diffraction spikes

[mindburner]

hi being new to dobsonians, I have read a few posts that describe issues along the lines of:

"just the usual newtonian coma and diffraction spikes"

is this just something that one has to accept and do you recon that the skyliner 300 dob will just be the same.

This is maybe a 'doh' question but it's just I didn't realise there may be a different view from that I was used to with a MAK

[John]

Diffraction spikes sort of come with newtonian terratory as does coma. The spikes are not too intrusive and you sort of get used to them, I even quite like them - and it's only on really bright stars. You probably won't notice coma unless you invest in really expensive wide field eyepieces - in lower cost eyepieces the astigmatism of the eyepiece masks the coma !.

Neither are showstopping issues of course - otherwise newts / dobs would not be as popular as they are !.

[perrin6]

Don't worry mindburner, you'll be too busy going 'ooh' and 'ahh' at all the wonderful views a 12inch can show you, to be bothered by coma & diffraction spikes.

[perrin6]

Sights I recommend you check out first with your 12inch :-

M81 & M82 galaxies, M82 looks amazingly detailed, in Ursa major

Jupiter under good seeing

The moon is gonna 'knock your socks off'

NGC 2392 The eskimo nebula in Gemini

M42 in Orion of course.

M64 the 'Blackeye' galaxy in Coma Berenices

NGC 4565 a beautiful edge-on spiral in C.Berenices

M35 & the more distant open cluster 'next' to it

M3 - a magnificent globular in Canes Venatici

After looking at them you will have forgotten about diffraction spikes entirely !

[acey]

Spikes potentially mean less contrast on planets (every spot on the planet's disc is smeared out into spikes across the surface). I moved from an 8" Orion dob to a 12" SkyWatcher and the first thing that struck me was that the diffraction spikes were more intrusive in the 12", leading to poorer planetary contrast. I found this to be due in part to greater scattered light in the SkyWatcher and dealt with it by baffling.

http://stargazerslounge.com/equipment-discussion/99482-improving-flextube-contrast.html

Spikes can be removed completely by using a curved-vane spider, though this doesn't actually eliminate diffraction (and reduction of contrast). But even with spikes, a Newtonian can give very good contrast - I'm certainly happy enough with my SkyWatcher now.

There are of course those who think spikes around stars are very pretty and part of the appeal. The spikes can even be useful in the case of splitting very close double stars, since by throwing light out into spikes, the star's diffraction disc is made smaller.

Since my real business is looking at faint fuzzies, it doesn't matter too much to me either way. As for coma, I've never noticed it: I'm too busy looking at what's at the centre of field, not the edge.

[NGC 1502]

As for coma, I've never noticed it: I'm too busy looking at what's at the centre of field, not the edge.

Same for me Ed.

[mindburner]

Sights I recommend you check out first with your 12inch :-

M81 & M82 galaxies, M82 looks amazingly detailed, in Ursa major

Jupiter under good seeing

The moon is gonna 'knock your socks off'

NGC 2392 The eskimo nebula in Gemini

M42 in Orion of course.

M64 the 'Blackeye' galaxy in Coma Berenices

NGC 4565 a beautiful edge-on spiral in C.Berenices

M35 & the more distant open cluster 'next' to it

M3 - a magnificent globular in Canes Venatici

After looking at them you will have forgotten about diffraction spikes entirely !

many thanks for the geat response. Basically im just worrying as I am about to splash the cash. Also fancied the reviews of the 180 MAK, so just wated to get the decision right

[mindburner]

Spikes potentially mean less contrast on planets (every spot on the planet's disc is smeared out into spikes across the surface). I moved from an 8" Orion dob to a 12" SkyWatcher and the first thing that struck me was that the diffraction spikes were more intrusive in the 12", leading to poorer planetary contrast. I found this to be due in part to greater scattered light in the SkyWatcher and dealt with it by baffling.

http://stargazerslounge.com/equipment-discussion/99482-improving-flextube-contrast.html

Spikes can be removed completely by using a curved-vane spider, though this doesn't actually eliminate diffraction (and reduction of contrast). But even with spikes, a Newtonian can give very good contrast - I'm certainly happy enough with my SkyWatcher now.

There are of course those who think spikes around stars are very pretty and part of the appeal. The spikes can even be useful in the case of splitting very close double stars, since by throwing light out into spikes, the star's diffraction disc is made smaller.

Since my real business is looking at faint fuzzies, it doesn't matter too much to me either way. As for coma, I've never noticed it: I'm too busy looking at what's at the centre of field, not the edge.

That has set my mind at ease. I had a look through your post on removing the scattered light and found it very interesting and creative. It's defianately something I would attempt once I have got a bit more used to the scope in operation.

thanks:icon_salut:

[mindburner]

Diffraction spikes sort of come with newtonian terratory as does coma. The spikes are not too intrusive and you sort of get used to them, I even quite like them - and it's only on really bright stars. You probably won't notice coma unless you invest in really expensive wide field eyepieces - in lower cost eyepieces the astigmatism of the eyepiece masks the coma !.

Neither are showstopping issues of course - otherwise newts / dobs would not be as popular as they are !.

Thats great. I just had visions of jupiter looking like a cross hairs, with search lights coming out:)