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Before you jump to another thread because you're not looking at one of Olly's amazing pictures please spare a minute or two to critic my picture.

Some background:

location: Hampton Wick (that's near Kingston upon Thames, under the London's dark skies ;))

no pier, just a flimsy but stable (as long as you don't hit it...) cheap folding workbench

mount: the ever so amazing bottom of the range EQ1

camera: Lumix GF1

lens: Hoya HMC tele-auto f/200 @ 1:5.6

exposure: 30"

20 lights, 2 dark, 20 bias

stacked in Deep Sky Stacker (it was a download DSS, install, stack with the recommended values, nothing special.

intended target: M101

sadly, my target was sightly below the 3 stars at the bottom of my picture :(

I will try another attempt this evening if weather permitting.

So please, go wild on my picture (I know you're not looking at anything spectacular...)

0b35ceca-7a2c-491b-b532-16c1e9e98a28_resized.jpg

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Well the stars aren't trailed, so your PA was pretty good :)

Viewing the full size, it looks like your focus was a little off but only a little. I found M101 a difficult target from a light polluted site as the surface brightness is fairly low. I am not sure 30s will be enough to pick it out. How about trying for M81&82? They are higher in the sky and brighter, also they are nearer the pole so you should be able to get longer subs before running into trailing problems.

Stick with it :)

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Thanks for the feedback, I've used our Rosedale polar alignment script to PA the mount (it was spot on for an EQ1).

yes the focus is a bit out and I've just realised his morning that my lens aperture ring was on 5.6 instead of 3.5 :( doh....

Just for the fun of it, here's my setup from last night while I was doing the PA

62c932ef-3e6a-41a0-8056-ea48cd2ff589_resized.jpg

I will try to locate M81/82 this evening, it's quite hard to locate faint objects under London's light polution :(

Will also do more exposure, last night was more of a "can I really do it?" session.

I can got up to 256 seconds on the GF1 I believe.

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Just coincidentally I received a 2nd GF1 in the post this morning. I broke the first one doing a DIY full spectrum conversion but it partially worked for a few hours before I killed it

Learning from my mistakes (I know what I did) I hope to have better luck second time around.

Removing the internal filters did make a big difference while it lasted :evil:

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HI Olly,

thanks for the good word, this is what I have setup on DSS:

dss.png

I'm still learning...

Thanks also for the link, that's going to help me as I'm out again tonight to have another go at M101. I do know exactly where it is, I'll be able to frame it nicely (I hope...).

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Can't help on DSS but once you have your stacked image it will be in linear form. A pixel reading 5000 counts will appear in the picure as half as bright as one showing 10,000 counts. This may be a scientific image (up to a point) but it won't be very interesting. In DS imaging we radically depart from the linear form by greatly brightening the faint signal while brightening the bright signal by vastly less. The eyes and ears do the same. This is called 'stretching' and is what allows so much faint detail to be extracted from a picture. The more exposures you stack the more you'll be able to strecch the faint stuff.

Olly

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This evening I'll make sure that I have the following set correctly

ISO:800

exp: 256" per shot (maximum my camera can do)

aperture ring: 3.5

I should be able to collect enough data this evening, I will use it to learn this stacking and stretching techniques.

thanks again for the help Olly. I'm at the bottom of the steep learning curve of astro photography, but I'm getting there slowly....

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For DSS, keep the exposure frames on Kappa-Sigma, change the offsets to median. Either take more darks or drop them altogether, if you don't have lots of them, they will do more harm than good. Try to take some flats and combine those as median as well; they will make the processing much easier.

When you have checked all the exposures you want to stack, click on register settings, click advanced, make sure the 'median filter' box is checked and then click 'Compute the number of detected stars', move the slider until it detects between 70 and 100 stars. This should give a good balance between accurate stacking and short processing time.

When saving the final stacked image, I save as 16-bit tiff and always use the option to 'embed adjustments in the saved image but do not apply them'. Then I do all the processing in Photoshop. DSS has a habit of clipping the white point with stars and loosing the colour if you save with adjustments applied. You can tweak the sliders and apply the adjustments to preview the image in DSS, but if you have a proper image processing package like Photoshop or Paintshop Pro it is better to use that for the processing and embed adjustments without applying when saving.

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Thanks for the great tips on DSS much appreciated. I do have Gimp instead of photoshop (can't afford nor justify it for what I do).

Regarding the darks, is there a good ratio as in lights V darks?

Flats,,,,, I think I will leave that for another time as I need to learn a lot more about it.

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Thanks for the great tips on DSS much appreciated. I do have Gimp instead of photoshop (can't afford nor justify it for what I do).

Regarding the darks, is there a good ratio as in lights V darks?

Flats,,,,, I think I will leave that for another time as I need to learn a lot more about it.

It isn't a ratio effect, rather to make sure you use enough that you aren't adding extra random noise, while subtracting the fixed noise. I used to aim for 20-30, more if the exposures were short. Now I dither guide and don't use them at all, only offset (also called bias) and flats.

Speaking of flats, they make the most visible difference to the final image of all the calibration frames. The sooner you learn, the better your images will be. For a simple start, chuck a white T-shirt of the end of the scope, point it at the twilight (or dawn) sky, set the camera to aperture priority, and fire off 20-30. If you have to set the exposure manually, aim to get the histogram peak 1/3 to 1/2 way across. They should be pretty short (less than a second) exposures.

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Speaking of flats, they make the most visible difference to the final image of all the calibration frames. The sooner you learn, the better your images will be. For a simple start, chuck a white T-shirt of the end of the scope, point it at the twilight (or dawn) sky, set the camera to aperture priority, and fire off 20-30. If you have to set the exposure manually, aim to get the histogram peak 1/3 to 1/2 way across. They should be pretty short (less than a second) exposures.

I'm going to try your method and see what I come up with. thanks again :)

Hopefully tomorrow you'll see a picture of M101 from me....

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so I went ahead and took from flats using a couple of white paper tissues instead of a t-shirt, took about 20ish.

Put everything back into DSS with your recommendations, sent the result into Gimp and played with the curves.

Here's what I came up with as a final image.

f5aeba2a-3d6f-4263-bfe5-6afaff9bde44_resized.jpg

I do see a clear difference between my first attempt at the start of this thread and this one, but there's still a lot to learn :)

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:D Hope your M101 comes out well.

Unfortunately it didn't.

Things that went wrong this evening, a little too much wind at some point lead to some star trail on some shots, didn't take enough 'lights' (each one's exposure was 2min).

I have a large tiff file if anyone can extract any data, when I try with Gimp, I can see a blurb of something where M101 is supposed to be and that's it.

http://8bbed13a61beb...dn.com/m101.TIF

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Hi Russell,

thanks for giving a go at it, yes it was slightly gusty and my workbench table just didn't like it :(

After putting my lens and GF1 specs through ccdcalc I realised that there is no way I can get a good picture of M101.

I have a cunning plan... I'm going to fit the QHY5 directly to the lens ;)....

I'm happy with my results from Friday's session, thanks for the tips of Olly and RikM.

Saturday wasn't too good, but it's good practice.

thanks also to everyone that jumped in the thread, much appreciated.

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Unfortunately I don't think the QHY5 will add much, although always worth an experiment!

If you want to get a better picture you're going to need more focal length!

If you want to try a different target, try pointing north between Cassiopeia and Perseus, there's some nice big nebula that might work well with your rig. Here's a shot I took when I was playing with the camera and the 50mm lens. I used one of those Joby tripods and had it wrapped around a fence :)

post-6495-0-40198500-1366580009_thumb.pn

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