Re-beginners problem

[Trevor-Austin]

Equipment is;

LX90 8" Alt/Az fork mounted

EOS450 both with prime focus adapter and 2" Crayford adapter push in adapter.

Backyard EOS

Deep sky stacker.

 

I have done a little successful-ish imaging some years ago, but decided to give it another go.  First nights images wouldn't stack as I am fairly certain they were out of focus, I forgot the simple step of zooming the star to focus in Live view and got this result for a 30 second exposure. I realised straight away focus was bad and just kicked myself.

However yesterday I carefully focused at 10* (it took me so long to setup that M42 had done a runner for the night so I just chose the next Messier object to get some star pics.  It looks to me like my swet point with trailing is 25 seconds and although nothing really to view I tried to stack however again I got only one picture will stack.  When I looked at settings and did the star test DSS couldn't find any stars.  Are they in focus or have I still got my focus wrong?  

 

Any advice greatly appreciated, and yes I have a wedge:), waiting for the adapter plate.

 

|The one picture of M42 is when I messed up the focus, the others are various timed exposures when I thought I had my focus correct.

 

[happy-kat]

There's some elongation on star shape on the images where focus isn't to bad. Might be 30 seconds is to long why not try 20 seconds next go. What star detection threshold did you try in DSS?

When image is either wind or mount stiction. Don't include those in a stack.

[Trevor-Austin]

4 minutes ago, happy-kat said:

There's some elongation on star shape on the images where focus isn't to bad. Might be 30 seconds is to long why not try 20 seconds next go. What star detection threshold did you try in DSS?

When image is either wind or mount stiction. Don't include those in a stack.

Hi and thanks.

If you look at my pics it looks like my sweet spot is 25 seconds, no real elongation that I can see there, but agree on the 30 seconds.  I went right down to 2%, on the badly focussed M42 it found 6 stars at 2% but still would only stack one, despite having 4 captures.

One thing I did do was include all good and bad images in the stack last night.  DId it maybe do star detection on just a bad one?

If I sent you my 20 second and 25 second pictures could you see how many stars you get detected, that will then rule out me doing something wrong in DSS if you get the same result as me, I have uploaded the two raw files for those timings.  There was no wind a very calm cold night (P.S. is stiction a typo or word I need to learn? )

LIGHT_25s_1600iso_+12c_20190403-23h26m48s682ms.CR2 LIGHT_20s_1600iso_+12c_20190403-23h25m36s991ms.CR2

[Mr niall]

What ISO are you using - there should be alot more stars on that for an exposure that long...

Still a little bit out of focus I think - the trick I use is to dial the ISO up as far as it'll go and just take lots of 3 or 4 second exposures and twiddle the focus accordingly. Do you know what focal length you are working at, a bahtinov is worth its weight in gold for longer focal lengths.

[happy-kat]

Stiction - the mount had a sticky moment while tracking this can cause jitters in star shape.

Don't include bad images in a stack.

[Mr niall]

12 minutes ago, Trevor-Austin said:

Hi and thanks.

If you look at my pics it looks like my sweet spot is 25 seconds, no real elongation that I can see there, but agree on the 30 seconds.  I went right down to 2%, on the badly focussed M42 it found 6 stars at 2% but still would only stack one, despite having 4 captures.

One thing I did do was include all good and bad images in the stack last night.  DId it maybe do star detection on just a bad one?

If I sent you my 20 second and 25 second pictures could you see how many stars you get detected, that will then rule out me doing something wrong in DSS if you get the same result as me, I have uploaded the two raw files for those timings.  There was no wind a very calm cold night (P.S. is stiction a typo or word I need to learn? )

LIGHT_25s_1600iso_+12c_20190403-23h26m48s682ms.CR2 11.43 MB · 2 downloads LIGHT_20s_1600iso_+12c_20190403-23h25m36s991ms.CR2 11.4 MB · 0 downloads

I got 9 stars at 2%, if you increase the white point as far is it'll go you can see there are only about 2 dozen stars in total - so you aren't doing anything wrong in DSS, its a capture issue. Are you shooting in RAW? 

[Trevor-Austin]

5 minutes ago, Mr niall said:

What ISO are you using - there should be alot more stars on that for an exposure that long...

Still a little bit out of focus I think - the trick I use is to dial the ISO up as far as it'll go and just take lots of 3 or 4 second exposures and twiddle the focus accordingly. Do you know what focal length you are working at, a bahtinov is worth its weight in gold for longer focal lengths.

1600 iso, maybe I was aimed at a low density area? Not a clue on focal length, my OTA is 2000, then I have the Mead APO 2" Diagonal and a Crayford Focuser then my EOS450D.

I tried a Bahtinov before and had no success at all, maybe I should try again. 

[R26 oldtimer]

I am also wetting my feet in imaging, and for those first, unfocused and trailed subs, found dss to be very picky. On the other hand sequator seems to be able to stack almost everything you throw at it. So, I suggest you give it a try as it is also free.

[Trevor-Austin]

1 minute ago, Mr niall said:

I got 9 stars at 2%, if you increase the white point as far is it'll go you can see there are only about 2 dozen stars in total - so you aren't doing anything wrong in DSS, its a capture issue. Are you shooting in RAW? 

