Go Back   IceInSpace > Equipment > Astrophotography and Imaging Equipment and Discussions

Reply
 
Thread Tools Rate Thread
  #1  
Old 20-06-2008, 09:14 PM
CometGuy's Avatar
CometGuy
Registered User

CometGuy is offline
 
Join Date: Feb 2005
Location: Brisbane
Posts: 942
Comparision - Canon 200 f2.8 and Canon 70-200 f2.8

I see a lot of threads if forums (both astronomy and photography) comparing the different versions of the Canon 200 lenses. I was doing an update on my website today and noticed I had a comparsion between the 200 f2.8 prime and 70-200 f2.8 non-IS zoom at this URL:

http://www.pbase.com/terrylovejoy/200_comparision

In my opinion the prime gives somewhat more contrast and pleasing star images at the image centre, but the zoom gives significantly better images towards the edges. I still think it is great result for a zoom though! I've also updated my 70-200 page with shots of the Crux at 70mm-200mm. These are just 75 second exposures with an unmodified 350D from backyard in Brisbane.

http://www.pbase.com/terrylovejoy/70_200

Terry
Reply With Quote
  #2  
Old 21-06-2008, 06:00 AM
iceman's Avatar
iceman (Mike)
Sir Post a Lot!

iceman is offline
 
Join Date: Sep 2004
Location: Gosford, NSW, Australia
Posts: 36,709
Nice, Terry. Great comparisons. Thanks for that.
Reply With Quote
  #3  
Old 21-06-2008, 07:25 AM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 5,966
Very interesting results.
One would expect quite the opposite (prime performing better at edges and especially in the centre).
Perhaps the better test would have been to image one bright star only, by placing it at the centre of the frame and at the corners, for comparison (I did this like that for some of my lenses, using Pleiades as a subject).
However, this method also gave very conclusive and quite useful results.
Reply With Quote
  #4  
Old 21-06-2008, 10:10 AM
AlexN's Avatar
AlexN
Tunnel Vision

AlexN is offline
 
Join Date: Mar 2008
Location: Brisbane, Australia
Posts: 6,708
yer i would have expected the prime to win..
Reply With Quote
  #5  
Old 21-06-2008, 10:28 AM
Suzy_A's Avatar
Suzy_A
Registered User

Suzy_A is offline
 
Join Date: Jan 2006
Location: Fremantle
Posts: 232
Here's another comparision...

http://www.the-digital-picture.com/R...omp=0&Camera=9

But not that these are with a full frame 1D. The results would be a bit different with a smaller image sensor camera eg 40D.
Reply With Quote
  #6  
Old 22-06-2008, 09:17 AM
CometGuy's Avatar
CometGuy
Registered User

CometGuy is offline
 
Join Date: Feb 2005
Location: Brisbane
Posts: 942
I have added some more information on the comparsion, have a look at my updated 200 Comparision. There is no question the in my mind the zoom is sharper, but bright stars are "less pleasing" and there is more vignetting when compared to the prime. I suspect the prime is more contrasty, but haven't actually verified this. But the zoom gives you a very nice 70 f2.8, 100 f2.8 and 135 f2.8 included in the price and it is also extremely well made.

Keep in mind this zoom was hand picked at local camera store so it shows almost no decentering (as is a common problem - actually the norm - with camera lenses). Decentering is the problem where misalignment in the optical elements causes one side of the image to come to focus before the other and can cause other problems with Image quality.

Terry
Reply With Quote
  #7  
Old 22-06-2008, 09:23 AM
[1ponders]'s Avatar
[1ponders] (Paul)
Retired, damn no pension

[1ponders] is offline
 
Join Date: Nov 2004
Location: Obi Obi, Qld
Posts: 18,778
Gee Terry, another one to save up for.

Terry, how do you "measure" for decentering? Is it simply through observation of the lens attached to the camera or do you have a magic gizmo to do the job?
Reply With Quote
  #8  
Old 22-06-2008, 09:57 AM
CometGuy's Avatar
CometGuy
Registered User

CometGuy is offline
 
Join Date: Feb 2005
Location: Brisbane
Posts: 942
Paul,

You can see it pretty easily if you do this test:

- Put the lens in to AF mode and focus on something in the distance that is bright and has a lot of contrast (eg a telegraph pole or tree sillouetted against the sky).
- Then switch to manual focus and take a shot with the subject in one corner, one in the center and the one in the opposite corner.
- Examine the results in the preview screen at max magnification. If you see one side and centre are in focus and the other side is blurred you have decentering - try another lens or take it back to be replaced! Next time I'd problably take a laptop along to the store.

Terry
Reply With Quote
  #9  
Old 22-06-2008, 10:08 AM
[1ponders]'s Avatar
[1ponders] (Paul)
Retired, damn no pension

[1ponders] is offline
 
Join Date: Nov 2004
Location: Obi Obi, Qld
Posts: 18,778
Too easy, thanks Terry.
Reply With Quote
  #10  
Old 22-06-2008, 10:11 AM
CometGuy's Avatar
CometGuy
Registered User

CometGuy is offline
 
Join Date: Feb 2005
Location: Brisbane
Posts: 942
One trick for reducing decentering is by inserting packing under the lens mount on one side, effectively tilting the optical axis. I was able to do this successfully to a 100 2.8 Macro I had.

Terry
Reply With Quote
  #11  
Old 22-06-2008, 10:30 AM
[1ponders]'s Avatar
[1ponders] (Paul)
Retired, damn no pension

[1ponders] is offline
 
Join Date: Nov 2004
Location: Obi Obi, Qld
Posts: 18,778
I'll call you if I need it done. Me open up a lens and muck around with the alignment? I cause trouble if I open up an eyepiece.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 01:26 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
Bintel
Advertisement
NexDome Observatories
Advertisement
Meade Australia
Advertisement
SkyWatcher Australia
Advertisement
Celestron Australia
Advertisement
OzScopes Authorised Dealer
Advertisement
Lunatico Astronomical
Advertisement
Astronomy and Electronics Centre
Advertisement