Hello friends,
I am not able to get a T2 adapter that fits 135mm Sony E-mount lens to ZWO ASI071MC. Can someone please help.
Thanks
T2 adapter for 135mm Sony E mount and ASI071MC
sreesha I am not able to get a T2 adapter that fits 135mm Sony E-mount lens to ZWO ASI071MC.
It is virtually impossible with the ASI071 because the flange to sensor distance is 17.5mm, and the Sony E-mount's flange to sensor needs to be 18mm. That 0.5mm distance make it virtually impossible to fabricate an adapter. The Swiss can probably do it :-).
Four Thirds adapters (which also have a short flange focal distance) exist, but they are possible only with ZWO cameras (like the ASI183) where you can remove the extra 11mm T-ring adapter. I suspect an E-Mount to such cameras is also possible (if you can get Sony to license the flange to you). The ASI071 does not have that luxury, however.
Chen
Oh that is terrible to know 
If I buy a 135mm lens with Nikon mount, will it solve the problem for 071MC?
Thanks
Sreesha
- Edited
sreesha If I buy a 135mm lens with Nikon mount, will it solve the problem for 071MC?
Yes, there are plenty of Nikon FD mount (flange focal distance of 46.5mm), and Canon EF and EFS mount (flange focus of 44mm) adapters to the T2 hole of the ASI071 (17.5mm flange to sensor). There is even one that has a built in filter tray.
It is the mirrorless cameras that have flange to sensor distance that are too short (18mm for Sony E, 19.25mm for micro 4/3, 20mm for Canon RF, 16mm for Nikon Z, etc; including lenses from my old Leica M3 -- 27.8mm flange distance).
Chen
- Edited
sreesha If you don't mind can you please help let me know if I should add any spacers (and what length) for the 135mm Nikon Lens?
The ZWO adapter is not precisely made, but they do come with Delrin spacers to let you dial infinity focus in.
For lens designs where all the internal glass move in unison, you don't really need spacers to place the stars at the infinity focus mark on the lens barrel. As long as you can reach focus, the focus ring of these lenses can be positioned anywhere, and you will still have field flatness.
You can of course dial in the spacers by observing this rule for backfocus:
I.e., look at the corners of the image and see whether the imperfections are radial or axial. Once all corners and the center have pinpoint stars, you have the correct spacing. If some corners are sharp but other corners are not, the adapter has a tilt.
When you add a filter in between the lens and the sensor, you also need to add a spacer that is 1/3 the thickness of the filter glass (assuming refraction index of 1.5). See page 8 of this Master's thesis (download and keep the document as reference for optical formulas)
I hate Delrin spacers, and use metal spacers myself. You can find metal T2 spacers (washers) like this set:
Chen
- Edited
sreesha So I can then safely buy a Nikon 135mm F2 lens?
Remember that at f/2, you may need a special filter, like some of the IDAS ones. Most interference filters are designed for a narrower ray angle.
In any case, you probably cannot use an f/2 camera lens at f/2 anyway. Probably more like f/3.5 to get a more aberration free optics. Stick to telescopes that are designed specifically for infinity focus.
That said, for very wide fields, I do use a Sigma 135/1.8 ART myself (with EF mount; but it is from Sigma's ART series, which are arguably better than Nikon lenses).
Askar has plenty of quite decent moderately short focal scopes; they should beat out a camera lens for astronomical use. I have their ACL200 (warning -- heavy as a real brick) and an FMA-230 (which I use as a guide scope; not at 230 mm focal length, but without the reducer, at 275mm). They also have a 135 and 180 in the FMA series.
The camera lenses just wastes a lot of glass so that they can accommodate focus at different distances. Telescope objectives just need to work at one focal distance. With that many glass elements, a f/2 lens is an f/2 geometrically, not in terms of light gathering. An f/2 lens is definitely not equivalent to a T/2 lens.
Even 200mm is plenty wide when coupled with a full frame CMOS camera. I dedicated a ASI6200 just for these shorter focal length lenses. For "real" DSO, you really don't need such a wide lens. There are only a few objects (like the California Nebula) that won't fit into the FOV of a 450mm focal length, with just an APS-C format sensor.
So, study the FOVs a bit before going out to buy a camera lens to use for astrophotography. It might just turn into something that gather dust on the shelf pretty quickly. It all depends on whether your interest is on large Milky Way expanses and dust clouds of our own galaxy, or on distant nebulas and galaxies.
Hint: when you stop the lenses down, which you will need to do to avoid horrible aberrations when the lenses are opened up, do not use the f/stop ring of the lenses (else you will get diffraction spikes from the corner of the iris blades). Use a series of filter step-down rings to produce a round entrance pupil.
My two cents: do not buy a camera lens on impulse (not even a Zeiss or Leitz). Study what the FOVs can achieve, and weigh their disadvantages when compared to an APO telescope that is designed just for infinity focus.
But its your money, perhaps it is worth paying to learn.
Chen