Yes I am capturing in raw, I'll do that now and see if I get the same...... and yes on the 25 second exposure at 2% I get 9 stars.  SO how did I capture so few, just bad luck pointing at a low density area?

[Mr niall]

Oh... I just checked, the LX90 is a 2000mm Schmidt Cas. That probably explains it, at about f10 you'd have to expose for about 120 secs to acquire the same amount of info as you would be able to collect in 20 seconds with an F5 system.

For the sort of length of exposure you'd need to get the detail you are looking for you're always going to struggle with that mount. Your best bet is to change targets to the moon or planets or get a focal reducer, which would take it down to about F6.

You need to massively increase your exposure times with that system.

[happy-kat]

Or use just a camera and camera lens (ideally without the heavy telescope also on the mount)

When you have more practice under your belt try with the telescope again.

[Trevor-Austin]

10 minutes ago, Mr niall said:

Oh... I just checked, the LX90 is a 2000mm Schmidt Cas. That probably explains it, at about f10 you'd have to expose for about 120 secs to acquire the same amount of info as you would be able to collect in 20 seconds with an F5 system.

For the sort of length of exposure you'd need to get the detail you are looking for you're always going to struggle with that mount. Your best bet is to change targets to the moon or planets or get a focal reducer, which would take it down to about F6.

You need to massively increase your exposure times with that system.

Ah damn, OK. So a 2" focal reducer of .63 or.5 would help.  I'm also waiting for an adapter plate so I can use my wedge, that should get me to 2-3 minute exposures hopefully.  At this time of year mars is behind a tree by 9:30 and I just find the moon so boring:) but I understand what you're saying so I know where I'm going wrong.  So in reality I need longer exposures and brighter subjects.

 

I do already have a 0.5 1.25" reducer, if I used eyepiece projection would that then work?

[Trevor-Austin]

20 minutes ago, happy-kat said:

Or use just a camera and camera lens (ideally without the heavy telescope also on the mount)

When you have more practice under your belt try with the telescope again.

That won't work on an LX, but I can piggy back.

[Mr niall]

32 minutes ago, Trevor-Austin said:

Ah damn, OK. So a 2" focal reducer of .63 or.5 would help.  I'm also waiting for an adapter plate so I can use my wedge, that should get me to 2-3 minute exposures hopefully.  At this time of year mars is behind a tree by 9:30 and I just find the moon so boring:) but I understand what you're saying so I know where I'm going wrong.  So in reality I need longer exposures and brighter subjects.

 

I do already have a 0.5 1.25" reducer, if I used eyepiece projection would that then work?

You're not going wrong - its just you dont have the ideal scope/mount combo for what you are trying to achieve.

You may not like this but... even with the wedge, you're going to struggle to get exposure times in the 2-3 minute region without guiding (which is another big expense). But yes, a combined focal reducer and wedge combo should have a big impact but in the early days.

I'm sorry I'm not familiar with the reducer you are talking about. But like everything else, yeah why not! Give it a try and see what happens!

Cracking scope btw. Would eat planets for breakfast! I've got the same problem with mars at the mo; but as it happens its just about at its furthest away point from earth at the moment anyway; I cant resolve anything at all in my 90mm so its probably not a great target either way.

You're biggest bang for buck will be piggy backing at this stage I'd say, will soften the learning curve considerably. You'll easily get 30-60 secs with a 50-100mm lens or similar on that mount and some fab results.

[Trevor-Austin]

56 minutes ago, Mr niall said:

You're not going wrong - its just you dont have the ideal scope/mount combo for what you are trying to achieve.

You may not like this but... even with the wedge, you're going to struggle to get exposure times in the 2-3 minute region without guiding (which is another big expense). But yes, a combined focal reducer and wedge combo should have a big impact but in the early days.

I'm sorry I'm not familiar with the reducer you are talking about. But like everything else, yeah why not! Give it a try and see what happens!

Cracking scope btw. Would eat planets for breakfast! I've got the same problem with mars at the mo; but as it happens its just about at its furthest away point from earth at the moment anyway; I cant resolve anything at all in my 90mm so its probably not a great target either way.

You're biggest bang for buck will be piggy backing at this stage I'd say, will soften the learning curve considerably. You'll easily get 30-60 secs with a 50-100mm lens or similar on that mount and some fab results.

Ah yes, guiding, my next learning curve:)  I already have a miniPC permanently connected to my scope, so I will be guiding, I get about 8-0 hours battery life out of the scope plus mini PC and all add ons so that shouldn't be an issue. I've got a Toucam Pro on it's way and I will guide using PHD2, which I think/hope will get me to 2-3 minutes OK. 

 

Yes I can get an image of mars, but at 12mm it is about the size of half a pea, not really worth doing, and then only for about 20 minutes before the tree eats it.  If that tree died I would gain about 30 degrees of sky.

I've got a 70-300mm good quality Canon zoom with the camera and had fun piggybacking last time so I'll try again.

[dph1nm]

Try superpixel mode in DSS. That seems better at picking up stars, although it does reduce the size of the final image. DSS needs a minimum of 8 stars in common between the frames to stack them.

NigelM