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How to make images bigger.


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Hi All,

I've started to use my 1100D for imaging but in some respects I'm a bit dissapointed.

I've been revisting some of the objects that I've imaged with my trusty SPC900.

The only problem is that they are tiny.

How can I make them bigger.

I'm using the 1100D with a 2" T ring adaptor and my 200P .

- Neil

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If you're undersampling (probably debatable at 1000mm focal length) you can use dithering when stacking, which results in a larger final image. Otherwise you need more focal length, which usually means a barlow or a different scope. Tracking and guiding at long focal lengths is not a doddle though.

Do you have an example of something that hasn't turned out as large as you'd like?

James

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Just zoom in on the screen and crop it where you want. The pixels on the 1100D are smaller than the SPC900NC, so viewed at the same pixel scale (e.g. 100ppi for onscreen viewing) the object will appear larger in your DSLR image, it will also have a lot more sky around it due to the larger sensor. That is the whole point of DSLR imaging, to get more sky in the shot.

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It's a common error to think that a big chip makes the object smaller. It doesn't, it just provides more sky around it. Only a change of focal length can increase the size of the object on the chip. How bg the chip is has nothing to do with it, other than that your coputer will zoom out on a big image to fit it to your screen.

Olly

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Hi All,

I've started to use my 1100D for imaging but in some respects I'm a bit dissapointed.

I've been revisting some of the objects that I've imaged with my trusty SPC900.

The only problem is that they are tiny.

How can I make them bigger.

I'm using the 1100D with a 2" T ring adaptor and my 200P .

- Neil

If you are using the same scope then you are getting the same size image, the image size only depends on the focal length of the scope not the size of the chip, with a dslr your FOV is considerably larger as it covers more of the sky compared to the tiny SPC900 chip. Either resample, drizzle just zoom in.

A.G

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A higher resolution camera with denser pixels will give you a larger final image. Your 1100D only have slightly denser pixels then the SPC900, wich results in barly any larger final image if you crop at the same resolution.

A barlow is probably the easiest solution, though it will require much longer exposures for deep sky. For planetary, the 1100D is not suitable as it lacks the 640*480 crop video mode - if this is what you're trying to do.

Edited by Jannis
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That combination of scope and camera has 1 arcsecond pixels, which is pretty much optimal for UK skies (maybe even oversampled). Unless you have really good sky conditions there is really little point trying to improve on this for DSO work.

NigelM

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which is pretty much optimal for UK skies (maybe even oversampled).

Just a bit curious about this - does the same apply for lunar/planetary? I'm guessing not due to teh short exposures used, but haven't really looked much into it.

I live in Norway, so maybe different limits here, but have no idea if it's better or worse here. Any way to find out the limit?

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Thanks everybody for the replies.

I've been doing a bit of playing about with DSS tonight and stacked some images using the custom rectangle mode and 3x drizzle. It's made me realise that I have a few issues to overcome before I get anywhere near where I want to be; guiding, focusing (which is now sorted) etc and possibly getting my 1100D modded as there's not a lot of red in my image.

I ended up with this https://www.dropbox....1ur/m57 Big.TIF

I did this https://www.dropbox.... Nebula PS1.tif with my SPC900 back in June and at the moment I'm honestly not sure which is the best one.

Of course the only thing I need now is some clear skies, one can only hope.

- Neil

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The images show the nebula at the sort of size I'd expect. If you'd like a larger image then you'll probably have to use more focal length. Unfortunately that will mean longer exposure times and make guiding more difficult. This is a DSLR image of M57 with my 127 Mak from a few weeks ago without dithering:

m57-2013-08-05.png

That's with a 450D, so with the 1100D there's no reason you shouldn't achieve something similar. Perhaps you just need longer exposures?

James

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I much prefer the DSLR...Stars show no elongation. Just more data needed I feel.

Steve

The SPC 900 one was my first attempt at a DSO and at that time I hadn't perfected polar alignment and it was done with my old EQ5 not the NEQ6.

The DLSR was done without any guiding but I do try to make sure my mount is perfectly level and take some time to get my polar alignment spot on. That was 25, 60 second exposures at ISO 800. Should I be taking more / longer ?

The images show the nebula at the sort of size I'd expect. If you'd like a larger image then you'll probably have to use more focal length. Unfortunately that will mean longer exposure times and make guiding more difficult. This is a DSLR image of M57 with my 127 Mak from a few weeks ago without dithering:

m57-2013-08-05.png

That's with a 450D, so with the 1100D there's no reason you shouldn't achieve something similar. Perhaps you just need longer exposures?

James

To get it that size I had to use a small Custom Rectangle and 3x drizzle.

May I ask how many exposures did you use to get it and what settings on the camera.

- Neil

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To get it that size I had to use a small Custom Rectangle and 3x drizzle.

May I ask how many exposures did you use to get it and what settings on the camera.

Don't have the details to hand at the moment (I'm fitting a focuser at the moment :), but I suspect it wouldn't have been that different from yours. Do you have the stacked (but otherwise unprocessed) TIFF file available anywhere?

James

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Do you have the stacked (but otherwise unprocessed) TIFF file available anywhere?

James

I haven't done any processing to that one apart from the stacking.

I could do another one without the Custom Rectangle and the drizzle.

- Neil

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Here you go. It's no bigger, but there's plenty there to see. I have perhaps pulled the black point up a bit too far, but it's just a quick five-minute twiddle and I'm not working on the best of monitors at the moment...

post-10871-0-06710100-1376608463_thumb.p

James

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James -

Wow! How did you do that so quickly.

This is where I think part of my problem exists.

I'm now getting there on capturing the data, the only problem is apart from the stacking I don't have much of a clue on how to process things. Photo editing is a black art to me. I only wish there was a decent and up to date tutorial somewhere that would at least start people off in the right direction.

- Neil

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Wow! How did you do that so quickly.

This is where I think part of my problem exists.

I'm now getting there on capturing the data, the only problem is apart from the stacking I don't have much of a clue on how to process things. Photo editing is a black art to me. I only wish there was a decent and up to date tutorial somewhere that would at least start people off in the right direction.

It's where you go after the stacking that really makes the difference. Photoshop is good to have, but expensive. If you don't already have PS then one of the new releases of GIMP that supports 16-bit images may be a good place to start. There are quite a few tutorials on youtube, some better than others. These ones are a little on the slow side, but might help you move forward:

James

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