M57 - Still having problems

[Rossco72]

Last night was a bit of a mixed bag, clear skies at last but only for a few hours. I got my first chance to use my new LVI autoguider and judging by the reasonably spherical stars I'd guess the guiding was ok. However I was still struggling with focus and I think the stars still look a little bloated. I just can't get the "live View" mode on the canon 450D to give me the benefits i had hoped for. It's also a bit of a blow that a 5 minute exposure takes a further 5 minutes to save!

Anyway, I tried several exposures with just the IR/UV cut filter and then tried a few on OIII and Ha but these were a bit of a bust, maybe the canon just isn't sensative enough?

Any thoughts or wisdom is welcome.

This is a guided 5 minute exposure at ISO800, IR/UV cut, Canon 450D and Televue 4X Powermate.

[adamsp123]

I am no expert imager but won't the 4x Powermate effectively increase your focal ratio by 4, if this is true that will mean you need 4x the time to get the same result photographically as without.

BTW Which scope were you using?

I suspect the filters will really reduce the photon throughput as well, for focusing I use a Bahtinov mask which is a most excellent device otherwise focusing is a big problem.

I am sure you will get some experts helping

good luck

[Catanonia]

Actually 16 times the exposure (4 squared).

Switch of noise reduction on your camera so that the image is saved immediately and not post processed on the camera. What the camera is doing is taking an internal dark for every picture you take. Your 450D is better than my 350D and that is what I use.

I do this, take 20 x 5 min exposures and at the end take about 5 darks as I pack up. Cuts down the time dramatically.

Is the 4x teleview a x4 teleextender or magnifier ? If it is like a teleconverter doubling your Focal Length, then your light capture needs to be 4 squared or 16times as long to get the same photons as it would without the teleextender. Something to think about. Adding converters may 'zoom' in, but also reduces your FStop by same factor and hence your light gathering ability.

Try for longer exposures and try a bahtinov mask for focusing or the old fashioned way. 15sec sub, view, adjust and take another until you get it right.

So to sum up.

a. You need 16 lots of 5 min subs with that teleextender on to get the equivalent light without it.

b. Use a bahtinov mask or take a shot for 15 seconds, view, adjust and do again till as close as possible.

c. Take loads and loads of pictures and stack them with DeepSpaceStacker (See my site for links)

Have fun

[Paxo]

the 4x powermate will also make it much more difficult to focus (how much will depend on which scope you were using). I have the 40D with liveview on. The technique I use is to slew to a bright star, increase the magnification to max on the liveview screen, then minimise the size of the bright star when focussing, when you have achieved this re-slew back to your target, seems to have worked in the past.

As suggested above try a focus mask (there are many types available, a hartman is very easy to make, I have ione for my big scopes, many people swear by the bahtinov variety, either way they make focussing much easier.

Steve.

[Rossco72]

Thanks for the heads up Cat. The NR thing was driving me crazy last night, especially when i tried a couple of 10 minute exposures!!

Although I was keen on the Zoom offered by the powermate, i hadn't really considered the effect of needing 16 times the exposure. I'll need to remember that for future.

Again, thanks for the info.

Cheers

Stuart

[Catanonia]

no worries mate, i fell for similar problem when attached barlow between scope and camera. It gave me 3x but made my photon capture required 9x the exposure rate.

remember, you get nothing for nothing in the universe.

[Whippy]

c. Take loads and loads of pictures and stack them with DeepSpaceStacker

Not wishing to be pedantic but it's DeepSkyStacker and it's here: DeepSkyStacker - Free .

Tony..

[Rossco72]

Thanks Tony,

I already have DSS but the stacked images were pretty poor, probably as a result of not having enough subs I guess.

[Catanonia]

Not wishing to be pedantic but it's DeepSkyStacker and it's here: DeepSkyStacker - Free .

Tony..

thanks for the correction

[minimalist]

Stuart, a couple of suggestions that I hope might help:

- first off, that's pretty good signal considering the very long imaging focal length with the powermate. As everyone says, avoid using it, even on this object, which is indeed small. Try a 1.5x or 2x at most... I assume the scope you use is the ed120?

- Looks like you have some reflection or light leak in your optical train, the gradient on the left side shouldn't be there. Check to make sure everything is optically tight and no screws protrude into the light path.

- The stars are indeed a bit out of focus. Here's what I do with liveview. I first set the camera to the highest iso (1600), liveview in exposure emulation mode. This pumps up the gain on the camera in liveview as high as it can go. Then, I slew to a very bright star like Deneb for example, and focus on it using liveview. I first use the 1x mode, then go into the zoom mode to tweak it. I also now use a bahtinov mask, makes focusing much easier.

- most people take darks. My experience has been that at the higher iso's, you will need to take at least 10, 20 is better, as suggested. However, after years of dslr use, I quit using darks. I found that DSS is pretty darn good at hot pixel removal if you use one of the kappa sigma stacking methods and take at least 10-20 lights. So, instead of taking darks, I take more lights, and in my experience at least I found this gives me cleaner final images.

Hope this helps. You definitely have a good start there, I'm particularly impressed how dark the background has stayed, you must have pretty dark skies.

Daniel

[Rossco72]

Thanks Daniel,

I was using the William Optics FLT132 for imaging with the ZS80 guiding.

A number of the "Darks" i took also had the gradient and I was wondering if this was a symptom of 5 minutes just being a little long for a single exposure on an uncooled DSLR?

I live in the city centre and am lucky if 3-5 star are visable at all just now, however I drive 30 minutes north and have scouted a nice location in the hills where there is no visable light from any towns or cities, there is a little amount of "glow" to the south but it's not too bad.

I have a 2x and a 4x powermate with the t-adapters to attach these directly on to my DSLR, specifically for smaller subjects like M57.

The biggest bonus from this thread though is finding out to turn off the cameras NR protocol. Each 5 minute exposure was taking 10 minutes and then I was taking darks which also took 10 minutes each and flats which were another 10 minutes each.

In summer especially this was really eating into my available time. Have that sorted now and hopefully the next clear night will be much more productive.

It also took a small amount of time getting the autoguider setup as this was my first time using it but it now seems pretty straight forward.

Thanks to everyone for taking the time to give advice and suggestions.

Stuart

[Catanonia]

Ouch that was a lot of time wasted

I did the same myself with my Sony A700 when I started out

Thanks Daniel,

The biggest bonus from this thread though is finding out to turn off the cameras NR protocol. Each 5 minute exposure was taking 10 minutes and then I was taking darks which also took 10 minutes each and flats which were another 10 minutes each.

Stuart

[minimalist]

Ahh lucky you to have such a dark site. As to the gradients in the darks, the 450D shouldn't show any, even at high iso and very long exposures. There is definitely a light leak somewhere. One thing you can do to trace it down is put the 450D in liveview mode at hightest iso, then use a flashlight to illuminate all the parts that connect the camera to the scope. If you notice the liveview getting brighter, then you've found your leak.

Daniel