Alternate EAF Mounting

w7ay

A few years ago, I stopped using the Borg Helical Focusers because it was really tough to make the small adjustments with your palm and fingers to achieve good focus.

Other than that, the helical focusers are quite attractive because they are much lighter than a Rack and Pinion focuser.

Since I was playing around with guide scopes, I decided to resurrect a Borg 7761 focuser to use with the 55FL objective (and an EVOguide field flattener). This time, using an EAF to rotate the helical focuser.

The ring gear is a rubber MXL gear that is used by the video "Follow Focus" folks; they are made to slip over camera lenses of different diameters, so it is not hard to find one that slips over the Borg 7761. And they were designed to work without a belt. The pulley in the picture is just a 15 tooth MXL pulley that is long enough to allow the helical focuser to move in and out.

https://en.wikipedia.org/wiki/Follow_focus

Two M4 threaded holes are drilled into the red body of the EAF itself.

The PC board of the EAF is just under the place that I drilled. But there is a good 6mm of clearance. Some other surfaces have even more clearances.

The two end plates (holding the stepper motor and the USB connector) need to be temporarily removed to do the drilling.

The Borg 7761 moves 70 µm per degree of rotation. So, I needed about 0.05º resolution. The EAF itself (5760 steps in 360 degrees) has 0.06º per EAF step. Add to that the ratio of the number of teeth in the pulley and the number of teeth in the "follow focus" ring gear,I have plenty of resolution.

So, just because the EAF does not allow much flexibility in how it is mounted, you can simply drill your own mounting holes for non-standard configurations :-).

Chen

marcdota

Now this I hope ZWO does moving forward - pre-tapped holes on maybe two sides with extra bolts to cover unused holes

w7ay

marcdota pre-tapped holes on maybe two sides with extra bolts to cover unused holes

Drilling the holes is really quite easy. And sometimes, you don't want them tapped, anyway.

Just this week, I had found a way to mount an EAF on a RedCat51 tube band without using bulky 3D printed holders.

In this case, the two holes I drilled were untapped M4 body holes.

The shell is first drilled and attached to the RedCat tube band without the internals.

The stepper motor and EAF circuit board are then placed back:

Yep, there is a lot of wasted space in the EAF. Apple's design group would have built a much more compact EAF from the same parts.

And voila, a neatly mounted EAF:

So, sometimes you want an untapped hole, and sometimes you don't.

My use-case is not for a RedCat, but for using the RedCat tube ring (69 mm) on an FOA-60Q's tube (68 mm) to drive the tilt thumbscrew of a SolarScope etalon. Part of the setup, without steel rods and bearings:

But this should work on a real RedCat51 using a follow-focus rubber gear on the helical focuser of the RedCat, and a pulley on the EAF, like what I did on the Borg.

The SolarScope SF-50's tilt screw is friction driven with a thick O-ring:

http://w7ay.net/site/Images/EtalonTiltProofOfConcept.mov

After further experimentation, I decided to keep going outdoors to adjust the etalon tilt, because two extra EAF jigs to adjust a double-stacked etalon is just too much weight to be worth it. The extra EAF, tube bands, stainless steel rods and pillow block bearings is just a lot of dead weight 99% of the time.

Now, what we really need is for astrograph manufacturers to build electronic focusers right into OTA, with a single small USB-C connector for both power and data, and get rid of all the knobs etc that astrophotographers will never ever use. This way we don't have any kludgy and ugly ZWO EAF mounting. The PrimaLuce Esatto is really close to an ideal electronic focuser, but it can be even more compact if built into an OTA to begin with.

Chen

marcdota

You know what would be a better, easier (technically), short-term low-hanging fruit solution? If ZWO were to open up the app for non-ZWO focusers 👀🤡🙈🥷

Srsly though - I might just crib this solution. Like everyone in this hobby, I have more than one OTA and would love to be able to easily transfer EAFs across tubes without faffing about with belts and adapters and what not. Two bolts, you're good.

w7ay

marcdota transfer EAFs across tubes without faffing about with belts and adapters and what not.

Belts, what are those? :-) :-).

I just quickly lashed this up on a real RedCat51 (WhiteCat, actually; I simply hate red instrumentation) that I pulled out of storage (terrible optics and collimation). Friction fed with an O-ring. The ring gear is actually from Pavle (deepskydad.com) -- without a belt, because of the way he assembled two 3D printed semicircles, the range is on +/- 80) or so, unless I move the ring gear farther from the EAF (more stress on the stepper motor bearings).

The O-ring is silicone and probably won't stiffen below freezing. But who knows how this will work in real life.

Many ways to skin a "cat," so to speak.

Chen

marcdota

BUTBUTBUT red paint makes our gear go bbrrrrrtttt D: loljk

Interesting. So in theory I can put a silicon (or rubber?) ring/sleeve on the one of the extra flexible couplers that came with the EAF. Then that means, if the distances work out I can easily transplant my current EAF to another tube (in this case, a nikon 300mm lens) and just use said extra flexible coupler to drive the focusing ring. Otherwise, just 3D print a gear with teeth spacing appropriate for the ring gear. Hmm.

