StuartT

4 hours ago, kev100 said:

Hiya,

I have a pair of these and, although I do see some CA during the daytime and on the moon (less than the daytime amount), it's not noticeable on anything else. I have heard of these sometimes arriving out of collimation from the supplier, but mine are are fine (though the first pair had to be returned for replacement after a couple of years as they went out of collimation and couldn't be fixed).

Try them out at night time, on the Pleiades, for example, and see how they fare (looks amazing in mine), or the Owl or Double clusters. You should be able to spot some galaxies too (like the Leo triplet, for example).

Kev

Brill! Thanks for this Kev. Very reassuring. Only had thick cloud so far of course! 🤣

1 hour ago, Felias said:

Actually that's what happens to my new intervalometer! I have been using the camera built-in intervalomer, but it is limited to 30 s exposures. So I have just bought a Neweer one (this: https://www.amazon.co.uk/Neewer-Shutter-Release-Remote-Control/dp/B00GV4DLP0/), which I have seen recommended, and it seems as if I need an interval longer than the exposure, which is pretty useless. I have been tampering with the settings and watching instructions online, but I can't get around this problem, it seems like it has been designed this way. Am I doing anything wrong? Can any one recommend another intervalometer?

That looks exactly the same as mine (I suspect they are all made by the same manufacturer). If so, you can set any interval you like. It's just that it measures the interval from the start of the exposure, not the end of it. This means you add the exposure time to the interval you want.

Example. You want to take a total of 40 exposures of 30 sec each, with 5 sec between them. So enter your LONG as 30s then enter your INTVL as 35sec then enter your N as 40. 

I just bought a pair of these and I wondered if any of you had experience of them? I've not had a clear night yet, but I tried them on a distant skyline object during the day and was a little alarmed at the degree of chromatic aberration. Are they uncorrected perhaps? I guess that might explain why they weren't very expensive (£100)

24 minutes ago, Shimrod said:

I asked this question a few days ago, and then found my own answer! Canon EF-S lenses have an extra protrusion to stop them being used in EF mount cameras (where the mirror would hit the lens). This protrusion is generally not found on third-party EF-S lenses, so you can use a clip-in filter fine with them.

There is a short video here showing someone converting an 18-135mm lens .

Thanks. This is encouraging as I have a Tokina wide angle on order. So fingers crossed!

the video is remarkable! Who’d have thought it was that easy. Just tried it on my 18-55 though and it didn’t just pop out like his did. I didn’t like to pull too hard and risk breaking my lens!

52 minutes ago, almcl said:

You might find this thread interesting:

 

I haven't been brave enough to modify my kit lens (yet) but if I can find a cheap second hand one...

thanks. Although I see that he didn't actually report back, so maybe he didn't 'cut a bit off' 

I must admit I can't imagine how that would even be possible!

Some non-Canon lenses may not have that protrusion, I guess?

1 hour ago, callisto said:

Did you get it new...Is it still under its 14/30 day money back refund?

 

Mark

I did buy it new, yes. Although now I look at the website again, it does say at the bottom that it is not for EF-S mounts. I really need to read things properly!! So I very much doubt they would refund it.

However, I would still be able to use it on the telescope with a T-adapter, so all is not lost. It just means I can't use it for wide sky photos, trails etc.

whaaaaat???

oh no!

😥

I just got a Skywatcher CLS filter for my Canon. But when it's fitted, the lens won't go on (as there is now insufficient space for the lens to protrude inside the camera)! 

I thought these things were supposed to be able to work with lenses? At least according to this video

Right. I understand now. I was thinking of field rotation between exposures, but missing the important effect of field rotation within each exposure. I can see why that would be a problem.

Thanks!

5 hours ago, Cosmic Geoff said:

It seems you are trying to do astro-imaging involving remote control of the telescope.  That will not be easy, and I think you need more specialised software for the purpose. Even standing beside the setup, I find that I need 'precise GoTo' or plate-solving to get the camera on target.

4 hours ago, TerryMcK said:

You would be better using AstoPhotograpyTool and utilize plate solving. Then to guide add a small guidescope and guide camera. Again more expense but you can add the free software PHD2 to guide.

APT has a fully fuctional free version but I don’t think it costs that much to activate. £6 per year rigs a bell. Just use Stellarium to choose your target. I think you can still use Stellarium via Ascom to show where your mount is others can chip in to concur.

