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Old 17-09-2005, 06:26 AM
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Striker (Tony)
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Sigma lense for widefield

Looking for a nice widefield lense to use with my 20DA.

Are these any good.

Sigma 105mm F2.8 EX DG Macro AF Lens 105 f/2.8

I'm thinking of getting say an EQ4 mount with drives so I can just throw the camera on top for field trips...any suggestions.

This would be a christmas present...I like to get my orders in early...lol

http://cgi.ebay.com.au/ws/eBayISAPI....MakeTrack=true
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  #2  
Old 17-09-2005, 09:31 AM
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Tony is it an ED lens .
I think you would want a lens worthy of the cameras capability.
I have been looking for a Camera lens to use with a CCD astro camera as you know and found the Nikon 180mm f2.8 $700US and 300mm f4 $900US to be very popular lens for this task without selling the house and both have 1 or more Ed elements in the groupings to minimise Chromatic aberations.
Are there any with an ED lens that will suit the Canon mount?
You will pay more for an ED lens though.
I think as you have a $2500+ camera you would want the best lens posssible for it.With in reason.
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Old 17-09-2005, 04:11 PM
rumples riot
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Sigma lenses are very good, but you might consider that a Canon lens with image stablising will be a better lens in the long run. I find that my best lens which is a 80-400mm VR Nikon gives me the best images. A mate of mine who does great terrestrial photography has all Canon lens for his 20D. The images that are produced are simply breath taking. You can find his stuff at this link. http://timtam.deviantart.com/gallery/

That aside the lens you have highlighted is a macro lens and not designed for what you want. You might want something line this: Canon EF 28-135mm f3.5-5.6 IS USM. Which is around $821 Australian and designed for what you want. The 28mm is reasonably wide although something like this might also suit: Canon EF-S 17-85 f4-5.6 IS USM. The 17mm is wider still. In case you don't know the smaller the number in mm the wider the angle that you get.

Anyway don't get the one you asked about unless you want to do macro shots. I have a macro 105mm and it does not focus well past 600mm. So that is not what you want for astrophotography.

Hope this helps.
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Old 17-09-2005, 04:17 PM
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Striker (Tony)
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Thanks Mark and Paul...

I already have a Canon 17-40 L series lense which I love so I will keep my eye on the higher quality lense in the future.

I even like the canon 70-200 L series in both F4 and F2.8..the F4 is around $1000 and F2.8 is $1700....$1700 is getting a bit much for me. they do have a sigma 70-200 F2.8 apo for $1000...might be worth considering at lower cost.
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Old 17-09-2005, 08:02 PM
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You will only be dissapointed with any zoom to image stars,chromatic abberration and coma are both very apparent.All zooms have to have compromises in their inherent design.Sure the really short focal length zooms dont show this as their images are bloated anyway.
The only lenses to consider for astrophotography is a high quality prime of any quality brand.
I have a Tamron 90mm F2.8 macro which is very good.A canon 85 mm F1.8 which is also very good.A Tokina 24 to 200 mm which is lousy at stars,but fine with ordinary low contrast images.
Just because a zoom produces good terrestial images,does not mean it will image stars without chromatic abberration and or coma (spherical abberation).

If I am wrong about Canon L zooms let me know.

If you want pics let me know.
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Old 17-09-2005, 08:20 PM
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Not with my lenses your not wrong avandonk. Even using DSLR Focus it was impossible to get nice tight stars. They always seemed to need just that extra tweek of focus. Soon as I switched to a prime lense (50 f/1.8) nice sharp stars. Mind you the lenses I have are nothing fantastic to start with, 80-200, 35-80 and the one that came with the 300D the 28-90.
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Old 17-09-2005, 08:31 PM
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The Canon EF 100mm f2, 100mm f2.8 USM Macro and 85mm f1.8 lenses have a good reputation for being sharp. There also seems to be a lot of quality variation from one lens to another so if you can try the lens first that is the best way.

I have the 100mm f2.8 USM Macro, and it is good (not excellent) wide-open. To get near perfect corner - corner performance requires stopping to f5. Here is a shot wide open with my modded 300D:

http://www.pbase.com/terrylovejoy/image/36529489

If you do a search for posts by 'Pertti' on the yahoo digital-astro list you will see some detailed lens tests.

Terry
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Old 17-09-2005, 08:41 PM
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Nice Terry. I look forward to being able to images like that with my 50mm, that's if I ever get the courage to get someone to rip the filter out of mine (after warranty of course).

