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Old 28-02-2015, 01:45 PM
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rat156
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Join Date: Aug 2005
Location: Melbourne
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Quote:
Originally Posted by Mqrko View Post
Thank you so much for your help. I'll reply to everybody in this post.

I'm willing to spend so no worries on this side.

I understand that I'm not able to fill the frame for most of the DSOs. Since it's inevitable, I'll crop then, no worries. I thought all the pictures I saw weren't and couldn't see much info in the description or exif.

I'm still reading articles about sampling optimization. So i'm sorry if I say something wrong.

I matched the focal length with my camera using this website.

For the D800:
- Sensor width = 35.9
- Sensor height = 24
- Resolution width = 7360

If I put 450mm focal length, it's enough for andromeda galaxy. It also gives me 2.23 arcsecond/pixel, which is good, right ? A 80mm refractor is the best for this.
I would also be able to take pictures of all the big objects like M7, M8, M25, M33, M34, M42, M45, etc...

If I increase the focal length, I will be oversampling for anything more than 1000mm (?)
Do I need to be between 1-3 arcsecond/pixel ? I would then need another camera to match the telescope.

I think using 2 telescopes would be too heavy for the mounts I listed previously so the EQ8, G11 are more suited for the load. I'm more interested in EQ8 for EQMOD. The price of the Paramount MX is too much for me. I could spend the money elsewhere with $10k difference.

I haven't considered the newtonian because of coma and it looks BIG.
Ritchey Chretien and Astrograph are the same thing, right ? The pictures I saw look nicer and I like the effect of the diffraction spikes. I would consider buying one if it fits in the car with all the equipment.
I picked SCT, because it's easier to transport, but I can change my opinion. I'm not in a rush.
Is there a big difference between this and SCT for visual purposes ?
Hi Marko,

If you are prepared to spend, then buy the best mount you can afford, believe me, or don't, but ask any of the astrophotographers on the forum and you'll get the same answer. Mount, mount, mount. The EQ8 and G11 are good mounts, but the difference between them and a Paramount or Astrophysics mount is like chalk and cheese.

You'll need a field flattener for using the D800 with an ED80, even then the image will be vignetted quite badly.

Your calculations are out as well, you need 0.5-1.5"/pixel (depending on your seeing, but better to oversample a bit than under sample (square stars)) see this website for more details
http://www.stanmooreastro.com/pixel_size.htm (the final sentence)
http://www.stanmooreastro.com/SamplingFratioMyth.htm

So for your camera a FL of about 800mm would be fine. This means a nice f/4 imaging Newtonian would be a great choice, Bintel have a 200 mm f/4 (1.2"/pixel) up to 300 mm f/4 (1200 mm FL, 0.8"/pixel) imaging Newtonian. This type of scope will probably require a corrector, but enquire around, maybe someone has some experience with them.

Astrograph is a generic term for a scope which the primary function is to take pictures, think of it as a scope optimised for astrophotography rather than visual. As such most RCs are astrographs, but not all astrographs are RCs.

Pretty much any SCT will have a FL which is too long for your camera, they are also plagued by dew formation on the corrector, the correction of which can cause other problems. Similar problems for big refractors. Newtonian scopes are far less susceptible to dew problems.

So, my advice...

You have already decided to keep the D800, so that sets your pixel size. Next research which scope best suits and decide on the FL. This sets the total mass that the mount will have to lug around. Then decide on the actual scope you want, a cheaper Chinese brand, or perhaps a more expensive European or US made scope. Then you will know how much is left of your budget to spend on a mount, buy the best one you can afford.

Cheers
Stuart
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