This is a test
Jun 24, 2018 11:04:14 #
What could be a better test of a lens' C.A. than the limb of the moon? This shot of the moon through my 600mm Sigma mirror lens(paid $150.00 for it)shows NO C.A. and extreme sharpness. My sky is filthy and highly light polluted, as I live two miles from DFW Airport and exactly between Dallas and Ft. Worth. On the clearest of nights, Polaris is invisible. I have owned Takahashi scopes, for which I paid over $2000.00 which could not produce this level of APO quality. The Sigma is the equivalent of an 86mm Maksutov. Lots of bang for the buck don't you think?
Jun 24, 2018 13:51:14 #
Streets wrote:
What could be a better test of a lens' C.A. than t... (show quote)
FYI - Mirror lenses are not susceptible to CA.
Anyway, nice looking shot.
Jun 24, 2018 16:56:22 #
The optical path of my Sigma 600mm Mirror lens has refractive element(s) at the camera end. Could this produce C.A. in some cases?
Jun 24, 2018 17:47:20 #
Streets wrote:
The optical path of my Sigma 600mm Mirror lens has refractive element(s) at the camera end. Could this produce C.A. in some cases?
Don't know the correct answer for that question. I have two mirror lenses: Minolta 500mm Reflex and the Tamron 500 Reflex. I have never seen any sign of CA with either one.
The Minolta has AF with Sony bodies and does a really good job at getting a good focus. But manual focus is just not very easy with that lens.
The Tamron is only manual focus and has very nice manual focusing.
Jun 24, 2018 18:11:52 #
Streets wrote:
What could be a better test of a lens' C.A. than t... (show quote)
Looks like a lot of bang for the buck, nice shot.
Jun 26, 2018 03:30:01 #
Jun 26, 2018 08:19:14 #
Ed Greding wrote:
Prime focus photography is done without a lens, thus no chromatic aberration.
Prime focus is not the reason for no CA. In the case of mirror scopes, they don't generate CA. But for refractor type scopes, an Apochromatic "APO" type is needed. My refractor I use for Astrophotography is a APO type scope which means that the objective is a carefully designed triplet lens combination with extra low dispersion type glass in the middle to control the CA. Cheaper scopes use cheaper objectives and can produce CA, even when used as a prime lens.
Jun 26, 2018 21:47:29 #
Streets wrote:
What could be a better test of a lens' C.A. than t... (show quote)
I have the 2nd version of this reflex lens. Reasonable image quality but bloody hard to get a good focus! The price is right!!
bwa
Jun 27, 2018 16:39:16 #
Streets wrote:
What could be a better test of a lens' C.A. than t... (show quote)
Very nicely done with a camera Lens.
Craig
Jul 9, 2018 16:19:13 #
Here's how it works by adding a Rokunar 1.4X teleconverter. Lens +teleconverter= 820mm. Price paid for set-up=$200.00. There does appear to be a trace of C.A. on the left edge, but it's not a big problem. Since the Moon is all shades of gray, simply desaturating the image would remove the C.A.
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