Astro photography with a meade Dsi Pro - What am I doing wrong?

[mothershipuk]

Hi Guys

Wonder if anyone can help me with this one....

My sequence for trying to get a picture of the stars with a meade dsi pro is as follows ( Bearing in mind I am learning this as I go along!)

1. Set up telescope, align.

2. Connect Laptop to dsi using cable and enter the envisage program for caturing an image.

3. Point the telescope at a bright star

4. Change eyepiece for DSi

5. Place the hartmann mask over and focus.

6. Remove mask

7. Voila! Bright star appears on the screen.

However, when I move scope away from bright star, say to M31 Andromeda galaxy the picture goes all fuzzy until I bring in another bright star or a planet.

I suppose my question is how can I take images of fainter star cluster and such?

Cheers

Justin

[beamer3.6m]

You most likely need to increase the exposure time.

When you look at a bright star the DSI is able to see it easily, even with short exposures. With my Toucam I can see very bright stars when the webcam is not normal record mode, i.e. 10 frames per second.

However, when you move to M31 for example you will need to increase the exposure time to say 10 seconds each to even it see it faintly on screen. 30 seconds would be better.

Then when you have it in sight at say 30 seconds and focus is ok and it is lined up ok increase the exposure again and image. Increase to say 1min and capture a number of images. Then stack them.

[Paxo]

Justin,

Sounds like your doing everything correct, and as B3.6M has said, you need to increase the exposure time. M31 is actually difficult to image and is probably not the best DSO to start on. For one, your DSI pro has quite a small chip ad so the whole galaxy will (probably as it depends on your scope as well) not fit on the chip. What you will probably image is the core which just looks like a large fuzzy ball. Secondly the brightness difference between the core and outer arms tends to result in an overexposed core. Nearly all of the fantastic images shown on SGL are stacked images, i.e. the detail is built up with time by combining images, Envisage does the automatically for you.

Why don't you try M27 as a target, it is a good size match for the chip and has a relatively high surface brightness. M13 and M92 (as you have expressed an interest in clusters in your post) are decent target at the moment as well, and are well within the capability of the camera to get presentable images. Also remember that depending on your mount/tracking, you may get star trailing in your images if you have the exposure time too long. If you have decent polar alignment, you may be able to get exposures up to a couple of minutes before trailing becomes evident.

Steve

[mothershipuk]

AAhhhaa ! Wow ! Thanks for the quick replies. Longer exposure times I will try and M27 here I come (well, as soon as the clouds go)

You mention decent polar alignment. I read about this in my telescope manual but havnt needed to do this as yet. I remember reading that in order to take long exposure pictures you really need a wedge! Is this true? There are 2 meade types for the LX90 I know of. Do you know which wedge would be best for me?

You mention the Dsi having a small chip and therefore not all the object will be seen. Would a focal reducer help here?

To be honest I would settle for any picture of the stars at the moment.

Thanks again. Speak soon

Justin

[narrowbandpaul]

a focal reducer will do good. if you use the meade ones they are f6.3 and f3.3 final focal ratios. This reduces the focal length, and it make imaging faster, and gives a wider view. All these things are good for starting out.

The f3.3 should work fine with the small chip of the DSI, i have used it with a canon350D, and it was hopeless. The f6.3 worked good though.

with the correct spacing employed the f3.3 should be fine. Then you have a really fast scope, and a much better field of view for beginning.

Good luck

Paul

[geoff_k]

Justin

As it is fairly high in the sky right now, can I add M57 the Ring Nebula to your list?

Quite near Vega so you can focus on that and increase the exposure when you move to M57. You will need at least 10 seconds as it is only mag 9.5.

It will certainly fit on the DSI chip and being a well-defined object is good to practice on.

Happy hunting!

Geoff

[Paxo]

Justin

I wasn't sure what scope you had - an alt az LX90 should still produce some decent images. There's no doubt imaging is much easier when you have the fork mount mounted on a wedge, but to get started you can still use in alt/az mode. The problem you will have using your scope 'as is' is that you will get rotation in your image as the object tracks in the sky. The software packaged with the DSI is actually quite powerful, and it has a de-rotation algorythm within it. To operate this you draw boxes round two stars, as you image, Envisage knows the relative positions of these stars and will de-rotate your image before stacking, so while you 'getting the hang of it' you should be able to get some decent images. This all works best with shorter exposures. One hint though, try and get your alt/az alignment as good as you can - it helps.

