Using ASI6200MC Pro with a Canon EOS EF L series lens: Page 2

Using ASI6200MC Pro with a Canon EOS EF L series lens

kaiyung

laszloilyes I use mine via it's ASCOM driver, and it sets the aperture. To control chromatic aberrations with wide open apertures, I put an appropriate sized step down ring on the front filter thread of the lens. You can get a set from Amazon, cheap.

Kai

w7ay

@laszloilyes

This is a ASI6200MC connected to a Sigma 135/1.8 ART lens using the Starizona adapter, with front aperture stops to stop the lens down to about f/2.93. The lens hood is removed to show the aperture stop. The ring gear for the focuser belt was custom 3D printed for me by deepskydad.com after I sent him some dimensions.

There is a trade off between using the internal iris (which is placed at nodal point) and using an external aperture stop. In the former case, unless you have 32 iris blades, will create difraction pattern in the form of radial spikes. On the otherhand, by placing an artificial aperture stop in front of the objective can lead to what is called aperture vignetting that causes a different kind of diffraction pattern -- you may have seen it before as a kind of halo around a very bright star with two notches in halo. I.e., at some point, the light cone causes the aperture to no longer look like a circular disk, but as something that looks like cat's eyes or a shape of an almond (whose Fourier transform is a halo with notches). You can read more about this type of vignetting here:

https://www.cloudynights.com/topic/547028-anyone-know-what-causes-this-artifact-on-bright-stars/

So, you get to choose between radial spikes (everywhere) or notches (near the edges of the frame).

This is why I avoid camera lenses except for short focal lengths, when I don't have much of a choice.

Chen

laszloilyes

w7ay Very nice rig Chen! So you have ASCOM focusing! Great! Before I got my astro camera and telescope, I used an unmodified Canon 5D MIII and EOS lenses and found manual focusing to be the biggest time drain during a clear night. I like the handle too. I have an EAF focuser on my newtonian that I could adapt.

I read up on the use of step down rings for aperture management. It's a new concept for me but I get it. Right now, using a reflector, I'm used to diffraction spikes... sometimes of ridiculous size. But I know that I get a very good result when using my L Series Canon 200mm f/2.8 lens (with or without a x2 extender) with the aperture stopped down to ~ f/4.5. That has given me a good result in the past without slowing the exposure time down too much. The diffraction is very minimal. But maybe will need to consider alternatives for my other lenses I haven't yet tried for AP, like my Sigma 105mm 1:2.8 Macro.

For now, I've opted to go with the TS Optics solution. It's less than half the cost of the Starizona (the one that accepts 2" filters). I already have a holding ring for the ASI6200MC pro so that should be no problem. But the focusing will be a problem for now.

enaiman

Why make everything so complicated when the Astromechanics adapter is offering both Focus and Aperture control and it is not expensive. Just order it and problem solved.
As far as I know it is not Putin who owns Atromechanics and you buying an adapter from there won't make the Ukraine war last longer.

laszloilyes

enaiman Thanks for the reply. With the sanctions in place, buying (a new) Astromechanics adapter will be problematic and I don't hold out any hope for the immediate future. I grew up during the "cold war" and know it can take an extremely long time for such political situations to "thaw." But maybe someone else will release such an adapter. I'll keep my eyes peeled for that!

w7ay

laszloilyes I used an unmodified Canon 5D MIII and EOS lenses and found manual focusing to be the biggest time drain during a clear night. I like the handle too.

I started with DSLR with the Canon 20D , then went through two iterations of the Canon 5D before I wised up and moved to the Sony A7 line for normal photography. Before the DSLR age, I was using film with my favorite Leica M3. My first attempt at astrophotography was in the early-mid 1960s with my dad's Nikon S (rangefinder copycat of the Zeiss Ikon) poked into the prime focus of a home built Newtonian.

Here is an image of Comet SWAN from 2006, taken with a Canon 20D and a small Vixen refractor, white balanced to daylight:

http://www.w7ay.net/site/Images/SWAN.tif

I do not have your 200L, but I do have the 100L, plus about a dozen other L lenses. But, my recommendation though is to go to real astrographs for longer focal lengths.

My Astromechanics is in storage, and I am currently not using it since I have moved to an all-macOS environment at home.

BTW, you are not likely to see many people repeat the Astromechanics product line due to intellectual property. I found out that Astromechanics did not license any of it, and had reversed engineered the communications protocol of the lenses -- so, companies like that would be sued out of existence in the rest of the free world that does business with Japan.

Chen

laszloilyes

w7ay Hi Chen, Thanks for the tips. I too shot film long ago - in fact I still have more years of film photography under my belt than digital! But as for astrophotography, I'm rather a newcomer. I had a "department store telescope" in my teens (Focal 3" Newtonian reflector 700mm) on an alt-az mount. Not very conducive to AP.

You did well with the comet! it looks so much like my stacked version of the recent "green" C/2022 E3 but yours is a single exposure on film! Nice work.

I have four fixed focal length Canon EF lenses ranging from 20mm to 200mm and a x2 extender that works these, giving me a range of alternative FOVs, wider than the 700mm I get with my astrograph. I'd like to try some wider Milky Way shots this summer using my ZWO ASI6200MC pro and I thought the EOS lenses would provide a way to get started before I figure out which optics I may later decide to use.

Thanks for all of your help.!

w7ay

laszloilyes You did well with the comet! it looks so much like my stacked version of the recent "green" C/2022 E3 but yours is a single exposure on film!

No, no, that was on the Canon 20D, not film. I see you are used to the smell of Dektol too :-).

You can see the stacking from the stars -- done completely manually, using layers in PhotoShop -- took a couple of evenings :-). That was when I used PhotoShop -- dumped Adobe when they went to the subsciption model, and perfectly happy using Affinity Photos now.

I'd like to try some wider Milky Way shots this summer using my ZWO ASI6200MC pro and I thought the EOS lenses would provide a way to get started before I figure out which optics I may later decide to use.

That'll work! The other thing that you can play with wide angle is meteor showers (Perseids coming in mid August). Just set the software to repeat 5 second exposures (or longer, if you don't mind star trails) for the whole night.

Chen

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