bothering about future upgradation. I made the same mistake when I bought a dslr and today I want to again upgrade to a cooled camera. Though for an entry level, a dslr is the best friend.

[Skyver]

Many thanks for your replies and suggestions.

I am hesitant about using a DSLR so I will go look for a CMOS that covers close to 2 Arcsecs/pic as mentioned.

I thought of the ASIair as it stores the images on a card to bring into the desktop as well as allowing immediate view of image on an ipad.

I understand it won't have the same resolution as monochrome and filters but to make life easy i'm thinking of a colour camera to begin with.

Is this a good idea or not.

oh' thanks for the advice on the reducer Dave.

Best regards to both and keep well.

Stewart.

[Davey-T]

9 minutes ago, Skyver said:

I understand it won't have the same resolution as monochrome and filters but to make life easy i'm thinking of a colour camera to begin with.

Lots of discussion on here about the merits of one shot colour (OSC) versus mono but for a simple life colour is a good place to start,

At the top of this page under resources, astronomy tools there is a field of view,  resolution calculator.

Using the imaging mode you can enter your scope and try various cameras to achieve a nice imaging resolution, somewhere between 2 and 3 arc seconds per pixel is fine.

Dave

[alacant]

On 29/03/2020 at 14:16, Skyver said:

try some imagery

Hi and welcone.

It should be good for taking video of the moon and planets and you can do that with a simple webcam.

You mention DSLR and dedicated camera too. It maybe doable. There's a thread for alt-az imaging here. 

HTH

 

[Laurin Dave]

I started imaging through a non ACF 10" LX200 with 0.63FR and a DSLR (Nikon D90 then modded EOS600)..  it had been de-forked and was mounted on an AZEQ6..  its corrected field was much less than APSC with significant coma over 60% of the frame and it suffered mirror flop when guiding and image shift when focusing .. I spent the price of a decent 80mm refractor trying to sort it out before realising the error of my ways and doing what is often recommended on this forum when folk start imaging and buying one ( or two or three of them) ...  ..  it is however great for the Moon and Planets..    What sort of things do you want to image?

I'm not trying to put you off and I don't know what your LX90 will be like or what mount you have just to make you aware of some of its possible limitations …  As for cameras I'm not aware of any affordable CMOS with pixels bigger than 6 micron (the ASI174mm)…   the one I'd think might be ok would be the ASI533mc..   certainly be good for moon and planets and possibly small bright DSOs ..

As also mentioned frequently on here as a great place to start is to read Steve Richards book Making Every Photon Count 

 

[Skyver]

Okay, having read all the advice again I am of the opinion not to spend time imaging with the lx90. I'll use it purely for visual. Although at some point in the future I may aquire a laptop to use the neximage 5, or possibly sell that.

A new and current imaging system is the way to go , fast and wide as a starter. I'd like to capture simply things I can see visually like M42 and M31 and that seems to be common ground here.

What I can't see is the Rosette nebula etc, especially from light polluted skies. I'm taken with the images captured using a Canon and Samyang 135 f2. Maybe piggybacking on the lx90 ?

But the images with an eq mount and a small refractor or Redcat are amazing for lightweight easy set up. 

Or there's always the new ( Google Pixel 4 on the rotary line in the garden).

I'll choose the refractor and then the appropriate CMOS cam to fit.

I have booked a few days in May down at Eddington Lodge in Devon to get some method in but it seems that may be curtailed or lost in the current crisis situation. Yet to find out.

I also want to find out about worthwhile upgrades to the lx90 so I'll peruse the other sections.

I thank you for your knowledge.

Keep well.

 

[Hicks]

I image with an LX90 8".

tl;dr The LX90 8" can produce really nice images. It is however far from the easiest setup to image with. Not that imaging with any setup is a piece of cake. So you may be right to consider a wider field setup for jumping in. Once you've overcome the imaging challenges that all setups share, the LX90 will still be there to challenge you at long focal length if you fancy it

Details

Without a way to lock the mirror, you can experience mirror flop which will knock your focus out as the scope tracks across the sky. This can however be limited by ending coarse focus in a counter-clockwise direction. Also, manual focussing is painful due to the image shift it causes, especially as you often need to tweak focus throughout an image session as temps change. A zero image shift focuser solves this (I have a moonlite focuser on mine).

The LX90 has a fair amount of backlash too. This can be mitigated to an extent as the RA axis will never need to reverse and if you deliberately don't do perfect polar alignment the DEC axis only ever has to correct in one direction too. It does need to be tamed to an extent however so that PHD can successfully calibrate. It can also make matching a targets position exactly from a previous session a little more painful.

Due to the high focal length, you'll also likely want to use a F6.3 focal reducer and match up a CCD accordingly. Even then, you will be imaging around 1270mm and perhaps 1" per pixel so guiding needs to be quite accurate to keep round stars. That means you need an off-axis guider too. A separate guide scope isn't imo a good idea as you will inevitably have to fight flexure. Even an OAG brings some issues, the pickoff prism will mean you may need to adjust the position of your targets in order to have a suitable guide star. On a good night I have had guiding < 0.6RMS however. Bad nights tend to be poor seeing or user errors (often the latter).

The other issue with using a focal reducer is the need to deal with spacing issues. If you go too close/far away on spacing you can see coma.

The SCT with a F6.3 also has quite a bit of vignetting. So flat frames become a must. Although imo they're a must anyway as you really don't want to find a session ruined because you had some dust motes you'd not noticed

Last Issue

There's just one issue I've not yet overcome with my LX90 and that's a rather high spike of periodic error which hits once every 9 minutes. It's rapid enough that it's not possible to guide out and means the exposure it occurs within is no good.

I'm not sure if this is some dirt in the RA or just a manufacturing tolerance issue, but it's frustrating to lose that exposure every 9 mins.

Unsolvable Issues

One final issue is, due to the fork mount setup you will find the long train of gear you hang off the rear cell of the SCT will impact the base. This will make imaging a relatively large portion of the sky around polaris, impossible. For my setup, the filter wheel impacts the base so I lose (give or take) a 25 degree circle around polaris.

This and the PE mentioned above are two of the reasons I'm considering a move to a CEM60.

Silver Lining

It's not all doom and gloom however.

All the gear I've bought to image with the LX90 over the years (had it 17 years now) ccd, guidecam, filter wheel, FR6.3, moonlite focuser, rasp pi, cables, dew heater... are all items I will continue to use even if I decide it's time to move on from the LX90 mount. As I really like the quality of the OTA, I'd likely defork it just replace the mount (maybe a CEM60). That means the only real sunk cost in all this would be the LX90 counter weight system and wedge.

That said, the above assumes you're happy imaging at a long focal length. Even with a better mount, long focal length imaging has many challenges. You can spend far less money and have a far easier time imaging if you go for a much lower focal length (and weight) setup. I thrive on challenge however and taming the LX90 has been frustrating at times but also as enjoyable as the imaging itself.

PS: Whilst one shot colour can be easier to get started with. I'd consider a mono ccd. You can get used to it and still produce pleasing greyscale images before adding a filter wheel into the mix, but once you do have a filter wheel, you open up not just colour imaging but narrowband too. That can be quite useful for moon lit nights as we lose enough nights to cloud as it it that it's nice to not have to suffer through the moon lit nights too.

Edited April 5, 2020 by Hicks