Old becomes New “Once More”
Way back when I started this blog to document and share how I adapted various equipment “camera bodies”, “Lenses” to the digital realm of photography, even refinishing / refurbishing old equipment . . . My biggest problem was adaptation of lens to digital camera of various makes or digital backs to cameras or lenses. Well Lets re-purpose some lenses for Astro Photography . . .
I love the idea that I can re-purpose some of my old Nikon F style lenses, (btw you can also do this with Canon Lenses as easily). Why you ask? Well for Wide Field Astro Photography for one . . . Planetary photography, Moon and Sun observations (use appropriate eye & camera protection if viewing the Sun, I take NO responsibility for damage to equipment OR injury to your eyes if you use this to view the Sun inappropriately) .
Here is a test shot of the moon using the above ZWO ASI120 MC-S astro camera.
As you can see in the photo above the field of view “FOV” for the 50mm lens on this small camera chip is about equal to what I get with a 300mm/d7000 APS-C sensor combination FOV. The ZWO 120MC-s chip sensor diagonal size is 6.09 mm , sensor dimensions are 4.8 x 3.6 mm, with a resolution of 1.2 MB, for a 1280 x 960 sensor dimension (native photo size) with pixel size @ 3.75 microns. That’s about the same size as an Apple iPhone 5S imaging sensor. That Crop Factor is about 7.2 X as compared to a full frame sensor.
Now as to adapting my Nikkor lenses to other cameras, as in this case, the ZWO asi120MC-s camera. There are several things one must calculate before you can just slap camera and lens together.
- Lens back focus
- cameras flange focal distance “FFD” distance from lens flange to sensor focal point @ infinity
Those two dimensions are the most critical, Chip size (sensor) will also play into it in regards to what the lenses designed projected coverage “circle of coverage or image circle” this is measured on the diagonal and can dictate what lens/sensor combinations will work or how much FOV you will have, be careful as some manufacturers will measure it at f/22 and not at it max aperture of say f/1.2 which you could observe vignetting which dissipates as F/stop is increased.
So if the Nikon cameras FFD is 46.50 mm that is the distance we have to work with, out adapter(s) can be no longer than the gap between lens and camera. You cannot us a lens that has less then the required FFD as it will not focus to infinity.
- ZWO 120 camera Flange to sensor is FFD = 12.5mm
- Nikkor lens FFD is 46.5mm
- The gap or working distance of our adapter must be 34mm length for the lens to focus to infinity
SO lets adapt . . . the following series of photos show how I adapted the Nikkor series lenses to the ZWO camera. This system works with most CCD’s in use but I can only say for sure for the ZWO cameras. I’d have to have specs and the actual camera to validate they work. This will also work with the new “G” series with the caveat that you cannot control the aperture, I would suggest older lenses that have an aperture ring.
Part(s) E : Dec mount scavenged from a Skywatcher accessory used to attach camera, F : Arca-Swiss compatible camera quick release plate, I am vested in a number of camera plates, one style being the Arca-Swiss style for a number of my camera/tripod setups, I find them very adaptable in creating custom mounting configurations, I also use the Manfrotto Quick Release plates for more robust configurations. These and a Vixen style or Losmandy mounting plates are great foundations, and lastly extruded aluminum can save the day. I can usually create a custom mount system in a day, one just has to be creative, with a drill, hacksaw and a file 😉
I am currently trying various (Short) focal lengths with this setup, as I do I will document the FOV of each lens and its acceptability for a later post, so until then I can only sat this works with short lightweight lenses. I am eager to try some crop sensor lenses such as the 10.5 mm wide angle lens, the 12 ~ 24mm wide angle and if I can I will borrow some others. More about lenses at the end of the post.
I am using the 17 ~ 31 mm Helical focusing adapter with this setup. As you can see the Helical focusing adapters come in many sizes and what is nice is that as you focus the adapter neither lens of camera rotate, the front and rear barrels move in and out to achieve the desired length. There is also sufficient stiffness to prevent loosing focus. When using this system with heavier lenses I would suggest using the lens mount to support the weight of the lens (most telephoto & zoom lenses have a built in mount) as the camera flange would not support a heavy lens.
There are many manual focus only lenses on the used market that are more then suitable for astro photography, you might have to stop them down to f/4 or f/5.6 to avoid coma or vignetting.
The following photos are of my current setup and how I intend to use the ZWO camera when piggybacking, I can use the same mount with longer lenses and camera in the position the scope currently resides.
Well there you go, a simple way to mount short camera lenses to the ZWO ASI 120 series cameras for wide field astro photography. There are as many ways to do this, mine is now the only way, just the way that works for me young padawan . . .
Parts sourcing; I use Amazon and the E of the BAY to source parts for my “misuse” out of the ordinary or proper usage of gear, there is no such word as can’t . . . sometimes it is just harder to do or to damn costly.
Lenses; There are tons of old Manual Focus Lenses at yard sales, in closets, as hand me downs from old uncle john or so many other sources that I can only say you can go pretty damn cheap or nothing at all. Ah . . . the caveat, that is the “Achilles heel” or better yet “the fly in the ointment” , For the most versatility I would stick with lenses in the NIKON, CANON, (M42) Pentax screw mount or T-Mount lenses as you will find these easier to adapt as the mounts are more common. You can also adapt C-Mount lenses but the are right at the limits of coverage and Flange Distance. Telephotos of fixed length 80mm to 600mm, might be slow but can offer good results. Zoom lenses can be usable as well but can lack sharpness and be harder to focus. Short focal lengths 80mm and down to 18mm can be very usable. Lenses designed for Crop sensors, the shorter focal lengths should offer good performance.
I would stay away from the newest bread of electronic controlled lenses as more then likely you will not be able to stop a lens down if needed although there are new adapters coming on the market that provide such control at a hefty price . . . I always believe in the one rule “KISS” (keep it simple stupid) there is less to fail which means less to cause a headache.
As for focus, I can set up manual focus by adapting a follow focus rig but it adds complexity and cost . . . I am ok with a Bahtinov Mask (you can source these through google and either buy or DIY one. A few tweaks and I am usually in focus, some gaffers tape secures the Helical focus adapter, put a piece on the lens focus ring if your a goof and bump a lot of things.
I hope this has been informative, This is only a starting place, I hope I have sparked more then a few grey cells out there to try this and expand yourselves and your fun meter. Please share this with others and if you found it helpful or just amusing then leave a comment.
Wishing all the Amateur Astro Photographers clear skies, all the photographer sharp focus, everyone else blessed be . . . now get off yer duffs and go make, take or create a photo . . . do browse therest of my rantings . . . ta!
Digi . . . aka(Tim) is waiting for the night.