I thought I'd share the results of my build but initially I'd like to extend my sincere gratitude to the developer, Robert. Not only is this the most satifying and well documented project I have ever undertaken - Robert tirelessly and selflessly supports and mentors the makers of this brilliant build. Good on yer mate!
I used one of the excellent Aisler PCBs and eventually went for the NEMA 17 PG27 stepper, using the Nano and DRV8825_HW203 combo with leds and pushbuttons. Components were ordered from RS, Ebay and Amazon.
I decided to go down the follow focus gears option as I don't like to use belts and pulleys on lenses due to the amount of tension needed on the belt and the resultant sidepull force on the lens.
I had limited room for the follow focus gear on the lens so couldn't go for one of the larger diameter ones - I also had to consider the clearance of the motor from the lens when calculating the drive gear size. I ended up with around a 1.5:1 ratio - because of the limited travel and fast lens speed this meant that I used 1/4 steps on the NEMA 17 PG27, giving me a step size of around 1.4 microns. This is probably overkill but I'd rather have more resolution than I need.
A word on the stepper - I originally went for a NEMA 14 non-geared motor. Due to the relatively heavy focusing action of my old MF lenses (Nikkor ED180 f2.8) the NEMA 14 didn't have enough torque - stiction of the lens focus ring due to the heavy construction and damping was the biggest problem, especially using the 1.5:1 ratio. In the end I went all in and got the NEMA17 PG27, which is brilliant and runs cool as I don't have to pump the current.
I also decided to use an outrigged USB socket as I was nervous about damaging the native Nano socket, or perhaps disturbing the Nano in its socket with repeated pluggings. This has taken up quite a bit of room in the case but is nice and robust, which is what I was shooting for being a clumsy old git!
Anyhow, I haven't got a blow-by-blow pictorial account of the build but here are a few images of the finished project. Thanks again to Robert and all the other makers that have shared their builds and advice.
The controller internals
The assembled controller
The stepper mounted on my dual rig
On the mount
Last edit: Richard Lawrence-Day 2019-01-22
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Hi Richard
Awesome, pictures tell a great story and very eye catching case!
Yes, I also have used the outrigged USB socket on some of my projects.
And the PG27 many people think is overkill but hey, it does perform!
I do have a soft spot for wide imaging rigs, especially dual set-up. Yours looks spectacular. What was your process for setting 0 and maxsteps with the Nikon?
I see you are using the DRV8825 controller via USB. Please email me (email address shold be in firmware) to discuss offline as I wouldn't mind some discussion with you about some changes that are coming. Please let me now where you are located
Regards
Robert
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Thank you for your kind words - I love widefield imaging! My setup uses 2 QHY163m cameras. - the one without the filter wheel is permanently set up to capture HA and the other deals with HaLRGB. I recently offloaded my mono CCD camera which was KAF8300 based for these higher resolution CMOS devices and I have to say I love them!
With the Nikon, I went for an arbitrary distance of around 2mm away from the maximum in and out travel, which gave me a total travel of around 23.5mm. I marked these reference points on the lens barrel to help avoid overshoot and give a visual cue when setting 0 and maxsteps in the controller. I once the controller was set up at 0 and using 1/4 steps, I jogged the controller along until I reached the fully out - 2mm mark and rounded it up, which gave me 17000 as maxsteps.
With 0 and maxsteps set, I then accurately measured the travel from 0 to 17000 using a digital dial indicator. It was then a simple task of finding the step size, which is around 1.4 microns (circa 23.5/17000). Using the dial indicator at 1 micron resolution gives me a repeatable backlash reading in both directions of 80 steps or approximately 0.1mm. Given the planetary gears on the stepper and low tolerance of the 3d printed follow focus gears I can live with that - I used the "paper in between the gears" technique to set the mesh.
I run the Nikons at f/3.46 (I use step down rings as an aperture mask to avoid diffraction spikes caused by the lens diaphragm), so my CFZ is around 26 microns (3.46 x 3.46 x 2.2) giving me around 18 steps within the CFZ at 1/4 steps on the NEMA 17 PG27.
I'll message you later for a chat as I'm at work ATM - I'm based in the UK BTW.
All the best
Rich
Last edit: Richard Lawrence-Day 2019-01-23
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I had the rig out for an hour last night for its initial run under the stars controlled by SGP - all I can say is wow!
I think I must have been a bit lucky - perfect V-Curve and focus nailed first time. I think this is testament to Robert's excellent design, code and advice. Needless to say I'm a very happy boy!
Cheers Rob!
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Hi Richard
Good to hear all is working well
If you get the time, can you post a snapshot of the SGP focuser settings , I am interseted what you plussed into SGP for stepsize etc
Its nice to have a rig that you can just go out, turn it on, tell it to go and sit back and relax.
Regards
Robert
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Use a Bahtinov mask to attain focus using the luminance filter - note the focuser position (mine was 378)
Using SGP's Star Analysis tool check the HFR reading of the test image (mine was 1.36)
Move the focuser out whilst taking further exposures until the HFR reading is 3-5 x the in focus HFR reading and note the focuser position (mine was 740)
I used the recommended SGP setting of 9 Auto Focus Data Points
From the SGP help page: Subtract the "in-focus" focuser position from the new (current) focuser position. Multiply this number by 2, divide it by the number of "Auto Focus Data Points" minus 1 and you now have a good "Step Size". In my case this was (740-378) x 2/9 -1= 79.44 - I rounded this up to 80 and I was good to go.