I looked into the 100 f/2.8 macro and the 100 f/2 when first looking for prime lenses. Just outside my price bracket at the time, but I was wondering how they compared to each other, and especially how the macro (and other canon macros) would work in astro imaging? I'd be interested to know your thoughts on them
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Old 17-09-2005, 09:29 PM
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Quote:
Originally Posted by [1ponders]
Nice Terry. I look forward to being able to images like that with my 50mm, that's if I ever get the courage to get someone to rip the filter out of mine (after warranty of course).

I looked into the 100 f/2.8 macro and the 100 f/2 when first looking for prime lenses. Just outside my price bracket at the time, but I was wondering how they compared to each other, and especially how the macro (and other canon macros) would work in astro imaging? I'd be interested to know your thoughts on them
Your best bet is the 85mm F1.8,bang for buck it can't be beat.
Sorry to post these again but it saves time.These taken with a 85mm F1.8 at F2.8.one full frame and a crop to show the real detail.
Yes unguided!
Attached Thumbnails
Click for full-size image (Combine1_PS01_crop22.jpg)
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Click for full-size image (Combine1_PS01_small.jpg)
128.1 KB21 views
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Old 17-09-2005, 09:59 PM
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I was told by somebody with extensive experience using Canon equipment for astronomy the 100mm macro was THE sharpest canon lens for astrophotography. I am not so sure about this - sharp yes - but sharpest maybe not. One thing I don't like about the macro is the length and weight are more than the equivalent telephoto. It is heavy enough that addition support should be considered for mounting the lens.

If I were to do it again I might have gone for the 85 f1.8 or 100 f2 tele.

Terry
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Old 18-09-2005, 07:12 AM
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Avandonk and Terry. Looks like either one of those will be my next lense purchase
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  #12  
Old 18-09-2005, 07:38 AM
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100mm F2 is in nice price range....only around $700 includding postage.

OMG...is this right.

http://cgi.ebay.com.au/CANON-EF-100M...QQcmdZViewItem

Last edited by Striker; 18-09-2005 at 08:13 AM.
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Old 18-09-2005, 08:26 AM
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Oh well...I bought it...I went for the Canon 100m F2 USM at a fantastic new price of $290 USD + $50 USD postage

Total being $450AUD No duty or custom fees as its under $500 and USPS is being used.

I say a Bargain.
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Old 18-09-2005, 08:33 AM
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Terry and avandonk, what are you feelings on using a 1.4X or 2X teleconverter. Would they degrade the image significantly when used with either a 50, an 85, or a 100 lens?


you can't help yourself can you Tony. Your worse than me
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Old 18-09-2005, 09:10 AM
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Tony,

Good one! You are also covered by Australian warranty for Canon lenses regardless of where they were purchased.

Terry
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Old 18-09-2005, 09:58 AM
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guys this has been a MOST informative thread!!!
Thanks, this will help guide my searching over the months ahead.
Looks like a rather expensive (on my budget) canon prime of 85mm or 100mm is the way to go.
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Old 18-09-2005, 10:18 AM
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Quote:
Originally Posted by [1ponders]
Terry and avandonk, what are you feelings on using a 1.4X or 2X teleconverter. Would they degrade the image significantly when used with either a 50, an 85, or a 100 lens?

The 1.4x and 2x teleconverters only work on some (longer FL) L lenses.For a list see
http://shop.centre.net.au/index.html...1CY&it=product

I have a 300mm F2.8L and a 1.4x teleconverter and there is almost no detectable degradation of image (CA) using the 1.4x.I have heard there is a slight degradation with the 2x.For the cost of one L lens around 100mm you can easily buy two of, 85mm F1.8 USM,100mm F2.0 ,100mm f2.8 macro,and the 135mm F2.8 softfocus (the soft focus can be turned off).

All is not lost though.I am going to modify a 500mm F5 achromat OTA by shortening the tube and then mount a reducer lens to convert it to a 300mm F3. I already have it working at 400mm F4 and the image is no worse than the
native configuration.I suspect a minus violet filter would solve any CA problems.
The 80ed is even a better candidate but I don't want to cut it's tube yet.
Obviously the 80ED would end up being a 360mm F4.5.
When I have it all working and tested on stars will let you know the details.
My aim was to design a reasonable quality fast refractor that was affordable.
Here is a pic of two exposures superimposed with Registar one 600mm F7.5 (80ED) and with focal reducer 0.63 380mm F 4.8.Both the same exposure.The pic with reducer through trees!
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Click for full-size image (comb_01_sm.jpg)
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Last edited by avandonk; 18-09-2005 at 11:02 AM.
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Old 18-09-2005, 10:20 AM
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Striker (Tony)
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Yes its been great.

Proof being I purchased another lense.

I'm still getting over purchasing a $1000 lense for $450 new.
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