One advantage of threaded/tapped holes is that you can use cap screws to secure the EAF to the holder, eliminating one allen key you can lose in the field

w7ay

marcdota One advantage of threaded/tapped holes is that you can use cap screws to secure the EAF to the holder, eliminating one allen key you can lose in the field

Remember that I mentioned the EAF shell to be made of thin (low grade) aluminum? This ain't what is on the skin of an F-22 :-). You probably don't want to depend on too many reuse of the threaded holes.

One of the things you need to look out for is how close you can mount the EAF to your lens. That is why I needed to use a huge shaft coupler (a 5mm to 10mm solid shaft coupler) to hold the silicone O-ring.

Belts and pulley is the safe way to go. Not hard to slip a belt on and off. But if you use MXL belts, you would need an MXL ring gear on the helical focuser. Pavle may have one that matches your helicall focuser diameter already. If not, he has done a couple of special 3-D prints for me (one was for the Sigma 135 ART lens, which is now a standard part he sells).

I don't use the standard ZWO EAF short mount plate with rack and pinion focusers, either. I have a bunch of these plates fabricated so that the EAF does not stick below the dovetail plate. With ZWO's plate system, inevitably, the EAF would stick below the plate of the mount's declination dovetail (don't work well if you have a dual saddle mount like what I use).

But it looks like with drilling into the EAF, we can simply use a single long plate to mount the EAF, without that right angle small plate, to accomplish the same thing. I have two Taks and a couple of FTFs that I can start mounting with direct plates and holes, instead of kludges.

Chen

marcdota

Oh yes I'm annoyed by that extending EAF. I had to resort to risers (in this case, M16 hex nuts) to ensure nothing hits. I'm guessing ZWO made a business decision to resort to what they did (mounting holes where they are now) because that's the thickest metal plate in the whole thing (as you said, the shell is thin). Maybe they'll er, ~bE iNsPirED~ by your custom short mount plates and update their design eh? Hahaha

Hm. Maybe I should check out small L/wall brackets in the hardware store. I have a SmallRig cheeseplate already, that can secured, and slide up and down, a standard dovetail via M6 or 1/4-20 bolts. I'd need the flexibility to accommodate manual lenses for ultra-widefield (~ 50mm FL) shots

w7ay

marcdota Oh yes I'm annoyed by that extending EAF.

Oh, ZWO knows about this style of mounting. I sent them photos of it years ago, when the EAF first came out. NIH syndrome runs amok at ZWO (if you are from the engineering world, you would know what "NIH" means :-).

I have other varients of the EAF short plates too. This is how I mounted an EAF to a Sigma 135/1.8 ART lens (notice 90 degree orientation -- but knowing what I know now, I would just drill a couple of holes in the EAF and don't use any plates; engineers, even retired ones, strive for simplicity):

By the way, here is another varient of RedCat mounting. This time using the Follow-focus rubber ring geras, instead of friction drive to a hard 3D printed ring gear. To get the pulley (already large) to reach the gear, I had to use two layers of the Tilta ring gears (one that fits over the RedCat focuser, and another ring gear that firsts over that ring gear. Each ring gear is only $2. So I ordered plenty sizes ahead of time to make up for the shipping cost :-). And things are always neater without belts. I have a couple more OTA/EAF belted pairs that I can re-mount using this scheme.

The ring gears come as double width that are designed to be cut to make it single wide. As you can see, I kept the smaller ring at double width, but sliced the larger ring into single wide.

Obvoiousy you can also use a smaller pulley and belts. I have ordered some belts to test with, but I don't think it will be better than this.

Chen

w7ay

marcdota Maybe I should check out small L/wall brackets in the hardware store.

Instead, check out this -- a US subsidiary in Seattle of a German company that is a web machine shop. The can do everything up to either 10mm or 12mm thick (my dual saddle plates are made by them), and all sorts of odd shaped holes, and for three or four years now can drill edge holes (like the two M2.5 tapped holes in the long ZWO plates). macOS program from them (free) for CAD, send the file and order by web and back comes nicely machines aluminium (good for me since cheap ground shipping to Portland is essentially overnight. Yes, they can anodize any color, including puke red.

https://www.frontpanelexpress.com/front-panel-designer#download
https://shop.frontpanelexpress.com/#Shop

Here are some of the weird stuff I got them to fabricate:

Almost like PreciseParts.com for planar geometry instead of cylindrical geometry :-).

Chen

marcdota

Unfortunately, I'm not from the US and I think the best solution for me would be cheeseplates with pass-through grooves. I need the ability to slide the EAF up or down, or left or right to accommodate different lenses (for now, two vintage lenses, since the Roki 135 lives in its own rings. Gods know if I'll find a 4th usable FL for AP that can be addressed by a specific manual lens)

Presenting the FrankenPlate, made with scrap parts from the terrestrial side of photography. The idea is given any lens/camera combo with an Arca Swiss-compatible foot, I can slap that on here and be on my merry way.

The secret sauce is the ability to move the cheeseplate holding the EAF to wherever the focus ring is.

The only question would be how to transfer the torque of the EAF to the lens, and currently I'm leaning towards using a focus ring that accepts an cut/open belt to eliminate backlash and the need for different belts. Using geared focus rings will also work but I'd need to figure out the exact diameters needed