HTH
Rich
Last edit: Richard Lawrence-Day 2019-01-26
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
I thought I'd share the results of my build but initially I'd like to extend my sincere gratitude to the developer, Robert. Not only is this the most satifying and well documented project I have ever undertaken - Robert tirelessly and selflessly supports and mentors the makers of this brilliant build. Good on yer mate!
I used one of the excellent Aisler PCBs and eventually went for the NEMA 17 PG27 stepper, using the Nano and DRV8825_HW203 combo with leds and pushbuttons. Components were ordered from RS, Ebay and Amazon.
I decided to go down the follow focus gears option as I don't like to use belts and pulleys on lenses due to the amount of tension needed on the belt and the resultant sidepull force on the lens.
I had limited room for the follow focus gear on the lens so couldn't go for one of the larger diameter ones - I also had to consider the clearance of the motor from the lens when calculating the drive gear size. I ended up with around a 1.5:1 ratio - because of the limited travel and fast lens speed this meant that I used 1/4 steps on the NEMA 17 PG27, giving me a step size of around 1.4 microns. This is probably overkill but I'd rather have more resolution than I need.
A word on the stepper - I originally went for a NEMA 14 non-geared motor. Due to the relatively heavy focusing action of my old MF lenses (Nikkor ED180 f2.8) the NEMA 14 didn't have enough torque - stiction of the lens focus ring due to the heavy construction and damping was the biggest problem, especially using the 1.5:1 ratio. In the end I went all in and got the NEMA17 PG27, which is brilliant and runs cool as I don't have to pump the current.
I also decided to use an outrigged USB socket as I was nervous about damaging the native Nano socket, or perhaps disturbing the Nano in its socket with repeated pluggings. This has taken up quite a bit of room in the case but is nice and robust, which is what I was shooting for being a clumsy old git!
Anyhow, I haven't got a blow-by-blow pictorial account of the build but here are a few images of the finished project. Thanks again to Robert and all the other makers that have shared their builds and advice.
The controller internals
The assembled controller
The stepper mounted on my dual rig
On the mount
Last edit: Richard Lawrence-Day 2019-01-22
Hi Richard
Awesome, pictures tell a great story and very eye catching case!
Yes, I also have used the outrigged USB socket on some of my projects.
And the PG27 many people think is overkill but hey, it does perform!
I do have a soft spot for wide imaging rigs, especially dual set-up. Yours looks spectacular. What was your process for setting 0 and maxsteps with the Nikon?
I see you are using the DRV8825 controller via USB. Please email me (email address shold be in firmware) to discuss offline as I wouldn't mind some discussion with you about some changes that are coming. Please let me now where you are located
Regards
Robert
Hi Robert
Thank you for your kind words - I love widefield imaging! My setup uses 2 QHY163m cameras. - the one without the filter wheel is permanently set up to capture HA and the other deals with HaLRGB. I recently offloaded my mono CCD camera which was KAF8300 based for these higher resolution CMOS devices and I have to say I love them!
With the Nikon, I went for an arbitrary distance of around 2mm away from the maximum in and out travel, which gave me a total travel of around 23.5mm. I marked these reference points on the lens barrel to help avoid overshoot and give a visual cue when setting 0 and maxsteps in the controller. I once the controller was set up at 0 and using 1/4 steps, I jogged the controller along until I reached the fully out - 2mm mark and rounded it up, which gave me 17000 as maxsteps.
With 0 and maxsteps set, I then accurately measured the travel from 0 to 17000 using a digital dial indicator. It was then a simple task of finding the step size, which is around 1.4 microns (circa 23.5/17000). Using the dial indicator at 1 micron resolution gives me a repeatable backlash reading in both directions of 80 steps or approximately 0.1mm. Given the planetary gears on the stepper and low tolerance of the 3d printed follow focus gears I can live with that - I used the "paper in between the gears" technique to set the mesh.
I run the Nikons at f/3.46 (I use step down rings as an aperture mask to avoid diffraction spikes caused by the lens diaphragm), so my CFZ is around 26 microns (3.46 x 3.46 x 2.2) giving me around 18 steps within the CFZ at 1/4 steps on the NEMA 17 PG27.
I'll message you later for a chat as I'm at work ATM - I'm based in the UK BTW.
All the best
Rich
Last edit: Richard Lawrence-Day 2019-01-23
I had the rig out for an hour last night for its initial run under the stars controlled by SGP - all I can say is wow!
I think I must have been a bit lucky - perfect V-Curve and focus nailed first time. I think this is testament to Robert's excellent design, code and advice. Needless to say I'm a very happy boy!
Cheers Rob!
Hi Richard
Good to hear all is working well
If you get the time, can you post a snapshot of the SGP focuser settings , I am interseted what you plussed into SGP for stepsize etc
Its nice to have a rig that you can just go out, turn it on, tell it to go and sit back and relax.
Regards
Robert
Hi Robert
Here is the screen shot of my SGP settings as requested
Cheers
Rich
Hi Rich
I see you have set the step siz in SGP at 80 - how did you derive this number?
Regards
Robert
Subtract the "in-focus" focuser position from the new (current) focuser position. Multiply this number by 2, divide it by the number of "Auto Focus Data Points" minus 1 and you now have a good "Step Size". In my case this was (740-378) x 2/9 -1= 79.44 - I rounded this up to 80 and I was good to go.
HTH
Rich
Last edit: Richard Lawrence-Day 2019-01-26
Richard
Thats awesome and I am sure will be a big bonus to others using or intending to use SGP
Robert