Using ASI6200MC Pro with a Canon EOS EF L series lens

enaiman

laszloilyes "Short EOS adapter for EFW & Cooled Camera (6.5mm backfocus version)"
Actually the "&" should have been an "OR" to make the statement true. It will work with 17.5mm camera + 20mm EFW OR 6.5 mm camera and whatever adapters you want.

Actually this is what you should have got instead:
https://www.testar.com.au/collections/filter-drawers/products/zwo-filter-drawer-for-canon-lens

laszloilyes

enaiman Thanks for the tip... I didn't actually buy the M54 filter drawer for this application. I already had it because I've been imaging with a telescope. The EOS application is new and I'm just trying to use equipment I already own. I have already seen the filter drawer you suggest but passed on it because I am using a full frame camera with a full frame lens. The 42mm adapter used to connect the hardware will clip my image too much to make it useful. I'm actually surprised that ZWO offers such a solution.

w7ay

@laszloilyes @enaiman said: Actually this is what you should have got instead:

Don't buy that one!

It uses an M42 interface, and that will cause severe aperture vignetting with your camera.

Starizona has a EOS adapter + filter holder + tripod mount that might work for you (I have been using it with a Sigma 135 ART with EOS flange and an ASI6200MC).

Chen

enaiman

w7ay That's better - thanks.

laszloilyes

w7ay Thanks for the suggestion. I think I found the Starizona model that you are describing. It is rather pricey but seems to fit the bill... the correct aperture, backfocus, and even a 1/4-20 mounting means. I'll look into this model further.

Tech@ZWO

laszloilyes
https://astronomy-imaging-camera.com/product/zwo-m54-adapter-replacing-efw/
There is an adapter to replace the EFW.

enaiman

Tech@ZWO Haven't seen that one before - thank you for sharing.

laszloilyes

Tech@ZWO Thanks for the help! I had not noticed this accessory before. It will meet the backfocus requirements and also have a wide enough aperture to support full frame imaging (as much as possible with a 2" filter).

I see that it will require removal of the tilt plate? That's not preferred for me because I have actually already tuned that tilt plate to offset tilt that I've encountered with my ASI camera but I may be able to work around that. Your help is much appreciated.

laszloilyes

@Tech@ZWO . My apologies... after further review, I see that the adapter screws directly to the tilt plate (and not in place of it). This seems to be the best solution available to me. Thanks again!

kaiyung

laszloilyes I got the perfect solution for you, and I use it for many of my EOS lens. Astromechanics makes a class of eos to astro cam adapter that also work as ASCOM compliant focuser! No extra hardware is required. From this link, item #2 should fit your bill.

https://www.astromechanics.org/ascom.html

Kai

w7ay

kaiyung Astromechanics makes a class of eos to astro cam adapter that also work as ASCOM compliant focuser!

Astromechanics is based in Russia, and because of sanctions, has no access to chips to build new parts. I had not long ago inquired about the M54 part, and received the information directly from them.

No, I did not include the user icon that I use in my postings to this forum :-). In any case, I wouldn't have ordered if I had known where they are located.

Chen

laszloilyes

kaiyung Thanks for the info. I was unaware of this option. Looks like a nice line of EOS EF adapters!

The M54 model meets my needs, in that it has sufficient aperture for my full frame camera and meets the 44mm backfocus requirements of the lens. The fact that it can adjust focus using ASCOM is a huge plus... I assume that the lens aperture is also ASCOM controllable?

w7ay Astromechanics is based in Russia, and because of sanctions, has no access to chips to build new parts. I had not long ago inquired about the M54 part, and received the information directly from them.

This is too bad. I was hoping to pursue this option but it doesn't seem viable now.

kaiyung

w7ay Love your avatar. Hate how a few dictators up top ruin everybody else working toward nirvana. Astromechanics was a nice guy when I interacted with him a couple of years back, and help troubleshot an ASCOM driver for him. I guess my 2 adapters will have to do for my lens collection.

Kai

w7ay

laszloilyes I assume that the lens aperture is also ASCOM controllable?

Yes, but depending on the iris of your lens, you may end up with many large spikes around bright stars. The most important piece of it is the focuser, though.

I have an old version of the adapter (M42) from a few years ago, and it is well manufactured -- the reason that led me to inquire more recently about the M54 version. But it looks like it is all moot now; at least for me.

By the way, if the Starizona adapter is out of your price range, TS Optics also has a M54 - EOS adapter with a 17.5 mm flange focal depth:

https://www.teleskop-express.de/shop/product_info.php/info/p12850_TS-Optics--EOS-Objektivadapter-fuer-Vollformatkameras-mit-2--Filtergewinde.html

Like the Astromechanics adapter, filter changing is more involved, but at least you know the adapter won't leak light.

Chen

enaiman

w7ay

Yes, but depending on the iris of your lens, you may end up with many large spikes around bright stars. The most important piece of it is the focuser, though.

The spikes you are mentioning here are due to the lens aperture being closed when the lens is disconnected from the camera. Such a lens is not good for astrophotography because the closed aperture will make that lens an f22 or worse; the spikes are just one of the effects.
A proper lens for astrophotography will have either a manual control for aperture (ring) or it will be wide open. If you can get an adapter offering aperture control (like the one from Astromechanics) then you can use any compatible lens.

w7ay

enaiman The spikes you are mentioning here are due to the lens aperture being closed when the lens is disconnected from the camera.

That is what the OP is asking for, an aperture control from ASCOM.

Any aperture (even at a nodal point of a compound lens) that is not a perfect disk will create a non-Airy point spread function. An N-gon shaped iris (that is typical of N-leaf iris) is Fourier Transformed into radial spikes. The smaller the N, the larger the spikes. I have some Canon L lenses that have 10 leaf iris that still produce diffraction spikes.

Chen

laszloilyes

enaiman That's a good point! Thanks. I am concerned about setting the aperture properly on the camera and I've found that wide open isn't really good (at least on the ones in my collection). I find I get chromatic aberration especially in the stars with a wide open aperture.

It so happens there is a trick to setting the aperture in advance to any desired setting but it is kind of a pain to change if you are in the field: https://www.youtube.com/watch?v=y1ZuK_dDweg

That's why I was asking if ASCOM supports aperture control, in addition to focus. I'm willing to preset it manually but I don't think I really want to take the rig apart in the field and use my DSLRs to reset it if I change my mind.

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!