Getting ready to join this thread..
I just got Cosina 100-500/5.6-8 Macro in OM mount for about $20. Seem to be in very good condition, but rather tricky to focus properly.
Initial shots at 100mm look promising, but beyond that appears to be rather too soft for my liking. Mind you, I tried it only once...
AhamB wrote:
Significantly alter DR? If there was any haze I'd think it should decrease contrast and make it slightly easier on the camera to capture the DR.
OK, I'll agree to anything. (cuz I don't really know...) All I know is that atmospheric conditions can affect the results dramatically. Like shooting on a hot night in Memphis around the end of July will produce drastically inferior results from shooting in the same place and time of night on a cold night in February. I suppose such a difference affects all attributes to some degree or another. I just don't know without a lot of extra reading, which more than others. If I read around on the astrophotography forums they all say they hope for cold clear weather, dark and hopefully high altitude locations. But that's about the extent of my knowledge.
Krosavcheg wrote:
Getting ready to join this thread..
I just got Cosina 100-500/5.6-8 Macro in OM mount for about $20. Seem to be in very good condition, but rather tricky to focus properly.
Initial shots at 100mm look promising, but beyond that appears to be rather too soft for my liking. Mind you, I tried it only once...
Awesome! Don't forget the 100% and a shot of your lens! Cool! I think this will be the first Cosina example in the thread IIRC.
On the softness thing try shooting it at f/11 or so... Or did you already?
Bifurcator wrote:
If I read around on the astrophotography forums they all say they hope for cold clear weather, dark and hopefully high altitude locations. But that's about the extent of my knowledge.
I'm not claiming to be an expert either, just trying to apply some logic but there may well be other factors which I am unaware of, which could effect the DR.
Wishing for cold clear weather is obvious because it will make for the least optical interference of the atmosphere (or troposphere... whatever ).
By the way: interestingly, the shot from the 7D has this focus distance in the EXIF: 4294967295.00m. That's 4.2 billion meters, which is only off by about a factor 10.
Weather affects the higher lp/mm MTF more than the lower lp/mm MTF. Small detail contrast is the first thing to go, then medium size detail contrast.
To affect global contrast... :-/ hm. That's some serious smog or light pollution.
But in a target that's mainly composed of small/medium-small details (the moon surface!) there's only the detail contrast there in the picture to give you an overall "contrast" indication. Hence - small detail contrast is perceived as being the same as global contrast in moon pictures.
The TRUE global contrast would be the average moon surface luminosity divided by the average surrounding space luminosity [ TF = (moonL-spaceL)/(moonL+spaceL) ]
Using arbitrary number (moonL= 0.9 and spaceL = 0.05)
Global contrast (TF) = (0.9-0.05)/(0.9+0.05) = 89
Double the amount of light pollution - halving DR - (spaceL is then 0.1)
Global contrast (TF) = (0.9-0.1)/(0.9+0.1) = 80
The "89" and "80" are the same "ModulationTransfer" indicators as used in an MTF-graph. But in stead of "lp/mm" your measurement standard would be "moonwidths per picture width" :-)
Bifurcator wrote:
Awesome! Don't forget the 100% and a shot of your lens! Cool! I think this will be the first Cosina example in the thread IIRC.
On the softness thing try shooting it at f/11 or so... Or did you already?
Not yet...just did few shots WO. 100 at f5.6 (not bad at all) and obviosuly 500 was at f8, which was less satisfactory, though a little sharpening would help..
AhamB wrote:
By the way: interestingly, the shot from the 7D has this focus distance in the EXIF: 4294967295.00m. That's 4.2 billion meters, which is only off by about a factor 10.
That is kinda kewl. And you're right that's very close to a factor of ten if the Moon was at it's farthest apsis. I guess we call that it's "apocynthion" when talking about the Moon?
theSuede wrote:
...your measurement standard would be "moonwidths per picture width" :-)
Thanks Suede,
Nice explanation! The math helped a lot. It put a perspective on it that gave me a pretty good notion anyway.
--
...moonwidths...
Krosavcheg wrote:
Not yet...just did few shots WO. 100 at f5.6 (not bad at all) and obviosuly 500 was at f8, which was less satisfactory, though a little sharpening would help..
OK, waiting patiently... New lenses are fun aye?!?
Hmm, I don't quite understand these crops. They look the same, yet one camera is full frame and the other is 1.5x crop camera. Shouldn't the D300 shot look closer, given the same lenses are used?
sirimiri wrote:
Lord that thing is long. How many elements does it have? I assume there's no aspherical elements cooked into the recipe?
In re-reading my first sentence.... (giggle)
Just two spherical elements in one cemented doublet at the end. That's why the lens is so long; with only one group, a 560mm lens has to be ~560mm long (and it extends even more when focused closer than infinity). A lot of the elements and weight in modern telephotos are there just to make the lens shorter than its focal length.
Here it is then.
Don't have the remote so the IQ test is not conclusive - very likely due to the shake caused by mirror. Shame timer can't be used with mirror lockup function..
Absolutely 0 sharpening in PP. Only reset contrast and shadows/highlights in Canon DPP.
Oh, and output sharpening only on the original moon shot (not the crop).
Just posted this in the alt images thread last night. There are better in this thread , but I was pleased with a first try. Shot with a Tamron 400/4 with a 2xTC using a 5DII. I was at f11...I think I need to play the the TC combo...I may have actually been shooting at f22. This is ~ 50% downsized.
That's 4.2 billion meters, which is only off by about a factor 10. 