Thanks both. In fact, I was just using Stellarium to identify fun things to look at, then getting it to move the telescope to roughly the right place, then manually fine tuning position w the hand controller. I guess I was just wondering if there was some way to tell Stellarium what fine adjustments I'd made (and hence 'correct' it's understanding of the scope's true position)

18 minutes ago, The Admiral said:

Stuart, if you are doing Alt-Az imaging might I suggest that you have a look at the (rather long) thread dedicated to such imaging (if you haven't already)?

 

Thanks for this. I'll check that thread out

12 hours ago, malc-c said:

Like I mentioned I'm no expert, and a lot of what Vlaiv mentioned went over my head, but from what I do know is that I think you are faced with a couple of fundamental issues.  There is a relationship between focal length and exposures.  It's probably no linear but at a guess for a given ISO and same aperture you need to expose twice as long for a scope of twice the focal ratio.  But the problem with long exposures is that you need to guide (unless you have such a high end mount that has fantastic tracking and minimal PEC.  Now an ALT AZ mount has two issues where imaging is concerned which compound the problem.  The first is that guiding becomes difficult as the drift tends to be on two axis rather than one when comparing an ALT/AZ  mount to an EQ, which is related to the second issue of field rotation.  If left unguided a long exposure will result in field rotation, which is approx 45 degrees in a three hour period.  This can then lead to stacking issues because each sub is rotated a few degrees.

So I guess to improve things you either need to consider a focal reducer or fit some form or wedge so the scope can be used in an EQ format and then possibly consider guiding so that more data can be gathered.

Hi. You're sure more expert than me! Yes, I am aware of the dual problems of long focal length and AltAz mount. I guess I just wanted to see what might be possible, even within those limits. Hence why I restricted myself to 30s exposures. So far I have been mostly looking at the sun and the moon (where those issues aren't really a problem). But if I decide I really want DSOs I shall buy some new toys.

Question though - since Deep Sky Stacker is able to deal with translation (during registration) why would field rotation be a problem for it? Can't it also rotate images as necessary?

10 hours ago, vlaiv said:

I'm not sure I'll be able to do much more than original processing with this data.

I managed to get this as luminance:

Tried to apply synthetic flats, but I don't think I quite managed to do it - three is zone below the galaxy that is till brighter than the rest of the background.

Background is now nice and even - but I don't think I managed significantly more signal in the target itself.

ooh! Definitely an improvement! Thanks so much for taking the time to do this 😊

Ok it gave me two options to save the 32 bit FITS file (integer and rational). So I exported both

integer.FTS

rational.FTS

Thanks again

4 hours ago, malc-c said:

Hi Stuart,

I'm no expert, but 46 x 30sec is only 23 minutes worth of data which isn't a lot IMO.  Granted you have a high ISO, which can result in a more grainy image, but even when I was imaging at 800 ISO I would still gather at least an hour on bright galaxies such as M31 and M81.   M51 is quite a faint target by comparison.   Also that's with a 200P so like your SCT an 8" but at half the focal length as the 200P is f5.

Do you have the LX on a wedge or is it in an ALT/AZ format, and are you guiding ?

Thanks. I wasn't sure how many frames to shoot, so this is helpful. I realise a f/10 isn't great for deep sky, but it's what I have 😉

Afraid I don't have the LX90 on a wedge, just the regular old altaz fork. No guiding (I'm not clever enough). That's why I stuck to relatively short exposures.

2 hours ago, vlaiv said:

You've cropped that image considerably, right?

With DSLR camera and very long focal length scope - you are way oversampling at 0.38"/px.

In order to overcome limitations of that, you'll need to employ couple of techniques. First - use super pixel mode debayering. Second - you'll need to bin your data, maybe even 3x3.

Ideally, you need long exposures and lot of them. When oversampling like that - worst thing is to go for 30s exposures as read noise becomes very dominant (signal is too faint per exposure due to very high "magnification").

Could you post stacked linear data? I think quite a bit more can be "squeezed" out of it by doing the above tricks.

Umm.. I'll have to look all that stuff up! 🤣 

Yes, the image is heavily cropped.

By oversampling, do you mean I am shooting at too high a resolution? I guess with my current setup, I can't really go any longer that 30 sec exposures.

What do you want me to post? The light frames? Or the text files that DSS generates?

