Hi,
we all know that refractor is much cheaper then ED. if the color correction is the main ishue, can we use minus violet filter on refractor for astrophotgraphy?
Thank you
Kimo
ED Refractor VS Refractor with minus violet filter
Re: ED Refractor VS Refractor with minus violet filter
Here are some stunning photos captured using the cheaper ST80 achromatic refractor by Darrell M. Dodge from Colorado.
For the sake of the discussion and comparison, no minus violet filter were employed in these photos:
M31 --> http://www.telosnet.com/dmdodge/astrono ... forweb.jpg
July 11, 2010
Deer Trail, Colorado
Canon 450D modified
Orion ST80 Refractor; CGE
7 images @ 120secs
Processed with Nebulosity and PS 7
M45 --> http://www.telosnet.com/dmdodge/astrono ... v09_da.jpg
November 21, 2009
Deer Trail, Colorado
Poor Seeing/High Wind
Canon 450D unmodified
Orion ST80 Refractor; CGE
3 images @ 180 secs unguided
M42 --> http://www.telosnet.com/dmdodge/astrono ... ne_ata.jpg
November 19, 2009
Littleton, Colorado
Moderate Seeing/Haze
Canon 450D unmodified
Lumicon DSF
Orion ST80 Refractor; CGE
3 images @ 60 secs unguided
Here's a nice video on ST80 modifications:
For the sake of the discussion and comparison, no minus violet filter were employed in these photos:
M31 --> http://www.telosnet.com/dmdodge/astrono ... forweb.jpg
July 11, 2010
Deer Trail, Colorado
Canon 450D modified
Orion ST80 Refractor; CGE
7 images @ 120secs
Processed with Nebulosity and PS 7
M45 --> http://www.telosnet.com/dmdodge/astrono ... v09_da.jpg
November 21, 2009
Deer Trail, Colorado
Poor Seeing/High Wind
Canon 450D unmodified
Orion ST80 Refractor; CGE
3 images @ 180 secs unguided
M42 --> http://www.telosnet.com/dmdodge/astrono ... ne_ata.jpg
November 19, 2009
Littleton, Colorado
Moderate Seeing/Haze
Canon 450D unmodified
Lumicon DSF
Orion ST80 Refractor; CGE
3 images @ 60 secs unguided
Here's a nice video on ST80 modifications:
http://www.astro.sg
email: gary[at]astro.sg
twitter: @astrosg
"The importance of a telescope is not how big it is, how well made it is.
It is how many people, less fortunate than you, got to look through it."
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email: gary[at]astro.sg
twitter: @astrosg
"The importance of a telescope is not how big it is, how well made it is.
It is how many people, less fortunate than you, got to look through it."
-- John Dobson.
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Re: ED Refractor VS Refractor with minus violet filter
An achromat is certainly usable for astrophotography and many nice photos have been taken using an achromat.
However, color is not the only issue: other aberrations exist as well (there are some articles by Roland Christensen) and will have to be addressed.
In the above photos, you will see the violet halo around some stars, but bear in mind these are bright objects. Dimmer objects will cause more stars to have violet haloes as you need to take longer exposures.
These photos are also taken at a relatively large image scale hence are forgiving.
If you're not fastidious about your photos and the finer technical points, then.certainly an achromat is a cheap alternative, especially if using a UHC filter as you probably would in Singapore.
On the other hand, if cost is an issue, why not an imaging newtonian? It will have few vices (assuming a good quality mirror. Most Synta mirrors are decent nowadays) other than the coma (correctable) and diffraction spikes, which can look nice. It's also faster although it is larger and needs collimation.
However, color is not the only issue: other aberrations exist as well (there are some articles by Roland Christensen) and will have to be addressed.
In the above photos, you will see the violet halo around some stars, but bear in mind these are bright objects. Dimmer objects will cause more stars to have violet haloes as you need to take longer exposures.
These photos are also taken at a relatively large image scale hence are forgiving.
If you're not fastidious about your photos and the finer technical points, then.certainly an achromat is a cheap alternative, especially if using a UHC filter as you probably would in Singapore.
On the other hand, if cost is an issue, why not an imaging newtonian? It will have few vices (assuming a good quality mirror. Most Synta mirrors are decent nowadays) other than the coma (correctable) and diffraction spikes, which can look nice. It's also faster although it is larger and needs collimation.
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