I can confirm what Paul said, the f3.3 reducer works fine with the DSI, however, this is totally unsuitable for visual use, you would probably get greater joy from the f6.3 reducer as already said.

Hope you get some more clear skies soon to give it a try. Another hint, carry out the dark frames collection (as described in the manual), it makes the image quality significantly better from Envisage. Take up Geoffs M57 as well, you can get some cracking images. M57 and M27 will also give you good practice on colour capture as well.

Steve..

[mothershipuk]

Thanks again,

Its a clear night and I am all excited about getting my first star pics. :cheers:

I have taken your advice and have bought a focal reducer f3.3 and have read a bit on the de-rotation software option. My aims tonight are to get some sort of image of M27 and M57 and will post my pictures up tomorrow (good or bad !) :oops:

Til tomorrow

Justin

[narrowbandpaul]

good luck..at least you got some clear skies!

Paul

[mothershipuk]

Hmmmm :crybaby:

If at first you don't succeed fail and fail again...

It was a gorgeous clear night. Set the LX90 telescope up in my back garden, took great care to align using an astrometric eyepiece and straight away found myself up against it because the collomation was out. After a few twists and turns of my bobs knobs I was able to carry on....

I set up the laptop with dsi pro connected and started the envisage software. So far so good After setting the telescope to 'high precision' I eagerly used the goto and sent the telescope to M57. We stopped first at Vega and there I centered the star and focussed it on the laptop using the hartmann mask.

The telescope then went on to M57. Although Vega was visible on the screen as soon as the telescope slewed away the screen went blank (you know ! on but without a clear picture)

So... with my new knowledge I increased the exposure, starting at 12 seconds then previewed, too bright, 10, 8, 5.7, 4, 2, all previewing too bright!! Btw, all the settings for evisage we on default. I played about with the offset, gain, contrast but still I couldn't get any decent pictures.

Tried this with and without a f3.3 focal reducer on.

After doing a rant around the garden like Captain Caveman (dont know if any of u remember him) I started the entire process from the beginning but still no decent images.

I have shamefully posted my incompetent images for your amusement and hope to hear your thoughts.

Speak soon

Justin

http://ukastronomers.com/page/activate/code/fytfzdrasjldmahpxydxd/username/mothershipuk#browse/photos/ajax/true

[blinky]

Did you do the auto adjust settings bit when you upped the exposure?

[mothershipuk]

Hi there,

I clicked the auto exposure before upping the exposure times. When I watch the instructional video on the meade website a whole load of stars are visible on the screen? Is this normal? Unless I am aimed at a bright star the screen is just fuzzy! HELLLLLP !

Cheers

Justin

[RobH]

Hello Justin,

It's a while since I used envisage, but from what I remember, auto exposure sometimes showed very little.

For something like M57, you will be able to get something with a 10 second exposure. Use auto exposure for focussing, although you should focus using a 3rd magnitude or so star to avoid saturation, then deselect auto exposure and stich your longer exposure in there.

There is a small graph which is near the exposure controls. This is the histogram which shows the light curve of what the camera is seeing.

There are 2 small sliders under this, a black one and a white one. Move the black one to the left, just to the left of the left hand side of the curve. Then move the white one down slowly and you will see the image brightening.

These 2 sliders set the black and white points of what you see on the screen. Set your save image mode to FITS. This will ensure that the image saved to disc is not affected by what you do to the histogram and all the data will be saved. This allows you to play around with it at a later date.

Have a go in daylight so you can get the feel of these controls....I had a bit of a hard time with the DSI and envisage when I first started but once I got the hang of the histogram, it got much easier.

Cheers

Rob

[Jeff RV]

Don't forget to draw a box around a star before imaging!! You will succeed eventually, and don't forget some of the exposures necessary will only be a fraction of a second.

Jeff.