16 minutes ago, Chefgage said:

Think I know what you mean now.  On mine if I want a 5 second interval then that's what I set it at. I see what you mean by that the interval in your case starts at the begining. So for a one minute exposure and 5 second inverval then this would mean setting the interval at 1 minute 5seconds. I thought you meant that the inverval time was a separate setting so that every time a one minute exposure was taken the camera would then wait another minute to take another exposure, hence my madness statement. 

For my intervalometer you just set the exposure time and then the  interval time is set at say 5 seconds.

yes, that's correct.

It's a bit silly to design it that way, but it's fine once you get used to it. Oddly enough, the intervalometer in Canon EOS Utility works the same way!  😕

Just now, Chefgage said:

You stated that the interval time needs to be longer than the exposure time so for any length of exposure the interval time needs to be longer. I was just giving an example based on your intervalometer.

no. You've misunderstood. 

20 minutes ago, Chefgage said:

If that is the case I would throw that intervalometer in the bin and buy one that operates correctly based on taking astro photos. If the interval time needs to be longer than the exposure time then this is madness. Taking 5 minute exposures would mean significantly less data collected over a session. 

I think you misunderstood. I didn't mention anything about 5 minute exposures. I was explaining that on some intervalometers if you want 5 seconds between exposures you enter it as 1m5s (rather than 5s). I'm saying the same as fwm891

You can do exactly the same job with it, the only difference is how you enter the value of the interval. It's pretty straightforward.

Last night I tried my first serious attempt at creating an image of a DSO (as it was very good seeing).

I selected M51 and using a Canon EOS750D at the prime focus of my SCT I shot;

46 lights, RAW, 30 sec at ISO6400

16 darks, RAW, 30 sec at ISO6400

16 bias, RAW, RAW, 1/4000 sec at ISO6400

Then I combined them in Deep Sky Stacker. It was set to a threshold which found between 100 and 250 stars and the stacking was with Kappa-Sigma clipping.

This is the result after stretching. A little underwhelming. Any tips?

(I didn't shoot flats as I can't figure out how to do that without an iPad!)

1 hour ago, Portech7 said:

Hi all

I'm hoping I explain this correctly. 

I have started using an intervalometer with my canon 1100D.

I set the intervalometer up as below:

1) delay: 5 second

2) exposure time: 1 minute

3) interval time: 2 second

 

 

On my intervalometer (Viltrox MC-C1) the interval timer starts from the beginning of the exposure, not the end of it. So your interval needs to be a few seconds longer than the exposure time (to allow the image to be written to the card). If you are shooting RAW the files are bigger and so take a little longer to be written. So if your exposure time is 1 minute, you should set your interval to, say, 1m 5s. Or maybe to be super safe, 1m 10s

great. Thanks so much both of you. Personal recommendations are worth their weight in gold.

ok, I think tonight's is better. 250 x 5 second exposures at 7 sec intervals combined using Startrails. 17mm lens, f/3.5 ISO 3200

I've got Stellarium steering my telescope, but it's a little out. I'm currently taking subs of M51, but I had to manually adjust the scope a little from where Stellarium  put it. (you can see from the capture that it's a little to the east of where it thinks it is)

1. is there a way to tell Stellarium to make a little adjustment to its alignment?

2. can I adjust the scope slew from within Stellarium? (as it's a bit tedious going out and tweaking the hand controller, taking a photo to see where it is, going out to tweak again etc etc etc)  

23 minutes ago, Stuart1971 said:

Ah, ok I used ISO 800 all the time on my DSLR imaging but with a CLS LP filter to cut out the town glow....👍🏼

ooh.. might have to buy myself one of those. I haven't bought any gear for days! 🤣

I have a problem with the autofocus on my Canon EF-S 17-55mm f/2.8 IS USM

Any suggestions as to a good UK repairer?

Thanks

9 minutes ago, Stuart1971 said:

16m...you mean 16 minutes,...or seconds, as if 16 mins I would have thought the stars would be much more and brighter....

If you take say an exposure every minute for 1.5 hours and then say 20 dark frames of the same exposure length and then stacks the light and the darks together you would get something like this....

 

no, I do mean 16 minutes. Otherwise, there would not be much trailing. Even 16 min is only 4 degrees of rotation.

The reason I don't have more stars is that I was at f/11 anf ISO100. (I live in town 😥